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CVTech CVT and brakes?

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wishin4snow View Drop Down
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    Posted: Apr/01/2010 at 11:56pm
I was wondering if anybody had any ideas about adjusting the new CVTech CVT. I can't seem to get top end out of the CVT. I put in the heaviest weights and shortest spring but it didn't seem to do much. Is anyone else having this problem?

I was also wondering where you guys get your master cylinder for your breaks. Every year we have a problem with our brakes and we might need a new one. Any websites or ideas?
-Kevin
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Post Options Post Options   Thanks (0) Thanks(0)   Quote adrive7 Quote  Post ReplyReply Direct Link To This Post Posted: Apr/02/2010 at 12:14am
The Polaris Master Cylinders are pretty solid. They are small, work well, and only cost like $12 through the sponsorship program if I remember correctly. 
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Post Options Post Options   Thanks (0) Thanks(0)   Quote jhu42 Quote  Post ReplyReply Direct Link To This Post Posted: Apr/02/2010 at 2:02am
Hi Kevin,

In order to get full extension of the CVT you need to check the math to make sure that your ratio makes sense.  Remember the CV TECH CVT will do 0.43:1  put this in your calculations and see what the speed at that ratio is.  If your speed is like 45-50 mph with that overshifting by the CVT, then the reason your not seeing the CVT shift more is because you only have 10 hp.  A reduction of 13-12.5 is the best for the CV TEch.  13:1 I think gives you about 37 mph.

Also a great way to prove that your cvt will overshift is to put it up on jacks and run it WOT.  You will see the wheels spin very very quickly, and the CVT will overshift.  That speed the wheels are traveling at is probably faster than the little 10 hp can push it in real life though.

Here's a video of us doing that jack test I just described



Also for master cylinders we use the clutch masters from Wilwood.  Big, yes, and guaranteed to pass break test.
Pick a diameter that works for you

http://www.jegs.com/p/Wilwood/Wilwood-Aluminum-Master-Cylinders/755319/10002/-1

Later,
Adam



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Post Options Post Options   Thanks (0) Thanks(0)   Quote collinskl1 Quote  Post ReplyReply Direct Link To This Post Posted: Apr/02/2010 at 11:03am
Holy driveshaft whirl Batman!!  We also run monster Wilwoods.  They're huge and take a ton of force to actuate... I wouldn't recommend them as we're looking for an alternative as well.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote TsangMasterGeneral Quote  Post ReplyReply Direct Link To This Post Posted: Apr/02/2010 at 12:44pm
We've run MCP's for the last couple years, they've worked pretty well.
My only complaint is that the reservoir is a bit small, which makes filling and bleeding a little more labor intensive. Other than that, they're really compact and work well.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote p.lewis Quote  Post ReplyReply Direct Link To This Post Posted: Apr/02/2010 at 1:12pm
One way to indirectly see how the clutch is shifting is to mark the sheave with a sharpie line radially from the center. Where the sharpie is rubbed off, that's how far it shifts. Aaen probably explains this in his book.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote johnpate01 Quote  Post ReplyReply Direct Link To This Post Posted: Apr/02/2010 at 7:50pm

I agree with what others have said.  Check your reduction ratio.  We are still using the stock weights and spring and it is shifting to 100%.

I am very happy with the performance of our small Wilwood master cylinders.  Using 0.625" bore and a 5:1 motion ratio we are getting really good performance out of them.

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Post Options Post Options   Thanks (0) Thanks(0)   Quote schooter Quote  Post ReplyReply Direct Link To This Post Posted: Apr/04/2010 at 2:14pm
wishin4snow,

Since you put the heaviest weights with the lightest primary spring in and still did not a full out-shift with the primary I would first make sure that you're indeed not achieving a full out-shift. As mentioned already, the method of drawing a line with a marker in the primary sheave works good otherwise I've just watched it to see if the belt is going all the way up on the sheaves.

A common issue with this, most likely your problem, is the belt tension. Moving the primary and secondary clutches 1/8" can make a significant difference in the force pushing the belt up the primary sheave. I would guess that you don't have enough tension right now. If you have too much tension you will probably notice slightly built up edges on the belt from the belt getting too hot.

As an additional note, check the side clearance on the belt, with the engine off. There should only be about .010 -.020" clearance between the belt and the primary sheaves. If you have too much the belt may not climb to the outermost edge of the sheaves and the engagement will jerk you. Too little clearance and your car will creep forward at idle and put the hourglass effect in your belt.

