i have a set of v4 sti heads coming my way

ideally i'd love to get them ported and gas flowed, but i'm guessing its gonna cost a fair amount???

i know standard heads will still make 400bhp so what is the advantages of porting and gas flowing the heads???

would you notice any difference realistically?

 

What is your engine spec/build going to be?

I ran STi heads mildly ported by myself on a 2.5 motor, and acheived circa 450/450...

 

not looking for much more than 400 if even that........

i'm not really sure of the advantages of doing head work and if its even noticable???

 

In my experience lag can be reduced with a set of well ported heads, so even if your not looking for more power, where you get it is just as important.

 

thats the main reason i want them done, so i dont have much lag

will it be much of a difference between ported and non ported heads?

 

If you really want to get the best from those heads and any other tuning you are planning, then getting them ported is the way to go. Any engine is ultimately limited by the head if you are going for the "ultimate" engine. But even if you are just looking for more power and better power on your existing set up, a properly sorted head will give better power, better turbo spool up, less lag etc and any tuning mods you do make will benefit from the better head.

Just make sure you know what you are getting. You want proven gas flow and balance across the cylinders so it must be done with a CNC machine. Check these.

 

yeah i seen that but i dont want to spend that much for head work!!!

thats the reason i'm wondering if its gonna be worth doing

 

Well I've done my own STi3/4 heads. The ports mainly needed taking casting flaws, seams and winnets out without enlarging really at all, the main problem area was where the valve seats meet the throat on the long side, this was very ropey as standard. I left the valve guides alone. The runner dividers I knife edged as well as I could.

The chambers I just tidied up sharp edges really and smoothed where the seats didn't sit properly in the chamber roof. I then cc'd the four chambers and equalised them, which was the longest job as one head's chambers were about 2 or 3 cc different from the other's.

At the inlet manifold interface it was just a case of gasket matching really, at the exhaust ports where they hit the headers, I left them alone as they don't really want to be as big as the gaskets anyway.

If it's done properly it can only have benefits. It remains to be seen whether I did it properly, but I didn't go too crazy with the dremel, so hopefully it'll be worthwhile. My target is 350bhp on a TD05-16G with all supporting mods.

 

I've done the same to mine, the casting surface at the bottom of the valve seat is terrible, it will not hurt flow to smoooth this out, it's more of a bluprint port and polish, blending rather than removing vast amounts of material so that it flows huge amounts of air.
If you just square away the rough casting marks and enlarge the inlet throats to the gaskets then you shold make good headway, this just ensures you have as less amount of obstruction in the inlet tract, on my MY99 Turbo that i did, i matched the inlet manifold to the gaskets as well, took the steps out of the throttle body inlet and enlarged the exhaust side a bit, this made the car run very well with out any other mods so it can work very well.
My V4 Sti has larger ports to start with compared to UK car i had, so less needs to be done (still in the process on my Sti) but like i have said, all it is going to get is a clean up really to make sure that it is a smooth as it can be to aid flow rather than increase it by large amounts

 

when the head comes from the factory the ports for each cylinder are the same.... they all flow the same and each cylinder produces about the same as a result.

When you set about the head with a dremmel you have no idea if you are improving the flow or making it worse. The design of a port is incredibly subtle and the only way you can tell if you are improving flow or making it worse is with a flow bench.

Also, with a manual method like this , each cylinder's ports will operate with different levels of efficiency... It's impossible to get them the same again... one cylinder making more power than others etc. I can't imagine that is good for the engine in the long term.

 

Well having looked at three sets of classic heads, I can say for a fact that they are definitely not the same from one chamber to another. They are terribly rough as standard and one head definitely had deeper chambers than the other on the latest set I worked on, even though the deck heights were the same. As it is now, they all have equalised CCs to within 1cc and the ports are all nice and clear. The exhaust ports are offset anyway, so there's no way the factory casting can be perfectly equal in performance from one cylinder to another!

 

Used these guys a lot, their work is amazing and picks up power everywhere in the rev range.

CNCHEADS - Subaru Impreza

 

Thanks for the info Martyn.