Which heads for 500+bhp
 

Hi,

Doing a few bits to my classic at present and thinking whilst I've got a few bit of it to rip the engine out and go for the 500bhp car I've always wanted.

Its currently running a Cosworth EJ 257 short block but running the standard uk turbo 2.0l heads.

Last had it mapped and dynoed at power station and Fuzz said it was the heads that are holding it all back to the current 400ish bhp..
Id love a set of cosworth heads but just cant fork out 6k for two heads plus all the gaskets on top..

Anyone else produce any decent heads that are more affordable?

v3 sti heads i've heard are the ones to go for, but im pretty someone who knows much much more than i shall answer you with a better answer.

if your going the syvecs route then avcs from newage sti would be the best otherwise some nice ported ver 3 sti heads or later ones.

v5 ported to within an inch of their life. you might also benefit from a cam and valve change. of course to pull it altogether you will need adjustable pullys. not a cheap option depending on how much time someone spends porting the heads.

How far over 500 do you want to go? I managed 523bhp with standard sti 3 heads using 20% methanol

Just want to get to the 500bhp mark without pushing everything to the limit..Not running methanol as thats cheating ;)

Ill gladly go way over that if things will take it, should do :thumb:

I've gone to 527 bhp on standard v4 sti heads.

Also on a cosworth 2.5 at 1.6 bar (GT35r) but with uprated cams and 10% methanol.

Hard to tell when you dont state what Turbo your running, i would say there is no need to go to the expense of V5 ported heads.

Folk have got results on standard heads, if your running syvecs then the answer is newage heads.

Depending on the year factor in inlet manifold changes and any wiring that may be required to use AVCS heads.

534bhpbut prob more important 470ftlbs on avcs heads on standard 2.0! this was on pauls rollers not dd rollers :)

There's no doubt that the heads are a limiting factor on 2.5 conversions, relative to turbo choice to a certain extent.
I wouldn't say that heads alone are holding your engine back to 400 bhp, as we've seen much more than that from stock heads on 2.5's. It's more about the characteristics from these, which are about a whole load of torque, with the graph dropping off just as you're beginning to enjoy yourself.
The Cosworth heads aren't any good for your car anyway being designed for US spec AVCS.
Assuming your heads are in good order, we can flow them and fit large stainless/inconel valves good enough to match the Cosworth spec from around £1500 upwards, depending on choice of retainers etc. A set of cams at £700 will add a whole stack of flow just at the point where your current set up is taking a dive.
They'll look something like this: (AVCS heads shown)
http://i49.photobucket.com/albums/f2...ewageheads.jpg

Hi,

Ok maybe im being stupid as new to imprezas but whats AVCS?

The problem i currently have with mine is this:

When the car was built years back the old owner (fuzz from powerstation) ported the exhaust ports and the new headers he purchased for the car..
Ive just got hold of some RCM headers but as you can see in the pics below the holes are much smaller then the old headers ports so wll create a big lip when bolted up the heads..

http://i283.photobucket.com/albums/k...1/IMG_0440.jpg
http://i283.photobucket.com/albums/k...1/IMG_0441.jpg

So im tempted to just grind the new header ports or go all out and just get some nice new heads and go for the 500bhp..

This was my graph but i had been running it on BP Ultimate so was knocking badly so fuzz had back things off hence the 400/400..Was 440 before at the same 1.5bar

http://i283.photobucket.com/albums/k...251/img021.jpg

Will i have to send my headers to get ported also if i go for your heads?

Cheers

Gavin

It's one of those. Yes, we can see a mis match, but then again we've run over 700 bhp on those headers without doing that. The gasket is actually larger than both the ports and the headers. Bear in mind that at the end of that pipework is a turbo, which is fed by pressurised exhaust gas. It isn't quite the same as an ultimate flow issue, like a downpipe. It's the reason why Harvey can get away with reducing the up pipe diameter, without losing power.

AVCS is the variable camshaft timing set up used on the inlet cams for STI newage.