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We're up to 115-120mph now until the Buzz begins! That's 6k rpm in 6th gear for me.
I removed the K Power PPF delete. I modified a stock PPF as y'all have done, mounted it to the trans crossmember. I had to clearance the PPF quite a bit for the larger diameter aluminum shaft. A circular saw and shop press made quick work of that job. I cut about 5" off the trans side.
So now from a mounting standpoint I'm at:
roadstersport engine mounts
cheap rubber trans mount
PPF mounted to crossmember with urethane mount from the KPower kit. All the stock hardware is retained on the diff side.
Roadster sport diff mounts. (I still need to get the stock snubber rubber things, I also burned off the rubber for the poly diff mounts, I don't think it really matters but I have some on order)
The aluminum driveshaft is prob 2/3 the weight of the steel. I think I am still going to pull the driveshaft and have it evaluated by my local shop. I measured .010" runout at the trans side, .003" at the diff side. Will get weights when it's back out of the car. I think I had 0.2* difference between the trans and the diff flange vertically.
The car's drivability, NVH and overall manners are much better setup like this. I could live with the general roughness/nvh before for a track car. To be clear, I'm talking about everything other than the horrid resonant vibe- just general manners. That bad vibe is not acceptable even for a full blown track/race car.
As far as the high RPM NVH, I'm not sure how to proceed. I noticed when I was banging out the PPF pressnuts that the whole back of the car resonated at the same frequency that I'm hearing on the road. I'm thinking that the heat shields, gas tank, sheetmetal in this area are amplifying the resonance- the stiff mounting of the diff with the PPF delete kit just added energy to the mix. It would be very interesting to remove some shields, maybe add some strategic sound damping mat and such (prob to the PPF too, that thing rings like a tuning fork) and see if it helps the severity.
I could def mess with the alignment some too, but it should be "close enough"
I also don't love how the PPF is only mounted at a single point at the front - I'd like to make a bracket that locates the top of the PPF to something sturdy, so we're helping to react the torque at the diff. I doubt that is what is causing the vibe, I was accelerating slowly to these speeds, but it feels wrong from a (backyard) engineering standpoint.
at any rate, this is a street car that I've intentionally left with short gearing, I am not too worried about getting that last 20mph out of the car right now. I will likely go through with the getrag diff swap when I decide I want more top end.
Hell yeah dude! Glad to see some good progress on your end. I ordered a set of diff mounting plates with the rubber isolators as well. I also figured they probably won’t make a difference but they were cheap so NBD.
I like your idea of mounting the PPF to the supplied trans mount. I wonder if getting another rubber mount like the one I posted and using that for mounting the front of the PPF would help even more. It’s such a long “lever” that I’m sure the front mount could be softened and still allow minimal diff movement.
We're up to 115-120mph now until the Buzz begins! That's 6k rpm in 6th gear for me.
I removed the K Power PPF delete. I modified a stock PPF as y'all have done, mounted it to the trans crossmember. I had to clearance the PPF quite a bit for the larger diameter aluminum shaft. A circular saw and shop press made quick work of that job. I cut about 5" off the trans side.
So now from a mounting standpoint I'm at:
roadstersport engine mounts
cheap rubber trans mount
PPF mounted to crossmember with urethane mount from the KPower kit. All the stock hardware is retained on the diff side.
Roadster sport diff mounts. (I still need to get the stock snubber rubber things, I also burned off the rubber for the poly diff mounts, I don't think it really matters but I have some on order)
The aluminum driveshaft is prob 2/3 the weight of the steel. I think I am still going to pull the driveshaft and have it evaluated by my local shop. I measured .010" runout at the trans side, .003" at the diff side. Will get weights when it's back out of the car. I think I had 0.2* difference between the trans and the diff flange vertically.
The car's drivability, NVH and overall manners are much better setup like this. I could live with the general roughness/nvh before for a track car. To be clear, I'm talking about everything other than the horrid resonant vibe- just general manners. That bad vibe is not acceptable even for a full blown track/race car.
As far as the high RPM NVH, I'm not sure how to proceed. I noticed when I was banging out the PPF pressnuts that the whole back of the car resonated at the same frequency that I'm hearing on the road. I'm thinking that the heat shields, gas tank, sheetmetal in this area are amplifying the resonance- the stiff mounting of the diff with the PPF delete kit just added energy to the mix. It would be very interesting to remove some shields, maybe add some strategic sound damping mat and such (prob to the PPF too, that thing rings like a tuning fork) and see if it helps the severity.
