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  #21  
Old 11-30-2019, 11:43 PM
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Head needs bigger valves. Your fighting a losing battle like I was when I built my mini drag bike. Needs more air flow in and out. And I personally would run a brp_es ngk and not a 3910 plug. Never could get one to work properly and it fouled out fast.
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  #22  
Old 11-30-2019, 11:53 PM
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That would fall in line with enough inertia to overcome the wall theory. Unfortunately bigger valves aren’t in the cards right now. Maybe at a later date. I will however try the plug. I don’t see the plug you referenced though.

I see BPR6ES...is that the one you mean?
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  #23  
Old 12-01-2019, 02:06 AM
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Quote:
Originally Posted by Mrmonk7663 View Post
This might be a better question that can hint at an answer...what does a 40 series do over a 30 series.
Quote:
Originally Posted by J.S.@SMS View Post
If Iím correct, the difference between the 30 and 40 series torque converters is the belt. The 40 series belts can take more power than a 30 series belt.
correct!
it's -to be precise- belt contact area.
the 40 series belt (thanks to it being taller and the pulleys having a larger diameter)
makes more contact (friction) with the sheaves..
once the engine power (torque really) overcomes that friction all all of the rest is just converted to slip and heat.

Quote:
Originally Posted by Mrmonk7663 View Post
I wish it was something simple and stupid but I really think itís the nature of the 30 series.
.....
Another question...anyone reading this build a modified engine similar to mine and successfully reach >6500 rpms?

Someone wrote this to me but it went too far away from my knowledge base to understand it all....Sid might make sense of it....

ď The wall your hitting (Iím assuming) is the OD Ratio of the torque converter transferred to the jackshaft final ratio. diameter, length, weight, and counterbalances throughout the drivetrain system all come into play when rotation speeds get up there. You gotta think of all the rotating parts some fixed and Some spring loaded and some engaging with centrifugal compression. So think of all the laws of motion, and then the inertia of each piece of the TAV system, and the constant pull back from the driven pulley, and also belt becoming sticky as it gets hot. Just abunch of opposing forces hittin the point of equal force of the engine output.
So if your want is to achieve +6000rpm while using a TAV look into 2stroke, do the math to figure out what inertia you need at the crank to push past the opposing forces of your drive train at the rpm range your looking for. Try a nitrous system, try do spark plug temps. Get a tri-fuel carb and experiment with different fuel types.

Or just run a smaller tire. If you know you can run past 6k then drop you tire size down a couple inches and youíll be surprised at the out come.

If your looking to learn some gearing knowledge for low hp high rpm do some research on rally car transmissions.
Also Nissanís run Tav style trans in a lot of there vehicles so if your lookin for nice spec data and power to weight ratios look there.Ē
Sounds all plausible really.. BUT
the driven at full speed is fully expanded an starts acting as a fixed size pulley (the moveable sheave is locked by the cam from spreading)
So at overdrive, that part of the equation doesn't have to be considered much further ..
I would have to double check if the belt is in full contact at that point,
but I'd assume so for now.

Now two more parts to be considered...
while the moveable sheave of the driver is not as close to the fixed sheave as it could be.
the weights should be fully extended by now and rest against the outer bell and moveable sheave's rim.
so no additional forces would actually compress the driver any further (ideally)
So again.. we have about the equivalent of a fixed pulley.
Again I'd have to check if the belt raises past the sheaves in overdrive,
but I'd say they don't for now.
in case the weights are not yet fully extended additional rpm might result in an increase in clamping force (sticky belt)
but with the heavier garter springs and just 4k rpm.. that's certainly not it either.

And lastly the belt.
A high quality belt is essentially unable to stretch.
yours looks to be in good condition and unless it's the cheapest chinese one out there..
I doubt it will stretch significantly enough.

So yeah, once max rpm is reached (for the current weight/spring setup)
the TC IMHO should act as a fixed pulley setup.
and while it does indeed rob you at the very least 20% of power
(in overdrive maybe even 30'ish) thanks to belt slip
I cannot see how the springs, weights and things would or could cause any issue with you revving to the moon.
(sure at one point any non perfectly balanced system will cause a death rattle and destroy itself.. but that didn't happen to yours either, right)

The only possible explanation would be that the belt is indeed dropping on the driven past the sheaves contact area
and/or rising past the sheaves on the driver,
that might then cause the power ratio to drop to less than say 50%
so available engine power just doesn't suffice any longer.

and again a "but"
that would mean after just a few runs at full speed you should see a significant wear mark on the belt's sidewalls,
and should've smelled the hot rubber of the belt.

