Can you varify engine rebuilders suggestion?

[Steve L.]

Guys,
I'm rebuilding my '73 L48 4speed. You guys have made some suggestion a week or so ago. My engine rebuilder suggests the following:

Seal Power/Feral mogual pistons h345np .030" these are apparently the hypereutectic.

A choice of one of the cams(all CompCams):

268H .454" 218 deg power band at 1500 to 5500

GM #3896929 .410/.390" 195/202 deg power band at 1800 to 5800

or .440/.440" 212/212 deg power band at 1200 to 5200

Heads are the original.
I want the least mods as possible. I imagine that the distributor will need to be reprofiled as well. It'l only be street driven with very little mileage.

Any comments?

Thanks
Steve L
73 coupe since new

[John H.]

Re: Can you varify engine rebuilders suggestion?

I'd go with the GM "929" cam - that's what it was "born" with, and is a great all-around trouble-free piece with excellent low- and mid-range torque; also use new stock GM valve springs.

[Duke W.]

Re: Can you varify engine rebuilders suggestion?

If you want to maintain the original idle and torque characterisitics, go with the OE 929 cam. If you want to "upgrade" to SHP idle and torque characteristics go with either the L-79 cam or L-46 cam. Both will sacrifice low end torque for higher rev power - a bit more so for the latter.

Whatever cam you use, more top end power can be obtained by head pocket porting/port matching and a three angle valve job.

I never recommend aftermarket cams for street engines. The OE cam selection covers everything from mild to almost wild, and they will provide better torque bandwidth for the same top end power as an aftermarket cam.

The Comp Cams 268H has similar duration to the L-46 cam, but a narrower lobe center for more overlap. It works best with headers to improve mid-range torque, but with manifolds it will kill low end torque compared to the OE SHP cams.

From what you stated in your criteria, it would be a poor choice.

Duke

[Pete Whelan]

Re: Can you varify engine rebuilders suggestion?

Steve,
One other choice for a camshaft is the Crane HMV260. This hydraulic cam will increase your low and midrange torque and provide a small increase in maximum horsepower without altering the idle characteristics of your engine. This cam was designed to be used with your cast iron exhaust manifolds and works well with cylinder head pocket porting and a three-angle valve job. I would also reprofile your distributor as well. I have been running this combination in a 327/300 and have been very pleased with its performance.

Pete

[Joe L.]

Re: Can you varify engine rebuilders suggestion?

Steve-----

The pistons will be fine. They are, indeed, hypereutectic with teflon coating. Although they are flat top with 4 valve reliefs, they will produce just a slightly higher compression ratio than the stock dished pistons when they are used with composition-type head gaskets (which your rebuilder will likely be using).

As far as the cam goes, the '929' is what was originally installed in your engine. As others have mentioned, it's a great, all-around cam. However, it has a propensity for creating pre-ignition problems. If your engine currently does not suffer from this, then I think that you will be fine with the '929' replacement cam. However, if you have been experiencing any significant amount of pre-ignition and you want to end it, then I wouldn't go back with the '929' cam. In that case I'd probably recommend that you go with the Comp Cams 260 or 268.

The L-79 and L-46/L-82 cams are fine, too. However, these cams are designed to produces their peak hp at an RPM range that exceeds what the bottom end of your engine was designed to support. That's why I don't recommend these cams for original base engine or L-48 350s with stock bottom ends. If you "take it easy" with the engine, there will be no problem. However, if you're going to "take it easy" with the engine, then why install a cam like the L-79 or L-46/L-82? In that case, you're better off with the '929' or the Comp Cams 260 or 268 which are designed to generate peak horsepower and torque in the range that you actually use AND within the RPM limitations of your L-48 bottom end. GM didn't use forged cranks and specially prepared connecting rods in the L-46 and L-82 engines because the pieces used in the L-48 were just as good.