1) Long stroke engines are more torquey! Some people claim that the longer strokes gives more leverage to the crank. This is simply not true. If there was an engine that was savagely over square and another one that was undersquare , but both had the same valve sizes and the cylinders were the same size there would be very little difference in the cylinder charging per engine speed. The gas velocities through the valves are identical . Infact there is a case that says the for a given cylinder size, and valve size, the bigger bore engine would charge more efficiently because it has less bore shrouding hence the ports can potentially flow better. There are other factors at work and there is no doubt an optimum point exists, for you must take into account combustion and the effect of surface to volume ratios of the combustion chamber itself (going too oversquare can give a unfavourable chamber shape prone to heat loss and poor combustion efficiency). Origination of the myth: It is true that for a given engine cylinder size, if the valve sizes are increased for a given valve timing the torque curve will tend to “pivot” around the peak torque region favouring top end. It’s also usually true that when manufacturers make a larger bore engine they will usually fit the largest valves possible-which will ten to give the engine better top end performance characteristics-however this I quite different from saying a longer stroke alone is better for low speed torque.

2)· Siamesed ports on the Mini A series make the engine more torquey. This theory for this overrated engine is ridiculous. Siamesed ports are not only bad for outright flow but also dampen out if not totally kill any tuning pulses. There can be nothing functionally good about Siamesed ports except packaging and potentially cost.

3)· Deleting twin exhausts and simplifying to a single under the floor pipe from a Y piece on a straight six/v6/Boxer six. Often done on the original straight six BMW 3 series where the original twin pipe system is replaced for a big bore single pipe that joins the twin 3 cylinder pairs very close to the engine. Regardless of the new back pressure level this is a SURE way to kill torque ( at low speed on an engine with Variable am phasing and some low speed over lap and all the way through the rev range on a more conventional fixed cam timing -esp 2 valve- engine). This also alters the noise characteristics of the engine a lot giving less 1 and half order.

4)· Con-rod to stroke ratio-exploding the myth. It’s not only the amateurs that come up with misguided opinions. A supposed “expert” in the field, who has written many books and used to post articles in engine performance magazines makes huge claims for increasing the con-rod to stroke ratio of an engine but typically fails to back it up with any quantified examples. It’s been claimed that doing this delays peak piston velocity (although also making it lower) and moving it in line with when the the cam shaft is at peak lift. Well let’s shed some light on the matter-an engine with a 81 mm stroke and a con rod length of 130 mm running at 6800 rpm will have an instantaneous piston velocity of 30.1 m/s (around peak) at 75 deg ATDC. Now increasing the con rod length to 140mm moves this peak piston velocity down to 29.94 m/s but will only delay it by barely over a crank degree! A similar neglible gain argument can be laid down over the favourable geometric angularity –he piston being driven less into the bore (thrust). If you’re an clean sheet engine designer, as long as you stay within sensible norms, I would therefore recommend that other considerations such a block height and engine weight predominate. If you’re trying to modify an existing engine I would say you’re better off spending the money else where to get the performance gain, such as the cylinder head, rather then getting custom pistons/rods.

5)· Ludicrous claims by “chip” companies. Now let’s totally forget about Turbocharged engines for the moment-it complicates things. There are several chip companies who claim ludicrous improvements, such as 10-15% increase in torque/power on a standard unmodified engine. In terms of fuel mixture with the flexibility afforded by modern engine management systems most manufacturers will tune their engines at full load to get maximum brake torque ( known as LBT)-this is the best torque for a given engine speed by varying the mixture. The number for Air fuel ratio for LBT varies depending on engine speed, it tends to be almost 13 :1 at low engine speeds and closer to 12.5:1 at higher speed. Cars with close coupled catalysts may use the fuel to cool the catalysts at high engine speeds (perhaps going o 11.8 :1).At part load all modern engines run 14.7:1 or stoichiometric. In terms of ignition timing, in order to achieve both best torque AND fuel economy you should aim to get MBT ignition timing-which is to get the best torque figures at given engine speed when sweeping the ignition. At low speeds if you calibrate higher you’ll often run into knock and there is absolutely no reason at full load to retard even more. With this in mind these chip companies must be getting these claimed output increases due to the fact that engine fall into a band of various tolerances. Also they often remap the car to run on higher octane fuel. This is all well and good, but the argument still falls over, due to the will and huge numbers that are often claimed, the fact that most engines ae not knock limited at high engine speeds, thus will not benefit in being calibrated for a higher octane fuel. Add to this that modern engine management systems will actively run into and seek up to the knock limit and run very close to this for optimum efficiency and you may see why I am very sceptical of a lot of these claims

5)· Thinking a four cylinder engine can have an exhaust note like a V8 (or any config you want) just by changing the exhaust system. Utter uninformed rubbish! The engine order derived noise are driven by the engine pulsing of various cylinders and there various interactions.

