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Old 02-19-2013, 08:10 PM
MalibuMike's Avatar
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Cylinder head adjustments

I'm wrking on a project, a wkend driver nothin too major...1980 2dr Malibu with a 454 & 400 trans. I jus had the the block took apart (361959) and I'm putting .060 pistons back in it with a mild street cam. Now my question is do I really need to have any head wrk done if I'm using a set of 336781 (113cc)heads & its never gonna see the drag strip?

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Old 02-19-2013, 09:11 PM
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"Now my question is do I really need to have any head wrk done if I'm using a set of 336781 (113cc)heads & its never gonna see the drag strip? "

What kind of work are you talking? A basic rebuild is minimum. New springs/seals. I usually try to replace the valves with new stainless as a precaution. BBC engines are known for "dropping" stock valves at high rpm. 2.19x1.88 valves really wake these engines up. 781 heads are 119+ cc.
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Old 02-19-2013, 09:34 PM
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valve size

Quote:
Originally Posted by BOBCRMAN@aol.com View Post
"Now my question is do I really need to have any head wrk done if I'm using a set of 336781 (113cc)heads & its never gonna see the drag strip? "

What kind of work are you talking? A basic rebuild is minimum. New springs/seals. I usually try to replace the valves with new stainless as a precaution. BBC engines are known for "dropping" stock valves at high rpm. 2.19x1.88 valves really wake these engines up. 781 heads are 119+ cc.
exactly what was posted.The engine livens up quite a bit with bigger valves
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Old 02-20-2013, 07:44 AM
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Most valve suppliers offer the smaller stem (11/32", like small block, Pontiac, Ford, etc.). If you're going to use oversized valves (2.190/1.880), take every "advantage.". The smaller stems significantly reduce weight. These stems are fine for all applications, as we use similar valves in high-end small blocks AND Pontiacs without issue (in SERIOUS race BBCs, we use 5/16" stems!). Agreed, the oval ports don't need a lot of work, as the larger valves seem to wake them up nicely.

The "trick" to keep costs down is to install "thin wall" guides (.502" OD) in the existing BBC guides. Even though they're "knock out" guides, we've found this to work VERY well. Anything over about .540" lift should consider bronze guides. I would avioid guide "liners". We've seen too many of them "move", causing catestrophic failure.

FWIW

Jim
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Old 02-20-2013, 12:46 PM
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Quote:
Originally Posted by MalibuMike View Post
I'm wrking on a project, a wkend driver nothin too major...1980 2dr Malibu with a 454 & 400 trans. I jus had the the block took apart (361959) and I'm putting .060 pistons back in it with a mild street cam. Now my question is do I really need to have any head wrk done if I'm using a set of 336781 (113cc)heads & its never gonna see the drag strip?
If the heads were sold to you as 113cc, check them to be sure- they are more than that stock but they may have been milled. Using the head volume and the piston dome volume along w/other measurements (piston below deck distance, head gasket thickness and bore diameter) will get you the actual compression ratio.

It's easiest to use a compression ratio calculator.

In addition to the sound advice posted by others above, know that if you replace the guides you will need at least a valve job. This is the time to add the larger valves. That way work won't be repeated unnecessarily.

Now, if you're not that concerned w/all out power, you can use the stock valves. Be sure the exhaust guides aren't leaking water, and as long as the valve margins are sufficient for being reground and the seats aren't damaged or sunk too far (from wear or previous valve jobs), many thousands of BBC engines are running just fine like that.

The main thing w/the heads you have is compression. If you have flat tops, the CR is going to be below 8:1. So look for a dome size that'll give you the compression ratio needed for the cam you choose- it's all interrelated.

One other thing is exhaust valve rotators used under the exhaust valves. They can be replaced w/spacers along w/new springs that match the cam. Be sure to check (or have checked) the spring installed height. With a mild cam, valve train geometry isn't usually a big problem- but if the heads have been milled extensively and valve jobs done, etc., the geometry should at least be checked.

One of the biggest reasons flat tappet cams go flat in a BBC is because the lifters fail to immediately rotate at start up. So check the lifter clearances to be sure they're not too tight. But before honing the bores, be sure to clean the lifter bores w/acetone, lacquer thinner, or carb spray scrubbed w/a shotgun bristle brush to remove the shellac-like build-up. Often this is all that's needed to have the lifters working smoothly in the bores.
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