998 low comp pickup engine
Turbo Mini Forums

Hi guys,

I'm looking into building a forced induction engine using the original a series engine that my pickup came with. I think its a 8.3:1 low comp engine. Are these engines any good? I will be rebuilding it anyway but with a target of 80bhp are the pistons and bottom end going to be up to the job?
I think i'll go for a different head maybe a 12g295 aswell as a sw5 cam and a vmaxx charger kit. Is this realistic?

Thanks
Chris

1976 mini pickup

I'm running upto 10psi with a low comp 998 running 8.7:1 (with turbo phil sorted 295).

oh and my engine was built in 1969.

Setup is moreof the issue than the engine giving out IMO unles its falling apart already...

I run a supercharger and I don't care the TB is on the wrong side.
VEMS + 12 PSI + Liquid Intercooler = Small Bore FUN!

Thats not bad for a 42 year old lump! Have you had it on a dyno? I wonder if its worth doing much to the bottom end then... Will have to see what it looks like when the heads off.

Chris

1976 mini pickup

Yep it was all setup by my local rolling road. That's what I mean by the setup is more important. If the fueling or timing is wrong its more likely to end up with a set of liquid pistons. Mines been running with a 40 year old bottom end with 60k on the clock since 2007. I will admit it only does about 3 k a year Inc a coup,e of track days.

I run a supercharger and I don't care the TB is on the wrong side.
VEMS + 12 PSI + Liquid Intercooler = Small Bore FUN!

You won't need to do anything special to the bottom end.

8.3 is low though. I run 9.3:1 and over 12psi no problems.

Fastest 998 mini in the world? 13.05 1/4 mile 106mph

www.twin-turbo.co.uk

8.3 pistons and 295 head will need either a lot of skimming of the head or a CR good enough for 30 psi ...

Good thing is you might use à 940 without worries.

Rusty by nature

I was wondering how much lower a 12g295 head would take the compression ratio. I guess if all the exrta volume is in the pistons i could run a more normal head ( with unleaded seats!) and still keep a low comp. I'll measure the camber volume when the head is off and see if its sensible

Chris

1976 mini pickup

Wil do you run and intercooler on the 12psi? The Orignal post was talking of a vmax kit...

IMO I'm happy with my 8.7:1 seemed safe with good fueling and ignition, the water injection now fitted has had a good effect on the temps that I was seeing before.

I run a supercharger and I don't care the TB is on the wrong side.
VEMS + 12 PSI + Liquid Intercooler = Small Bore FUN!

Yes I run an IC, air temp rarely go above 35 acording to the sensor.

Fastest 998 mini in the world? 13.05 1/4 mile 106mph

www.twin-turbo.co.uk

998 non cooper head are 24 something, thats 10,3 whith flat top piston

12G202 are 25 something

12G295 are 28,3, thats a little short of 9.0 with the flat top pistons

You can work your dishes backwards from your CR and the volume of the standart 998 head
Something like v = V+1 / V where V is swept volume, v is chamber volume including piston dishes and gasket volume, then you change the chamber volume to the 28,3 of the Cooper.

You'd better double check my formula, it's getting late ...

Rusty by nature

202 heads unskimmed have more volume its 26 cc but i have also had a 202 head that was unworked that had 28cc. It is better to measure your dish if poss and deck height at tdc then calculate your compression ratio as i have rarely had a standard engine come up to spec. The most recent one i took apart had a difference of 6thou on the deck heights.

My small bore turbo project http://www.turbominis.co.uk/forums/index.php?p=vt&tid=473901

JLay, you are right.

BUT the stated CR is calculated with the spec so for comparison purpose I guess it is OK to work it this way.

Anyway, Pickup76, does your rebuild implies new pistons ?
If so, nothing can replace measure.

Rusty by nature