What are "THE" heads to have?
25 December 2006, 02:35 PM
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What are "THE" heads to have?
Not that i need any but what would be the heads to get for later on if i saw them available.
Are earlier STI heads better?
Anyone got any info on this for me please
Are earlier STI heads better?
Anyone got any info on this for me please
25 December 2006, 04:25 PM
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Are they all interchangable, ie, would STI3 heads fit and work on my 02WRX lump?
This is not a mod im considering for a whil, but would be nice to know a thing or two about it
This is not a mod im considering for a whil, but would be nice to know a thing or two about it
25 December 2006, 04:53 PM
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Yes sti3 heads are the best but only fit to a phase 1/1.5. I suppose they would fit if you used an early manifold and then buggered about with the wiring. The easiest thing to do for you however would be to get some different cams/valves etc for your wrx heads. I have a friend who is doing the exact same thing.
25 December 2006, 04:55 PM
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Originally Posted by coulty
Yes sti3 heads are the best but only fit to a phase 1/1.5. I suppose they would fit if you used an early manifold and then buggered about with the wiring. The easiest thing to do for you however would be to get some different cams/valves etc for your wrx heads. I have a friend who is doing the exact same thing.
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25 December 2006, 05:53 PM
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Havent the STi heads got Variable valve timing?
What model was VVT introduced in and how is this controlled - ECU ? If so surely you'd need an STi ECU if you fitted STi heads on a WRX or is there more to it than that ?
Remember on WRX bottom end you're not getting the strength associated with forged internals of the STi block so I wouldn't take it too far. I should imagine, guessing here, that the STi cams are profiled to take into account VVT and to benefit from the extra 1k rev limit ?
It's just one big learning curve this
What model was VVT introduced in and how is this controlled - ECU ? If so surely you'd need an STi ECU if you fitted STi heads on a WRX or is there more to it than that ?
Remember on WRX bottom end you're not getting the strength associated with forged internals of the STi block so I wouldn't take it too far. I should imagine, guessing here, that the STi cams are profiled to take into account VVT and to benefit from the extra 1k rev limit ?
It's just one big learning curve this
Last edited by funkyspider; 25 December 2006 at 06:02 PM.
25 December 2006, 08:51 PM
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There has got to be some advantages of the newer ie: newage heads with VVT etc. Are there now some versions of the VVT that can vary both inlet and exhaust cam?
25 December 2006, 09:12 PM
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Originally Posted by funkyspider
Havent the STi heads got Variable valve timing?
What model was VVT introduced in and how is this controlled - ECU ? If so surely you'd need an STi ECU if you fitted STi heads on a WRX or is there more to it than that ?
Remember on WRX bottom end you're not getting the strength associated with forged internals of the STi block so I wouldn't take it too far. I should imagine, guessing here, that the STi cams are profiled to take into account VVT and to benefit from the extra 1k rev limit ?
It's just one big learning curve this
What model was VVT introduced in and how is this controlled - ECU ? If so surely you'd need an STi ECU if you fitted STi heads on a WRX or is there more to it than that ?
Remember on WRX bottom end you're not getting the strength associated with forged internals of the STi block so I wouldn't take it too far. I should imagine, guessing here, that the STi cams are profiled to take into account VVT and to benefit from the extra 1k rev limit ?
It's just one big learning curve this
thats why i start threads like this mate, theres just SO much to learn
25 December 2006, 09:38 PM
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VVT is still not better than the STI 3 heads....hence why they command such a premium when they come up for sale. I have a Version 3 STI Type RA V-Limited and there is a definite "surge" when the car comes on cam.
25 December 2006, 10:02 PM
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Originally Posted by Midlife......
Ported Sti 5/6 I think Neilo has gone for for his bugeye 
Yes i have purchased a set of "what started out as" sti5 heads, but they have also been ported and have custom ground cams to gain a little more over standard sti5 cams as well.
STI3 as has been said do have the most agressive cams of all the standard cars, but the newage ones do have AVCS on their side which can help the power down lower in the rev range which also has its benefits.......
25 December 2006, 10:54 PM
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Originally Posted by Danny Boy
There has got to be some advantages of the newer ie: newage heads with VVT etc. Are there now some versions of the VVT that can vary both inlet and exhaust cam?
VVT is there to improve driveability on standard cars, however it can be a hindrance and is often removed in the quest for big power.
Plus Subaru had to keep up with Mitsubishi and their MIVEC system!
25 December 2006, 11:07 PM
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Originally Posted by cookstar
What cams is he using, is there much gain to be had in cam changes?
26 December 2006, 10:45 PM
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My understanding was that the VVT has been removed in some high power applications purley for the fact it was simpler. However being able to vary the valve overlap charateristics has to be able to give advantages in high power situations as well as you will still have the compromise of getting the turbo to spool as quick as possible and still trying to achieve the best top end flow.
Allen Bell's STi7 is a case in point i believe.
Cheers
Dan.
Allen Bell's STi7 is a case in point i believe.
Cheers
Dan.
26 December 2006, 10:52 PM
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My recolection of the characteristics of the classic style heads was that the STI3 had the wildest cam profile of all the standard cams as mentioned before plus because of the the shape of the comustion chamber and the position of the spark plug the casting was much less prone to cracking betweek the plug hole and exhaust ports.
The STi5 heads seem to be more than a match to the STi3 ones as far as flow goes though, although the castings are very prone to cracking between the plug hole and exhaust valve seat. This can sometimes cause issues but alot of the time is fine too.
For example Bob Rawles STi5 is still running standard STi5 valvetrain and is pushing almost 500bhp.
