Cylinder head spec ?

[MrD]

Righty i bought a dx head some time back,was quoted £350 for the b@##oks of porting,skimming and 3 angle seats etc,by a bloke who builds race engines.Now although that is a great price,i think it`s still a little bit too much,and can`t really justify that. I could get an abf engine for that money !

Was planning on taking the dx lump out,and getting an abf this year,but to be honest i love this engine,love the way it revs and just wants to let rip !
So i was thinking about doing the spare head myself,i have worked on heads in the past,ford and vauxhall engines,and made quite big power increases,by just matching to the gaskets,and skimming,cutting valves in etc.
There is also a fantastic guide on c/gti,project 8 valve head .
Then in the future if i get bored of this lump , i can just bung a 2ltr bottom end in and keep my head etc.

Few questions i have are how much to get skimmed off it ? 40 thou + 1mm so would 80 thou = 1/2 mm ? Should i get it skimmed to within an inch of it`s life,so just leaving enough meat for a reface if need be ?
I am also running a Kent gs2h cam,i assume it will still be non interference by skimming it ?
Will i have detonation issues by raising the compressinn ratio ?
Is it worth getting uprated valve springs,caps and collets ?

Cheers folks

[filmidget]

Just replied about machining on your bonnet thread, thus

I can recommend a machinist - Just collected Ant's head from him... He chemical/pressure cleaned the head, skimmed gasket and manifold mounting faces, replaced valve guides, machined valve seats, and even cleaned up the valves and lapped them in. He also decoked and cleaned up the corrosion to the ports and chambers (it was ported already). All for £90! (might be 'cos take few bits in to him though).Not worth doing the non-machining work yourself at those prices...

Why you wanting new seats? Old ones will probably be fine?

Regarding the porting: I just had a go myself - I figured at the prices quoted, ie about £350, you are only getting about ten hours porting work? Plus when the power gets up near 135-140bhp the limiting factor seems to be the valve sizes anyway, which is big money. And as you have said, if wanting that sort of power then 16v seems more practical/effective.

I had a look around the web, then just matched head/manifold ports, took out the steps from valve seat to head, and smoothed out the nasty corner out the bottom of the ports. I didn't need to replace the valve guides out, so didn't really tackle that area (possibly a mistake in hindsight).

Having since looked a commercially produced 'stage 1' head they hadn't done any more than me, apart from around the valve guides.

I also fitted a GS2H cam, and it was fine with the standard (double) valve springs and steel caps. I just had a minimal skim and the clearance was fine (didn't think losing the option of skimming the head later, especially after all the work done on the head, was worth the tiny increase in power)

Mine was a GU head (2mm smaller inlet valves than DX) - Utilising a Weber, with K&N panel in standard intake trunking, and 'dual outlet' cast iron manifold it made about 125bhp on rolling road (up from 90bhp standard). Revved like hell too.

It will be interesting to see what Ant's 2e block/DX Stage 1 head/Newcam cam combo makes when it's all built up.

[MrD]

Will keep an eye out for reports on that one !
No idea how much bhp i am putting out,it flies though,and upset my mate who has a 2ltr 16 v mr2 !
Made all the difference paying to get it tuned up propper ! knocked over a sec and a half of my 0-60 time !
Will be going r/road once i have done the head and put the stainless manifold on,removed the centre box,will see wha it does then,really need to get the Koni`s on the front too,handles well scary.
Too much camber !

[filmidget]

Pretty certain Ant will be doing an in-depth FAQ article - we took plenty of pictures when we stripped the head down before I took it to be machined.

Imagine he will be getting it RR'ed too - I think he will be happy seeing anything over 130bhp, so long as it's torquey, as this engine is for his daily so not really built as a screamer (only really putting the cam in 'cos it came up for sale locally).

I am still trying to convince him to put a 4+e 'box in for the ultimate cruiser, plus the torque of the 2.0l should fill some of the big gaps between ratios.

[MrD]

Could do with a 6th gear in mine !

[KindredSpirit]

I had aW reg 'Metro' once in years long gone (1.3 'sport') but loads of blue smoke.
Went like sh** off a shovel .
I sorted the ports out in one day, polished them etc ., new valve stem seals, decoke etc.
Went even better after that.
Sorry.

