MaeckyMY98

Hello!

What you Guys think will be the best shape for the combustion chamber when using european GT Heads on a 2,5 Block?

Do youthink the diameter should match the diameter of the bore?
are the edges wich are there any good in the 2,5?
are they a spot for detonation?

How you meassuring the exakt volume of the Head?

MaeckyMY98

Anyone? No Ideas? Suggestions?

69WRX

Never touched a subaru engine, but used to set up my own race bike engines so I can give you my opinion if it helps.

Personally I would match the diameter of the combustion chamber to the cylinder diameter as like you say a lip could cause detonation
I once totally wrecked a new set of pistons in 5 laps of mallory park ( about 6 miles ) from detonation due to trying out a new fuel.
To check volume I used a burette, basically a thin glass tube with markings on.
Get the piston to TDC, best use a dial gauge to do this. Fill the burette with a mix of fuel and a little oil, Ratio approx 5:1.
Take note of where the fuel level is on the burette then fill the cylinder to the top of the spark plug hole then take a look at the level on burette and work out how much fuel was used
This will tell you the volume. I have no idea of what the volume should be for your engine but im sure some of the guys on here will be able to.

Hope thats of some help.

Andy

Absolute Shower

I'd like to see details re this also, as I'm about to take the plunge on the 2.5L route using UK wrx 2002 heads...think it must be best to have them shaped to the 2.5L bore...

tweenierob

Do NOT use the 2002 WRX cams IMHO.

Rob

Absolute Shower

Hi Rob,

Do I need to use Sti3 cams or something like it? Would the 02 oe cams just not flow enough and cause timing/running problems?

Did you get your heads shaped for the 2.5L bore? If so, who did it and how much?

MaeckyMY98

I think it would be fine to match the bore to the cylinder but simple remove the edge?
wich angle?

I think best method to find out reall combustion volume it with a glas/plexi plate fitted to the head an the filled up with fuel and measure the amount.

69WRX

quote.
I think best method to find out reall combustion volume it with a glas/plexi plate fitted to the head an the filled up with fuel and measure the amount.

This will tell you the exact volume of the head, however you need the volume of the combustion chamber with the head fitted back on.
Dont forget there are other things to take into account. i.e. head gasket thickness, shape of piston top and distance from piston top to block.

Andy

tweenierob

Unfortunately you are a bit limited with replacement cams, on two 2002 cars i have been part of and one other that i have experienced...

Gotta go will continue when i get to work...

Rob

tweenierob

On the two cars i have been part of and the other car the top end has been sacrifised using the std cams, My choice would be to use Ver 5 Sti valvetrain and your manifold etc.

I worked my own heads and tbh they did work well but i would reccomend Pavlo to do another set, The most important thing to sort out on the combustion chambers is not so much the bore match but the high points and sharp edges.
John Banks may be worth speaking to regarding heads as Pavlo also did his.

I would say correctly worked heads using a std 257 could be worth up to 8degrees timing.

Rob

MaeckyMY98

Sure you had to consider the Piston top and the Head gasket also but this you can calculate the volume of the head combustion you can not calculate (or maybe just i cant ;-))
So first you need the head volume while shaping it to the right size to campare between the cylinders an the you need it to calculate the complete Volume.

sharp edges (more or less) and high points are normaly added to the Head for mixing the fuel air mixture and giving the same A/F mixture in the whole combustion chamber (at least this is on N/A engines like this maybe not on a turbo engine). The mixture is squezzed out between the upwards moving piston and the high point in the head wich mixes the air and the fuel better up.

So complete removing of these spots and edges is a good thing? Do we need this higher areas on the Turbo engine also to mix the mixture better up or are these spots only a cause for knocking?

Who have worked on a head for e EJ257 engine?
What have you done to the combustion chamber?
Wich shape?
Wich results you get with this heads compared to an OE head?
Is a bowl head the best solution? everythin smooth and plain?
Do you polish the combustion chamber?

