Lotus Elan

Peak Power and Torque

PostPost by: Europa88 » Wed Jan 20, 2021 11:44 am

Pitstop TC 1594cc.jpg and
Can any one give me heads up on this rolling road printout? I'm not into bragging rights, just interested as to why I'm producing peak power at 7051 RPM which coincides with the soft cut on the rev limiter (hard at 7100rpm)
specs as follows
1.625 inlets 1.4 exhaust
L14 cams... Spring seats machined
Head flowed to blend in larger valves
Type 47 tubular exhaust
Dellorto DHLA 40s with standard 33mm chokes
Original cast crank
Powermax pistons +20 thou
Original rods
All bottom end fully balanced
MBE ECU
Wasted spark coil ignition

Any comments gratefully received. This is a road car, but I intend to track day it as often as I can :)
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PostPost by: nmauduit » Wed Jan 20, 2021 1:23 pm

at first glance this would just mean that the porting is well done, so that you may get a bit more power if the engine was let further up in the rpm (not recommended with stock cranck). Incidentally, it seems you should be able to tune it to a more tractable way by optimizing the jetting to improve the richness at the transition (overly rich around 3500-4000 ? though I am a bit puzzled with the scales on the AFR graph) - good fast road engine in my book.
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PostPost by: Europa88 » Wed Jan 20, 2021 1:33 pm

Thanks for the comment, I suspected that it may be able to produce more power at higher revs and perhaps an all steel bottom end may be on the cards one day. The AFR chart does appear to show it runs very rich 3500-4000!
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PostPost by: rgh0 » Thu Jan 21, 2021 9:09 am

I would need to understand how they corrected rolling road at the wheel measured out put to engine HP ( which is whats shown on the graph) to comment.

The big dips and the start and ends of the curve are certainly part of the test methodology as the engine does not do that. Peak engine power with that cam and your mods I would expect to be around 7500 and flat to 8000 rpm

On a rolling road, at the wheels peak HP occurs at a lower rev point than engine delivered at the flywheel HP. This is due to the rolling road friction losses rising combined with the engine frictional losses as engine torque starts to drop at high revs. This can be compensated for approximately but most of the built in adjustment programs in rolling road dynos are crude and don't do this accurately and over report engine HP ..... deliberately to make customers feel good.

Do you have an actual rear wheel HP and torque curve without any correction to engine HP as that is more meaningful to comment on.

Overall though it looks like you have a well done engine with a little need to get the mid range AFR right though that will not be costing much HP. The torque and HP dip in the curves is inherent in longer duration cams. Playing with the detailed cam timing, ignition timing and carb mixture can minimise this dip but needs to be done for individual engine build and consumes lots of dyno time ( and money :lol: ) for those last few increments

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PostPost by: Europa88 » Thu Jan 21, 2021 12:33 pm

Thanks for the input Rohan.

Unfortunately I don't have uncorrected data other than peak values of torque and BHP.
As I understand it most rolling roads apply an algorithm to standardise readouts across a wide variation of ambient temps and altitude and as you say this at best is somewhat crude. Also I am not aware if this is an accepted practise which all adhere to. It would be crazy for each dyno manufacturer to come up with their own take on this
(but I suspect they do)

Just to say this is an Europa not an Elan...Though I would kill for a nice Sprint DHC :) Not sure if transmission losses are similar, I would have thought there is not much in it.

The engine feels great on the road (I haven't tracked it recently) But it really wants to rev. I hear conflicting advice on RPM limits on the standard crank. Which brings me to another question, would I benefit or indeed lose out if I stroked this engine to a 1700cc bottom end? I have an old crossflow block (2737e) which I could line bore and fit steel caps with a new steel crank, but would I be better off machining the steel crank into my original lotus block?

