Project 90 (Stock 89cc And Beyond)

[burnttoast]

Apr 15, 2011 20:01:21 GMT -5 90GTVert said:

Lots of time. When I decide I want an engine I will spend time on eBay every day, sometimes multiple times in a day, searching for all sorts of terms and going through every item even when the search term is 100s of results looking for that one deal. Eventually something will come along. No deals means no projects (not paying $400-500 for a motor), so I have a good incentive. lol It's like lots of other things, if you don't have a lot of money to spare, you probably need to invest a lot of time instead.

quoted for the truth right here.

great idea for a project thread, very instrumental. reminds me of everything I had to teach myself years back when there was nothing around yet online in terms of scooter knowledge..

yup, in times before myspace and facebook

Keep up the good work Brent. Hope to catch up and post here soon.

[90GTVert]

Thanks. Good to see you around.

[190mech]

Do you think the 3mph gain is due to a better engineered vari,or is the OD larger allowing the belt to ride higher?

[90GTVert]

I absolutely believe it's the design of the ramps and such. The larger OD wouldn't explain the increased acceleration all over and the increased cruising speed either. The acceleration increase is significant, not slight. It's very obvious and comparable to what some of the pipes achieved. Heck, if you look at the pic that shows travel, I never got the belt far enough out to take advantage of the larger OD. I've used at least 5-6 of these exact varis in the past and always seen gains. I didn't expect it to be so drastic on here though. Goes to show you can always keep learning.

[90GTVert]

Hoca Performance Torque Driver


I haven't tested a performance torque driver yet, and T1's transmission is all apart at the moment, so it seemed like the perfect opportunity. The torque driver I'm using is a Hoca piece sold as part of a complete performance rear pulley package by Parts For Scooters. It's part number 169-126 there. The clutch and bell that it includes are nice pieces as well. They seem to have a little more grip than the stocker and hold up well in other engines that I have them in. You can also find these from other sellers sold separately.


The top torque driver in the image below is the stocker. The lower one is the Hoca unit. As you can see, the stock torque driver has a pair of grooves, and the Hoca has multiple pairs. The Hoca torque driver allows you to choose different pairs of grooves for fine tuning if necessary.






The stock unit uses a dual-angle groove. This allows the pulley to begin it's travel in a groove with say a 45 degree angle. I don't actually know what the exact angles are, just making a rough guess. With the guide having to travel at that angle, it resists change more than if the groove were just straight up and down at a 90 degree angle. Resisting the change translates to higher RPM.

Once the pulley is about halfway open, it moves into the second angle of the groove. That's about 60 degrees, so closer to being straight up and down. Again just a very rough guess on the angle. Once in the second part of the groove, the pulley is less resistant to change and RPM will decrease as it transitions to a higher "gear" with greater ease. You can usually clearly feel that "shift".

The single angle grooves of a performance torque driver allow the CVT to operate at a much more constant RPM. Where the dual-angle groove may have you revving at your peak power RPM initially, when it "shifts" it will drop below peak power to allow for lower RPM cruising. A pair of grooves with one angle means no shift. That means your CVT has a much easier time staying within peak power RPM from the rear pulley's fully open and fully closed positions. The real downside here is that cruise RPM will increase compared to the dual-angle grooves.


I went for a test ride and maximum speed stayed the same as stock at 51MPH with the addition of heavier sliders. Acceleration however was much improved. Keeping within the powerband makes a very nice improvement. The acceleration increase was not as prevalent as it was with the Hoca variator, but still quite nice. Cruise speeds did increase slightly to the mid 40s, a little better than stock but not quite as effective as the variator. Hill climbing and riding into the wind were also improved.


This is a good mod for someone looking for max acceleration and not so concerned with max speed gains or low cruise RPM. The installation and setup is pretty simple. If you buy the whole rear pulley set it's a very fast bolt on mod.

[2strokd]

Good stuff as usual! The Hoca rear pulley is a great deal IMO. I used one on Skeedr for a while before the overrange. I am still using the Hoca clutch in Skeedr with great results. However, i am going to replace it out of fear of it blowing up! The OR kit paperwork says to use a good clutch and bell with it. It will spin the clutch up over 20,000rpm. Its a good clutch but im not trying to test it like that! It blows up it could send shrapnel right into me and my leg and who know who else. Im getting a Malossi unit ASAP.

[90GTVert]

Yeah, I think that's a non-issue for anyone without an overrange transmission (most of us ). Malossi is now making one that is reinforced specifically to be safer with overrange kits that turn the rear pulley so fast correct?

[190mech]

Maybe Skeedr needs a steel scatter shield over that clutch like the race cars have...

[2strokd]

Yes, im going to get a Malossi delta asap. As far as the scatter shield. Sounds heavy...

[90GTVert]

Skeedr : Soon to be SFI approved! lol

[90GTVert]

Squish Style Cylinder Head


This time around I'm swapping the stock style cylinder head with a squish band style cylinder head. My main hope is that the improved design will be more resistant to detonation. This engine has had detonation from the beginning if I let off of the throttle from wide open. Nothing too serious, but I was still curious to see if the combustion chamber design would have any effect.





Stock.




52mm, high compression, squish style, cylinder head. I looked for a 52mm head that had a recessed combustion chamber, to no avail. This one actually measures 49mm across the combustion chamber. That's OK though, the stock head measures about the same and then it's flat as well.




