July 2010 Chevy High Performance Letters - Performance Q & A

Kevin McClelland May 24, 2010 0 Comment(s)
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The speed limiter is put there for a reason. It's not there to keep you from breaking the law; it's to protect you. The original tires on a vehicle are where the speed limit usually comes from. If you've upgraded your tires from the original speed rating, it's not a problem to raise the speed limiter. This is the case with your Cobalt passenger car. Now, on the chassis dyno, we've seen very nasty results of raising speed limiters. Trucks and SUVs have speed limits based on the driveshaft's critical speed limit. When this limit is surpassed, the driveshaft begins to flex, and once the shaft has bent beyond a minimal amount, you have reached a point of no return. The shaft bends to the point that it pulls the driveshaft right out of the transmission with catastrophic results. It usually damages the transmission, the undercarriage, the fuel tank, and whatever else gets in its way. Then the shaft comes out from under the vehicle at tremendous speeds and takes out the observers of the dyno test! Please respect the vehicle speed limits applied by the OEMs on trucks and SUVs unless you have upgraded the driveshaft with either a thicker wall thickness or a larger-diameter shaft.

Finally, to gain full tuning ability of your '05 Cobalt, check out HP Tuners. They offer the closest to GM development software that I have ever worked with. Just about any parameter is available for modification with their software. Yes, it's pricey, but with their VCM Suite of tuning software you get enough credits to tune at least two vehicles, and sometimes four. If you can get a buddy to go in with you on the package, the dollars are less than buying two tuning modules from other aftermarket tuning companies.
Sources: hptuners.com, jetchip.com

One Tough Truck
Q: I'm building an S-10. The motor in progress is a 434 Dart block, all forged bottom end with AFR 210cc Competition heads, a Victor Jr. intake, and a Holley 850hp carb. It will not be a daily driver, but will be a radical street truck with an occasional trip to the local track. My question concerns the cam. My plan is to use a solid roller. The compression comes in at 10.5:1. I know a hydraulic roller is best for the street, but I can't find one with enough lift to take advantage of the excellent flow these heads produce. What would your advice be on the best cam? Solid may be right, but will a hydraulic roller work? And maybe your opinion on how much power this combination might produce. Thanks a lot, guys, and keep the wrenches turning.
Donnie Griffin
Baxley, GA

A: This is going to be one fun truck to drive. A fellow line mechanic we worked with back in 1979 had a '76 LUV truck with a 377 small-block in it that was a real handful. That truck wanted to go every which way but straight. Luckily, it never met anything very solid!

As for your camshaft, we'd stick with a solid roller for many reasons. You're spot on that you can have better profiles with the solid design, and the mechanical design will be a much lighter valvetrain package. This will aid in valvetrain stability when the thing sees high rpm that we're sure it will. Check out one of the new Lunati Street/Strip roller profiles for your pickup. The camshaft that should work quite well with your package is PN 501B2LUN, which specs out at 243/251-degrees of duration at 0.050-inch tappet lift, 0.582/0.582-inch max lift, ground on 110 centers. These new cam profiles give you the flexibility to drive on the street without beating up the valvetrain. We'd recommend going with 1.6:1 ratio rockers on the inlet side to bring the max lift up to 0.620-inch. This will bring the intake and exhaust lift within 2 to 3 cfm of your AFR Competition cylinder heads' peak flow.

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