+7mm Crank OEM Cylinder Porting

[Smoker]

Okay. Seriously...

Has ANYONE ever actually built a +7mm OEM cylinder engine???

[brrrappp]

Too bad Kel Caruthers isn't a member here.

[Smoker]

Too bad Kel Caruthers isn't a member here.

Well, definitely.

I'd love to shake his hand in person, but even to say hello over the net would be amazing!

I'm not worthy to ask a legend like Kel any questions.

[slinger]

Okay. Seriously...

Has ANYONE ever actually built a +7mm OEM cylinder engine???

Yes I have!!!!
If I remember right you end up with around 2mm (maybe a little more) positive piston to deck height as appose to 1.25mm for a +4mm stroke so nothing amazing there! Just be realistic with your power goals, 80-83 hp is a very achievable number below 10k with out the need to think about it to much.

[Smoker]

I know what your saying /thinking though, It would be nice to have the YPVS setup. I think I would have paid to have one built.
Hope you build it, and we can follow your progress and how you make out on your build.

Nothing stopping me from going for insane power, just a personal preference. I always thought riding with small engines would force me to get faster by learning good technique. Learning has always been more important to me than winning. Funny (or, not) how that philosophy seems to be reflected in my bike projects.

Not using the OEM cylinders because I want the power valve, although I would prefer to have it.

Bottom line is, I want to use the OEM head. To me, it's one of the most beautiful motorcycle heads ever made - and I was lucky to get a billet copy.

Then, there's the part about doing something different. There are tons of super fast bikes and engines out there, already.

[Smoker]

there is no reason at all why it can not be done, especialy as a good 2-stroke is as square as possible. an RD/RZ might even be better of with a bigger stroke than bore to compensate for the crap transfer ducts.

Kinda-sorta understand a little about a "square" engine.

This statement is very encouraging!

[Smoker]

Okay. Seriously...

Has ANYONE ever actually built a +7mm OEM cylinder engine???

Yes I have!!!!
If I remember right you end up with around 2mm (maybe a little more) positive piston to deck height as appose to 1.25mm for a +4mm stroke so nothing amazing there! Just be realistic with your power goals, 80-83 hp is a very achievable number below 10k with out the need to think about it to much.

SWEET!!

Doesn't mean I can get it done, but I have considerably more hope. Just wish I had more time.

Onward then....

[Questo vecchio rz]

Too bad Kel Caruthers isn't a member here.

Well, definitely.

I'd love to shake his hand in person, but even to say hello over the net would be amazing!

I'm not worthy to ask a legend like Kel any questions.

Heres a quick video on Kel, narrated by none other than Dave DeSpain!
He's into his 80s now , and was getting it done likley before most of us were born!
https://youtu.be/jUCebazy8zs

It's been a few years, but last I knew, Kel was working over here at Chapparael Cycles in San Bernardino.

I met him there and once at Laguna Seca. Got a handshake and autograph.

I think he was or is in charge of the new bike aeembly division, they likley sell 1000s of bikes a year. My guess is he's retired as this was 10 years ago or so when I met him there.

[MK]

Kinda-sorta understand a little about a "square" engine.

And I always had the impression that you want your bikes as queer as possible

[Smoker]

Kinda-sorta understand a little about a "square" engine.

And I always had the impression that you want your bikes as queer as possible

Okay.

There's defininetly something lost in the translation.

[Smoker]

On that note...

Got a feeling Kel would think my projects are a big waste of time.

[brrrappp]

Kel Caruthers did an interview in the last issue of Cycle World.
I think he's an enthusiast with a very curious mind and I feel certain that he would not look at your projects as a waste of time.

By the way, I am fairly certain he was the guy that made those over stroked over bored 680cc Daytona 200 Specials for Kenny Roberts and Eddie Lawson back in 1983.

[JanBros]

If I remember right you end up with around 2mm (maybe a little more) positive piston to deck height as appose to 1.25mm for a +4mm stroke

made a drawing and I ended up with 3mm



the liner also sticking out is because I will start with blank liners in Banshee cylinders, so I can make a double exhaust port as wide as possible at the top to get good blowdown, and using the liner as bridge in the middle.

[Smoker]

If the domes are cut, so the piston can travel 3mm higher, that means an OEM gasket can be used at the base of the cylinders, right? No spacer.

And, so... the port timing will not be messed up in any way. Correct?

[JanBros]

change the stroke and port-timings will change off course. but that's just a question of placing the cylinder at the best height and make changes to the ports.
as in our RZ/RD's the ducts are straight up, you can hardly mess-up the transfer-flow if you alter the bottom of the port as in this case it has next to no influence on the inflow into the cylinder.