Danger Mouse Part 7 - Maximum Trade-Off

Messing With Rocker Ratios And Bigger Cams

Our hobby is filled with rumors and speculation. There's always some new hotshot claiming to know the coolest trick to squeeze out just a bit more power than the other guy can. However, the fact is that in today's high-performance world there's little that hasn't already been tried, and if it's not currently popular in the aftermarket, that's probably because it doesn't work that well, or at least not anymore. Old-timer tricks typically yield very little extra power when applied to the latest high-performance hardware. That's especially true when it comes to today's newest cams and cylinder heads. We proved this to a certain extent last month when we tested GM's iron Vortec cylinder heads. These castings have been around for several years now, and they proved their superiority over the old stuff by making more power than even the best-regarded factory heads-the camel humps-could. But there's always someone who thinks applying old-school technology to new-school parts will help. We guess that's not really a flawed line of thinking either, but it can cost you time and money with sometimes less-than-favorable results.

With all the testing we've...

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Ratio Roundup
This month, a reader suggested an old trick to us via email. His idea was to run different rocker arm ratios on the four corner cylinders (i.e. 1, 2, 7, and 8) because in the past that was something that usually yielded a little more power. Well, we're here to tell you that he was neither wrong nor right. The extra power could have been there, if Danger Mouse (DM) had not been using a set of very efficient cylinder heads or had been using an intake manifold that did not work well the rest of the package. However, DM is equipped with only the best, and after talking to Edelbrock about the equalized runner properties of its Air-Gap manifolds, we didn't think that running different ratios on the four corners would help. Today's very efficient cams, heads, and intake manifolds don't need different ratios on the four corners to make the most power. Still, we wanted to try this test and see where it led us, but instead of swapping ratios on just the four corner cylinders, we opted to trick the engine into thinking it had a different cam by running different rocker ratios on the intake and exhaust valves. We tried the 1.5-intake/1.6-exhaust combo first and then reversed it (1.6-intake/1.5-exhaust). This gave DM back some torque between 2,500 and 2,900 rpm, which it had lost way back when we went from the very small XE256H camshaft to the XE262H cam in Danger Mouse Part 4 (December '02). So if you've already got two different sets of rockers just lying around, go ahead and try this swap. You've got little to lose, except maybe some time.

Our first test involved swapping...

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Spaced Out
Back in DM Part 4 we also tested a 1 1/4-inch open carb spacer from Wilson Manifolds and got a little more top-end power with it. We know there's usually some extra power to be found when testing different carb spacers, and we wanted to see if DM would respond to a new four-into-one tapered spacer. We thought this might also complement the Vortec heads and Air-Gap manifold with the larger cam.

Cam Trade-Off
We found the typical less-torque-for-more-horsepower trade-off when we switched to the next-size-larger COMP Cams Xtreme Energy camshaft. Before installing it, we had figured that with only 6 degrees more duration at .050 and about .015-inch extra lift over the previous cam we'd ran, the XE268H camshaft would have worked well with the un-ported Vortec heads and dual-plane manifold. However, after testing with the bigger cam, low-end torque fell off, and the only power gains were at the very top end of the scale (perhaps we should have run DM up higher with this cam). Ironically, both peak torque and average torque and horsepower with both cams remained almost identical (see Test 18). But it's low-end torque that moves a street car, and given the choice, we'd always choose the cam that could make higher vacuum and build as much as 13 more lb-ft of torque down low for our engines. That's certainly not to say that more power can't be made upstairs (23 more ponies in this case) with a larger cam, and because the bigger cam will pull harder at the top end, it could be a lot more fun to drive all-out. We didn't have time to try the 1.5/1.6 rocker combination with the new camshaft. We'll have to try that next month to see if it gives DM back some of its low-end torque again.