A Question on Cylinder Heads

[Leighos]

Would it be fair to say the EJ20R's get their 22kw advantage (205 vs 183) over 'A' type EJ20H's mostly due to better flowing heads?

I'm only speculating here, as turbos are fairly similar in size and flow and surely ECU tune cant be that radically different, so it could be the head design right?

I ask this as I am currently rebuilding a spare engine (just with factory STi forged pistons etc) and was wondering if it would be worth getting a set of GTB (or V3/4 WRX or Forrester heads if they are the same) to replace the standard ones.

My car is a BD5a, converted to single turbo, TD05H, yellow injectors and 1S ECU. Not looking to make it a super fast track car or anything, just mild street tune - so a few extra KW here and there would be nice

[Guest boostcut]

id say mostly due to more boost, better turbos and different cam and computer combo

[funkytown]

the heads of the earlier legacies dont flow as well as a the later ones..

id bet some kw lie there.... i mean why are AVCS heads prefered.. or the earlier v3/4sti heads.. to make more power.

but also what boostcut said.. it the bolt ons. a short block is a fairly "dumb' unit.. it is what it is. and will make similar power if the same bolt ons were applied to different shortblocks.

[Guest]

Just speculating

EJ20R , more boost, more timing, sharper air fuel mixtures. Probably the reason why they go bang more often as well.

At stock power levels the heads are not holding these cars back

[funkytown]

 Qwerty said:

Just speculating

EJ20R , more boost, more timing, sharper air fuel mixtures. Probably the reason why they go bang more often as well.

At stock power levels the heads are not holding these cars back

would you agree it would easier to make "extra" kw from the later heads? ie say winding up boost or putting in a link on two identical save heads?

also would you expect the same power and torque if you used the same set up and simply changed the heads.. \? (im not assuming.. genuinely phoning a friend).

[Guest]

I have seen a stock ej20h make arround 190kw atw which is very similar to what BE/BH have made tuned up.

Which makes you think maybe the ej20h head is not so bad.

AVCS heads are worth going to not for top end power but better bottom end / spool

On vf3x sized turbos i have not seen alot of difference in kw between v3/4 v7 and a v8 spec c

[funkytown]

this is where my lack of ej20x knowledge fails me.. but as best ive been told the early heads, the likes of the BC / BF legacy heads in particular do not flow as well as the later heads, the cams not as aggressive.

id agree with you comments on the peak power on vf3x sized turbos and spool characteristics and the ACVS aiding spool

[Guest]

yes heard the same about the earlier heads but never seen anything quantitative

[Koom]

I'd swap to the solid lifter heads purely to get rid of the hydraulic lifters. Although I haven't had any dealings with the WRX/later Legacy ones, my early Legacy hydraulic lifters were the bane of my life the whole time they were in the car.

[BC5RA]

 Koom said:

I'd swap to the solid lifter heads purely to get rid of the hydraulic lifters. Although I haven't had any dealings with the WRX/later Legacy ones, my early Legacy hydraulic lifters were the bane of my life the whole time they were in the car.

Nobody has ever tried to push number through early heads for that reason.

[EJ20T]

besides the boys in the group a days, in a way having rockers makes it easy to run big cams, i used to see some agressive stuff around for RS type heads

[BC5RA]

 EJ20T said:

besides the boys in the group a days, in a way having rockers makes it easy to run big cams, i used to see some agressive stuff around for RS type heads

Likewise. Very nearly bought some Hollow Group A cams for mine, but that leads to engine management.