5spd auto rear swap

[boxdogracing]

After a few chances over the years didn't pan out, I just arrived home with a 12/43 rear from an auto spider. I have wanted lower rpm on the highway since my first drive. Right now with original rear I'am running 56mph@3K + 76mph@4K (GPS speed/w 195/60/14) I will post new #'s with the auto rear in a few days.

[BenjamminsFiat]

boxdogracing,

Yes, please keep us updated. I have a 76 I got a couple of months ago and after driving it around a while, I find it's geared way too low for my tastes. Maybe it's my imagination, but I never seemed to notice this in my old '73, both are/were 5-speed.

It's not something that's high on my list of things to do with the car at this point. Plus, I'm worried that a rear end swap (not that I've ever done one) would make the gearing go too far the other way. But as another forum poster pointed out, having to switch gears after 30 feet and halfway through an intersection is kind of a pain. The problem is probably exacerbated by the fact that there are no hills where I live and you have to take the highway to get anywhere

You know, this is another one of those examples where having a forum is crazy helpful. People with the resources, skill and knowledge to do this type of modification post their results here, benefiting who knows how many other people. Never underestimate the value of a good write up or even just posting the results.

Speaking as someone who was a lurker for a while both here and at other forums, it's was always surprising to me how many times I'd find the information I need buried in a thread from years ago...

So thanks boxdogracing, for posting your intended project. I'm really looking forward to at least hearing how it worked out for you.

Thanks

[TulsaSpider]

""You know, this is another one of those examples where having a forum is crazy helpful. People with the resources, skill and knowledge to do this type of modification post their results here, benefiting who knows how many other people. Never underestimate the value of a good write up or even just posting the results.

Speaking as someone who was a lurker for a while both here and at other forums, it's was always surprising to me how many times I'd find the information I need buried in a thread from years ago... ""

I concur and I think we are lucky. I recently bought a 95 Z28 and looked for a forum..... egads, the amount of posts is mind boggling and impossible to navigate. We have it pretty good!

[Twister]

I've been told this swap works well on the 2.0L which has power to spare. I'm looking for one myself, or the ring & pinion.

[So Cal Mark]

personally, I don't recommend the swap to an auto diff. I like the acceleration the 430 provides and at fwy speeds I'm right in the torque sweet spot. I've taken long trips and cruised at 4k+ for hours. The exhaust note at that speed is pretty awesome with my setup

[BenjamminsFiat]

You have a point, Mark. I drove mine 1,500 miles home right after buying it with the engine screaming the whole way. It was kind of nerve-wracking to me given that the car was an unknown to me at the time. I don't have a cool exhaust like yours... yet ; )

I went and researched some of the power characteristics of Fiats and couldn't find all that much. However, it seems with the 2L engine, the power band is really pretty flat (the 1608 is much more narrow). I'm hoping that my 1800 is similar. Is there some published dyno charts or even just raw data out there? I have to believe that people have gotten their cars dyno'd a bunch. I'd like to see some of that data. There's nothing like adding a bunch of objectivity into a discussion. While I'm typing and trying to explain why I think the auto rear-end would be great for my car, I find myself using words like "feels bad" and "shifts too fast".

Either way, with a flat curve I'd gladly trade a tiny bit of passing ability for better gas economy. But that's not even the biggest issue. The main reason I'm interested is so I can stay in first gear just a little longer. I live in a downtown setting so it's crazy annoying in traffic.

As I mentioned, it's way down on the list... i'll probably go electric anyway eliminating the need to shift. Electric motors, now there's a torque curve to envy

I'm still super interested to hear how it goes, bdr!

[Tobi]

A 205/70 14 tire could help + the automatic rear end + the automatic transmission .
A Fiat Spider is a "sports car"! The only annoying thing at 70 mph is that I can not step on it and go full throttle for a couple of hours like I used to on a Autobahn

[boxdogracing]

[quote="BenjamminsFiat"]

I went and researched some of the power characteristics of Fiats and couldn't find all that much. However, it seems with the 2L engine, the power band is really pretty flat (the 1608 is much more narrow). I'm hoping that my 1800 is similar. Is there some published dyno charts or even just raw data out there? I have to believe that people have gotten their cars dyno'd a bunch. I'd like to see some of that data. There's nothing like adding a bunch of objectivity into a discussion. While I'm typing and trying to explain why I think the auto rear-end would be great for my car, I find myself using words like "feels bad" and "shifts too fast".

+1 I would be very interested in dyno #'s associated with these motors. I also like the info on forums, and sometimes object opinions are all that can be offered. My build is running a 2L 5spd with a turbo setup I built. So I have no intention of making claims as to acceleration this swap on any other application than my own. Of course the rpm #'s are universal and as with everything that goes into a build it is up to you to decide how you want you're build to "feel" when completed.

Good to see so much interest, my wrenches are calling...

[fiatfactory]

.

[BenjamminsFiat]

When I had initially heard about the rear-end swap (on this board), I believe those who commented mentioned the same thing. That only the 2L engine had the power to pull it off.

I'm still really interested in how hard it is and what the procedure is like. I've been wanting to upgrade my engine anyway, lol. I found a couple of posts in the archives of Mirafiori about this from way back.

