Porsche Boxster/Cayman S Transaxle/Gearbox

[Sulley]

I've decided to pull my Corvair transaxle to replace with a 6 speed Boxster S gearbox. From what I've learned this is a good option for the Manta Mirage. You want to get a 2000 - 2004 model year. The S is the only one to use. Do not use a standard gearbox. The Boxster S gearbox is a G86.20 6 speed and the standard is a G86.00 5 speed. There are multiple sources for an adapter plate and everything you need to bolt the transaxle up to a small block Chevy. One positive aspect is that this gearbox does not need flipped or the ring gear flipped as the Boxster is set up as a mid engine vehicle from the factory. I've attached some pictures for reference.

[Blueovalz]

It looks to be a pretty good alternative. A consideration, especially in my specific case, is the height of the engine block with a non-inverted transaxle. I'm using the 930 box, and in a flipped ring-gear (non-inverted scenario), the motor would be roughly 6" higher than if the transaxle was inverted (for the same geometry of the half-shafts). In an OEM Mirage, this may be permissible, but in my case, the engine would not fit under the rear bodywork. Lowering the entire drivetrain would be an alternative in this case, but half-shaft angle and transaxle ground clearance then becomes a concern.

Obviously using an inverted system presents issues as well, such as a requirement to run a dry sump system (due to the lowered engine height) unless the entire drivetrain is raised sufficiently, which then also increases half-shaft angles. In the inverted scenario, the benefit is a lowered center of gravity for those considering every aspect of performance.

[Ken Walsh]

I'm running the 930, as well--but I have mine inverted. The lowest clearances I have are at the bottom of the KEP adapter, and the bottom of the oil pan. I plan on installing a Kevlar "flack jacket" skid pad under the oil pan (or maybe just a 1/8" aluminum plate) to help protect my pan.

Even with that I will have to keep a close eye out, for speed bumps, tall crickets, etc, etc, etc.

[Sulley]

I'll have to take some measurements as I hope I didn't go down the wrong path by going with this transaxle.

[Manta22]

Sulley;

The conversion from a Corvair to a Porsce transaxle won't be easy. The Corvair rear suspension uses the axle as the upper transverse link while the Porsche uses a separate a-arm. You need to modify your rear chassis and fabricate that part of the rear suspension.

[Sulley]

Neil are you saying the axle shafts are actually an integral part of the rear suspension that the Boxster doesn't share? If I did the rear modifications that Jerry did on his Mirage do you think that would work? Or would I have to graduate to say a C4 link set up?

[Manta22]

Yes, the Corvair is different. I didn't see what Jerry did-- sorry.

[Sulley]

Neal - here is a link to his build. Scroll down to post #35 and you will see the rear set up.

http://mantacarsforum.com/showthread.php/2759-Mirage-%28Re%29build-thread-Jerry/page4

[Manta22]

There is a lot more to do when you go from a Corvair to a Porsche transaxle. The suspension needs to have a lateral link to replace the function of the Corvair axle in the rear suspension.

[Ken Walsh]

There is a lot more to do when you go from a Corvair to a Porsche transaxle. The suspension needs to have a lateral link to replace the function of the Corvair axle in the rear suspension.

All, we might be doing the "dreaded crossing of threads" here. For more info on using a Porsche transaxle in place of a Corvair unit, you might want to check the following thread, starting around posting #55.......

http://mantacarsforum.com/showthread.php/2759-Mirage-(Re)build-thread-Jerry


(In the future, I'll do my best to keep my transaxle comments in the (duh) transaxle threads(!))

[Jerry]

I like this idea too ...

http://www.kitcarchassis.com/index.php

[Blueovalz]

The Audi 01E is a commonly used transaxle behind V8 motors. I think the 450HP capability noted may be a bit high, but it holding together depends on other factors as well. I believe they are getting harder and harder to find, thus necessitating other options. Even though the 016 will bolt up in the same fashion, it's rating is even lower than the O1E.

[Jerry]

I like the rear sub frame and A-arms, the Audi trans I don't like too much.
Boxster or 930.

I saw a Boxster S trans for $1400. tempting ...

[Sulley]

So basically from what I can see when using a trans like the Boxster S if in conjunction with the stock set up I'd just have to fabricate a brace for the lower spindle where the current Corvair trans mounts these. Otherwise it plausible that I could drop in the Boxster S gearbox with new half shafts.

[Manta22]

Sully;

You will need to fabricate whole new upper & lower a- arm assemblies for your rear suspension if you get rid of the Corvair transaxle. The axle acts as the upper "a-arm" in a Corvair setup.

[Sulley]

Neil I had my 'ah hah' moment and now I get it. The axle is the 'upper' control arm and the lower strut going to the corvair transaxle is the 'lower' control arm and as you pointed out my new S gearbox will need a new rear suspension fabricated.

I guess I could do David's subframe, a C4 link set up, or something from scratch.

[HalfMoon]

I'm planning on using my Boxster 987 (2005) six box. Heavier, but able to take ALOT more punishment. Seems to me the way to go is David's C-5 rear subframe with the C-5 rear suspension components.
101810191020

[marfen]

That's a sweet c5 rear subframe. Judging by the looks of the lower control arms it looks like the attachment points are stock C5. Who is David? thx

[HalfMoon]

That's a sweet c5 rear subframe. Judging by the looks of the lower control arms it looks like the attachment points are stock C5. Who is David? thx

David Savage MantaCar.com
https://mantacars.com/productsindex.html

[marfen]

David Savage MantaCar.com
https://mantacars.com/productsindex.html

Thanks.

[marfen]

I wonder if he's still making those. Another alternative is Chris at activepower who also will make you a rear subframe for c5/c6 .

[HalfMoon]

I wonder if he's still making those. Another alternative is Chris at activepower who also will make you a rear subframe for c5/c6 .
Do you happen to have a link. There's alot of Active Power companies out there in Google land.

[HalfMoon]

I wonder if he's still making those. Another alternative is Chris at activepower who also will make you a rear subframe for c5/c6 .

Oh, and if your wondering about the subframe at MantaCars, yes he's still making them. One g downpayment, 8 weeks.

[marfen]

Do you happen to have a link. There's alot of Active Power companies out there in Google land.

activepowercars.com Chris builds GT40 replicas and also has done some montage/m6gt replica work as well. His backhalf C5 is 2x2 sq tube vs the round tube backhalf of Dave Savage's that is being discussed here. price appears the same for either. The activepower setup uses different geometry than the stock corvette attachment points that appears to be on Dave's setup. I am sure either setup will be great and save a lot of work.