This is something I have been contemplating for many years to give more bottom and midrange torque, but I'm loathe to give up the revvy feel of the 72mm crank!
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PostPost by: 2cams70 » Thu Jan 21, 2021 2:31 pm

I prefer smooth free revving engines too. I'd recommend a steel 72mm crank in your existing engine over a conversion to a long stroke1700cc engine. Depends what your preference is - grunty and crude or smooth and sophisticated!
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PostPost by: Europa88 » Thu Jan 21, 2021 2:54 pm

Can I have Grunty and sophisticated? Asking for a friend :lol:

I think I will probably go the 72mm steel crank route joking apart. It just suits my style of driving!
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PostPost by: bitsobrits » Thu Jan 21, 2021 11:02 pm

2cams70 wrote:I prefer smooth free revving engines too. I'd recommend a steel 72mm crank in your existing engine over a conversion to a long stroke1700cc engine. Depends what your preference is - grunty and crude or smooth and sophisticated!


I have a 1720cc twincam that I would say is grunty and sophisticated. Fully ported head, high lift/short duration cams, 10.3CR, alloy flywheel, on Dellortos with 35mm chokes, Bean 4-2-1 headers. Smooth and revvy all the way to the 7k rev limiter. No stumbling, no torque dip, just bliss. It can be done.
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PostPost by: rgh0 » Fri Jan 22, 2021 12:25 am

Europa88 wrote:Can I have Grunty and sophisticated? Asking for a friend :lol:

I think I will probably go the 72mm steel crank route joking apart. It just suits my style of driving!



Yes with the right build it can certainly be done. Ford built these engines as standard with this stroke and they have been used in Formula Ford as race engines in essentially standard form for years so no fundamental issues with the overall performance. You can improve on Fords standard 77mm stroke design with lighter pistons and rods which are available at reasonable cost these days. Even longer stroke engines are possible and are supposed to perform OK so 77 mm is not really the upper limit from a stroke perspective for a good performance engine

Re the dyno results
The Europa will have potentially greater dyno losses due to the all indirect gearbox depending on which gear the runs were done in. A friend of mine had a consistent difference of around 10 to 12 at the wheels HP between the same engine including inlet and exhaust configuration in his 7 and TC Europa with the Europa lower. The actual engine was a 190+HP competition 1600cc twin cam. We finally concluded after a number of engine swaps and dyno runs that about half of this was due to how you had to tie down of the Europa on the rolling road increasing tire losses and about half due to the all indirect gearing in the Europa box with greater losses if testing done in top gear compared to the 7 with its direct top. Less difference in losses if testing done in third gear but the Europa was still higher probably due to the helical gears in the Europa box versus the straight cut gears in the Seven.

There are standards for correcting dyno result to standard atmospheric pressure and temperature that are built into modern dynos and would be consistent across most dynos. However no standards for how you correct for rolling road losses to translate wheel HP to flywheel HP. Each dyno manufacturer will have their own algorithm method and its hard to interpret computer adjusted dyno results unless you know this and know what gear the dyno runs were done in.

In the end it is rear wheel HP that actually propels the car and is the number you should be most interested in !

cheers
Rohan
Last edited by rgh0 on Fri Jan 22, 2021 3:39 am, edited 1 time in total.
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PostPost by: 1owner69Elan » Fri Jan 22, 2021 1:59 am

2cams70 wrote:I prefer smooth free revving engines too. I'd recommend a steel 72mm crank in your existing engine over a conversion to a long stroke1700cc engine. Depends what your preference is - grunty and crude or smooth and sophisticated!


Not sure I would characterize a stroked TC as "grunty and crude" as opposed to "smooth and sophisticated". I'm with the above posts from Steve (bitsobrits) and Rohan (rgh0) that a stroked engine can be grunty (lots of torque) AND smooth and sophisticated.