Mark A

iTrader: (1)

Rob

Are you saying the best option would be STi5 valve train (valves & cams etc)in a phase 1 head (casting) and a phase 1.5 inlet manifold?

Reason for doing this would be;
-Reduce cracking around the spark plug?
-Better balanced inlet manifold

Mark

Absolute Shower

I always thought a smooth clean surface was best for the big bang as it leaves less carbon deposits....but then, I'm no expert.

Cheers for the info Rob...not sure exactly what I'm going to do with it all yet (no light at the end of the tunnel!).

One thing for sure, the heads need to match bore size - I really dont like the sound of a lip inside the cylinder!

p1mark

the chambers do not need to be polished, but certainly need to be smooth. correct AFR is more important to stop carbon build up, but carbon build up is not a huge problem. you are going to get it using unleaded fuel unless you run the engine at racing speeds all the time. if you are doing any work in the inlet ports as well, you should not polish them for sure.

any sharp points or rapid angle changes, wether on the edge of the chamber leading into the bores, in the centre of the chamber, or on the lead into the valve seats should be avoided. the material at these points will always be a little bit hotter, therefore just giving that little bit more of an excuse for det to start.

Absolute Shower

Got it, ports polished more important...

Anyone know a place I can get STi v5 valve train from?

p1mark

shower, read again mate.

you should not polish your ports. the profile should be smooth, but not polished. i have proved on a flow bench one more than one occassion to people that did not believe this that there is no difference in CF/M flow between a polished and rough port. so there is no point in doing it. unfortunately a lot of customers like to see a polished port, so a lot of tuners do it! a slightly rougher finish actually helps atomisation of the charge, due to a small 'tumbling' effect as it flows over the peaks and troughs of the port finish. its all tiny gains though, and not really applicable unless you are talking about a full race motor. the shape and contour of a chamber or port is far more important than its finish. i work solely on NA bike engines where things like this can make a difference, with an FI engine there is a lot easier ways to get power in big spades, as we all know!!!

Absolute Shower

I see...cheers for confirming this - wont bother with polish etc...just make sure shape etc is okay.

Can I just fit STi v5 cams straight into my 02 heads without mods and would this be enough (once lip in bore removed) to make use of the full 2.5L engine?

tweenierob

Mark, the best manifold to use (proven) is the early phase one manifold... i personally rate this over all the other MY inlets. STi5 Valvetrain wont fit into phase one head casting.
My choice on phase 1-1.5 would be Sti3 cams or Type Ra like i used.

P1mark, exactly my thoughts... any sharp edges need to be adressed for starters.
The exhaust ports are the most important IMHO, Gas flow through these make the biggest difference.

Rob

tweenierob

Sorry just to add, my reference to sti5 and manifold was on the 2002 Wrx

Rob

Absolute Shower

Rob, ref your last reply...so I'm okay to use STiv 5 cams on phase 2 heads (02 WRX) and get the high points and lip sorted but not polished. If so, just need to sort set of cams - know anyone that supplies STi v5 cams or maybe remakes them and not for silly money?

tweenierob

The cams will need to be reshimmed etc.. best move IMHO is to speak to Paul (pavlo) about it. He can also sort out the reshimming porting etc so that you can basically just bolt the heads on finished.

Rob

Absolute Shower

Okay cheers Rob - tops.

Think I'll see what my local garage can do first (as they're local, plus they setup full rally spec cars) and then contact Paul if can't do heads work.

MaeckyMY98

Anyone have pictures of a allready shaped Head?
Wich Headgasket are you using after shaping the Head? Same will mean a lower CR.

Absolute Shower

Dont you have to use the 2.5L gaskets as wont the 2L gasket produce a small lip in the bore just like the heads if used?

RB5_245

If you're trying to do it cheep cheep this guy might be able to help you, just make sure he guarentees you of the condition. I got a dodgey turbo of him once, but he's an alright bloke.


Dave

Edited to add: that is he'll be able to get you cams/heads