The Coscast head was fitted across the range and as such you can find it on both dizzy and dispac ignition models. Likewise should you really want to change heads all you need to do is swap over the exhaust cam, cam sensor housing and you can retain your dispac set up.

 

ah right, so other than the head being cast by the germans rather than the cosworth folk there pretty much the same?
was there not something different with the oil galleries or something? thought the coscast were a superior head over the later ones,ill have to look for a dispac one then is that electronic setup name?
iv only really had vw's and minis and a couple of vauxhalls inbetween so dont know a right lot but loved the torque and power of this engine i wanted another

 

if you have a KS head, general consensus is that its a reactive issue, rather than proactive.

i.e leave it alone until (if at all) it goes porous

 

Exactly, as a matter of fact, the KS700 head is made of stronger material than a Coscast (just slightly) and a really fine quality. If it ever gets porous it is even possible to fix without taking it off.....

If it is a KS400 or KS859 then you might want to change the head proactive afterall, these are much softer and have suffered from loosened head bolts more than once....

Too bad the Wikipedia article is much more comprehensive in Dutch about this than the English version....
http://nl.wikipedia.org/wiki/C20XE

http://en.wikipedia.org/wiki/C20XE

 

so the valves and ports are all pretty much the same then just the coscast head was an earlier version and designed and cast by cosworth

cheers ill prob just leave it then,if its not broke dont fix it style

so those other two head verions,how come there were afew different types?will the numbers be cast into the head somewhere?

 

valves are the same, ports are the same, although the KS heads have dimple effect like a golfball on the port runners. early coscast heads had larger outside diameter valve guides and bucket shaped valve spring platforms, much nicer port finish. cosworth did some development heads based on the 2 litre block but the actual final production units were designed by opel, cosworth only cast and finished those early production run.

variations of heads in cronological order, coscast (no GM markings) kolben schmidt (big OEM german parts manufacturer) with GM markings, later coscast heads with GM markings, then the other variations in casting for coilpack engines.

 

I thought the later -LN (low noise) XE's had slightly smaller exhaust ports on the head??

 

Valves might be the same but ports are not. My early Coscast head had tiny ports compared to some later heads that Philip2 showed me in his workshop.

You couldn't miss the difference even by eye.

 

right so now im more confused than when i first started haha

the coscast head is in essence not all its cracked up to be?

compared to later ones they have bigger valves but ports are smaller? later ones have smaller valves for emmison puposes?

 

read again, bigger valve guides

valves are the same, ports are the same (other than the factory finish on them)

if you had the 3 main types on a work bench, all in good order, you would choose the early coscast from a gte16v, it is the best head. but what we are saying, it isnt worth going out and buying a coscast and fitting it as preventative maintenance for a porous head that statistically you might never get.

 

Darren, the ports are not the same, I've seen it with my own eyes and measured them.

My inlet ports on my early Coscast were quite a bit smaller than a later GM head and my ports were already ported and polished the GM was standard.

I've just had my inlet ports machine bored to a much larger size by Philip2 and he's just finishing off the matching an polishing along with new valve guides .....

Should be ready soon


This might go some way to explain why my first tuned engine made fantastic power at low to mid revs but felt strangled at high revs? Or it may not. My other standard GM head engine feels stangled at low-mid but deff better at high revs than the tuned engine .... hence the porting work on the CS head.

 

Darren, the ports are not the same, I've seen it with my own eyes and measured them.

My inlet ports on my early Coscast were quite a bit smaller than a later GM head and my ports were already ported and polished the GM was standard.

ok.

well to remove any vaguness from my statement, i have 2 early coscasts (no GM branding) and a GM KS700 which are the same other than the port finish mentioned.

 

I've got 3 early ones in my possession at the mo and in fairness the only difference between them is on my ported one. The inlet ports on the GM one in my Silk Violet GTE ARE slightly bigger to look at than the Coscast items I have. Either way, on a standard unit both heads help an XE achieve the same power output so it is only really relevant when you start asking for lots more air to be pulled through them. Pointless flowing them below the 200bhp mark as the standard heads will happily flow enough air for that.

 

later dispac heads are the ones to go for, believed that some of the heads are already 25.5mm around the throat areas. coscasts imo are over rated, i always sell the ones i ever get and stick with porous modded GM head, but each to there own

 

My coscast inlet bores measured 22.4mm at the smallest point, and as already mentioned I had already ported this head some 10yrs ago removing as much metal as I felt comfortable with at that time.

They could have been as small as 20 or 21mm but I have no records now. That's two times 20mm for each inlet valve of course. I think Philip has taken these out to 26.5mm but he would have to confirm this.

All in all there is quite a variation all things considered.

 

dispac gm head ports are alot larger than early coscasts.