Also while you surely wouldn't gain more speed..
the engine would see less load thanks to the additional slip
and would be allowed to rev up way past 4k.

So I don't think slip is actually a problem here
If that'd be the case, a viable soution would be the speed limiting weight set for the TavKit btw..
instead of simple rods it has allthreads and a nut on the weightpack
setting the nuts to the outermost position should allow the belt to stay in full contact with the driver (and therefor the driven)
it might prevent overdrive but ensure full belt contact.

5k shouldn't be an issue with a stock Tavkit (chinese or not)
and with you only seeing four.. I cannot see it being the culprit really.

Next time you rev the engine with the rear propped up,
observe what the TC does.. if the belt raises above the driver
or the driven looks to be sticky at the 6k rpm.
if not.. it should be fine


Plug:
the underscore is a placeholder for a number (9 I'd say)
the heat value matching your requirements... NGK BRP9ES
would be the spark plug to search for p.e.

And while Joe certainly knows what he's talking about..
bigger valves just to hit 5.5k rpms maybe 6k?
that sounds more like a way to pass the 7k line to me *shrugs*

seeing how stock engines rev way past 5 easily without anything but carb rejetting an exhaust header and a removed governor..
(sealed box stock engines)

'sid
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  #24  
Old 12-01-2019, 07:37 AM
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Put a clutch on it and see how it performs. Iíve built an engine similar to this but I installed 26 lb springs and a 26mm carb and still had to up the jet size. My motor runs and revs great but the 30 series breaks every time I ride. You also need plenty of crank case ventilation. Just try the clutch and see if it performs better, that would quickly eliminate the engine as your issue but use a good clutch.
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  #25  
Old 12-01-2019, 11:12 AM
Mrmonk7663 Mrmonk7663 is offline
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Belt is cheap Chinese. Belt is not ripped but there is still rubber dust all over the place. I can wipe it from the backplate.

The engine doesn’t stop at 4K....it revs to 5k with the Tav.

While running the belt in driver is at highest point. In driven it’s down but I don’t know if it’s down too far or not.

I ordered the 7” driver. I’ll buy a quality belt. The BANDO belt is the best available I believe, even superior to the comet.

Clutch...I’ll try that if all else fails but that will definitely kill the torquey fun factor.
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  #26  
Old 12-01-2019, 11:51 AM
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Yes it will but it will let you know what your motor can do and also will let you see what the torque converter won’t let it do. I wasn’t suggesting leaving the clutch on just as a test to see what the TC was doing.
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  #27  
Old 12-01-2019, 12:07 PM
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I agree with that. But I know the engine will do more than what it’s doing. A stock engine will float the darn valves with no govenor. My go kart with 20” tires floats the valves. Header I take only. The only thing I know for sure is the 7” driver allowed my go kart to rev more than the 6”.

I’m not against the clutch test. But before I do that I need to test the parts arriving before buying a clutch to experiment with.

And just for my clarity you are suggesting a simple direct drive clutch to rear sprocket for testing correct?
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  #28  
Old 12-01-2019, 12:11 PM
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Yes. Just to see if your motor has issues or if the TC is the limiting factor. My 30 series does weird stuff with my higher performance motors. Belts get hot and sticky and springs break, sheaves stick and etc....
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  #29  
Old 12-01-2019, 01:04 PM
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Got ya. I’m sure the belt gets sticky. I know the driver gets really hot and there is a lot of belt dust. But the belt has no visible damage other than the dust. I have a comet belt in my parts pile I can swap just to cover more bases.

---------- Post added at 02:04 PM ---------- Previous post was at 01:21 PM ----------

Ok. Progress folks. The problem is some kind of inertia issue. Physics related. Anyway, I installed aluminum weights with white springs. Rpms went up. Installed aluminum weight stock springs. Rpms went up. Not fully into overdrive. Put driven back in 2nd hole.

Currently it has aluminum weights and stock springs with 2nd hole driven. Bike hits over 6100 rpms and settles in at about 5800 rpms in my short testing space. Overdrive still not fully engaged. Jetting is a bit off up top.

5800-6100 rpms is the upper range of the cl1 cam so that looks good. Speed increased to 45mph.

Now I know I’m headed in the right direction. The issue was the weights of the driver. Even though stock weight with white springs should have same engagement as aluminum weight/stock springs....the latter had a tremendous impact on the rev range. It also engages later than the stated 3300 rpms. Closer to 3800.

I also switched to a comet belt.

