Formula 5 question?

[nudemetalz]

....esp in RS125 frames ay

I looked at Steve's RG/TZR50 on TM and have been considering it.

[Henk]

Hey Nudz, why not just find an RG50? I hear they go alright & are light & cheap.

And like bloody hens teeth it would seem, I've been trying to find one for bloody ages.

[nudemetalz]

They were a dime a dozen back in the 90's.
Back then there were 5 of us that owned one each and we used to do own our race around the Port Hills.
Great fun machine

[F5 Dave]

I took my road one to Cold Kiwi from wgtn 6 times.

[F5 Dave]

....esp in RS125 frames ay

I looked at Steve's RG/TZR50 on TM and have been considering it.

oh yeah, can't see it. He's moved out of wgtn now.

Wonder what happened to Chris Sales old one. Chap in Msterton bought it, rode it a couple of times & hasn't been back. That was fast. I could ask Mike.

[jasonu]

They were $1000 each back in the 90's.

Which is what I paid for David Diproses race proven RG50.
I soon found the std ignition was not the way to go and for another $250 DD sold me the RM80 ignition he had removed from the same bike just before he sold it to me. Cheeky buggar!

[F5 Dave]

They were $1600 brand new & I couldn't afford one. When I finally could my road one was $600 & later one which was being ridden to work was $450 & a week later a race bike.

Think I got $500 for my road one when I sold it.

[husaberg]

Been doing a bit more research lately.

The XL100S engine is 53mm x 45mm (as Husaberg points out)
If you can get an XL75 engine (same as an XR I believe) the bore/stroke is 48mm x 41.4mm. If it can be resleeved to 56.5mm (most 125 4T SOHC Honda's are a 56.5mm piston) you get a capacity of 104cc.

You can get some serious revs without excessive piston speed - ie 14,000rpm still under 20m/s.
Wondering though, even with a hot cam, piston compression etc if the 20mm carb restriction would negate any advantage?

A couple of issues here the stuff you are suggesting of course can be done but destroking engines is rarely a good idea as the comp ratio and the resultant combustion shape if it is remedied suffer not to mention the extra costs involved also you will be mixing 3 gudgeon pin sizes there a least.

Cams are available to suit but do cost these engines are used by the NS100 HRC or what aver it is called and used considerably in flat track and other classes inc Super-moto there is even a Honda std supermoto styled model sold in 50 80 and 100cc form. APE I think. The Dream 50 is based on a similar bottom end (the CB50). They rev on the counter in std 100s form to around 12000rpm if not higher. so don't worry about the stroke and the cams being sohc to much.
I will finish the post later.

[richban]

A couple of issues here the stuff you are suggesting of course can be done but destroking engines is rarely a good idea as the comp ratio and the resultant combustion shape if it is remedied suffer not to mention the extra costs involved also you will be miking 3 gudgeon pin sizes there a least.

Cams are available to suit but do cost these engines are used by the NS100 HRC or what aver it is called and used considerably in flat track and other classes inc Super moto there is even a honda std super moto styled model sold in 50 80 and 100cc form. APE I think. the Dream 50 is based on a similar bottom end the CB50. They rev on the counter in std 100s form to around 12000rpm if not higher. so don't worry about the stroke and the cams being sohc to much.
I will finish the post later

Kevin used that flat track honda grind my old Vespa. And that was a weapon. The question is how big can you go on the valves coz that may be the limiting factor in making an engine to foot it with a fast 2 stroke. If you made 140hp per liter from a 2 valve old piece of crap like that, I would be very surprised. Can't remember what the stroke was but I am sure it was long. So it might have an edge in low end power over a 2 stroke. Best thing to do is just put a skinny fast kid on it and the job is done. I've seen a few of them around lately.

[Rick 52]

Kevin used that flat track honda grind my old Vespa. And that was a weapon. The question is how big can you go on the valves coz that may be the limiting factor in making an engine to foot it with a fast 2 stroke. If you made 140hp per liter from a 2 valve old piece of crap like that, I would be very surprised. Can't remember what the stroke was but I am sure it was long. So it might have an edge in low end power over a 2 stroke. Best thing to do is just put a skinny fast kid on it and the job is done. I've seen a few of them around lately.

