Question: Duntov Cam in 327 / 340 HP Engine

[delray56]

Hi All,

I bought my first Corvette, a 62 Roman Red convertible (4 speed), this past summer and am installing a Tremec 600 transmission this winter. I have torn down the engine to see what's inside, even though it was running great. It was an original 327 / 340 HP car (has the 6500 rpm tach) but the engine code of SA indicates that it is a replacement block (casting code 11/61). I'm new to the group and would like opinions on whether to put an original spec cam in this engine. It has high compression pistons, double hump heads, and aluminum high rise intake. The cylinders are bored .040 over, and the crank is ground .020 / .020. The crank pilot bushing bore was only 1.065" OD, and was messed up, so I'm having it bored out to fit the standard 1.090" OD pilot bushing.

The pistons and bores are like new so I'm simply replacing rings and honing the block.

The cam specs are unknown and it is a hydraulic lifter type. I'd like to bring the engine back to original performance with the addition of the Duntov cam and solid lifters. Crane makes the cam currently. I am curious as to driveability vs a more mild cam. I'm not afraid of adjusting valves every year. Any insights are appreciated. Can I reuse the old pushrods with the solid lifters?

Dave B in Ohio

 

[Hib Halverson]

First of all, if you have the engine apart, before you assume the bores are ok, I'd measure them. Just to make sure that there were no problems with the previous machine work.

Also, if you end-up doing just a hone, use a bottle brush hone from Brush Research rather than an old-school cylinder hone and don't forget to manipulate the drill motor such that you get a proper cross-hatch.

Unless the car has a taller than stock axle ratio, I think the Duntov Cam will work fine.

Reuse the old pushrods as long as they're not worn or bent. The old test of rolling them across a flat table top still works well, today.

 

[delray56]

Thanks for the quick reply. I neglected to mention that I mic'd all bores front-to-back and side-to-side / top and bottom. Range of measurements was 4.040" - 4.042". Piston skirts have no wear marks and measured 4.034" - 4.035". My local shop is honing the cylinders since I don't have the hone. I ordered the cam and lifters today. Looking forward to hearing the engine with this new cam and driving the car with overdrive. Rear end is either 3.70 or 3.55. Haven't checked precisely yet.

 

[kpic]

4.041 ±0.001 bore and pistons are 4.0345 ±-0.0005 Where the pistons measured perpendicular to the pins? Piston skirts aren't always round; often they are barrel shaped to reduce friction.

Measure one bore and the piston that goes in it; not all the bores and pistons. You're not after, a tolerance analysis; measure a bore and the piston.

The amount of clearance depends on the piston's material.