Bill,
Most of the time, I fully agree with you. But I have to take exception here.

The teeth are hard but the rest of the sprocket is not that hard. You can machine a slot quite easily with a high-speed steel bit.

You will not be going in 1 degree increments. If you are decking the head, you want to degree the cams to make up for the change in cam chain length, due to moving the cam centerline closer to the crank centerline, and to blueprint the lobe center angle.

If you did try for 1 degree increments, you would end up with a slot anyway, because it's about a 5 mm hole. You can plunge cut it, but slotting works fine and prevents scalloping the slot.

Lots of people simply elongate the holes with a die grinder. It works for the ignition sensor too, to advance the ignition timing, wtihout buying more parts.

Those of us without deep pockets, need to save money where we can. I have a mill at work and I was a machinist in a previous life, so I took advantage of it.

 

Here are a couple pictures of a Thorsten Durbahn airbox for the RC51. It is a large volume increase that results in a good midrange torque boost and about 11 HP up top with proper tuning. It seals on the underside fo the tank. Food for thought.

You wouldn't have to worry about difference in ram-air vs. float pressure.

 

Well ive been thinking about this alot.

My aluminum gastank will have a "tunnel" in the middle. The gastank will seal to a baseplate that is attached to the carbs.

The tunnel will house the air filter and will provide good volume and air flow to the velocity stacks.

I will still be using the ram air scoop in its original location to provide cool air to the airbox.


Ill see if i can have a friend machine the cam sprockets, if not ill break out the die grinder.

Should 4 degrees in either direction be enough? My head is not decked whatsoever.

 

nowhere near that much. are you trying to change the lobe centers on the stock cams?
I wouldn't change it unless you know what you want to accomplish.

 

I might as well not change anything. I was going to try and make the timing a little more accurate than the stock setup. I need an rc motor, gear drive and fuel injection.

I meant to say 4 degrees total, as in slot the hole 2 degrees each way.

Since I need to get this bike going, Ive Binned the ram air setup for now.

 

Something else to consider on ram air: It was mentioned above that the float bowls need to be pressurized. This is correct and is a must to even attempt tuning this kind of setup. Now, RCVTR posted Thorsten's airbox from an RC51 and mentioned satisfying the need for pressurization that way. I'm sorry, but that's incorrect. Pressurizing the whole carb assembly is not going to pressurize the inside. The floats will still be at the same pressure as the tank.

Additionally, when you pressurize the float bowls you now have that extra resistance to flow from the tank. This necessitates an external fuel pump in order to get flow through the float valves.

I really hope this works out for you but honestly you're jumping head-first into unknown territory. Nobody without an engineering team is going to get it right without first throwing in the towel and beating your head against a wall over and over. Honestly, I think you should suck it up and hit up ebay for some parts. Airboxes with funnels go for cheap, and dented tanks can be pulled, smoothed, and painted. I'm sure you have the ability to do that based on what we've all seen. I DON'T want to discourage you, but I've seen this project come really far in a short period of time. It would be a shame to see it come to a screeching halt because of this ram air idea.

 

+1 spend a little money and save your sanity...if you have any at 19 yrs old...I didn't
RC

 

Well for time sake iv given up the ram air idea, for now atleast.

I still have a ton of work ahead of me.

Build aluminum gastank and airbox, Build subframe around radiator. Plumb radiator.
Re build wiring harness, finish rearsets, and a million other little things.

and I cant really spend any money, Im about 6k in dept from medical bills. And I need another surgery, and dont have insurance.

 

I do have to take issue with this. Nitrided anythings are surfaced hardened everywhere. I could be wrong, though, and the gears could be laser or flamed hardened just on the teeth. My guess is that they are not using either of these processes.

Also, if you are using a high speed steel bit, what are you using it in, a die grinder?? If you are making an argument for exactitude and using a die grinder, hmmmmm.

How are you determining your timing change, are you using a degree wheel? Or where you able to provide some type of measurment on the gear and cam to align?

 

the surface may be hard everywhere, but not the material under the surface.
I may have used a carbide cutter, I can't reccall.

I mounted the gears in a rotary table on a vertical mill, located the existing hole, plunged through it, then side-milled a groove ~2 degrees in both directions. The gears are thin enough that you can pocket mill to full depth in a single pass. It cut like butter.

The mounting holes are for clamping only. Not for locating. elongating holes with a die grinder is perfectly legitimate.

A degree wheel.

 

Plunge cutting through the surface is the difficulty that I am talking about. When we degreed cams on the 600f2 we serated the slot for timing changes so that we could make quick changes without pulling out a degree wheel, removing side covers, mounting a needle to the engine, etc etc.

Yes the bolts only clamp, but if a person is unwilling to go thru the work that you did, degree wheel, dial indicator, and a ton of time in setup, slotting ~2 degrees is completely inaccurate and a waste of time for them.

I had three hours into measurements when I mapped the cam profiles for the exhaust and intake, after I got the setup. I would say that someone with less experience could spend that amount of time measuring their changes to cam timing and see very little reward for it if they don't get things right. .010" off the head will result in a very miniscule change. I ran the calculations for a 2" gear, and it was .010 degrees. Maybe I am doing my math wrong, but machining the heads doesn't really seam like its a major change, chain stretch could be greater.

 

Fair enough.

I get 0.3 degrees for a 2" gear radius. Probably not a big deal. I wanted to blueprint mine. I went with the recommended lobe centers for Moriwaki cams.

I milled the slots long enough that I wouldn't run out of slot before I got it adjusted. +/- 1 degree would be more than adequate, unless you are making changes to the cam timing to change the amount of overlap.. That may have been all I did. It was 4-5 years ago.

I'm not arguing. I think we're on the same page again.

 

Thanks for the intellectual interaction. I just worry about this as my students chase the same crazy ends, like putting dual exhaust on a yzf-250. I told them to buy a honda, we can't beat the aftermarket in parts or performance. even if it was .3 degrees of change, for the average consumer, this is not something that would effect them. The chain stretch has a greater effect, and chasing .2 hp with potentional failure is not worth the time of a undedicated individual. The fact that you put a degree wheel on yours is beyond what most people can grasp. Have a good week.