Holley Carb Jet size reduction for 1972 LT-1?

[Bill B.]

[Duke W.]

Re: Holley Carb Jet size reduction for 1972 LT-1?

Fuel and spark advance calibrations changed nearly every year due to tightening emission standards. You can go leaner on the main jets until you get a bit of lean surge, then go back up one size.

There's a lot to be gained by optimizing the spark advance map - convert ported vacuum advance to full time with a B28 VAC and light springs to bring the centrifugal in sooner. You want to get it as close to the 365/375 HP 327 engines map as you can.

Once the spark advance map is optimized the next project is optimizing the fuel map. See my tuning seminar for additional info.

http://www.metroli.org/pdf/2012%20Nationals%20tuningseminar.pdf

Duke

[Timothy B.]

Re: Holley Carb Jet size reduction for 1972 LT-1?

William,

If you want to experiment with the main jet try this, take a big swing at it and reduce the jet size down to 60 and see how it runs on the MAIN circuit at cruise RPM's. If it surges in the cruise RPM's 3-4500 like Duke mention's then go back half way to 64 then see if it surges. If no surge go back half to 62 or if surge then go up half way to 66 and test.

The point here is to keep going half way to either the low or high size until it runs just out of surge. You can then figure out the sqin area of the reduction in jet size and add that value to the power valve channel restriction (slightly larger holes) to return the air fuel to the factory setting for wide open throttle.

You would need a few gaskets and don't over tighten the bowl screws and strip the holes in the main body.

If you don't want to go through all that I would probably stick with the factory jet size, my experience is that these settings are richer than the engine really needs but best for all around street driving, just make sure the tune is good.