290 HP 350 anyone used before?

[rich weyand]

New to these forums, not to these trucks. Been lurking for several years and finally signed up.

The static compression ratio matters because the cam closes after BDC, when the compression stroke is under way. The compression from full valve closure to TDC is the dynamic compression, and this determines performance more than static compression. Since the closure point is in degrees, at higher rpms a later closure helps fill the cylinder, while at low rpms it hurts. So a later closure will benefit horsepower up top and hurt torque in the bottom.

My truck originally had the 260 hp block in it. I replaced it with the 290 hp block. I have since recammed it, so I have run all three options in the same truck. Carburetion is Edelbrock 1406 through air-gap manifold with Hooker headers and H-pipe through dual Flowmaster 40s.

The 260 hp block is a solid engine with nice torque in the bottom end.

The 290 hp block has less torque at low rpm than the 260 hp, but it gets nicely feisty when you get some rpms under it. The 50-90 passing times at "war emergency power" were great. This engine made the truck a two-lane terror, but it's slower off the line than the 260 hp.

After a year I re-cammed the 290 hp engine with a torquier cam. The 260 hp and the 290 hp cams are both 50 year old grinds with slow ramps, which hurts dynamic compression on the compression side of the spark, and dumps the charge early on the power side of the spark, hurting mileage and power. Modern fast-ramp grinds give the cam designer more options on duration and overlap without being intake-late and exhaust-early.

When re-camming, I consulted with engine designers, engine builders, and street rod guys. The consensus: horsepower is what you race, but torque is what you drive. If you are building a circle-track engine, where you will be full-throttle and near-redline all the time, that's a lot different than building a street engine, with lots of 0-30 starts and motoring around in the mid-range. Torque is even more important in a 5000-pound truck to get the darned thing moving.

All that said, the Comp Cams 12-235-2 was the most recommended cam for the low-compression stock 350. 12-300-4, 12-231-2, 12-235-2, and 12-238-2 are four cams that have fast ramps, high torque, and work well with the low-compression heads. I listed them there in order of increasing lift, increasing horsepower, and decreasing torque.

In my situation, with no Interstates even close and lots of country road uphill and downhill, I went with the torquiest of the bunch, the 12-300-4. It runs off the torque curve at 4500 rpms or so, so I increased one weight in the tranny governor by one size so move the shift points down about 500 rpm.

Best all around, though, for cheap power in a new-out-of-the-box engine is to get the 260 hp crate engine and put the 12-235-2 cam in it. With decent induction you can expect 290 hp at 4000 with 415 lbft of torque at 2500.

Of course, if you are handy at engine rebuilding and have access to the tools, you can build yourself up something really nice. BTDT when I was younger. Also, if money is not an issue, you can buy a GM Performance Connect & Cruise powerplant that will give you up to a 556 hp LSA with 4L85E.

But if you just want to drop a stock-ish 350 in with a little sweeter cam for under 2 bills, the 260 hp crate with the 12-235-2 is probably the way to go.