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Home > 998cc > K100 Small Bore - To Turbocharge or not?

Paul S

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8140 Posts
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Formerly Axel

Podland

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."


robert

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back home in oxfordshoire.

drop the valves into the head a bit ?

620 kg ,old falkens ,open diff.13.1s @109.1mph . (wheelspin from mid track)
88mph to 112mph in 4.39s.highest 1/4 terminal 112.1mph


Paul S

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8140 Posts
Member #: 573
Formerly Axel

Podland


On 27th of Nov, 2007 at 04:23pm robert said:
drop the valves into the head a bit ?


I like your logic, but I'll have to investigate what the implications are to the valve length, collets, cam buckets etc.

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."


wil_h

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Betwix Harrogate and York

I could use the 'D' word.

Decompression plate.

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

Prescott Modified Series Production upto 1400cc course record holder
Oliver's Mount Modified Series Production upto 1400cc Hill record holder
Thoresby Park Modified Series Production upto 1400cc course record holder

www.twin-turbo.co.uk

On 2nd Jan, 2013 fastcarl said:

the design shows a distinct lack or imagination,
talk about starting off with a clean sheet of paper, then not bothering to fucking draw on it,lol

On 20th Apr, 2012 Paul S said:
I'm mainly concerned about swirl in the runners caused by the tangential entry.


Joe C

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Carlos Fandango

Burnham-on-Crouch, Essex

lol, i was thinking that wil.

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

On 28th Aug, 2011 Kean said:
At the risk of being sigged...

Joe, do you have a photo of your tool?



http://www.turbominis.co.uk/forums/index.p...9064&lastpost=1

http://s95.photobucket.com/albums/l154/min...2006/?start=all



robert

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back home in oxfordshoire.

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 .

620 kg ,old falkens ,open diff.13.1s @109.1mph . (wheelspin from mid track)
88mph to 112mph in 4.39s.highest 1/4 terminal 112.1mph


Jordan

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Liverpool, North west

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


Paul S

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8140 Posts
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Formerly Axel

Podland

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."


Joe C

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Carlos Fandango

Burnham-on-Crouch, Essex

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?

On 28th Aug, 2011 Kean said:
At the risk of being sigged...

Joe, do you have a photo of your tool?



http://www.turbominis.co.uk/forums/index.p...9064&lastpost=1

http://s95.photobucket.com/albums/l154/min...2006/?start=all



wil_h

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Betwix Harrogate and York

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

Prescott Modified Series Production upto 1400cc course record holder
Oliver's Mount Modified Series Production upto 1400cc Hill record holder
Thoresby Park Modified Series Production upto 1400cc course record holder

www.twin-turbo.co.uk

On 2nd Jan, 2013 fastcarl said:

the design shows a distinct lack or imagination,
talk about starting off with a clean sheet of paper, then not bothering to fucking draw on it,lol

On 20th Apr, 2012 Paul S said:
I'm mainly concerned about swirl in the runners caused by the tangential entry.


Jimster
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Sunny Bridgend, South Wales




On 27th of Nov, 2007 at 07:52pm minimadj said:
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


I didn't weld a plate to the head, I just had all the oil and water ways welded up, my deck is now thinner than it was

Team www.sheepspeed.com Racing

On 15th May, 2009 TurboDave said:

I think the welsh one has it right!


1st to provide running proof
of turbo twinkie in a car and first to
run a 1/4 in one!!

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wil_h

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8527 Posts
Member #: 123
Post Whore

Betwix Harrogate and York

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

Prescott Modified Series Production upto 1400cc course record holder
Oliver's Mount Modified Series Production upto 1400cc Hill record holder
Thoresby Park Modified Series Production upto 1400cc course record holder

www.twin-turbo.co.uk

On 2nd Jan, 2013 fastcarl said:

the design shows a distinct lack or imagination,
talk about starting off with a clean sheet of paper, then not bothering to fucking draw on it,lol

On 20th Apr, 2012 Paul S said:
I'm mainly concerned about swirl in the runners caused by the tangential entry.


Joe C

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11100 Posts
Member #: 565
Carlos Fandango

Burnham-on-Crouch, Essex

i think theyre about 280 deg.

On 28th Aug, 2011 Kean said:
At the risk of being sigged...

Joe, do you have a photo of your tool?



http://www.turbominis.co.uk/forums/index.p...9064&lastpost=1

http://s95.photobucket.com/albums/l154/min...2006/?start=all



Paul S

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8140 Posts
Member #: 573
Formerly Axel

Podland

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."


TurboDave16V
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SouthPark, Colorado

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.

On 17th Nov, 2014 Tom Fenton said:
Sorry to say My Herpes are no better


Who remembers this first time around: https://www.youtube.com/watch?v=hzUflxkPFAM


matty

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Turbo Love Palace Fool

Aylesbury

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. *wink*

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



Paul S

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8140 Posts
Member #: 573
Formerly Axel

Podland

On 28th of Nov, 2007 at 03:53pm TurboDave said:
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.


Sorry to correct you but the K100 was 987cc. It developed 90 hp.

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."


Paul S

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8140 Posts
Member #: 573
Formerly Axel

Podland


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. *wink*


Could do an offset regrind using standard shells to gain a bit, but need a bit more really.

The main problem is the valve pockets getting too close to the top ring groove.

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."


robert

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back home in oxfordshoire.

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 .

620 kg ,old falkens ,open diff.13.1s @109.1mph . (wheelspin from mid track)
88mph to 112mph in 4.39s.highest 1/4 terminal 112.1mph


Paul S

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8140 Posts
Member #: 573
Formerly Axel

Podland

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."


Paul S

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Member #: 573
Formerly Axel

Podland

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."


Jordan

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Liverpool, North west




On 28th of Nov, 2007 at 10:53am Jimster said:

I didn't weld a plate to the head, I just had all the oil and water ways welded up, my deck is now thinner than it was


Thought you did.
Sorry bout that memory lapse.*blush*

Back once again like a renegade master


matty

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Turbo Love Palace Fool

Aylesbury

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?

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



TurboDave16V
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SouthPark, Colorado




On 28th of Nov, 2007 at 05:54pm Paul S said:

the K100 was 987cc. It developed 90 hp.



Huh?
I thought (assumed?) they were all 1100cc.

Cheers for the correction.

:)

On 17th Nov, 2014 Tom Fenton said:
Sorry to say My Herpes are no better


Who remembers this first time around: https://www.youtube.com/watch?v=hzUflxkPFAM


Paul S

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8140 Posts
Member #: 573
Formerly Axel

Podland

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."

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