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Chevy Small Block Part 17 - PT. 17: Fresh Off The Old Block

DM Is Rebuilt and Ready for a New Year

Mike Petralia Feb 1, 2004
Sucp_0402_04_z Chevy_small_block_part_17 Engine 2/12

With a new year usually come new promises. New commitments are also often made, only to be broken later on. But Danger Mouse (DM) will not be broken, nor will we break our promise to give you the best real-world dyno tests with it this year. Although we've got big plans for DM, rest assured that everything we do will still be in the scope of things you can duplicate yourself, usually for just a little extra cash.

When DM was first envisioned, we planned to test any and all combinations that could be thought up, in order to see what worked and what was a load of you know what. Some of our tests have worked very well, and DM peaked has peaked with 480 hp on pump gas last year using an off-the shelf EFI system from F.A.S.T. and no power adders. Sure, we also made over 600 hp with a small Weiand blower, but the main scope of this project has always been motor-only power. We'll stay that way for most of this year, but there are a few HUGE surprises in store later on.

Sucp_0402_05_z Chevy_small_block_part_17 Dyno_chart 3/12

Back in DM Part 14, we first tested Holley's Street Avenger Throttle Body electronic fuel injection (TBI) and got results that were less than we'd hoped for (see: SC, November 2002). After that test was done, and following a string of steady power losses we'd been experiencing in the last few tests, we'd decided that DM had to come apart for inspection and rebuild. You might think that rebuilding a street engine after just one year of use is unnecessary, but keep in mind that DM lives on the dyno. And the dyno cell is a very harsh environment.

What we mean is that dyno pulls are made at wide-open throttle and there's usually nothing but idling in between. Imagine how your engine would feel if every time you warmed it up, all you did was mash the throttle and raced it for about 10 seconds and then idled around only to mash it again and again. Now try doing that about 1,000 times in a 12-month period and you'll understand why DM needed a rebuild.

Sucp_0402_06_z Chevy_small_block_part_17 Chart_comparison 4/12

Speed-O-Motive Takes Control
Along with our decision to rebuild DM this year came a deal we struck with our friends over at Speed-O-Motive, who're installing a new DTS engine dyno as this is being written, to take over all the maintenance and testing duties for DM. That frees up time for our staff to pursue other life-affirming goals, like getting a life. The crew at Speed-O, from which now on they'll be referred to, were eager to accept the challenge, and rebuilt DM in less than 2 weeks to keep us on schedule. But, Speed-O's dyno was not ready for a test, so for the first test of 2004 we returned to Vrbancic Brothers Racing and bolted DM onto their DTS dyno to maintain consistency in our testing regime.

Before We Begin
Before we jump right into DM's latest test results, we wanted to go over the rebuild specs for you. DM had seen a lot of dyno pulls last year and its bearings showed it. So a new set of Speed-Pro bearings, along with a fresh set of file-fit Speed-Pro moly rings, were installed. Also, to correct the deck clearance problem DM has had since its beginning, (the piston pin height was too low, so the original set of pistons sat .050-inch down the bore, leaving a huge quench area), we installed a new set of forged Lunati pistons with more pin height to give DM a true "zero" deck.

Then a new set of World Products Sportsman II iron cylinder heads were bolted on and a new Lunati hydraulic roller cam was installed. We reused the same COMP Cams roller lifters, pushrods, and 1.6:1 rocker arms that'd become a stable of DM's past testing. To top things off, a new, coated Holley Street Avenger manifold (PN 300-36S) was installed and topped off with the same Holley HP750 carb we'd used back in Part 14. All of this was to give the Holley Street Avenger TBI fuel injection system we planned to retest a better chance at making some power gains.

Sucp_0402_11_z Chevy_small_block_part_17 Oxygen_sensor 8/12

This EFI system also uses an oxygen sensor (included) that gets plugged into the exhaust. Any muffler shop can weld in the bung that also comes in Holley's kit.

Testing-Year Two
We learned a lesson once again this year. But this time it wasn't because we'd made any mistakes. To the contrary, this time we did everything right. We simply learned that you can't make tons of extra power just by switching from a well-tuned carburetor to fuel injection. There might be a little power there, but don't expect to set any records, that is, unless your carburetor was out of whack to begin with. We were pretty sure of all this already from some of the tests we've tried in the past, but we wanted to give it one last try.

So once again, we removed the carburetor and bolted on Holley's TBI unit, complete with a new progressive throttle body, and new software to control it. What we got was a motor that made good power, but never more power than it did with the carb. This is proof of exactly what we've been saying all along: With EFI you can get better starting, better all-climate running, and maybe even better fuel economy, but you probably won't get better power. That's not to say that EFI is bad. It's actually very good. And once you've gone EFI you'll probably never go back. It's just that EFI is a big jump and may take quite a bit getting used to.

Dyno Testing Part 17
The results shown here are listed chronologically as tests 29 and 30 and represent the power made with the rebuilt short-block using the new Lunati pistons, Sportsman II heads, Lunati hydraulic roller cam, and Holley intake manifold, and we've made comparisons to test 27 and 28, which were done with the old short-block.

Sucp_0402_12_z Chevy_small_block_part_17 Adapter_ring 9/12

We found some extra power when we installed Holley's air cleaner adapter ring. The ring is included in every kit, normally to make sure that any air cleaner will fit on the throttle body. Dyno operator George Vrbancic told us that he'd found power using the ring before and, sure enough, after we dropped it on, power picked up.

