Open vs Closed chamber

[Cudadrag]

I'm sure this has been talked about before but I have not seen. My question is if you are building an engine where stock compression and cylinder volume must be maintained is it not more adventitious to use a closed chamber head design? It seems to me all the advancements in combustion chambers (especially in the aluminum heads) have been with the open chamber designs.

I know most stock builds also require a stock head build thus your choices may be limited. But there are some exceptions.

Any thoughts?

[pishta]

If you can build a closed chamber head that has a quench area like the heart shaped 302 heads, you can run higher compression ratios that an open chambered head. The ultimate closed chamber head would be one that used the piston top to channel the AF mix right into the spark. By putting the spark in the same "channel" as the intake and exhaust valve, you have a superior combustion chamber that will result in added cylinder pressure and detonation control. I just read an interesting article on this subject and that is what it outlines. Look up "soft head" in Google, and try to ignore all the other BS that comes up with that search string

[dgc333]

To add a little to what Pishta said about detonation control; I built a 360 this past year and used the late model magnum head which is a modern closed chamber design.

With zero decked flat top pistons and a 0.039" head gasket I have 10.6:1 compression. I am using a Comp XE268H cam in this engine. My point is that the pretty much ideal quench spacing between the closed portion of the head and the top of the piston is allowing this engine to run on 89 octane gas.

[dust]

Originally Posted by pishta

just read an interesting article on this subject and that is what it outlines. Look up "soft head" in Google, and try to ignore all the other BS that comes up with that search string

http://www.theoldone.com/articles/The_Soft_Head_1999/

??

[dave571]

Originally Posted by Cudadrag

.... It seems to me all the advancements in combustion chambers (especially in the aluminum heads) have been with the open chamber designs....

.

Any thoughts?

I'll have to say that I disagreee with this part of your statement.

Eddy's, indy's, bulldogs, all aluminum, and closed chamber.

The performance advantages of a closed chamber are well documented. They were deleted as an emissions measure. Reduced NOX.

If you can go with closed, and stay within your class guidelines you will see better performance IMHO.

[Cudadrag]

I guess the fight is between open chamber bench flow vs. close chamber's compression savings. It is clear (at least what I have seen) that open chamber designs have higher flow rates then closed. I'm also guessing that open chamber heads would be more ideal for engine builds where compression ratios are not restricted. Or where boost is added.

I assume there is some math that would answer the question open chamber vs. closed chamber to a specific engine build.

I am not sure why I'm stuck on this thought. My thoughts for my Cuda was just pack a BB with 12.5-13.5:1 compression and bolt on the most ungodly high flow open chamber heads I can afford (matching a cam and intake of course) and blast the damn thing down the track. But now that I'm older I'm thinking there must be a smarter and more efficient design. Maybe with closed chamber heads.

[rumblefish360]

The latest heads have a closed chamber for many reasons.
1 of them is to allow the use of flat top pistons and let them and the closed chamber work together for a hi ratio.
This keeps the assembly light and cheaper for balanceing.
No big domes to mill and re-finish and balance with lots of mallory.
Though this can be the case with flat tops, it's less likely going to be a huge hassle.

With a flat top and closed chamber, you'll more easily get higher comp. ratio, a better flame front and quench bennifits from mild street car to wack race engine.

Hi flowing heads are a simple function of how well the ports flow the air in and out. Chamber design has a say in this, but I think the debate on which is better for this is solved for you by the aftermarket and there research and development teams.

[Cudadrag]

Now that I look around the Eddys and Indys of the world it does appear that closed chamber is the design of choice. I'm guessing that my age is showing cause in the 70s and 80s open chamber with high domed pistons were the way.

I'm glad I'm at least thinking in the right direction even if my tech info is a little behind the times.

My kids are now grown and I'm just getting back in the seen. (2nd full year) with the E.T. Duster. Now looking to the SS or Comp classes for the Cuda.

There are FAR more choices then ever before especally if you include crate blocks. Head flow numbers that were unheard of 20 years ago available right out of the box. Tighter and more specialized grinds on cams. Stroker kits by mail order. It looks to be some very fun and fast times a head.

[rumblefish360]

It's true, times have never beenbetter for parts!

[Cudadrag]

I loved the Soft head artical http://www.theoldone.com/articles/The_Soft_Head_1999/

(Now thats a closed chamber design!) I have not seen this design on any head I've seen.

I do have one question. If the head design denotes a flat intake pancaked with the flat piston would this not create a large quench area in itself? I understand the design would force the mixture to the exhast trench side for the burn, but it appears to me unless the intake and piston surfaces were "perfect" little puddles of mixture would/could be trapped thus creating alot of detonation problems?

[pishta]

detonation is usually caused by a hot spot in the chamber, a sharp edge, glowing carbon deposits, etc. when you say perfect, they almost are. They face the head on a machine that runs right across the closed part of the chamber and the piston crowns are also pretty flat as they too are faced when they are building a motor of that caliber. they use known compressed head gaskets and the clearances are tight indeed. I saw a Ford 302 head that was closed, and you could see ".010" on the closed portion of the chamber. That was from the piston top, and it wasnt from contact, but from the burn!!!

[Cudadrag]

I agree most det problems are round the edge but trapped mixture can also be a problem. But it appears near 100% is "trenched". I also would guess this design would be more beneficial in the high rpm low stroked multi valve world then the 2 valve long stroke drag race world.

I would think the smaller trench area would create very high dynamic compressions. Is today's exhaust seals capable of handling this design? They noted in the article of over 23:1 in the trench. If so, that is one hell of an exhaust valve.

[pishta]

You are not going to blow an exhaust valve off its seat with 23:1 compression. Diesels run that all day, and night. Think of the pressure when the mix ignites, its way up there.

[HankL]

In the middle 1990's
during the short time Bob Stempel was CEO of GM
he came to Duke U Engineering school
and gave a talk.

In the Q&A session afterward one of the students asked about engines and MPG and why it wasn't better.

In his reply Stempel gestured over toward a German grad student at Duke who had worked for Audi and Stempel said that he had heard that day that the 'ideal' cylinder head for highest fuel efficiency AND highest power was with a single exhaust valve in the center and 4 small intake valves arranged around the outside of the bore - but that design was very bad for NOx and wouldn't pass emission regs.

Much later when I read TOO article on soft heads it seemed that his 'dual sparkplug exhaust trough'
cylinder head was similar.

Perhaps the ideal cylinder head
is a tiny center mounted combustion chamber
surrounded by flat quench areas
with a single large diameter sodium filled exhaust valve
with at least two sparkplugs nearby this exhaust valve
and 3-4 multiple intake valves arranged around the outer area.

It is possible a cylinder head design like this
might run 87 octane on 14 to 1 compression ratio.

It is also possible that each of the intake valves would have a different lift to create swirl.

[dust]

This is a good thread, thanks to those who contributed to it.

[Odilon_df]

Hi,

The last 318 (74-82) made in Brazil was intended to run on ethanol and they are only 38cc chamber volume. I don´t know if some of these came to USA but they are very common here..... Good stuff to raise compression rati