Streamlining CBR600 for Bonneville & Vetter Challenge
 

I have a 1988 Honda CBR 600 that had a damaged fairing that needs replacement. So what I plan to do is build a dustbin type fairing with cargo space for 4 bags of groceries, and see if I can get into the 150 mph club at Bonneville and then get over 100mpg at the Vetter Challenge.

The numbers from the aero/rolling resistance calculater are

Wt 660 lbs
Crr 0.015
Cd 0.30
A 6.5 sq ft
CdA 1.95ft/0.18m
Eff 22%
Dr Tr 95%
Para 500 watts


This should get me 101.26 mpg @ 65 mph, and should need 49.5 bhp at 155 mph the bike is supposed to have 85 bhp.

Looking forward to the build and seeing it in person at Bonneville:thumbup:.

The first things on the to-do list are fit up belly pan and make apropriat brackets, then make new lowered seat pan; this should lower the seat height and rider by about 3" which will reduce frontal area by about 1/2 sq ft from the stock set up.

what?

I, for one, would like a wide dustbin fairing.

Air tech has narrow ones that, though they may be period correct for vintage racing, are not necessarily what an everyday rider would want for big MPG numbers, or wind protection outside of a full tuck on a skinny 125.

Redyaris, you pick some tough challenges. You teach us alot about bike building and provide good discussion on engine tuning larger engines for MPG.

Seems that an advanced design engine with variable valve train, atkinson on demand and displacement on demand and advanced spark and fuel management systems and wide or dual ratio transmissions would be a large contributor to your goal.

Yousta be the bike guys got all the high tech, now it's the car guys. Even in B segment cars!

beatr911
The dustbin fairing for the CBR 600 will be 24" wide at the front and 20" wide from behind the rider tapering down to an 8" wide rear bulkhead for mounting license and lights. the top of the rear cargo space will be lower than on the VT500 and round on the top in order to reduce side wind affects. I find I am more interested in what I can do with the bikes I own than simply going with the bike best suited to win the vetter challenge. In fact I find I learn quite a lot from this approch, which then gets applied to the next project. the final project will be a WR250 in a year or two, that one will be an all out attempt to win the Vetter Challenge over all...

Usually shoulders and hips are the same width: 20-22 inches. This can be the widest part of fairing. The lowered seat height should be 27 inches. Decide if you want to lean foward or lay back on the bike and arrange the controls to fit you comfortably. A body of rotation formed from a 5:1 aspect wing profile should minimize drag. Figure in some angle of attack to gain a bit of downforce for stability at high speed. For Bonneville consider some extra rear fin area. Internal flow should be ducted to reduce drag. Look at aluminum spars and ABS skin. Once the aero package is determined, power requirements will be known so tuning and gearing can be optimized.
Sound like a great project.

I have chosen to lower the seat height to what can be accumplished without cutting the frame, this is about 2" - 3" which will give me a seat height of 29" +/-. I will be leanig forward, but some what less than stock, because of the lower seat height. I will not add any rear fine area as that will cause unnessisary affects from cross winds in normal raod riding, in fact I will be trying to reduce the rear side area to that which will accomidate 4 bags of groceries. the top of the behinde the rider cargo space will be a semi-circle; again to reduce side wind affects [at Bonneville if there is more than a 3 mph cross wind the runs are postponed, not so on the road...]. Much of this is from what I have learned from my VT500 project over 3000 miles. I will be using the same basic design as the VT500; which is aluminium skin over aluminium bulk heads. Much more care will be directed toward internal air duckting than with the VT500. On the CBR 600 the radiator is high and wide which will make ducting easier, and the front fender does a much better job of streamling the front wheel/forks. The transvers inline engine layout make cooling easier than with a V-twin Layout.

I have been thinking about the 4 bag cargo space and where to put it. I would like to lower the overall height of the bike to reduce side wind affects, and what I have come up with is that the rear cargo section should start out at 24" wide so that the four bags of groceries can be placed lower. In order to do this I need to place the bags wider apart and lower down beside the wheel travel zone. This may also be the solution for a recumbent layout. I doubt that the additional width will be much of an aero penalty.

Yaris,

Couldn't have said it better myself!

Very good approach, especially on the first pass of a large project!

Jim.

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...

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.

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.

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...

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?

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

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.

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.

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...

Wich is only really suitable on engines with rocker arms.
I believed the CBR 600 was a DOHC with the cams on top of the valves.

Anyway, cam phasing sounds like it has more potential (angle wise) and is not detrimential to durability wich valve clearance increase can be.

Of course cam phasing needs the cam sprocket to be trimmed wich is not always possible and always more fiddle than enlarge valve clearance on a rocker arm setup.

That is a nice range of ratio !
I wish I could have such a potential (15/43 to 16/37 tops)

bI think reducing lift isn't that big of a deal since at idle you're pretty screwed no matter what in terms of charge motion and bikes run at pretty high rpm otherwise.

The cams are chain driven right? I guess the teeth are quite big then. Bike cams have a giant amount of overlap, so you could probably get away with just shifting the cam position by one entire tooth, but if that one entire tooth is like 20 degrees then the later intake valve opening could induce quite a bit of pumping loss at higher rpm. From looking up CBR600RR cam pictures on google though, I'm counting like 36 teeth or something on the cams, so one entire tooth might not be so bad at 10 degrees. The later valve closing would push the power peak up quite a lot though since bike cams close pretty late already...might not be bad for top speed run :)

36 tooth sounds familiar for cams in general.

I might be wrong but I think whatever you do on a motorbike engine is detrimental to top end, since those engine are very optimised.

Delaying the inlet would have the effect of "atkinsoning" the engine though, wich should be good for MPG but bad for high speed.

