T-20 Max power and rpm

[jerseybigfoot]

Does anyone have any experience with the maximum hp and rpm the T-20 will handle?? I have a I just rebuilt an early t-20 for installation in my Scrambler. The Scrambler liquid cooled sled engine has about 70 hp @ 8500 rpm. I have modified the trans input shaft to accept a 10 1/2' Polaris CVT limiting the trans input speed to about 8000 rpm.
Should I add a trans cooling circulation pump to the case?
I have the option of installing disc brakes on my jackshaft which is the first reduction off the transmission to reduce the braking load on the transmission.

[jpswift1]

I cant vouch for the power that you are running in your liquid cooled Scrambler, but I drove Hydromike's Attex 503/R and I think the 503 Rotax was in the mid 50 HP range and was spinning between 6000-7000 RPMs. The T-20 got warm, but it held up just fine. Some of the earlier Attex T-20's had disc brakes on both sides of them so maybe you could pick one of those up. If I were building a racer that extreme I would want to play it safe. That sounds like one wild machine! I saw some pictures of it at Phillipsburg, PA. I would love to see some videos of it too! Good luck with the project.

[mark m.]

Marc. Just what mod did you make to the input shaft of the trans? Reduced the diameter? Sleeve for larger dia.? Shortened shaft? Inquiring mind would like to know.

FWIW Kevin Griffin with his 4 cyl. Mitsubishi in his MaxIV never hurt his trans as far as I know. However shredding belts off was his biggest problem.

Mark

[hydromike]

Marc,

I too have thought about the idea of a small cooling system for the T-20 by plumbing a small oil cooler into the threaded hi/lo fill plugs. I'm astonished at how hot the T-20 can get and still operate safely. The trans in both the 503 and the D/stock get quite warm, but I'm really surprised at how warm the RIMs trans gets. I don't know if it's because it's lodged down beneath the engine and both racers see a lot more air circulation, or what.

Do you happen to have the horsepower curve for the Kioritz 440? I'm wondering where the peak horsepower comes. I think that if you're pushing 50-60 horsepower in the 5-6 grand range, that would be pretty comparable to what my lowly 50 horse pig is putting out. All bets are off after you push that 7000 rpm envelope and scoot past 60, 70 and 80 horsepower. I bet it would be fine as long as you don't really flog it at the top end. The trans in the 503 is an early "supported jackshaft" model, and since you're using the same setup, I think you should be in great shape.

Do you have any idea what the finished Scrambler is going to weigh? The 503 is a featherweight, and I was wondering if it holds up well only because of that....

~m

[jerseybigfoot]

Marc. Just what mod did you make to the input shaft of the trans? Reduced the diameter? Sleeve for larger dia.? Shortened shaft? Inquiring mind would like to know.

FWIW Kevin Griffin with his 4 cyl. Mitsubishi in his MaxIV never hurt his trans as far as I know. However shredding belts off was his biggest problem.

Mark

I enlarged the keyway on the t-20 shaft to suit the clutch, the shaft sleeve is from solid stock bored one end to suit the t-20, the other end drilled to accept the retaining bolt. The slot in the sleeve hold the key captive.

Also the Polaris cvt is offset inboard about an inch and a half alowing the engine to be mounted closer to the body centerline.

[mark m.]

Thanks for posting the pics Marc. Looks great. I have done alot of the same for different applications. That offset inward by an inch and a half is a huge improvement as far as relieving the large cantilever pull on the input shaft. I have many times looked at the stock clutch arrangement and wondered how the input shaft holds up as well as it does.

[jpswift1]

Thanks for posting the pics Marc. Looks great. I have done alot of the same for different applications. That offset inward by an inch and a half is a huge improvement as far as relieving the large cantilever pull on the input shaft. I have many times looked at the stock clutch arrangement and wondered how the input shaft holds up as well as it does.

Mark, I wonder why Borg Warner never did this originally to relieve some of the strain on the main input shaft. I am also surprised that the stock main input shaft holds up so well......especially after taking the Attex race machines out with Don and Hydromike. Those things hold up to some serious power.
.

[mark m.]

Jeff, the reason it holds up the way it does is that the material used for the shaft is alloy 8620 case hardened to rockwell 58-62 with a softer tough inner core. They do deflect under load but there yield point is high.

[jerseybigfoot]

Mark. The Polaris clutch also has the advantage of lots of aftermarket cams and available springs. All the bushings can be replace as well.
BTW how is your starcraft project???

[mark m.]

Marc, the only thing I have done to the Starcraft is rebuild the transmission. It was a mess but all the gear teeth were in good shape. Maybe this post is good timing as I will be needing a set of clutches for it. Where did you get the Polaris clutch...ebay perhaps? Are they the same included angle as the Comet? Need special belts?