hybrid build! 25d, 251, 253, i need some help!

[Dufek125]

So after turbo plans fell through due to a junk block im stuck down the n/a path again. Kinda by choice lol. Anyways, I lost all comp in my #4 cyl the other day and its looking like valve seals. A guy I know has a set of fully rebuilt 253 heads, ported and polished, that he offered to sell me. My questions are, does the 25d manifold bolt up to the 253 heads? Its sohc so would me ecu be able to run it? I'm guessing yes because it can run a 22e without problem. And, right now I have the factory hybrid motor, 25d internals in a 251 block, what kinda cr am I looking at if I did this? Higher? Lower? About the same? Pros and cons to this vs. Just rebuilding my 25d heads? Any advice appreciated!

[johnegg]

no the 25D manifold will not bolt on to the 251/253 heads.

 

25D internals, do you mean crank? because they moved the thrust bearing, i don't think that crank will work in a 251/253 block.

 

the ECU will run any engine that has the same sensors and wiring as the 98.

and although you might get the 251/253 to run on the 98 ECU by using the 25D throttle body and wiring from the intake, there is no guarantee you will not have an odd CEL like EGR. (you may also need to use the 98 cam and crank sprockets.)

[Kennyfvholla]

When says 25D internals in a 251 block, he means a 99 25D/251 motor. The 251 lower end with 25D pistons and top end.

 

And, in agreement with John, the intake manifold won't bolt to the heads. Do not buy anything he is selling. Rebuild your 25D heads and have them milled 0.03" to raise the compression, making it between 11:1 and 11.5:1 compression. Or, just use a Cometic 0.027" head gasket for the same result.

[Dufek125]

That will bump it up that much? I figured like low 10:1 maybe..