Building my EJ257 longblock....many questions and opinions

I just ran it through an online compression ratio calculator which could be wrong.

 

Its not below 9 to 1 for sure.

 

This is from Jeff @ PDXTuning. I'd like to think he knows 'something' lol.

http://forums.nasioc.com/forums/showthread.php?t=630797&highlight=pdxtuning+compression+ratio

 

Thats pretty close to right actually, once I changed my numbers to reflect it not being a zero deck motor, and I put in the head gasket thickness in MM instead of inches....lol

I actually get 8.8 to 1

 

WJM says the same thing. I think this is a very desirable ratio since I can then use the Stock STi head gaskets.

 

That chart is off. Stock compression for 04~06 STi is 8.2:1 according to the FSM. However, if all those measurements are correct, then ok. I wont argue.

However, the piston to deck clearance on a stock EJ257 is 0.50MM. I measured it 5 separate times to be sure...meaning I made sure it was at TDC, measured twice, then re-TDC'd it and measured twice...etc. So really I measured it 10 times. :lol:

Last time I checked an EJ205, it was nearly 0.00mm. I know the EJ25D, 1997~1999, the pistons end up ABOVE the deck by .5~.7 MM. You HAVE to use the AA610 gasket or the pistons hit the head.

 

Jeff's differences could very easily be the tools you are using I mean .38 mm is TINY TINY TINY and hard to measure. That being said it's obviously very close to the real answer though. Did you read through what Jeff said on Nasioc? It's a very good read.

I think the 8.8:1 CR is right though......it's so close to the charts, to Matt's measurements, and to your measuresments that it's a safe bet to say that it is definately going to be under 9:1.

 

.38mm is not hard to measure or see. A simple digital caliper set is all you need for that.

Or, clearance. A simple feeler gauge is easy to use...

 

Oh well it's probably user error but it's still close enough to say that the CR will indeed be 8.8:1ish....right?

 

I'd say so.

 

Yep, I would say you are going to be very close to 8.8

 

Then it's official. The STi head will be pulled off the block and posted for sale.

I will get the WRX heads from Mike and will go that route.

 

I see.

 

It makes more sense and is more budget oriented. I mean I'm only gonna push 450-480 hp daily on this thing if even that much on pump/meth. No sense building the daylights out of the engine when I won't be pushing it in the least bit.

 

I think you will love it. Bumped compression, bigger turbo, more displacement...should be great. And you can always go the other route with AVCS and hydra if you win the lottery and have cash to burn.

 

Yeah it's just better and AVCS really has nothing to do with power (I can debate that but the end result it really doesn't). If the car drives like my 18g on my 2.0L now then I am A-OK with that! Matt told me Dan's Sti with GT35R feels just like a 18g'd 2.0L. Scott has said the same about customers of his.