6) · Doing a capacity increase/conversion, but not understanding the fundamentals (BMW 2.5 litre- 2.7 litre) of dynamic engine architechture, using an inadvisable combination of con-rods/pistons and ending up with a CR of less then 8:1 rather then the intended 10:1 and finding the engine doesn’t produce much more torque then the standard 2.5. Yes I’ve seen this done quite recently

7)· Trying to rectify the above situation by skimming the block but not taking into account the fact that the cam timing has now changed

8)· Altering ignition timing of an engine “by ear” – no strobe, only to find later when checked that the engine was now timed at 50 deg BTDC at idle speed!

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evelrod (Automotive) Oct 9, 2002
Well Marquis I certainly cannot fault your credentials but I can make a couple of fairly informed (BTDT) comments!

1)---In my experience most older 'long stroke' engines were and probably still are tuned for lower rpm use, hence better torque is more important than ultimate hp. which is not to say hp is not available if one wishes to tune this type engine for it. Also displacement tended to be larger for some of the late in series longer stroke types.

2)---I agree 100% as I race a 1963 Austin Cooper with a 1380cc A+ , 45 Weber, LCB ex, 10.3 CR, etc. Torque is REALLY tough to design in. It's an uphill struggle .

3)---Agree. We did some Jag tuning in the 60's more for sound than performance and found this to be accurate.

4)---Having raced two identical Lotus twincam engines differing ONLY in rod length (and piston configuration for valve clearance due to longer piston dwell time at TDC ) I must respectively dissagree. The longer rod engine was much more tractible in almost all situations. It tended to make power earlier and did not suffer in the 8000+ rpm range to any degree dicernable by the 'seat of my pants' dyno. In the original Cosworth 1100/1300cc twincams rod length/piston speed was not a problem but in the 1558cc version the longer rods were of great benifit in slowing peak piston speed. I simply went one step further with Nissan L-18 type rods and modified pistons.
Your are correct in stating performance gains via cyl head mods is by far more benificial. In racing you must , however, utalize all avenues for performance increase.

5a)---You nailed this one. I laugh everytime I see one of these rediculous adds for unreasonable performance gains by 'simply' buying ($$$$$$) a chip. All OEM engines are compromised to one degree or another and obviously improvement CAN be had with proper re programming the prom. but 15% improvement (and some even higher claims) are ludicrous.

5b)---This one is new to me. I have used 180 degree headers on SBC used in short track and they make the little V8 sound like a straight 6!

6 & 7)---Shade tree stuff. Unfortunately all to common in the backyard engine builders shops. Basic Automotive Science 101. If you go through the older posts here you will find a gent who tried to save money by using Fiat pistons in his BMW. I'll bet it had AT LEAST a 3 to 1 CR

8)---Man---that's how I learned to do it back in the 1940's. I still do it that way on my 1930 Model A Ford standard coupe. (I have to use a strobe on the MINI as it is VERY sensitive and must be EXACTLY 29/30 degrees).

And I will add one of my own. How about the myth that by using 'premium' fuel your car will always have better performance, power, etc.?

A question since your a qualified person to ask. What is your opinion of the Bosch 4 pronged plugs (aside the fact that at 6 bucks each they will certainly add to the coffers of Bosch)?

Rod

SWB (Automotive) Oct 9, 2002
Marquis,

Would you please send me an E-mail? I'd be interested in learning more about your work. a_racerr@hotmail.com

You said it when you stated the 'virtues' of the Siamese inlet port! I've had some experience with these and I can attest to the poor flow quality inherent with their design.

I tend to agree with evelrod about the rod length:stroke ratio. I have not been able to spend the time/money to verify the results, but I believe there is much to be gained by not going off the deep end. That is not to say longer is always better or vice-versa, I believe there is a distinct range through which an engine will be optimized for a given use. It is also my belief that an engine's true performance potential starts with the lower end, which will either be verified or not by the attendant support systems above (cylinder head, camshaft design etc.)

In keeping with the purpose of the post, don't forget those who eliminate an air filter in hopes of that last little bit of performance.

My favorite though, involves persons bolting on oversized carburetors to engines which can not make use of them, or any type of component mis-matching for that matter. I'm not saying we don't make mistakes, but some are easier to prevent than others...

Sean

franzh (Automotive) Oct 10, 2002
Marquis:

WELL DONE! As in the "Harry and Sally" movie, YES! YES! YES!

You posted comments many of us have been fighting for years, and also, RIR!

For the outsiders, RIR is a well known acronym for a beloved forum member, who is right quite a bit more often than not.

Other common items: "These electronics are really killing the engines today!" (Overheard at a conference recently, explained by an engine builder as to why his engines are not producing the raw power he claims. Forgot to mention the 1hp to 1cc easily obtainable today, not possible 20 years ago, and remain fully emission compliant.)