Let us know what you find out.


Edited by schooter - Apr/05/2010 at 12:27am
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Post Options Post Options   Thanks (0) Thanks(0)   Quote BajaSaeAdmin Quote  Post ReplyReply Direct Link To This Post Posted: Apr/06/2010 at 9:47pm
Moved to Design Discussion..
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Post Options Post Options   Thanks (0) Thanks(0)   Quote RonGeorge Quote  Post ReplyReply Direct Link To This Post Posted: May/04/2010 at 12:30am
To pick up on your point about belt-sheave clearance, after SC, we noticed that this gap had significantly risen to about 0.04". This might partly explain why our belt is not traveling all the way up on the primary sheave. We're running 90 gram weights on each arm and the CVT doesn't do much. Its in low to mid ratio , never high. We're busy tuning the crap out of it. Any advice would be handy.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote johnpate01 Quote  Post ReplyReply Direct Link To This Post Posted: May/04/2010 at 1:03am
90 grams seems pretty light to me.  Maybe it is because we are using the new model CVTech, but if I recall, our stock (installed) weights were around 285 grams each.  I know for a fact that it is shifting to basically 100%, although it is a little touchy with the throttle.  We probably could have gone a lighter, but we didn't have time to test at all, although it seemed to work nicely as it was when it came out of the box.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote schooter Quote  Post ReplyReply Direct Link To This Post Posted: May/04/2010 at 1:11am
To correct the excessive gap between the belt and primary sheave you'll either have to put on a new belt or shim the primary. Adjusting the clearance varies from brand to brand. Last year we ran a Comet (salisbury style). To adjust the clearance on that one I had to heat up the spider with a propane torch (while trying not to melt the cushions) and move it with respect to the fixed sheave then add shims between the spider and ramp plate. If you're lucky the manufacture of your CVT will have shims and instructions on how to shim the primary, otherwise get creative.

Here's a good article about belt clearance http://www.wheatfarm.com/snowmobile/info/drive%20clutch%20adjustment.pdf

Before you spend much time tuning make sure your engine is reaching max rpms and generally just running good. It's always good to clean the carburetor. If you do still have problems with the belt not getting all the way up on the primary sheave then it may be time to tune. Also keep in mind that there's more parts to tune than just the weights. If you by chance have a particularly steep cam installed on the secondary that may be causing a excessive rate of upshift in turn causing the engine to bog down. A good way to check this is to find a long straight-away and get the car to full speed. If you can't hold a generally consistent top speed or if you just keep slowly going faster, you may need to change cams (shallower). You can probably imagine things can get a bit involved.

Anyway, make sure the engine is running like a champ, get the belt clearance fixed, then do some testing.

Keep in touch


Edited by schooter - May/05/2010 at 1:05pm
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Post Options Post Options   Thanks (0) Thanks(0)   Quote RonGeorge Quote  Post ReplyReply Direct Link To This Post Posted: May/04/2010 at 9:11pm
@schooter

At SC Engine tech, we noticed the engine redlined a little over 3600. But having that as a guage may not say anything. We didn't have our engine dynoed yet and that's the next step. We have no idea what this 2 year old engine of ours is actually providing.

I talked to Bill at Gaged Engineering and asked him his opinion on our belt-sheave clearance at idle and he seemed to think .040" clearance was fine. So then the problem is not there, instead it could be the at secondary spring. Tomorrow, we hope to make some runs with that spring loosened up a bit to see what kind of effect it yields. Will let you know.

An interesting observation was that in our 150 ft. acceleration runs last week, we noticed that the final times were smaller for heavier drivers than it was for lighter drivers. The gaps weren't significantly high, but about 10-20 seconds of average difference was seen among drivers and it was enough to provide a general trend. The worst times were recorded when we had the featherweight 150 pound driver in (who also happens to be a runner ).

