Using Compression to Make Horsepower in a Small Block Chevy - Danger Mouse Part 23

Part 23: Squeeze Play

By Mike Petralia

550hp And Climbing
Warning!! Disclaimer! Do not try this at home! At least, not until we can perfect it first. Yes, this month was really cool. We went Loco and we pumped up DM's compression with a new set of pistons. Then made over 550hp on 91-octane pump gas, but it all came with an unacceptable sacrifice. Peak power was high, but check out the low end and you'll see what we mean. Even though we picked up 45 horsepower at the top, the pump gas detonation DM suffered at the low end of its curve hurt average output, especially torque. We needed to control that detonation and get back that lost low-end power.

The one thing that we really needed to fix the problem was the one thing we didn't think of getting before this test. A computerized, adjustable, timing control. Yes, next month we'll put a timing curve back in the distributor! (You're probably wondering why DM didn't have a timing curve in the distributor to begin with? Well, that's entirely my fault. A few months back, in a pinch I yanked the distributor out of my Mean Little Rat and forgot that it had a locked-out advance mechanism. Until now, it had been working fine for DM's testing, since a locked out distributor works well on the dyno most of the time. But, today my careless indiscretion came back to haunt me. -MP) So next month, first order of business will be to re-test with a new programmable ignition box, if we can get one in time.

What Made The Power
Part 23 was all about the squeeze. While it's well known that increasing compression can increase power, we wanted to know how far the envelope pushed before we got pinched. So, in an effort to show you guys what can really be done with compression, and what kind of headaches too much of it can cause, we squeezed DM from 10.0:1 up to 12.5:1 using a new set of Lunati forged pistons that feature a 10cc dome, (previous pistons were flattops with four valve reliefs).

And, as usual, we wanted to keep it all on 91-octane pump gas, which worked pretty well, considering the overall results. And a bit more tuning to kill the detonation will practically guarantee us more power down low, which will also bring the average power up across the board. Of course, this combination may be a bit extreme for an everyday driver, but we're already way past that point and if you wanna' build a grocery-getter, refer back to DM Part 6 or 7 where we really made pump gas shine. Otherwise, check out how the big boys play!

Dyno Testing Part 23
We're comparing this month's test to Part 21 - Test 36. In that test, Speed-O-Motive had just replaced the COMP Cams Xtreme Energy XR280R solid roller cam, Edelbrock Victor Jr. intake, and Mighty Demon 650 carb with a larger COMP Cams XE286R roller cam, big Edelbrock Super Victor intake manifold, and an out-of-the-box Holley HP1000 double-pumper carb.

First up for this month, Part 23 - Test 37, Speed-O's crew swapped in a new set of 10cc-domed Lunati pistons and bolted on a Carb Shop-prepped Holley HP950 with "Super Boosters" and trick 3-circuit metering. We first ran it on pump gas and got some great peak power figures, but detonation-induced power losses at the low-end hurt all around. So next we simply switched fuels to 105-octane VP race gas and were immediately rewarded with more power (compare: T37 vs. T38).

Then, after remembering that DM's current distributor had no timing curve in it and was locked out at 36-degrees total advance, we thought there might still be some power left in a timing curve. So we swapped in a new Pertronix distributor with a hi-po ignition module and picked up even more power (see: T39). Also, Test 39 was the first test ever in which DM AVERAGED 400hp over an extremely wide rpm band from 2500-7000 rpm! In fact, average torque was also the highest it's ever been, which is a HUGE achievement, because it's the average power that gets you down the track. Peak numbers are good, but the engine with the most average power will almost always win the race.