Sounds like maybe kitcarchassis.com makes the adapter for using the LS to the 5 speed, but wondering about how reliable it is, at least compared to the 6 speed?

I make parts for the mechanic at the local Porsche dealership who does all of their race car work and he races a spec Boxster himself. He says they have problems with the 5-speeds. I have been at the shop several times when he has had one open with broken gears. That is under race conditions but if the low torque Porsche motor is tearing them up I don't know how long they will last behind a V8. The starter location is not relevant with the LS adapter since I use the compact gear-reduction drive starter that does not have a snout.


It’s not possible to mate the 5 speed to the GM engine using an adapter because the starter location is not applicable. Furthermore, the transaxle is weak and the gear ratios are not a good match for the V8. It’s a throw-away transaxle as our industry sees it.

I heard there unreliable junk compared to the six speed. Ths came from a local shop that builds BSR's for track use. Boxster Spec Race Car. Supposedly they finally changed the rules allowing the six speed. Initial BSR had to be the stock 5 speed.

Well I personally mated my Boxster 5 spd tranny to a late model GM 5.7liter LT1 engine with a few custom pieces and ran for about six years without destroying the tranny, however I also did some track days and found the top end was lacking because of the gear ratios. Otherwise for street use it served the purpose well; still have available if interested.

Now moved up to a LS6 motor form a Corvette and mating to Audi 01X tranny which will have great gearing and top end around 180 mph. I did purchase the LS1 adapter setup from Kitchassis this time around rather than custom fab everything. LS6 motor has been installed but not yet completed the MegaSquirt EFI system, but hopefully within a couple weeks will have running. My memory tells me the Boxster 6spd maybe a better tranny, but the gear ratio was not much better than the 5 spd. !

Somewhere I read that there was only about 100 rpm difference between the two. I was only going to use it for the daily driver. I don't race, so for all practical purposes, it most likely will be ok. I don't pop the clutch, or burn out either. I was told the 6 was a stronger trans?

I had another comment similar to this one that really made me paranoid, thus, just after I had bought it of course.


I talked to the Porsche mechanic yesterday and he says they often strip the teeth off of the gears in the 5-speeds even with the stock engine and it makes less than 200 HP. I would definitely recommend the 6-speed or 01E.

What kills them are high gear oil temps. If you can keep the oil cool they work fairly well.