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

Part 23: Squeeze Play

Mike Petralia Jul 1, 2004 0 Comment(s)

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DANGER MOUSE PART 8

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DANGER MOUSE PART 10

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DANGER MOUSE PART 22

DANGER MOUSE PART 23

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Sucp_0407_02_z Chevy_engine_build Piston_head 1/12

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.

Sucp_0407_05_z Chevy_engine_build Danger_mouse 2/12

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!

Sucp_0407_06_z Chevy_engine_build Dyno_graph 3/12

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.

Sucp_0407_07_z Chevy_engine_build Dyno_chart 7/12

Danger Mouse specs for Part 21 - Test 36*:
*Last test from previous month355 cid, 10:1 cr, 4.030-bore 4-bolt Motown block, 3.48-stroke Lunati crank, 5.7-inch Lunati rods, Lunati flat-top forged pistons, Total Seal ductile iron Gapless top rings, Edelbrock Victor Jr. heads (64cc chambers, 215cc runners, 2.08-inch intake valves, 1.60-inch exhaust valves), Edelbrock Super Victor intake manifold, COMP Cams XR286R solid roller camshaft installed at 105 intake CL (248/254 at .050, 286/292 adv, .606/.612 lift with COMP 1.6:1 rockers, 110 LS), Holley HP1000 carb, and 38 degrees total ignition advance

Sucp_0407_13_z Chevy_engine_build Compression_tester 8/12

Do you have a compression tester? If not, check out this new one in the Sears Craftsman catalog. It costs $50 and comes with a complete kit and carrying case. We broke it in on DM this month and measured 210 psi cranking pressure, which is quite a bit.

Danger Mouse specs for Part 23 - Test 37:
New 12.5:1cr Lunati pistons, Carb Shop modified Holley HP950, 36 degrees total ignition advance

Danger Mouse specs for Part 23 - Test 38:
Same as T37, but swapped to 105 octane fuel

Danger Mouse specs for Part 23 - Test 39:
Same as T38, but installed Pertronix distributor with timing curve starting at 18 degrees initial

We're always looking for new ideas. Do you have a better one for Danger Mouse?

Send your test suggestions to:
Super Chevy Magazine
Attn: DANGER MOUSE
720 Hundley Way
Placentia, CA 92870
Or e-mail: terry.cole@primedia.com

Note how DM's torque kinda' moved all around the map at the bottom of the curve, but stabilized up top. Most likely, that was due to detonation with the pump gas in T37 and a lack of any type of timing curve in T38. T39 had the benefit of both higher-octane gas and a timing curve to boost low-end power considerably. Also note that top end power never changed.

Sucp_0407_14_z Chevy_engine_build Belt_drive 9/12

Another part that got a workout this month is this new COMP Cams belt drive. We practically wore out the old one after two solid years of abuse. And we've already put the new one through its paces by advancing and retarding the cam this month in search of more power. Turned out that the engine worked best with the cam installed on a 104-intake centerline (2 degrees advanced).

The Word On Compression
We cheat by using a Reher Morrison Racing Engine's computer program to quickly calculate any compression ratio. But even though the computer does our math, we still need to input critical data to get things right. Your compression ratio is actually just a comparison of the volume in the cylinders with the piston at TDC vs. BDC. Or, how much the air and fuel gets "squeezed" when the piston moves up the bore. If you've got a 10:1 compression ratio, your mixture is squeezed down to 1/10th its full size at TDC, yet it still contains the same mass, which gives it such explosive power.

The compression ratio formula involves calculating the Swept Volume (SV) of the cylinder, which is everything BELOW the piston top, and calculating the Total Chamber Volume (CHV), which is everything ABOVE the piston top. The Swept Volume formula looks like this: (bore x bore x stroke x 12.87 = SV). The 12.87 is the only magic number here. Within its mystical confines are the calculations to figure volume of a cylinder and the conversion for cubic inches into cubic centimeters, which is the only easy way to do this. All the other numbers are either measurements that you take, or figures supplied with the parts.

The accepted formula for calculating compression ratio is:
CR = (SV + CHV) / CHV

In Example 1, the parts manufacturers have supplied key figures, making our lives much simpler.

Sucp_0407_15_z Chevy_engine_build Compression 10/12

Since DM had so much compression this month, timing was critical. We checked and rechecked advance everything couple runs. Interestingly, even on pump gas, DM still made the most power with 36 degrees.

Example 1:
B = 4.030-inch (Bore)
S = 3.48-inch (Stroke)
CH = 70cc (Combustion chamber volume)
G = 9cc (Head gasket volume)
P = 10cc (Piston dish volume w/ 4 valve reliefs)
DV = 0.020-inch (Deck Volume i.e. piston-installed height)

First calculate the Swept Volume: (B x B x S x 12.87)SV = 4.030 x 4.030 x 3.48 x 12.87 = 727.39cc

Next calculate Deck Volume, if there is any in your engine. DV is the small area that's left over at TDC when the piston does not reach the deck. In Ex 1 the pistons are 0.020-inch down the bore at TDC. The deck height measurement replaces the Stroke in the SV formula to calculate Deck Volume.

DV = 4.030 x 4.030 x 0.020 x 12.87 = 4.18cc

Now calculate your total CHV:(CH + G + DV + P)

Sucp_0407_16_z Chevy_engine_build Royal_purple 11/12

We'd like to welcome aboard Royal Purple as the first, and only official motor oil of Danger Mouse! (You know you're getting big when you land a sponsor!)

*Using dished or domed pistons will add or subtract volume, respectively, to the CHV equation and the head gasket's volume, along with the piston's installed height, must be taken into account.

CHV = 70cc + 9cc + 10cc + 4.18cc = 93.18cc

To calculate the compression ratio, simply add Swept Volume (SV 93.18cc) + Total Chamber Volume (CHV 727.39cc) then divide the sum by Swept Volume (SV 93.18cc).

Ex 1's compression ratio is 8.8:1.(93.18 + 727.39) / 93.18 = 8.8

But in DM this month we installed domed pistons, which removes volume from the CHV figure, instead of adding to it like a dished piston would. Also, DM's Victor Jr. heads have a small CH volume; and its head gasket (G) volume is less than Ex 1 as well. DM's pistons are installed at 0.005-inch below deck, so DM - Part 23's equation for CHV looks like this:
DM's CHV = 64cc + 8.6cc - 10cc + 1.05cc = 63.65cc

Swept volume does not change in this case, since it's all below the piston top. It would only change if we altered the bore or stroke of the engine, but we didn't, so we plug DM's figures into the rest of the CR equation and get:
(63.65 + 727.39) / 63.65 = 12.43cr

See how easy that was?

Sources

Comp Cams
Memphis, TN 38118
800-999-0853
http://www.compcams.com
Royal Purple
Porter, TX 77365
888-382-6300
www.royalpurple.com
VP Racing Fuels
San Antonio, TX 78265
210-635-7744
www.vpracingfuels.com
Speed-O-Motive
West Covina, CA 91790
626-869-0270
www.speedomotive.com
Holley Performance Products
Bowling Green, KY 42101
270-781-9741
http://www.holley.com
Total Seal
Phoenix, AZ
(800) 874-2753
totalseal.com
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