I have a stroked TC (1692 cc) with a lightened flywheel for street use that revs fluidly and quickly to its observed 7K redline. Yes, lots of low end torque that extends all the way to redline. This is hardly a tractor engine. High lift, short duration cams. Ported SAS Weber head. 40 DCOE's for responsiveness and tractability for the street. 181 hp @6900 and 143 lb-ft @ 5100 (dyno at the flywheel).
For a road car, I think most people would be hard pressed to prefer an engine with less torque, less horsepower, less responsiveness, but with peaky revs. Somehow the notion that a properly setup TC that happens to be stroked is somehow "less sophisticated" and "crude" IMHO is just wrong. But perhaps you are just trying to be provocative.
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Lotus TC Dyno.jpg and
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PostPost by: 2cams70 » Fri Jan 22, 2021 6:04 am

Having had experience behind the wheel of most of the Kent series engines - 997cc Anglia, 1100cc crossflow. 1300cc crossflow, 1600cc crossflow, 1500cc pre-crossflow and Lotus Twin Cam I can say that as you increase the sroke of the engine (bore remaining constant) you gain in some areas but lose out in others. The longer stroke engines are definitely not as smooth or revvy as the shorter stroke ones all else being equal. The longer you go in stroke the higher the piston speed and the more mass you have thrashing around. It comes down to the laws of physics. Some of us enjoy going beyond 7K too. It's no stress for a regular pushrod crossflow to rev. to 7K. Why not make best use of the Twin Cam head!? An uprated specification based on the standard bottom end dimensions is a very nice thing too. You don't need to stroke the engine to get more performance.

I must say also that whenever power and torque curves are posted on this site I very rarely see the data below about 3,000RPM. For a road engine 1,000 - 3,000RPM is an important speed range. It seems a lot of the engine builders don't like to disclose the data in that range!
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PostPost by: rgh0 » Fri Jan 22, 2021 9:32 am

2cams70 wrote:...... The longer stroke engines are definitely not as smooth or revvy as the shorter stroke ones all else being equal. ,,,,,,!


Certainly with all other things being equal, smoothness decreases as engine vibration due to the inherent secondary couple imbalance in a 4 cylinder engine increases with stroke increase. If you reduce reciprocating mass in the pistons and rods with increased stroke you can balance these things and maintain the same level or achieve even less vibration and better smoothness.

The definition of "revvy" is some what looser and hard to pin down but if it relates to the acceleration characteristics of the engine through the gears and ability to pull strongly to maximum revs of the engine. The stroke has only a limited contribution compared to many other factors but it does affect rotating mass which can affect engine acceleration and can limit maximum revs and produce a reduced "revvyness" perception . They don't call the formula junior short stroke engines "screamers" for nothing :lol: Again good design can reduce rotating mass with lighter cranks and rods and flywheel and higher maximum revs to make a revvy long stroke twin cam along with all the other mods needed to make a revvy engine at any particular stroke

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PostPost by: 2cams70 » Fri Jan 22, 2021 9:51 am

Yes but you can drop all those nice light bits and pieces in a Twin Cam with standard stroke and have an even sweeter engine again! It's all what your personal preference is I guess.
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PostPost by: rgh0 » Fri Jan 22, 2021 10:00 am

2cams70 wrote:Yes but you can drop all those nice light bits and pieces in a Twin Cam with standard stroke and have an even sweeter engine again! It's all what your personal preference is I guess.


Yes absolutely agree and that's what I do ..... and it sure sounds sweet at 8500 rpm :D

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PostPost by: Europa88 » Fri Jan 22, 2021 1:27 pm

I think I will just enjoy the car as it is short term. But I will consider both options on short and long stroke when it comes time to rebuild. If I was to go the long stroke crank route, which would be the better option
Tall block and 77mm steel crank or a 77mm steel crank in my L block? I’m guessing the former could be more expensive as I would need Steel mains caps and line boring. Probably Rods and pistons too. Are the standard rods any good for 7500rpm?
Would I need forged instead of the cast Powermax pistons too. Thanks for all the advice.. this is undoubtedly the best platform for discussing The TC engine, I’ve ever come across.
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