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

Part 23: Squeeze Play

By Mike Petralia

CLICK BELOW TO SEE ALL OF THE STORIES COVERING THE BUILD OF PROJECT DANGER MOUSE

DANGER MOUSE PART 1

DANGER MOUSE PART 3

DANGER MOUSE PART 4

DANGER MOUSE PART 5

DANGER MOUSE PART 7

DANGER MOUSE PART 8

DANGER MOUSE PART 9

DANGER MOUSE PART 10

DANGER MOUSE PART 13

DANGER MOUSE PART 14

DANGER MOUSE PART 15

DANGER MOUSE PART 18

DANGER MOUSE PART 20

DANGER MOUSE PART 22

DANGER MOUSE PART 23

DANGER MOUSE PART 24

DANGER MOUSE PART 25

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.

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

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

Test 36 Test 37 T36 vs. T37 Test 38 Test 39 T37 vs. T39
RPM TQ HP TQ HP TQ HP TQ HP TQ HP TQ HP
2600 353 175 371 184 +18 +9 371 184 365 181 -6 -3
2800 375 200 365 194 -10 -6 377 201 385 205 20 +11
3000 390 223 378 216 -12 -7 374 214 384 220 +6 +4
3200 393 239 388 236 -5 -3 389 237 396 241 +8 +5
3400 388 251 388 251 0 0 390 253 396 256 +8 +5
3600 395 271 391 268 -4 -3 402 276 406 279 +15 +11
3800 407 294 404 293 -3 -1 413 299 416 301 +12 +8
4000 416 316 414 315 -2 -1 411 313 421 320 +7 +5
4200 421 336 422 338 +1 +2 416 333 424 340 +2 +1
4400 428 359 426 357 -2 -2 422 354 429 360 +3 +3
4600 437 383 439 385 -3 -2 438 383 445 390 +5 +5
4800 448 409 453 414 +5 +5 453 414 459 419 +6 +5
5000 454 432 463 441 +9 +9 464 442 469 447 +6 +6
5200 455 451 466 461 +11 +10 470 465 473 468 +7 +7
5400 453 466 467 480 +14 +14 469 482 472 485 +5 +5
5600 452 482 464 495 +12 +13 466 496 467 498 +3 +3
5800 450 497 460 508 +10 +11 462 510 463 511 +3 +3
6000 443 506 456 521 +13 +15 458 523 460 525 +4 +4
6200 430 508 453 534 +23 +26 455 537 455 537 +2 +3
6400 416 507 447 544 +31 +37 446 544 448 546 +1 +2
6600 N/D N/D 435 547 N/A N/A 438 550 438 550 +3 +3
6800 N/D N/D 425 550 N/A N/A 427 552 427 552 +2 +1
7000 N/D N/D 414 552 N/A N/A 414 552 414 552 0 0
Max 455 508 467 552 +12 +44 470 552 472 552 +5 0
Avg 420 365 426 395 +6 +30 427 396 431 400 +5 +5

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.

DANGER MOUSE COMPONENTS FOR PART 23
CAM COMP CAMS SOLID ROLLER XR286R (PN 12-772-8)
CARB HOLLEY HP950 MODIFIED BY THE CARB SHOP
GASKETS FEL-PRO (head PN 1003, intake PN 1206)
HEADS EDELBROCK VICTOR JR. (PN 77599)
LIFTERS COMP CAMS ENDURE-X SOLID ROLLER (PN 888-16)
MANIFOLD EDELBROCK SUPER VICTOR (PN 2925)
PISTONS LUNATI CUSTOM FORGINGS
ROCKERS COMP CAMS 1.6:1 PRO MAGNUM (PN 1302-16)

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.

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)

*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
Bill Mitchell Hardcore Racing Products
51 Trade Zone Ct
Source for World Products
Ronkonkoma
NY  11779
Pertronix
440 E. Arrow Hwy.
San Dimas
CA  91773
800-827-3758
www.pertronix.com
COMP Cams Royal Purple
Edelbrock
Dept. 5.0
2700 California St.
Torrance
CA  90503
310-781-2222
www.edelbrock.com
Speed-O-Motive
131 W. Lang Ave.
West Covina
CA  91790
6-26/-869-0270
speedomotive.com
Fel-Pro
26555 Northwestern Hwy.
Southfield
MI  48033
Total Seal
Phoenix
AZ
800-874-2753
totalseal.com
Holley Performance Products
1801 Russellville Rd.
Bowling Green, KY 42101
KY  42101
270-782-2900
www.holley.com
VP Racing Fuels
210-635-7744
www.vpracingfuels.com
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By Mike Petralia
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