Scooter math and the truth about top speed

Post by **noiseguy** » Sun Jun 18, 2006 12:51 pm

Where to start:

1) Observation on the tire pressure is good. The scoot's only meant to hold 180 lbs, so I'm guessing the specs guy that put in the tire pressure based it on that and it's 30 MPH top speed. Also, the primitive Spree suspension probably likes 20 PSI tires. Try running at 30 PSI to see if that helps.

2) I understand the reference to the HPV's in terms of gearing, but keep in mind that HPV's only have about 1/3 HP to work with, ever. Human powered, after all. You can get more power from the Spree plant, which was left at 2 - 2.5 HP for regulatory reasons. If you follow a HPV design, you'd create a Spree recumbent... and risk getting run over.

3) All mods you do to the pulley will be on the inner half. If you want to be more careful, you can re-space the inner half around with thin washers to maintain it's centerline.

4) As for the larger belt, I think that is done to keep from spreading the rear halves of the pulleys any more than necessary, although variator designs use this spring loading as part of the variable ratio drive.

5) Top things are pulley mods, cleaning up the intake casting, fire-cleaning the exhaust and deresticting, and increasing compression by taking .020" off the head on a lathe.

If you want to go beyond that, look at the exhaust and transfer ports inside the cylinder. If you measure them, either with a scale or degree wheel, you'll note that they're smaller than the listed port timings in the Honda manual. These could use cleaned up too. A slight raise of the exhaust port should help, and a light porting on the exhaust transition to the pipe to match.

Also, I've started to build expansion chambers, having finally broken down and bought a home welder. These work wonders on increasing top end power over the stock system. LMK if you're interested.

darat · Post by **darat** » Sun Jun 18, 2006 1:14 pm

maybe u should send me one to try out lol.. jp.

maddog · Post by **maddog** » Thu Jun 22, 2006 3:11 am

to transfer h.p. x torque into speed you need to change the gear ratio, wind creates friction and weight is also a factor, if you want speed don't get a spree!

85stroka · Post by **85stroka** » Thu Jun 22, 2006 3:55 am

maddog wrote:to transfer h.p. x torque into speed you need to change the gear ratio, wind creates friction and weight is also a factor, if you want speed don't get a spree!

winds not considered to add "friction" it's called "drag" co ask your pilot buddies.
For every 18lbs added slows you down 1 mph on a ped, Dave Toba did the test

Farfignugin · Post by **Farfignugin** » Thu Jun 22, 2006 6:51 am

yes, but drag is still considered "wind resistance" and friction is a resistatnce...but he is right about the speed part...

fulltilt · Post by **fulltilt** » Thu Jun 22, 2006 7:53 am

Not sure what maddog's three identical posts were trying to say. To transfer hp x torque into speed? Huh? You don't transfer hp into anything. Hp is a function of the bmep brake mean effective pressure) of the engine. The engine has a torque curve. The torque changes throughout the speed range of the engine. You can calculate hp from torque at any point on the curve by the equation hp=(torque x rpm) / 5252. Because it's multiplied by rpm, you could have a point after the torque curve has started to decline that actually makes more hp because the rpm has continued to climb. If the engine were hooked directly to the wheel, the torque at any speed of the engine could not overcome the factors resisting movement, (friction, drag, etc.) But torque can be multiplied, (hp cannot). So we change a gear ratio until we get to a point where we can use the power of the engine. Probably what you meant, just not what you said.

Post by **noiseguy** » Thu Jun 22, 2006 9:58 am

Exactly. I'm guessing that the Spree is batting in the BMEP = 2 range. If you look at the jug it's fins are tiny compared to the Elite 50 of the same year. It can't reject much heat.

That said, the Spree porting on the two scoots I measured DOESN'T EVEN MATCH THE TIMING IN THE HONDA MANUAL. The ports are all about 2mm short, which is a huge discrepancy. I need to run the calcs again, but for example, the advertised timing on the Elite 50 and Spree are the same, about 70 deg BBDC. The Elite port is 11.5mm tall, the Spree is 9.5mm. The 11.5mm, by my calcs, is much closer to the 72 deg BBDC timing. Both have the same stroke, and should be identical. The Elite port is also wider, but that's another thing.

fulltilt · Post by **fulltilt** » Thu Jun 22, 2006 1:59 pm

Has anyone messed with advancing the ignition timing?

darat · Post by **darat** » Thu Jun 22, 2006 5:32 pm

I think one person has.

maddog · Post by **maddog** » Fri Jun 23, 2006 10:53 pm

Hey noiseguy, did you ever get a machine shop to bore the jcc pistons, i know the mainland is far behide us but if you want speed its easy to create but it will cost ya!!!!

hrnytrtlsgsxr · Post by **hrnytrtlsgsxr** » Fri Jun 23, 2006 11:12 pm

fulltilt wrote:Has anyone messed with advancing the ignition timing?

on the dio engines most would retard the timing for better top end.There are adjustable cdi's,coils that retard,flywheels that are adjustable and some whole rotor kits. But they are all dio based although the cdi can be plugged into the spree wiring harnest. It's an FSN and will cost $150. they do have at least one at VT cycles if it was not sold yet.

darat · Post by **darat** » Fri Jun 23, 2006 11:24 pm

150$ wow how much of a top end would u get.

maddog · Post by **maddog** » Sat Jun 24, 2006 12:18 am

cycle shop class- what the * is that!

Post by **noiseguy** » Sat Jun 24, 2006 3:34 pm

Bores still need to be done up...

been concentrating on getting some stuff built for guys and getting my truck on the road.

You can manually move around the timing a few degrees by ovalling out the mounting holes on the pickup. Greg was working on a kit for this, don't know if he came up with anything.

darat · Post by **darat** » Sat Jun 24, 2006 11:21 pm

yeah i wonder if he did to.