The 1947 - Present Chevrolet & GMC Truck Message Board Network - View Single Post

Flathead Smith · 04-18-2018, 02:32 PM

There should be a number engraved on top of the jet. That number is the jet size in thousands of an inch. So for example, a #68 is 0.068" and a #72 is 0.072". I think most stock Quadrajet jets ran from #66 to #78, though I'm sure the aftermarket offered other sizes.

Figuring that ethanol has about half the BTU content of gasoline and that it is mixed at around a 10% blend here in the States, I guessed that increasing the jet size 5% would be about right. So I increase the jet size from #68 to #72 and it did help drivability of my truck, though fuel mileage dropped about 5%, which is what one would expect.

04-18-2018, 02:32 PM	#5
Flathead Smith Registered User Join Date: Aug 2011 Location: DeArmanville AL Posts: 47	Re: dimensions of quadrajet JETS There should be a number engraved on top of the jet. That number is the jet size in thousands of an inch. So for example, a #68 is 0.068" and a #72 is 0.072". I think most stock Quadrajet jets ran from #66 to #78, though I'm sure the aftermarket offered other sizes. Figuring that ethanol has about half the BTU content of gasoline and that it is mixed at around a 10% blend here in the States, I guessed that increasing the jet size 5% would be about right. So I increase the jet size from #68 to #72 and it did help drivability of my truck, though fuel mileage dropped about 5%, which is what one would expect.