Project 90 (Stock 89cc And Beyond)

[reiko1078]

I was thinking about doing some port work on my stock 49cc piston. Any advice on how to approach it? Is it worth it? Has anyone else done it?

[reiko1078]

Check that..... Cylinder*

[90GTVert]

It should be similar to what I've experienced on the 90. The power level will differ, but if done properly you should be able to get good gains. Since th 49cc lacks the torque of a bigger motor, be careful not to get too aggressive unless you will be doing mods to keep within the powerband. Even the 90cc struggles with a stock setup when the port duration and shape is too aggressive.

[90GTVert]

Project 90 : Phase 1 Review

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I've completed all of the modifications that I wanted to try one at a time on a stock 90cc Minarelli. Now I'd like to give my thoughts and opinions on some of the best mods. To do so, I've put together a top 3.



#1 : Cylinder Porting And Adjustment


This modification topped the charts for max speed and did as well as any other mod for cruising speed. I may have been a little more aggressive than some would be or should be for a daily ridden street scooter, but excellent results could be had keeping the setup more mild as well. A mild setup can be done for the cost of gaskets. If you push it a little more as I did, you may need to add on about $30 for a high compression cylinder head. Even with the head, you should come in at $50 or less.


If you don't feel comfortable porting a cylinder, a big bore kit like the Hoca 54mm could be a good option as well. With a price of $150 though, I would choose #2 above the big bore kit for starters.




#2 : Hoca Performance Variator


The Hoca variator came in a close second. It showed as much of a gain in top speed as any mod other than the cylinder porting. Cruising speeds increased as well, on par with some of the other top mods. One of my biggest reasons for liking this one so much is that the scooter was really much more pleasant to ride. Accelerating well, staying in the powerband, and feeling smoother in general. This one will set you back about $50, but it is well worth it IMO. I just don't think the stock variator does the 90+cc engines justice.




#3 : Performance Exhaust


An aftermarket exhaust would be my next choice. The stock cylinder may be a little mild to make the most of any of the performance pipes, but you can still see great gains. This class is next in line to the previously mentioned mods for top speed and cruising speeds are right there with the rest of the top mods. Acceleration is also comparable to the rest of the bunch. Check out each individual test to see which pipe you like the best.




Honorable Mention


I have to mention the other free mods. Removing the airbox snorkel and modifying the torque driver both showed gains and they cost nothing. You do need to upjet with the airbox mod, but for the purposes of this project I leave out tuning supplies in costs. Neither of these things showed big improvements at this stage, but it's hard to argue with free.

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[drawkward]

Been a few days since I've checked the project.

Extremely impressed - and inspired - by your port modification write up. What exhaust were you using when you went riding after the port mods? Stock? I'm definitely doing this one next week. Thanks for doing this. I don't know about the others with larger bores, but for me, this is VERY helpful information.

[90GTVert]

Yeah, just the stocker. It felt like I had a tuned pipe the way I lost power down low and it hit up high. lol

[190mech]

I kinda think porting has much to do with the "2 stroke lag",a good pipe with that type of porting gets exciting!!

[90GTVert]

Yeah, I hope it does get "exciting". :riding:

I'm still debating if I wanna just make the Hoca variator a part of the "control" for the second bit of testing. There's no doubt in my mind that it would be at the top of my list every time after what I saw and felt the first go round. I suppose I'll test it first and as long as I get good results that will be the baseline for other tests in part 2 if there are no objections. A lot of the mods have kind of shown their hands, so I think the exhausts and carb setups will be what is really being tested. Perhaps do that for theis section and then add on the rest for the last bit of testing? Plans may change, but that's sounding good to me at this point.

[2strokd]

I gotta add a little something about the Hoca vari. I just got out Zip back together and the only changes are a switch to premix, head gasket removal, and the addition of our Hoca vari and some sliders... I must say it made quite the improvement! I cant blame it on the HG removal because ive never got gains like that in the past.. It probably helped some but not as much as the addition of the Hoca vari and sliders do im sure.

Oh, shoot! Never mind! I just remembered i added the Hoca rear pulley and a Malossi torque control. Sorry about that.
Anyhow, it stays right in the power with no sudden RPM drops or raising.

[drawkward]

You guys work for Hoca or what? Just kidding

Never knew that the after market vari's were that much better. The only reason I haven't done it yet is because I have so many different weights for the stock vari's.

I think I have the same 52mm cylinder as you, Brent. Got it from Carlos, 71mm tall version. Even more of a reason to give it a try. Once I get my pipe I'll do some port work based off of your information (i have the stock stroke - 42mm, so I think it might have to be a little different.

I've heard people say that a good pipe actually cools the piston and cylinder better. Would that mean that you could run a tighter squish setting. The pipe's added cooling could offset the detonation caused by tighter squish?

[90GTVert]

Phase 2 On Hold


I began testing and tuning with the Hoca variator along with the ported cylinder to use as a baseline for the second phase of Project 90. When I pulled the stock variator off, the threads on the crankshaft were stripped. That really didn't surprise me, because I've been seeing metal shavings every time I remove the nut from the time I got the engine. It looked like it had been re-threaded already.




I threaded it to the largest size that I could get good threads with, which turned out to be M9 x 1.25.




I continued testing and was hoping to have a couple of updates to post today, but the threads on the crankshaft stripped on a ride yesterday. The new threads only lasted a bit over 100 miles.




The threads stripped and the nut backed off enough to grind the fan against the cover and kickstarter.




The key broke as well.




Not only are the threads gone, but the splines on the crank were stripped some as well at the end.

[90GTVert]

I'm trying to get another stock crank. I will probably port match the cases to the cylinder while it's all apart, but otherwise I'm hoping to get it back together and restart the second bit of the project. I was seeing some nice gains and the Hoca variator proved itself once again so it will definitely be part of the baseline for the next go round.

[90GTVert]

P90 is now a pile of parts.




I hope a replacement crank will fit. This thing has been attacked more than machined. It's about 76.5mm ID.




The crank was machined way down to about 73mm.




I'm not sure what the OD of a stock crank is? The 45mm full circle I have here is 76.8mm after being machined down.

[lshigham]

Man, that's been mangled good and proper - makes my luck look good!

[drawkward]

Shit, I measured mine a while back just out of curiousity... I can try to dig up some info - but I don't think I ever wrote it down Mines a 42mm crank though.

I feel bad admitting this, but I was hoping eventually you would case match to measure the difference. Sorry for the continuing bad luck with this one!