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Old 04-27-2006, 09:37 PM
Humbucker's Avatar
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Join Date: Dec 2004
Location: Chattanooga, TN, TN
Cobra Make, Engine: Superformance #1408
Posts: 80
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Default Woah! Went to the dyno - Jet Sizes!

Some of you have been following my upgrade progress. I had a stock Ford Racing Crate Engine, 392ci, 430hp, Performer RPM intake, with a Holley 750 with a stage 3 Jet Performance modded carb. It had 71's in the front and rear before the upgrades, which consisted of AFR 185 heads, and a Victor Jr. intake. Ran smooth as silk.

While trying to figure the jet sizes after the upgrades, I went up a size here and there on the primaries and secondaries until I ended up with 75 fronts and 78 rears. Still lean. I took it to a local performance shop today with a dyno, air/fuel meter, etc. We made about 5 pulls and ended up with, get this... 86 in the fronts, and 90 in the rears. No joke. We're still a bit lean as it's ranging from 14:1 to 15:1, but the tuner suggested a different carb as he felt we went up about a far as we should go. We even had to drop the air bleed sizes a couple sizes to richen it up a bit.

He also mentioned going up this high in jetting will kill some of the snappy throttle response, and would probably stumble off idle if the gas is punched. He was right. What's the solution? Should I go to a larger carb now? Maybe an 850? The carb I have now has the power valve in the secondaries removed and blocked off. Should I put one back in and try to retune? Scottj seems like a very informed fellow, and he suggested backing down to a 650.

I'm confused (again!) Any suggestions now that you know a bit more?

BTW, I'm not sure what my car dynoed before, but I gained 56hp at the rear wheels by going from 75F/78R to 86F/90R with the new upgrades.
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Jake - Ringgold, GA
Superformance #1408

Last edited by Humbucker; 04-27-2006 at 09:41 PM..
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