Yes if your not quick enough to bring a trophy home yourself..Put a 54kg 13yr old on a XL100s ported and a inner rotor ignition bigger header powered RG 50 framed F5 bike and Bobs your uncle !!or your son in my case..
Very pleased he rode very well and got better through the day ,The bike is easy to ride and is a brilliant first bike to learn on but is never going to be a match for a RG or Derbi powered RS ,When he can ride this to the limit we can put him on a competitive bike and he wont be in Bgrade bedlam for long

[richban]

Yes if your not quick enough to bring a trophy home yourself..Put a 54kg 13yr old on a XL100s ported and a inner rotor ignition bigger header powered RG 50 framed F5 bike and Bobs your uncle !!or your son in my case..
Very pleased he rode very well and got better through the day ,The bike is easy to ride and is a brilliant first bike to learn on but is never going to be a match for a RG or Derbi powered RS ,When he can ride this to the limit we can put him on a competitive bike and he wont be in Bgrade bedlam for long

Let me know if you want a new cam for it. Might be able to get a good deal for an up and coming youngster.

[husaberg]

Kevin used that flat track honda grind my old Vespa. And that was a weapon. The question is how big can you go on the valves coz that may be the limiting factor in making an engine to foot it with a fast 2 stroke. If you made 140hp per liter from a 2 valve old piece of crap like that, I would be very surprised. Can't remember what the stroke was but I am sure it was long. So it might have an edge in low end power over a 2 stroke. Best thing to do is just put a skinny fast kid on it and the job is done. I've seen a few of them around lately.

I guess the tracks he's planing on racing he won't need GP bike power levels. It could make a decent bucket on a tight track. Open track different story.
Given a bit of time on the net at powroll, TB etc he could get a lot of ideas a lot of pistons in the right kind of spec are available for pit bikes etc.
http://www.ooracing.com/store/index....&productId=601
http://www.akunar.com/PRO_PISTONS.htm
Have a look at DR atv for piston designs.TKRJ etc

http://webcamshafts.com/mobile/motor...)_sohc_2v.html
http://webcamshafts.com/mobile/motor...)_sohc_2v.html

Well it looks like you can cram in some decent size (by 2 valve Honda standards anyway) valves in one at least. I say Keep the crank stroke std.
bump up the comp sort out the timing both valve and ignition it would be a fun little bike. One of those pit bike inner rotors probably as the guy above fits on easy.

Yes support the local guys with regards to cams too but it can give you ideas with what is done overseas.

[richban]

I guess the tracks he's planing on racing he won't need GP bike power levels. It could make a decent bucket on a tight track. Open track different story.
Given a bit of time on the net at powroll, TB etc he could get a lot of ideas a lot of pistons in the right kind of spec are available for pit bikes etc. Have a look at DR atv for piston designs.TKRJ etc

http://webcamshafts.com/mobile/motor...)_sohc_2v.html

That valve is not as small as I thought it would be. Is that standard inlet 24mm? The valve should not limit power up to about 14 - 15hp. So a well designed cam good compression and you should see improvements.

[husaberg]

That valve is not as small as I thought it would be. Is that standard inlet 24mm? The valve should not limit power up to about 14 - 15hp. So a well designed cam good compression and you should see improvements.

I have seen them opened up and was surprised by the sizes. but they have a flatter combustion chamber compared to the traditional Honda singles.
The real surprise is the size of the CB50 ones they are nearly as big. the xr75 was basically Honda's race motor at the time bigger bore and shorter stroke than the 80 which it predates. According to some the 75 head flows better too. There is a huge amount of info on the net about them and they have there own tuning industry. For a F5 they would be fun I was going to do one at one time but my father gave my old bike away or loaned it to someone whatever when i went to grab it it was gone. They were real revers compared to the std style 100 and 125s etc.

[nudemetalz]

I have also had a CB50 at one time (as well as a CB125T)..and was surprised at how well it went stock. It revved to 12K without much effort, even with the long long long inlet and piddly carb.

Hmmm,...XR75 head on a CB50, huh......damn you, Husaberg for putting all of these ideas in my head