Hyperblade's KP61 Racecar "KP61R" Discussion

[Roman]

Haha wow, thats some uncanny synchronization! 

 

[Truenotch]

Looks like it's going well!

What's your theory on the vibration? Are you sure it's not related to wheel speed? It definitely looks and sounds more intense in 5th and 6th gear.

[Hyperblade]

23 minutes ago, Truenotch said:

Looks like it's going well!

What's your theory on the vibration? Are you sure it's not related to wheel speed? It definitely looks and sounds more intense in 5th and 6th gear.

The new vibration is definitely related to wheel speed. And worse in 5/6 gear. Best guess is wheel balance, have been told the 8 year old tyres (probably some performance gains to be had with a new set...) can get out of round over time... But my wheels also aren't normally balanced, may turn out they need to be.

It was probably there previously with the coil vibration which must have been masking a lot of it and confusing the picture.

 

Must post up about the 0 psi oil pressure at 8000rpm too...

[Roman]

What do you mean by coil vibration? 

Man this looks absolutely hectic driving in that much traffic haha. 

Absolutely loving seeing the ongoing development of this car, it absolutely kicks ass.

[Hyperblade]

11 hours ago, Roman said:

What do you mean by coil vibration? 

Man this looks absolutely hectic driving in that much traffic haha. 

Absolutely loving seeing the ongoing development of this car, it absolutely kicks ass.

Bad coil causing what we believe is a partial misfire under load at higher rpm.

Handicap races (Race 2) are all about how quickly you can pass everyone in front, before the faster cars catch you later in the race. So anticipating which cars are coming up and working out best places to pass them (e.g. maybe backing off one corner earlier to set up next corner) losing the least amount of time is the key. Normally means you have to be pretty aggressive at putting your car in spots.

Just feels like lots of annoying expensive repairs at the moment, I would really like to get back to doing cool stuff e.g. itbs

[Truenotch]

I'd say it's very unlikely to be a wheel or tyre balance issue. It looks pretty aggressive, so I'd guess you are more likely to find something happening in the diff, gearbox or driveshaft.... It reminds me of the gnarly vibrations I had from my old single piece driveshaft (which was bad enough to not be able to see out the rear view mirror).

0 oil pressure at 8krpm sounds less than ideal too. 

 

Ahh racecars, they're so much fun 😅

 

[mjrstar]

^^ I'd also be surprised if it's a wheel balance issue, I've never bothered with balancing on my car.

If you have some sorcery to identify frequency of the vibration (either rpm or hz) then narrowing it down could be done using some science. For instance anything pre diff is going to be significantly higher frequency than wheel speed.

Something in the video sounds kind of gear meshy to.me.  Have you ensured the gearbox output shaft to driveshaft slip joint has enough travel?

 

[Hyperblade]

4 hours ago, Truenotch said:

I'd say it's very unlikely to be a wheel or tyre balance issue. It looks pretty aggressive, so I'd guess you are more likely to find something happening in the diff, gearbox or driveshaft.... It reminds me of the gnarly vibrations I had from my old single piece driveshaft (which was bad enough to not be able to see out the rear view mirror).

0 oil pressure at 8krpm sounds less than ideal too. 

 

Ahh racecars, they're so much fun 😅

 

I can't rule anything out but vibration is coming through the seat and also through the steering wheel (although if something was affecting engine bad enough that is mounted to cross member which has steering shaft attached).

I had bad vibrations from the old driveshaft, but the new carbon one sorted that out. 

Diff appears to be fine, and gearbox input/output appears fine at the moment.

4 hours ago, mjrstar said:

^^ I'd also be surprised if it's a wheel balance issue, I've never bothered with balancing on my car.

If you have some sorcery to identify frequency of the vibration (either rpm or hz) then narrowing it down could be done using some science. For instance anything pre diff is going to be significantly higher frequency than wheel speed.

Something in the video sounds kind of gear meshy to.me.  Have you ensured the gearbox output shaft to driveshaft slip joint has enough travel?

 

Driveshaft setup is AE86 Flange > Hilux Flange > Hilux UJ > Carbon shaft > CV joint > S2000 gearbox Flange

So no sliding yoke (old steel driveshaft had one but we had to much vibration hence the CV).

Movement in and out through the arc of rear travel is 1mm (was within range of CV at the time of installation)

I contacted a developer of one of the apps that can do that analysis previously when dealing with the vibration from the first driveshaft and unfortunately at the time they said it wouldn't work to pick it up (Can't remember why)

I should try and replicate it on jackstands when i get it going again, that would be a step to at least trying to find the cause.

Keep the ideas coming, open to all suggestions for things I haven't thought of, nothing is off the table at present (other then short on time to get ready for next event naturally as all racers are).

[Roman]

Do you still have situation where there was only 1 dowel locating the gearbox adapter plate? Could imagine some gross stuff happening if even a little bit out of alignment 

[mjrstar]

Ooh I'd be having a close look at the cv, it probably turns faster than design spec, and could have been running pretty hot too?

Hayabusa Starlet guy had cv problems can't remember the exact cause or remedy.

