NHRA Chassis Certification - Performance Q & A

Kevin McClelland Feb 15, 2010 0 Comment(s)

Cam-Converter Honeymoon
Q
I'm selecting a camshaft and torque converter for my '69 Corvette Stingray. This will not be a daily driver and will need to run well on pump gas. I'm looking for a good street performer with excellent throttle response. I'm more interested in low to midrange torque than high-end horsepower. The car is equipped with a 3.08:1 gear in the rearend, so I know that will make things a little more challenging. I'll also be upgrading from the TH400 to a 700-R4 at this time. I just feel like the relationship between the camshaft profile, torque converter stall, transmission gear ratios, and rearend ratio are critical to get the performance I'm looking for. I'm also concerned that with a 3.08:1 rear ratio, I have the proper powerband to enjoy overdrive in Fourth gear.

Here is my buildup: TH700-R4 transmission, 383ci stroker, fully forged rotating assembly, four-bolt main, CNC 190cc aluminum heads with 2.02/1.60-inch valves. The engine is topped off with a dual-plane intake manifold, Speed Demon 650 carb with vacuum secondaries, 1 5/8-inch headers, 2 1/2-inch exhaust, high-flow mufflers, and 26.5-inch tires.

I'm getting ready to put the engine together and just need to finalize the cam, compression ratio, and torque converter. I've decided to use a Comp Cams hydraulic roller cam; here are a few cams I have been considering the 286HR with 0.050-inch duration numbers of 230/230, 0.560/0.560-inch max lift, ground on 110 centers. On the milder side I'm leaning toward the 280HR that specs out at 224/224 duration at 0.050-inch lift, 0.525/0.525-inch max lift, also 110 separation angle.

Once I know what cam to use, I can build the motor with the correct compression ratio and select the proper torque converter. Thanks.
Ken Newberry
Via email

A
The relationship between the camshaft and the torque converter is probably the most important marriage in an engine build. If they don't like each other no one will be happy! You're building up a really nice package. If you've been reading my column for any time you know I'm going to err to the small side. This will give you a better all-around driving package. Let's see what else Comp has to offer.

You have chosen two very nice camshafts. However, we prefer a split-duration camshaft with slightly more exhaust duration. That said, we'd go with an XR276HR profile. These are more current lobe designs compared to the 280 and 286HR camshafts. The XR profiles have 4 degrees more intensity and quicker opening between advertised duration numbers and 0.050-inch duration numbers. The XR276 comes in at 224/230 degrees of duration at 0.050-inch tappet lift, 0.502/0.510-inch max lift, and is ground on 110 centers. This will give you a very decent idle quality without having to run an overly loose converter. With this camshaft in your 383 we'd recommend a stall speed of around 2,400 rpm. Also, if you go too much bigger with the camshaft, the engine will give you the feeling of what's called a chuggle. This is a slight bucking that you can feel in Fourth when the converter is locked at slower engine speeds.

By using the smaller camshaft we wouldn't worry about pulling the 3.08:1 gear out on the open road. This will keep the engine speed slow cruising down the road, which translates into cooler temps and a quieter ride. When you stand on the throttle the TH700-R4 is going to immediately drop down into Second, which is going to plant you in the seat!
Source: compcams.com

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