What do those #'s mean for the jets like 70 up front and 50 in back. I know what they do but what do they mean, i hear about changing like 6 #'s but i don't know exactly what that does. Thankx in Advance

jet size number relates to the amount of fuel a jet will flow, NOT the size of the hole..so make sure you buy new jets of a different number if you want to change and dont waste time drilling out the hole size on the jet if you want to do it right. You can drill out a jet and have it flow LESS fuel because you just destroyed the chamfer of the hole...higher the number the more fuel the jet will flow, and try going up at least 2 sizes at a time to get away from the tolerances of the jet rating..

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70 chevelle ss396 conv
66 chevelle ss396 hdp/conv

I wanted to know what the #'s meant. like what does 70 mean compared to 50. psi?

GumBall
According to Doug Roe's "Rochester Carburetors", the jet size is the diameter of the hole in the jet in thousands of an inch.

#70 jet has a 0.070" diameter hole.

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Fred Aldrich
Web Site: www.GeoCities.com/~69_chevelle (http://www.GeoCities.com/~69_chevelle)




[This message has been edited by Fred Aldrich (edited 08-07-99).]

These guys are both right, sort of. On a Q-jet, the number is the hole size in thousands, on a Holley and others, the number is a relative that is not actually a size. Just keep in mind that bigger flows more gas, smaller, less. A stock Holley might have 65 in front, 68 in rear, but will vary quite a bit. A stock Q-jet usually starts out with 68 in front, again will vary quite a bit, no changeable jets in rear. A 6 number change is pretty radical. tom

[This message has been edited by tom3 (edited 08-07-99).]

In an old ASAP catalog I have (anyone remember them?) they have a listing of Holley jet numbers and the associated size. For example, #70 is .073". #72 are .079. #76 are .084". There's not much correllation between number and size. Of course the size in inches was supposed to be the nominal size...there are substantial variation due to manufacturing tolerances. And of course, I'm assuming that this old catalog is correct. I never asked anyone from Holley for verification.

Thankx guys i figured out what i needed 2.

Thankx again