Perhaps galling because it never deflected enough to turn the rolling elements?

[Hyperblade]

39 minutes ago, Roman said:

Do you still have situation where there was only 1 dowel locating the gearbox adapter plate? Could imagine some gross stuff happening if even a little bit out of alignment 

No 2 dowel pins and now like 7 bolts holding the engine to gearbox.

27 minutes ago, mjrstar said:

Ooh I'd be having a close look at the cv, it probably turns faster than design spec, and could have been running pretty hot too?

Hayabusa Starlet guy had cv problems can't remember the exact cause or remedy.

Perhaps galling because it never deflected enough to turn the rolling elements?

Interesting thought.

I've always had it heat shielded, so heat shouldn't be an issue.

The driveshaft shop knew my specs (rpm etc), but considering they managed to make it short I don't have a lot of faith in them.

But it's interesting idea that as it doesn't have enough movement and that might be an issue (other side of my brain is going please for the love of god no more driveshaft issues...).

Thanks for the suggestion!

[kpr]

how much angle is your uni joint running on?   If only have the one uni and isn't running straight,  it will accelerate/ decelerate every time it turns.  

if have 2 unis aligned correctly they cancel each other out 

[Truenotch]

11 hours ago, Hyperblade said:

The driveshaft shop knew my specs (rpm etc), but considering they managed to make it short I don't have a lot of faith in them.

We had a similar issue with rear axles for the 86 at work (too short). Andre was not stoked about it. 

[Hyperblade]

On 18/08/2025 at 22:41, kpr said:

how much angle is your uni joint running on?   If only have the one uni and isn't running straight,  it will accelerate/ decelerate every time it turns.  

if have 2 unis aligned correctly they cancel each other out 

Sorry delayed reply as been busy and then had to work on car, driveshaft is at 2 degrees.

But have to remember it has been fine before, so it's something that has changed. 

On 19/08/2025 at 09:14, Truenotch said:

We had a similar issue with rear axles for the 86 at work (too short). Andre was not stoked about it. 

I was pretty rope able.  I tried literally every other store around the world to make me the driveshaft none would as they didn't do Japanese stuff. Certainly a big market there for someone to fill that gap.

 

Check out main thread on an update of the vibration issue, we may have got to the bottom of it (will find out at next test day, the day before racing)...

[Truenotch]

15 hours ago, Hyperblade said:

Check out main thread on an update of the vibration issue, we may have got to the bottom of it (will find out at next test day, the day before racing)...

Haha, holy shit man. 10mm of toe out on a solid axle. How!!?? I guess whoever straightened the diff didn't check it afterwards? Have a search to see if there's a truck alignment place near you with an induction heater (magic wand) on their alignment machine - those things are amazing and by far the fastest way to straighten a diff. 

It will be a different car when you get that fixed. Even in a straight line.

[Hyperblade]

9 minutes ago, Truenotch said:

Haha, holy shit man. 10mm of toe out on a solid axle. How!!?? I guess whoever straightened the diff didn't check it afterwards? Have a search to see if there's a truck alignment place near you with an induction heater (magic wand) on their alignment machine - those things are amazing and by far the fastest way to straighten a diff. 

It will be a different car when you get that fixed. Even in a straight line.

It has either been like that since day one when I got the car.

Or

It may have been caused by this when the car came back down, we did check it over at the time, but probably didn't check it for being straight.

 

 

 

[Rhyscar]

Yeah damn that rear diff is crazy. How confident are you it will solve your vibration issues? Extra load through the rear could cause weird drivetrain vibration - but it would be a long shot, whereas the level of vibration you're seeing seems like there should be 1 or 2 obvious causes (or perhaps it is just 4-6 minor effects all resonating!?)

Wheels being bent not ideal, but I've never seen bent wheels cause whole car vibrations. 

 

 

[Hyperblade]

On 29/08/2025 at 14:28, Rhyscar said:

Yeah damn that rear diff is crazy. How confident are you it will solve your vibration issues? Extra load through the rear could cause weird drivetrain vibration - but it would be a long shot, whereas the level of vibration you're seeing seems like there should be 1 or 2 obvious causes (or perhaps it is just 4-6 minor effects all resonating!?)

Wheels being bent not ideal, but I've never seen bent wheels cause whole car vibrations. 

 

 

We don't think diff is causing vibrations been like that for a while 

Have to remember the car has been fine so must be something that has changed.

Not sure on the bent wheels solving it, but have to think they weren't helping, also weren't balanced 70-90g out that's quite a bit. And if there both out of sync at the right offset on an axle you could end up with larger vibration then from one alone.

Only thing can do is check and test each componeta and narrow it down.

Will find out next Friday if the balancing/straightening helps at all.

 

 

 

[CUL8R]

Axlelign should be able to do the diff, otherwise Ray @ Blackwells Commercial has an induction wand..

[Rhyscar]

Great news that the vibration is solved - not so great about gearbox housing. Weld up and re-use or replace?

 

I've always found the sniff test for identifying which oriface is leaking a fun game  

 

17's on a starlet look like hard work! Unsure if it would be worthwhile.