Lotus Elan

a day at the dyno

PostPost by: nmauduit » Tue Oct 01, 2019 8:10 pm

My street S4se had been waiting a few years for that day, but eventually

20191001_094154.jpg and
1700cc big valve Q420 at the dyno


I did not build this engine (the original one, Stromberg head, is stored), just swapped the unknown cams (probably CPL2 reground) for known Q420, Weber 40DCOE with 34mm chokes. It is believed to be a 1700cc (old build invoice from the 80s), running on RON 98 gas.

I had previously sorted a bit the carbs on the road with the help of a lambda wideband sensor (Innovate), though the electronic ignition (123.nl) or other electrical gremlin makes the tacho recording chaotic (rpm signal lost at high revs), hence not as usable as it should... so a reason more for dyno fine tuning...

The day started with a decent compromise with the carbs jetting (conclusions from road test in parenthesis)
Emulsion F16 (F2 too rich)
Main 135
Air 170
Pump 35 (40 too fast)
Idle 40F8 (45 or 40F9 too rich)
the first goal being to fine tune the ignition timing
first pull gave 126.8 @6300

Initial 123.nl curve was maxing out at 33?, but to my surprise this was still not enough (32? was dropping the power at least 2.5hp in the concerned zone), so after a number of pulls the following compromise was adopted

1000 12? (not tuned)
1400 18? (not tuned)
2000 25?
3500 32?
5000 34?
6500/6800 34?
8000 19? (acting rev limiter in case rev limiter does not work)

I prefered not to push beyond 34? on this street engine: this curve provided a 129HP new reference, from which the carbs jetting were optimized (Main mostly between 130 and 135, air over 155-190) to

Main 135 Air 180
final street result 130.5HP (about 164Nm torque @5150 - ~121 ft.lb that is)

(Main 130 Air 190 was marginally better by 1/4HP but a bit lean at high revs 13.5-13.6 right at the cut - torque was a bit better by a couple Nm, too)

p1050485.jpg and
quite a few pulls to gain 4 hp...


I may come back to try the leaner setting after I recalibrate the lambda sensor, to check if indeed it is too lean at high revs or still ok, not that much of a difference anyway. The curve appears quite flat from 5300, I suppose this is admission limited since I have a road TTR exhaust line supposed to take up to 160HP (stock big valve head, not ported).
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PostPost by: innesw » Tue Oct 01, 2019 8:26 pm

Bravo Nic!
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PostPost by: murt30097 » Wed Oct 02, 2019 12:15 am

Nice power Nic.

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PostPost by: benymazz » Wed Oct 02, 2019 4:39 am

Sorry if you mentioned it in the post, my reading comprehension skills are not great - are these figures "at the wheels" or corrected for losses in the transmission?
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PostPost by: diablo » Wed Oct 02, 2019 7:19 am

Please send a PM to me for the adress of the company who did this test , je suis en Normandie . Merci .
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PostPost by: nmauduit » Wed Oct 02, 2019 8:30 am

benymazz wrote:Sorry if you mentioned it in the post, my reading comprehension skills are not great - are these figures "at the wheels" or corrected for losses in the transmission?


no I did not : these were corrected figures, taken in 4th (straight through) of the Lotus 5 speed gearbox, 3.77 diff with Quaife TBS, TTR sliding shafts, old 175 70 13 cheap street tires on steel 4.5" Lotus rims.

I don't pay too much attention to actual figures, the goal was to see what kind of improvement could be done - and to that end it was useful (about 3% gain, half from timing, half from richness), esp. considering I was not expecting the need for more spark advance and would not have tried on the road. I don't think I could have felt 1% or 1.5% improvements on the road.
Last edited by nmauduit on Wed Oct 02, 2019 9:58 am, edited 3 times in total.
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PostPost by: 69S4 » Wed Oct 02, 2019 8:55 am

nmauduit wrote:
benymazz wrote: I don't think I could have feeled 1% or 1.5% improvements on the road.


I wonder how sensitive the 'seat of the pants' dyno is? How small a change can you 'feel'? I read somewhere ages ago that it's around 8%. Anyone more sensitive than that?
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PostPost by: RichardHawkins » Wed Oct 02, 2019 8:07 pm

My seat of pants dyno is worn out, but a long time ago a motoring journalist LJK Setright said that if you can't feel the improvement it was not worth the money. I continue to spend money for improvements I cannot feel.

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PostPost by: Frogelan » Fri Oct 04, 2019 4:47 am

Well done Nic!

A very interesting day at the dyno which seems to be at Montigny sur Loing (Seine et Marne).

The car looks very good!
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PostPost by: nmauduit » Sun Oct 06, 2019 9:24 am

Frogelan wrote:A very interesting day at the dyno which seems to be at Montigny sur Loing (Seine et Marne).


it is indeed! Damien is a car enthusiast running this small operation and races his turbocharged Toyota from the 90? (I must admit my ignorance of these, 400 to 600 HP with 1.7bar of boost, this is clearly out of my league). He was very friendly and helpful with operating the dyno, though I did all the tuning of the car myself (carbs and timing) as he only knows about electronic cartography and injection of more modern cars. This may not suit everyone, but was perfect for me.

The car was too small for the dyno, it took us more than an hour to figure out how to strap it on, but he remained cool and friendly all along - and eventually we came up with a trick involving a large number of straps that was enough for a small engine. Remaining test were very smooth, we decided to calibrate the dyno for my transmission in neutral rather than free rolling with the (hard) clutch applied for the time it takes to get down from 6500+ to 2000 rpm, so the protocol was to get into neutral when lifting off as reaching the limit. In case you're interested for your car when the time comes I'll tell you the contraption to strap it on there...
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