Are V8 automatic transmissions interchangeable with I6's? The reason I ask is that a factory rebuilt transmission lasted 6 years with the RENNTech 3.6 before it needed replacement. The mechanic said typical rebuilt transmissions don't last as long as a good used one so that's what I had installed before the car was wrecked. I'm considering transplanting the drivetrain into a clean chassis so it would be opportune time to update the transmission if possible. I would also like to know if the manual transmissions are interchangeable and if they are any stronger than automatics...

The answer to interchangeability as far as bolt on, the answer seems to be no, from the other threads about a manual swap. However the 16V trans does bolt up to an I6 and I will be documenting the swap shortly... Allegedly handles around 350 HP. Probably more robust than the Autos, but I have no plans to ever buy an automatic again either way. I believe the factory autos are weak anyway. Depends on your standards. Renntech has auto trans upgrade parts don't they?

If you are going to make some serious power, I suggest to upgrade to bmw m5 gearbox. These are bulletproof getrag units...
merc 16v box will allso do the job but not over 350hp...

Does it bolt up? I was thinking when the HP gets that high rip out the gears and have them treated and strengthened and such, its gotta be good for like a hundred more maybe? And with a real good flywheel/clutch, the 350 will stretch...Nothing lasts forever anyway.

Some say that it will boltup 100% cause the 16v is useing getrag box and bmw m5 is allso getrag unit...but my personal opinion is that if it won´t bolt up, its way easyer to make it bolt up than strenghting gears and you can be sure that then it will hold cause these boxes are used with 1000hp around here (europe). when mateing merc engine to bimer box, its pretty logical to use a better clutch/flywheel and there are pretty much of them on the market for m5 box...

sounds like something to check on. But, half the reason in getting the 16v box was the tight gearing as well. I don't know what the M5 ratios are, are they taller? Strengthened gears are probably just as easy, pull them and send them off. With mating a different box up, you have to measure then fabricate, then custom driveshaft, and then custom shifter, etc. ease isn't part of it anyway, with ridiculous power I'd strengthen the gears of any transmission. I don't even know how much abuse anyone has attempted with the 16v box.

Or, I can offer you your transmission re manufactured using kevlar bands and clutches... Far stouter then the OE material.

And as mentioned above, the I6 and V8 bell housings are indeed different...


It's also not the HP that's the problem w/ transmissions, it's the torque. You could put a 16V box on a car that's making 500HP, just as long as it's not making much torque.. However, drop it onto a something making loads of torque (ie, a V8) and it won't last long at all.

Jonathan

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Jonathan Hodgman
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Are you saying the 16V's 5-speed can fit the 16 engine? Are the 5-speeds in 300E's the same as 190E's 16V's?

They aren't the same trans. The 16V is stronger, and quite a bit closer gearing. If I'm not mistaken, the 16Vs are all dogleg and only some of the 300Es are, or none? The 16vs trans will bolt up to the 103/104 engines. I think it has already been done somewhere, and I will provide visual documentation to prove it as soon as I start. Waiting on bolts. I will also provide info/exact specs on those so as to avoid the ridiculous dealer cost as well. Then performance info.....