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Old 05-06-2021, 04:31 AM   #1
murrdogg24
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Default Head gasket on hybrid build

I'm trying to finish up my hybrid 257/207 build and I'm having second thoughts about what headgasket I should be using. Engine builder that I bought the SB from recommeded JE Proseal .039. I was planning on using OEM EJ257 head gaskets and the machine shop that chamber matched my EJ207 heads said they recommended OEM gaskets. I already put the heads on with OEM gaskets but I didn't measure deck height so now I'm thinking take the heads off and measure deck height and cc the heads to calculate quench. Am I overthinking this or can I just stick with OEM? The SB is seasoned and builder said he took off about 4 thou from the decking. Machine shop said they barely took 1 thou off the heads.
Here’s some pics of the head work

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Old 05-07-2021, 12:20 PM   #2
murrdogg24
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So nobody has done a hybrid build and used OEM head gaskets I take it
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Old 05-10-2021, 01:40 PM   #3
Homemade WRX
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You CAN use OEM gaskets. But seeing as you didn't measure your piston to deck height, no one can guess at what you have. I know you say the builder guesses he took 0.004" off the deck.

With that being said, hybrids have been done for going on two decades. This isn't new.

Then factor in that your chambers are also modified, and I don't see combustion chamber volume numbers, I don't think anyone can really help you with the lack of info given.

Is your concern clearance to the head or compression ratio?
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Old 05-10-2021, 03:45 PM   #4
murrdogg24
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My concern was with valve to piston clearance so I think I'll take the heads back off and do the measurements. The engine builder was not forthcoming with any helpful information as far as specs such as tolerances and I don't know if he measured deck height or anything. My assumptions were when you bought a prebuilt engine they provide this sort of information to the customer but he's acting like his build specs are top secret or something..
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Originally Posted by Homemade WRX View Post
You CAN use OEM gaskets. But seeing as you didn't measure your piston to deck height, no one can guess at what you have. I know you say the builder guesses he took 0.004" off the deck.

With that being said, hybrids have been done for going on two decades. This isn't new.

Then factor in that your chambers are also modified, and I don't see combustion chamber volume numbers, I don't think anyone can really help you with the lack of info given.

Is your concern clearance to the head or compression ratio?
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Old 05-12-2021, 03:59 PM   #5
Homemade WRX
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If you have the shortblock there, you can measure the piston to deck clearance if you have a simple dial indicator and stand. Heck, if you're really concerned you can clay the valves.

If you're using stock cams and aftermarket pistons, they leave copious amounts of room in the valve pockets.
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