Before removing the stock head, I took a measurement of the compression. 152psi.




I set the squish head up with 5 head gaskets to get 150psi. I know it's not exact, but I think 2psi is a fair comparison.




Squish clearance is 2.15mm. I was going to try to set the squish the same as the stock head, but compression figures would be crazy if I set them to the minimum clearances. The minimum clearance for the stock head was around 1.5mm. At just 1.79mm on the new head, compression went up to 170psi. The max clearance on the outer edge of stock was about 2mm, so this is close enough to matching that for me.


I took the scooter on about a 20 mile ride, being hard on it to make sure it was hot of course. I saw no power or speed gains. What I did notice is that the crackle of detonation upon releasing from WOT was much less. If I just cut the throttle off or released it normally, I didn't hear any spark knock. To hear the crackle, I had to roll off of the throttle slowly. Even then, I only heard it right around 1/4 to 1/2 throttle for a moment. A definite improvement.

My initial thought with this mod was that perhaps I could increase compression to the point where I found the detonation again to see if it was enough to see any improvement in performance. Seeing that I still didn't completely relieve detonation, I didn't feel it worth all of the time trying to figure out where that point is. I feel like it would still be very close and gains would be minimal. That's not to say this isn't a good thing to do, but it's more of a fine tuning mod if you're looking for the most from a particular setup I believe.

[190mech]

Looks like the squish type head has a quite small volume(CC's) and would work well with long exhaust durations.Its a shame there is not more aftermarket parts for the 90's,they are such great engines!

[90GTVert]

I never measured this time, but the hi-comp head should be about 9cc. Stock is around 12cc IIRC. The info is on the site somewhere, I just forget where. lol

[90GTVert]

Torque Driver Modification


I've tried an aftermarket torque driver, but what about working with the stock unit? Here's a picture of the groove that the pin rides in on the stock torque driver. Notice how the groove goes very near the seal at the top, but not so close to the seal on the bottom.




The pin starts in the top of that groove and gradually moves to the bottom. When at the top, the pulley would be fully closed. When at the bottom, the pulley would be all the way open. The problem is, the short stock groove won't allow the rear pulley to open quite as far as it possibly could.

The picture below shows a stock torque driver that has been modified by elongating the groove to allow the pulley to open farther. I used a torque driver that was previously modified so I can go back to stock for future tests in this project. You can see all of the details about the modification and changes in pulley opening by clicking HERE. There's also a thread by another member about this modification HERE.




I went out for a brief ride to test the mod, which somehow turned into 57 miles on an 80 degree night. Max speed did increase to 52MPH, up by 1 over stock. Cruising speed increased just slightly, maybe 1MPH average. Both are the result of keeping the engine in it's powerband just slightly longer I believe. Otherwise, no perceivable changes. While it's not much of a gain, it's still a gain and it's completely free if you have the tools and are willing to do it. It may show even greater gains on an engine with more power.


I wanted to note, this is not the only modification you could do to the stock torque driver. This is the easiest, but you could go as far as to cut a set of completely new grooves if you have the time, tools, and patience. Notice that there's plenty of room left for a new set of grooves on the stock torque driver.




Just as an example and a learning experience, I cut one groove in the stocker to mimic the straight grooves in the aftermarket unit. I started out by measuring the pin that rides in the groove in a drill bit gauge.




Once I knew that, I drew a line at 90 degrees as a centerline and a 45 degree line to guide the new groove. I marked a few holes with a punch, and drilled them out with a 15/64" bit.




After plenty of time with a dremel and files, my stock torque driver has a groove much like that of the aftermarket unit. If you do this, be very sure that all edges are smooth. Test the movement assembled before moving on to the next groove.




The even tricker part is to do the exact same thing at 180 degrees on the torque driver. If both grooves aren't properly aligned at all points, it won't work. I never went that far. I have a perfectly good aftermarket unit for now. You can see though, that if you are willing to invest the time and effort you can save yourself a lot of money. Test everything on the bench for proper motion and make sure nothing binds before ever attempting to use it on the scooter. As long as you don't mess up and pass the seals or something catastrophic, if the mod doesn't work as planned you can simply go back to using the stock grooves.

[90GTVert]

...And now for the bad news about that last ride. 57 miles wasn't actually the distance back to my house. That was about 6 miles short. I was cruising along (at WOT as usual) and I started to hear a rattle. Moments later, the engined died. I gave it a minute, but it wouldn't restart. I ended up going home in the back of a truck.

This morning I went out to see what happened. I hooked up the compression tester and got a reading of only 80psi. Upon trying the kick starter, it was obvious that the reading is correct. I just tested yesterday for the cylinder head mod and had over 150psi.

I pulled the cylinder head off and noticed a couple little indentations at the very edge of the crown, but nothing too alarming. Upon pulling the cylinder off, I realized that one of the circlips was missing. Oh nevermind, I see where it is...







The piston is done, but I believe the cylinder will be OK with a quick hone. It has scarring fairly severely by the transfers on one side. I think it can be usable and work well enough to continue the project with it.




I've gotta get a 52mm piston kit, do a little work to the cylinder, and hopefully I can get it back to it's original specs to maintain accuracy.