Bad/Silly practices and exploding Engine myths! 6

[patprimmer]

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]

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'. LOL

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]

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]

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]

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&quot. 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

 

[EngJW]

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]

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]

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&quot 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]

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&quot 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]

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]

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]

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]

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]

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]

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]

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]

In 1914 the Delage GP had twin cam, multi valve, and Bently had it at least by the early 20's Regards
pat

 

[NeilRoshier]

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?

 

[Marquis]

View this thread to get some of my comments and views in trying to figure out reasoning for twin plugs vs single on a boosted engine versus a NA.
thread71-47020

 

[NeilRoshier]

Thank you, very interesting.