mazmike

iTrader: (5)

how can you tell what size head gasket to fit
my engine is a 1997 sti BUT it has wrx heads what bhp can they take i am looking for about 380 as just fitted new sc36 turbo on remap by steve simpson found engine problem so rebuild needed. is £300 good for a set off sti heads i will still have to spend money on they ,skim and so on ,what bhp will they handle heads of a 1997 as well .

joz8968

iTrader: (13)

MY97/98 STi 3/4 heads good for 460-500+ I think.

Std HG thickness is 1.6mm for the MY93-98 ph.1/1.5 engines.

merlin24

iTrader: (1)

As what joz said plus the '97/98 WRX/STi heads use the same basic head casting - its just the valvetrain which is different between the two.

Mick

mazmike

iTrader: (5)

is it worth £300 +rebuild +head skim if the max poweri need is 400bhp

joz8968

iTrader: (13)

If you're looking at 380bhp then the WRX heads tend to give up at about that level - they tend to surge and do weird things.

If you want to GUARANTEE for 400+ then really you should replace with STi 3/4 heads...

BTW, you'd prob need to fit the SC42 turbo (or at least the SC40 or TD05 20g) and get mapped on at least V-Power, if you want 400+.

You'd also need a New Age TMIC or a FMIC and at least 550cc injectors, mapped Apexi PFC or Simtek, etc (but I'm sure you already know that... ).

joz8968

iTrader: (13)

Sorry, to be clear, you have MY97 WRX heads and not the early MY93-96 WRX ones, right?

In that case I would have thought the MY97 WRX heads should manage over 400, as there's not hydraulic tappets in those.

So yeah, prob a waste of time/money fitting the MY97/98 STi heads... so long as you'd be happy at 'only' 400+ that is!

mazmike

iTrader: (5)

thanks for that but i think they are not solid lefters wont no untill apart .i have got v9 crank eagle or v9 rods rcm pistons rcm pulleys rcm oil pump fmic 800 injectors decat headers fuel lab fpr simtec brand new sc36 turbo on remap steve simpsone had to stop some thing wrong with number 4 piston/small end so rebuild now but not shore what to do.mite just repair it or put 2.1 in .keep it to 360/380bhp untill gearbox goes and then uprate 5 speed or 6 speed

joz8968

iTrader: (13)

Yeah, I'm not sure whether the MY97/98 heads are solid or hydro. Mick (merlin24) will be along in a bit to tell you lol

That said, even if they ARE hydro, I think they are still BETTER ones than the early WRX heads (better/bigger ports, etc), so should make 400, regardless...

harvey

iTrader: (48)

STi 3 or 4 heads without any work on them can support 550 bhp plus and I guess WRX heads which will have a lower rev limit can support similar, perhaps a bit less. It is not the heads themselves that are the limiting factor but the valves and valve gear so STi heads are preferable to WRX heads and a car with STi heads has potential for more subject to what you do.
As for gasket size, in part that will decide on how much you have skimmed the heads but if you are buying your gaskets from Roger Clarks for instance and tell them what pistons and heads you are using, any head skim and thickness removed they will be able to tell you what head gaskets will give what compression ratio. OE compression on your engine was probably 8:1.
I think the combustion bowl on 97/98 WRX and STi is the same but there may be differences in the piston combustion capacity and that needs checked out. When I do this sort of thing I use a Burette to get accurate figures but the data will already exist for what you are trying to do if you have the basic facts like what pistons.

mazmike

iTrader: (5)

thanks harvey
so if i was to go to 450bhp-max wrx heads would be fine.is it worth sending £300 heads/£80 skim recut seats & values £?

harvey

iTrader: (48)

The power is not really the deciding factor on the heads, it is the RPM you intend to use. You can skim the heads 3-5 thou to get them flat before a rebuild but the need for that will depend on how bowed they are at present so that takes examination. If you are going to skim 3-5 thou to get them flat you might as well skim 20 thou to get the benefit from higher compression.
Now that you have the heads off you might as well grind in the valves as a minimum but whatever other head work you might want to do depends on how keen you are to get more power and availability of funds.