Pro Motor Cowling Design Question

[Lights]

Sam

I know that Sam. This is not a pissing match man. And it is not rocket science either. My last two 125cc Pro motors started out as a Yamaha TZ Road race 125cc cycle motor. Which burnt gas not methanol. I inspected a VRP 125 and a Yamato 500 pro motors heads to make my heads. Them motors had the same size bore and stroke as both of the motors that I built. They were VERY VERY close to the same squish band depth and head volume as the stock heads from the gas road race bikes. So It can be done don't over complicate it.

Mark

[sam]

I know that Sam. This is not a pissing match man. And it is not rocket science either. My last two 125cc Pro motors started out as a Yamaha TZ Road race 125cc cycle motor. Which burnt gas not methanol. I inspected a VRP 125 and a Yamato 500 pro motors heads to make my heads. Them motors had the same size bore and stroke as both of the motors that I built. They were VERY VERY close to the same squish band depth and head volume as the stock heads from the gas road race bikes. So It can be done don't over complicate it.

Mark

Would you mind demonstrating this with your motor? 3 laps

[Lights]

No problem, I would be glad to. But let's make it four laps. That is what I am use to running. I should have my new hull ready for the Pleasant Prairie WI race. You want to come up and see it run?

Mark

[Al Peffley]

Reviving this Thread

There is a distinct difference between the Dickfors cowling design and the Mostes/Betta designs for O-250 (see the excellent Bitterfield, Germany UIM Formula 250 racing photos link on this website). Is the cowl built to a builder's or owner's specs, or both? Both of the European hulls are fast...

Al

[David Weaver]

May Also Depend Upon...

There is a distinct difference between the Dickfors cowling design and the Mostes/Betta designs for O-250 (see the excellent Bitterfield, Germany UIM Formula 250 racing photos link on this website). Is the cowl built to a builder's or owner's specs, or both? Both of the European hulls are fast...

Al

The Carbs being used on the engine. I would use a different cowling design to an extent for Mikuni carbs than for Delardo. Mikuni's seem to prefer somewhat disturbed air under the cowling, while Delardo's seem to prefer still air within a tighter box.

[pro350hydro]

The Carbs being used on the engine. I would use a different cowling design to an extent for Mikuni carbs than for Delardo. Mikuni's seem to prefer somewhat disturbed air under the cowling, while Delardo's seem to prefer still air within a tighter box.

I AGREE!

Sattler

[Al Peffley]

Thoughtful Inputs

Thanks, I may need to add two small air intake slots on the sides of my new cowling to get the air disturbance effect for my Mikuni's...especially in late summer, with hot/humid weather and stagnant air conditions.

Al

[Al Peffley]

Cowling Extension Mod with Intake

I would like to modify my used short cowling into a longer cowling with an intake duct like the ones on the Betta and Mostes hydro cowlings. Does anyone know of a good fiberglass craftsman who can make me a light weight cowling that is located on the west coast? Would it be better to just have a new cowling made rather than modify my existing short cowling with a front end extension? I need that "disturbed air effect", since the motor I will be using has Mikuni carbs, not Dellortos.

Al

[tommat]

I would like to modify my used short cowling into a longer cowling with an intake duct like the ones on the Betta and Mostes hydro cowlings. Does anyone know of a good fiberglass craftsman who can make me a light weight cowling that is located on the west coast? Would it be better to just have a new cowling made rather than modify my existing short cowling with a front end extension? I need that "disturbed air effect", since the motor I will be using has Mikuni carbs, not Dellortos.

Al

You might get hold of Corey Sampson in Spokane. He has made cowlings for our Apel's and is quite adept at working with fiberglass.

[Tim Small]

Disturbed Air Effect

Disturbed air effect? For what?

[David Weaver]

Do Not Know Why

Disturbed air effect? For what?

But, it work mo' better. Brendan Vishoot has all kinds of problems with his 125 VRp until we got him to remove a piece of board that created a small box (this was located right in front of the carbs). Thereafter, no mo' problems and he took a second and third)

[Al Peffley]

Great Response - Thanks

I believe you, David. I have owned both designs of carbs on motorcycles, boat motors, and a car (I changed out my leaking Solexes to Dellortos on a '69 912 Porsche). I have seen one racer use cylindrical motorcycle K&N filters (maybe for a Harley custom chopper application?) attached to the front of his Dellorto carbs to reduce the chance of a water intake. That application will certainly work to eiminate turbid airflow at the carbs' intake bezel. K&N will make special order filters on request. The airflow information in the response on this thread should give them enough info to select an optimum filter surface area spec for this application (thanks for sharing your calculations).

As I said earlier in this thread, I noticed the Demler team using a large black plastic plenum intake box inside one of their cowlings similar to an injection system intake box on a race car (looks like it also has some sort of adjustable, flap-type door control line on it if you blow up the side-view picture for a closer look). I don't know of anyone (except possibly Rossi by his comment earlier and Demler Racing, via the dockside photo) in the US that has really tested the flow characteristics of different cowling shapes on different style carb's performance. If they have, I'm sure they don't share a lot of the test results for competitive advantage reasons.

If corner punch performance drops on my hydro using a cowling, I will need to fabricate a more protective airbox for my Mikunis -- the unintended ingestion of max water over and around my stock Yamato carbs cover earlier this year was devastating to my motor's rings and pistons. BTW - Does anyone out there have a spare, two-cylinder Motoplat coil in excellent shape that they are willing to sell me (my spare coil is bad)? I plan on running my 250cc Rossi with the metal-body Dellortos that came with it.

Thanks to those of you who identified cowling-maker sources as soon as you read my post. I have decided to try the cowling shape that the Italians are using due to its simple design features and anticipated cost effectiveness (read: assumed lighter-weight design features.) The Dickfors design works well also, but looks a little more complex to mold and finish (more complex contours on the molded rectangular intake end, and looks like it has a smaller rear plenum area in front of the carbs.)

Cheers,
Al
R-25

[Al Peffley]

Cowling R&D Tests Update

I tried a small cowling on my 250cc hydro this weekend. Rex re-fit the pistons and rings for me and I also changed the reeds in my motor. Wow, did my Yamato motor run much richer! I am still experimenting with inlet features since it loaded up faster when I gently pulled the pipes. Too many changes at once, I guess...

Al