"Gotta run the 93 octane gas, it makes your car run better and gets better milage". Explained by an overanxious dealership salesman, backed up by their service manager. BTW, it runs just fine on 87 octane, and has for 8 years.

Franz

InHiding (Mechanical) Oct 10, 2002
How about "it is common knowledge that Honda components don't like aftermarket components, so if you put aftermarket components on your car, like those plugs and wires, you shouldn't be surprised if parts start failing left and right, and (of course) the warranty wouldn't cover that."

Marquis (Automotive) Oct 10, 2002
Hello Evelrod

Interesting comments on number 4- the con rod length to stroke ratio
What kind of order increase in power did you find?

Interesting.

In your opinion what would you attribute this down to?

When I see performance gains I split them up into the following areas

Increases in engine breathing or charge efficiency-commonly known as Volumetric efficiency, often due to less restrictions-improvements in outright flow,or tuning changes of some kind, whether they be simple ram induction tuning or perhaps resonance tuning

Then there are combustion improvements- perhaps from a faster burn, higher CR, better-more thermally efficient chamber. I measure alot of this using a useful parameter called BSAC or Brake Specific Air Consumption- basically a measure of how well an engine uses it's own breathing. Just because an engine has a high VE, it doesn't automatically mean the engine can utilise this breathing well!

Then there is friction and improvements associated with all the various components and ancilliaries

Now my illustrated numerical example shows that there's very little differences in instantaneous peak piston speed-both in magnitude and position, even when you go up in con rod length by 10 mm. From this I would doubt I'd see a benefit in cylinder charge efficiency. 1 dimentional "quasi 3 -d" Cycle simulation codes have corroborated this and I haven't seen benefits on our test beds/dynos.

I can't see how they would effect combustion if the compression height is kept the same.

But perhaps there's a benfit in engine friction due to the reduced angularity of the con rod, and the favourable geometry-less thrust into the bore. Perhaps the benfit is more apparent at higher engine speeds (8000 rpm plus)? Although your comment did seem to indicate that there was a benefit throughout the rev range.

In terms of four prong plug use, In all my testing I have never found one plug type (assuming the correct heat ranges are used) giving an instant torque increase. In fact I found that the four prong and 3 prong plug types often shroud the flame kernel inthe combustion chamber during the initial stages of combustion ( 0-10 % burn- see Heywood). It's fairly easy to see why they are specificed however, in terms of longevity and plug life though. Likewise the use of Platimum materials. If you want an increase in performance from plug changes, change them more regularly - a 5 litre Porsche 928 engine will gain approx 6 bhp from a plug change if the old ones have been in for a little while!

Thanks for the compliment Franz.

Some engines where the manufacturer or the engine builder has specified too high a CR-for the octane used ( usually 92 MON-for you guys and about 95 MON+RON/2 for us)- will have a very steep ignition loop -that is- if you were to keep piling on the ignition, and you were using, say, 107 octane fuel-so knock was not an issue,the torque output would rise steeply- a very steep response surface. On the streets on standard gas/petrol- these engines would usually be kept fairly retarded with knock sensors or by ign specs. If THESE engines were reoptimised AND used higher octane fuel they'd certainly benefit. Also, some of the new breed of modern engine management cars will actively run into knock and seek it out and therefore run at a new level (usually dbl -1 degree - detonation border limit). A car with a low CR will typically have a flat response to increased ignition and won't run into knock - it will just go over MBT ignition timing (American engines are very often tuned this way...as typically Detroit doesn't like to rely so much on knock sensing).

SWB (Automotive) Oct 10, 2002
Marquis,

Do you find BSAC more important that BSFC, or do you use them in conjunction for a more accurate picture of thermal efficiency? How would either be analyzed in part or as a group?

Sean

Marquis (Automotive) Oct 11, 2002
SWB
I guess BSFC and BSAC are intimately related by the Air fuel ratio the engine uses.
It's convenient for me to use BSAC by simply dividing my torque figures at a particular engine speed by the VE.Other people such as Roger Duckworth (Keith Duckworths son-of Cosworth technologies) use Power divided by measured airflow, but it makes not odds-it's just a difference in units. What you end up -or should end up with is a smooth curve that has a minimum around -perhaps just below peak VE region and then steeply rises after that. The smoothness of the curve is also an indication of how reliable the dyno data is, if the data is all over the place and scattered- this data/test is NOT reliable- It could be the way the torque is being measure-could be the fuel balance device that is being used to calculate fuel flow hence VE....in any case it's no good!

