Miata PPF discussion, use it or no?

chetcpo · **Posted:** Mon Oct 23, 2006 12:57 pm

**This discussion was split from Adam's build log so as not to clutter it up.***

locostv8 wrote:

FWIW it seems that I remember somewhere a 7 using that rear cutting up thier newly finished tunnel to allow the instalation of that long torque arm.

This is why I am locating my diff and engine/tranny before I design the tunnel. I don't think that it is critical to use that piece (which would need modified) to connect the tranny to the diff, but it is an option I am currently keeping open. I know in Keith's car (which was well recieved by the C&D people) he simply bolted the parts to the chassis with some rubber bushings.

THAWA · **Posted:** Mon Oct 23, 2006 1:43 pm

The PPF is integral to the miata. I'm not sure how confident I'd be in a locost without one.

locost_adam · **Posted:** Tue Oct 24, 2006 12:43 pm

As per chetcpo,
I will build the tranny tunnel once the PPF is in. I may use the Mazda item, but at the moment I am planning on fabricating my own with some angle iron.

calvin · **Posted:** Tue Oct 24, 2006 3:12 pm

here is the picture of Keith's friend doing that:

http://www.cheapsportscar.net/flip.php?x=198

He has some other pictures of how everything was modified to make it work. To me it seems like he did it without making additional interferance into the passenger compartment.

chetcpo · **Posted:** Tue Oct 24, 2006 7:42 pm

calvin wrote:

here is the picture of Keith's friend doing that:

http://www.cheapsportscar.net/flip.php?x=198

He has some other pictures of how everything was modified to make it work. To me it seems like he did it without making additional interferance into the passenger compartment.

Thanks for the pic. Look back by the rear bulkhead. That's the only place that it really gets in the way but that's also where the back of the passenger seat usually goes. What he has done is pretty much what I had in mind.

Scott · **Posted:** Tue Oct 24, 2006 8:19 pm

That looks really good, but, it is more weight. I'm not sure what the PPF weighs though, so maybe it's worth it, maybe the same results can be replicated for less weight, dunno' till I get there.

chetcpo · **Posted:** Tue Oct 24, 2006 9:09 pm

***The following is from a related post, I added them here because they pertain to the discussion.***

chetcpo wrote:

Well I haven't done my tunnel yet because I've been putting off the decision of whether or not to cut down, reweld and use the Miata PPF or to just bolt the tranny and diff to the frame. I understand what the PPF does in the car, it sort of melds the tranny and rear end into one unit. Therefore when it is used the only true chassis mounting points for the entire drivetrain are the two engine mounts up front and the outer flanges of the diff housing in the back. So, if I get rid of the PPF I will have to somehow manage to secure these pieces together. Bolting them down with rubber bushings probably allows too much movement between the two and bolting them solid to the frame is really no different than using solid engine mounts. (since the engine-on soft rubber mounts-is bolted to the tranny) So what to do?

Another issue is passenger space. The rear diff driveshaft plate is offset to the pass side 3/4" and with the PPF around it there is only about 14.5" or so for a passenger seat.

So here's my real question. What happens if I bolt the tranny and diff straight to the frame with no bushings, thereby making the chassis the PPF? Bear in mind the engine bolted to the other end of the tranny is on rubber mounts. Will this put undue stress on the tranny and break it or the bellhousing? Will it shake, rattle and shimmy making my car an unpleasant place to be?

HHHMMMMMMMMMMMMMMMMMMMMM. Lots to think about.

Scott wrote:

My 2 cents (and no, you can't have change)

I would solidly mount the diff. to the frame, metal to metal (or a delrin or other really hard synthetic material)

I would use rubber or at most polyurathane for the transmission. The u-joints will make up the difference between the transmission and the diff, so there shouldn't be a vibration issue there.

Now, how to mount it. Are you planning on having lots of passengers? It might not be that important if not. There are smaller seats, albeit less supportive, that'll fit in the smaller space, but at 14.5 inches, it might only be a technically called a seat. Another idea is to build a bench type setup for the passenger, using up all available inches, then leave the racey stuff for the driver.

I believe Keith T. had an interesting solution to the PPF mounting for the diff.

I guess this is where you can let the creative juices flow (big help, I know)

modernbeat · **Joined:** Sun Sep 10, 2006 11:29 pm **Posts:** 370

I think I'd skip the PPF and use an RX7 rear housing that had the extended nose.

KB58 · **Posted:** Tue Oct 24, 2006 11:44 pm

Be aware without the PPF there's about 1300ft-lb worth of torque trying to rip the differential out of the chassis...

modernbeat · **Joined:** Sun Sep 10, 2006 11:29 pm **Posts:** 370

KB58 wrote:

Be aware without the PPF there's about 1300ft-lb worth of torque trying to rip the differential out of the chassis...

That's why I'd avoid using the short nosed Miata housing...

And use something with a longer lever arm to resist the torque and make up for the lack of a PPF like the RX7 Housing...

Photos from Randy's SoloMiata page.
http://members.aol.com/solomiata/Drivetrain.html

Scott · **Posted:** Wed Oct 25, 2006 6:07 am

geez, if that thing were any longer you wouldn't need a driveshaft

one thing i've noticed as a miata owner, mazda didn't put anything on the car that really didn't need to be there, so i say use the PPF or similiar methods

KB58 · **Posted:** Wed Oct 25, 2006 9:22 am

The torque figure I threw out is the engine's torque multiplied by both the tranny and diff. It's a worse-case situation where the car is in first gear, given the gas, and the wheels do not slip. Reality says the tires will slip - unless racing slicks are used... With "normal" tires though, the diff mounts will never see that level of torque, but the problem is, it could with the right tires.

It would be cool if Keith Tanner would add his comments. I was suprised that he felt the PPF was not needed, but didn't give a reason why. As he works with Miatas and built a Locost I especially like to get his input.

chetcpo · **Posted:** Wed Oct 25, 2006 9:48 am

Would something like this work? It should arrest any torque in the front to back plane. Pardon the poor drawing, it sucks but should give you an idea of what I'm thinking.

Want2race · **Posted:** Wed Oct 25, 2006 10:57 am

calvin · **Posted:** Wed Oct 25, 2006 12:13 pm

In Keith Tanners's log you can see where he initially built the car without one (remember that other picture was of a firend of his car) and the diff moutn did fail. He came up with a substitute. That story starts somewhere around photo 647

http://www.cheapsportscar.net/flip.php?x=647

LocostUSA.com

Miata PPF discussion, use it or no?

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