998 project engine
Turbo Mini Forums

The plan so far is to use parts from several low mileage 998 engines which i've collected, selecting the best parts. I'll try and use some of the earlier full skirt pistons, as i seem to remember wil and ben saying that they've had more sucsess with these over the later slipper type?

I'll use new rings and bearings, but keep work to a minimum as im on a tight budget (throw away engine).

I already have a gt15, thanks to peter, and a large cossie intercooler from an escort. Not sure what the actuator will run too, but im presuming it wont go upto more than 4-8psi on std??? The aim is to run 12-14psi using a bleed valve. I'll make up an adapter for the std exhaust manifold to take the GT15 as i dont have enough wedge to do anything fancy. I'll be using MS for ignition.

The only thing, i think, i dont have under control is the cylinder head. I want to use a 12g295 to keep gas speeds up and increase low rpm performance. I have one on the shelf, but the heads well passed best, although its not been skimmed. I also have a std turbo head and a collection of other 940's. But im not sure what to use, the 295 would necessitate buying new valves, but would a std 940 head (33/29) with standard valves (and nice large recut seats) withstand turbocharging?

As for compression ratio, i was hoping to run 8.5-9.0:1 (mg cam), i'll start low (8.5:1) and increase if im not happy.

Your thoughts are very much welcome!!

Edited by andeh on 10th Jun, 2006.

I've seen the future and tbh its Pie

I'd personally spend the money on the 295 head. If you use a 940 head you will need to get the block pocketed, which if it is a throw away project engine will be a waste of money when you bin the block, whereas the head can be unbolted and used again.

Thats a good point tom, cheers.

Fortunatly i have acess to a milling machine in my dads workshop, so get free machining work if i do it myself, so valve pockets wont be a problem.

I still like the idea of the 295 and i would use it again on the 850 when i do it, but using a std 940 and being virtually free is very tempting.

I've seen the future and tbh its Pie

I have been reading up a bit on squish to try and get a better understanding of it. From what I have read (and this is not forum reading) I get the impression that for out and out power squish can be more or less ignored. Yes it helps more fuel get burnt more efficiently, but if you are happy to have high unburnt hydrocarbon reading then you are better spending money in other places than trying to improve squish.

However like Peter I am biased in that I love the 940 head on a 998.

http://www.twin-turbo.co.uk
http://www.hillclimbandsprint.co.uk/default.asp

A man without a project is like a like a woman without a shopping list.

having no mot here on the island, thats an interesting take on squish vs. high hydrocarbons.

saying that though, firstly im sticking with the std 998 flat-tops, gonna suck it and see as it were.
would think the flat tops, flush with the deck would be good on the squish front.

"Turbo's make torque, and torque makes fun"

"did you know you can toast potato waffles?"

Actually Joe, that is what I am doing. I have a 1030 at the moment with flat tops and a 940 head and 276 cam. I intend to just put another 940 head on with slightly opened out chambers and a T2 and see how it goes. Probably run about 9:1. The 276 cam may get changes to an MG.

I am happy to be proved wrong about the squish, but that is what I picked up from reading around the subject a bit.

http://www.twin-turbo.co.uk
http://www.hillclimbandsprint.co.uk/default.asp

A man without a project is like a like a woman without a shopping list.

I've decided on the following spec for my 998:

295 Head with 28cc chambers.
Flat topped "Mega" pistons
T2 on Mirage manifold
Std 998 cam with 1.5:1 rockers
EFI
EDIS

Lightened verto steel flywheel with HD cover
Std drops and helical gears
4 pin diff

Looking for 100 curly wurlies from a reliable 10k miles a year engine. (Also 50 mpg!!!!!)

If I was going to use the 940 head, and I had access to a milling machine, I would consider lowering the exhaust valve seats rather than pocketing the block. Keith Calver recently did this for an article in minimag. You would need to use the dished, full skirt 20773 pistons though to get the compression down.

Saul Bellow - "A great deal of intelligence can be invested in ignorance when the need for illusion is deep."
Stephen Hawking - "The greatest enemy of knowledge is not ignorance, it is the illusion of knowledge."

Peter, I agree that squish is important and ultimately will make more power. But in the reality of the engines were are making, and I know you are trying to push the limits of the A series much more than me, it seems trying to engineer in squish is way above most peoples knowledge. I f I was designing an engine from scratch then yes squish is vey important, but when modifying an A series I don't see it as vital. Like you say there have been good power results from engines that should have low squish so for most of us mortals it can generally be ignored. Perhaps this a a bit of a defeatist opinion, but modifying a 60 year old engine is always going to be a compromise.

http://www.twin-turbo.co.uk
http://www.hillclimbandsprint.co.uk/default.asp

A man without a project is like a like a woman without a shopping list.

I smell a red herring!

I think that in the area around the exhaust valve, 295 or 940, valve pockets or not, there is no squish!

The main area of squish in the A series is the beak, is it not?

Saul Bellow - "A great deal of intelligence can be invested in ignorance when the need for illusion is deep."
Stephen Hawking - "The greatest enemy of knowledge is not ignorance, it is the illusion of knowledge."

I've decided on spec, i'll stick a de-bossed MG head on with chambers to suit. Cam will be morspeed ph2 for now, but i'll also give a 1275A+ cam and maybe an MG cam a go at some point.

Managed to find a perfect crank, looks new, and some good s/h bearings, also look new. I think i've found some full skirt dished pistons aswell. I'll measure them later, all i need is a block and its looking like the half dozen or so i have here arnt suitable except for an a-series one. Worth concidering?

I've seen the future and tbh its Pie

Andeh,

Have you got round to building this engine yet and if so how does it go? I'm toying over going down similar line myself and I'd rather not reinvent the wheel if needed.

I've only collected parts thus far as i have been busy moving house/setting up a new workshop. Needless to say this engine will be built this summer along with the supercharged version and my short stroker.

The only things that have changed are the crank, which got toasted during a spil in my workshop, and i've sourced some +30 pistons.

I've seen the future and tbh its Pie