[MikeH]

As has already been said, for £350 you should be getting new valve guides and stem seals, fully ported, 3 angled valve seats, balanced chambers, back-cut valves.

If you're using standard valve sizes, the seats shouldn't need replacing. Inserting valve seats is a precision, expensive job to get done properly, so you don't want to go there anyway.

As for skimming the head, it depends on what cam you've got, as to what CR you should go to. In rough numbers, a 1mm (40 thou) skim will take the head from 10:1 CR, to 11:1. If you use a mild-ish cam, you don't want to go beyond about 11 or 11.5:1 on an 8v, and it definitely depends on setting up the fuelling and ignition properly. If you're using a GS2H cam, 11:1 would be about right, to avoid overheating and pinking problems.

As for uprated hardware in the valvetrain, it depends on the spec of the rest of the engine, and what you want to rev it to. Standard stuff is ok to about 7k revs, which is about the top of the power band of your cam

[MrD]

Yeah the bloke who was going to be doing the head builds race engines,price was because i was through a friend of his,would have been a top job,but just can`t justify that ££ on a head though.


So with my cam,exhaust,panel filter.
I will get 40 thou skimmed off,get new guides put in,new studs,port it myself (just removing the bit`s below the valve seat where there is a nasty step,and matching to the gaskets in the ports) was thinking of cutting the guide boss down a bit ?
And getting the guides bullet nosed,is it worth replacing valves,springs ,valve caps etc ? or should the ones in the head be ok ?

Bottom end is standard trim,230 thou miles,runs as sweet and as silent as any new engine i have heard,and does not miss a beat,however hard i drive it.
Was going to go abf route this year,but would like to keep the head once it`s been played with,and chuck it on a 2ltr bottom end,eventually..
Regarding the bottom end,what could be done to improve output ? Mate said don`t worry about balancing etc,really does not make that much difference,has seen results.

I was thinking of new rings and a hone and just checking all other bearings etc,don`t wanna go down the re bore route,as then i will be looking at new pistons etc so would make it un financially viable

[MikeH]

If you can't afford to port the head properly, don't spend the money on a bottom end rebuild instead. I wouldn't bother about balancing on what's basically a mildly tuned road engine.
The original valvetrain should be fine.

the bottleneck in any cylinder head is round the valves. attention to detail in there will make a lot more difference than work done on the ports. 3-angled valve seats are a big part of getting the right result. Maybe you should ask your mate if he can get the valve seats and backs done, and bore out the valve throat. That'll get you maybe 80% of the gains of a full porting job. Maybe he can do that for a bit less. If you fit new guides, you need to get the seats recut anyway, so you might as well get it done properly.


£350 inc VAT is pretty good value for a proper porting job, if it includes a check and refurb of the head too.

[MrD]

Ok cheers for the input It was the full works,was told for his knowledge alone what i would be getting was a bargain,i would be paying a third of the rate for the amount of work he would put into it !
Might just save up the money,and get it done propperly

[KindredSpirit]

Make sure bottom end is up to it.

[KindredSpirit]

...sorry - computer is playing up, had a lot more to say, but it keeps disconnecting.

[KindredSpirit]

Had probs with my GTX with overheating - wanted to do a better performance top end - advised against because bott. end wear.
Daughter blew up a Escort RS turbo @ 50 mph on the M1 due to similar prob - con rods & pistons everywhere.

[MrD]

Ah right ,not good ! Have been informed by a very reliable source (Friend of the engineer who was doing the head work) that dx bottom ends very rarely show signs of wear !
It`s not missed a beat yet ! And i drive it very hard,bounce off the limiter before i change gear,most of the time.
How will i know if my bottom is getting slack .Is it a strip down job ? measure stuff with plastigauge etc ?
If it does go pop i suppose it`s the kick up the bum i need to sort out the 2ltr bottom end,although i would rather keep the dx lump for now,car has had a lot of money spent on it ove the last few months,and i am running low

[MrD]

I don`t suppose people like Tsr,blydenstein etc publish the spec of their heads,would be handy having some measurements ,so i have some sort of limit to work too ?
Still waiting for my valve spring compressor to turn up yet,want to strip it down and have a look,i have noticed on the face of the head,there are cracks between 2 and 3 cylinders,it`s in the thinnist part of the metal,not sure how deep it is,better not be scrap,bought of ed38 ages ago.