Chevy LT1 Head Questions - Performance Q&A

Kevin McClelland Jun 1, 2009 0 Comment(s)

As for the cylinder heads needed for your block, you are correct that you have an LT1/LT4 casing-number block. These blocks were offered in both two- and four-bolt main configurations. The cooling system is a reverse-flow design, which requires either production LT1/LT4 heads or aftermarket heads specifically designed for the reverse-flow cooling system. These engines came in '92-97 Camaros, Corvettes, and Impalas. A few of them snuck into '98 Camaros as that model was swapping over to the LS1 engines. There are plenty of heads out there to choose from.

Back to your cylinders. Make sure before you build up this engine that you measure the cylinder walls and check for out-of-round bore diameters. It's better to find them on the front side of a build.

It's All About The Math
Q: My '67 Camaro has a 402 big-block and a TH400 transmission with 3.55:1 gears. My 60-foot time is 1.749, and my eighth-mile e.t. is 7.727 at 85.68 mph. In the 1,320, I have run as fast as 12.128 at 109.57 mph. This car has a 3,000-stall converter, a single-pattern cam with 302 degrees duration and 0.544 inch max lift, and an Edlebrock Torker II intake with a Holley 850-cfm double-pumper. I understand that the dual-plane would probably work better, but I can't get it under the hood without a scoop. Can you give me a ballpark estimate on the horsepower for the car with full interior and the spare and jack in the trunk? How much can I gain with a lower gear ratio? Everyone around here bracket-races in the eighth-mile. Do you have a table for gears such as 4.11, 4.56, 4.88, and 5.13 running a 26x10 Hoosier slick? Thanks!
Marcus Humphries
Dawson, TX

A: Your Camaro is running very well for its minimal modifications. If I were to throw a number at the power of your engine, it would come in around 425 hp. The car is moving well on the torque built by your 402. The main problem with lowering the gearing to match the eighth-mile racing distance is that your First gear becomes so low that it's almost impossible to hook the car up! You have a good 60-foot time for a basic street car, and the 26x10 Hoosiers are doing their job. Putting a ton of gear to match your horsepower peak to the finish line might give you fits.

With the 3.55:1 gears and a 26-inch tire, we'd say you're probably in the low 4,000 range going across the eighth-mile line. There are gear ratio calculators online that you can use. Check one out at Or you can use this formula to calculate your engine speed based on any gear you wish to try. First multiply your tire diameter by your desired engine rpm. Next choose a gear ratio and multiply by 336. Then divide the tire diameter result by the gear ratio result. This will give you the miles per hour of this combination without any slippage. Remember, the miles per hour may vary due to tire growth and converter slippage.

Always keep in mind: Mild big-blocks move the car mostly on torque. Chasing the horsepower peak to lower your e.t.'s may not give you the results you're looking for. Running much lower than a 4.11:1 gear may cause you more trouble in the 60-foot than it's worth. Good luck, and drive a tight stripe!


Spline Count
Q: My '84 Camaro Z-28 has the HO 305 VIN code "G" engine, coupled to a TH700R-4 transmission. I don't know if the transmission input shaft is a 27- or 30-spline. I have read that in '87s and later they were 30-spline. Some say the switch was made in the '86. I also read that the switch occurred mid-year in the '84. I'm confused. Is there a way to tell if my transmission is a 27- or 30-spline input, short of removing the transmission and visually examining the input shaft? Thanks.
Steve Parsell
Lyons Falls, NY

A: Man, I think this has turned into a great game of telephone! You know, when information gets distorted as it passes from person to person.


Connect With Us

Get Latest News and Articles. Newsletter Sign Up

subscribe to the magazine

get digital get print