Using closed chamber pistons with open chamber heads [Archive] - Chevelle Tech

: Using closed chamber pistons with open chamber heads


rednecks70
Jan 25th, 06, 10:38 PM
I'm having my 454 rebuilt and would like to get the compression up to 10.5:1. Talked to my builder today about using closed chamber pistons because nobody makes an open chamber piston that gives you decent compression with a 120cc head. He advised against it saying the dome is designed for a closed chamber and the air flow/burn would hurt horsepower. So if any of you have done this I would like to hear your results.

On another note, why don't piston manfacturers make a prodcut that their customers need? We have several choices for cyl. heads which almost all have 116cc to 120cc combustion chambers and nobody makes a piston to give you 10 to 11:1 compression??? Seems to me there is a huge need here to be filled and the first company to come up the product would clean up!

RB69SS396Conv
Jan 25th, 06, 10:44 PM
No the closed pistons won't work with the open head.

The closed chamber is more squared off, where the open chamber is more rounded at the corners. The edge of the closed dome usually hits on the edge of the chamber; I think on the exhaust side, away from the spark plug, if memory serves me right.

Guess how I know that.

Problem is, it was probably 25 years ago. I don't remember. You know how they say your memory is the second thing you lose as you age; the thing is, I forget what the first one was supposed to be.

rednecks70
Jan 25th, 06, 10:56 PM
He did mention that the pistons would have to be cut to work correctly but doesn't want to go this route because of the dome shape.

BillK
Jan 25th, 06, 10:59 PM
red,
Speed Pro (TRW) L2465 is listed as 10 to 1 with 119cc head. Thats with
.025" deck hgt. If you deck the block and get "0" deck it will probably be closer to 10.5 Also, I am pretty sure that Wiseco and JE make pistons to do what you want.

rednecks70
Jan 25th, 06, 11:11 PM
red,
Speed Pro (TRW) L2465 is listed as 10 to 1 with 119cc head. Thats with
.025" deck hgt. If you deck the block and get "0" deck it will probably be closer to 10.5 Also, I am pretty sure that Wiseco and JE make pistons to do what you want.

In the catalog I have the L2465 shows 10.68:1 with a 106.9 combustion chamber. I don't think I can get the combustion chamber down that far. If you have any part numbers for the Wiseco or JE pistons I would be really grateful.

540Hotrod
Jan 25th, 06, 11:36 PM
Beats me...I've run open chamber heads on closed chamber pistons many times with no issues. May not be perfect....but it works fine.

Basic TRW 11.0-12.5 type domes.


JIM

Wolfplace
Jan 26th, 06, 2:32 AM
I'm having my 454 rebuilt and would like to get the compression up to 10.5:1. Talked to my builder today about using closed chamber pistons because nobody makes an open chamber piston that gives you decent compression with a 120cc head. He advised against it saying the dome is designed for a closed chamber and the air flow/burn would hurt horsepower. So if any of you have done this I would like to hear your results.

On another note, why don't piston manfacturers make a prodcut that their customers need? We have several choices for cyl. heads which almost all have 116cc to 120cc combustion chambers and nobody makes a piston to give you 10 to 11:1 compression??? Seems to me there is a huge need here to be filled and the first company to come up the product would clean up!
=
They don't make them because open chamber heads are all over the map cc wise so,,,, the question becomes what do they make??

SRP/JE makes a piston that is 10.0 @ 118 advertised. This piston will give you anywhere from about 9.4 to 10.6 without much issue. by simply adjusting the deck & chamber volume.
You need zero deck (9.78 with this piston) & 112 for 10.5

All the aftermarket heads will normally go to 110 flat milled.

The 2465's will give you 10.5 with the block decked to 9.,78 (.005 down) & a 115cc head

The Brodix RR head is available in 119 or 115 for the same price & 110 for an additional charge

Or you can have a piston made any way you wish for a "nominal" fee :D

71454Chevelle
Jan 26th, 06, 6:46 AM
Closed chamber pistons will work with open chamber heads.

I'm running the TRW L2349 closed chamber piston with a set of 049 open chamber oval ports; no problems at all.

GRN69CHV
Jan 26th, 06, 7:23 AM
I built my .030 over 454 motor with H693CP -22cc dome pistons. Equivalent in a TRW forged is L2465's (fairly sure that's right). The open chamber design have a land around the circumference of the piston, whereas the true closed chamber pistons, the dome goes all the way to the edge of the piston. Aftermarket open chamber heads have a slightly wider combustion chamber to accomodate valves up to 2.30/1.90 combinations, this also alows the fitment of the CC pistons.

jbird
Jan 26th, 06, 11:00 AM
I ran Ross 13:1 (big .700" dome)closed chambered pistons with 781 open chamber heads with no problems. Ran great. 6.29@108 in a 3150lb Camaro. I would be leary of any machine shop that says it won't work. As far as I know it's pretty common knowlege that it will.

