Moped rider
Well at least I am pulling 16+ HP now Carl. Started as a base line of about 13Hp. Nice crisp sound and plenty of torque. I will get down on Saturday and run some test laps. Cully is running the engine out of the red bike at the moment while he makes some bearing repairs on his engine. Looking forward to some fast laps on Sat/Sunday
Moped rider
Well at least I am pulling 16+ HP now Carl. Started as a base line of about 13
Nice crisp sound and plenty of torque. I will get down on Saturday and run some test laps. Cully is running the engine out of the red bike at the moment while make some bearing repairs on his engine. looking forward to some fast laps on Sat/Sunday
Who You Calling a Pig
Ahh shit, looks like I am in real trouble nowOriginally Posted by Ned Kelly
the A grade mid pack just got real interesting. Time to take a concrete and throw it into the corners harder.
For the record Qkkid was in my bed, not the other way round
Long Haired Yobbo
The FXR is kind of like the benchmark bucket at the moment isn't it?
I seem to remember Richban reporting a dyno figure like 17.5hp If thats correct it is quite alot to compete with.
(Ahh Found it and added link)
I never seemed to meet THE GP125 at Kaitoke at any point but judging by what others have said it was probably easily the fastest staight line bike there in the weekend. Quite alot faster than any FXR there.
Is all that because the GP makes beter tourque or somthing?
Tex on his GP 125 seemed to have heaps more effective power than I had on the overcarbed FXR I was on, yet I cant imagine it being much (if any) more powerful in peak power.
Heinz Varieties
Forum whore
FXR's making 17.5 rw-hp (I thought they were less) and with their wider 4-stroke power band they will be a lot to compete with. Looks like our GP's arn't there yet.
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Hardcore Biker
I never seemed to meet THE GP125 at Kaitoke at any point but judging by what others have said it was probably easily the fastest staight line bike there in the weekend. Quite alot faster than any FXR there.
Is all that because the GP makes beter tourque or somthing?
Tex on his GP 125 seemed to have heaps more effective power than I had on the overcarbed FXR I was on, yet I cant imagine it being much (if any) more powerful in peak power.[/QUOTE]
I'd doubt mt GP125 has more power than an FXR, it,s a matter of being able to use it. TZ's GP would pull away from me on the straights even tho I'd got a much better run out of a corner, then I'd have to take him under braking. Track knowledge counts for alot.
Life is a lesson-if I bother to listen
No8 Wire Extraordinaire
Bearing in mind differences in Dynos my understanding is an FXR std probably does 16hp with a wide spread. Makes sense that Rich's mildly tuned FXR does 17.5. When the guy put the GN or whatever carb on yours the chance that he put the right jet in it is slim.
So a decent GP with nigh on 20hp & a decent spread should be an easy match for an FXR. The news that the bikes in wgtn aren't highly developed is pretty old. A decent rider on a ok handling bike with some good power can do the buss. I'm not saying I fall into that category but when I had the H I used to regularly just walk away from the field with 18hp & it was quick turning but not particularly pretty handling. I think if you put that old engine in a decent frame with a good rider he should do the same. - Oh look, Glen did just that & on his first outing was right up there. He'll go further with some more time on it.
The FXRs are a great starting bike, but the GP should have more potential, or at least equivalent.
Don't you look at my accountant.
He's the only one I've got.
Forum whore
the GP Sux when you compair them standard
17 wheels ???? dont think so
brakes what brakes
the frame is made from noodle straws and bungie cords
as a standard bike the fxr is just soooo much better
but it's booring
the gp needs to have 17" rims stiched on to it (not to hard)
and slight mods to the engine
then you have got 17 hp (or there abouts)
and a bike that handles like shite and has no brakes
just like all the fast guys back in the 80's
put the gp into another framenow that is potential say 17.5 hp (19.5 maby) in an rs
dan then it shows up how bad I ride crybaby:
I think I'm just going to ride the rg50 this year
"Instructions are just the manufacturers opinion on how to install it" Tim Taylor of "Tool Time"
“Saying what we think gives us a wider conversational range than saying what we know.” - Cullen Hightower
No8 Wire Extraordinaire
for sure the GPs handle terribly std. Gyro had a very fast watercooled 100 back in the day. Felt like the front end wasn't connected though. Yes the RG50 handles great in comparison, much fun to ride & teaches you to peddle faster to keep up with the bigger bikes or in Auckland you aren't short of 50 competition (as we were very strong in 50 class when Jay & Hamish were riding & Fishe & Chris Sales before that. Miss those days).
Don't you look at my accountant.
He's the only one I've got.
Forum whore
Yea, that's the interesting thing about cylinder heads and compression set ups, particularly with gear box ratios that are unsuited to racing (GP125's,ax100's small frame Vespa's etc)
So many people (previously myself included) forget about the fact that to "copy" alot of two stroke performance stuff from racing circles is not always applicable, due to the fact on the sort of machines we use for tuning, because of the gear box ratios, require long wide power bands, where as "real" race stuff normally has 6 closely spaced gears, enabling larger exhaust port areas (for one thing) that will give you heaps more peak power (at the expense of torque).
