Chevy LT1 Head Questions - Performance Q&A

Kevin McClelland Jun 1, 2009 0 Comment(s)

Bulletproof Baby
Q: I am considering a small-block engine build for my '85 Chevy pickup. I am not interested in a high-revving engine. I'm looking to build a torque monster, a high-torque tow vehicle. I have a used 350 four-bolt block with a two-piece rear main and cranks that I could build into a 355. Or I could stroke it and build a 383. Or I could sell them and use the money toward a Dart 400-cid short-block.

In the end, by the time I get a roller cam and rockers and all the other goodies, the total dollar difference will probably be less than a grand. My block would have to be machined for the 350-more so for the 383. The 400 block would come all machined, so my starting costs would be close.

Is this a case where there is no substitute for cubic inches? Also, could you recommend an iron head and cam?
Bob James
Franklin, IN

A: Building a mild-mannered torque monster for your tow truck is all about displacement. The larger you can make the engine, the milder you can go with camshaft profiles and cylinder head port sizes to create gobs of torque.

We really like the new Special High Performance (SHP) blocks from Dart ("Minimal Assembly Required!" May '09). This purpose-built block for street performance hits right on target. The days of using 400 blocks from the junkyards are behind us. These new blocks, which Richard Maskin and Dick Arons came together to design, feature all the upgrades you would want in a street-performance small-block.

Designed for high-performance and heavy-duty applications producing up to 600 hp, the block features Siamese cylinder bores that have a minimum of 0.230 inch of wall thickness even when bored out to 4.165 inches! It also has a true priority-main oiling system, ductile iron main bearing caps (with splayed four-bolt caps on center mains), thicker decks with blind head bolt holes, and clearance for long-stroke crankshafts. The blocks are machined to accept all factory hydraulic roller hardware and factory thrust plates. The block even has both clutch cross-shaft pivot ball locations. The block comes fully machine with semi-finished bores for final honing. The 4-inch bore PN is 31161111, and the 4.125-inch is PN 31161211.

Dart also features two short-blocks using this block, a complete 372-cid and a complete 400-cid assembled short-block. These dyno-proven packages feature a torque-plate-honed block, hypereutectic flat-top pistons with full floating pins, cast-steel crankshafts, forged 4340 I-beam rods, Hastings moly rings, Clevite bearings, and coated cam bearings. To round out these packages, top end kits are available for both, with the 372 producing 470 hp and 470 lb-ft of torque with a mild 224-degree hydraulic flat-tappet cam. The 400 steps it up a notch with a hydraulic roller camshaft spec'd out at 230 degrees duration at 0.050 inch tappet lift, which produces 525 hp and 525 lb-ft of torque.

Now for your torque monster. We'd go with the Dart 180cc Iron Eagles on the 400-cid engine. You will need to build a dish piston to keep the compression right around 9:1 for heavy-duty use. Dart recommends its 200cc runners on the 400-cid engine, but again, you're not looking for big top-end numbers. It's torque, baby. The 180cc/72cc Iron Eagles come either bare (PN 10210010) or assembled with a 1.437 dual spring assembly (PN 10211112). You may wish to go with the bare heads and use the associated valvetrain recommend by the camshaft manufacturer.

As for the cam, this will be the heart of the torque-building package. You could push the duration slightly, but we recommend sticking to the conservative side. Look to the low to mid-teens for duration on the inlet side, and low to mid-20s on the exhaust side. Check out the Xtreme Roller line from Comp Cams.


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