Sams454SS
Jan 26th, 06, 1:38 PM
I'll add to that also, I have 3993820 oval port open chamber heads on top of my 454 LS-6 (late casting date) with the stock pistons and it works fine for me.

rednecks70
Jan 26th, 06, 2:03 PM
=
SRP/JE makes a piston that is 10.0 @ 118 advertised. This piston will give you anywhere from about 9.4 to 10.6 without much issue. by simply adjusting the deck & chamber volume.
You need zero deck (9.78 with this piston) & 112 for 10.5

All the aftermarket heads will normally go to 110 flat milled.

The 2465's will give you 10.5 with the block decked to 9.,78 (.005 down) & a 115cc head

The Brodix RR head is available in 119 or 115 for the same price & 110 for an additional charge



Hey Wolfeplace, if I use the 2465's and get the heads milled down to 110cc will the intake manifold have to be cut as well?

Also do you have the part number for the SRP/JE pistons that makes 10:1 with a 118cc chamber?

Thanks!

496malibu
Jan 26th, 06, 3:54 PM
i believe if you use a open chamber piston on a closed chamber is where you run into problems.

bracketchev1221
Jan 26th, 06, 3:58 PM
I have closed chamber pistons with 781 heads on a 396. I did have a clearance problem with the sides of the dome hitting the head. I gasket matched the combustion chamber to the head gasket and this solved all problems. I would go with a SRP or JE piston They market specifically a 10.25-1 piston for big block chevys, check their catalog.

Wolfplace
Jan 26th, 06, 5:24 PM
Hey Wolfeplace, if I use the 2465's and get the heads milled down to 110cc will the intake manifold have to be cut as well?

Also do you have the part number for the SRP/JE pistons that makes 10:1 with a 118cc chamber?

Thanks!
=
Not if the heads are done properly.
The intake side of the heads should be cut the same amount as the face.
You may need to cut the bottom of the intake or top of the block depending on how much is removed though.
Best to have the block cut if possible.
This is not normally necessary unless you cut the crap out of the heads & or heads & block.

The SRP is a 212135 or 136 depending on bore for a stock rod 454
Again, this piston won't make 10.0 if you don't deck the block as above.

And, closed chamber pistons will not always fit.
Most do, some hit so just because someone say's I did it & it worked is not the best recommendation. :sad:
They usually work but you will not know for sure until you bolt your heads on your engine,,,

jbird
Jan 26th, 06, 5:55 PM
=And, closed chamber pistons will not always fit.
Most do, some hit so just because someone say's I did it & it worked is not the best recommendation. :sad:
They usually work but you will not know for sure until you bolt your heads on your engine,,,

The same thing can be said about some open chamber pistons and some open chamber heads. That's why you always check. :rolleyes:

mr68
Jan 26th, 06, 9:38 PM
we are using trw L2349 closed chamber pistons with 049 oval port heads on my father in laws 66 el camino 468, as well, no probs, they will work on open chamber heads. car runs 11.14 at 120 mph !

Mike Feudo
Jan 27th, 06, 12:00 AM
It will work but it's not right. The dome is all wrong for the combustion chamber.

Wolfplace
Jan 27th, 06, 12:28 AM
At the risk of being redundant,,, :rolleyes:
" closed chamber pistons will not always fit.
Most do, some hit so just because someone say's I did it & it worked is not the best recommendation.
They usually work but you will not know for sure until you bolt your heads on your engine,,,"

It will work most of the time but not always.
Really pretty easy deal, just set the head on without a gasket & turn the engine over.
If it clears you are fine
If it picks the head up you ain't
This is assuming a .039-.041 gasket.

Or to quote jbird,,, "That's why you always check" :)

jbird
Jan 27th, 06, 11:27 AM
It will work but it's not right. The dome is all wrong for the combustion chamber.

As I said before, I ran Ross 13:1, .700", 36cc dome, closed chamber piston with 781 heads that had been angle milled .080", with 2.25/1.90 valves. Ross actually lists these as working with open chamber heads. When I checked valve to piston clearance, the valves fit very nicely into the valve pockets in the pistons, with no clearance issues. So what exactly do you mean by the dome is all wrong? The function of a dome on a piston is to take up space to raise the compression ratio, nothing else. Obviously, if the dome more closely fits the shape of the chamber you can use a bigger dome to get even more compression, but thats about it. I know all about the flame travel theory and all that stuff, but I doubt you could measure the difference in power between the two. If you think thats really an issue with L2465 pistons, well your just splitting hairs. MAY not be optimum, but saying the dome is all wrong is in my opinion, well, all wrong.

rednecks70
Jan 27th, 06, 2:21 PM
I know all about the flame travel theory and all that stuff, but I doubt you could measure the difference in power between the two. If you think thats really an issue with L2465 pistons, well your just splitting hairs. MAY not be optimum, but saying the dome is all wrong is in my opinion, well, all wrong.

