Open Chamber Heads vs Closed Chamber Heads....

Prefer Open Chamber or Closed Chamber for Racing

  • Open Chamber

    Votes: 5 17.2%

  • Closed Chamber

    Votes: 24 82.8%
  • Total voters
    29
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318willrun

318willrun

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  • I think open chamber heads perform better for hot rods/race cars, all else equal including compression.
  • I think closed chamber heads can add bottom end spunk when used to raise compression on a low compression motor in daily drivers, tow trucks, etc.
  • This question keeps rearing it's head in many threads throughout the years, lets start a thread just for the topic
:popcorn:
 
Glad you brought it up. Inquiring minds want to know .
 
It's been pretty much proven time and again that closed chamber heads that are taken advantage of (quench) make more power.

If you're not going to take advantage of quench, it doesn't matter.

Lastly, IMO, it's really splittin hairs either way unless you're building something race only and want every last drop you can get.
 
The only reason Mopar went to open chambers in 68 was to reduce NOx emissions. There is no performance benefit in open chambers.
 
DFX 340 Duster said:
Did the raised area of the stock 340 pistons provide quench with the open chamber heads?
Click to expand...

Very little if none at all. Optimum quench "they say" is "around" .035". I think the piston on the early 340 was around .020" or so out of the hole. The head gaskets they used from Chrysler were the .020" steel shim gaskets. The chamber depth opposite the spark plug (which is where quench would occur) is generally in the .095" deep area. So, the .020" on both the piston and head gasket cancel each out. So you're lookin at a quench distance of about .095". That's not enough for any quench......although the piston being out of the hole adds compression, which was the goal.
 
Open chambers tend to have less issues with valve shrouding, but this isn't universally true. Also, an open chamber is marginally better for flame travel. Most engines designed in the last 30 years, especially overhead cam engines have shallow open chambers.
 
C130 Chief said:
Open chambers tend to have less issues with valve shrouding, but this isn't universally true. Also, an open chamber is marginally better for flame travel. Most engines designed in the last 30 years, especially overhead cam engines have shallow open chambers.
Click to expand...
Agree.....
 
Open chambers lend themselves better to lower emissions. Closed chambers are better for performance. These aren't hard and fast rules, there are exceptions such as with multi valve and DOHC heads and such, but speaking in terms of old school 2 valve per cylinder engines like we discuss "HERE" the closed chamber will win, IMO when taking advantage of quench.
 
skrews said:
The only reason Mopar went to open chambers in 68 was to reduce NOx emissions. There is no performance benefit in open chambers.
Click to expand...
Let's just say what it really means, open chamber heads are a smog head.
 
Well a "Hemi" head is about as open a chamber as it gets, the poly head as well. As for closed chambers making power, take a look at an old Chevy 235. Plenty of quench, but absolutely diabolical for flow. Also, shallow open chambers have less surface area, which means less area for combustion heat to be absorbed into the head. The shape of LA head combustion chambers are more than a little bit a result of the valve angles. If the valves were more in line with the cylinder axis, the chambers could be shallower with less shrouding. But, the engine would be wider, rockers longer, the whole thing heavier and more expensive because it had more iron in it, etc. Remember the LA was a budget rework of the A engine so it would fit into economy cars and cost less in volume production than the poly. Since the chambers were on the large size to begin with, adding the quench pads was a cheap easy way to increase compression and still keep HC emission levels reasonable.
 
C130 Chief said:
Well a "Hemi" head is about as open a chamber as it gets, the poly head as well. As for closed chambers making power, take a look at an old Chevy 235. Plenty of quench, but absolutely diabolical for flow. Also, shallow open chambers have less surface area, which means less area for combustion heat to be absorbed into the head. The shape of LA head combustion chambers are more than a little bit a result of the valve angles. If the valves were more in line with the cylinder axis, the chambers could be shallower with less shrouding. But, the engine would be wider, rockers longer, the whole thing heavier and more expensive because it had more iron in it, etc. Remember the LA was a budget rework of the A engine so it would fit into economy cars and cost less in volume production than the poly. Since the chambers were on the large size to begin with, adding the quench pads was a cheap easy way to increase compression and still keep HC emission levels reasonable.
Click to expand...

