Rear gear selection...

mfj

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What gears would you recommend for me. I WAS running 3.73's with the 3.4 Whipple. On a 28 inch tires, that felt about right. Now doing a single 76mm kit. I can't decide on 3.55's or 3.27's. Remember, I will be on 28 inch tall tires. Give me some ideas please!! :banana::banana:
 

blowngt

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What gears would you recommend for me. I WAS running 3.73's with the 3.4 Whipple. On a 28 inch tires, that felt about right. Now doing a single 76mm kit. I can't decide on 3.55's or 3.27's. Remember, I will be on 28 inch tall tires. Give me some ideas please!! :banana::banana:

28" tire here and 3.55s.

I had originally tried 3.31's and a 26" tire but when I switched to a 28" tire I lost MPH out the back. With the 355's everything works much better.
 

Teej281

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Well keep this number in mind. Running a 28" tire vs a 26" tire is like subtracting .4 away from the rear gear. So running a 3.55 and a 28" tire is going to be close to running 3.08's and a 26" tire. And likewise, 3.27's with 28" tires will be like running 2.73's or close to it with 26" tires.

Just some food for thought while deciding! I'd keep what you have now and then figure it out from there what you think the best course of action is. Saves money now and might save you from being unhappy later.
 

C666

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3.55 or 3.73 what trans and how fast do plan to go ET wise?
 

mfj

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Still a 6 speed manual. I would guess close to a 150 mph trap, or more? Depending on the DA, which always sucks in AZ
 

tt335ci03cobra

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On a single 76, I hear they spool 12+#'s by 3800 on a decent setup so maybe a 3.73 won't be too bad. Drive it for a bit with that and see if you like it. I'd do a 3.55 if I had your car. The 3.27 only if you run high boost often. That's a gear for 1000whp. I think single cars do better with a little higher gear to get into the power band off the launch and twin cars can get away with a little lower gear because they spool a little quicker. My $.02
 
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Ryan2KRedL

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I'd suggest 3.55 gears if you are keeping the 6 speed.
I ran 3.31's in mine and while it ran great mph at the track (148mph on pump gas tune), it was sluggish down low and on the street.
I upfitted to 3.55's and noticed an improvement in response on the street. Never got a chance to run it at the track with the 3.55's.
Currently going auto and will probably leave the 3.55's in there.

Ryan
 

tt335ci03cobra

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A 3.55 on a 28" tire is similar to about a 3.08 (3.15 mathematically) sent through a factory 25.4" tire

Mph: 28" @ 6.5-7,000 rpms W/ 3.55

6,500. 7,000

G Mph. Mph
1. 57.34. 61.75
2. 85.69. 92.28
3. 117.32. 126.35
4. 154.52. 164.25
5. 190.65. 205.32
6. 246.93. 75.69 (@2,000 rpms)

Mph: 25.4" @ 6.5-7,000rpms W/ 3.55
(stock 03/4 cobra tire/gear)
6,500. 7,000

G. Mph. Mph.

1. 52.1. 56.02
2. 77.73. 83.71
3. 106.43. 114.62
4. 138.36. 149
5. 172.95. 186.25
6. 223.16. 68.66 (@ 2,000rpm)

I'd say 3.55 is perfect on a 4.6. Anything higher will be detrimental to your turbo setup. Anything lower than a 3.55 will bog on a 4.6 with a 28" tire in stop/go traffic because it would be the same as something lower than a 3.15~ on a 25.4" tire.

Now if your shifting at 6,000rpms, then go a lower gear like a 3.27 so you can stay in your power band longer but it would necessitate you getting an m2mb wotbox so you can have boost off the line, but then the car will also bog a bit in stop/go traffic with a 3.27.

I got my numbers off walace gear's online calculator so they are probably accurate.
 
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mfj

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28" slick or DR?
MT ET Drags (slicks)

A 3.55 on a 28" tire is similar to about a 3.08 (3.15 mathematically) sent through a factory 25.4" tire

Mph: 28" @ 6.5-7,000 rpms W/ 3.55

6,500. 7,000

G Mph. Mph
1. 57.34. 61.75
2. 85.69. 92.28
3. 117.32. 126.35
4. 154.52. 164.25
5. 190.65. 205.32
6. 246.93. 75.69 (@2,000 rpms)

Mph: 25.4" @ 6.5-7,000rpms W/ 3.55
(stock 03/4 cobra tire/gear)
6,500. 7,000

G. Mph. Mph.

1. 52.1. 56.02
2. 77.73. 83.71
3. 106.43. 114.62
4. 138.36. 149
5. 172.95. 186.25
6. 223.16. 68.66 (@ 2,000rpm)

I'd say 3.55 is perfect on a 4.6. Anything higher will be detrimental to your turbo setup. Anything lower than a 3.55 will bog on a 4.6 with a 28" tire in stop/go traffic because it would be the same as something lower than a 3.15~ on a 25.4" tire.

Now if your shifting at 6,000rpms, then go a lower gear like a 3.27 so you can stay in your power band longer but it would necessitate you getting an m2mb wotbox so you can have boost off the line, but then the car will also bog a bit in stop/go traffic with a 3.27.

I got my numbers off walace gear's online calculator so they are probably accurate.

Thanks for the information guy. I already have a MSD- Modular 2 step for launching at the track. But that was very helpful information. I am going to go with some 3.55s
 
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tt335ci03cobra

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Thanks for the information guy. I already have a MSD- Modular 2 step for launching at the track. But that was very helpful information. I am going to go with some 3.55s

Hey your welcome, good luck, keep us posted if they work out well for your combo/setup.
 

C666

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28" slick will grow 1-1.5 inches so 3.73 or 3.90 if you sell your 3.73's let me know I want some or 3.90's
 

tt335ci03cobra

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Maybe on a built block with a high a/r, with heads, cams, sullivan, and about 9.8/1 or higher compression with e85 it could see 1000whp, a stock compression cobra block with factory head/cam combo on 116 will probably be in the mid to maybe hi 800whp or so range @ 25#'s with a big a/r.

With stock heads/cam/block, you'd need a single 85-88 to make an honest 1000whp at anything less than 25#'s, just my $.02 though, I could very well be wrong.
 

C666

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Big Billet wheel 76 will make good power seen a 03 cobra mod motor with heads n cams go 8.7 at 159 with a Billet 76
 

mfj

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I already have a 5.1L Stroker with Ported heads and comp cams lol. And yes, I already have a Sullivan intake manifold. I also already run e85, lol
 

SVTsteele

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I know its an old thread but howd the 3.55s do with the 76mm on the 6 speed? Im running a 3.15 now and its real sluggish around town but i have 0 traction issues holding 780whp on 305/35/19 et streets.
 

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