I could def mess with the alignment some too, but it should be "close enough"
I also don't love how the PPF is only mounted at a single point at the front - I'd like to make a bracket that locates the top of the PPF to something sturdy, so we're helping to react the torque at the diff. I doubt that is what is causing the vibe, I was accelerating slowly to these speeds, but it feels wrong from a (backyard) engineering standpoint.
at any rate, this is a street car that I've intentionally left with short gearing, I am not too worried about getting that last 20mph out of the car right now. I will likely go through with the getrag diff swap when I decide I want more top end.
if i understand the setup right this is the config that gave me the worst issues. Had a realllly bad vibration/deep noise from the car when just slightly accelerating in 5th and also the bad 70mph violent vibration that bracing the ppf to the subframe helped with greatly.
Yeah, can confirm, soft trans mount took my NVH from moderately annoying to borderline comfortable. Good point on the driveline angle consistency too. I’ll order another rubber mount myself for the PPF as well!
I banged on the car for a few hrs yesterday, all still good. No launches yet but 2-5th gear runs and it feels fine. Had a passenger and he (with a stock seat) said he couldn't feel anything abnormal. My Sparco is mounted to the floor (literally the seat pan is on the floor) so I'm going to def feel a lot more than him.
I dropped the shaft off at my local driveshaft shop today.
They reacted better than when I brought the steel one in, but had one comment. On the diff side, the builder used a "conversion U joint" with a grease-able center. The U joint on the yoke side is a non grease-able unit. The preference for high rpm driveshafts is the non-grease able type- the greased ones you cant really adjust the u-joint tight enough to run smooth at higher rpms. I'd be interested to hear if anyone out there can confirm this, or if it's just this guy's experience. I know the non-grease able ones are stronger with no cross drilling etc.
There were also no balance weights on this shaft. We'll see what they think. They are going to replace the grease-able U joint with a more appropriate spicer, go over the rest, and balance it.
I'll get a weight on it too. If I remember right, the shipping weight of the steel shaft is 26lbs.
Well damn, here's some information that I wasn't previously aware of. So the greaseable joints on our steel shafts wouldn't have been ideal for high rpm use according to him as well. Did he say why the greased type can't be tightened enough? I'm trying to wrap my head around why that would be...
More importantly, still 115-120mph for the buzz? Damn I'm actually hoping the driveshaft shop says the shaft needs balancing and that gets rid of it for you completely!
Well damn, here's some information that I wasn't previously aware of. So the greaseable joints on our steel shafts wouldn't have been ideal for high rpm use according to him as well. Did he say why the greased type can't be tightened enough? I'm trying to wrap my head around why that would be...
More importantly, still 115-120mph for the buzz? Damn I'm actually hoping the driveshaft shop says the shaft needs balancing and that gets rid of it for you completely!
I was shutting down top of 5th, so I didn't get into the buzz zone. We'll see if it's any better after I get it back, but it's tough to find enough empty road around where I live to safely get up there.
I'll also ask for more detail on the grease-able vs non. He was in a rush today but said something about the grease-able ones have looser tolerance (that gets pumped full of grease) vs the sealed units that are not designed for servicing. Maybe at high rpm the grease flings out? I certainly experienced that with the steel shafts- the kPower steel ones left a ring-of grease in the transmission tunnel/rear subframe.
what did the steel one you had made come with? It's prob not a big deal either way.
I was shutting down top of 5th, so I didn't get into the buzz zone. We'll see if it's any better after I get it back, but it's tough to find enough empty road around where I live to safely get up there.
I'll also ask for more detail on the grease-able vs non. He was in a rush today but said something about the grease-able ones have looser tolerance (that gets pumped full of grease) vs the sealed units that are not designed for servicing. Maybe at high rpm the grease flings out? I certainly experienced that with the steel shafts- the kPower steel ones left a ring-of grease in the transmission tunnel/rear subframe.
what did the steel one you had made come with? It's prob not a big deal either way.
I feel you there. Much easier to duplicate the 75mph vibration than anything else. I have yet to take my car up to 120+ because of that, but need to do so soon.
Ahh yeah that makes sense. My original KPower shaft flung grease out of the rear joint too. I don’t think the front joint flung any grease but I’ll check tomorrow. Both joints had zerk fittings on them. My current shaft has zerks on both ends as well, but I haven’t noticed any grease around the joint area. I’ll check it and report back next time I have the car in the air.
This is almost off topic, but today I was working under a truck and noted it had a heavy rubber damper hanging off of the differential. I totally forgot that was a thing. Wonder if hanging a damper off of our diffs would make a noticeable difference in the vibration. I do assume, however, that the damper would need to be selected specifically to match the frequency and severity of the vibration. I wouldn’t know where to start with that.
Asking out of curiosity and for posterity, have any of you with these issues considered finding a way to adapt the PPF concept to the BMW transmission? Godless Commie has a great thread on the subject, but his project is extremely involved.
