Best car for an engine swap, RX8 and my idea.

buzzboy said:

jgrewe said:

There was a guy that put a VW Tdi in an FC Rx7 a while back. I think he ended up pulling it out because it just didn't do anything well. I'm guessing it was all in the gearing.

Be still my cetane pumping heart! I'd take the time to change the gearing in that case. A car that light with TDI torque would love a 3.00-3.25 gear. I guess that would complicate things, but not be impossible. I'm sure there's no mazda diff anything under 3.90

Well, specifically there are 2 issues.  First is that the diff in a 2nd gen has a huuugggeeee pinion gear (in length).  It wasn't shared with anything else.  However, there are kits to put in 8.8s that have minimalish fabricobbling required.   Just need about $2.5k in your checkbook.

The diff swap solves / helps the 2nd issue.  It has like a 23.5" tall tire stock.  This exacerbates the gearing issue.

3.9 was the tallest gear available for the fc.  Found in automatics.  If it's a non turbo, you CAN get an LSD 3.9.  That would be in the GXL sub model.

In reply to buzzboy :

The FC weighs so close to the weight of an A3 Jetta (or MkIII if you are so inclined) that I couldn't tell you which is lighter.  Probably the VW is lighter.

Remember TDIs are not very spectacular with torque.  A 1.9 TDI only makes 155 ft-lb.  That's almost the same as the nonturbo 13B that came out and way less than a modified 13B.  The difference is that the Diesel runs out of breath while the 13B can keep on going, and going, and going...

Pete. (l33t FS) said:

The Ranger transmission has horrible gearing and the shifter comes up near the firewall.  If you're going to have a trans that has huge ratio differences between gears you may as well not bother, because you will always be in the wrong gear and driving won't be very fun when you shift at 7 and the revs drop to 4.

Agreed on the crappy for a sports car shifter location, but overstated on the gearing IMO.

The Miata/RX8 5-speed generally has similarly 'wide' gear spacing to the Ranger 5-speed with the exception of 3-4, which is narrower than the 2-3 on the Mazda but similar to the 2-3 on the Ford. While they're all similar, the (biggest) 1-2 rpm drop is even actually slightly bigger on the RX8 5-speed than the Ranger 5-speed. Off-hand, I don't recall many complaints of 'always being in the wrong gear' driving a 5-speed Miata or RX8 though.

The Miata/RX8 6-speed is designed to jam an extra gear in a similar total gearing range as the 5-speed, which trades extra shifting for narrowed gear spacing vs the 5-speed unlike a T-56 which uses the extra gear more to expand the gearing range. But it turns out that while the 5-speed will obviously have wider gear spacing than the 6-speed, the (biggest) 1-2 shift rpm drop for the Miata/RX8 6-speed variants is also still effectively the same as the 1-2 drop for the Ford 5-speed.

I'll admit that the 3-4 shift on the Ranger 5-speed is probably wider (7.0k-4.7k) than ideal, but I'd also argue that the 4-5 shift (105mph on NC Miata) on the Miata/RX8 6-speed (especially the early RX8) is similarly narrower (7.0k-6.0k) than ideal. That doesn't make the gearing on either particularly horrible though.

I don't believe the rx8 ever came with a 5speed manual.

Here is a chart that I put together for various gearboxes and their ratios.

Edit: I am surprised at how close the Ford M5R1 and the GM tremec t5 are!

wvumtnbkr said:

I don't believe the rx8 ever came with a 5speed manual.

 From what I can find it was available as a 5 speed only in the first year and not in the US.

In reply to buzzboy :

Manual trans 4 ports had a 5 speed trans, manual trans 6 ports had a 6 speed.  Manual trans 4 port were not sold in the US, and the unit looks like a derivative of the FD transmission.

In reply to Driven5 :

The RX-8 trans has almost the same gear ratios as the Competition 5 speed that Mazda used in IMSA GTU, except with a granny 1st that you can safely ignore.

I'm kind of a fan once I found that out.   Closer gears is always better.

In reply to wvumtnbkr :

Just to be pedantic, the NC and RX8 ratios in your chart are both for early models. The late NC moved to a .787 6th, and the late RX8 used the same ratios as late NC but with a 1.536 3rd.

Everything I've seen on the M5ODR1 says that it's:

3.72

2.20

1.50

1.00

0.79