I guess if your building something to bracket race or professionally race in NHRA, NASCAR, etc. you wouldn't want to mismatch the dome/chamber but for our street driven, backyard tuned cars I would agree with you jbird, I'm certain there are bigger issues with my car that could enhance horsepower. Thanks for replies.

P.S. Looks like the 2465's (open chamber pistons) will work after all, when I ran the numbers they looked good with a 110cc. It was real misleading when the catalog reads 10.68:1 with a 106cc chamber (assuming I was going to use a 118cc). I didn't take into consideration the deck height, gasket thickness, and smaller combustion chamber available from Brodix.

Wolfplace
Jan 27th, 06, 2:59 PM
P.S. Looks like the 2465's (open chamber pistons) will work after all, when I ran the numbers they looked good with a 110cc. It was real misleading when the catalog reads 10.68:1 with a 106cc chamber (assuming I was going to use a 118cc). I didn't take into consideration the deck height, gasket thickness, and smaller combustion chamber available from Brodix.
=
LOL,,, well said John
It would be nice if the catalogs would be a little more specific when they quote compression ratios,
Like telling you this is with the piston at zero deck or whatever they happen to use instead of making you guess.
Guess they figure we need to sharpen our math skills :D

BTW, they also make the 2465 in a light weight version & it is set up for pressed or floating pin.

Also, if you haven't gotten your Brodix heads yet let me know if I can help.

jbird
Jan 27th, 06, 5:18 PM
Here's what I had to do to get my open chamber pistons to clear the sparkplugs in my open chamber heads. (the notch in the domes)

http://205.240.64.155/~jcampbell/pistons1.jpg

rthlc
Jan 27th, 06, 6:10 PM
I was planning on running closed chamber pistons with my 781's, they seemed to fit fine until I put in 2.19/ 1.88 valves. (Already had the shortblock when I got the heads) Then I had to ditch my shim head gaskets and flycut the pistons for clearance (zero decked, L2349F .060, 60203 voodoo cam).

Sometimes it helps to check TWICE, clay is CHEAP

Mike Feudo
Jan 27th, 06, 7:32 PM
The top of the piston is part of the combustion chamber. Putting a squared off chunk of alum in a chamber with a sloped wall is not going to do a thing for performance.

mr68
Jan 27th, 06, 10:09 PM
mike fuedo with all due respect , the el camino runs 11.14's at 120 mph, it's not exactly a slug. great power for a 3700 lb car. even with mismatched pistons to chambers. the later ls6 crate motors used closed chambered pistons with #990 open chamber heads, thats how they went from 11.0 compression to 10.0 compression, i'm referring to the later ls6 crate motors ,not the one from the 70 chevelles. look up the piston # you will see .the gm part # is 3976013 its a closed chamber piston and it was used on open chamber (990 heads) on the ls6 crate engines.

rednecks70
Jan 28th, 06, 9:56 AM
=
Also, if you haven't gotten your Brodix heads yet let me know if I can help.

The builder is a Brodix dealer so I'm sure he wouldn't be happy if I purchased the heads from a 3rd party, I'm just hoping he gives me as good of a deal as you would, I know your prices are rock bottom. If I wasn't on the east coast I would send you the whole engine, thanks for all your help!!

dr
Jan 28th, 06, 10:36 AM
Closed chamber pistons with open chamber heads will work. In 1990 I bought a new crate engine from G.M. 454/450hp LS6. It came with closed chamber pistons & open chamber sq. port heads. Factory rated at 10.23 to 1 as/per G.M. Preformance catalog which I purchased the motor from. Catalog lists all part numbers including pistons & heads. I would have to find the catalog to get you the part numbers if you want them. Dave

Mike Feudo
Jan 28th, 06, 11:47 AM
Gm used the 990 head to lower the compression of the LS-6 crate because it was the easiest (cheapest) way to do it.

Wooderson
Jan 28th, 06, 12:56 PM
TRW 2307 (LS7) pistons too much compression for you? It's an open chamber piston with a .580" dome height and .400" dome thickness. I run these in my 454 on two parts 87 to one part 110 octane. Domes cut to .430" height. I have also ran this engine on straight 93.5 unleaded when it was still available. Heads used were 049 ovals and 990 rectangulars.