I don't want to re-post a bunch of stuff, but here's at least part of the post (you can see the whole post at this link, but the car was a 78 2L w/IDFs):
http://www.mirafiori.com/archive/_F_I_/2030.html

95 horsepower at rear wheel/ 116 flywheel(calculated). The dyno
tested from 2,000rpm to 5,700rpm. I told him to use 6,000 but
maybe he was nervous. Anyway, I ran two runs changing only
mainjets:
REAR
WHEEL FLYWHEEL
RPM 135 145 135 145
2,000 40 40 49 49
2,500 52 50 64 61
3,000 64 62 78 76
3,500 73 70 89 85
4,000 82 79 100 96
4,500 90 88 110 107
5,000 94 94 114.5 114.5
5,300 95 95 116 116 ...Power peak
5,500 92 94 112 114.5


135mj 145mj
rpm --torque--
2000 103 103
2500 108 105
3000 111 108 torque peak
3500 110 106
4000 108 104
4500 105 102
5000 98 98
5500 92 94

And here's a completely unrelated post about the gearing:
http://www.mirafiori.com/archive/_F_I_/2114.html

Anyway, if the great and wise Fiat oracles tell me it's not smart to do with an 1800 engine, then I won't be doing it to mine until I upgrade. But I'm still really excited to track your progress and see the results!

[spiderrey]

I just sold the auto rear end out from under my spider, a 70 with a 2 liter built to Crofts fast road specs. It was amazing at highway speeds, fast acceleration when you jumped on it at about 60, it ran hard up and past 125. iIhad lots of fun with this setup but, when ever we ran our little club runs up the canyon it felt like I lost to much bottom end, I didnt always have instant power on hand when exiting a corner through the canyons. i missed the torque that I got from the stock rear end on the bottom end. With that setup the car would suprisingly break the rear tires loose if I was running in a straight line at times. Second gear was a blast, so Im in the process of going back now.

[BenjamminsFiat]

Jeez, all you guys have such awesome cars! Maybe I need to stop posting in the Performance sub-forum to keep the jealousy to a minimum ; )

I'm actually having an e-mail conversation concurrent with this one about almost the same thing (horsepower). It was started by mentioning fuel injection and the Mega Squirt system. So many things to do...

It occurred to me that I've only had my current spider for 3 months with very little driving done. I'm not even sure it's tuned correctly. I'm sure that's a contributing factor to my reticence and aggravation to really wind the car up in the revs. I'm just not comfortable with the mechanics of the car yet... and would hate to blow something up. I guess you could say I'm babying it in other words.

Either way, I'll still be following this thread with enthusiasm. I hope it works out for you BDR! I'm a big fan of modifying and customizing until you get the car that YOU want. And thanks so much everyone for taking the time to educate me on this.

[boxdogracing]

Back from first high speed burn, new #'s 62mph@3K + 84mph@4K
By the way my original rear was 10/39, all with 195/60/14 tires

10/39 3.90 rear 56mph@3K + 76mph@4K

12/43 3.58 rear 62mph@3k + 84mph@4k

Those are the hard #s I wish I had an accelerometer as this change has of coarse has made all gears a little taller.

In my case I really like the change, the car likes to hang in each gear longer. I think I could see boost in first gear given better road condition's. Overall the car feels more powerful, I guess it could be my driving style. I don't really like to ring it out in every gear. I do realize the car had to lose some low end acceleration I just don't feel it. With boost available from under 2K my car pulls hard for what it is. I'am sure it accelerates better with turbo and tall rear than all stock. So in my mind I have lost nothing. I may swap the 3.90 in for a couple drag runs this summer just to see the #'s. For those of you unfamiliar just changing the rear theoretically will lower you're elapsed time, but MPH should be the same. I would be interested to see the difference, and will post if I do.

For those of you interested in the process of swapping the rear, the Fiat spider is one of the easiest I have done. Just jack up the car, support it by the body in front of the rear wheels so the rear hangs. remove Ebrake cables and brake line (I pinched mine with needle nose Vise grips and cut between Vise grips rear as I had a new one anyway, otherwise you need to cap/plug). Remove the four drive shaft bolts. Take every bolt out of the rear links at the rear. Now the rear should hang freely by the shocks. I used a jack to support the rear one side at a time. compress the spring slightly, remove the top shock nut, and lower the rear. Going back together once I had it back up hanging by the shocks every thing easily lined back up, bolted together, connected the Ebrake and bleed the breaks.

[BenjamminsFiat]

It's late, and I'm tired but I had to post and say congrats!

I'm glad it wasn't complicated (thanks for posting the procedure you used at the end) and that you seem to like the change. Those numbers ARE very impressive. Now that we have those RPM/MPH numbers, do you feel like taking your car for a run on the dyno? : )

I'm kidding of course, but would you mind if I ask what your engine setup is? Any estimate of the hp/ft-lbs your engine produces?

Thanks again!

[boxdogracing]

I would love to take my car to a dyno, if I can find one for reasonable $. I'am located between D.C. and Balt. MD ideas welcome.

My turbo build thread is located here: http://www.fiatspider.com/f08/viewtopic ... 17&t=10708

I'd be happy to help with any other info on the build if interested.