[jbranson]

Aaron,
There are only two covers that I've noticed. Vert style and sloper 160/175 style. I think the CL175 sloper covers might have a larger breather pipe attached but all the sloper covers are interchangable as far as bolt patterns go.
I'll take a look at all mine...the CL sloper may be a bit more heavy duty....the engine case rear mounts changed from the 160 to the 175 sloper so maybe they beefed up the cover too.
JohnnyB

 

[jbranson]

Yep..the CD175's may have used a different looking cover...I know I had one around here somewhere.

JohnnyB

 

[jbranson]

Wow, looks like the oil holes may be offset about the same amount as the change in incline of cylinders between the vert and sloper. That's a new on one me. It's just dumb luck that I've kept the oil covers with the side cover they came on when I've built engines.

That top cover came off a 68-69 CA175 with a pressed steel frame.

Do you need regular sloper cover...I probably have one lying around.
JohnnyB

 

[jbranson]

Aaron,
I take a look and let you know on Monday...if I have one...which I probably do, I'll send it on Tues.
JohnnyB

 

[jbranson]

Aaron,
You cracked the head cover in a get off??
Wow...that had to be a pretty hard hit, hope you checked the forks and frame. Something had to move quite a bit to crack that head cover.
They leak pretty easy though...after I got Hiroshi's bike running Mary noticed an oil leak on the head cover. We screwed around with it and found two tiny pieces of old gasket stuck to the cover and that was enough to make it leak. Surprised me...I figured with eight head bolts holding it down, and being up high like that it would never leak.
You've got one on the way on Tues. I found three of them in my spares.
JohnnyB

 

[jbranson]

Ohhh...ok, that makes more sense.
JohnnyB

 

[jbranson]

Aaron,
By STATOR...I hope you mean ROTOR...? Cause I don't do anything to stators...but I do change the taper on the rotors.

How to you like the VP U4? I've wanted to try it, I think it's probably the best fuel for our bikes. Where are you getting it? Bring enough for me the next race

I didn't get a chance to check the cam timing on that new megacycle cam you sent...I have a feeling their new machine is a lot better than the old one and the cam is probably very close.

At some point I'll come up with something for cam timing. I've seen several methods....seems to be the easiest might be to use a reground CB200 cam with a modified CB175 sprocket on it...that way the cam is already set up with the flange and bolt holes, you just have to bore out the center of a 175 sprocket and cut some slots. Of course it means buying a new cam. Might be possible to sell good used cams to other 175 racers. I'll have to take a close look at the CB200 cam compared to the CB175.

I'm guessing a couple or three degrees of cam advance might get us a little bit more power...but we'll have to re-clay the pistons again too.
JohnnyB

 

[jbranson]

Just looked at the VP U4...only 92 octane....might not be the best for high dome old engines like ours....I'd feel better with something like 96 octane.

Have you melted anything with the U4 yet?

JohnnyB

 

[jbranson]

Aaron,
Usually I only consider static compression, it's the defacto standard for determining engine compression. Too many variables and unknowns to get a good fix on dynamic compression.
So many considerations of cam timing, gas velocities, intake and exhaust dimensions and behaviour.

As for valve size...the bottom line is an engine is an air pump, the more air you can get in and out (which carries more fuel) the more power you make. In my case the larger valves are the result of computer flow bench testing that showed the valves were the main restriction point for air flow.

I'm sure there are theoritical sweet spots for intake track diameter (gas velocity), valve size and cam timing...but for now I stick with the known routes to improved performance. Sorting out optimum gas velocities and such will provide improvements I'm sure, but not until the fundemental weaknesses of the engine are addressed, such as air flow and compression ratio. As engine development goes we are only a fraction of the way to the end game. Tweaking gas velocity for greater than 100% volumeteric efficiency with intake tract size and exhaust pipe size are just that...tweaks...first we address the major factors that are limiting our hp. Primarily inlet air flow, compression and displacement.

I'll review the formulas for dynamic compression and see what I come up with, but that's a guessing game I think at this point. Real figures would requre a lot of data on intake charge behaviour, combustion chamber dynamics, cam timing, and exhaust system simulation. etc.
JohnnyB

 

[jbranson]

Well now you've kind of hit on the rub of DCR.

I'm sure you've heard that compression doesn't make hp it make torque. Ever notice that stock cams make more torque? Now notice that stock cam intake timing closes the valve sooner....increasing DCR...which increases torque....you end up with a torquier cam.

Ok...now, problem is we need to get air inside the engine too...which means high valve lift, long overlap...intake valve stays open longer....reduced DCR. So...how to we keep DCR up and still keep the intake valve open long enough to get the air we want inside the cylinder? Well....we increase Static compression ratio (SCR). Static compression ratio is a factor in calculating DCR so if we can get SCR higher...then we can run longer valve timing and keep DCR high.

The problem with "torque" cams that close the intake valve quickly is that at high rpm, where you want to produce HP as opposed to torque the cam timing is preventing enough air from getting into the cylinder. As with most things it's a compromise. Yes you can run the stock cam for greater torque...but it will limit rpm...because of reduced intake flow...thereby limiting max hp.

In the case of our engines the ideal would be to change cams (or maybe cam timing) for individual tracks. A stock cam might perform well at Loudon, a 122-20 at Mosport, a 122x4 at Bonneville Salt Flats.

If we can increase cam timing and close the intake sooner we might get more torque....decrease cam timing and keep open later maybe more max hp...tough to tell when you are moving the the exhaust valve timing and intake open timing at the same time.

This is why turbo and surpercharger engines can get away with shorter cam timing and still make hp....they can close the intake valve sooner for torque...and still stuff in the air they need with boost.
JohnnyB

PS. I'm pretty sure DCR above about 8.5:1 starts getting dangerous on naturally aspirated vintage engines. As DCR goes up combustion chamber temp goes way up.


Edited by - jbranson on May 04 2005 11:45:04 PM