Comparing the Hemi head here is apples and oranges, because the Hemi was designed from the ground up for performance. It had quench, because it had the pistons to make it happen.

When speaking in terms of non domed pistons and conventional non hemi heads, the closed chamber wins.

I'm not arguin anymore. I gotta go take a dump.
 
RustyRatRod said:
Comparing the Hemi head here is apples and oranges, because the Hemi was designed from the ground up for performance. It had quench, because it had the pistons to make it happen.

When speaking in terms of non domed pistons and conventional non hemi heads, the closed chamber wins.

I'm not arguin anymore. I gotta go take a dump.
Click to expand...
Don't take a dump, leave one!
 
Most /all of you guys are talking WOT situations.

But a streeter spends most of it's life at Part Throttle and modest Rpms.
Even on the run to 65mph; with 3.23s, yur looking at just 3780@ zero-slip in second gear (Tflight), perhaps 4200@ 10%@slip.
How can tight-Q and less surface area affect these, when coupled with high compression?

I mean the compression ratio by itself brings very little to the table; many articles have suggested just 5.2% peak WOT-power gain , when going from 8/1 to 11/1.
And we know that when throttled, as in cruising, The effective compression ratio could be sub 5/1. So how does Tight-Q and Hi DCR, and small surface area, make such a funtastic street-engine?

Ok I'll tell you what I think.
Just one aspect.
On an 8/1 360 the total chamber size has to be 105.35cc.
On an 11/1 the total is 73.74
Ok; have you ever had a big fluid-transfer suction device, that you were using to suck the oil out of one jug, to put into another. And it had a big old air bubble trapped in it? Remember how spongy it felt ? You ripped on the handle, but the device only filled half way. After a couple of cycles you probably realized that this was not very efficient, and so, you bled the bubble out. On the next pull, the device filled right up.
Back to the engines. Imagine the piston falling on the intake stroke; one with 105cc of air already in it, and the other with just 74cc. At low rpm/low throttle openings, who cares, if you need more power, you just open the throttle a wee bit more. But when you whack it open, with your tires stuck to the road and the rpm at 3500, You want as much air to find it's way into the cylinder as possible, I ain't got no time for the big-azz 41% more cc chambers to decide to get moving. And then to compress a less dense mixture to only 8/1. No I want the denser charge to be compressed to 11/1 , and to arrive at the rear tires to set them on fire!
But That's just what I think,lol.
BTW, that's also why I run plasma Moly rings. Some guys think power is all about rpm and big cams and such. But I gotta say, if the cylinder is lazy, and only pulls in a fraction of the air that it should , and then compresses it to only a fraction of what it could, well, that's a double crippling whammy, so then well,yeah, band-aid it up with a hi-stall and semi-race gears.
But I'm no engine builder, so I just have opinions.
Somebody else can talk about squish and surface area.
 
So all of yall who come out in droves thinkin quench is the greatest thing in the world now think open chambers are the cat's.

Damn
 
Catch 22.... some people like the open chamber and use a piston to fit AND get some good quench. This is what I’m told;
The open chambered head has an edge in flame travel, air in and out of the head due to the shape.

OK... draw back? Heavier piston.

Others have said to me the closed chamber is a better way to go. They say;
You can get a good chamber with less cc’s to make more compression easier with a lighter piston and with less of a dome if needed.
Draw back? Some say to actually get a good chamber requires a lot of grinding and yet not equal a good open chambered head.

What do I do? Simple really. I choose a closed chambered head, (easy to get these days, after all, who is making an open chambered head new?) And light weight flat top. Adjust the compression ratio with deck milling and gasket dimensions.

