K100 Small Bore - To Turbocharge or not?
Turbo Mini Forums

I have a dilema.

I recently bought a K100 head and throttle bodies.

Now you know I am a fan of 998s and dont like 1275s, plus I like to do something different. So I thought I would do a forced induction 998 with a K100 head.

After a bit of research into the original K100 conversion, I convinced myself that I could engineer a solution. I think it is possible with offset boring at +0.080" to get the bores close enough to the original K100 bore centrelines. It may be necessary to relieve the block a minimal amount to clear the exhaust valve.

The biggest problem is pistons. I can get +0.080" P20950 pistons from Minispares. A good design, no slots and proven at 150hp plus.

According to Russell/Calver, these pistons have enough meat in them to dish them, so it should be possible to lower the compression to 8.5-9.0:1.

The problem is then the valve reliefs. See this picture of the original Gregg Temkin engine:



This is an 850 block offset bored to 68mm.

The valve reliefs need to be about 4mm deep to clear the valves at overlap.

The problem is that the top ring is only 6.5mm from the top of the piston.

I just think that this would take too much out of the piston, with dishing as well.

The only other option would be to use 1098 flat topped pistons, 0.150" down the bore, but the only ones I can find are slotted and do not seem up to forced induction.

So unless I can find decent 1098 pistons, it looks like a non-starter.

I might just build a NA 998 90hp screamer.

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."

drop the valves into the head a bit ?

Medusa + injection = too much torque for the dyno ..https://youtu.be/qg5o0_tJxYM

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 could use the 'D' word.

Decompression plate.

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

www.twin-turbo.co.uk

lol, i was thinking that wil.

if your blowing it will it need milder cams with less lift? not that theyre available....

hmmm thats a point ,if the cam is way more than you need ,then drop the lobe hieght in the lathe round it off with a file and get it hardedned,ooorrr,move the cam timing to make less lift on overlap , ooorrr,call ae tech up and ask about this ring to crown hieght , you may find they already make pistons for another engine that have a slim crown and they haave worked well ,oooorr machine the pistons and coat them with a heanium type coating ,theres a company on chelt or gloucester that does it .um .think that it for now ,sounds like theres too much cam in there paul .

Medusa + injection = too much torque for the dyno ..https://youtu.be/qg5o0_tJxYM

How about doing what jimster did and welding a decomp plate to the head. Itd take a bit of time but itd give you clearance

Back once again like a renegade master

Well, ultimately whatever you can do with the compression, the cams are fixed and too much duration for a turbo.

I think the 90hp NA option will do just fine.

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."

Have you considered a blower? would be a bit less sensitive to the cams, plus I suspect you were only going to run lowish boos anyway?

How wild are the cams on the 8V head? What would be a 'classic mini' equivalent?

276, 286........

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

www.twin-turbo.co.uk

Team www.sheepspeed.com Racing

How wild are the cams on the 8V head? What would be a 'classic mini' equivalent?

276, 286........

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

www.twin-turbo.co.uk

i think theyre about 280 deg.

I had 285 in my head, but it is a bit high for a turbo.

I did consider fitting the M24 supercharger, that would be an alternative and not so hampered by the high duration.

At least with the twinky, I could spread the LCA to lower the overlap, time the exhaust earlier and the inlet later.

Ummmmmm???

Edited by Paul S on 28th Nov, 2007.

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."

Cams are 285 IIRC - and a big lift to boot. Is this too much for a 998? Well - it was only 100 cc more in the original application.

Interesting stuff.

Can you stroke a 998 crank?

If so wouldn't this be an option to shorten it and leave the pistons down the bore slightly, giving a lower CR and shallower valve pockets?

Don't forget you've got an ally head, better control on fuelling so you can't rule out slightly higher CR's than the 5 ports use.

https://www.facebook.com/pages/Fusion-Fabri..._homepage_panel

www.fusionfabs.co.uk



1/4mile in 13.2sec @ 111 terminal on 15psi

Edited by Paul S on 28th Nov, 2007.

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."

On 28th of Nov, 2007 at 04:44pm matty said:
Can you stroke a 998 crank?

If so wouldn't this be an option to shorten it and leave the pistons down the bore slightly, giving a lower CR and shallower valve pockets?

Don't forget you've got an ally head, better control on fuelling so you can't rule out slightly higher CR's than the 5 ports use.

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."

its the 0.050 thou lift duration that really effects things ,a cam on a bucket tends to have a different gap from 0 lift to 50 thou ,can you graph the duration at 50 thou paul ? if its under 210 you may be ok with a re phase .

Medusa + injection = too much torque for the dyno ..https://youtu.be/qg5o0_tJxYM

I feel the DTI and crank wheel in use at the weekend.

Also if I stretch the LCA to 112 degrees I would only have 61 degrees overlap.

The other advanatge of the re-phase would be that the valve reliefs would not need to be so deep.

Edit: incorrectly calculated overlap.

Edited by Paul S on 6th Dec, 2007.

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."

The K100 spec:

http://www.bmbikes.co.uk/specpages/K100.htm

Just need to build a bottom end to handle 8000rpm if I want the 90 hp from the NA !!!!

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."

Back once again like a renegade master

Hows about the idea talked about a while back of bushing to rods little end and driling the hole off centre (towards big end)?

Increases deck volume and you won't lose any cc's?

https://www.facebook.com/pages/Fusion-Fabri..._homepage_panel

www.fusionfabs.co.uk



1/4mile in 13.2sec @ 111 terminal on 15psi

By George, I think I've got it!

Use an 850 crank.

With the +0.080" pistons, this will give a respectable 952cc. The pistons will sit down the bore enough so that there will be no need for dishing or valve reliefs.

According to Vizard, a correctly prepared 850 crank will run to 9000 rpm, as long as you use one of the later thick tailed ones.

Just need to widen the centre main bearing housing in the block, which may be a bit tricky but easier than a lot of the other options.

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."