9 replies to this topic

[BoboGib]

Model:Jet Black
Year:1988
Description of problem (please be as in depth as possible):

I had been recently had problems with water loss but with no visible leak. While doing some bodywork, myself and MinimadJonsey thought we would have a quick look. When we pulled of the oil filler cap it literally dribbled water out and there was the obvious emulsified oil. So upon getting it home I have taken the head off to find a crack from the No2 cylinder to one of the water jackets.

No my question,

I have the choice of 2 heads in my garage that I can use to replace it with.

I have a standard 998 head, which I believe is unleaded. Or a standard, untouched 12g295.

I know that if I fitted the 295 it would lower the compression but what effect would this have on the car? I don't want to skim anything off the 295 as it is going on my forced induction project as soon as my long awaited parcel from a distant land turns up.

So which one should I fit? And what effect would be seen if I fitted the 295?

[Pauly]

If it was me and I was using the 295 for something else, I would fit the standard 998, if the engines standard and staying that way then its double the work to swap heads again.

[BoboGib]

The core engine itself is standard but it has a maniflow single box system, cooper freeflow manifold and twin hs2's.

[BoboGib]

Morning bump. Really would like an answer to the question.

I know that if I fitted the 295 it would lower the compression but what effect would this have on the car?

[Yoda]

Personally i would fit the 295 as i believe you would benefit more from improved inlet size over slightly lower compression. In my day, (i am an old git) i opened the chambers even more with a die grinder which gave me far better flow of gasses and improved low end power. Try to find a copy of Vizards original book and it explains the benefits far better than i can. plus has drawings of the best chamber shapes to use.

[BoboGib]

Thanks for the input mate. I should have mentioned my engine has flat top pistons in it so hoping that will alliviate the lower compression somewhat.

[Yoda]

No worries, one more point i will make though, with that head and the free flow exhaust, you may need to change your carb needles or a slightly stiffer springs to keep fuel mix rich enough.

Edited by customcart, 09 April 2010 - 06:20 AM.

[BoboGib]

Cool, cheers again for the input. I had it rolling roaded after I put the exhaust and carbs on and it was set up relitivly rich (2.6% co iirc) so hopefully it will run ok till I can afford to get it set up properly again.

[BoboGib]

OK well made my mind up, think i'm going to stick the 295 on and see how it goes. Whats the worse that could happen.

[BoboGib]

Well the 295 is fitted and up and running. Taken it for a test drive and runs sweet. Little bit of a flat spot but other than that its definitely better than the standard head.