Simple but yet effective. Is it the best way? IDK, I don’t have extra deep pockets to dyno these things. I just do what my wallet can afford. Make the best of what I can afford and what’s out there. It works for me! It’ll probably work for you.

If your stuck with open chambers, then just work with them. This is mostly splitting hairs this subject.
 
C130 Chief said:
Well a "Hemi" head is about as open a chamber as it gets, the poly head as well. As for closed chambers making power, take a look at an old Chevy 235. Plenty of quench, but absolutely diabolical for flow. Also, shallow open chambers have less surface area, which means less area for combustion heat to be absorbed into the head. The shape of LA head combustion chambers are more than a little bit a result of the valve angles. If the valves were more in line with the cylinder axis, the chambers could be shallower with less shrouding. But, the engine would be wider, rockers longer, the whole thing heavier and more expensive because it had more iron in it, etc. Remember the LA was a budget rework of the A engine so it would fit into economy cars and cost less in volume production than the poly. Since the chambers were on the large size to begin with, adding the quench pads was a cheap easy way to increase compression and still keep HC emission levels reasonable.
Click to expand...
Agree again.... :thumbsup:

RustyRatRod said:
Comparing the Hemi head here is apples and oranges, because the Hemi was designed from the ground up for performance. It had quench, because it had the pistons to make it happen.

When speaking in terms of non domed pistons and conventional non hemi heads, the closed chamber wins.

I'm not arguin anymore. I gotta go take a dump.
Click to expand...
:eek: What to do you MEAN the Hemi head doesn't count in this debate???? The factory "race" engine from Ma-Mopar itself don't count????? Precisely my point, ALL else equal (equal compression, equal quench), I'll take the open chamber.
 
318willrun said:
:eek: What to do you MEAN the Hemi head doesn't count in this debate???? The factory "race" engine from Ma-Mopar itself don't count?????
Click to expand...
No it shouldn’t count because it wasn’t a offering to the people. Just the racers. And there not readily available to us now. Work with what’s available to us now.

Precisely my point, ALL else equal (equal compression, equal quench), I'll take the open chamber.
Click to expand...
Can’t be done... impossible
 
I went 9.74@2850 pounds and my son went 10.08@3200 pounds with a set of damaged open chamber (340 style) Edelbrock heads I bought for 400.00 and ported. Did I want open chamber heads? No. But the price was right. Between flat top pistons, a stock deck height block, Felpro gasket, and open chamber head I left a lot on the table. Do they work? I would so yes they can work.
 
Quick somebody call up Trick Flow, Dart, AFR, Brodix, Profiler, and let them know they are all doing it wrong LOL. Hell even the new "HEMI" has a closed chamber.
 
skrews said:
Quick somebody call up Trick Flow, Dart, AFR, Brodix, Profiler, and let them know they are all doing it wrong LOL. Hell even the new "HEMI" has a closed chamber.
Click to expand...


None of those are actually closed chambered heads. And, the trend is getting the chambers even softer.
 
318willrun said:
Agree again.... :thumbsup:


:eek: What to do you MEAN the Hemi head doesn't count in this debate???? The factory "race" engine from Ma-Mopar itself don't count????? Precisely my point, ALL else equal (equal compression, equal quench), I'll take the open chamber.
Click to expand...

I didn't say it didn't count, dummy.
 
Your results may vary. lol I'm going to do what I do. lol
I like a closed chamber with a flat top .
take a zero deck short block and switch from a ported 906 to a ported 915. there is difference. 915 all the way.
 
fishmens67 said:
Your results may vary. lol I'm going to do what I do. lol
I like a closed chamber with a flat top .
take a zero deck short block and switch from a ported 906 to a ported 915. there is difference. 915 all the way.
Click to expand...
915's would have more compression, not fair... :D Domed with open chamber..... :poke:
 
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