Q&A

Monday Mailbag: Increasing Horsepower, Gas Mileage & Compression

Got questions?

            We’ve got the answers—Mondays when the Summit Racing tech department tackles your automotive-related conundrums. This week, we’re talking budget horsepower and compression ratio.

 From: P.W. • Rosholt, WI

Q: I have a 1984 Chevy Z28 Camaro with an HO 305 engine and five-speed transmission. I want to increase horsepower and gas mileage while staying on a budget of around a thousand dollars. Do you have any suggestions for the parts I need to get the job done?       

A: For a quick and inexpensive upgrade in power, top off your engine with a K&N Washable Lifetime Performance air filter (KNN-E-1450). It’ll ramp up your Camaro’s airflow and provide superior filtration over stock. Next, balance out the increased flow of the filter with a pair of Hedman Street Hedders (HED-66481). They’re specifically designed to fit like stock while generating serious power and performance. To tie your new mods together, equip your ride with a Hypertech ThermoMaster computer chip (HYP-11352). It reprograms your engine with more aggressive timing and fuel curves for dyno-proven horsepower production. This combination of modifications keeps you in your budget range and gives you the best bang for your buck.

From: J.S. • Redgranite, WI

Q: I have a 383 stroker engine that’s making 525 horsepower and 450 foot-pounds of torque. I’m running a Trick Flow Super 23® top-end engine kit with a 9.1:1 compression ratio. I would like to increase the compression to 14.1:1. Would that give me more horsepower? Also, I was thinking of using a 7.5-inch GM rear axle. Do you think it will support the engine’s power?

A: You would see a large increase in power production with a 14.1:1 compression ratio. However, you’d have to make some serious upgrades in order to complete the project. Your current setup won’t flow enough to operate properly at the higher compression.

It’s important to match your engine’s compression with the recommended ratio for the cam you’re running. Too little compression (or too much cam duration) will cause cylinder pressure to drop, which will lower the power output of your engine. Too much compression (or too little cam duration) and cylinder pressure will be too high, causing pre-ignition and detonation. Use the Compression Calculator in the Expert Advice section at SummitRacing.com to find the exact specs you need.

As for the rear axle, the 7.5-inch GM is too small to support the added power created by the increased compression. You’d be much better off with a beefier Ford 9-inch rear.

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