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Don Kirn has built race-winning drag and circle track racing engines for over 20 years. The fourth generation Kirn has just joined the family business which began life as an engine shop back in 1911.
Send your engine questions to horses@racingnetsource.com

Don:
I started drag racing an old '72 Chevy truck I have had for years and I want you to know I am not a professional engine builder, so don't laugh at some of the things I did.

The engine is a 1975 454 with unknown mileage. I put a new cam, solid lift .558/.566 lift and 310/320 duration. Cam kit, new springs, seals, locks and retainers, 7/16-inch push rods (that's a story in itself), 1.72 roller tip rockers, double roller time chain. It has an rpm air gap intake with a 25-year-old (plus-or-minus) Holley 750 carb, high volume fuel pump.

I rebuilt the turbo 400 trans and put a 3000 stall converter and 4.11 gears in the rear. The heads are stock oval port, I think 110-cc. Pistons are stock, maybe 9.0 compression. The numbers on the heads say it is a '76 Caprice, the motor says '75.

I ran it this spring with some 28-inch slicks and the rpm's were more than I wanted to run on the old crank and pistons; it crossed the line at 6000. It ran 13.70 in the quarter, but then some axle wrap took out the driveshaft and transmission. I fixed the problems and borrowed some 29.5-inch slicks and ran a best of 13.22 at 98 mph (crossing the line at 5500 rpms). I think not too bad for a first time effort in a 4000-lb truck.

I borrowed an 830 Holley and made one pass. It didn't hook up and ran 13.09 at 102 mph and crossed at 6100 rpm. The next attempt busted the spider gears and carrier.

The 830 seems to be better, so what about running an 850? Isn't 6000 rpms too much on that old motor? Should I look at getting some taller tires or smaller gears? What do you think of my parts selection? The motor runs good and revs faster than my brother's 11-second 355 c.i. Chevy, so I must have accidentally got something right. Any ideas on horsepower?

Thanks for your time.
Any comments you make will make me happy.
Johnny Works

Dear Johnny,
Sounds like you've maxed out your 454. You are correct in not wanting to turn it over 6000 rpm. My recommendation would be to find someone with a cylinder leakage tester. That would tell you a lot about your used piece. Anything above 25-30 percent hurts the power a lot. With a tester you can see where it's failing past the rings requires disassembling and rebuilding, but if most of the leakage is past the valves, it's possible to just pull the heads and have some head work done.

Your choice of parts is good, but don't try any nitrous on the engine with cast aluminum pistons. I think rebuilding the engine, complete with new forged pistons, good rod bolts, and stainless valves would give you some confidence when it goes over 6-7,000 rpm.

An 850 cfm would work well for your combination, especially if you rebuild the engine and increase the compression ratio. The other breakage problems need to be addressed also, but that's a whole different can of worms.

I hope this will help you with your new hobby. Good luck.