QUESTION :
Is your goal to vastly improve FE while not affecting top speed ?
OR
Is your goal to reach a given MPG (100 IIRC) and try to get as much speed as possible ?

If you are looking for the second option, the compromise is gonna be trickier I think ...

I don't think this is true. Anything with fixed cam profiles isn't optimized anywhere because it's a compromise for everything. With phaseable cams you can have 1 optimal operating point (for power), and an optimal "curve" for efficiency. For example the CBR600RR has a 15k+ rev range, peak torque at 11k, peak power at ~13k. BMEP at power peak is actually somewhat poor considering how much overlap is available.

Car engines with close to zero overlap at the top end can achieve higher BMEP at peak power (typically 100Nm/L ish), though car engines don't rev as high so it's a little easier to hit higher BMEP, though if you look at liter bikes the story is still the same. By retarding the intake cam on a bike, the "midrange" (which is like the 7-11k range or something lol) will suffer a bit but the very top end probably gains a little. All in all, a peakier powerband, but possibly more peak power, and less torque down low but better combustion stability from less overlap. At least that's what I think should happen.

Bike engines have so much duration that they're essentially already "Atkinsoned", but there's way too much overlap for good part throttle efficiency.

Power band and over lap is not just a matter of cam timing. Cam duration is the same regardless of where you time the cams and could only be optimized for a lower rpm with a re grind. Changing the timing could help though.

[QUOTE=renault_megane_dci;338709]Wich is only really suitable on engines with rocker arms.

Not true[/COLOR]
Cam phasing done right requires more time and effort than I am willing to spend on this project. It would be cheeper and better to get a cam regrind with less overlap and duration. I doubt I will do either...

Doing what I can with what I have is the objective.
Mostly with stream lining...

The cams turn at 1/2 engine speed so 10 cam degrees is 20 crankshaft degrees.

It usually isn't difficult to slot a bolt-on cam sprocket to allow timing adjustments, and there are aftermarket sprockets for many sport bikes that come pre-slotted.

cheers,
Michael

Sure, but the fact is that the lift and closing points appear to be much more important than the overlap or else car engines wouldn't be making much power. Scavenging helps but the closing point is matched to the intake harmonics which has a bigger influence on volumetric efficiency.

By moving the cam the idea is obviously not to optimize it for a lower rpm, it's to reduce the negative effects for efficiency and combustion stability at lower rpm of having large overlap (which possibly further trades off more low end torque), and possibly increase top end power (would depend on specs).

What a crowdy audience about this engine tuning thing !
Good thing RedYaris tolds us he doesn't want to mess with the engine internals.

I suspect that we can agree that a 4 cylinder 600cc, 85hp @ 11,000rpm motorcycle engine is not the best choice for a fuel economy bike, and no amount of internal engine modifications will do all that much good without spending more money than it is worth. One would be much further ahead buying a used bike that is more suited to the task.
As I own the bike allready and my choices are sell it for peanuts, watch it rust away, or streamline it and see what that does, I have chosen to streamline it to see what a sport bike would perform like today if the FIM had not baned dust bine fairings in 1957...
If I can get close to 100mpg in the Vetter challenge, and get into the 150mph club at Bonneville then mission accumplished.

I have the under tray done and will install it this weekend and begin work on the front side panels. I have the 34 tooth rear steel sprocket, which will be paired with the 17 tooth front sprocket, to reduce the engine rpm by 30%. It will be interesting to see how low this bike can go on the fuel economy scale. I will post some more pictures soon.

Here are some pictures of the progress so far. In my designs the under tray is very important in that it is part of the suport structure for the streamlining/body work.

Very interesting read, redyaris! BTW, how did you do in the Vetter?

Redyaris, great fab work. Looks like it will be very strong. Kinda sounds like you are making a bit of an exoskeleton structure.

Other than gearing, any other changes to the engine, driveline?

Stan
With my Honda VT500 Streamliner I got 73mpg on the 225 mile 2012 Vegas to Barstow Vetter Challenge. I will be doing some small improvements to see what can be achieved with no gear ratio changes [due to shaft drive] and then I will look into having some gears made for the VT500, to change the primary gear reduction by 20% - 30%...

beatr911
I have no plans for changes to the engine or the drive line other than going from 15/43 sprockets to 17/34 sprockets. The rear frame is so much more rigid with the new support struckter, bolted onto where the passanger foot rests used to be bolted on. I am wondering at this stage how the bike will behave from stand still, especialy starting on hills, with the 30% reduction in rpm.

redyaris,

I'll bet you will get used to it pretty quickly.

I changed the gearing on my rear sprocket from a 43 tooth to 34 (26%) and it took only a short time to slip the clutch that little extra.

Jim.

Here are some pictures of the slow progress on the CBR600, and a picture of a home made wind tunnel buit by a friend of mine for a science olympics event for junior high and high school stundents. the students where given a 3"x3"x9" long peace of styrofoam insulation and where challenged to build a "car" like object, and the winner would be the team that had the lowest drag as tested in the home made wind tunnel. the original block of styrofoam had drag of 100 the best "car" had a drag of 31. After the event one group asked if they could improve on there design and they managed to get down to a drag of 26.
There is now a group of high school students who understand basic aerodynamics...

not only understood but practiced and it will stick to their mind that much better !

Very cool! That wind tunnel looks like a replica of the Wright Brother's first wing tunnel.

http://wright.nasa.gov/airplane/Images/tunnel.gif

Hey, can you use it to tuft test a section of the fairing at a time in your shop?

Oh, as a baseline, what is the stock potential of the CBR600? A co-worker just purchased an F4i and appears to be getting our sickness. He normally drives a diesel monster truck.