5spd auto rear swap

[baltobernie]

I heartily recommend Ed York (York Automotive) in Mt. Airy. $50 per hour, and he let me work on my carburetor between pulls. He races a 2002, so has lots of Weber expreience. One of the local favorites for spec Miata tuning, too.

BTW, we got 104 RWHP from my 1800. Search "New Head" thread for details.

[boxdogracing]

That dyno sound sounds great. It will probably be about 4-6 weeks, and i'll be running Megasquirt (perfect for dyno tuning). Right now I have modified the L-jet to be safe, not to produce max power. I will dyno this car and post #'s when complete.

[BenjamminsFiat]

I'd be super interested in seeing your numbers.

Funny coincidence, I had a conversation regarding dyno-ing a car with Megasquirt on it just last week.

Are you still glad you did the swap? I hope you're enjoying a job well done!

[PittsburghKevin]

I have a spreadsheet that shows MPH for Gear and RPM tables given different combinations of transmission, differential, and wheel size. http://phiee.org/shared/Fiat%20RPM%20MP ... ulator.xls. The topic comes up from time to time and I was interested in the 131 transmission.

To use the spreadsheet:
GREEN tables are data tables. The information should be accurate. If it isn't please let me know.
GREEN Fields with GREEN Borders show values to be entered. This is where you type tire size, transmission, and differential model & year. If the spreadsheet understands it it tells you good next to the field.

BLUE table is the output table. This is the calculation for the selections that you made.
GREY table is just random calculation and value to make displaying the end results easier.

[Sunracer]

I had a 3.58 rear on my spider for a while, great top end with a built two liter. But I switched it to a 3.90 for two reasons. One was ehnn cruising with my FIAT buddies I was always far ahead as the car could easily cruise at 85-90mph, so I would have to stop and wait for everyone. The other was i=on mountain roads with tight hairpin turns I found myself having to downshift into first and often lacked the right gear as the spread between ratios was so wide. If you want more I suggest you look for one of the rare 4.10 third member gear sets that are out there for the early diffs or swap the rear, driveshaft and panhard rod from a spider 2000. PB

[Exit98]

When I first got on this Forum I saw a post from somebody who said it seemed like he was in fifth gear by the time he got to the bottom of his driveway. I laughed because I knew just what he meant.

As soon as I got my 76 I knew I wanted to go from the 4.10 to the 3.90. I also knew there was little chance that it would happen as my list is too long and my skills too limited to imagine that I’d take on such an optional project.

Then I blew the rear.

So with Ralph’s encouragement and help from the Jersey guys, Ralph, George and Scott who provided the pieces needed from a parts car, and lots of help and support I’ve now got a 3.90 rear. It has been about a month now. It has really transformed the car. I expected that I’d see the biggest improvement (from my point of view) on the highway at 70 MPH or so, and it has dropped the revs about 450 rpm, but what I’m really enjoying is around town and zipping along the back roads. Now I’m in third gear way more often and find myself in 4th gear forgetting I have another one to go. I know it’s a little slower off the line but I really don’t care.

I like revs as much as the next guy, back in the day I’d rev my 72 to 7000 routinely. But once I’m settled into a cruise, at whatever speed, I like to tone down the roar.

There are others here who’s opinions I respect who don’t agree with this switch, but if you think you want to give it a try I gotta say, go for it. I’ll never go back. If anyone wants details of what’s involved just let me know.