All right, we've almost perfected it: running high compression on pump gas, that is. And while it's still not something we'd recommend for your everyday commute, it sure is an easy way to make stout power! Last month some dissenters deemed us certifiably insane when we increased Danger Mouse's compression ratio to 12.5:1 and then dyno'd it on 91-octane pump juice! The results we got, over 550 hp, proved only temporarily insanity and this month we wanted to push the envelope further to see if this type of combination can live and make a whole lotta' power doin' it!
Last month, peak power was high, but the low end suffered from detonation. That's because the distributor we'd been running had a locked-out advance curve. So we simply set it at max-38 degrees-and let 'er rip. Turned out that the one thing we were lacking in last month's test, but desperately needed, was a timing curve. So this month, the first and only bolt-on, or, more precisely, plug-in, we tested was a new MSD Multi-Function Ignition Controller, (read: computerized ignition box). With MSD's new box plugged-in and a trusty old Windows 98 laptop running at full speed, we tweaked DM's timing curve enough to rid us of that pesky detonation. But, as seems to lately be the case, the power we got perplexed us more. The end results were far from what we'd expected and will probably confuse the issue even further, but we've no choice but to share them to you.
Perplexing PowerWe ran this month's tests again with 91-octane pump gas to see if we could tune power into the combination by tuning out the detonation. The weirdest thing happened to us on the way there. We were surprised when, after all of the day's 25 tests were through, DM made the best low end power without much of a timing curve! In other words, it didn't detonate, even when we put 35 degrees of advance back into the engine at 2,500 rpm! In fact, DM made even more power from 2,800 to 4,800 rpm then it did last month, but then things went all weird on us again. Power began to fall off, so much so that by the top of the rpm band, DM was down by 29 hp! Why? We haven't figured that out yet.
One possible explanation is that this month's tests were done at a different dyno facility, Vrbancic Brother's Racing vs. Speed-O-Motive, and running a different set of headers, which could have had a pronounced effect on top-end power in an engine of this caliber. Another could be that we obviously were not running the exact same fuel as we ran last month, and the quality of gas that comes out of the pump has long been questionable.
It could be that last month's 91-octane really only rated about 89 on the R+M/2 scale and that could have caused the detonation. Maybe this month our octane was a little bit higher? Since we have no way of testing fuel for its octane rating, we'll never know. But higher octane or not, we still don't know why DM lost so much power at the top end of the scale? That could be more the result of the different dyno headers.
We're not saying that Vrbancic's dyno is a dud. Quite the opposite in fact. We've used their shop time and again for tests and will continue to use them long into the future. We trust their numbers and have seen nothing but good, repeatable results in the past. It's more probable that the air in the shop itself was partially to blame. Last month we tested on a cool, dry day, but we can't wait around forever for the weather to change and this month we tested in hotter, humid conditions. Now, we know that the dyno is supposed to correct for this, but correction factors are just mathematical calculations and the engine doesn't breath in and spit out numbers. It breathes air and spits out power. If the air's too hot and wet goin' in, the engine won't spit as much power goin' out-plain and simple.
It Gets Even WeirderSince peak numbers are only a small part of the power making game, we've grown accustomed to analyzing average power gains to determine if a change was worth the effort. Well, this month's test averages perplexed us as well. Even though power was up at the low end, the drop at the top made average gains net zero! At least in the torque department. Average horsepower actually fell off by 3, which really sucked, considering how hopeful were going into this test. One positive note about this month's test was that in a car, the motor would have pulled harder off the line this month than it did last month. But we'd have to short-shift it and that's not really an advantage to in our book.
Dyno Testing Part 24Instead of comparing this month's test, Number 40, to the last test from last month as we usually do, we're comparing it to the second test from last month, Number 37. That's because in that test we were running locked-out ignition at 38 degrees and 91-octane gas. This is the combination that was detonating and losing the most low-end power, so it was the one we wanted to compare to. Ironically, this month, in test Number 40 DM did not detonate, even though the engine set-up was exactly the same. The two exceptions this month were fuel from a different source and testing done at a different facility.
Danger Mouse specs for Part 23-Test 37*
*Previous test from last month: 355 cid, 12.5:1 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" intake valves, 1.60" exhaust valves), Edelbrock Super Victor intake manifold, COMP Cams XR286R solid roller camshaft installed @ 105 intake CL (248/254 @ .050, 286/292 adv, .606/.612 lift w/ COMP 1.6:1 rockers, 110 LS), Carb Shop modified Holley HP950, 38 degrees locked-out ignition advance, 91-octane
Danger Mouse specs for Part 24-Test 40:
Same as above but with 35 degrees ignition advance starting at 2,400 rpm, ramping up to 38 total at 5,500 rpm, 91-octane
We're always looking for new ideas. Do you have a better one for Danger Mouse? Send your test suggestions to:
Super Chevy MagazineAttn: Danger Mouse720 Hundley WayPlacentia, CA 92870Or e-mail: email@example.com
Msd 8977 Multi-Function Digital Controller CapabilitiesIt's actually kind of a shame that our only use for the MSD unit we tested this month was adjusting the timing because it can do so much more than that. The Individual Cylinder Timing (ICT) function is particularly useful in high power applications.
It also has multiple timing retards and a three-step rev limiter for things like: burnout, launch, and peak rpm. The Sequenced Shift Light operation allows you to program a different shift light point for each gear you pull which can really help knock down e.t.'s once you get a handle on it. And the Boost Retard function helps stave off detonation when you start pumping pressure into your engine.
*Digital Operation*Individual Cylinder Timing*3-Step Rev Control*Start Retard*Multi-Stage Retard*Launch Retard*Gear Retards*Boost Retard*Run Timing Curve*Sequenced Shift Light