The Wrong Combination Can Set You Back - Danger Mouse Part 5

Heads That Are Too Big Can Hurt Power

Mike Petralia Jan 1, 2003 0 Comment(s)

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

DANGER MOUSE PART 1

DANGER MOUSE PART 3

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DANGER MOUSE PART 5

DANGER MOUSE PART 7

DANGER MOUSE PART 8

DANGER MOUSE PART 9

DANGER MOUSE PART 10

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DANGER MOUSE PART 14

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DANGER MOUSE PART 18

DANGER MOUSE PART 20

DANGER MOUSE PART 22

DANGER MOUSE PART 23

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Since Danger Mouse (DM) is SUPER CHEVY's in-house test engine and we vowed long ago to test any combinations suggested to us, this month is our first example of mixing the wrong components. The culprit here is not a bad part. Rather, the culprit is the improper selection of a combination of parts. Last month, we said we'd swap cylinder heads to see if the stock GM camel hump castings were keeping DM from making more power. Since the inception of DM, we've received many letters from readers suggesting we equip it with a set of World Products S/R Torquer cylinder heads to help out in the horsepower arena. We did just that but did not make any other adjustments in conjunction with the new heads. As with any swap you make, how your upgrades work with each other is the determining factor in whether or not your "better" part is actually "better" for your current setup (or whether you'll need to make some adjustments in order to use your better part). The root of the power loss we suffered came from the fact that the S/R Torquer heads (S/R stands for "stock replacement") were bigger than the stock GM heads in all the critical areas. And on a low-rpm street motor like DM, bigger is not better. The S/Rs had larger combustion chambers (67 cc vs. 62 cc on the milled 461 castings we'd been running) and larger valves (2.02/1.60 vs. 1.94/1.50). The large combustion chamber dropped Danger Mouse's compression ratio 1/2 point, putting it just below the 9:1 mark, and the larger valve sizes, particularly on the intake side, probably reduced charge velocity enough to hamper the cylinder's filling at low speeds.

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Improper cylinder head selection resulted in less power and torque. Although the net result of our test wasn't a horsepower gain, it proved a positive lesson in choosing the correct parts.

What We Learned
All this month's test proved is that it's extremely critical to know exactly what parts you have before you start replacing them. That might mean having your car sit in the garage for a few days while you remove the heads and measure everything prior to ordering the new parts. But that's the only way to be sure you won't be taking a step in the wrong direction. Had DM originally been equipped with a set of heads that had big 76cc chambers, the S/R heads would have boosted compression and that would have probably made more power. Also, if DM was a higher-rpm engine or had more cubic inches, ala stroker 383, it could have made good use of the S/R's larger valves as well. Even though we know we could mill the S/R heads to get an equal compression ratio and re-test them to see the results, we'd rather not start modifying parts this early. Instead, we'll box up the S/R heads and re-test them again another time when DM's got either more inches or more rpm to play with.

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