chrisdicko

iTrader: (21)

What type of work can you get done on yours heads? Is there different stages of head work?

I.e 1st Stage port and polish,
2nd Stage valves etc?

trell

Heads are the biggest restriction for and engine, My mate worked out the equation to do with the inlet valve size to power ratio. It was brill i will see if i can get it off him.

But basically it all depends on what you are looking for out of you engine.

I know a little about it but i wouldnt advise incase i was wrong tbh.

But obviously the more air you car get into the engine to mix with petrol and the more you can get out ie exhaust the more power you can look at.

Ie standard sti V2 has X mm bores where as the wrc car of the same age would have oversized bores with uprated cams if that makes sence.

bit confusing sorry

chrisdicko

iTrader: (21)

I'm not planning on any head work to be honest, but am interested in what people do, and can be done. As everyone talking about rebuilding their engines, but don't ever seem to do much head work.

Most I've read seems to be a few people get their heads ported and polished, and other big power builds get uprated cams. Although I don't really know what that is either to be honest, lol.


Cheers

dunx

iTrader: (3)

Less critical on a turbo motor !

dunx

P.S. Edit vaporised into the ether !

banny sti

iTrader: (68)

If you want to rev the car higher, you will 1 piece valves, bucket less shims, uprated valve springs, titainium retainers. A port and polish will just smooth the path for the gases to flow quicker, you do not want to go too far as this will slug reponse if you are trying to move too much gasses.

Same prinicple applies to oversize valves too big and you are going to slow the response of the car but improve top end as you will be flowing more air due to the increased valve size.

Cams depend on the size of the turbo and what you want from the car, whether you want mid range or top end.

Banny

Fai17

iTrader: (2)

Pennine done my heads....big spec(ish)!

By the sound of revving at idle it sounds responsive

Shaun

Valvetrain can be altered to assist higher, more reliable revs (as already indicated, but with all other things being equal). The heads themselves can be "opened up" by means of porting / bigger valves to allow more air flow. More air flow can mean more power all other things being equal. As already stated, increased "opening up" of the heads whilst increasing overall flow potential, can decrease air speed which can affect response / torque.

Some heads are better than others, but the STi heads on most scoobs seem to bode well. For instance, an untouched set of Newage AVCS heads can certainly flow enough for 600bhp.... even if the rev limit potential is less of something that has re-worked valvetrain.

If you have a Newage and you do not intend in going for mega power (600+), I wouldn't worry about touching these heads. Spend your cash on something else imo.

I spent £2.5-£3k on fully worked Cosworth Heads. These have uprated valvetrain to help enable a potential 9k+ of revs. Fully ported with +1mm valves. Should be good enough to flow any volume of air I would ever want in the future. BUT and it is a big but, they are wasted to a large degree on my current turbo set-up (and probably costing me spool / torque). Future mods with a much bigger blower, I suspect, will see these heads show a clear benefit. The bigger the turbo, the more air you need to flow and the higher the rev limit you may want to make more use of, for the greater power at the top end.

OK, so I can currently, and do, rev to 8200rpm on my 2.5. Not sure you would want to / or be able to do that on standard Newage heads..... but with a GT30, it has little benefit apart from being able to hang on to a gear longer.

Be very careful if you ever consider in touching your heads.... you could end up either wasting a load of cash or doing something that could change the dynamics of your engine (and not always for the best).

chrisdicko

iTrader: (21)

Nice one, thanks a lot for that. Especially Shaun for the in-depth write up!!


Cheers


P.S. I have AVCS heads, so will probably never touch them.

shaunyboyuk

To be honest, i wouldent bother on a turbo engine as it wont make too much diffrence. Porting an N/a engine will make a diffrence in engine response. With my heads off ive found them to look fine, castings not too rough, etc. Only time i would go into etail is on an n/a engine that i was trying to squeeze max power out of. Also nevver polish an inlet as turbulance is good for swirl of air and fuel. Port inlet, plish exhaust .