8 replies to this topic

[Harryracinggreen1990]

hi , im wanting to mod my cylinder head before it goes back onto the block, does any body know off the top of thiere heads how much i can get the head ported and polished for and any more work i can have done on it, such as valve work , have heard people saying about re cutting seats but im a bit new to this so any help will be aprecatied, many thanks!

[R1minimagic]

It depends what you want doing really, cost can range from around £150 to over £1000

What is the engine spec for starters?

[Alex_B]

You will only really want to get it ported, it has been proven now that polishing the inlet ports actually reduces performance due to the atomised fuel sticking to the edges, where as when its a bit rougher air gets trapped on the walls which creates a nice low friction path where the fuel stays atomised.

as to cost I wouldnt know about that I am afraid,

and you only need to re cut the valve seats if they are needing it because of imperfections, or upsizing valves,

what is the engine spec you are after and people can advise on if you need to get bigger valves or not :)

[Cooperman]

When porting a head the valve guides have to be removed. So after fitting new guides the valve seats need re-cutting to ensure they are centralised to the new guides and the new valves need lapping in.
The combustion chambers need some re-shaping to de-shroud the valves, so the head needs skimming to get the combustion ratio correct and, ideally, slightly higher than standard.
For a properly done head allow about £450 for the head porting and combustion chamber re-shaping, new guides, new valves, seat cutting, valve lapping and skimming. With new springs and caps allow a bit more.

[Harryracinggreen1990]

its an A+ 998 witch im trying to make a fast road, so doing all the tuning i can , if that helps lol , thanks for the replies :)

[Cooperman]

Try to find a 12G295 head and have that ported & polished and skimmed to get the C.R. right, as the standard head really is very poor and requires a lot of work just to get it as good as a standard 295 head.

[dan187]

i've just spent about £450 getting my head done with larger valves and some chamber and port work.

[Cooperman]

That sounds about right. The compression ratio must be calculated and the head measured and skimmed as necessary. How folk can fit a flowed head without realising the need to measure, calculate and machine for the correct C.R. always amazes me.

[Turbo Phil]

The small bore {non 295} heads are very time consuming to do as the ports are so small access is difficult. The performance gains, even when properly modified, are also limited. The better option, as already said. is to get a 12G295 casting. Trying to find one of these in decent condition for a fair price is a nightmare though. On all the ones I've seen & worked on have needed a full overhaul. The standard valves & seats wear terribly. So you need to budget for the new parts required, which will mean new springs, valves, guides & skimming etc, not just the port work.
The 12g202 is also an option. It will require more time on the port & chamber work, but can be made to work very well & can be bought far cheaper than the 295 castings.
I've seen some work done at the prices quoted above & it has ranged from good to shockingly bad. If you shop around you can get the work required done at a good price & of a good quality.

Phil.

Edited by Turbo Phil, 17 April 2013 - 06:24 AM.