Preferred Gears for turbo set ups? - Ford Mustang Forums : Corral.net Mustang Forum
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post #1 of 60 Old 02-15-2007, 11:55 AM Thread Starter
 
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Preferred Gears for turbo set ups?

I have a 91 mustang that i plan on getting a turbo kit for. I have 4.10 gears right now, but would i be better off with a taller gear. 3.73s maybe? not sure if it really matters.

this is my set up now:
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post #2 of 60 Old 02-15-2007, 12:09 PM
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3.27 or 3.55 depending on tire size.


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post #3 of 60 Old 02-15-2007, 12:15 PM Thread Starter
 
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im still sitting on the stock 15 inch rim, but ive got a set of et streets on the way. Would you still say 3.27 or 3.55s?
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post #4 of 60 Old 02-15-2007, 12:38 PM
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Go with 3.27's. 3.73 is way too much gear for a turbo car. If you plan to run a 26'' tall tire 3.27's will keep you in the powerband longer.

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post #5 of 60 Old 02-15-2007, 12:47 PM
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yea 3.27's turbo's like longer gears... keeps them spooled longer so cars are faster

i had 4.10's in my 98 when it was a built hc n/a car but when i rebuilt it and went turbo i dropped to a 3.27 gear

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post #6 of 60 Old 02-15-2007, 12:56 PM
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does anybody have 1st hand experience with a turbo car with 3.73's then swapping to 3.27's or similar?

1982 Ford Fairmont Futura H/C/I, fuel injected and turbocharged [email protected]
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post #7 of 60 Old 02-15-2007, 01:11 PM
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does anybody have 1st hand experience with a turbo car with 3.73's then swapping to 3.27's or similar?
yes. in my '94 incon car. the 3.27's were harder to launch because the bog/spin line became narrower, but that was the ONLY downside of the 3.27's.

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post #8 of 60 Old 02-15-2007, 01:14 PM
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im still sitting on the stock 15 inch rim, but ive got a set of et streets on the way. Would you still say 3.27 or 3.55s?
i was referring to tire height. sorry.
26" go with 3.27. 28" go with 3.55. although 3.55's would be ok with either tire height.

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post #9 of 60 Old 02-15-2007, 01:16 PM
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does anybody have 1st hand experience with a turbo car with 3.73's then swapping to 3.27's or similar?
I've seen a couple of threads on turbomustangs.com, can't seem to find them now. Sweet Fairmont though, any pics!

Luke M.
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post #10 of 60 Old 02-15-2007, 01:17 PM
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yes. in my '94 incon car. the 3.27's were harder to launch because the bog/spin line became narrower, but that was the ONLY downside of the 3.27's.
I noticed the same thing after switching. You actually get into your powerband quicker with the 3.27's as you load the engine more. To add to that…burnouts too became a bit trickier. As soon as you get any hint of bog the turbo's would instantly spool blowing the tires off!


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post #11 of 60 Old 02-15-2007, 01:28 PM
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also, my gas mileage went down when i switched from 3.73 to 3.27. the turbo seemed like it was always spooling.

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post #12 of 60 Old 02-15-2007, 01:33 PM
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I've been pondering this also. I currently have 3.73's in my 95' conv. Going with a turbo'd 363ci.

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post #13 of 60 Old 02-15-2007, 01:41 PM
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If you want the most out of the quarter mile, gear the car appropriately, regardless of induction.

For instance, if you want to finish at 140 figure out what gear gets you 140 mph at redline with your tires. If you aren't hitting your max RPM that you want at the stripe, put in a bigger gear. Vice versa if you run out of gear before the stripe.

For street driving, it's a matter of preference.

I could go into the dynamics of turbo performance, but most people trust their ass more than science.

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post #14 of 60 Old 02-15-2007, 02:09 PM
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What about 3.08 gears peeps?

More than a stable full of stangs to list...

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post #15 of 60 Old 02-15-2007, 02:22 PM
 
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Im planing on boosting my car im saving for the kit newtrod sell's on here.I have 4:10's in my car now with a 28inch tall tire the actual tire is 28x11.50-15 hoosier quick time pro's,but I was think steping up to the hoosier slicks 29x10-15 so maybe I didnt have to switch the gear.Any info???
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post #16 of 60 Old 02-15-2007, 02:32 PM
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Quote:
Originally Posted by ATOMonkey View Post
If you want the most out of the quarter mile, gear the car appropriately, regardless of induction.

For instance, if you want to finish at 140 figure out what gear gets you 140 mph at redline with your tires. If you aren't hitting your max RPM that you want at the stripe, put in a bigger gear. Vice versa if you run out of gear before the stripe.

For street driving, it's a matter of preference.

I could go into the dynamics of turbo performance, but most people trust their ass more than science.
Turbocharging absolutely effects the vehicles 1/4 performance in relationship to gears different than all other types of induction. A change in rear gears will have an actual effect of the torque curve you engine puts out. Putting in a "bigger" gear because your not reaching your ideal rpm in a turbo application quite often can be detrimental to performance.
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post #17 of 60 Old 02-15-2007, 02:40 PM
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Turbocharging absolutely effects the vehicles 1/4 performance in relationship to gears different than all other types of induction. A change in rear gears will have an actual effect of the torque curve you engine puts out. Putting in a "bigger" gear because your not reaching your ideal rpm in a turbo application quite often can be detrimental to performance.
Show me the data.

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post #18 of 60 Old 02-15-2007, 02:49 PM
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Show me the data.
Call up any speedshop that has uses a mustang dyno and has first hand experience with turbo's.

Or…take a visit to www.turbomustangs.com and search out some before/after dyno runs with gear swaps.

Rear end gears multiply the torque the engine puts out to the ground. The higher (numerical) gears reduce the load on the tranny and engine while a lower (numerical) gear increases the load. Increased load means quicker turbo spooling…which in effect broadens the engines torque curve.
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post #19 of 60 Old 02-15-2007, 02:57 PM
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Call up any speedshop that has uses a mustang dyno and has first hand experience with turbo's.

Or…take a visit to www.turbomustangs.com and search out some before/after dyno runs with gear swaps.

Rear end gears multiply the torque the engine puts out to the ground. The higher (numerical) gears reduce the load on the tranny and engine while a lower (numerical) gear increases the load. Increased load means quicker turbo spooling…which in effect broadens the engines torque curve.
Absolutely, although the term load as you're using it is misapplied. The only "load" the engine sees is the weight of the car. All you're doing with a bigger gear is slowing the car down, which in essence slows the engine down, and slower spinning engines make more boost (which is a BS measurement) for the same airflow and thus power.

However, quarter miles times aren't run on mustang dynos. Also, a steady state dyno should give you the same number regardless of gear ratio. If it's not, then something is ****ed up.

A transient dyno with the proper weight and drag coefficients in it should give you a pretty good idea of how the car will perform. Getting that data plugged in can be quite troublesome though. Even the EPA doesn't hit it spot on when they made us do our testing. That's why real world MPG is different from EPA estimated MPG.

Having said all of that, making "boost" quicker does not translate directly into having a faster car.

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post #20 of 60 Old 02-15-2007, 04:45 PM
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Absolutely, although the term load as you're using it is misapplied. The only "load" the engine sees is the weight of the car. All you're doing with a bigger gear is slowing the car down, which in essence slows the engine down, and slower spinning engines make more boost (which is a BS measurement) for the same airflow and thus power.
Nothing misapplied with my statement. There are many different uses for the term "load", and as such mine was quite applicable.

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However, quarter miles times aren't run on mustang dynos. