barge

Question time.

If I had the heads taken off my car [93 wrx, fully decatted, induction kit, lightened flywheel] what gains will I get if I had the following done Ported, polished heads, bigger better valves, 3 angle seats, skimming etc ??

From days of my youth in Ford Xflows & the like, a big mod then was to play with the head & valves, does this also work with Scooby engines ??

I basically want to get the max out of my car before I go down the FMIC & Link ECU upgrades.

Are heads from STi different from WRX ?? are the heads interchangeable ?? Is there a head that I should look at getting or avoid ??

Anyone know anything about the above ?

Any advice appreciated.

Cheers

Stuart.

UkLegacyT

hi stuart, i asked this question ages ago and no luck with info, so come on guys, anyone know?

duczz

The heads on the STi models are different from what I belive mainly due to having sodium filled valves and different cam profiles although Im not sure of all models are different in this way. Also some STI heads come standard with solid lifters. But once again im not sure which models or versions have which combination. hope it helps a bit ....

Alfer

The folks in US (Cobb Tuning) in particular has done much in terms of head/valves modifications due to the lack of turbo models in the past years. Try emailing them or something.. apparently gains (in N/A models) are in region of 20 - 40HP..

Oh.. one more thing, I found (from several dyno sessions), having a good ECU is the one of the first thing you should do... having gigantic intakes and exhaust is pretty much useless if the ECU does not know about the increased flow and send the wrong fueling....

I have a non-turbo 2.0 and this is what happened.

- Stock 66KW = (at wheels)
- Pod Filter and Large intake $700 68KW = (at wheels)
- Added a cheap $200 piggy back ECU = 77KW (at wheels)

... I reckon the ecu was a damn good bang for bucks.



[Edited by Alfer - 3/21/2002 1:38:26 AM]

dosenöffner

Bad Alfer. Don't use 'ECU' and 'bang' in the same sentence.

The STi3's onwards have solid lifters.

Compression ratio is also different I think (to allow for higher boost).

Alfer

Huh? What wrong with "bang for bucks" for ECU?

SMG

I still havent put the heads on the flow bench that i have done, but will do so very soon, there are differant port sizes on some heads, i am doing some wrc heads and i will be doing some development work, if you boys are interested in my findings i will post some of my results. In general the bigger the port the the more air it will flow at higher revs, but unless you are running high lift cams you will see litte gain. example, no point in having a head that will flow @ .450 lift if your valve lift is only .370. With a higher flowing port you tend to loose lower velocity speeds which means lower flow at lower lifts. The impreza port is a large port to start with, bigger on the early heads. Your main gains will be found round the valve seat. 3 angle valve seats are very good, but most heads these days have them from std, you can run a thinner seat but then there is less material to take the heat from the valve. Look for gains to be made in your cam selection, but remember if running a lot of boost you dont want to much duration or more to the point overlap or you will loose most of your low down cyl fill straight into the exhaust. Ive gone on far to much, but have tried to cover the basics, hope this is of some help. steve.

Alfer

I have an extract from a tech article from SPD Tuning Service (US):

"The same is generally true of the expense and effort to port and polish or match castings. These are the last little tricks of racing engines. With the modern castings, the finish is seldom even marginal. Someone the other day told me that he had his exhaust off and the ports of the pipe did not match the ports on the heads. He wanted to know what could be done to correct this obvious problem. What he was reffereing to is the fact that if the head pipe is bigger than the exhaut port, a "step" is formed. This "step" is there for a reason. About twenty years ago some body noticed that with that step low RPM torque was improved without any loss on the top end power. Subaru was listening."

barge

Thanks for the infor steve, I would be interested in your findings