Streamlining CBR600 for Bonneville & Vetter Challenge

[redyaris]

Doing What You Can, With What You Have

As importasnt as the work that Craig Vetter does with the Vetter Challenge is; I think it is just as important that some one demonstrat that any bike can be streamline for very good effect. There are millions of bikes out there that are not 250's, in fact most of the bikes on the roads & highways are between 500 and 1200 cc. So that if I can demonstrate that even a 500 - 650 cc bike can get very close to 100 mpg, and carry 4 bags of groceries, under Vetter conditions, people will be incuraged to try it themselves with any bike they have on hand...

[renault_megane_dci]

Nice project, starting handsomely.

I like the "atkinsoning" concept proposed by one guy but that is definitely not the way forward as far as high speed trim is concerned.

Also a swith on / switch out atkinson cam timing setup is not DIY friendly, what is more on a (usually very optimised spacewise) bike engine.

[redyaris]

My VT500 at 5000rpm, in 6th gear, at around 75mph gets, aprox 87 mpg.
For the CBR600 to get over 100mpg it will need to spin at 3000rpm - 3400rpm at 75mph.
The question is will the CBR600 engine be happy at this low an rpm under these conditions?
My GS 500 did not like going below 3500rpm...

[renault_megane_dci]

Originally Posted by redyaris

My VT500 at 5000rpm, in 6th gear, at around 75mph gets, aprox 87 mpg.
For the CBR600 to get over 100mpg it will need to spin at 3000rpm - 3400rpm at 75mph.
The question is will the CBR600 engine be happy at this low an rpm under these conditions?
My GS 500 did not like going below 3500rpm...

Erratic running at low rpm is caused by air flow reversion. It is caused by too much overlap and aggravated by too low velocity in the runners.

So, low rpm operation can be improved through less overlap (free) but might require cam regrind towards less duration (can prove expensive).

Smaller carbs can help in this matter (check Suzuki Inazuma 750 vs GSX-F 750)

Also, I might be wrong but a much bigger load through very tall gearing means your carbs are more open to sustain the speed despite less rpm hence more velocity.

Finally, I believe a guy called motoman partially filled his head inlet tracks with epoxy to improve mid range torque.

[serialk11r]

Originally Posted by renault_megane_dci

Erratic running at low rpm is caused by air flow reversion. It is caused by too much overlap and aggravated by too low velocity in the runners.

So, low rpm operation can be improved through less overlap (free) but might require cam regrind towards less duration (can prove expensive).

Smaller carbs can help in this matter (check Suzuki Inazuma 750 vs GSX-F 750)

Or one can just move the position of the stock intake cam. Will shift the powerband a bit, but most of the horsepower should be there. Bike cams are naturally low volumetric efficiency at low speed, they just have too much overlap to be economical. Bike compression ratios are pretty high so I don't know how worthwhile cam regrinding would be.

EFI would help though...

[sendler]

This could be a fun project if you don't end up spending too much. A 600 supersport engine is probably one of the worlds most inefficient engines at the 15 hp it takes to commute at highway speed. It will be interesting to see the best this bike can do even with radical streamlining and gearing changes. 70 mpgUS?

[renault_megane_dci]

Originally Posted by serialk11r

Or one can just move the position of the stock intake cam. Will shift the powerband a bit, but most of the horsepower should be there.

"Less overlap (free)" was cam phasing (in my head ...)

[redyaris]

The simple way to reduce duration and valve over lap is to increas valve clearance.

The stock final drive is 15T/44T, the furthest [available] from that is 17T/34T.
At 70 mph the change in final drive will drop the rpm from 5200rpm > 3500rpm.

The stock FE is 48mpg combined.

[3-Wheeler]

Originally Posted by redyaris

My VT500 at 5000rpm, in 6th gear, at around 75mph gets, aprox 87 mpg....

Red,

I'm having a hard time believing that you actually get 87 mpg at 75 mph!

I have an old VF500 Honda that gets maybe 85mpg tops at 35 mph. And this includes some EOC as well, along with summer heat and thinner air density. On the highway at 55 mph, it only gets 70 mpg. My guess would be 55 mpg at 75 mph.

My Honda Insight which gets 120 mpg in the same summer conditions as the motorcycle, "only" gets 100 mpg at 55 mph, and I doubt it would still get 87 mpg at 75 mph, even with smooth undersides and long tail.

Something sounds fishy about your claim. Just thought you should know.

Jim.

[redyaris]

3-wheeler
I will be running the Vetter Challenge Vegas to Barstow on the 18 of November at which point we shall see...? You could be right...?

The sample size for the 75 mph / 87mpg is one, and that was a short fill, with no account for wind speed and direction yet that is what I got. So until more test runs, this is the only way we will know/find out...

The calculater in the Tools is on your side...