"Pork Chop" Cranks for GT/TR750

Suzukidave · Post by **Suzukidave** » Mon Jun 01, 2009 7:05 am

For right now we went with a smaller , easier to fit in setup

tz375 · Post by **tz375** » Mon Jun 01, 2009 8:03 am

Kris,

Do you ave a copy of Tom Turner's TSR software by any chance? That's what Bill used with Dave's Hot Street porting. At your target RPMs and HP numbers, those dimensions would not be close.

John Aylor explained teh CR issue much better than I did and he's right on the money.

There are several free software packages on the web for exhaust design, but my preferred tools are Bimotion and MOTA. I can model the ports and exhaust system in Bimotion and then run simulations in MOTA. Then I start to experiment with slightly different combinations of port shapes and sizes and pipe dimensions until I get a wider fatter taller power curve.

All it takes is too much time

Post by **Suzsmokeyallan** » Mon Jun 01, 2009 9:08 am

I know Honda used porkchop cranks on their later 2 strokes, with tin covers to make them "round".But that was more for smoothing the "flow" in the crankcase at the reedvalve, not to increase primary compression.

So Moo what would you think about cutting the covers off a porkchop crank on such a Honda. Surely doing that wont just show up as any appreciable increase in performance.

Richard im not sure about your reply as to the HP figures of the motocross bikes. By this i mean considering the low levels of difference you showed them to be against GP bikes which are in a totally different league. Id more place them against other stock general production high performance bikes to be fairer.
There was a test done in a mag a while back, (i think it was the mid 90s) about pitting a CR500 against a 750 cc road bike. From what i recall they could not get a small enough rear sprocket to stop the dirt bike from still over revving in the top end.
However even with the highest gearing they could find, the CR500 was still making the road bike look rather bad on the clock till it could finally get by due to lack of higher gearing, this 'pass' happened somewhere around 120 mph.
If anyone can locate that test id sure like to see it again
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ja-moo · Post by **ja-moo** » Mon Jun 01, 2009 10:42 am

Suzsmokeyallan wrote:
So Moo what would you think about cutting the covers off a porkchop crank on such a Honda. Surely doing that wont just show up as any appreciable increase in performance.

There is a lot of development in the "newer" motors. And those motors were designed around the crank with the tin cover. I would think if you took it off, it would show a decrease somewhere.

the CR500 was still making the road bike look rather bad on the clock till it could finally get by due to lack of higher gearing, this 'pass' happened somewhere around 120 mph.
If anyone can locate that test id sure like to see it again

It's all power to weight ratio with accelleration. And add in the bigger profile of a streetbike, at 120 it's pushing a lot more air also.

tz375 · Post by **tz375** » Mon Jun 01, 2009 12:05 pm

Allan,
Thanks for the insight into those motocross motors. pretty impressive for mudslingers. The point about the numbers is that one cannot compare numbers without understanding ALL the related design issues. In other words, those numbers don't prove that high CR is good, or that it's bad. They are just numbers from one point in time.

JA already explained most eloquently the integrated design issues which leads us to the underlying issue and that was - will a change in primary CR have an effect on performance in an old motor with many design changes to incorporate modern technology.

There are two valid answers, computer modeling and empirical. and then there's speculation and rationalization which is way more fun and and a whole lot less work, which is what we're doing.

Computer modeling is a great way to predict the impact of different changes and the numbers I ran for Dave's reed motor seemed to indicate that a reduction in primary CR was good when coupled with the extra transfer port area and teh pipes he's using.

In reality the dyno will tell us how close we got with those numbers but they are a good indicator of what that motor is capable of. But it's just a tool and doesn't provide insight or experience, just a basis to try to apply it and understand what the numbers tell us when we change a series of variables.

Post by **Suzsmokeyallan** » Mon Jun 01, 2009 2:22 pm

Richard all this is speculative as you said without a dyno to actually test the theory and proposal.
However if enlarging the volume of the lower cases was such a good idea it surely would have been developed years ago to some degree.
All it would have taken is more space around the journals to some extent to accomplish this.
I'm still not convinced 100% though, id have to see it actually proven and thats where i rest my case.
Take for instance that Honda webbed the cranks and then fitted covers over them to improve flow, then theres another company leaving the chopped cranks open for all the turbulance it can create.
Theres too much stuff here for figures to blur and get different ideas and readings off of to just say "THIS IS IT"

tz375 · Post by **tz375** » Mon Jun 01, 2009 3:56 pm

So we are in agreement.

One example to prove the point. Take a TZ350E/F and replace the top end with one off a TZ750. there's a minor bore difference but the reed top end has a much wider powerband and similar top end. Does that come from the reeds or the extra crankcase volume?

The question is rhetorical because they are inextricably linked.

If Kris wishes to send me all the dimensions from his motor and the pipes he plans to use, I can run the model with stock or pork chop cranks and see if the software changes duct pressures or volumes and see what it predicts.

Kris Bernstein · Post by **Kris Bernstein** » Mon Jun 01, 2009 8:34 pm

Sadly, I was not able to open the attachment of the pipe drawing as I would love to see those numbers. I am still a ways off but I promise to share as soon as I have something to share. I'm still in the "collecting bits" stage of this project but hope to put dremmel to cylinder wall very soon!

Kris

Suzukidave · Post by **Suzukidave** » Mon Jun 01, 2009 9:04 pm

As Teaser commented this chamber was designed around my custom porting specs .

tz375 · Post by **tz375** » Mon Jun 01, 2009 10:55 pm

Kris,

FYI, MOTA didn't like those pipes at anything less than about 6K so they may be the way to go for your race spec motor. The pipes Dave is using look much better, on the computer at least, and have way more low to midrange.

We need to get it on a dyno to see what really happens of course.

Jughead · Post by **Jughead** » Mon Jun 01, 2009 11:35 pm

Smart Asses.

I mean that in a good way.

Kris Bernstein · Post by **Kris Bernstein** » Tue Jun 02, 2009 1:24 pm

I added pictures to my PhotoBucket album of the Ohlins mono-shock that will be fitted to the Seeley 750 and a spicy picture of the Magnesium Triple Clamps that will hold the Ohlins forks to the steering head...

http://s638.photobucket.com/albums/uu10 ... Bernstein/

Suzukidave · Post by **Suzukidave** » Tue Jun 02, 2009 9:50 pm

Durn Kris ... you dont play fair

Kris Bernstein · Post by **Kris Bernstein** » Wed Jun 03, 2009 4:26 am

That's it! I've been DURMED! Eric say's I'm off the list.
So the 11.5 oz. triple clamps are the last straw....derm the torpedo's....full speed ahead...
I will have to do up some manner of spacers to fit the 999 clamps to the Seeley steering head. The stem is Ergal and I don't think I want to cut and weld on that. I'm finishing up a 907 Duc with 999 aluminum triple clamps and fitting the clamps to the 907 frame was easy as the steering stem is steel. cut, turn a spacer, weld....no problemo....now it gets more tricky on the Seeley.....

Kris

Suzukidave · Post by **Suzukidave** » Wed Jun 10, 2009 1:34 pm

http://www.bridgestonemotorcycle.com/do ... olume6.pdf

"Pork Chop" Cranks for GT/TR750

send me all the dimensions...

More pictures of Seeley bits

Durm!!!???