Which heads are better to start building for a street driven BBC? I have asked around a little bit and most people are saying the Closed chamber heads. The 781s/049s are open right? Can someone shed some light on whats the difference and which is better. Some casting numbers reccomendation would be great also
Thanks!

http://www.nastyz28.com/ubb/Forum5/HTML/011943.html

Pics of the different chambers...

Either can work well. Both have advantages.

Closed chamber gets compression, and is more efficient from a combustion standpoint, less thermal loss on the chamber/piston.

Open chamber has an easier path for airflow, but will require a heavier piston (dome) for equal compression, and you lose some efficiency.

781/049 are open chambers, as well as 820's...

Semi-closed are 290, 215, 063's.

Closed are 390 and 702.

There are others but those are common ones.

781s are very common and a very doable drag head if done right. I have 781s on my 396+.060 and it equates to about 8.13:1. I pour high octane in and my motor didnt need it, it ran better with 92-94. My combo [stock valves,Crowers springs,3 angle,and runner cleanup] ran 12.67 this last season with minimal tuneing. I have a pair plus one 2702 heads that I was targeting to install but since it ran that good in full trim I will rethink. There are about three types of closed chambers so make sure you know which ones you want.

Everything I have ever read says the 049/781 are the best breathers. The open chamber deshrouds the valves and allow more air to flow out around the circumference of the valve. The biggest problem is getting compression from them without a dome. I did have a buddy with a 65 396 in a chevelle that had closed chambers (98cc) that ran 12.20s on the motor. But now he as open chambers and his compression has dropped alot (13 to 1 - 10 to 1)still it seems to have gained a stronger top end. Lost some down low cause of compression. I have 049s with 2.19s and 1.88s with the chambers opened up to the cylinder edge and then plained back to the 118cc. I will have to run a big dome to get to 12 to 1 like I want. The only other thing I can say is the last L88 went from closed to open chambers and gained HP. In fact the 71 Ls6 did the same and gained back most of the HP it lost by lowering the compression (only 25 hp lower but went from 11.25 to 9 to 1). I think Ovals are in most cases best for the street but that is a different discussion. Just what I think.

Wow.
Well seems like a tie almost. What should I get? I have a machine shop guy that has them all. Hes talking me into closed chamber heads.But if I dont want 12-1 or something its not good to have them right? I dont want compresion that I have to run 96 octane fuel or something. I want the motor to run on 91-92 octane MAX.
what casting numbers should I get. The heads Im offered are $100 set

[This message has been edited by badazz81z28 (edited January 06, 2005).]

It's a piston choice deal here b/c closed chambered heads make compression easier then open chambered heads especially on the old 454 P/U motors that came with true flat-tops in them.

But if you are going to buy pistons, then use the heads that will give you the CR. you want to go with them..

Anmd don't forget to figure in piston, down in the hole a stock-about .025", as well as a decent quench dimension of about .040" so it will all calculate out right figuring your CR.

pdq67

buy the open chambers, some flat tops & my D1 Blower & hammer them all. LOL.

Bob

Just buy Opens and choose the correct piston for the CR you want. It will make better power. What 454/502 can you buy from chevy now with closed? or really any commonly avalible head that is for streeters.

I'm gonna kick this off again AND say take your pick after doing a search for the "BSE" motor combination here and over on both Team Camaro and Team Chevelle!!

Ed's closed chambered, large oval, heads do darn good, imho...

Ed doesn't post anymore b/c of all the controversy that he stir's up.. BUT in my book, his motor theory is great!!

AND the deal about using cheap, reworked, stock heads really trip's my trigger since I'm a tight-a--, er, eh, "frugal"..

Even tho I went new Merlin ovals on my 496" motor before I read about all this stuff.

pdq67

Ya but aren't merlins open chambers? Don't get me wrong closed do work. But better than a open? If they were so great the aftermarket would be making more of them. To belive this is wrong is the same thinking that says the Edelbrock Trantula is the best intake ever made (what one local thinks) if thats true they would still make them.

The GMPP heads/Edels are a somewhat closed chamber... They are not an open chamber.

Edel also makes a 100 cc head.

The closed will work fine.

I prefer them due to the combustion efficiency and they flow fine at street/strip levels.

However,
piston availability IS better with open chamber stuff.
So if you plan to upgrade to a different head later, without a piston swap, an open chamber might be a better choice.

GM went open chambered heads for one BIG reason, they are cleaner, "smog-wise", then closed chambered heads!!

We just can't get a true open chambered head small enough to create a good CR. number using flat-top pistons is all UNLESS you buy expensive, race type heads!!

I honestly figure if Dart/W/P's would bring out a 90 cc cast-iron Largwe oval port head THAT uses stock valvetrain parts, they would have a real winner!! AND I don't care if it is open or closed...

I would bet money on them selling a sh-t-pot full of them to no other then old 454 P/U motor guys!!!

pdq67