I wonder if there's anyone knowledgeable in the dynamics of governor engines to help interpret why the engine & CVT behaved this way. If you have found something like this from testing experience, I would love to hear from you.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote CLReedy21 Quote  Post ReplyReply Direct Link To This Post Posted: May/04/2010 at 9:45pm
If you're seeing better times with heavier loads then your secondary is either A too stiff, B has too much preload, or C has too tall of a ramp.  Belt drive CVT's like the ones we have are torque sensing so when you give it a heavier load and let it hook up it'll pull harder when you've got the secondary wound up too tight.  I assume you're using Gaged parts since you referenced them so I'd try dropping to the 26 degree secondary helix and starting at a light preload working your way up until you get the backshifting you want.  From there all you have to do is get your engagement and running rpms where you want them and you've completed iteration one.  Do through that cycle a couple more times and you should have a pretty quick setup.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote schooter Quote  Post ReplyReply Direct Link To This Post Posted: May/05/2010 at 1:02pm
I agree with Chris, that goes along with what I was saying with the angle of the cam (or helix, same difference). As far as the belt clearance, .04" isn't ideal but probably isn't enough to affect the position of your belt as much as you seem to be experiencing.

Sounds like your cam is too steep. Here's a few things to keep in mind with choosing cams and springs for your secondary.
  • Major adjustments are made by changing cams
  • Fine adjustments are made by changing springs
  • Even finer adjustments are made by changing preload
Cam Angle
  • Increasing the degree of the cam increases the rate of upshift
  • Decreasing the degree of the cam increases the rate of backshift
Spring Rate
  • Increasing the secondary spring rate increases backshift
  • Decreasing the secondary spring rate increases upshift
Preload
  • Increasing preload delays upshifting in the secondary.
  • Decreasing preload allows the secondary to upshift sooner


Edited by schooter - May/05/2010 at 1:06pm
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Post Options Post Options   Thanks (0) Thanks(0)   Quote CLReedy21 Quote  Post ReplyReply Direct Link To This Post Posted: May/05/2010 at 6:33pm
^  What he said.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote RonGeorge Quote  Post ReplyReply Direct Link To This Post Posted: May/05/2010 at 7:20pm
Chase,

By cam, do you mean secondary helix angle? Gaged doesn't make a 26 stock, if that's what you guys are suggesting me to decrease the angle to. http://www.gagedengineering.com/secondary.html  From which line and at what point are you measuring this angle? Look at that helix cage. I'm looking at it this way, and this is our number :



If this is correct, then I can see why decreasing that angle will involve more force, and hence slower upshift.

Bill suggested we try a 7.5" secondary pulley, instead of 8", and also loosen up the secondary spring by a hole or two. We have it in the 7th hole right now, from the left. I'm not sure if this "fine tuning" might help but we haven't tried. Tomorrow is test day.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote schooter Quote  Post ReplyReply Direct Link To This Post Posted: May/05/2010 at 7:59pm
Yes, by cam I mean helix, it's just another name for helix. You correctly identified the angle in your picture. However, according to what I saw on Gaged's website they offer helix's with 33, 36, 38, 40 degree ramps. So I'm not sure where the 30 degrees is coming from. Below is a good diagram showing the helix angle, shown as PSI. The diagram shows a helix with varying helix angle.

Let's assume you have the most shallow helix Gaged offers. Then I agree with Gaged, you will probably need to decrease the diameter of your secondary sheaves. You could try putting in a secondary spring with less spring rate or using less preload. But if you're seeing 10-20 seconds variation in 150' runs there is something wrong going on. Is that a typo? So I don't think changing springs or preload will affect things enough. Just curious, what are your times for 150' acceleration?




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Post Options Post Options   Thanks (0) Thanks(0)   Quote RonGeorge Quote  Post ReplyReply Direct Link To This Post Posted: May/05/2010 at 8:11pm
Schooter,

While at SC for our acceleration event, it was not so good. But then, we didn't have a tuned clutch and we were running the wrong belt. We attained 07:42 seconds or something like that for the 150'.  The next day before the endurance race, we changed to the correct belt and finished 22nd without a scratch.

Last week, when we tested on our state-of-the-art-not 180' track, our average times were in the 7:80's. Heavier drivers brought it down to 7:50 seconds and lighter drivers took that time beyond 8 mins, the worst being with the lightest driver (8:40 seconds)

I think I maybe understand our problem. Our CVT is really efficient at backshifting where it stands. This is even confirmed by the decent sled pull results we had at SC. Our engagement speed seems to be spot on where we want it (low 1700's) but that secondary pulley just doesn't want to separate out entirely and get our system to high ratio.

If Bill can't provide a 26 degree helix, we'll try the smaller secondary pulley and see what that does. Will let you know. There's probably many things we can learn from this experience.
-Ron George
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Post Options Post Options   Thanks (0) Thanks(0)   Quote CLReedy21 Quote  Post ReplyReply Direct Link To This Post Posted: May/05/2010 at 8:11pm
You should check back with Bill because we are in possession of 2 26's a 28 and a 30.  They stock the 26's after a frantic call from a idiot in Tennessee before Auburn last year.

