290 HP 350 anyone used before?

[68c10owner]

Originally Posted by Jake Wade

I fiqured that was who you was talking about. I saw where he brought that up over at Team Chevelle, pretty much left everyone hanging.

Whether he is right or wrong, fact is, If you have chosen the optimal camshaft for your desired operating RPM range, have the optimal cylinder heads, it makes no sense to have less than optimal CR .. even though it doesn't matter to the cam.

That's all I got to say. over and out.

He did leave everyone hanging which is why I pm`ed him to find how what he was talking about. I mean, makes sence to me. Valves are closed in the compression stroke, no way to build cylinder pressure if valves are open even the slightest bit. So on the compression stroke it doesnt matter what the compression is because the cam isnt doing anything on that cycle. Now cylinder pressure is something else all together and that is easily fixed with the right cam. Sure a 40yr old grind is not going to build proper cylinder pressure. But a modern grind with similar specs will make more cylinder pressure with the same compression and make more power in the same rpm range.

I was just trying to help out here and clearly my opinion is not very popular so with that I wish you good luck. The 290hp engine is a decent engine, I was happy with it for what it was and should bring you plenty of trouble free miles.

[Jake Wade]

Anthony, its all good, it was good discussion. I would like to hear what Mike Jones or Harold Brookshire had to say.

[MikeB]

Originally Posted by 68c10owner

For 25 years I was told you needed to match the cam with the compression until a few weeks ago when I had a discussion with Chris Straub. He is the one who told me you don't cam for compression, you cam for the desired RPM range.

Both statements are correct. However, if you are replacing the cam in an existing engine, and have to live with the CR, then you MUST take that into consideration when selecting a new cam. Otherwise, you MAY pick up some RPMs and horsepower, but you WILL kill torque and throttle response. This is especially true for an engine that already has VERY low compression, like both Goodwrench engines. In fact, they have been measured at closer to 7.8:1 than the advertised 8.5:1. You may want to Google "Goodwrench 350 actual compression".

Originally Posted by 68c10owner

The last point in the cycle is the intake closing. This occurs slightly after Bottom Dead Center, and the quicker it closes, the more cylinder pressure the engine will develop.

Seems it's closed a little sooner than you think.

Well, "slightly" is a relative term. And it's very easy to know EXACTLY when the intake valve closes. Looking at CompCam's 268H, which has been very popular over the years, you will see the Intake Closing Angle at .006" tappet rise is 60 degrees ABDC (After Bottom Dead Center). I don't know about you, but I wouldn't call 60 degrees a "slight" part of 180 degrees. And this cam at 268/268, 218/218 has less duration than the one GM puts in the 290hp crate engine!

[76stepside01]

I just got this motor, and now I'm wondering if it be worth it to upgrade the cam?

[68c10owner]

Originally Posted by MikeB

Well, "slightly" is a relative term. And it's very easy to know EXACTLY when the intake valve closes. Looking at CompCam's 268H, which has been very popular over the years, you will see the Intake Closing Angle at .006" tappet rise is 60 degrees ABDC (After Bottom Dead Center). I don't know about you, but I wouldn't call 60 degrees a "slight" part of 180 degrees. And this cam at 268/268, 218/218 has less duration than the one GM puts in the 290hp crate engine!

I know what the compression is listed at and what its actually was measured at. This isnt my first time.

Your not going to find many shelf cams that are going to be able to build cylinder pressure in a lower static compression engine and still make more power. You can change the valve events to increase or decrease cylinder pressure but your still going to need the correct duration to make power.

Originally Posted by 76stepside01

I just got this motor, and now I'm wondering if it be worth it to upgrade the cam?

If your looking for a nice daily driver hot rod leave it alone. If your looking for serious power from it you should have started with a different engine. Its a fun engine for what it is, drop it in and enjoy it.

[JPsChevy]

Originally Posted by 76stepside01

I just got this motor, and now I'm wondering if it be worth it to upgrade the cam?

I'm not touching my 290H.P. I'm just installing it in the truck if it ever shows up, should be here thursday.

[flashed]

I have one of each ,a 290 HP in my wife's 72 Malibu convertible and one 260 HP that was just installed in my 72 Chevy truck ,Im happy with them both . Both of mine are completely stock and both have plenty of power .

[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.