Danger Mouse specs for Part 14, Tests 27-28

: 355 cid, 9.4:1 cr, 4.030-bore four-bolt Motown block, 3.48-stroke Lunati crank, 5.7-inch Lunati rods

Test 27: DM Part 14*

GMPP Aluminum Fast Burn heads (62cc chambers, 210cc runners, 2.00-inch hollow stem intake valves, 1.55-inch sodium filled exhaust valves), GMPP single-plane intake manifold, Holley HP750 carb with 73/84 jets, COMP Cams Xtreme Energy hydraulic roller camshaft XR-282-HR (230/236 at .050, 282/288 adv, .510/.520 lift, 110 LS), GMPP 1.5:1 aluminum roller rockers, 36 degrees total advance

Test 28: DM Part 14**

Installed Holley Street Avenger 900-cfm four-barrel electronic throttle body fuel injection.

Danger Mouse specs for Part 17, Tests 29-30:

355 cid, 9.9:1 cr, 4.030-bore four-bolt Motown block, 3.48-stroke Lunati crank, 5.7-inch Lunati rods

Sucp_0402_13_z Chevy_small_block_part_17 Air_tuning 10/12

With the improvement in power that came from the air cleaner ring, we wanted to see if further tweaking the airflow into the throttle body could help build more power. We tried this K&N velocity stack that we stole out of a complete K&N air cleaner kit. It, too, helped build just a little bit more power.

Test 29: DM Part 17*

Freshly rebuilt with World Products Sportsman II angle-plug iron heads (64cc chambers, 200cc runners, 2.02 intake valves, 1.60 exhaust valves), Holley (PN 300-36S) dual-plane intake manifold, Holley HP750 carb, Lunati hydraulic roller camshaft (215/224 at .050, 268/279 adv, .489 lift, 112 LS). COMP Cams 1.6:1 roller rockers, 34 degrees total advance.

Test 30: DM Part 17**

Installed Holley Street Avenger 900-cfm four-barrel electronic throttle body fuel injection.

*Compare Test 27 to Test 29 and note how DM made better mid-range torque with the new package in T29 (T29=412 ft-lb at 3,600 rpm compared to T27=393 ft-lb at 3,600 rpm), but topped out with less peak power than (T29=399 hp to T27=419 hp). That's typical when changing from large runner heads with a big cam to smaller runner heads and a smaller cam.

**Compare Test 28 to Test 30 and again note how DM made much better torque with the new package (T30=405 ft-lb at 4,000 rpm compared to T28=389 ft-lb at 4,000 rpm), but this time DM topped out with more peak power than (T30=394 hp to T28=391 hp). We came into this test hoping to make more power, and we achieved that goal, which shows that with the right combination of parts you can definitely improve the power of a TBI engine.

Sucp_0402_16_z Chevy_small_block_part_17 Ring_spacer 11/12

After we found some extra power by installing this simple plastic ring, we began to wonder if maybe a carburetor would benefit from the same. But Holley includes this ring only as an adapter; it's not supposed to make extra power. Carburetor experts and racing engine builders George and Bob Vrbancic both think the extra TBI power came from the fact that a throttle body normally chokes airflow into itself because of the large injectors that hang directly above the venturi bores. Unfortunately, you cannot move the injectors any higher to increase airflow because that'll cause the fuel to spray outside of the venturi. So, instead you can try to improve airflow into the venturi by smoothing its entrance. Apparently, this plastic ring accomplishes that. And installing a tall velocity stack, which has been the normal way to improve airflow into carburetors for years, added just a little more power still, further proving our theory.

Test 27 Test 28 Test 29 Test 30
2600 359 178 373 185 362 179 371 183
2800 383 204 387 206 385 205 383 204
3000 398 227 397 226 401 229 389 222
3200 402 245 396 241 410 250 395 240
3400 398 257 394 254 411 266 398 257
3600 393 269 391 268 412 282 397 272
3800 394 285 386 279 410 297 403 292
4000 407 307 389 296 415 316 405 308
4200 417 334 404 323 415 332 401 321
4400 421 353 409 343 412 345 391 328
4600 417 365 409 359 407 356 391 342
4800 413 378 402 368 402 368 392 358
5000 408 389 394 375 398 379 392 373
5200 402 398 381 377 389 385 387 383

5400 396 407 367 378 380 391 380 391
5600 390 415 365 389 374 399 375 394
5800 379 418 354 391 358 395 350 385
Max 421 419 409 391 415 399 405 394
Avg 397 325 388 309 397 316 388 309

Sucp_0402_14_z Chevy_small_block_part_17 Mounting_system 12/12

Here you can see a close up of our trick mounting system developed to secure the air cleaner adapter ring and K&N velocity stack. No good dyno shop would be complete without a roll of duct tape! Also, check out the fuel pressure regulator built into the back of the Holley throttle body centered between the two hoses. The inlet hose (right) gets high-pressure fuel from the electric pump and return hose (left) sends unused fuel back to the tank.

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


Comp Cams
Memphis, TN 38118
West Covina, CA 91790
Holley Performance Products
Bowling Green, KY 42101
Vrbancic Brothers Racing
Lunati LLC
Olive Branch, MS
Muskegon, MI 49443,



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