Don Terrill’s Speed-Talk

The local dirt track has decided to allow 4 barrel factory intakes with a 2 barrel adapter due to the scarcity of the old intakes. The Chevy guys are using the off road high rise marine intake and a 500 cfm 4412 Holley. I recently found a carb in decent shape, but some changes have been made to it. The jets are 67, power valve 45, and the throttle blades have 1/8" holes in them. The engine is a 9.1:1 350 with un-ported 1.94 valve 462 heads. The cam is and Elgin hydraulic roller, (230/230, 480 lift 108 lsa), and for exhaust the rams horns that angle to the rear and some small case size Flowmaster mufflers. I am trying to decide on jetting, I don't think the pv is a problem, and I am unsure of the holes in the butterflies. There is almost no test and tune time available, so I would like to be able to get close on the first try.

A 4412 comes with a 73 jet from Holley. A lot of the circle track carb builders use a PV to lean it out at the top as they tend to go rich, too lean at lower speeds if you jet for higher RPM. I'm not convinced that is the best course for one...

My inclination is to put the stock jets in for a start. The motor isn't exactly a powerhouse. The owner/driver kills everyone because of driving skill and his ability to set up the suspension. It would be interesting to see what he could do with some horsepower.

The 67 jets are not right, Jmarkaudio posted 73 jets for a start, I agree, what size are the power valve holes. The 1/8 inch holes in the throttle blades seem pretty close, maybe a tad large for your cam.

I didn't have any 73s so it got 74s. I took closer look at the holes in the butterflies, and they are not owner drilled. The holes are very centered and very clean. My initial thought was someone installed aftermarket butterflies with holes, but the screws still show the factory crushed screw retention.

215 butterfly is factory installed with those holes; some tracks look for that number as part of tech. A 45 powervalve with that cam may be flirting with closing at higher rpm. A 65 might give you a margin of safety until the jetting is sorted out. As Mark mentioned; some folks are using a larger power valve restrictor and a smaller jet utilizing the p/v to close at high rpm in order to lean the high side. A little more info on the rest of the circuits would help.

Thanks for the call on the Power valve. Most of my personal stuff is either street or drag strip. My head isn't tuned to 2 barrel circle track.