I've derrived Volumetric Efficiency values for a production engine's publicised WOT BSFC figures. This is because Porsche tend to release this data in their owners manuals, where as very few other manufacturers do, and I was doing work on the Porsche V8 engine. It's very very difficult to obtain figures such as port flows and VEs from manufacturers and the only options seems to be measuring it yourself, which sometimes-for obvious reasons this is simply not viable! To go from the BSFC values to Volumetric Efficiency I had to assume an AFR ratio throughout the rev range.The engine in question didn't have close coupled catalysts so it is unlikely it overfueled to cool them-although strangely some companies still can overfuel for simple component protection!
Now I'm at an advantage here compared to most , in that I know what kind of AFRs mappred cars typically run at at full load (usually LBT) at various engine speeds from my data base. I then checked the BSAC values and VE values did a sanity check and found that they lay within accepted norms of my database. The 928 engine is VASTLy oversquase and has huge huge main bearing sizes -so it added up that it didn't utilise its air particularly well.

evelrod (Automotive) Oct 11, 2002
Good morning Marquis. I'll try to put into words what I am having difficulty in remembering. We built the 'long rod' motor as a 'mule' for testing and it only ended up in the race because , surprise, it performed well and we had a problem with the #1 engine. In it's final form it had a different cyl head but for the original tests it used the same Brian Hart/Vegantune head as #1.

Number one engine---Cosworth rods 5.025"(I think) 482g 350g rotary weight.
Venolia pistons---crown ht. 0.185" Deck ht. 0.013"
482g total less rings.
Number two---Datsun L-18 rods 5.3" 685g and 511g rotary weight.
Hepolite pistons---crown ht. 0.225 Deck ht. 0.010"
482g total less rings.(note here that these pistons had to have the valve pockets cut an additional 0.125" to clear the valves, added dwell time of pistons at TDC (?).) Compression ratios were within 1/2 point of each other.
Compression tests of each engine after initial run in were--
#1 175#-165#-165#-165#
#2 165#-160#-165#-160#

Cyl head---Brian Hart/Vegantune # 1107 12-21-72
Cams---276 IN 280 EX @ 0.050" Ground on 110 centers
set @ 105 ATDC Set @ 110 BTDC
Assembled May 1990
Weber 45 DCOE-9 38chokes 130m(#1) 160a 45p(#1)
135m(#2) 50p(#2)
Lucas 23D electronic @ 35 total advance on #1
Lucas 23D electronic @ 32 total advance on #2

Torque to turn the bottem end over was 18ft/lbs break and 4 ft/lbs to rotate #1 and 15ft/lbs break and 5ft/lbs to rotate assembly #2.
I don't recall the exact dyno results but as I remember they were nearly the same at the high end (#2 made slightly less) but the long rod engine had a slightly broader powerband. Also it did not like the spark advance to be over 30/32 degrees and the carbs needed a bit richer mix.

Now for the subjective part. On the track we went out early morning to practice and ran a bearing on # 5 main. Very unusual occurance(I had installed the wrong length plug in the rear oil gallery obscuring the oil hole to the main!) so the crew hurridly changed the top end to the 'mule' and we made the race. I was not happy as the engine seemed rather 'slow' off the corners but when I came in for fuel and driver change I noted that my lap times had been consistantly LOWER than with the "good" engine??? In fact I did 11 laps at between 2:09.1 and 2:09.4 and that was just a 'tick' off the lap record! Also noted was the fact that the oil temp was 15 degrees cooler but, I made no connection at the time. The 'mule' ultimately got it's own top end and it continues to this day as a vintage engine in a Lotus Cortina in New England. I don't know what became of #1. I retired from competition shortly after that and now only compete in "vintage" events with a Mini Cooper.

The only records I have are the build sheets for the #1 engine and of course all the stuff for the Austin Cooper 1380 A+ engine. I will keep better track of this paperwork. I never thought I would ever need it again.

Rod


evelrod (Automotive) Oct 14, 2002
Marquis: As I re read my post above I am not sure that I have answered your ? sufficiently. Sorry. I did not include any text referance or publications of contemporary theory (David Vizard or Smoky Yunick as example) on rod ratios as I am assuming that you, as an engineer of some note, would already be familiar with them.

Rod

patprimmer (Automotive) Nov 5, 2002
Rod
Grumpy Jenkins also writes a lot about rod length in his book on small block chevies.
I have no data, but every engine that I built that ran better than expected over a wide rev range, had a few common traits:-
Relativly long rod to stroke ratio.
Absolute minimum safe deck clearance.
Too big a cam.
To small a carby
Good straight all downhill individual port runners. (ie the discharge nozzel can see a downhill run to the back of the valve)
Constant depression carbies or at least vacuume secondaries
About 10:1 comp (back in the days of 98 octane leaded gas)
Conservative heads with reasonable size ports with most of the work done around the valve guides and bosses, inside radius concentric with outside radius, diverting gas flow away from shrouded side, unshrouded chambers and a lot of detail under and on the valve seats.
Lots of attention to detail re assembly and fit.

