Dyno Results - Need Tuning Help

[North Coast Cab]

Below is my dyno graph form today. AS you'll see I am rich through the mid-power band and too lean at the top. It's for a race car which runs typically between 5-7k. I'd like to pick up some power in the middle, and m,ore importantly save my motor on the top end.

46mm PMO's set up as follows:
38mm venturis
150 mains
180 air correctors
55 idles
130 idle air
F11 emulsion tubes
3.0 , Webcam 120/104, 1 5/8" headers, dual 3" out M&K
Electromitive Single Plug Direct Fire, BPR7EIX Plugs
Suggestions?

[TonyG]

Details...

What engine, what mods, what ignition, what induction, what exhaust...



TonyG

[cstreit]

John,

Air corrector jets will help with mixture above 5500RPM. Smaller jets are richer mixture IRRC

[TonyG]

145 main

170 air corrector

36mm venturi. 38mm is too big for a 3.0 making 200HP to the wheels.

Give that a shot. Also, you might want to consider a wide band 02 sensor setup so that you can test your air/fuel ratio without having to go to the dyno.

TonyG

[North Coast Cab]

Thanks. I run and LM1, but only saw that it was rich all the way through. I was very surprised with the top end leaning out.

I have sapre 145 & 140 mains, but only 190 & 200 airs. I'll have to pick-up some 170's.

What will the venturis do?

[TonyG]

I would question that dyno run with respect to their a/f ratio meter setup.

Something is wrong.

The TQ curve doesn't look like what it should look like based on your cams/carbs/exhaust.

Your TQ curve should be climbing towards 5000 rpms, not slowly falling off. Having a peak TQ around 3700 rpms doesn't make sense.


The first thing you need to do is to calibrate your 02 sensor on the LM1. Or better yet, calibrate it, then swap in a new one, calibrate it, then do a couple of runs and compare.

The smaller venturis will increase the "signal strength" across the jets. The engine will have better midrange and will be "crisper", and will have a better transition from the idle circuit to the main circuit.


TonyG

[North Coast Cab]

My Lm-1 was about .2 leaner than the dyno's, so I'm pretty confident they're accurate.
I'm told the motor should have higher compression pistons for this cam, so that may be part of the problem.
I'm targeting 210RWHP for my class, so I'm very close ther, but I'd like to fix the top end lean issue and increase the mid-range power if possible.

Thanks for the input, John

[TonyG]

>>>I run and LM1, but only saw that it was rich all the way through. I was very surprised with the top end leaning out<<<

If your LM1 was only .2:1 leaner than the dyno's measurements, then how were you surprised? I'm confused.

Anyway... that TQ curve looks all wrong based on the cam specs. Even if did not have the higher compression pistons you think you should have, the TQ curve should still look basically... opposite of what it does now.

What size intake ports are you running?

TonyG

[TonyG]

Here's a quote from Webcam with respect to the power delivery of the cams you have:

>>>Strong mid and upper end power for hot street and club racing. Carburetors or mechanical injection.<<<

Do you know what the lobe center line angle is for these cams? (I don't).


TonyG

[North Coast Cab]

No idea. I'm already in over my head at this point.
I'd like to tweak the carbs now and then research more options on twin plugging and changing the pistons over the winter.

[TonyG]

>>>No idea. I'm already in over my head at this point.<<<

Anyway... making the presumption that the dyno chart a/f ratios were what they are represented to be (rich in the midrange and lean on the top end).... the recommendations I have you should flatten out your a/f ratios and give it more power through 6k rpms.

TonyG

PS> I would verify the a/f ratios before I changed a thing.