Single Cylinder LSR Motorcycles

[Calkins]

As I'm trying to find almost non-existent Triumph parts for a streamliner build, I was thinking about a side project.  My question is, do big bore, single cylinder, four stroke bike do very good as LSR bikes?  I have and can get old Yamaha 500cc TTs, XTs, and SRs and 600cc TTs, XTs, and SRXs.  I thought about runniing an open bike, with one of these engines, at El Mirage.  So I'd be looking at a 135mph to 175mph range in A/G or A/F, 500, 650, 750.  Maybe 100hp on Alky and a superlite Speedway frame, like a 200# total bike weight.  Thought, ideas?

[sabat]

In my humble opinion, no. Because there is no difference in the rules between a 1 cylinder 500cc machine, and a 4 cylinder 500cc machine, the greater valve area of the multi-cylinder engine will make more power, all else equal. -Dean

[John Noonan]

Dean,

Unless said engine has no valves...other than say a power valve..

[Calkins]

The 500 is a two-valve and the 600 is a four-valve, twin carb, twin pipe.

I knew I would be handicapped by the lack of cylinders, but I didn't know if the lower weight and the high amount of low-end torque would help.  I'm looking at El Mirage as sortof a drag strip.

[Calkins]

I guess the reason why I ask is because I saw AHG up in the Build Dairy is building something like that.

http://www.landracing.com/forum/index.php/topic,5741.0.html

Mine would probably be the air cooled, OHC, TT600 motor/tranny, 5-speed, Alky at first then Nitro, ported, cammed, 674cc big bore or bigger, twin carbed, twin piped, blah, blah, blah...

[sabat]

I didn't think about 2-strokes, good point. That's clearly the way to go with a small motor.

For a 4-stroke, I would guess that the added weight of a 4cylinder would be more than offset by the increased power potential. Weight also promotes traction of course.

But hey, build what you like, as long as you are happy looking at it and riding it, who cares. How about a late model Triumph TT?

[Calkins]

I didn't think about 2-strokes, good point. That's clearly the way to go with a small motor.

For a 4-stroke, I would guess that the added weight of a 4cylinder would be more than offset by the increased power potential. Weight also promotes traction of course.

But hey, build what you like, as long as you are happy looking at it and riding it, who cares. How about a late model Triumph TT?

I was just asking about these two Yamahas because I have some of the stuff already.  The dirt bike in the picture is my gravel jammer, street and trail legal.  But, I could tear it apart to run.

[Seldom Seen Slim]

"...674cc big bore or bigger..."

There's a potential bit of give-away.  The 750 class runs from 651 to 750 -- so you'd be at a size DISadvantage with 674,  Stick to under 650 and you'll be as big as possible in the 650 class.  Otherwise you'll be running against Scott Guthrie records and other folks, too -- who went to the displacement limits in the classes.

[Calkins]

Here's the records.  I'm planning on doing El Mirage though.

El Mirage Records: 1.3 miles
A-G 500 - 156.925
A-G 650 - 168.488
A-G 750 - 162.000 Minimum
A-F 500 - 163.000 Minimum
A-F 650 - 167.000 Minimum
A-F 750 - 170.000 Minimum

Muroc Records: 1.5 miles
A-G 500 - 159.115
A-G 650 - 0
A-G 750 - 131.279
A-F 500 - 0
A-F 650 - 0
A-F 750 - 0

Bonneville Records: 3 miles
A-G 500 - 165.740
A-G 650 - 155.016
A-G 750 - 171.550
A-F 500 - 170.833
A-F 650 - 167.476
A-F 750 - 167.824

[sabat]

160 naked on a 500 is no joke. I'm guessing you will need a 2-stroke or a 4 cylinder to get over those gas records. Nitro may be a different story.

[sockjohn]

I was just asking about these two Yamahas because I have some of the stuff already.  The dirt bike in the picture is my gravel jammer, street and trail legal.  But, I could tear it apart to run.

