970cc K-Head Turbo Racer
Turbo Mini Forums

Hi all,

I have to say I was inspired by the turbo cars that came to my rolling road day last week!

Ive been thinking of doing a 970cc K-head turbo for my racer for a while and seeing the wealth of knowledge and engine builds last weekend thought this would be a good place to ask a bit of advice.

Im going with 970cc crank so I can use the 1275 block. This will let me fit the K1200 bike head and all that stuff. I ran a 1380cc K-head engine last year so thats no a problem.

The thing i need a bit of advice with is the turbo set-up.

What sort of set-up would you recommend? What turbo? What boost? What sort of power/torque do you think is possible? Any advice would be a good start.

Cheers all

Chris

i would say going from the rolling road at yours the other weekend, a GT17 will do almost anything lol

Yes i moved to the darkside

Instagram @jdm_brett

well you need to set yourself some goals, rpm limit, power band, minimum power and compromise these figures untill you settle on a suitable boost level and powerband then the turbo selection will be pretty straight forward.

turbo 16v k-series 11.9@118.9 :)

Denis O'Brien.

Ok,

Well power wise.. I was running 165ish bhp with the 1380. So I want more than that really.

RPM limit of the 970 crank is 9k at least (I realize this may be too high for a turbo)

Power band - Well its a sprint car so can be quite high up. From last seasons racing I used the launch control off the line, that was set at 4500rpm and didnt drop below that for the whole run.

So im guessing 4000-9000?

Chris

http://www.squirrelpf.com/turbocalc/index....=42&map_sel2=47

try here

Yes i moved to the darkside

Instagram @jdm_brett

with that rpm range your power ought to be achievable :) youll need to do a bit of maths to figure out your airflow and boost requirements, and from there you can start to figure out what boost and therefore what turbo you need. info on garretts website, and sure someone posted a calcualtro up recently, would enter some known figures (like the recent rolling road day) to guestimate your BSFC and go from there :)

turbo 16v k-series 11.9@118.9 :)

Denis O'Brien.

If you are bumping the peak power up to about 8500rpm, and the capacity down to 970 you end up with similar requirements to a 1300 with a peak at 6000-6500,

I'd Give a GT2052 a go, the GT17 woud work well to but they are just a bit to hard to find in good condidtion. also the TDO4 is woth a go too, with the 23T compressor.

Cams permiting, I think if you push the rev range even higher (10k) you should be able to manage 200hp+

I didnt want to say it.. but 200 was my real goal. :)

Cam will be custom profile to whatever I want.. perks of being in the business!

I dont mind buying a new turbo. I need the best

Chris

what are you thinking of bore and stroke wise? 73.5 with a billet crank and LOOONG rods?

well ive got a proper 970 crank so will be using that.

i wanted to go billet crank but had to have 5 made :(

Will be using custom steel rods and maybe some forged bike pistons

Bike pistons are a good move, get that gudgeon pin nice and high!

You'll basically end up wit hsomething very similar to Eric's Clan (but with a few extra valves).

My personal thoughts on this are that it may well prove to be a handfull of an engine in a FWD chassis. But there's only one way to find out. The main reason I've stuck with the 998 small bore is to keep rpm low and hence build costs low. also if you intend to use 9000rpm, look at suitable gearing for this. For hillclimbing I'd be looking at a top speed of 100 to 110 mph in 4th.

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

Yer, will take into consideration for the final drive selection.

What's the idea behind a higher gudgeon pin? Think I might have found a suitable bike piston!

Correct me if I'm wrong but 71.5mm pistons give me capacity just short of 1000cc?

Chris

If using a genuine 970 crank, .040 (71.66mm) will give you 999cc.

You need to get some properly looong rods for this setup, but that is a good thing. The loss in torque is easily compensated for with the turbo.

Edited by Vegard on 12th Oct, 2010.

the A series piston has the gudgeon pin below the centre of gravity, the higer above the COG the more stable the piston.

Thought it was +40 that made that?

Anyway I'm going to be using bike pistons so imperial measurements are not much use!

71.5mm with a cooper s stroke of 61.9mm is 994cc I think?

Cheers joe! Makes a little more sence!

Chris

No worries, so if I go with normal mini pistons +40 is the size I want :)

Is it worth the hassle of bike pistons? Is the high pin, super short sideskirts, and valve clearance pockets already machined in the only benefits?

I'm assuming most bike pistons can take 12:1 at 12k + rpm will be fine with a turbo running 9k?

I honestly cant see why bike pistons would be a hassle. Go for it, theyre super lightweight which is great for the revs you want and could they be cheaper due to being mass produced?

Paul

I seriously doubt it!

Bike pistons sound good to me!
I guess the rods will be the dear part.

If something is worth doing, it's worth doing half of.

Yer I guess. But I'm having custom longer rods done anyway so I'm guessing making the pistons fit wouldn't cost me anymore!

Be nice to have circlip not press fit aswell

Chris

Would circlips survive 12k? What do bikes have?

If something is worth doing, it's worth doing half of.

i would not run a circlip at those rpm, a floating gudgeon with teflon buttons yes

Yes i moved to the darkside

Instagram @jdm_brett

Not sure, I was thinking either circlips or teflon buttons?