I will still be swapping cams and putting the 7” driven on when they arrive. Now I’m getting excited.

And thank you to all who have helped this far.
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  #30  
Old 12-03-2019, 10:41 AM
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Default Everybody says TC, nobody says belt application....

Leave it to me to think in simpleton, but not seeing the forest for the trees is often kinda my way....
My last TC used an asymmetrical belt, and if I had ever put that belt on backwards, or had ever used a common symmetrical V-belt, I'd bet dollars to doughnuts my minibike would have given me problems very similar to the ones you've been having. Instead, it was an absolutely terrifying speed screamer.
Simpleton speak as I mentioned, but maybe????????
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  #31  
Old 12-03-2019, 09:11 PM
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Quote:
Originally Posted by Mrmonk7663 View Post
That would fall in line with enough inertia to overcome the wall theory. Unfortunately bigger valves arenít in the cards right now. Maybe at a later date. I will however try the plug. I donít see the plug you referenced though.

I see BPR6ES...is that the one you mean?

Or a BPR5es. Donít remember which I used exactly. But it helped a lot. Never would run right with the 3910 plugs.
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  #32  
Old 12-03-2019, 10:01 PM
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I picked up a 6es. And I appreciate the belt orientation idea but I assure you it was in correct.

My 7”
Driver is here along with my 265 cam. 22lb springs (currently 18) and belt will arrive this week then I’ll throw it on and retest. I also have pink garter springs to lower the engagement a bit as it’s around 3800 with stock springs and aluminum weights (500rpm more than the advertised engagement with this combo)
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  #33  
Old 12-04-2019, 11:38 AM
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Forgot to mention also. On my mini drag bike if it was lean up high at wide open throttle it wouldn’t rev higher either. It actually limited it.

But my 44c magnum driver and 40 driven would rev to 6300 rpm no problem with a timing key only. After the billet flywheel it went to 7500+ and melted the insides of the driver ! This was all on my mile built 420cc engine. I was in a build off with it. If you wanna look at the thread.
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  #34  
Old 12-04-2019, 12:22 PM
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I forgot about plugs. I've made that mistake before by installing an ar3910x racing plug in my stock compression minibike. The bike wouldn't rev up past around 4k maybe 4500.
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  #35  
Old 12-04-2019, 07:01 PM
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Really? That is really interesting about the plug. Any idea why it would do that? Bike is now apart waiting for the remaining pieces but hopefully I’ll test again on Sunday.

As far as 40 series...I only have one on hand at the moment but it’s for a jackshaft setup. No backplate. I might try one in a future build if I put a bigger head and >.300’cam.
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  #36  
Old 12-04-2019, 07:37 PM
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that's indeed good info..
I never would've guessed a so called "racing" plug is that crappy tbh...

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Old 12-04-2019, 07:43 PM
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Well, a racing plug is good for a racing engine, but it's just too cold for a stock compression engine like mine.
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Old 12-04-2019, 08:25 PM
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Quote:
Originally Posted by J.S.@SMS View Post
Well, a racing plug is good for a racing engine, but it's just too cold for a stock compression engine like mine.
hmm MrMonk's got his head shaved (tonsure so to speak )
And Joe's was likely not exactly stock either
(going by what engines Joe usually present to us.. it likely qualifies as a racing engine I'd say)

And if it doesn't run right on any of Joe's engines (as I read his initial comment)...
chances are it's indeed not as good of a plug (neither for racing) as one might think when reading "racing plug" ...

Going out on a limb here, but let's say I keep note of
"3910 plug... be aware of it might be causing problems..avoid if possible"

Just to be prepared for the next soul having a weird engine not revving issue.

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  #39  
Old 12-04-2019, 08:47 PM
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Lol. I have read tons of comments about premature fouling of the 3910. Regardless I’ve ditched it for the ngk. The ngk is cheaper too. What kind of gap should I be using on this thing? If all goes to plan I will have solid updates on Sunday.
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Old 12-04-2019, 11:16 PM
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Quote:
Originally Posted by Mrmonk7663 View Post
Lol. I have read tons of comments about premature fouling of the 3910. Regardless Iíve ditched it for the ngk. The ngk is cheaper too. What kind of gap should I be using on this thing? If all goes to plan I will have solid updates on Sunday.
Everything Iíve read about the 3910x suggests itís a cold plug. A ďRacingĒ plug is probably optimized for combustion chambers with fairly high cylinder head temperatures. It probably works best in racing. I could imagine early fouling if used for more casual purposes.
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