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I was doing a search on 4G15 engine setups and came across a couple of posts (i think by xlr8) about the possiblity of using an EFI head with carb pistons as the carb ones are flat top and raise CR.
Is it just the pistons that can be interchanged or does the EFI head bolt on to the carb block and work without swapping the pistons over into the EFI block? I'm not looking to do any bottom end work on the engine, so the answer i'm hoping to hear is that the EFI head can bolt on to an undisturbed carby block and run ok
I'm specifically speaking of a USDM 8v EFI head on a JDM (i think 8v as there's no indication of 12v) carburated block.
Thanks in advance

The EFI head bolts to the carby block no problems! The blocks are near identical except for the pistons in any case. The oil sump is sometimes different between models but they are interchangeable depending on the chassis you are using.

The original EFI conversion I did was just a Hyundai G4DJ head onto an original (for an X1 Excel) G4AJ block using harness, ECU, fuel tank (with pump and hard lines) and MPI relay from the donor G4DJ vehicle (X2 Excel).

G4AJ = 4G15 8v carb (hemispherical combustion chambers)
G4DJ = 4G15 8v EFI (kidney shaped combustion chambers)

If the donor block wasn't originally fitted with a hemi head them you wont see any increase in CR as I believe that some of the late model carb'd vehicles had kidney shaped chambers and dished pistons as well so it's worth checking!

Neat, thanks for the info! This would be for my 3G dodge colt.
I guess there's no easy way to tell the combustion chamber shape without removing the head eh?
And if i did mistakenly get a carb block with dished pistons i won't lose anything as it would be the same as my current dished EFI pistons - if i understand correctly the EFI 8v head works on all carb blocks (except CR difference), even if the donor carb block turned out to be from a 12v carb?
Sorry for all these questions I found a few carb 4G15s and i'm not sure how to tell one from the other

I believe the 12v blocks have different pistons again and I have never tested that combo so I cant give any guarantees it will work. Im not saying it wont - just that I never tried it.

Ahh ok thanks again, guess i'd have to pick one out and hope it's 8v with hemi shaped CC with flat pistons when i bring it home and take the head off