I'm holding out hope for an oddball engine/transmission swap kit to become available soon, and this thread is making me question what sort of misery I might find if the PPF has to go.
the original motivation for the Kpower swap kit is it’s advertised as a plug-and-chug solution.
turns out, it ain’t. Saw a few threads on Facebook (high HP Miata group) where folks have shared similar experiences with this swap.
i think another user BBundy also did a swap with PPF retained. He made an adapter bracket- I’ll look for the thread. It looked really well done.
edit- like this
Seems that most people run into these issues with the stock rear end, and just spend their way out of the problem with the Getrag kit. I’ll likely be among them soon enough.
"During construction and development, we made sure that a PPF frame was still installed in the vehicle between the gearbox and the differential. This means that the transmission does not have to be screwed rigidly to the body, which leads to immense vibrations when driving."
Wish I'd read some more posts from the Facebook group beforehand. I'd likely have bought the SPS kit instead or planned on dropping even more coin for the Getrag swap at the same time lol
The original motivation for the Kpower swap kit is it’s advertised as a plug-and-chug solution.
turns out, it ain’t. Saw a few threads on Facebook (high HP Miata group) where folks have shared similar experiences with this swap.
I don't mean to **** talk them everywhere, but that seems to be the overwhelming theme I encounter with K Power products in general. I really wanted to do a K swap a few years ago, but the longer I waited the more I found examples of quality issues being unaddressed at their production level, while they instead focused on rolling new products out. QC seems to be done after the product reached the customer and they found the issue. It's to the point I'm surprised I don't see more negative conversations on them in general. Maybe that's because they do seem to try to fix the issue after the fact, but to my mind after a few years on sale the problems shouldn't happen in the first place.
Yeah, I’m kinda feeling this way about them currently too. Better to ask for forgiveness than permission? I guess for one party it is…
I was honestly pretty stoked to be working with KPower when I forked over several thousand dollars to them for my swap kit. I’d never looked super hard but at a glance it seemed like most K-swap guys were happy with their kits/service. My buddy David has a K24 in his NB1 and didn’t have any serious hangups with his conversion.
It wasn’t until I did the swap and started researching the vibration until I actually watched Greg Peterson’s videos on the subject. In one of his videos, he overlays an email thread between him and KPower referencing five or six other users at the time having the same driveline vibrations with KPower Getrag 260/ZF5 swaps paired with Miata differentials. This video was five years ago! And KPower’s talking to us right now as if our issues are standalone.
Alright I don’t want to start ranting too hard either, I’m not the dude who’s gonna fab up his own trans swap kit from scratch. I’d still be (somehow) blowing up 6 speeds or turning down the boost if it weren’t for this kit. Maybe they oughtta just link this thread on their site so future buyers know what they’re getting into lol.
In reference to this week's earlier posts: I checked out my driveshaft today. No grease fling out of either joint on it. Guess the original driveshaft either had some additional lube between the seals when it was built, or was trash in this regard as well lol.
I ordered a pack of rubber isolators to run in between my PPF and crossmember, and hit the buy button on M8s instead of M10s. D'oh. M10s are on order and should be here tomorrow.
Already had the car in the air today and wasn't taking no for an answer, though. The isolators I got are female on one side, male on the other. Took two of them and cut the male ends off, then drilled through the center so I could run an M10 bolt through them. Put one on either side of the crossmember, ran an M10x120 bolt through, and added a beautiful stack of washers on top. Preloaded them sufficiently with a nut and added a second nut on top with some loctite to act as a lock. Ran the car up to 5.3-5.5k rpm in 6th gear (~115-120mph) before the vibration really got violent. It was still present and noticeable around 5k rpm. Don't think the vibration changed much. I don't think this setup is very stable for the PPF and am still going to swap in a single M10 isolator tomorrow. My lower rubber diff plates/bushings are showing up today so I'll probably throw those in tomorrow as well.
I emailed SPS to see if they could share pictures and dimensions of their custom PPF. Long shot but maybe it will work for the K Power swap cars, I'll follow up if they get back to me.
I emailed SPS to see if they could share pictures and dimensions of their custom PPF. Long shot but maybe it will work for the K Power swap cars, I'll follow up if they get back to me.
Should have the shaft in hand tomorrow, too!
Ahh not a bad idea! Wonder if they sell them separately, although I’m sure that’d be the most expensive PPF ever purchased if shipped from Germany lol.
Hoping you get good news about the shaft (that it was not dialed in and needed a good balance).
Originally Posted by sixshooter
That ppf is much higher above the crossmember than mine.
What? Weird. That’s where I’ve been running mine. Measured it again when I bolted everything together. Pinion angle is 2.1* currently.
Also, a quick follow up. The vibration is no different with the car in the air (haven’t tested on the road), but NVH is noticeably lessened. Guess that’s no surprise lol.
There is a quote among some KPI racers I love, "Thats the first we've heard of that problem. We didn't see it during testing. However, here is a solution for you can pay us for"
05-26-2024, 08:58 PM
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