Bonneville Speed Week And Chevy Engines - Performance Q&A

Kevin McClelland Mar 1, 2009 0 Comment(s)

Comp Cams designed its Nitrous HP line of camshafts specifically for street use with nitrous. They have relatively wide separation angles, and longer exhaust events to expel the added exhaust gases from the nitrous-enhanced combustion. Comp offers them in both hydraulic flat tappet and roller designs. What is interesting about street rollers is that the seat timing (0.006-inch lift) is much greater than their hydraulic flat tappet counterpart. This is because you can only open the valve so quickly off the base circle of the cam with a roller tappet. You can actually open the valve faster right off the seat with a flat tappet design. By 0.050-inch tappet lift the duration is the same, but the real story happens by 0.200-inch tappet lift. To have equal duration at 0.050 inch, the roller design has 8 degrees more inlet duration and 9 degrees more exhaust duration at 0.200-inch tappet lift. This is where the hydraulic street rollers really shine over the flat tappets. At really short street durations, the flats have slightly better idle quality, but it's all done by the time you stand on the throttle.

Check out Comp's Nitrous HP camshafts. I would recommend going with the hydraulic roller design, which is sold under grind number NX276HR. This camshaft specs out at 276/288 degrees duration at 0.006-inch tappet lift, 224/236 degrees at 0.050-inch tappet lift, 0.502/0.520-inch max lift, and is ground on 113 centers. The wider centers help reduce communication on overlap because of the added cylinder pressure from the nitrous load. If you can't afford to upgrade to the retrofit hydraulic rollers, go with the NX268H grind. This cam comes in at 268/286 at 0.006 inch, 224/236 at 0.050 inch, 0.477/0.490-inch max lift, and is ground on 113 centers. As you can see by the specs, the inlet lobe is quite a bit shorter at the seat timing numbers, which helps the idle quality. Check with Comp Cams for more information on both of these selections.

With the hydraulic roller camshaft swap you should easily have 375 hp with your current combination. With refinement, on the Jones, you should be well over 500 hp, which will push you into mandatory-rollbar territory with your Corvette. Great job with your Vette, and enjoy.


Confusing Shifts
QI am in the process of installing an LS2 crate engine in a '57 Bel-Air using an aftermarket frame. The part number of the engine is 19165484. What type of 4L60 transmission will work with this engine? I am set to use the '98-and-later Corvette one with a two-piece bellhousing. I just read an article on a website that said if your engine uses a 58x crank trigger, your only option is a 4L70 transmission. This transmission was used in the GTO, the Trailblazer SS, and the '07-and-later fullsize trucks and is unique in that it has an input shaft speed sensor. The 4L70 transmission has a slightly higher torque capacity than a 4L60, but the added input shaft speed sensor is a must for compatibility with a 58x PCM. Is this true? I could not find anything like this before we ordered the engine. I basically said "put your transmission on it and stick it in your hot rod and go." Any help would be greatly appreciated.
Jerry Cox
Ocala, FL

AEngine controls and transmission controls are moving faster than the speed of light these days. GM has now gone to installing transmission control modules (TCM) in the valvebody of the transmissions to communicate with the engine control module (ECM), which is responsible for engine management. Gone are the days when the powertrain control module (PCM) controlled both. This is where swapping in some of the latest of the General's trick parts gets rather tricky. Swapping in some of the newest powertrains requires that you use the TCM/ECM combo or go with aftermarket-specific controllers to manage your driveline.


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