Which Gears if Supercharged?

U

UpRise_5.0

Founding Member

Jun 16, 2002

664

1

16

Canada

Sep 24, 2007

#1

• Sep 24, 2007

• #1

Hey,

Im going to be supercharging my 1994 Mustang GT with the mods in my sig, with a SC-trim or S-Trim. I have to have my gears redone and wondering if I should go to 3.73s, or stick with 3.55s.

Im running street tires as well (275/40/17), through a T-5. Will I have more traction with the 3.55s, more gear at the end of the 1/4 mile, etc?

Thanks

 

The Green GT

No 13 year olds are safe around me.

10 Year Member

Jan 8, 2006

1,269

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99

Louisiana

Sep 24, 2007

#2

• Sep 24, 2007

• #2

3.55's will give you that extra traction if you are S/C.

But you could always get some sticky ass tires.

 

M

martfr2

New Member

Oct 30, 2006

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0

Sep 25, 2007

#3

• Sep 25, 2007

• #3

I would keep the 3:55 they work well with SC. My brother has an Novi2000 with 3:55 car runs great. He babies the car so don't have 1/4 numbers. But it kicks ass on the freeway!!!

 

Wi Stang

Member

Jun 27, 2004

248

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16

Fountain City, WI

Sep 25, 2007

#4

• Sep 25, 2007

• #4

I would stick with the 3.55's.
I ran those on my car. (When it was running )
I am not too sure what level of boost you are planning on running, but last year my car put down around 500rwhp, and I was going through the traps at about 123 mph. On a street tire with the 3.55 gears, that was pretty close to the top of my rpm range.
This year after some weight reductions and a little more tuning, I was actually touching the rev limiter before I could get through the traps at about 125 mph.
This was on a 315/35/17 nitto DR.

 

FlyBy763

Member

Apr 23, 2004

439

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17

Palm Bay, FL

Sep 25, 2007

#5

• Sep 25, 2007

• #5

3.73s are about the most you want to go...thats what I have and I am at the top of 4th at the end of the 1/4. Traction is also a big issue with 3.73s, and I dont make that much power. I have 275/40-17s

 

The Whistler

New Member

Sep 2, 2007

6

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Palm Harbor, FL

Sep 28, 2007

#6

• Sep 28, 2007

• #6

3.55 is what I have with a positive displacement KB. With a centri you could easily go with a 3.73's. My buddy Chad has 4.11's in his Cobra with a centri and MT drag radials.

 

Stanger007

Founding Member

Sep 26, 2001

2,015

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46

Baton Rouge, LA

Sep 28, 2007

#7

• Sep 28, 2007

• #7

I've got 4.10s now and love them - for as little as I go to the track (4-5 times a year), I'm gonna keep them as long as I can get away with it... too much fun on the street.

Wes

 

final5-0

Mustang Master

Apr 6, 2003

6,817

12

79

DFW Texas

Sep 29, 2007

#8

• Sep 29, 2007

• #8

I've never had a forced combo
but
I've spent a lot of time in the past
lurking around in the pa forums of many different sites

Here are my thoughts on gear ratios based upon all that research

I've seen many things said about all this so I'll break them down
to what I see as two big concerns

1) Optimum gear for 1/4 mile

This is T H E main reason blown combos go for a lower numerical
ratio like 355's. You really don't have to look hard at all in those
forums to see them complain about running out of RPM with
ratios of 373's and steeper.

2) Traction

These forced combos make a L O T of power
so
There is gonna be a point as the power builds where the tires just
can't hold traction any longer

Of course ... when driving around on the street .........
some road surfaces hold better than others :Word:

but

If a combo with this kind of power production capability uses 355's
or 373's ... it ain't really gonna make any noticeable difference in
how it does or does not hold traction IMHO.

Lets get real here

My little NA combo will not allow full throttle in 2nd gear if I wanna
maintain full grip so a combo with 100 or more rwhp is gonna
blow away the tires all the more easily
sooooo
I really don't see traction as a valid reason for subtle gear
ratio changes myself

Grady

 

S/CBlack95GT

New Member

Apr 6, 2003

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Tampa Palms, FL

Sep 30, 2007

#9

• Sep 30, 2007

• #9

I have had both with my blown combo and I prefer the 3.73s for acceleration.

 

Joe 5.0

Founding Member

Feb 1, 2002

1,184

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38

Macomb, MI (metro detroit)

Oct 10, 2007

#10

• Oct 10, 2007

• #10

I have 3.55's with my S-trim / 347 / TKO 500 combo, and I would prefer 3.73's.

Since I have Nitto 315's I dont have much traction problems on the street (altho I dont drive like a maniac anyway).

I miss the 1st & 2nd gear jump that 373's give (had them in a bolt-on 94 GT 5 speed).

The better question is how much racing and how much street driving will you be doing. If is just a street car that goes to the track then keep the 3.55's. Its not worth the money spent, and will cause major traction issues unless you have uber sticky tires.

Put that money towards some better tires or a rear end rebuild.

 

94Cobra69SS396

Member

Dec 27, 2004

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7

Fontana, CA

Oct 10, 2007

#11

• Oct 10, 2007

• #11

I'm running close to the same setup as you are but have an S-trim with the stock pulley and make 433 rwhp. I have 3.55 in mine but it is also my daily driver so I won't go any lower.

At the strip I run a MT ET Street (non radial) that is 26x11.5x17. I have them mounted on a pair of 17 inch GT rims that are 8 inches wide so the tire is 28 inches tall when aired up to 16psi. I launch at 6000 rpms and have a little wheel spin for about 10 ft but it hooks after that. I'm also running a stiff suspension and I leave the sway bar connected so I could run better with a drag oriented suspnsion. I turn 118mph and still have rpm left with the 3.55s.

I also run a 26x8.5x14 MT ET Drag on my Chevelle with 3.73s. I've run 128mph in 1/4 and with the 26 inch tall tire I'm at 6500rpms at the end. A 28 inch tall tire should put me at around 6000rpms at the same 128mphs.

IMO, with your current setup and a superchager, you will be fine with either gear.

 

gcomfx.com

Founding Member

Oct 22, 2002

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Republic, MO

Oct 11, 2007

#12

• Oct 11, 2007

• #12

I'm doing a rebuild of the rear end right now. We're pulling my 3.73s and going with 3.55s. I have some shorter Nittos D/Rs on the car now and I was out of gear at the 1/4 mile on the 75 shot. There is no way I could spray the 125 shot on my 331 and make it a full quarter. My ET Streets are taller, but I don't plan to run them all the time.

It'll be nice to finally have a correct speedo. BTW - a supercharger is in the plans for my car as well. Once I get this 331 lined out and some bills paid.

 

ProKiller

Founding Member

Apr 26, 2002

3,064

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PA

Oct 11, 2007

#13

• Oct 11, 2007

• #13

just pick one and be happy with it. i've never had 3.55s so i can't speak for how well they work, but 3.73s i've had in both cars and love the pull it gives me. it does get a little annoying when the cruising down the highway doing 80, but other than that i love it.