A good example of an excellent bucket tuning motor (as we all know) is an MB100, not only for the fact that it is crankcase induction (a clear advantage), but almost as importantly, you can fit the MB50 gearbox (6 speed), and not only are you able to make good power with these engines, but you are also, with the 6 speed close ratio gearbox, able to "keep the engine in the power"..if you had a well tuned 22 P.S MB100 with an original 5 speed gear box, I suspect you would have trouble when you went from 4th to 5th gear......
But that has been covered a few times!
Interesting about the curve shape and the compression ratios/squish head.
Your thoughts (in my experience) are correct in regards to high comp (over compressed), and short "peaky" curves.
For street tuned engines, I run about 13.6:1 and actually don't use squish heads at all anymore, as I found that since I never really exceeded that ratio, a squish head was not required,(as there is little chance of detonation at this level) as well as that fact that even with lower ratios than 13.6:1 squish heads, while if used with higher compressions will produce more peak power (at the expense of power width) with lower ratios the power was the same peak, but narrower that with out.....
Basically, with a ratio of around 13.6:1, you have alot more "over-rev", and, in this situation, that is what you want to achieve!
Honestly, the curves you just posted are not bad at all (really) and personally, I believe that you can achieve something like 17 NM of torque (12.5 FT/LB) and 19 P.S with a GP125 engine, while making power for approx 2000 RPM.
Much more suitable for a 5 speed box!
Before you want to change your pipe design, if it is possible, can you make the changes to your primary compression that you discussed, get a standard (oringed) head, with compression ratio as I mentioned, and run that on the dyno.....
For the pipe design, this would be a really good reference for me!
Also, I while back (first few posts) I mentioned about exhaust port and transfer timings of 188 deg and 131 deg (respectively), which you pointed out where the same as a tuned RM125 (I think)
I really believe that this is more suitable for what you are doing....
No8 Wire Extraordinaire
MB is actually 4 speed std, although you can fit the MT50 5 speed (or MB50 6 speed).
Don't you look at my accountant.
He's the only one I've got.
Pretengineer
I don't think that the MB is crankcase induction either, The reeds go into the back of the barrel, I was under the impression a case inducted motor was when the reeds feed straight in the back of the crankcase, leaving the opportunity to play with quite significant boost port sizes and more space for transfers.
Sorry to take this off topic, what head volume do you think would be optimum for the H100 dave? I was going to set it up at about 14:1 as the gear box works well, so a narrow power band isn't a problem.
Forum whore
The 2nd pic max hp 18.3 @ 10,000rpm and max torque 10.4 ft-lbs @ 8,500rpm. Bike belongs to Chambers, and the motor is basically a standard GP125 with a bit trimed of the top of the cylinder and fitted with a RM spec pipe.
This is more the spec motor I want. Working from memary here, (my notes are at work), Specs are:-
1.75mm machined from the top of a std cylinder. "O" ringed, Ex opens 86 ATDC, 64% of Bore Width, which is std, Trans 114 ATDC, Std Inlet Opens 145 BTDC Closes 55 ATDC,
Std Head, no head gasket, Compresion ratio 7:1 with No Squish, Primary compresion 1.45:1, KX80 ignition, Ignition timing at a guess 24-26 BTDC with no auto retard, GP125 24mm carb with modified bell mouth and 105 main jet,
RM spec pipe. Max hp 18.3 @ 10,000rpm and max torque 10.4 ft-lbs @ 8,500rpm. A wide flat power curve with a little peak at the end. A similar motor with a RG250 pipe made 17Hp.
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Forum whore
A Handy Coverter:- http://www.mr2ownersclub.com/converter.htm
Yes your right, we have about 18-19 Ps and 14 Nm now (1 ft lb = 1.356 Nm ...) so 17 Nm would make this bike very drivable.
Pic 1 is Chambers GP125 and Pic 2 is a Dyno graph of the RM125 from Graham Bells book. 22.6 Hp @ 10500 Rpm and 12.3 Ft-Lb at 9,500 Rpm. 1000 Rpm between peaks.
This will be my aim 19 or so Hp and 12.5 ft/lb (now 10.5 ft/lb) with 2000 Rpm between peaks. The old trade off, sacrifice a bit of Hp for more torque and a broader power band.
So the problem is more about increasing the torque than making more Hp.
How can we use the new style of porting to increase the torque? SS90 do you have any suggestions?
.
Race it don't store it !
Hey Carl I will give your GP RS a run for you any timethe GP Sux when you compair them standard
put the gp into another frame
dan then it shows up how bad I ride crybaby:
I think I'm just going to ride the rg50 this year
Do you want a run on my 150 diesel LOL!!!
See you on Suday
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