Discussion Forum - Northstar Chevelle Club

4-door Chevelle · Super Poster

Dyno pull

Enganeer · Mega Poster

Your fuel ratio is way rich. Shoot for 12.5.

Doubl pumper / vac secondaries?

Look like your fuel ratio is climbing up to 2600 rpm and then the secondaries open up and dump alot in.

My guess, is the primary jets are on the small side and the rear jets are too big.

If vac secondaries, maybe a lighter spring to open up sooner.

-- Edited by Enganeer on Wednesday 2nd of June 2010 04:20:13 PM

4-door Chevelle · Super Poster

Yes, I was seeing that I am running rich. I have the Holley 670 Street Avenger carb, the stock configuration is 65/68 jets that I bumped to 68/72 but currently have 70/75 in there so I think I will go back to 68/72. I run the standard purple spring in the vacuum secondaries.

4-door Chevelle · Super Poster

I was just told (again) by another racer to plug the primary power valve and just bump the secondaries to 73. This is suppose to even out the flow of fuel while reducing it a tad in the secondaries.

-- Edited by 4-door Chevelle on Wednesday 2nd of June 2010 07:51:30 PM

John D · 2K+ Club

Invest a few $$ in:

http://www.jegs.com/i/Holley/510/20-13/10002/-1
and
http://www.jegs.com/i/Holley/510/20-12/10002/-1

As mentioned in that article I linked to, plugging the primary power valve will render your car basically un-drivable on the street.
By playing with jetting, secondary springs, and pump cams you can fine-tune the carb response to your engine/chassis combo.

4-door Chevelle · Super Poster

Yea, I wish I could to test-n-tune tomorrow at BIR but just can't swing it. Holley echoed what you said John about street driveability if I plug the primary PV so I am going to jet it down and try reading spark plugs again.

I thought I would read a lot more horsepower than it did???

Winston Wolf · Member

Definitely don't plug the power valve if you are driving it on the street. I would lean it out a stage and you will probably be ok.

I've made a few pulls on that same dyno. It's a Mustang, so the readings are lower than a Dynojet, but any tuning you do will be more accurate on the actual street due to the eddy current load inducing setup. If that was a Dynojet dyno I would tell you that the a/f is probably right on while on the street.

4-door Chevelle · Super Poster

Yea, the guy doing the pull talked about the Mustang and Dynojet but he talked so fast I didn't exactly catch what he was saying.