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High rpm gearbox issues


kpr
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my poor old t50  doesn't want to shift gears at 10k rpm.   around  8k seems ok.  just that bit more is a no go.  All the gears seem about the same

So yeah probably not a very common thing.  But trying to figure out if its a limitation of the box,  its just old  junk i can fix.  or if can modify it to work better.  have heard of people filing the teeth down on the synco's or the likes

Or same deal with J160 boxes. anyone used them at 10,000+ rpms?    could be an option to swap to.

 

Have tried the usual stuff btw, adjusting clutch etc.

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Clutch friction plate mass. 

 

My old evo freshly built box simply would not shift at high rpm,it had the "big" evo 9 clutch and flywheel. (junk) 

The less work the synchro has to do (by changing speed of clutch friction plate between gears) the quicker you will be able to rip a gear.. 

The other thing that helps is closer ratios - same deal, synchro is going less wok as the rpm change between gears is less.. 

 

So many people overlook the ability to rip gears at high rpm in thier race cars.. It's critical in my opinion. 

I run dual cone carbon synchros in my Honda box, coupled with a lightweight friction plate and close gearset, and it's at the point where people ask if it's running a sequential box, it's just so fast. 

 

Someone like ATS will a carbon clutch, which is basically a carrier hub, then a sheet of carbon with a spline inside it as the friction plate. Ultimate lightweight.. 

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Agree clutch.synchro and gear mass are the main factors but you can help yourself a bit too. A clutch pedal stop adjusted so that there is the minimum movement required to free it - and no more - will help. So may a change of gearbox oil.

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^ clutch was adjusted like that, to the point thought may have not quite been releasing.  so gave it a little more, no dice

 It has the small 200mm friction plate. but will see if anything "light weight"  is available without going too silly. 

Maybe will throw some fresh syncro rings and sleeves in it

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11 hours ago, kpr said:

^ clutch was adjusted like that, to the point thought may have not quite been releasing.  so gave it a little more, no dice

 It has the small 200mm friction plate. but will see if anything "light weight"  is available without going too silly. 

Maybe will throw some fresh syncro rings and sleeves in it

Is there a carbon synchro upgrade available? 

20170906_135038.jpg

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Yeah found the same thing.     looks like couple of them maybe the same was w/g box.  but not much coming up for them either 

dog box way out of my budget.       Think i'll throw some new oem parts at it if cant find anything else.   I probably didn't put a new spigot bearing in the end of crank, when put the junk engine in. so probably a suspect worth looking at that could be causing some drag if its toast.  

It used to work fine with 9k limiter and bigger 212mm clutch.   so thought another 1000rpm wouldn't be too much to ask. 

 

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  • 2 weeks later...

One thing that i would check, is what happens when you try to change gear.

As in, from 10,000rpm does the engine decellerate too quickly for next gear, or not enough? 

(Running g4x ecu? 1000hz Graphs plz)

Adding a clutch switch and a gearbox speed sensor would allow you to setup flat shifting.

This has a mode where as soon as you hit the clutch while at full throttle. It cuts ignition and or fuel instantly. So this cuts rpm quicker than waiting for throttles to ramp shut. As youre not relying on removing the air supply to drop rpm. So this might help if the motor isnt losing rpm quick enough.

Then since it knows the next gear ratio it starts disengaging the cut as soon as you approach the right engine speed for what gearbox speed you need for that gear. The goal being to get the motor at the exact rpm needed. So it also helps if the motor is losing too many rpm.

It dynamically adjusts the goal rpm, so even if vehicle speed rises or falls during the shift it gets to the right spot.

Its fiddly to get the clutch point to the right spot. But it might help perhaps.

Edit: thinking about it more I realize the above stuff might help your clutch but maybe not synchros while the clutch is disengaged.

Hmmm. Might still be worth seeing if the rpm goes too high or too low during the shift period though.

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Its just a G4  ecu.  The gear cut control looks pretty basic

Pretty sure its a mechanical issue. as never once got it to change at high rpm.   

but yeh that would be a good setup to have, to take bit of human error out.  

Have some new parts on order to throw at it, hopefully will make it better

 

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  • 2 weeks later...

yeah few places do them,  but would rather try a j160  than  spend 3k on close ratio gearset for t50.

I did come across another issue related to the junk engine in it.      It real sloppy on deceleration, due to poor ring seal.   its like popping neutral on overrun  compared to the good engine.  
So revs will be hanging longer than they should. 

Also looking into super light  clutch/flywheel combo. 

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On 25/07/2022 at 22:10, Roman said:

One thing that i would check, is what happens when you try to change gear.

As in, from 10,000rpm does the engine decellerate too quickly for next gear, or not enough? 

(Running g4x ecu? 1000hz Graphs plz)

Adding a clutch switch and a gearbox speed sensor would allow you to setup flat shifting.

This has a mode where as soon as you hit the clutch while at full throttle. It cuts ignition and or fuel instantly. So this cuts rpm quicker than waiting for throttles to ramp shut. As youre not relying on removing the air supply to drop rpm. So this might help if the motor isnt losing rpm quick enough.

Then since it knows the next gear ratio it starts disengaging the cut as soon as you approach the right engine speed for what gearbox speed you need for that gear. The goal being to get the motor at the exact rpm needed. So it also helps if the motor is losing too many rpm.

It dynamically adjusts the goal rpm, so even if vehicle speed rises or falls during the shift it gets to the right spot.

Its fiddly to get the clutch point to the right spot. But it might help perhaps.

Edit: thinking about it more I realize the above stuff might help your clutch but maybe not synchros while the clutch is disengaged.

Hmmm. Might still be worth seeing if the rpm goes too high or too low during the shift period though.

 

Could you set up something in the ecu to make the engine slow suddenly when the clutch is used ie to change gears?  

Maybe like those DSG vw things that fart at gear shifts 

Or a truck that uses the Jake brake between shifts 

 

I dunno how you would slow it down quickly though, heaps of timing advance to make the combustion happen sooner and try to send the piston back down the hole?/broken ring lands  

 

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1 minute ago, cletus said:

 

Could you set up something in the ecu to make the engine slow suddenly when the clutch is used ie to change gears?  

Maybe like those DSG vw things that fart at gear shifts

 

That's an ignition cut, with the fart being the unburnt juice igniting downstream.

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38 minutes ago, cletus said:

 

Could you set up something in the ecu to make the engine slow suddenly when the clutch is used ie to change gears?  

Maybe like those DSG vw things that fart at gear shifts 

Or a truck that uses the Jake brake between shifts 

 

I dunno how you would slow it down quickly though, heaps of timing advance to make the combustion happen sooner and try to send the piston back down the hole?/broken ring lands  

 

Advance the vvti a bit further and kiss the piston slightly to drop the rpm quickly

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so helpful haha.  

But yeh  some tuning stuff is sure to help to a point.     Swapping engines soon, so will throw the new parts in box at same time.   maybe a combo of things is making it trash. kinda hoping the spigot bearing is screwed in the junker engine too. 

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