cylinder heads

[sawood12]

Are all 8v cylinder heads the same?

I'm considering having my head gasket replaced later this year and thought about getting a used head and refurbishing it and maybe installing larger valves and a different cam (I believe the 944 N/A cam in a turbo is a good upgrade) so when I get the HG replaced later in the year I can swap the heads.

Not sure if flowing the heads make much of a difference on a turbocharged motor, but at least with a refurbed head I'd know that the top part of the engine is nice and fresh.

 

[TTM]

The exhaust ports on the turbo head are ceramic-coated.
When the coatings peel off and make their way to the turbine... well, you get the picture []

I would be interested too see if the NA camshaft and bigger valves would work well with a K26/6. I suppose most people fit them with bigger turbos to get most of the flow in the upper rev range, and as the K26/6 typically runs out of breath past 5k rpm it would be interesting to find out if it performs better up there if used with a better-flowing head.

 

[sawood12]

I guess if I were to get an N/A head and install larger valves i'd have to have the exhaust port re-coated anyhow? Just wondering what my options are for donor heads if I were to go down this route. I figure if i'm going to get my HG replaced this year then it is an opportunity to do this rather than having to have the head off again at some stage in the future. I have no idea what costs are involved at this time, i'm just considering options. There is no rush as my HG is OK at the moment (there, i've just said it - just wait till next time i'm out in the car!!) it's just one of those pro-active maintenance items i've been putting off for a while.

 

[pauly]

I had the head flowed on my 87 Cosworth and it definately made a difference to the pull over 6k, it was done by the guy that did the head for Gravetts car when he won the BTCC, 16v though obviously. I'd get a price on some exhaust valves first though, could be very pricey.

 

[333pg333]

Look out for a 2.7 head? Do a cam and even a k26/8 swap.

 

[sawood12]

Well that's the plan Pat, though ultimately i'll go for something a bit more modern than a K26. But, as always, cashflow is my ultimate mistress!

I quite like the idea of doing it in stages as well to see what difference each individual element makes. The larger turbo is the last step in my plan as I'm quite curious to see exactly what I can get out of the K26/6 with a Vitesse MAF, flowed head etc. I know somewhere where I can get the head crack tested and machined so shouldn't be too expensive, but valves and all the other bits will be the pricey bit. I seem to remember from another post I might be looking at around £60 a valve? If that's the case it all depends how much the other stuff comes in at - also planning a new clutch and lightened flywheel which takes priority if the buget is bust.

I guess the 2.7 head already has larger valves so might be a simpler case of a head re-fresh?

 

[333pg333]

Well there are different stages of head work you can get done. I stupidly got caught up in doing the 'lollygobbleblissbomb' version and that has cost a small fortune. I can only speak of a few brief times I've had that head on an engine that held together for a week or two (I'm currently into my 5th rebuild []) but even on run in miles the head / cam combo felt like a totally different beast. It really seemed to transform from Jeckyl to Hyde once up into the revs. I can only just remember it with fleeting-shrinking brain cells, but it was wonderful. This was on a 3L though. The last version was running at 9psi and 5000rpm limit and with the Vitesse stg 5 turbo, so nothing was really waking up quite yet, but even then you could feel the dragon about to launch. I never got it into the next step as the 4th engine failed at the next dyno session when we were due to up the boost / revs. So that's why the current latest version is in the US getting built under the one roof by one person. Short story long, it's almost done and there has been a lot of changes too, but I'm really looking forward to having that head / cam combo back. We don't realise just how constricted our stock 8v head / cams are. Beware, it's not just a matter of opening up and polishing to the 'N'th degree, there is a lot of tech expertise that goes into a good combo. Way above my head, but there are people you can talk to. Still, the 2.7 is a good starting point and perhaps as an economical alternative, not a bad option comparitively?
As far as doing things in stages, well I'm in two minds about this. On one hand we often don't have the choice not to due to financial constraints and it marries in well with the "Oh I want to see how this all goes in stages" syndrome. I have done both, and in terms of being able to quantify your mods, well sure it is a whole lot easier to do them in stages. I have done a few things at a time and you never know what is doing how much....but the opposite side to this coin is that if you got someone to put together a package that worked together, this would make more sense in a performance (and quite possibly overall budget aspect) concept. I have a friend that is putting together a 400whp kit. I'm not sure what this entails, but it shouldn't be too much with your UK pound, although yes, more than the @60pound valves might cover. [&:]
There's a company in the US that sells a Garrett Turbo with a mount that bolts up to our cars. It's not too prohibitive and might be a good answer to the "Where do I go after the K26/8" question? Might be worth an enquiry?
http://tinyurl.com/cu3cue

 

[sawood12]

Ahh, in that case I might be better off waiting a while and taking my car down to John Mitchells place and getting a job lot done at once. I seem to remember he did an upgraded head with new BB hybrid turbo on another car (on a 944 turbo cab if I remember correctly) which is what I sort of had in mind. Anyway, i'll see what the quotes for the parts are and decide.

 

[333pg333]

That's what I'd advise. Get someone to give you an estimate and then work on that budget.

 

[Diver944]

Remember that the 2.7 head is designed for the 104mm bore of the 2.7 engine and I don't knpow how it would work on a standard 100mm bore of the 2.5 engine.

We left my 2.7 head uncoated as Jon was convinced it was pretty much overkill and that Porsche only did it as it was still fairly early days for Turbo road cars back in the early 80's and of course safety and longevity was uppermost in their minds

 

[JarmoL]

Hi there,

In addition what Paul said above the 2.7 head won't fit to a 2.5 block (without welding and machine work) because one of the coolant passages is spaced differently. So a 8 V 2.5 N/A head is the one if you want to have porting done on the exhaust ports also.

Jarmo