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-   -   AFR on the Throttle Stop (http://www.classracer.com/classforum/showthread.php?t=66578)

eman588G 06-12-2017 12:17 PM

AFR on the Throttle Stop
 
Just recently got a Racepak and ran S/C recently and now have some data. On the Stop my average AFR is around 10.5 and wide open average around 12.2. Question, Should the AFR on the stop be closer to my 12.2??

nomad 06-12-2017 04:52 PM

Re: AFR on the Throttle Stop
 
A lot will depend on what the engine actually wants. If what your car is doing is what it's supposed to do then what you are seeing is correct for you. Don't get all tied up in the numbers because what the other guy is seeing is rarely what you should.


We always place our curser at 2 seconds on the timeline. We check cruise RPM and O2 here. Quick enough you'll see trends or changes.


I'd check out the power valve thread here if you have a S/G or SS/T car.

eman588G 06-12-2017 08:35 PM

Re: AFR on the Throttle Stop
 
The cruise rpm and the 02 appear to be around the same on each run. This was the first race with the racepak and the 02 so I don't really have a ton of data. In the past, it sounded like the motor wasn't running clean when it first went on the stop. Raised the stop rpm and it sounds better.

Just want to eliminate any possible inconsistencies, with the tuneup.

Will look for that power valve thread.

sst7250 06-29-2017 02:41 PM

Re: AFR on the Throttle Stop
 
AS pointed out don't get to caught up in chasing an "ideal" number there. You need to find what works for your combo and what makes it repeatable. Having said that there are things you can do to change stop AFR's. Depends on what stop and what carb as to what you will need to do.

B1Ken 06-01-2018 04:23 PM

Re: AFR on the Throttle Stop
 
Quote:

Originally Posted by eman588G (Post 537134)
Just recently got a Racepak and ran S/C recently and now have some data. On the Stop my average AFR is around 10.5 and wide open average around 12.2. Question, Should the AFR on the stop be closer to my 12.2??

That seems awfully "fat" on the stop. I would think that would cause dialability problems with changing temperature. I was shocked, looking at A/F ratios with my APD carb on the stop when it showed it was about 15:1 !! I don't know how accurate that was but it had the WOT at about 13.2. That carb gave me a very flat rpm on the stop. Unfortunately, I still couldn't dial the car anyway. An APD carb. has a primary power valve, which is nice because it allows you to adjust A/F on the stop. I increased the primary jet size a bit to get the A/F ratio lower on the stop.


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