Hi all,

I'm working on a RX-8 LFX swap project and see there are several on here with good build threads. I see a lot of internet mentioning that the MV7 has the following gear ratios:



However, I found this Cadillac spec sheet that has different ratios:
https://media.cadillac.com/media/us/...2011.tab1.html

Does anyone know what the actual gear ratios are and how to confirm?

Thanks!

 

ThePass has the ratios in his build thread. I would go with the ratios he posted since I'm sure he looked into it properly.

That said, MV7's are unicorns. Almost nobody choose a manual caddy back in the day, and finding one is near impossible. I have the MV5 in my car with 3.42 rear end. First gear is...useless. I only use it to load my car onto my trailer (and it climbs up the ramps with ease). Second gear pulls super hard, I'm certain (I don't try) I could easily light up my 245 (200 treadwear) tires in second without trying hard. I start in 2nd gear even on hills. The LFX has torque, it really doesn't care what gear you are in, it just pulls.

Your car will weigh more, but I doubt you would use 1st gear with either tranny unless your diff is set up for fuel mileage. That leaves 2nd, 3rd & 4th. They aren't that far apart between the two transmissions.

You may want to talk to Andrew at Keisler Automation and get his take. He's always been very friendly and helpful when I've asked him questions (and about a Miata no less).

Good Luck

 

I think you're way overthinking this, since I'm following along as you post on a couple forums and facebook groups lol.

There are a couple of mv7s on ebay, and car-part lists a few, but most have 140k miles or so.

 

Save me from my brain!

 

The ratios you posted here are what I have in my notes as well.
If I was doing an LFX swap today that was going to use one of these two transmissions, I'd do the MV5 for its better availability and certain compatibility with clutch related parts. Consider that even if you find one good MV7, if you have an issue with it down the line you're then committed to finding another MV7 replacement. To switch to an MV5 you'd have to get a new driveshaft and crossmember.

 

Oh, I thought the MV5 and MV7 were physically identical, just different ratios. That's not the case?

 

The output flange at the tail, and the position of the crossmember mounting points are both different.

 

I see. And to double on firm, Andrew Kiesler also confirmed the output flanges are different. I'm using his kit on an RX8 so MV5 it is. Thanks for the info.