05 STI heads on an 07 XT

[Setnev]

I have a set of B25 STI heads and I'm planning on putting them on my 07 XT. I know the 07-09 EJ255 has a deeper dish piston than the 05-06 but have a smaller combustion chamber. I think the calculated compression ratio is about 8.11:1 with that combination. A couple of questions...

 

1.) Can anyone share their experiences with this combo?

2.) Can I run the base stock tune with this combo until I get it tuned for the lower compression? If so, what can I expect in terms of performance, or lack there of?

[Outblack]

You’ll end up with 8.7-8.8:1 cr

 

 

 

It needs to be tuned, you’ll have a more responsive car off boost but on pump gas you’ll most likely be tuned for less boost

[Setnev]

You’ll end up with 8.7-8.8:1 cr

 

 

 

It needs to be tuned, you’ll have a more responsive car off boost but on pump gas you’ll most likely be tuned for less boost

 

I found this:

 

https://imgur.com/a/yHDgTk0

 

The 07 has the deeper dish pistons and has D25 heads like the 08+ WRX. According to this, I'll be dropping compression.

Edited June 18, 2019 by Setnev

[Outblack]

Ahh ya I read that wrong

[Gabo]

You’ll end up with 8.7-8.8:1 cr

 

 

 

It needs to be tuned, you’ll have a more responsive car off boost but on pump gas you’ll most likely be tuned for less boost

 

My current motor is a 9.0:1 compression motor, flex fuel tuned. You'll be limited in how aggressive your tune can be (ignition wise) on Cali piss 91 octane but that's about it. I'm running almost identical boost levels in 91 and E85 and by similar I mean maybe a 2-3 psi difference if that. My high boost setting fyi is 25 psi.

 

A higher compression motor will most definitely be more responsive off boost. Sometimes I make it all the way to work without hitting any boost

[Setnev]

I hate that I only have access to 91 here in Northern AZ. E85 is available in AZ, but I have to drive 2 hours to get it, IE not worth it. Maybe I'll just save my heads for when I move to Washington. They've got E85 everywhere up there.

[Gabo]

I hate that I only have access to 91 here in Northern AZ. E85 is available in AZ, but I have to drive 2 hours to get it, IE not worth it. Maybe I'll just save my heads for when I move to Washington. They've got E85 everywhere up there.

 

I guess in this regard CA has an advantage. E85 is becoming more common every year. I have at least three stations on my way home and that's because I haven't bothered to look for more.