Thats my question, how much am I going to want the msx box when i'll have the 2.7 @ 225? Who has one or one w/o and how happy are you were you?

Makes a world of difference for track driving. My 2.5 with 200 HP just sings with MSX gears. Huge difference for me. Stock gearing car just winds out gears forever, not bad for the street, but if youre going to track the car its definitely a worthwhile investment.

I have MSZ in my box, very close from 2nd into 3rd, the S for 4th is great, the Z in mine is not to good on the highway for cruising.

Interesting thread on the subject. I have a 2.5 (200hp) that also loves to scream with a stock gear box. Car is driven, not tracked though. I was thinking about getting one of the tall 5th gears for it. I think they are the "H" gear? Can't remember. It's nice having an engine that revs as it finally makes 1st gear feel like something you can use.

IMHO, MSX is useless in a road driven car as you will be cruising the freeway at high RPM = bad mileage, noisy, more stress on the engine. The MSX is great for AX because it lets you keep the engine on the power band in that environment.

Root, Putting an H gear on an air cooled engine of lower displacement is not a great idea as you will have your smaller displacement engine working harder at lower RPMs = less cooling air. RPM = life in an air cooled setup. Larger displacement /6 and water cooled engines are a different story and you can easily gear a 901 to have a similar gearing to a 4spd 930 box which has taller gears.

Sounds like my spare box will be looking for parts such as a LSD and MSX...watching your car makes me drool Grant......

Hey Man, I got an MSX set for sale if you are interested. PM me. As for LSD, you are on your own there, I dont have any

If the primary use for the car is AX see what gears your local AX courses accommodate. I seldom use even 3rd gear for AX. 1st & 2nd should be those redone with 2nd being the key. I use a GA 2nd up to about 63 mph (7100 rpms with my tire size) and will ride the limiter for 50-60 feet to avoid having to use 3rd.

While I would love an H or HA 2nd, they are a very rare mainshaft ....the alternative being a 904 mainshaft....bring money. I went with a B 1st tho I think (now) that a C would be better. At any rate, the GA brings 3rd closer negating the need to change it.
Your 2.7L will be able to torque thru the lower range of 2nd ......35ish mph...if you cam it right and will allow you to use 2nd for everything but the start for 95 % of courses. Time spent shifting a 901 box is time wasted an AX......just my .02.

the 2.7 should give you a ton more flexibility than a small motor.
use a gear chart, calculate your tires in... and the tracks.

I know we run mostly short tracks, but the F/J/S/O/V in our 901 is so nice on uphills in the heat of the moment. I think I'm only 900rpm between 4th and 5th. Ran Eagles Canyon 3 weeks back with a big uphill straight. That box gave me positions on cars with more HP.

A similar thread came up about this awhile ago with some good info. I think gearing is one of the most important but most neglected item of all performance items. First decide what you want to do with the car and how much power you have.

For instance on my 3.6 first gear was useless. Instead of not using it and starting in second, I re-geared first (good for 53 mph) so it was almost as tall as second. I also installed a taller second. For fifth, I installed a very tall gear for cruising and mileage. Those that have gone for a ride in my car will tell you how quiet it is at highway speed. What I have is a tall but close ratio gearbox in gears 1-4 and a "overdrive" gear for the freeway. For my application it is great but for yours it may be totally wrong.

Bottom line, there is no perfect gearing for all things. Decide what you do most and gear for that. I would not install short low ratio gears in a car that you drive on the freeway frequently. It will drive you crazy. Think it through.....it's an important decision.

what is the letter of the stock 901 5th gear?

i need some sort of overdrive as i easily top out in 5th hitting the rev limiter. did that with the car loaded with luggage and 2 people on the drive home from the RRC.

going up the steep hill from reno to lake tahoe i hit the rev limiter in 5th and the car was still pulling like a freight train ...

i believe i was going around 130mph, can't remember the exact number,
Andy

Stock 5th is a ZD, you could do well using a flipped H gear in 5th. I would bet that your box would do even better if you converted it to a 4spd like the 930. Youwould save some $$ too because then you would no longer need 1st gear stuff. To convert to a 4speed you need only get a stock N 3rd gear that you flip and put into 4th and an H gear.

Are you coming to the clinic, Andy? We could do it there or I can show you. I will be doing it to another box.

If you hit the rev limiter in a stock 901/914 gearbox, you were traveling more than any 130MPH. What is the diameter of your rear tires?

With stock size tires, redline would be over 150 MPH.

Here is the gear chart:

Here is a link to a download able gear/speed calculator:

http://www.carquip.com/parts/gchart/index.asp

Here are my projections for the 901/930 conversion using a flipped H in 5th and a flipped N in 4th
Click to view attachment
Click to view attachment

The looks of those ratios is why I refused to give up the 5 speed with a tall first. The difference from 2nd to 3rd is a huge jump. You have to figure that 5th for a cruise gear is a throw away gear now leaving you with a 3 speed for the street......not too fun if you ask me.

Look at the ratios on my tranny. You get 4 gears to zip around in and a cruise gear with low engine rpm drops between shifts. 4th gives me all the speed I am willing to drive this car. Also, I would not gear any taller in first than this setup if you have to drive in city traffic. It can be annoying if you get stuck in traffic and it's somewhat hard on the clutch. For a 2.7, I would drop first to about a 48 mph max at redline. This chart is based on a 6800 rpm redline
Click to view attachment

If you knock out your 3rd gear it is almost identical. Also, you are using a different r/p than the stock 7:31 901 set. Are you using a 915 box? With the 930 ish setup youcan use 1st and 2nd as you do and they are geared so that traffic will not be a problem, but when you want to get on it you can run 2nd from 3K (40mph) to red line (80mph) and shift up to 4th if you want. It makes 2nd a more versatile gear and leaves 4th and 5th to kick ass on the free way. MHO. The ratios are almost spot on to the 930 gearing, Porsche must have had a reason Also, mine is more budget minded, all around good times, no hassle. You are using different 2nds, 1sts and r/p ratios and different trannies which in the long run = $$$ Not a problem if one were so inclined. Mine cost $325 for the H gear from Carquip (or less from a private vendor) and $50 for an N 3rd from me if I have one. With seals, it is under $500 and will still kick ass.

That is a smooth gear chart, though.

Also, I am talking about this configuration for a 3.6 (Andy's), not my 2.7. Your 1st and a stock 2nd in a 901 are almost identical. I can always gear 3rd (4th) so that it is shorter. Since a flipped 3rd is identical to a Z gear, an X gear would lower 3rd (4th) a little to close up any gap, but that would be based on personal preference of feel. My intention was to mimic the 930 box with the 901, though.

Mine is a 915 now but I started with a 901 with a flipped "I" gear. Just didn't like that wimpy 1st. For the budget minded, it's a tough decision for sure. I do have a lot of $$ in my tranny....One of those wallet squeakers you hate to do but are glad you did it when the shock wears off. My first gear alone cost more than a 901 rebuild but I can stand on it in first without too much worry.

Don't forget that the 930 tranny had an engine with boost behind it making those ratios a lot more livable. For us N/A guys I think closer might be better and why you see a trend for 6 speed trannies out there. I guess if your wallet won't allow a re-gear you gotta do what you can....

I hear ya there

Here are both charts in Excel format. Enjoy.