I need some insight on my pistons. I have Summit part number TRW-L2268F30 pistons. They are Speed Pro forged pistons, with a .266(35.5cc) dome. When I ordered these I didn not see anything about closed chamber heads. I got my new Summit catalog in the mail and they say for closed chamber heads by them. I went on the Summit site and looked them up and it says the same thing. The problem is I have 781 Open chamber heads. My question is will these work? Whats the difference? On the website it also lists different compression ratios with different size chambers. It lists a 119cc chamber being 9.9 to 1 compression, which is what the 781 should be around, and I dont know of any 119cc closed chambered heads. So since they list a compression ration for a 119cc head will they work in my heads? I am worried. Please help if you can. Thank You. Marc

They will fit. It's the other way that would be a fit issue. Closed head and open dome.... Now as far as problems, what is you compression and performance goals? You know these slugs are not designed for your head and will not work as good as an Open chamber dome. Why don't you just send them back to Summit? I have never had a problem returning things with them....

Originally posted by pcs0snq:
They will fit. It's the other way that would be a fit issue. Closed head and open dome.... Now as far as problems, what is you compression and performance goals? You know these slugs are not designed for your head and will not work as good as an Open chamber dome. Why don't you just send them back to Summit? I have never had a problem returning things with them.... Good advice.
You will be happier with the power created running the proper piston designed for the combustion chamber.

they are already installed in the block. The other option would be to get closed chambered heads, but my compression would be too high i think. I want it to stay between 10 and 10.25 so i can run it on pump gas. The other thing is I have spent around 1000.00 dollars on the 781 with big valves and porting work. How much of a restriction are we talking about with using the 781 heads? thanks for the help. marc

post a picture here of the chamber on your head and the piston top that shows the dome form a few angles. I'll bet you have the heads on????

Im wanting to get around 500Hp and 500tq with this motor. Will it be possible? It is a L88427 block bored .030, CC292H cam(.550 lift int&ex. 244 duration @.050), stealth intake, Holley4150HP 830cfm or Mighty Demon 825cfm carb. Will the 781 heads and pistons not allow this? thanks for the input and help guys. marc

heads arent on but i dont have any pics of either. sorry.

L2268F30 piston has the following specs:

1.765 compression height
.020 deck clearance
.0035 skirt clearance
.266 dome
35.5 cc dome
701 grams

11.25 to 1 compression with a 106.9 cc chamber
10.18 to 1 compression with a 116.9 cc chamber
9.99 to 1 compression with a 119 cc chamber

Now, you need to measure your pistons installed deck height and also measure the cc's of the 781 heads you have (varies alot from 119cc spec...mine are 115 cc). Also know the head gasket volume and then you can accurately calculate the actual comression ratio.

using the dcr calculator it looks like my compression is 10.5. that should be ok. i am just worried about the closed chambered pistons with my open chambered heads holding me back from my goals that i stated above. any help? any advice? are the 781 open heads going to hurt me soo bad that i need to consider going to a closed chamber head? but then will my compression be too high for pump gas? thanks for the replys. marc

the dcr is 7.6 using the CC292H. should i think about getting a different cam to up the dcr?

Yes, I'd try for a DCR of 8.

Have you measured your heads yet? You should to get a more accurate idea of what you have. Depending on what's been done to them, there can be a 5cc variance or more.

You might want to go with a solid cam to help meet your goal. There are a few guys with UD276/284F10 in 427's here. Which is about as small as you want to go with 10.5-1. The Comp XS282S or Crane CC280 are all very similar. Comp and Crane also have a 285/295 solid. You might post again to get cam recommendations.

does anyone have any advice on how the closed chambered pistons and open chambered heads will work with each other? is this going to be a major hold back on power? thanks

Man, just to be safe, you might want to contact TRW about using those pistons with open chamber heads. I have read in a couple of different publications that open chamber heads are shaped much differently than closed chamber heads, and that domes designed for closed chambers may not clear on an open chamber head. Never hurts to be safe.