October 2011 Chevy High Performance Q & A

Scales are for Fish

Kevin McClelland Sep 1, 2011 0 Comment(s)
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Also, the TRW pistons in your build don’t have dedicated wristpin oilers from the oil ring of the piston. This can cause issues for extended wide-open throttle runs. Also, they have limited valve pocket depth in the piston crown. This limits the size and duration of the camshaft you can run. From what we’ve seen, the max duration you could probably run with these pistons without cutting the pockets for clearance is the mid-240 duration range at 0.050 inch tappet lift. For sure, whatever package you put together, you will need to check the piston-to-valve clearance to ensure that you won’t have contact between the valves and pistons. Most builders will tell you to run 0.080-inch clearance on the intake and 0.100 inch on the exhaust. We’ve run them much tighter and would say that you could safely run them at least 0.020-inch tighter than these numbers.

Finally, for a camshaft, go with a mechanical flat-tappet. The hydraulic rollers are very rpm limited because of the total valvetrain weight on a big-block. To get one to rev to 6,000-rpm clean without valve stability issues is very tough. Mechanical rollers on the street are a ticking time bomb just waiting for the needle bearings to shatter into hardened metal fragments that will destroy your engine. With the cylinder head and a mid 240-duration camshaft, your engine will want to run into the 6,500-rpm range. Hydraulic flat-tappets are good, but the mechanical will give you the best of both worlds between a mechanical roller and a flat-tappet design. Since you are looking to run COMP Cams products, look into an Xtreme Energy XS282S mechanical that specs out at 244/252 degrees duration at 0.050-inch tappet lift, 0.590-/0.598-inch max lift, and is ground on 110 centers. With this camshaft your ACCEL distributor will be just fine with the gear on it. This camshaft, in conjunction with the Dart oval-ports, will exceed your 500 hp requirements.

Hope this gives you a direction for your Chevelle. Enjoy it and cook some tires for us!

Sources: compcams.com dartheads.com

Shifty Business

Q: I have questions about rebuilding a TH350-C. Who can help me? I have everything done except the valvebody. I bought a shift kit, but things don’t line up. I think it’s for a TH350, but without the C part. I sincerely need help with this, it’s driving me nuts. Thanks for any help you can offer.

Dustin Cross
Via email

AThe TH350-C was released in 1980 and ran through 1986, when GM redesigned the TH350 with a lockup torque converter. They were used to increase fuel economy. The shift kit you have is for a standard TH350 and doesn’t accommodate the converter solenoid and the appropriate passages. You need to pick up a B&M TransPak PN 30235. This is the next step up from a standard shift improver kit. The TransPak gives you two stages to choose from. First, a standard shift improver, and the second stage gives you full control of the trans. You can hold the trans manually in any gear for as long as you wish. The trans functions normally with the shifter in the Drive position. Check with B&M for more information, or just get one on order. Don’t forget where all those little balls go!

Source: bmracing.com

We love letters, especially technical questions. Submit your tech questions to Kevin McClelland at chevyhi@sorc.com. Regular shout-outs and good tidings are also always welcome.

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