Hi guys, I have a 454BBC with peanut port heads as of right now. I believe that I have flat top pistons. Would a swap to the 781's help me at all? Would I see a difference. Thanks a lot for any advice,
Chris

If you can swing the expense, Edelbrock has a 100CC version of their Alum Head for use on flat top motors.

Look for a pair of casting# 215, 063 or 290. These are semi-closed chamber heads that can be milled down to around 102cc chamber size. These should get your SCR up to around 9.1-9.2.

Install some 2.19 / 1.8 valves with some bowl blending and lay the chamber walls back a little and they will flow about as good as the 781 open chambers.

What is the difference between the open and closed chamber heads? Would I see that much of a drop in CR if I went to the 781's. I would fo aftermarket, but don't have the $$$ right now. The 781's have the 2.19/1.88 valves installed on them now. What if I got them milled down? These just happen to be failry convienient (sp?) and that is why I am wondering. If I went with the 781's, would I see a power LOSS? I just figure that they would flow better than the peanut ports.
Chris
P.S. 71454, is your car a street car? How do you like those 4.30's?

I doubt that you have flattops,even the low compression big blocks w/open chambered heads had a small dome on them, but with flat tops and 781's you might have 7.5,8 to 1 comp, defeating the purpose of the better flowing heads. The 781's have 118cc chambers with big blocks its roughly 6cc per compression point in chamber volume. My 781's were milled .020 and cc'ed,machinist says 116cc now. Closer chambers were right at 97-100cc,,,open chamber 118-121cc.

So if I got the 781's milled down, would they give an improvement then, or would it still not give me enough compression for what I am looking for. Should I just not bother with the 781's and look for a different set of heads?
Thanks,
Chris

The 781's are great heads along with 049's,,,if you do find out that you have flattop pistons,look for a set of closed chamber 215's,206's. Or...you could put in a new set of pistons too and be good to go.

Originally posted by RedSS454:
P.S. 71454, is your car a street car? How do you like those 4.30's? Chris,

When I first started building my car I wanted a race car that I drove on the street periodically. Since then I have changed my mind in what I want my car to be; a street car that I race periodically. Since that decision I have been "toning down" my combo. In the future I will probably take a little of the gear out of it. Most likely will go to a 4.10 or maybe 3.90's.

The 4.30's really are not that bad. With a manual transmission I don't get the slippage that automatic / high stall converter cars get. With 29" M/T Sportsman Pros out back at 60 mph I turn just under 3000rpm.

On the motor this gear/tire size combo for my car seems about right, but the few times I've used nitrous, it seems to be over geared. Things just happen way too fast with this gear and N2O. :eek: ;)

So, closed chamber heads are better with flat tops? Would a set off an LS6/L78 Rect Port heads be worth it? They are the 291's.
Chris

i believe the peanut ports are also around 120cc, so if you have an aftermarket cam and intake with headers, then i think the 781's will definately help. if it's a stock motor then maybe not. i had a buddy who had a stock flat top, and yes most truck motors were flat tops, with a set of 049's with the big valves an rpm intake and a comp 282 solid with 2" headers in a 67 camaro and it ran 7.20's in the 1/8mi. i doubt that performance could be equaled with a set of peanut ports, no matter what you did to them. i'm not saying that you need the same parts as he used, only that there is performance to be gained by ditching the peanut port heads for the 781's.

My '75, 454 P/U core motor I made my 496 out of had good '781's on it stock AND true, one valve notch flat-top pistons!!

I figure she was all of 7.9 to 1 CR, stock!!!

Pick up a set of old -206's b/c they are listed at 96.7 to 97 cc's stock and are early, true closed chambered heads that are not laid back like the semi-closed -215 type heads that are like 101 cc's or so..

These stock with .020" thick shim headgaskets on a 4.25" bore, (454 sized motor), should put your CR. right at 9.34 to 1., figuring a stock, .025" piston in the hole measurement...

Or plane them down to 90 cc's and get shorter pushrods and you should then have right at 9.9 to 1 CR.

This is the only way I have figured out how to get good CR. outta the old, stock, cast flat-top pistoned, 454 P/U motors!!!

pdq67

The 291 head has an awful big intake runner for an 8-9to1 street motor. They work great with lots of cam and compression but not in your case. Find a set of closed chamber ovals.