These were not real race motors, but good strong, easy to drive, durable, every day street sleepers.


patprimmer (Automotive) Nov 6, 2002
Pat Daly
I couldn't agree more. Some of my best results with American V8s have been with 780 list 3310 Holleys and the occassional 950 or 1050 three barrl. By big I meant Dominators or twin 660s on the road. It's all relative I guess.
Holleys book recomendations are really for medium performance road cars.
I just think that most street roders use enormous carbies on otherwise stock engines with poor results.
Regards
pat


derekwhite (Automotive) Nov 24, 2002
Hi all,

I recently found this list while doing some research for someone who has some flash gasification patents. I can’t believe how much I have learned— thanks.

Firstly, in line with what several of you have said, the biggest mistake I have seen in building high performance engines (usually for engines that will never actually race, just sound bad and burn rubber) is the overemphasis on peak power. In most real races, rallies etc. the engine doesn’t run at it’s maximum power rpm all the time and unless you have a boat, plane, CVT or a round banked track you are going to be running in a range of up to a few thousand rpm. Over carbed, over cammed engines may look good for maximum power but are much less useful and usually get worse lap/stage times.

Marquis said:

“Interesting comments on number 4- the con rod length to stroke ratio
What kind of order increase in power did you find?
Interesting.
In your opinion what would you attribute this down to?”

I always thought this was to do with the relationship between the peak combustion pressure and the angle of the rod relative to the crank pin. Longer rods may make the rods perpendicular to the crank (tangential to its rotation) when the combustion pressure is at its peak. Cheers, Derek


cups (Mechanical) Nov 27, 2002
How about claims that certain oil additives can reduce internal friction and let the engine run cooler, seems to work on my Harley - but difficult to proove.

evelrod (Automotive) Nov 27, 2002
"Gee Maw, do I hafta---"--- Snake oil, cups. Snake oil!
Trust in capitalism---If there was GREAT benifit in any one of these additives touted on TV and the media, the major mfgrs. would be on it like a "duck on a junebug"!!! Read some of the posts in the Auto Lubricant Engineering forum for a full rundown. I can relate several personal examples of 'big name teams' and 'big name drivers' shilling for these oils and additives and NEVER actually using them in their race cars!!! Trust this also cups---I am NOT the only one to have seen this happen. It's all about $$$.

Rod

TheBlacksmith (Mechanical) Nov 27, 2002
Please Rod, in this era of uncertain oil supplies and increasing pressure to achieve dramatic increases in fuel economy, if this stuff worked as advertised, the major auto manufacturers would KILL the other ducks getting to the junebug!

Blacksmith

GregLocock (Automotive) Nov 27, 2002
Rule of thumb at the moment : US manufacturers under CAFE will spend about $7 for every kg of weight saved. On a typical car this will reduce fuel consumption by 0.03%. Given that the oil fill costs of the order of 4-8 bucks, a more expensive snake oil that was even slightly effective would be used, don't you think? Of course it's all a conspiracy by the manufacturers....
Cheers

Greg Locock


kimbo1 (Mechanical) Nov 28, 2002
To answer one of you, I have seen no gain from 4 prong spark plugs. 1 only spark, will jump to the shortest path anyway. they might last longer due to distributing the wear amongst the probes.
As to comments on rod/stroke ratio - how can you possibly discount rod angularity and cylinder side loading as irrelevant?
As to longer stroke engines not producing more torque there's a little physics formula which says torque equals force times radius, a longer stroke means the force from the conrod is applied at a greater crank radius and thus generates more torque - this argument has nothing to do with cylinder charging efficiency. Assuming we get the same BMEP through head design at that rpm, torue must be increasedWhat is it you think I am missing here?
All other myths you pointed out I agree with!!

InHiding (Mechanical) Nov 28, 2002
As to longer stroke engines not producing more torque there's a little physics formula which says torque equals force times radius, a longer stroke means the force from the conrod is applied at a greater crank radius and thus generates more torque

But for a give displacement, if you have a longer stroke, you have a proportionally smaller piston area. The force acting on the piston is proportional to its area, so what you gain in radius is exactly offset by your loss in area.


evelrod (Automotive) Nov 28, 2002
Isaac, in MY experience with MY racing engines, given EQUAL displacement, the longer stroke engines tend to optimize power in the mid range and the shorter stroke in the upper range. HP and TQ figures DO range up and down a bit but are very close in most cases. There is just SO much more to this statement than is obvious. Long stroke needs shorter rods, smaller pistons, cumbustion chambers tend to be smaller with smaller valves due to smaller bore, etc. Short stroke can benifit from longer rods (all these were in the same type Lotus "L" blocks, Ford 105E) larger bore with the ability to stuff in bigger valves etc.
Optomizing the long stroke engines , TQ was usually best in the 3500 to 6500 rpm range with top HP at 7500+ and the short strokes were in the 4500 to 7500 rpm range with a HP at 8400 or so. This is NOT to say that the longer stroke engines did not make power in the upper ranges, both engines would rev to 9000+, just saying they tended to be best in the lower ranges where the short stroke engines tended to be best in the upper ranges. The type of car and allowable gearbox ratios , overall weight etc. was a big factor in choice of powerplant. The race track configuration played a big part in choice also.
All I am pointing out here is that there NO absolutes in racing. Long stroke, short stroke, oversquare, undersquare, it begins to look more like a pointless argument. Whatever works best ultimately gets used.
In production autos, cost was probably the determining factor. "Need a bigger engine? Just make the thing bigger. What? Not enough $ in the budget for a new concept. Limited bore spacing? Well then, lets just make the stroke longer----"

