3.27 vs 3.55

[bigal0043]

In a follow up from my first post, I have since acquired a less than 1k miles T5 from a 90 mustang ($300) And have a fully rebuilt 351 Cleveland with edelbrock intake and carburetor. I also picked up a fox body 8.8 with 2.73 and a limited slip ($150). The plan is to fully rebuild this rear end and convert to 5 lug and disk brakes. And also 17” rims.

I plan on my roadster to be a cruiser, not a lot of city driving and don’t plan on doing any racing. I am leaning toward new 3.27 ring and pinion but open to being convinced to go with 3.55. I see most roadsters being built with 3.55.

Online calculator the 3.27 in 5th gear at 2100 rpm is 70 mph and the 3.55 in 5th at 2300 rpm is 70 mph.

[Lickity-Split]

I have a T5 with 3.73 rear gears. Driving leisurely, first gear is good for about 6 mies per hour needing shifting to second. As a result, much of my driving begins with second gear because first is too low, making it basically usless. With such a low first gear in the T5, I'd go for the 3.27.

With a different trans that had a higher first gear, I'd go with a 3.55.

[MB750]

Personally, I'd go with the 3.27. Coincidentally that's what I have. To me it's more than high speed cruise RPM, I like my lower gears having more legs too.

[Jeff Kleiner]

The Mustang T5 has a 3.35:1 first gear which when combined with a 3.55 rear is kind of short and will have you grabbing second before you get across the intersection—-second gear is a party though! :D

Jeff

[Ducky2009]

Things to think about. Do you have a stock cam? 2100 RPM would be good. Bigger cam, idles above 1500 RPM.... 2100 RPM may not be a smooth ride.

[john42]

Things to think about. Do you have a stock cam? 2100 RPM would be good. Bigger cam, idles above 1500 RPM.... 2100 RPM may not be a smooth ride.

How big is big? I have a TrickFlow Stage 1 cam, idle set to about 850rpm, cruises very smooth @70mph at about 2k RPM. Have a T5 and 3.27. First gear in parking lots when burbling into car meets is both fun and you have to pay attention to not start a lurching dance.

[Blitzboy54]

The Mustang T5 has a 3.35:1 first gear which when combined with a 3.55 rear is kind of short and will have you grabbing second before you get across the intersection—-second gear is a party though! :D

Jeff

Same, if I was to do it again I would go with a 3.27

[jwebb]

I didn't think FFR supported a 351 Cleveland in the roadster?

[Jacob McCrea]

I have the same transmission in a Type 65 with 3.27 gears and a Ford Racing 302 (Windsor) crate engine. The car has 19" wheels and I believe the tires are larger diameter than most, so the final drive ratio feels taller than I expected. But I wouldn't change the gears unless it made sense for tracking the car. You should be in good shape with the torque from the Cleveland, although you may be over the torque rating of that transmission.

[Jeff Kleiner]

Same, if I was to do it again I would go with a 3.27

If you do it again keep the 3.55 rear and use a T5-z! This is my favorite because of it's 2.95: first gear and .63:1 fifth. The overall reduction in first when combined with a 3.55 rear works out to 10.47 and fifth overall is 2.24. I think both are ideal.

For comparison the Mustang spec T5 with 3.35 first works out to 10.95 overall with a 3.27 rear and a stump pulling 11.89 when used with a 3.55 rear. The Mustang spec T5's fifth is .68 which equates to 2.22 overall with a 3.27 rear and 2.41 when used with a 3.55.

Jeff

[Jeff Kleiner]

I didn't think FFR supported a 351 Cleveland in the roadster?

They don't.

Jeff

[bigal0043]

I didn't think FFR supported a 351 Cleveland in the roadster?

Correct, long story on how I acquired it but going to give it a whirl on installing it. I’ve read a couple other posts on other members who have done it, so I’m ready for this challenge.

[bigal0043]

Keep the comments coming, so far looks like I’m sticking with the 3.27 choice.

[MB750]

Keep the comments coming, so far looks like I’m sticking with the 3.27 choice.

Why don't you stick with the 2.73 for a while to see how it works for you? Back in my youth I had an 88 GT with the 2.73 ratio and the one thing I really liked about it was how long the gears were. In a car that's 1000 lbs lighter, it might actually work.

But if you do pull the 2.73's, lemme know. I'll take them off your hands if they're still serviceable.

[Jeff Kleiner]

Why don't you stick with the 2.73 for a while to see how it works for you? Back in my youth I had an 88 GT with the 2.73 ratio and the one thing I really liked about it was how long the gears were. In a car that's 1000 lbs lighter, it might actually work.

