New engine build

[seniorchristo]

I have been acquiring parts the past few years in order to build a more powerful fast road engine for my S3 Elan. I finished the build this past summer and was finally able to schedule time on the Quicksilver Racing dynamometer to fine tune and document the results.

The engine consists of the following parts:

701M 6015 block
83.5mm CP forged pistons
77.6mm stroke crankshaft
10.5 to 1 compression ratio
1.625" intake valves
1.4" exhaust valves
Tony Ingram ING-425 -V cams
34mm chokes

initial carburetor jets:
Emulsion tubes - F16
Main 140
air correction 170
Pump jets - 40
Idle jets - 50F8

Results;
Horsepower - 155 HP at 6750 rpm
Torque - 134 at 5100 rpm

Fine tuning of the carburetor jetting was accomplished by balancing the exhaust temperatures of all 4 cylinders.
After a little back and forth the final jetting was as follows:

Main Air Exhaust temp.
1) 135 170 1329
2) 130 170 1341
3) 135 170 1320
4) 140 170 1324

I have never heard of such wide variation in carburetion jetting. Sandy (Quicksilver) assured me this is common for every engine he builds and dyno tests. What do others think about these results?

Chris

[rgh0]

Hi Chris
Outcome is about right in terms of power / torque for your engine specification.

I am not convinced that using surface measurement of exhaust system temperature is an accurate way to determine air fuel mixture on a Weber twincam as lots of other variables can contribute to that temperature and the jetting variations may just be changing the mixture leaner or richer and away from optimum to compensate for these other variations.

Personally I have always set the engines up using all the same settings in each choke and the average exhaust gas air / fuel ratio.

cheers
Rohan

[seniorchristo]

Thanks for the reply Rohan!

Using air/fuel exhaust mixture would have been my guess at the best way to maximize power also.

These dyno runs were done with the air box but no filter installed. This caused a loss of 2-3 HP and may have also affected air flow to different cylinders. I think maybe carb mounted filters are a better arrangement.

[TBG]

Rohan - what Idle jets were used above in Chris's post? I am presently on 135 Mains, 200 AC and 45F8 idle and have not quite hacked the fumble. D

[seniorchristo]

TBG

I am running 50F8 idle jets.

[TBG]

Thanks Chris - I will give them a whirl. D