Rod

patprimmer (Automotive) Nov 29, 2002
Rod
I expect that the retooling cost to increase bore spacing and valve size is a lot more than the cost of retooling to increase crank stroke, and/or change gudgeon pin height, rod length and/or deck height.
Regards
pat


evelrod (Automotive) Nov 29, 2002
That is my point, Pat. Most engine changes/power increases are dictated by the 'bean counters'. With the possible exception of Porsche, engine mfgrs are overly influenced by the boys up front (and they may know very little about engines)! A good example would be when Ford went from the 105E to the 116E (and Kent) for a cheap displacement and power increase, along with a new cyl. head design. Evolution not revolution!

As to the oversquare/undersquare engines, I simply have found that my longer stroke engines tend to be better 'torquers' than the short stroke engines. A lot of things come into play as bigger bore pistons have more surface area but combustion chambers tend to give more room for bigger valves (not always true) shorter stroke may utilize longer rods---too many variables + and - for me to make iron clad statements without a LOT of experimentation which I cannot afford to do at this point in my life. Therefore---I'll just stick to what has worked for me in the past---the best engines have tended to be near square with longish rods and flat top pistons having minimum deck ht. and camshaft timing a little longer on the exhaust side.

Sorry that all this has gotton a bit off topic. My inability to properly explain my position often leaves me 'gasping'.

PS---I am now racing a 124hp Austin Cooper in 'vintage' and THAT engine design must surely be THE worst of all possibilties! A lot of fun , though.

Rod

patprimmer (Automotive) Nov 29, 2002
Sorry Rod, I was trying to support your arguement, not contradict it. I also agree with your statements re stroke, bore etc. There are many interelated variables re bore/stroke, displacement, cylinder head airflow, squish area,, volumetric efficency, thermal efficiency, surface area to volume, flame travel, spark advance, piston speed, rod angularity, compression ratio, piston acceleration, piston to valve clearance, valves shrouded by bore, cam timeing, airspeed, and others I can't think of at 5:30am. The number of variables and the numerous interactions make it impossible to fully consider all aspects of a change to one parameter. I just try to consider the variables that will have the most impact, and the changes that are easiest to make re their potential effect, especially if they are likely to improve both performance and durability.
By the way, I don't see where you have got off topic
Regards
pat


WGJ (Automotive) Dec 3, 2002
Reference to Marquis (Automotive)'s comments at the beginning of this thread.....

"Siamesed ports on the Mini A series make the engine more torquey. This theory for this overrated engine is ridiculous"

I am not contending this, but, poor old 'A' Series - need to keep comments in context, I think. The 'A' Series appeared in the UK as a post-WWII improvement to Austin-Morris' engine lineup. It was the first small Austin engine with overhead valves, I think, offering performance and economy benefits for small package cars.

With expensive fuel and cars that few could afford, the 'A' Series was designed (I believe and I'm sure they'll be someone out there to correct me) to power a range of family 4-seaters and reliably turn in 35mpg.

What made it popular with tuners was the competition. Asthmatic 1172cc Ford sidevalves (the OHV 105E didn't appear until 1959), fragile Standard Triumph engines and the jumble of car engines dating to pre-WWII often didn't lend themselves to tuning with the relative ease which the 'A' Series would allow performance improvements.

I believe that Harry Westlake was respnsible for the design of the 'A' Series combustion chamber - a design that was imitated widely and internationally in the industry. As some will know, the engine was used for all types of competition in Europe from trials cars through single seater (Formula Junior) and saloon car to international rallying and drag racing (I've seen one).

The siamese inlet port was never more than a way to reduce the overall length of the engine by using undersquare design and six ports in lieu of eight, taking up less space and providing more room for passengers.
Speaking as a hick from Europesville, given the same power output, I always preffered the long stoke, siamesed 'A' Series to the Ford 105E buzzer as a motor to queue in traffic with. Once on the open highway, however, it can be a different story. Sadly the 105E was often a candidate for blow-by surgery by 60000 miles, whereas the 'A' series would soldier on seemingly forever, provided it had an intravenous 20/50W drip.

