Okay I don't wanna start any arguements but what do you guys think is better? Running small domes (like .133) with closed chamber heads, or bigger domes (.250) with open chambers?? I'm aiming for a "semi streetable" 10:1 CR

I've found a guy who has a set of each for sale, but he says open or closed chambers is all personal preference.

What do you guys think?

The smaller the dome,the better the flame travel,slightly more power.

Be careful!!!

I have .133 domes with the 101cc semi open chamber(290)heads and ended up at 10.5 so 98cc closed chambers will push that up even more.

I just finally worked out my detonation problem, you may have read my woes in other post.

9 times out of 10 the open chamber will flow more when we're talking "old tech" big block Chevy stuff.

So I'd take airflow over combustion issues. You can't burn what never gets in there! You can get compression with smaller domes with a little miling. A .250-.300 dome isn't all that big considering the funky shape of a big block chamber/dome anyway. A dome that size isn't going to be blocking much anyway.

Always be sure to actually CC heads. I often find heads with much larger actual chambers than what the books list. Especially on this older stuff that may have had a few valvejobs. I had a set of 96cc heads that actually measured 115cc once! We had to mill them like crazy and install new valves to get chambers back in line.


JIM

The best head is probably the one you own. If you are starting from scratch, don't bother with iron. It will get real expensive.

Normally a closed chamber makes a better street head because they make more torque and when set up correctly allow much higher compression before detonation.

i have direct comparasons for you. my 68 chevelle has 215 closed chambers my father in laws 66 elky has 049 open chambers. both heads were ported by the same guy. the setups are indetical except he has an auto and i run a 4 speed. we both have 10 to 1 motors he has .250 dome i have .125 dome he is 122cc i am 107 cc. the cars are both super strong he runs 11.21 at 120mph, i run 11.21 at 121 mph. it really is a toss up . the most important thing for you to consider in my opinion is if you ever change to a modern aluminum head they arepretty much all open chambers , so the open chamber pistons can stay in there and you would'nt have to buy new ones. that is what keeps me from going to aluminum heads my small dome. ray

I run small domes (.100) with #215 closed chamber heads (101 cc) and have 10.5 to 1
works well in my heavy,undergeared car..no detonantion problems either graemlins/thumbsup.gif

i prefer small chamber small dome. properly set up it seems you can run more compression and timing.

You may find this link helpful when looking at this. BTW The closed chamber design ranged from 96 to 109cc from early to late ... all as cast.
The 1970 LS-5 heads cast 290 had 101cc chambers.
With my flat pistons (30 over) and this head my CR is 9.75:1

http://www.angelfire.com/fl/procrastination/motor.html

I have run and experimented with both closed and open chamber heads of the square port type. I am not going to go into scientific details but open chamber heads have the overall advantage because of improved breathing. Chevrolet was looking for more power and this was achieved even with a slight dip in compression. If you already have a set of closed chamber heads it's not necessary that you scrap them. After all, you can open up the chambers by porting them a bit as I did.

Just an FYI,all the pro stocks run flat tops with small chamber heads...

I think the guy's pretty much agree that properly set up closed chambered heads can use slightly higher CR. and still run the poor gas we have now due to a slightly more eff. chamber vs the better suck, but the slightly poorer detonation resistance of the open chambered heads..

AND we can get a fight going on this if we want to really get on this topic so that's all I'm gonna say!!

pdq67

Originally posted by sapper92310:

I've found a guy who has a set of each for sale, but he says open or closed chambers is all personal preference.

What do you guys think? Thats what I think.
Unless you've got the peanut port heads, a big block chevy will run fast,
with open or closed, rectangle or oval port heads.

The breathing issue might have something to do with the displacemant of your engine too.

A guy with a 540 needs more air flow than my 396.

For sure if you are scratch building a new engine design, a small chamber with flat top or even "inverted dome" or dished pistons will burn better.

But I'm a strong believer in airflow, and typically the open chambers flow more air. No matter how big the engine is, you need the most amount of airflow possible. I'm not talking about bigger ports, I'm talking about what gets past the valves into the cylinder. In fact, on a small bore motor like a 396, ANYTHING you can do to help get the air into the cylinder will help. Now this may only involve opening up the closed chamber heads around the valves some.

The newer design "closed chamber" type heads that all mfg's use are light years away from what we are dealing with. They have very shallow chambers that still allow LOTS of room around the valves for airflow, yet maintain small cc's.

Once again...you can't burn what doesn't get in there!

JIM