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TygerTung
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Posts: 9
From: New_zealand
Registered: 06/02/2008
Time spent: 0 hours

(Date Posted:06/02/2008 6:46 PM)

G'day, I'm from New Zealand, and over here have a class of racing knowen as "Bucket Racing" Class Restrictions:
125cc 2 stroke restricted
0-150CC 4 stroke
Superbucket engines must be derived from non competition motorcycles. Motorcross, Road racing, Enduro and Go Kart
motors and transmission parts are not permitted. There shall be no restriction on the make, type or design of carburettor,
ignition, exhaust, piston, cam, valve springs or cooling system except for class eligibility.
All engines of less than 100cc capacity may be turbo or supercharged. 125cc 2 stroke engines are restricted to carburation
equivalent to a single 24mm carburettor and must be aircooled.

Basically everything else is open except from fuel which is AVGAS.
100CC 2 Stroke can have watercooling and any size carburettor

What the class is about is you get a cheap commuter bike and do whatever you can do to it relitivly cheaply and go out racing!

I have a custom frame that someone in nelson has made up with 17" wheels and slicks. Motors have been a variety of honda singles until they blow up etc.

I also have raced a CG125 in the production class quite successfully.

I want to build a really fast honda single to beat all the FXR150's people are running these days.

I was thinking the best idea would be to use a GL145 piston as it has the dome on it to bring the compession up.
Gearbox, XL125S 6 speed? I have XL125S casings. Am going to use a RM125 flywheel and stator as it is very small and light with the stator going on the outside of the flywheel. GL145 crank as it is lightwheight with the two small webs. What would be the best idea for the head? I have a 185 or 200 head here that has been ported out nicely, or would I be better off to use a 125 head for more compression? Maybe better off with a GL145 head as it has a ballbearing cam and bigger valves? Could port out a GL145 head or an XL125S head myself? What compression ratio can I get and what is the maximum you can have without detonation on one of these engines? What about the cam and valve springs, what is the best option there? I have a mystery hot cam in stock, and I got some performance valve springs for a toyota 2E engine which are a bit stiffer than stock. I'm after massive power, it doesn't have to have a real broad rev range as I am road racing and it should be pretty easy to keep on the boil with the 6 speed box.

How reliable can it be? I would like it to last a season before I have to pull it down and replace the valves, maybe replace the rod every second season?

Any help and advice would be greatly appreciated!

Cheers,

Sam
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Swiss
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1#



Rank:none
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Posts:776
From: USA
Registered: 03/26/2004
Time spent: 0 hours

RE:How to build a really hot 150?
(Date Posted:06/02/2008 8:24 PM)

Easy first question is what are the FXR150s and what are they running?  RPMs and power? 

Swiss
generatorshovel
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2#



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Posts:89
Registered: 02/17/2005
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RE:How to build a really hot 150?
(Date Posted:06/03/2008 4:06 AM)

When you sort it out Sam, I'll have one too Wink
Tiny

--------------------------------------------------------------
It CAN be done

TygerTung
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3#



From: New_zealand
Registered: 06/02/2008
Time spent: 0 hours

RE:How to build a really hot 150?
(Date Posted:06/03/2008 7:44 PM)

The FXR 150 is a sports commuter bike with a DOHC 4 valve head, 150cc 4 stroke. It's air/oil cooled, It seems to be 1/4 of a GSX600 motor. Internet says they have 20hp, but I don't believe that. Probably more like 14 or so hp? Rev to about 12 or so I think.
Swiss
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4#



Rank:none
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Posts:776
From: USA
Registered: 03/26/2004
Time spent: 0 hours

RE:How to build a really hot 150?
(Date Posted:06/08/2008 12:55 PM)

Looks like pretty tough to compete with a 4-v head, which was always the limitation for the small Hondas.  I don't know what aftermarket racing parts are available for the Suzuki, but you know that the Honda has lots of stuff available.  Basics for performance apply.  Bigger valves and air flow, big cam, big carb, high compression, hot spark.  HP is normally made with higher rpms like the Yoshimura built engines.  I know that the pistons are available.  You don't need a lot of low rpm power in roadracing, but it looks like you guys race for 1-3 hours at a time so reliability is very important.  A hard running hand grenade won't do you any good.  Run the bigger 200 head with either a modified piston or have some pistons built for the compression ratio that you want.  You might do like Generator shovel did and weld in the combustion chamber to aid the squish area and raise the compression ratio.  Main thing is that you want the larger valves and greater flow of the big heads. 

Back in the early '70s I off road raced with a guy from Anchorage, Alaska that was running an SL100 on alcohol.  He ran one of the 4-cylinder pistons and claimed his compression ratio was about 13-1.  Since he was running alcohol it was fine with that high cr, but he constantly ran it to 13-14000 rpms and basically broke rods whenever it broke.  He said that parts were cheap enough, he just pulled it down and rebuilt it.  I want to build a nice "200" engine and when I do I will use a 70mm RTL piston with a stock 49.5mm stroke so that it will turn some high rpms.  What are the valve sizes of the GL145 head?  Are they bigger than the 200 valves or just bigger than the 125 valves?  You could run an ultra high rpm 150 engine with a 70mm bore and a long rod 39mm stroke.  This would allow a lot of rpms and the rest of the engine would have to be built to take it.  At 150cc the ported 200 head should work with it.  You would need a big carb to feed it and if you can use one from the new CRF150R with the pumper it would work pretty well.  ONe of the small button mags that they are running on the Pit bikes would help you with quick revs.  Otherwise, lighten the crank. 


How about frame restrictions?  A light frame could remove 10-15lbs from the bike.  Would really help acceleration! 

Swiss

Swiss
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5#



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Posts:776
From: USA
Registered: 03/26/2004
Time spent: 0 hours

RE:How to build a really hot 150?
(Date Posted:06/08/2008 2:07 PM)

Almost forgot, you could also run the 200 head with a high compression 200 piston at 65.5mm and destroke the crank down to 44.5mm for some better high rpm..  Of course, again custom rod length.  Just another option for you.

Swiss
TygerTung
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6#



From: New_zealand
Registered: 06/02/2008
Time spent: 0 hours

RE:How to build a really hot 150?
(Date Posted:06/11/2008 8:28 PM)

I already have a rather light frame, frames are open. Heres a picture of the machine in action.My Bucker racer in action
TygerTung
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7#



From: New_zealand
Registered: 06/02/2008
Time spent: 0 hours

RE:How to build a really hot 150?
(Date Posted:06/11/2008 8:36 PM)

How would you sort out this custom rod length? Would I have to manufacture my own rod? Sound quite complicated. Can I use an XL100 crank or somthing similar to get the short stroke I would need if I was to run an XR200 piston? I have heard that the cranks can self destruct at high rpm because they can't handle the revs.

The other option I guess would be to run a 4 valve head off a VT250? This has been done before but aparently the big ends didn't like it and they would blow up every once in a while? I don't know for sure how often this kind of expiriation occured though, aparently they would reliably run to about 14000 all day long. I would like to stay the 2 valve route though, giving the big finger to technology, doing it the old school way.

Would it be possible to get 20hp out of a 2 valver or is that just asking too much?

The longest races we do are 1 hour and you will probably only do about 2 of them a year. races are usually only lasting for about 12 minutes or so, but I don't really want to be pulling apart the motor more than once a year as I have many other projects and also have to look after my wife!!!
Swiss