Don't forget you will need speed rated tires, for the class you're entered in.  Doesn't matter if you won't go that fast, the record in the class sets the speed rating for the class.  This may be an issue with the dual sport, or it may not be.  If it takes new rims/wheels to get the proper tires, really going to take the fun and cheap out of the plan quick.

"...674cc big bore or bigger..."

There's a potential bit of give-away.  The 750 class runs from 651 to 750 -- so you'd be at a size DISadvantage with 674,  Stick to under 650 and you'll be as big as possible in the 650 class.  Otherwise you'll be running against Scott Guthrie records and other folks, too -- who went to the displacement limits in the classes.

The problem with that is he is then going for 600cc sport bike records, and any smaller and I'm guessing  going after 500c two stroke records.  Sounds like a recipe for frustration to me. 

I met a guy who I forgot his name was running a Buell Blast (pushrod) and he looked to be having as much fun as the guys running blown Busa's and didn't have to compete with the sportbikes since it was a pushrod bike, so if you're goal is to have fun, go do it.   

But if you want a chance at a record, I would get a 500cc two stroke, whether it is dirt bike or a Kawasaki triple.  The 500cc two stroke dirt bikes aren't that rare, and don't have that much demand so would be a pretty cheap option.  Buell blast's and Ninja 500's  are cheap bikes as well if budget is a concern. 

[Calkins]

I was just asking about these two Yamahas because I have some of the stuff already.  The dirt bike in the picture is my gravel jammer, street and trail legal.  But, I could tear it apart to run.

Don't forget you will need speed rated tires, for the class you're entered in.  Doesn't matter if you won't go that fast, the record in the class sets the speed rating for the class.  This may be an issue with the dual sport, or it may not be.  If it takes new rims/wheels to get the proper tires, really going to take the fun and cheap out of the plan quick.

"...674cc big bore or bigger..."

There's a potential bit of give-away.  The 750 class runs from 651 to 750 -- so you'd be at a size DISadvantage with 674,  Stick to under 650 and you'll be as big as possible in the 650 class.  Otherwise you'll be running against Scott Guthrie records and other folks, too -- who went to the displacement limits in the classes.

The problem with that is he is then going for 600cc sport bike records, and any smaller and I'm guessing  going after 500c two stroke records.  Sounds like a recipe for frustration to me. 

I met a guy who I forgot his name was running a Buell Blast (pushrod) and he looked to be having as much fun as the guys running blown Busa's and didn't have to compete with the sportbikes since it was a pushrod bike, so if you're goal is to have fun, go do it.   

But if you want a chance at a record, I would get a 500cc two stroke, whether it is dirt bike or a Kawasaki triple.  The 500cc two stroke dirt bikes aren't that rare, and don't have that much demand so would be a pretty cheap option.  Buell blast's and Ninja 500's  are cheap bikes as well if budget is a concern. 

I guess I didn't even think about running my dirt bike with differnet tires.  Would handling be scary with a stock bike at those speeds?

[Calkins]

For the frame, I'm going to do a single backbone and down tube, without a lower frame rail.  This is the way the stock frame is.  Motor mounts are at the middle of the front and the rear. What would be a suitable tubing size to use?  For streamliner roll cages, the spec is a minimum of 1.25" by .090" steel tubing.  That seems a little small, even for chrome moly, for a open bike frame.  I think that I'm going to try to use chrome moly for the final frame, maybe do a rough build in mild steel.

[McRat]

Back when I was dinking with Yamaha thumpers, you could make them faster, but you couldn't make competitive power.  This was desert racing though.  For the amount of money you'd spend trying to turn one of them up, you could just buy a more powerful engine.

Light weight is important in most forms of racing, but it seems LSR is not one of them.   

[Calkins]

I'm just wanting to throw something together, using parts I already have, to have fun with and make laps.  I don't care to much about setting a record.  I'm thinking about throwing a stock engine in it at first to get my licensing passes.  I've yet to get to El Mirage or Bonneville and I'm using this project as an excuse to get me there.