I'm looking at 914/6 transmission gear ratios because I have one in my shed. I'll be the first to say that transmission gearing is not my strong suit. According to Charlie Davis the 914/6 transmission has:

1st: Same
2nd: Taller
3rd: Taller
4th: Same
5th: Shorter

I'm not sure why the 5th would be shorter. My guess would be to keep the 6 cylinder revs up for cooling as well as to keep it in the high 6 power band. Am I wrong?

If I rebuild this tranny to mate with a 2270, I'm thinking that it would be smart to put the 4 cylinder ZD 5th on there since I'll have plenty of torque down low.

I have the guts from a /6 tranny in my garage. The factory reason was to spin the fan faster to compensate for the 10 degrees hotter the engine ran in a 914 chassis. They also changed the redline on the temp gauge because it ran too close to the original line.

Clay is spot on.

I'm putting that gearbox you tore apart back together via Evil and I'm thinking ZD but I have my reservations.

1. That 2.5 runs hot in my 911 with a jailbar front cooler.
2. Now put it in a teener...

I'll have the front cooler which is ducted and radiator style vs. the jailbar in the fender well so I think it will be OK.

Thoughts? ZD or...? I spoke with a friend who has a factory 2.0 twin plug teener and his tranny had the 904 shaft and 912 gears. How does the ZD compare to the 912 final?

and the fact that the 911 engine had about a 1,000rpm higher redline and cruising torque was not as good as the 2.0L 4s.

I have an 8,000rpm redline and no torque. Now what?

I have a ZD fifth in my 914/6. It runs at 3k at 70MPH all day long with a 190 degree oil temp.

But I have a 911 Carrera cooler mounted in the right rear corner with the fan hooked up.

Front cooler = freedom. I wouldn't worry about heat. Plus you can always upgrade to a larger cooler.

But if you want my ZA gear Eric, we can probably work something out.

Shorter gears

912 4 or 5 speed final is X 28:24 (0.8571) versus the ZD 31:22 (0.7097) and the ZA 29:22 (0.7586), so it's even shorter than the ZA, by quite a bit. The 912 5 speed is you MSX gear source.

What about a D first gear for a torquey 2270?

OK.



I'm a gear dummy. What does that mean?

Six Gear Chart

Four geras are ; A-F-N-V-ZD

Real reason was: To not be as fast as Porsche's 911 flagship.

You can take that as subjectively as you want.

Why is a boxster engine 'detuned' compared to a 996 engine of same displacement?

The MSX trans is the 'hot' setup for AXing, and most likely what's in your close ratio transmission. The MSX transmission has:

1st: A - stock first gear
2nd: F - stock second, which is part of the mainshaft
3rd: M - shorter than stock
4th: S - shorter than stock
5th: X - shofter than stock

The stock 912 five speed has MSX gears for 3,4,5. So if you were building an AX box, then a 912 five speed would be your donor trans.

gear chart time bitches....

(this is for my car... but the ratios are shown... the MPH will be off by a few % due to my tire sizes)

MSX can be fine
but they are kinda tall for a -6
they are really better suited to the -4's because the -4's often have a lower redline

MSX is great for 6K or even up to 7k
above 7K they are too tall

choosing gears is kinda like jakes description of a complete system
it depends completely upon your redline, track length, wheel sizes, torque curves, etc
when you start reving a motor over 7 and up to 8+ you really need shorter gears than MSX

I ran MSX (well actually Ka, S, X) on both a -4 and my current 911S motor at 7300. You wouldn't believe the difference when I went to the FJOSV. With the MSX I couldn't even use the X and S was even too long of legged for above 7K

brant

I'm starting to catch on with Brant's description and Boy-Wonder's chart... especially given the engine I have. It doesn't wake up until after 4k and would top out over 8.

I too, run @ 3K RPM doing 70mph. No oil cooler up front, yet, so I've run around 205*/210* this summer. However if I drop down to 60mph the temp drops dramaticaly: 180*/190*.

Never goes over 200* in the winter no matter what my speed. No idea what my gear ratios really are- supposed to be the same as a 906 .