WRX heads Version 7 onwards

[Guest]

Just wondering if anyone knows much about the differences in casting design, shim arrangement, flow, etc in the later model imprezza range. The early heads have been a hot topic of debate with differences discussed but I am yet to find out how the later range compare between themselves and also the earlier models. Do the version 7 non sti castings flow any better than say version 3 heads? Also the non STI later model stuff is all shim over bucket as I am aware? did the STI remain shim under bucket or did it go to shimless buckets? Any discussion on this topic would be interesting.

[Koom]

There are some shimless bucket type heads in the later model ranges. I don't know the specifics but would assume that they are STI or Spec C specific.

There's also the different variable cam's available in the late model heads too.

[Guest]

Thanks Koom, Yeah I think STI may have gone shimless from 04 onwards? I could be off here though. So the STI have the Variable Cam timing while the non STI continue to not have this even right up tot he present? I wonder how the flow rates compare to early stuff. There were obviously some changes along with the new intake manifold etc...

[Koom]

I'm not really sure of much more of the details of the later stuff. Pretty much just what I said up there and thats it :-[

Just found out that the shimless ones were the ones to get when running some ideas past our team manager a while ago. I'd say he'd know all the details about which heads were best and what the specifc details are.

[Guest]

Yeah shimless sounds good, not only is the risk of shim spitting at high revs/ aggressive cams reduced, but also the weight should be less. I am wondering if Version 7 shim over (non sti) can be converted to Shimless. Hrmm

[Optical]

v7+ sti is shimless. also a bigger diameter so can take higher lift cams

the ports arent as good stock, but can be ported to be better

some v7 wrx's got avcs

wrx port casting looks to be the same (by eye)

wrx springs are softer and the valves are solid instead of sodium filled or whatever

cam lift is ~same. i'm not sure about duration and centreline

[Guest]

Cheers for the input Optical just to clarify....... (see bold)

 Optical said:

v7+ sti is shimless. also a bigger diameter so can take higher lift cams

the ports arent as good stock, but can be ported to be better Compared the GC8?

some v7 wrx's got avcs

wrx port casting looks to be the same (by eye) From version 7 on?

wrx springs are softer and the valves are solid instead of sodium filled or whatever

cam lift is ~same. i'm not sure about duration and centreline

[Optical]

yes and yes. well, ive seen v7 and 8, i havent heard of other differences apart from the spec c heads and non jdm stuff

[Stoffa]

can V7 sti onward shimless buckets be used in V5/6 sti heads?

[Optical]

yep

[Guest]

Wonder what the shimless buckets retail for... not cheap I imagine

[Stoffa]

I'm sure you should be able to find some stuffed V7 heads at some stage, then you'd maybe get half of the sizes you need and only have to buy half new. I'll be looking for some now to go with my new cams

[Guest]

 Stoffa said:

I'm sure you should be able to find some stuffed V7 heads at some stage, then you'd maybe get half of the sizes you need and only have to buy half new. I'll be looking for some now to go with my new cams

What do you currently have Stoffa? Shim over WRX heads?

[Stoffa]

shim under I think, V5 Sti.

well the shims are between the retainer and the bucket

[Guest]

Yeah, ok would there be any great improvement in going shimless? I can understand the theory behind it for shim over. Thought Shim under were great as they were.

[Stoffa]

i'm looking at going to higher lift and longer duration cams http://www.camshaftshop.co.nz/index.php/EJ20-Non-AVCS-Version-5-6/199-C-Camshaft/camshaftshop_view.tpl.html

I've been reading up as much info as I can and some people suggest going shimless once you get that much lift, I'm trying to get the car to rev hard all the way to redline(if my current turbo will still make power up there). So hopefully going shimless will stop any chance the shims slipping out of place at high RPM.

Also when I was talking to the guys at possum borne they mentioned it as a good upgrade.

Although when I talked to one of the guys at Kelford he did say i'd only need to upgrade the springs and the factory shims and retainers would be fine. But my car has kind of got to the point where I "do it once, do it right"