The helix angle will be stamped on top.  But yeah, you've got the idea.

7th hole seems pretty stiff, especially for a 30.  I run a softer spring and I'm still running less preload.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote RonGeorge Quote  Post ReplyReply Direct Link To This Post Posted: May/05/2010 at 8:23pm
By the way, that neat picture you had of the helix was compiled by Randy Nouis, a GM engineer. You can tell he's must be engineer because of the great stuff he wrote about CVT tuning for Snow Tech magazine. I wonder why he never went on to write a book about CVT's and tuning like Aaen did. His writing was very insightful.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote schooter Quote  Post ReplyReply Direct Link To This Post Posted: May/05/2010 at 8:59pm
Well I know Randy Nouis was a owner of Super Torquer, a company that made CVT parts and I believe made high-end complete clutches. He specialized in the some of the best stuff, antique snowmobiles. I think he set some records with a RXL 250 racer. It's interesting to know that he's now a GM engineer. I agree, he should've wrote a book. I compiled all his articles written for Snow Tech so I basically have a book already.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Unproductive Quote  Post ReplyReply Direct Link To This Post Posted: May/06/2010 at 12:17am
Ron, are you guys running one 90 gram weight per arm, or two?
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Post Options Post Options   Thanks (0) Thanks(0)   Quote RonGeorge Quote  Post ReplyReply Direct Link To This Post Posted: May/06/2010 at 3:31am
I should correct myself here. The helix angle is actually measured as 26-30 on our clutch. This probably means that at the bottom of the ramp, it is 30 deg. At the top it levels off to a more milder 26 deg. 
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Post Options Post Options   Thanks (0) Thanks(0)   Quote RonGeorge Quote  Post ReplyReply Direct Link To This Post Posted: May/06/2010 at 3:32am
Bob,

Just one 90 grams per arm. That's an issue because ideally the weight should be distributed on either side (45-45) in order to not throw the COG off. That's important.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Unproductive Quote  Post ReplyReply Direct Link To This Post Posted: May/06/2010 at 7:00am
Put two 90 gram weights per arm(180 gram total), that's how we ran it last time and it seemed to well, the car was pretty quick(IMO, because we had no data). You guys have slightly different ramps now so it probably won't be perfect.

Edited by Unproductive - May/06/2010 at 7:00am
-Bob
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Post Options Post Options   Thanks (0) Thanks(0)   Quote CLReedy21 Quote  Post ReplyReply Direct Link To This Post Posted: May/06/2010 at 2:30pm
Ron does your helix not have the angle stamped on the top?  Every one we've ever gotten from Gaged has had it stamped right on the top of the helix.  The problem with measuring them is that those angles are traced out radially around the Z axis of the helix.  It's very hard to measure one accurately.

I agree with Bob that you need more weight exactly how much is a personal preference thing on how you want the car to act.  You'll have to balance it with the spring for engagement, but you definitely need more belt pressure than what you can get with only 90 per arm.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote RonGeorge Quote  Post ReplyReply Direct Link To This Post Posted: May/06/2010 at 11:29pm
We found a bag of 90 gram weights and we installed them in the primary, making it 180 grams per arm. We also took the secondary spring tension down a hole and that increased the acceleration and 150' time of the car from what it was previously. We're doing average of 6 secs now. The belt, however, is pretty worn out by now and we'll need a better one to make judgments of the system. As of now, the belt's running radius is limited, i.e, it does not complete its entire sheave travel as we found out with a sharpie. 0.4" inches or so of the top surface of the primary sheave has not been touched by the belt. Our helix is a 26-30, 26 is the angle at the top and 30 is the angle at the bottom. It was marked so on the inside surface.


Edited by RonGeorge - May/06/2010 at 11:33pm
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Post Options Post Options   Thanks (0) Thanks(0)   Quote schooter Quote  Post ReplyReply Direct Link To This Post Posted: May/07/2010 at 12:13am
Good to hear the improvement. To see if the belt is getting pulled all the way down on the secondary you can also draw a line on the secondary sheaves. However, if that belt is significantly worn I would first get that replaced. If the belt still isn't traveling all the way out on the primary you could try putting in a set of primary springs with less spring rate. You'll have to set down the engine idle so you don't burn the belt or creep forward if you do put in a lighter set of weights. I talked with one team at Wisconsin last year who had their primary (Polaris P90) engage at something like 500 rpms just so it would shift the belt out at the rpms they wanted.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Unproductive Quote  Post ReplyReply Direct Link To This Post Posted: May/07/2010 at 5:43pm
Originally posted by RonGeorge RonGeorge wrote:

Our helix is a 26-30, 26 is the angle at the top and 30 is the angle at the bottom. It was marked so on the inside surface.


