3.73 vs 3.55 you know the drill
 

I've got 3.08's and want more. Any reason to not get the 3.73 over the 3.55's? Do you need to have anything besides the speedo recalibrated? computer problems, etc? thought it would also be a good time to get pulley's installed too. Gears would speed up the accessories, pulleys slow them down for a net of zero?

With the marginal difference in RPMs at highway speeds, I would recommend the 3.73's - even though I have the 3.55's http://www.mustangworks.com/msgboard/biggrin.gif

Pullies are a good mod too. If you're worried about the alternator not getting enough charge from the larger pulley - don't. It really doesn't have that much effect. Unless you are going to be sitting in traffic for hours on end would it really hurt you. I've had my March pulleys on for ~5 years now and have never had a problem - same battery for the last 4 years to boot!

Good luck,
E

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1991 5.0 LX Coupe - 38,000 miles

13.17 @ 106.14 mph w/ 2.138 60'

For an AOD'd stang, 3.73s.

If you had a C4, daily driven (long distances) stang or even 5-sp manual, it'd be a different story.

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351W-powered 1979 Ford Mustang notchback
Stock 5.8L under custom made 4" cowl, C4 w/ shift kit
Holley 750 cfm, Edelbrock Performer RPM intake
1 5/8" MAC shorty headers, Al driveshaft
2.5" Off road H-pipe, 2-chamber Flowmasters
Front: 225/60/15, Rear: 255/60/15 Eagle GT II
Weld wheels (15x6;15x8), 8.8" Rear w/ 3.55s
14 x 4” K&N air filter. Only a few months b4 Project FOX begins!!! http://www.mustangworks.com/msgboard/cool.gif

"Red, thou art my companion. Hasten now your quickened metamorphosis to Green that I may conquer all who dare abide there beside me. May they be left thither behind burnt black." ---Fox Body

i'm getting 3.73's.
yes, the speedo will be a bit off, but a speedo shop can fix that, and the difference is so marginal, just do it.

Don't fear the gear.

Get 4.10's... changing to 3.55's would be a waste. Are you just a street racer or a real racer? If you take the car to the track there is no reason not to get 4.10's. The idea of a gear change is to make use of all your gears, not just 1-2-3 w/ a stick, use 4th... you should top out in 4th at slightly higher RPM's then your shift point. My car in overdrive was at 2600 @ 70-75. I drove it all over, my only car for 3 months. 3.55's are just way to conservitive...

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Joe Zemaitis, Grand Rapids Michigan

1991 Mustang GT. Mods to date: 4.10 rear end, new POSI, aluminum driveshaft, AOD w/ shift kit, 2 1/2 off road h-pipe, 2 1/2 flowmasters and 2 1/2 tail pipes. Electric fan, Removed air pump and egr tube. Hotchkins upper and lower control arms. New energy suspension rear busings. Hoosier Quick Time Pro 27x10.5x15 and bolt on subframes soon to be welded. Everything else is STOCK. Totally stock ENGINE. 14.29@96 with 130k miles.

I'd go for 4.10's. I drive my car all over the place and love the 4.10's. it's still not bad down the interstate. One thing to watch out for if you have an aod. I put in 4.10's and the aod I had was shot within 10 miles. So i converted to a tremec tko. But i love the 4.10's wouldn't change for anything. But if you are strictly only looking at 3.73's or 3.55's, go for the 3.73's, i think you'll be glad you did.

Sorry, I forgot to mention I have a 1990 LX 5sp with 76k miles and no mods other than K&N filter. Just street racing and daily driver; 26 miles a day. Probably go with the 3.73's. Best to get a Ford dealer to install? I've heard they are a B---- to do and get it right. thanks
Stan

You should probably get an aluminum drive shaft too. You'll have some vibration (almost all owners) at higher speeds.

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1993 Mustang GT - K&N, March Ram Air & Pullies, 73mm C&L MAF, Edelbrock 65mm TB & EGR, 1 5/8in Equal Length Super Competition Hooker Headers, 2 1/2in H-Pipe w/hi-flow cats & Flowmaster 2 1/2in Cat-Back Exhaust, FlowTech Cut-Outs, Nitto DR's, 3.73 gears, FMS Aluminum DriveShaft, Pro 5.0 Shifter, Pro-Shift Lite, 8.5mm MSD Super Cunductor Plug Wires, PowerSlot rotors, PowerMaster 140amp Alt., LX lights, Cobra R hood w/SVO scoop, Saleen spoiler, Cobra Bumper, 3in chrome tips.

Just checked it out on the analyzer. With stock tires your 80 mph rpm is 2190 with the 3.08, 2524, 3.55, 2652, 3.73 and 2916 with the 4.10.

With the stock motor it may slow you down to go higher than 3.73 but I would go 3.55 for a mild daily driven mostly stock car. How often will you notice the 0.1 - 0.3 in the quarter?? With more exhaust and intake mods the motor will make more power at higher rpms, and would respond to the 3.73 or 4.10 gears, remember those AOD guys have a deeper overdrive gear too.

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Frank W 90 5.0 LX Notch MAC 2.5"cat bk FMS alu ds, MSD coil, MAC shifter 2.73 gears user site
88 Notch 2.3L FOR SALE! My two Notchbacks
74 Chevy Laguna Type S-3 305 now 454 soon My web site

4.10's if it's an auto and the 3.73's if it's a 5-speed.......unless you're gonna blow that thing, then you might want to stick w/ 3.55's.

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'90 LX 5.0;12K original miles;FMS 3.55 gears; March pulleys;Edelbrock Performer Heads;BBK 1 5/8" equal length shorties;MSD 6AL ignition w/ blaster 2 coil;FMS E303 cam;Pro-M 75mm MAF;BBK 70mm TB; Eibach drag-launch spring kit;Southside weld-on subs;9" K&N cone filter charger;Hurst shifter;Cervini 3" turbo hood;A/C delete;gutted cats;2 chamber Flomasters;Corbeau racing seats;FMS 30# injectors;JMS custom chip;Holley 190lb fp;TFS track heat intake (12.299 @ 113mph w/ a 1.78 60')
....soon to be b

Put in the 3.73:1 gearset!!!