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Discussion Starter #1
Last August I ran my all time best ET in 1/8, 7.12 @ 95, My data logger showed lambda at 0.89 on that run (AFR=12.5 for E10 gas in Calif.). Since then lambda has increased due an ignition problem and ET has come up as well. I have fixed the ignition problem but lambda is now at 0.94. So my question is, should I rejet the carb to get back to 0.89 lambda? I have been running 76 primary/80 secondary in my Holley 750 DP.
 

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I would try making a change. Head towards dropping the lambda number down. If the MPH does not go up, then leave it. I always jetted at the track for MPH. If it was not increasing, the motor was not making any more power and it wasn't worth it. Otherwise as a bracket racer, the car was consistent it didn't matter.
 

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Lambda .86 always seemed safe and prudent for N/A gasoline combos. Excellent point with the E10 blend, which would require slightly more fuel in comparison to straight gasoline.

I've ran my Nova anywhere from 12.3 to 13.1 (.83 to .90) with no noticeable change in mph or ET. I know I'm probably wrong, but at this point I feel everyone gets too caught up in the details of AFR when in application (at least with the LS) it just doesn't really affect a huge change.
 

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Bob, when I used to run a borrowed 750, it had 71/80 jetting. We put that carb on several combos and it was always faster than what was on the car.
On the dyno we tried going up and down multiple sizes, and always left the session with the same jetting. Of course, that might be totally wrong for your combo!:eek:
 

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Discussion Starter #5 (Edited)
Update

Took the Nova down for TnT last weekend, hoping to tune the AFR and get ETs back down to what I ran last summer. That did not happen. :no: First, we had the worst head winds I have ever seen at the track with some gusts as high as 40 mph. While I waited for winds to die down, I changed the plugs and checked all connections. Only got 4 runs in, and they all showed lambda starting at above 0.9 and dropping to as low as 0.7 down track. The plots below show 2 of those runs. The third plot is from a test run 2 days later at an undisclosed location :cool: and shows it was closer to what I expect the lambda curve to look like, bouncing around 0.9. Note that I did not make any changes to the car after I left the track, but the elevation was about 1000 ft lower at this location. I talked to my carb builder and he thought the high speed air bleeds might be partially plugged with dirt. I will try spraying carb cleaner to clear them,but will have to wait until the rain stops to see if that makes a difference. To be continued....
 

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What you can rely on 100% is tuning your fuel system for MPH. The timeslip is your most valuable tuning aid you have available, bar none.
Absolutely, like Ray also said jet to MPH. Time slip is the best tuning barometer.
 

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Absolutely, like Ray also said jet to MPH. Time slip is the best tuning barometer.
I totally agree. My problem is ET and MPH dropped way off over 3 months and I thought I had found the reason (an electrical issue) and fixed it. But my MPH is still down and the AFR is very erratic all of a sudden. Still have some trouble shooting todo. :confused:
 
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