head Talk

[old355]

Lookin into buy new heads for my 350 i was lookin at the GMP vortec head here is the stats on these could somebody tell me what cam i should use wit these heads An where my Comp ratio would be.

Completely assembled, ready to bolt-on
225cc intake port
77cc exhaust port
65cc combustion chamber
Improved airflow
Flows 281 cfm @.600"
Uses Fel-Pro #1470 exhaust gasket, may require minor trimming.

[techinspector1]

I think you'll be very disappointed with these heads on a 350. They would work well on a 434 SBC, but will be way down on velocity with only 350 inches suckin' on 'em. In my opinion, the best heads money can buy for a 350 would be the Airflow Research Street 180cc units. With 9.5:1 static compression ratio and the right cam, you can make 450+ hp and 470+ ft./lbs. of torque with 'em in a 355 package. Build the motor with a tight 0.035" to 0.045" squish and you can make that power on the street with pump gas and zero detonation. Use a Holley 0-4779 750 cfm carb, Comp Cams 12-432-8 Hyd Roller, Edelbrock Performer RPM Air Gap manifold and 1 5/8" headers with 2 1/2" pipes. Use Keith Black #KB193 hypereutectic pistons with the 65cc AFR's for a static compression ratio of 9.52:1

Just so you know, there are rules of thumb for figurin' out intake runner volume. Cubic inches times 0.50 for a good running street motor and cubic inches times 0.55 for a max effort motor.

[old355]

now i see you inputed roller how hard would it be to change my motor over to a roller set up.i i wouldnt mind keepin it a flat tap cuz money is real important here got 1 other build to think about as well.

[techinspector1]

Now, the best way to do this would be to start with a roller block with one-piece rear seal ('88-up Chevy automobile). The trucks used the flat tappet cam for another couple of years after that. The reason for the roller block is because converting a flat tappet block to a roller tappet cam is expensive ($1,000 give or take). A guy could harvest a roller short block from a boneyard for a couple hundred and only have to buy the cam, re-using the roller tappets from the short block.

If a guy wanted to use his flat tappet block with a flat tappet cam, he'd be down on power from the figures posted above because of the superior characteristics of the roller tappets, allowing quicker lift and more area under curve than is possible with flat tappets. Plus, you never need to worry about the cam going flat. There is no break-in worry with rollers. You just oil 'em, stick 'em in and drive.

Any build you undertake is all about a combination of parts. You have to sit down and figure everything out ahead of time. If any of the parts don't work with the rest of them, then you've built a turd.

The combination I've listed above is tested and proven by AFR. Any deviation from the parts listed will result in less performance. If, for instance, the pistons you are using are not the same volume (-12cc's) as shown above, then static c.r. will be different and may or may not work well with the 65cc heads listed above. And if you don't set the squish, again, you're just asking for trouble.

The squish can be altered with the piston deck height (the measurement from the crown of the piston to the block deck with the piston at TDC) and the gasket thickness. You might run a 0.015" gasket with a 0.025" piston deck height to attain a squish of 0.040", or you might run a GM 10105117 gasket (0.028" compressed) with a 0.012" piston deck height for a squish of 0.040" or you might run a 0.040" gasket with zero piston deck height for a squish of 0.040". It makes little difference how you get 0.035" to 0.045" squish, just as long as you get there.

Just an aside about pistons and squish. Stock Chevy pistons have a very thin ring around the crown of the piston where they meet up with the underside of the head and will not meet the requirements for establishing a good squish. There is just not enough flat surface on the piston crown to squish the mixture over toward the spark plug at TDC. Keith Black manufactures their dished pistons with the dish in a "D" shape, leaving an excellent flat area on the piston crown to mate with the underside of the head at TDC to provide an excellent squish.

[old355]

see i didnt want to go thru all of this i want to use my block i have an get around 400 horses wit out a roller set up .

[techinspector1]

Go for it and best of luck to you.

[old355]

what cam would you throw out there if i still ran wit these heads not everybody has a big budget build out here i jus want to get 400 horses out this 350 that been in my car for 1 year, i know changin heads would help cam as well but i want the right set up the motor is already 9:5 1

[techinspector1]

Call your favorite cam grinder and ask for a recommendation. It's a free service.

[gassersrule_196]

yeah rollers are a bit expensive, this winter ill be converting to isky solid roller

[pat mccarthy]

roller cams are not that much when you thing about a re build if you wipe the flat cam if you go solid roller it would not be to bad 210. for the rollers and 240 for the cam

[old355]

whats the diff. i want to make nice power 400 wit a set of vortec cuz i got the intake already it jus sound like this is what he wanted for me. head i know but tear my motor down again NAW that aint happin.

[techinspector1]

whats the diff. i want to make nice power 400 wit a set of vortec cuz i got the intake already it jus sound like this is what he wanted for me. head i know but tear my motor down again NAW that aint happin.

If you had said you were lookin' for 400hp in your initial post, I would have answered you differently.

Here's a budget-friendly approach.....
From 1996 through 1999 Chevy produced the best-flowing OEM iron cylinder head they have ever made. It was used on 350 Vortec 5700 truck motors (RPO L31) and should be readily available in boneyards. These heads used a 170cc intake runner. Look for a sawtooth design cast into the end of the heads and the casting number 12558062 or 10239906 under the valve covers. Some, but not all, of the heavy duty trucks used a different casting number (10239906) with Inconel exhaust valve seats installed. If left unmodified, in the opinion of some, this seat will disrupt low lift flow, so unless you want to dink with grinding on the seat and throat of the port, use the 12558062 heads that are induction hardened. Get the rail rockers and the valve covers with the heads and make a deal with the boneyard that you can exchange them if they are found to be cracked upon magnaflux inspection at the machine shop. Disassemble, clean and inspect. If found valid, freshen up the valve job and replace the seals. Toss the springs and retainers that came on the heads and install these springs and retainers from Crane Cams. They should drop in with no machine work and will allow more lift than the stock springs and retainers. Using the stock 1.5 rail rockers will eliminate the expense of machine work to install guide plates for use with aftermarket non-rail rockers. Or, if you feel bucks-up, you can use aftermarket roller rail rockers without guide plates.
http://store.summitracing.com/partde...5&autoview=sku

With your 9.5:1 c.r., use a cam with around 230 degrees of duration @ 0.050" tappet lift.

[pat mccarthy]

the only thing i would add is they crack big time and after working thru 3 set of heads on the last one i would buy the pbm or rhs heads last guy i did a set for had alot money and time finding a set of gm casting that were good and just because they not crack at the time check they could latter on the pbm and other are thicker casting

[old355]

now if im lookin for a cam for it lift wise i could go to 500 or more if the heads have the right springs in them.

[techinspector1]

now if im lookin for a cam for it lift wise i could go to 500 or more if the heads have the right springs in them.

Be sure the springs are compatible with the cam profile or you'll be buyin' more than springs. Talk with the tech at the cam grinder when you order the cam.