Ron, care to explain that again in terms of low ratio(numerically)/high ratio?
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Post Options Post Options   Thanks (0) Thanks(0)   Quote RonGeorge Quote  Post ReplyReply Direct Link To This Post Posted: May/07/2010 at 10:39pm
Bob,

So what we're looking at is a multi-angle helix.  Consider 26-30. If I'm understanding this design correctly, the ramp that moving roller is initially contacting is a 30 degree (low ratio) with horizontal. It traces out the path of a helix along the helical radius, round the cylinder of the cage with CVT ratio change. It then ends up at the bottom where the same angle is now 26 degrees. I believe it is this done this way in order to give the secondary clutch the ability to upshift faster, past the "low squeeze" area of the clutch. The shallower 26 degree at the end helps with back-shifting when the system senses load. It helps to some degree, but a majority of the backshifting depends on whether the belt is able to counteract the flyweights in the primary to wedge open the primary sheaves apart.

Please correct me if I'm wrong.

Edited by RonGeorge - May/07/2010 at 10:45pm
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Unproductive Quote  Post ReplyReply Direct Link To This Post Posted: May/08/2010 at 11:48am
Ok, that's what I thought.


Edited by Unproductive - May/08/2010 at 11:49am
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Post Options Post Options   Thanks (0) Thanks(0)   Quote jeiB Quote  Post ReplyReply Direct Link To This Post Posted: Jun/18/2010 at 5:12pm
hey guys,

just wanted to get the discussion going about the CVTech cvt again. Here is a video of our cvt testing that we did before comp.

http://www.flickr.com/photos/mcgill-clubs/4680780343/in/set-72157624049569039/

As u can see, the cvt isnt fully shifting. Our design top speed was 38mph but we were only seeing 30mph. We have a reduction of 15.24:1 and 25in tires.

That run used the heaviest weights in the driver and the lightest spring in the driven but we still didnt see any improvement/change. Engine was revving to the proper rpm.

Any suggestions...? has anyone verified that they are indeed fully shifting the cvt?

thanks
Jeremie B.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote CLReedy21 Quote  Post ReplyReply Direct Link To This Post Posted: Jun/18/2010 at 5:20pm
Secondary preload could be too high/spring too stiff/helix too steep.
-Chris Reedy
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Post Options Post Options   Thanks (0) Thanks(0)   Quote jeiB Quote  Post ReplyReply Direct Link To This Post Posted: Jun/18/2010 at 5:28pm
i actually disassembled the driven and i also set the preload to the minimum. i dont think u can change the helix/ramp angle on the cvtech
Jeremie B.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote CLReedy21 Quote  Post ReplyReply Direct Link To This Post Posted: Jun/18/2010 at 6:04pm
Well first off, it might be the camera angle or some kind of silly CVTech thing, but it looks like the pulleys aren't aligned properly.  Driver looks like it's spaced too far right which will rob alot of efficiency and probably not help your shifting problem any.  Didn't notice it the first time, but it jumped out at me this time.

Past that I would put the rear up on jacks and take another video with no load on the car.  It might be that with rolling tire resistance, drivetrain loss, aero drag etc you might not be able to hit 38.  If it can do it on jacks then you know that you're just running out of power/it's not making it to the wheels.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote jeiB Quote  Post ReplyReply Direct Link To This Post Posted: Jun/18/2010 at 6:33pm
it does shift all the way when the car is on jacks. Also its true that the pulleys arent fully aligned especially when its shifted out. I may need to work on that.

We definetly have to do more cvt tuning next year...thanks for the tips
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Post Options Post Options   Thanks (0) Thanks(0)   Quote CLReedy21 Quote  Post ReplyReply Direct Link To This Post Posted: Jun/18/2010 at 6:46pm
With the gaged we set it up biased towards lining up fully shifted versus lining up at idle.  Idk which way that would be for you, but think about which way the pulleys move and maybe bias it towards top end.
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