Evelrod should set up a Mini Cooper hire car company for those that need the experience.

evelrod (Automotive) Dec 3, 2002
WGJ---I have a lot more experience with the 105E based racing engines than the 'A' and later 'A+' engines.
My '58 street Sprite managed better than 40 MPG on a regular basis. No valve or blowby problems but, it did break a crank at about half it's life!(The racing Sprites got NEW bearings after EVERY race!) The Anglia, the Consul/Cortina GT and, the 7 Lotus Cortina/Elans that I played with never broke a crank but did loose a couple of rods (no pun) once upon a time.(The bearings averaged 50 to 100 hrs. and still were "as new"). As I see it the main problem with the A series is the 3 main setup whereby the center main must feed #2 and #3 rod journals. It caused me grief in the past and present.(Of course in the past we did not turn 9000 RPM).

By the way, it is a FIVE port head! (I use a Richard Longman GT-15 if you know what that is)

Rod

jlwoodward (Mechanical) Mar 3, 2003
I guess I am jumping into this kind of late, but I just wanted to add a couple of comments.

Long stroke/high torque - I remember this argument back in the old days of large 6 cylinder engines before the trend toward square engines. Since these engines had such long strokes, they operated at lower rpm because of piston speed limitations. They had large displacements, which in itself produced a lot of torque, and the torque peak was at low speed. Thus, an entire different feel from the later high speed V8s. Of course they ran out of steam much earlier.

Con rod ratio - I could never make any sense out of this. I tried overlaying plots of piston position, speed, and accleration. I could barely see any difference. However, I would in no way argue with David Vizard or Smokey Yunick. The only thing I can think of is that on the order of the time scale of the combustion process, the longer dwell time makes combustion approach the ideal constant volume process that is assumed in thermodynamic calculations. Also, if piston movement is minimized, less of the cylinder wall area is exposed for heat loss. Are any of the engine simulation programs sophisticated enough to show a difference.

John Woodward

Marquis (Automotive) Mar 4, 2003
Jlwoodward,It's nice to see someone who thinks things through for a change rather then follows. Interesting and intriguing theories.
In terms of the con-rod to stroke ratio and your comments on longer dwell. A sophisticated 1 D engine simulation package such as Ricardo WAVE , GT power or MANDY should indeed pick this phenonmenon up as con rod length and stroke are an input and the dynamic geometry is siumlated throughout the engine cycle. The only trouble with cycle simulation code picking this kind of phenomenon up is that the actual combustion data is more often then not an input in the form of a Wiebe function ( the codes real strength is predicting Volumetric efficiency- which has time and time again shown that there is minimal effect in terms of air flow with a different stroke to rod length ratio).
So this combustion data input for the Wiebe function infers that the engine must be run first, and if there is a subtle nuance, perhaps in, say the 0-10% burn region of the longer rod ratio engine , it would have to be run first to evaluate it on simulation - which i kind of like fixing the barn door after the horse has bolted!
I have found on several test bed runs that the difference is within dyno to dyno variation, however I don't discount it's effect totally, only that's it tends to be exagerrated by people, and that it certain isn't a phenomenon that exhibits itself on airflow/Volumetric efficiency of an engine- due to the minimal effect on instantaneous piston velocity we've just agreed on!

NeilRoshier (Automotive) Mar 4, 2003
Marquis I appreciate your views on the rod/stroke issue, but in thinking of the effect are you assuming a good/efficient burn with little to impede the flame front propogation in the CC? I am aware of enthusiasts who modify the Lampredi Fiat TC engines by installing a chev small block rod (6.0") in this relatively long stroke design (84mm bore and 90mm stroke) with a custom forged piston to suit the new rod. This has (supposedly) the advantages that are often given for the longer rod argument, however my specific query is this: Given that to have a sufficiently high CR in this engine requires a large intruding piston dome, which presumably will interfere with the flame front and thus combustion effeciency, would there be an advantage in the combustion (there are other advantages perhaps such as reduced weight, better bearings and reduced friction) in such circumstances (note I don't have an opinion either way, but suspect there may be some advantages)
regards Neil

NeilRoshier (Automotive) Mar 4, 2003
Marquis I appreciate your views on the rod/stroke issue, but in thinking of the effect are you assuming a good/efficient burn with little to impede the flame front propogation in the CC? I am aware of enthusiasts who modify the Lampredi Fiat TC engines by installing a chev small block rod (6.0") in this relatively long stroke design (84mm bore and 90mm stroke) with a custom forged piston to suit the new rod. This has (supposedly) the advantages that are often given for the longer rod argument, however my specific query is this: Given that to have a sufficiently high CR in this engine requires a large intruding piston dome, which presumably will interfere with the flame front and thus combustion effeciency, would there be an advantage in the combustion (there are other advantages perhaps such as reduced weight, better bearings and reduced friction) in such circumstances (note I don't have an opinion either way, but suspect there may be some advantages)
regards Neil

derekwhite (Automotive) Mar 4, 2003
Hi Neil,

If I understand your question correctly, you'd like to know if the longer dwell time due to the longer rod/stroke ratio will give the usual combustion advantages even in cases where domed pistons interfere with the combustion efficiency. My guess would be that combustion would still be noticeably improved. I am guessing that the delays caused to the flame front by the dome are small compared to the improved combustion efficiency from longer dwell at the top.

