I have a 350 w/flat tops 4 valve relief, 441 casting heads, standard rebuild, no porting, balanced and bored 020 w/ torque plate. I have a 270 magnum comp cam w/.470 lift. Old dual plane Edelbrock and a 600 Holley (stock). Compression check was 130 to 140 cold. Runs fine, sounds great, plugs are clean, can't get it to ping no matter how much timing. With 3:08's, M-20, no traction bars, 4000ft, it run 10 flat in the 8th. It just doesn't seem very crisp. Is this too much cam for my compression?

If they are replacement type cast flat tops, then they are probably .040 or more in the hole. With 76cc heads and standard type head gaskets, your looking at about 8.5-1 compression. Assuming your timing chain isn't shot, your cranking compression readings indicate about that low of compression too. For your compression, you have too much cam. You need about another 30-50 psi to start getting into the "crisp" response range and still be safe on pump gas. My suggestion? Replace the cam with something along the lines of a comp cams 260 high energy, isky 262 supercam, isky 264 mega cam, comp cams 260AH-8, etc...something in the 210 to 216@.050 range on a 108 or 110 lobe center. With your gears and a stick, it would be a lot more fun to drive IMO.
Some things you can do to help your current situation is get the distributor recurved...I'm thinking along the lines of 18-20 degrees mechanical advance, all in by about 2800 rpms, with 18* initial timing. Low cranking pressure engines, especially those with 76cc gm iron heads, like a lot of initial timing and need about 38-40 degree's total for best perfromance.

-441 heads may be 76 cc jobbers and with .020" shims you can be at 9 to 1 CR.

With .039" composite headgaskets you may be at 8.67 to 1 CR.

Imho, a 270 cam will run it's best right at 9.75 to 10 to 1 CR.

This may be why it isn't crisp!!

pdq67

The most power producing solution would be heads. Go smaller on the cam and yes....it will be more crisp, but at the same time...your almost stock now. Stepping back on the cam and youve basically got a stock engine.

A descent set of 64cc heads that flow better will definitely increase power everywhere! If you could ebay some 165-180cc aftermarkets.....or even an upgraded set of vortecs with the right intake youd be worlds ahead(once again....not only would you want something that flows....but youd want a combustion chamber around 64-68cc to bump compression a bit too)!

But if thats not an option....to answer the original question, yes, the stock heads and low compression arent liking your cam selection all that much. That setup as is would like a mostly stock cam.

Would advancing the cam 4 -6 deg help you? That should make it crisp..

it needs more compression, period.
I've run a 270H for a couple years now, it's definitely not too much cam. In the new 383, it'll idle at 650 rpm.

Paul is right, this cam needs 9.7:1 compression. If new heads are not in your current economic future, pull the 441's off, have em milled .020" and put em back on with a set of felpro 1094 shim gaskets.

You'll get her running right for less than a hundred clams.

Is it the duration that is too much or the lift. I have 268 Comp cam. I guess I'll be saving for some heads. I love the way the 270 cam sounds.

It's the duration. The lift is fine. The more duration you have the more compression you need or the engine gets "lazy".

Is it the duration that is too much or the lift. I have 268 Comp cam. I guess I'll be saving for some heads. I love the way the 270 cam sounds.

Do what Jim said! Easy fix!

Yes, the 270H does sound good! :thumbsup:

Agree with all the above,..the 270 is a great cam,..mill the heads (and check your push-rod length,..will likely need a shorter set).

Also, if you can slip in a 3.55 or 3:73 gear out back that would work a bit better with the cam and give you little more torque mulitplicaiton.

Lastly,..are you running a vacuum advance to manifold vacuum?..and with a VA that's all in below your idle speed? if not, there's some off-idle and cruising 'crispiness' that's untapped.

Good luck!

Do what Jim said! Easy fix!

Yes, the 270H does sound good! :thumbsup:

Yup love the rock of the car sitting at a light and the throaty lope of the cam through the exhaust. Keeps a grin on my face sitting still as well as driving.

I sure hope that my car runs ok. I just put new a.f.r 180 street heads on my 355 and also put a 270h cam in. My compression ratio should be 9.32 with the 68 cc heads. I have only driven it maybe 5 miles so far. I want to put some miles on it before I test to see how good it runs.

I sure hope that my car runs ok. I just put new a.f.r 180 street heads on my 355 and also put a 270h cam in. My compression ratio should be 9.32 with the 68 cc heads. I have only driven it maybe 5 miles so far. I want to put some miles on it before I test to see how good it runs.


Your car will be fine. 9.32 static puts you right about 7.67 dynamic. If you have a stock convertor your bottom might be a little soggy.