But if you do pull the 2.73's, lemme know. I'll take them off your hands if they're still serviceable.

I built one for a customer who provided a 2.73 SN95 rear end and a Mustang spec T5. I encouraged him to let me change the gear set while I had the rear end apart to convert it to Fox width but he thought it would be fine. Guess what happened 2 weeks after he got it home? A set of 3.55s :)

Jeff

[Dgc333]

The Fox Body 8.8 I picked up has 2.73 gears. I pulled it apart to rebuild, the gears were in great shape so I decided to leave it alone until I had driven the car.

Well I have my 33 to the point I have been able to drive it. It has a 5.7 Hemi (~ 400HP), T5 and 305/35-20 rear tires. I was stunned at how easy it is to break the rear end loose with small stabs of gas in 1st, 2nd or 3rd gear. At this point I can't imagine why I would want steeper gears.

IMHO, If the gears are in good shape leave the 2.73s in there until you have driven the car then decide if you want steeper gears.

[DanQ]

I agree with the comments on leaving in the 2.73 gears, at least try them out. My '33 HR is being built with the stock 3.08L gears, and I am sure it will match my driving style (old man). You will also appreciate the lower engine/exhaust noise as well. That motor will pull strong with any gears you have in such a lightweight car. It would be very different if you said you were planning to go to the track or wanted unbelievable acceleration. It cost nothing to leave them in for a while, you can always switch the gears out easily.

[AC Bill]

A 351 should have plenty of grunt with the 3.27's all day long. But they go like a scalded cat with the 3.55's. Your out of first and second gear pretty quick, but it's still pulling hard in third and fourth. Usually your already over the speed limit on a Hwy by the time you shift into fourth. It's a fun gear on winding roads too, as compression braking is more apparent, and it's fun hitting the short straights with a burst of acceleration.

[CraigS]

I can't fault the thought of trying the 273s but...dang you will be throwing away a lot of acceleration. I had 308s in my MkII w/ 400hp 351 and 327 made it significantly quicker. My MkI w/ stock 302 and T-5 had 355. That worked w/ a 225hp engine and the super short first gear was made up for w/ much better 2nd and 3rd gear accel. For yours I'd go 327

[Railroad]

Just to add to the head scratching, Ford has 3.31 gears available. I swapped them for 3.73 in my GT500. I need to dig them out and put them up for sale.

[TBull]

I've had both gear sets in my two cars. My first MKII was 450 HP and 3.55 gear set first witha T5Z and then a TKO 500. Like Jeff said I found 1st gear too short. My latest has the 3.27 and I much prefer it. If I build another car it will have the 3.27 again.

[nuhale]

I recently went to 3.55 from 3.27. Gen2 coyote/TKO600. The car was great with 3.27 at highway driving. With my setup the 3.55 feels much more “awake” in 1-2. I do miss the low rpm at 80-85 on highway. It’s a few hundred RPM higher. These can easily be swapped so give it a go and change if you feel need.

[Jim1855]

Just an FYI
The early T-bird IRS had 3.27s as an option. The 2015 Mustang ISR uses 3.31s. Not really a big difference, or not worth worring about.
I choose 3.31s for use with my 427 but way too early to tell how it will work. I've run 3.27, 3.46 and 3.73. 3.27s are my selection.
Jim

[TBull]

I think you car's HP and Torque play into this as well. The car was great with 3.27 at highway driving. With my setup the 3.55 feels much more “awake” in 1-2. All of that went into my consideration of what rear gear to run. I believe many well built big blocks have used the 3.08 gear sets as well. Just a thought.

[wbulk]

After several years of driving with the 3.50s in my 9" I switched to 3.25s over last winter. My engine is a SB 5.0 with 330 hp that I have the rev. limiter set at 5,600 with a mid teens 212-218 @ .050 duration CompCam. I was lucky to find a new set of 5th OD .81gears a few years back replacing the .68s. Overall I really like this combination and am very satisfied with it. This test for me was after a couple of drives was, did I second guess my decision and want the 3.50s back. No not at all. The 3.35 first now was longer and the .81 OD was just right on the freeway and became just like another gear that fit in. I never thought about it again.

[TBull]

I agree WBulk. I forgot to mention my current car has a TKO-600RR with the .82 5th gear, but I built the car with road courses in mind.

[Tremelune]

I find visuals help me understand gearing a lot, so I drummed up this calculator that draws the gears on a graph:

http://gearwars.net/

Might help you understand what the car will be like for various gears/speeds.