A big advantage to longer rods is lower maximum piston acceleration so lower forces and thus higher rpms possible. If you haven't already got it, the formula for max piston acceleration in feet per second squared is:
Gmax = ((N^2xL)/2189)x(1+1/(2A))
where N=rpm, L=stroke, A=Rod Length/Stroke

cheers, derek

Marquis (Automotive) Mar 4, 2003
Hi Neil, I'm with you and agree.
Interesting points made, regarding Piston dome flame front shrouding needed by this deep chamber hemi.

Based on what I have seen on single cylinder experiments here I would say the flame front shrouding factor would predominate. It would tend to delay your 10-90% burn times not to mension adversely affecting the surface to volume ratio of the combustion chamber.

This would be surported by the trend for manufacturers going toward shallower more compact chambers and flatter piston tops, unless it is say, a small derrivative of a given configuration where they have no choice.

Before Someone who's TOTALLY missed the point cites the New Dodge Hemi as an eexample which contradicts the above or the 2 valve Porsche 993, - I'll shoot that argument down with that fact that they've had to get around the issues of a deep chamber/high-CR-intruding piston dome by using twin plug.
For more on Hemis with twin plugs see my article question written on the twin plug Porsche Boxer.
In these days of stringent emissions regs and need for heavy ignition retard on start more attension is being paid to combustion efficiency.

peebee (Electrical) Mar 4, 2003
ivymike: just read your Oct. 10 post on Honda parts, I suppose this response is a bit late, but:

I've got a Honda that will not pass Illinois emissions inspections with a Honda gas cap. The Honda dealer won't even sell gas caps here because he knows they will fail the test. The only option is 3rd party.

evelrod (Automotive) Mar 4, 2003
Marquis, I was not even aware that the new Dodge hemis were twin plug. Is that a first for US production engines? Can't seem to remember. Logical for twin plugs considering the AQMD's regs in California.
Twin plug engines in racing are not new. The first one I had a hand in was a twinplug 1600 Alfa GTA in 67, I think. And of course the Ed Pink and Keith Black hemis with THREE plug designs. I have no idea if that trend continues. Curious design as the pistons were flattops!(?)

Rod

PS---I think Nash had twinplug hemi straight 8's in the thirties. Probably others.

Marquis (Automotive) Mar 4, 2003
Hi Rod,

I don't know if it's a first for American engines.

I knew about the wonderful old Alfa GTAs though.
Alfa did quite a few avant garde things in terms of engineering, some good some weird!
The Big Valve angle Hemi needed it though.

Porsche 911s used twin pluggers for racing.
It works well if you can up the CR with it too.
I guess it was done back then by admirable eccentric engineers going the extra mile, while it's done on certain chambers shapes out of neccesity now!

patdaly (Mechanical) Mar 4, 2003
Rod, there may be more, but the one I do know was 2.3L 4 cylinders in late 80/early 90s Ford Rangers had twin plugs.

derekwhite (Automotive) Mar 4, 2003
Thanks for the test info Marquis. I guess my guess was wrong!
A lot of pre-1910 cars had twin plugs. The big 1909 Benz that I helped get running again for my wedding in Sweden 18 months ago had twin plugs (half on trembler coil half on magneto.) I know some early US cars like the 1907 Stearns 30-60 had twin plugs. I am always amazed at some of the early French racing engines (the Bugatti Brecias and Salmson GPS) which had twin plugs, four valves (and in the Salmson DOHC and a supercharger!) cheers, derek

patprimmer (Automotive) Mar 5, 2003
In 1914 the Delage GP had twin cam, multi valve, and Bently had it at least by the early 20's
Regards
pat


NeilRoshier (Automotive) Mar 5, 2003
Marquis thank you for your thoughts, and derekwhite your summary of my question was very correct. The piston dome for more than 11:1 CR protrudes a large amount (and has sharp corners on the dome according to pictures seen) and according to published tests requires a spark advance of 40-44deg at 7000rpm. This would seem to support the thoughts of the piston intrusion adversly affecting combustion?
I believe a similar amount of advance was required by the ford pinto. The magazine cars and car conversions did a twin plug conversion to the pinto and greatly reduced the advance required and increased the power (by what measure and compared to what I'm not sure). Am I correct in thinking that such a conversion would be beneficial where the flame front travel is interrupted by intrusions (from either the piston or CC shape) and the new ignition source could be placed to counteract/compensate the disruption to the flame front?