I think it kind of depends on what kind of launch you want and what the first gear ratio is. Is it a 2.66 first? I might go 4.10's if you want a big launch. If you just want a good launch a 3.73 might be OK.

 

2.97 is the first gear on the wide
2.66 on the close ratio
also what do you mean by launch I am used to drag racing and that is what I am thinking you mean

 

I had asked the question, what is a good ratio and was told that a good launch ratio for street driving is 11:1, and defined as the result of multiplying the first gear ratio by your rear end ratio. This is about where the '03-04 Cobras are. If you are running 1/4 miles you probably want something higher, if you are running track you may want something lower to reduce shifting. This probably depends on urge kind of low end torque your engine makes and the weight of your car too.

 

I had asked the question, what is a good ratio and was told that a good launch ratio for street driving is 11:1, and defined as the result of multiplying the first gear ratio by your rear end ratio. This is about where the '03-04 Cobras are. If you are running 1/4 miles you probably want something higher, if you are running track you may want something lower to reduce shifting. This probably depends on urge kind of low end torque your engine makes and the weight of your car too.

i've been googling that for days, couldn't find anything. remember where you heard that?

 

you said you're getting the .50 6th and the 2.66 1st? as far as i've seen, not an option on the magnum. it's 2.66 and .62, or 2.97 and .50.

i have the t56 with .50 6th and 2.97 1st, with 3.73's. i'm currently looking to see if 4.10's would be worth the swap. big issue most people bring up with 4.10's is trap speed and what gear you'll be in, if you drag. this site is great reference, http://www.paladinmicro.com/pmicro.php?frm=SpeedInGearCalc.htm. for me, trapping over 6k isnt' a concern, so with 4.10's i'd be at 116mph and 6k in 4th, which isn't bad though i may need 28" tire if my speeds get too much higher. when i first put in 3.73's i still had the t45, but it had a 3.37 1st gear. my main thinking is that with the 2.97 1st of the t56 plus a 4.10, i'm still not gonna be as short as the t45 with the 3.73's. on 1/4 mile i can trap in top of 4th(depending on speed), and in the 1/8(which is all i'd probably run), i should be able to trap in 3rd. other huge thing for me is the ridiculous .50 od. with my 3.73's it's almost useless. cruising at 80mph i'm just under 2000rpm. that's just too low and i have absolutely no power there, any bridge or slight incline and i have to downshift, lose speed, or step on the gas more than u should, real pain. cruising at 85-90 is fine, which is around 2250rpm. just swapping in the 4.10 and i'd cruise at 80 at about 2300rpm. big negative for me is the fact that the 3.73's are just about new, less than 5k miles probably. but at the time it was the right gear and i wasn't planning on a 6 spd. my final tune will hopefully will be done within the next few weeks, after which i'll run with the 3.73's for a while and see how i like it, as well as talk with the shop to see what they say. for comparison, i should be close to 600rwhp. but i'm thinking 4.10's are the way to go with the t56 mag.

 

What about 3.90 or does that not exist for the 8.8

I thought I said that the 2.97 was the wide ratio in my second post

Also speedracer are you saying to go with close ratio with 3.55 like the cobra

 

in your first post you said you were considering the close ratio version, which you later said close = 2.66 1st.

i personally wouldn't recommend any gear other than frpp, so that means no 3.90. from what i've read, it's more of a "does nothing well" more so than "best of both worlds" gear. to much like 4.10 in gas mileage and rpms or whatever, but too much like the 3.73 when it comes to peppiness. if you go with what speedracer said and you road race, 3.73's r probably better, puts final ratio at 11.08. and the more i've read if you do run 1/4 mile with enough power to trap around 130+, you're gonna be gearing out, unless you can get to 7krpm. it's rare to find someone unhappy with 4.10, i have though seen people go back to 3.73. but for the most part, it's the 3.73's that change to the 4.10, and are more than happy with no regrets. also think about your last transmission. like i said 3.73's with t45 is more similar to 4.30's on the t56. so 4.10's aren't that bad, more similar to the 3.55's with stock t45. sucks but may come down to trial and error, pick one, and just may have to swap. that's where i'm at now.

 

Yeah 410s with the .50 final gear isn't sounding to bad but I have read that 410s cause a lot of noise and vibs with the IRS any truth to that

 

As a turbo guy...
I have run the 3.27, 3.55, 3.73, and 3.90's, all with different tires sizes and combos. The 3.90's are made by Motive and they worked just fine for me. Too much gear for turbo's though. Forget about 4.10's...you will NEVER hook, even on DR's. For the .62 6th gear, I run a 3.55. I think it's the best all around gear for our power level. Now I also have 9.2:1 compression and huge cams, but we're talking cruising here. Cruising at 80 I'm at 2100 rpm. The 3.27's were GREAT for huge top end runs...but the 3.55's are honestly better IMO. I still get plenty of top end (193 mph in 5th versus 207 mph w/ 3.27's), but made the change to 3.55's for a bit more low end grunt due to the high rpm nature of my combo. Plus, while it would go 200+, I never really found any roads capable of supporting that speed, so i geared it back to 3.55's so I could still do 180-190 without breaking a sweat.

 

so what your saying is to go with close ratio with 3.55 if going turbo am i correct in my thinking please correct me if i am wrong.

i was hoping someone with turbos would chime in. thank you smokin04

 

and i don't know what the torque curve is like for turbos vs centri, but in my research of this gear issue i know plenty of people run 4.10's and hook fine. may need longer burnout or softer dr or dump clutch at 3k vs 5k, but i know plenty of people do it fine. their problem is trapping before redline in 4th, but for that they just go to 28" tire. which is essentially the same as 3.73 with 26" tire.

 

I'm actually going to attempt 3.55 with a close T56, stock 4.6L 3v, but I'm looking for good launch (not drag), good street driving and good highway mileage.

 

when is your project going to be done. my plan is to be at 450-500rwhp on a built 01 cobra motor with teksid block and twin 57mm turbos.

but am defenitly wandering how the close ratio does with 3.55 please let me know when you find out

 

Close ratio with 3.55's will be fun to say the least. You will be cruising at 70 at roughly 23-2400 rpm depending on tire size. Old school thoughts here: Less power needs more gear, more power needs less gear. OP, just got to experiment man...at 500 rwhp 4.10's may be what you want, but a built motor at 8 psi w/ twin 57's is going to be more than 500. FWIW, at 12 psi with no timing and pump on a STOCK 04 motor I made 680 rwhp. Just sayin'...good luck with your decision.[/QUOTE]

that is why i ask the questions first then build.

when i meant built just the bottom end stock top end but the car will mainly be driven on the street with the occaional auto x event and the 04 heads are better flowing than the 01's i just figure that 8psi would be good until i go to a dyno and get it tuned. if i make more power than that is fine but if i didnt meat my goal then i will have to up the boost. to be honest though i never liked the idea of 4.10s in a street car unless you have the final gear to help with the added rpm's.

in my 05 i put 3.73s in it and it was a blast but it was a automatic so i got board with it and sold it(stupid me i miss that car)

also my tire size that i am going to try to run is 295/30r18 but might be hard with the added track width of the irs in the fox but with the s197 rear wheel i might be able to make it work.