Out of all the classic style heads im pretty sure theese are the best two options.
What i would like to find out is how some of the newage heads match up to theese classic sytle ones?
The STi5 heads seem to be more than a match to the STi3 ones as far as flow goes though, although the castings are very prone to cracking between the plug hole and exhaust valve seat. This can sometimes cause issues but alot of the time is fine too.
For example Bob Rawles STi5 is still running standard STi5 valvetrain and is pushing almost 500bhp.
Out of all the classic style heads im pretty sure theese are the best two options.
What i would like to find out is how some of the newage heads match up to theese classic sytle ones?
27 December 2006, 12:26 AM
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so are we saying uk heads by design ( as in casting ) are crap or just whats in them
if i took a uk head, port and polish new uprated cams, retainers valve and double valve springs would it be in comparison \ better than to say a sti3 head
and at what stage do head really make a difference ?
i compare my car (std internal 02 wrx ) to p1marks p1 which have the same mods give of take a few brand names
mine reliably kicks out 386 bhp on the rollers, Marks 404 bhp
im guessing with my cast pistons i am not runing as hot top end so that will lose me some horses but still his head (ported & polished) be gaining > 10 bhp @ 400 bhp
is this a linear gain against horse power ?
can you see what im getting at, in my position it would not be worth spending say 2.5k changing heads for 10 bhp - spend that on a gt30 twisted set up and im am sure to see more gains
**** it ... can't afford any way
edited to say - this is on a 2 litre I understand that a built hybrid 2.5 needs head work to alter the squish point
if i took a uk head, port and polish new uprated cams, retainers valve and double valve springs would it be in comparison \ better than to say a sti3 head
and at what stage do head really make a difference ?
i compare my car (std internal 02 wrx ) to p1marks p1 which have the same mods give of take a few brand names
mine reliably kicks out 386 bhp on the rollers, Marks 404 bhp
im guessing with my cast pistons i am not runing as hot top end so that will lose me some horses but still his head (ported & polished) be gaining > 10 bhp @ 400 bhp
is this a linear gain against horse power ?
can you see what im getting at, in my position it would not be worth spending say 2.5k changing heads for 10 bhp - spend that on a gt30 twisted set up and im am sure to see more gains
**** it ... can't afford any way
edited to say - this is on a 2 litre I understand that a built hybrid 2.5 needs head work to alter the squish point
Last edited by WRX_Rich; 27 December 2006 at 12:28 AM.
27 December 2006, 08:53 AM
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I think what id say to that rich is that perhaps marks car should be making more power than it is, assuming that its making more boost than you as well.....(although i dont know that)
The sti5 heads can flow more air as standard than UK heads in simplest terms, but as you say if you used your UK heads, had them ported and polished with custom cams then i would expect to see far more than 10-20bhp increase. The other thing that you have to remember is that although the "peak value" hay only be 10-20 higher the area under the graph may be significantly larger than before.
I think as you say though the gains are more pronouced on the 2.5 as with the exception of the newest stis no heads were build for the 2.5 so your trying to get 25% more air in to the cyliders (and out) using the smaller heads so it will never be that efficient.
The sti5 heads can flow more air as standard than UK heads in simplest terms, but as you say if you used your UK heads, had them ported and polished with custom cams then i would expect to see far more than 10-20bhp increase. The other thing that you have to remember is that although the "peak value" hay only be 10-20 higher the area under the graph may be significantly larger than before.
I think as you say though the gains are more pronouced on the 2.5 as with the exception of the newest stis no heads were build for the 2.5 so your trying to get 25% more air in to the cyliders (and out) using the smaller heads so it will never be that efficient.
(Is that accurate)?
27 December 2006, 01:19 PM
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Not necessarily although it could reach that if you did it properly......new valves, retainers, lifters, cams, and port and polish.
port and polish from RCMS is 595+vat, may be cheaper elsewhere but not by much, so add that to the cost of the heads to buy (assuming you are not using your current ones) then add any custom cammage.
Alternatively use a set of stock STI5/6/P1 heads and have those flowed. That is what i was originally going to do then i got lucky and was offered a set that had slightly more agressive cams in them also, i wouldnt count on that every day though!
If you were to "build" a set of heads from scratch thoguh id expect it to cost near 2.5k yeah.....cams are bloody expensive (~800) and fresh valvetrain you would be lucky to get change out of 600 quid. The the port polish at 700 inc vat for example and youve got 2100 straight off....
although it could reach that if you did it properly......new valves, retainers, lifters, cams, and port and polish.port and polish from RCMS is 595+vat, may be cheaper elsewhere but not by much, so add that to the cost of the heads to buy (assuming you are not using your current ones) then add any custom cammage.
Alternatively use a set of stock STI5/6/P1 heads and have those flowed. That is what i was originally going to do then i got lucky and was offered a set that had slightly more agressive cams in them also, i wouldnt count on that every day though!
If you were to "build" a set of heads from scratch thoguh id expect it to cost near 2.5k yeah.....cams are bloody expensive (~800) and fresh valvetrain you would be lucky to get change out of 600 quid. The the port polish at 700 inc vat for example and youve got 2100 straight off....
30 December 2006, 09:53 AM
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Depends on what MY of head to block combo you want to have.
I believe there are differences in the combustion chamber volume from phase 1/1.5 to phase 2 heads. This would alter your compression ratio which would alter the tune of the engine alot!
I believe there are differences in the combustion chamber volume from phase 1/1.5 to phase 2 heads. This would alter your compression ratio which would alter the tune of the engine alot!