Quick question

[aidanep71]

So I'll be forging my engine in a few weeks time and have been told by a tuner over here that if I want to make any decent power I'll need to get the head ported and polished as there crap what are your thoughts on this I always thought it was the inlet mani that was the problem. My spec will be

Wisecco pistons stock cr

Scat rods

1mm metal gasket

Custom mani and downpipe

Garrett t25 turbo

5efhe cams

Adjustable cam gear

550cc injectors

E manage ultimate

Cusco flywheel

Fmic

K&n air filter

The head was already rebuilt a few months back but just got the valves re seated and zisco seals

All input welcome

[Azz]

It would help to match the inlet head ports to the inlet manifold, head work is always a bonus but if your going less then 300bhp its not needed

[aidanep71]

I won't be going for mad power just don't want it to be held back by something like that for the sake of a few more quid to free up a few more ponies

[Hawwy]

Just get it forged from td

[aidanep71]

I'm building the engine myself just want some advice on what to do with the head

[AdamB]

Leave it stock, you won't run into any trouble with a T25. It would cost a fair few quid to port a cylinder head properly, you would probably gain like 10bhp up top, but you will likely lose 30bhp low-mid range so if your chasing numbers then go for it, but for a nice road runner then leave the ports stock size.

[aidanep71]

In the long run I will prob fit a t28r tho and don't want to take the head off again to get it done after as a friend of mine recently got his mapped on a t28r and it topped out at 1.2bar and stopped making power and he was told the head was the problem

[AdamB]

Well that depends on a lot of things like fuel used, what intercooler, what diameter intercooler pipes, what size exhaust, what the engine timing was etc etc the list is endless really. What power was it making at 1.2 bar? Generally the heads restrict flow around the 350bhp mark , which is about the range you would expect a t28 turbo to stop making power, possibly a little before. It's hard to say really as it will be dependent from engine to engine, no one really does cylinder head work properly so getting a volumetric flow at which the head restricts is hard to say .

I guess that this is on some form of budget seeing as your choosing the t28 over a GT series?

Edited April 2, 2014 by AdamB

[aidanep71]

Used standard pump fuel on a autobahn intercooler and a 2.5" exhaust. Not sure what it made at 1.2bar as he turned it back to 1bar to be safe and it made 240hp. Yea I thought they were ok for half decent power but urman reckons that the heads areshit and hold them back

[AdamB]

It's the throttle body which restricts a lot of flow, for over 350bhp you really need a 65mm throttle body off the top of my head. I dare say there will be gains to be had even if slightly lower than 350bhp.

[aidanep71]

Would changing the throttle body itself make any difference or is the manifold rubbish too. Any other throttle bodies that fit without modification

[AdamB]

The manifold itself isn't a bad job in fairness, although it depends where in the rev range you want the power. Obviously the stock manifold has quite long runners so it brings the powerband down. Some manifolds have been known to take over 400bhp.

I'm not 100% sure on any that fit without modification, but I've heard the Skyline ones fit pretty damn well. Other than that possibly an SR20 or a 3SGTE but unsure on the size of that.

[morgey]

Wasn't socks running an unported head at like 376hp? Even the stock inlet manifold?

Have a look at his build and see I may be wrong.

[Chris_GlanzaV98]

im think your right morgey

[aidanep71]

I'd prob be pissing against the wind anyway as my intercooler pipework is only 2"

[AdamB]

2" is fairly small roughly only good for around 260-280bhp. 2.25" will be good for around 350bhp and 2.5 inch good upto 450bhp. Although it will depend on the surface roughness of the pipe due to frictional losses.

Just to add from my previous post about throttle body sizing, to make 350bhp+ you'll need a minimum of 60mm, that will be good for upto 380ish.

Edited April 4, 2014 by AdamB

[aidanep71]

Yea space is very tight on the front of the ep71 so used 2" the core I have is also 2" . Would I need to only increase the size of the cold size or would both be needed as the pipe off the turbo is only 2"

[AdamB]

You will be fine just running the 2" to the turbo so just worry about the cold side really. Also try to avoid any angles, a 90 degree bend equates to an estimate of a loss in power by 5%, that includes adding up the angles, ie 3 x 30 degree bends.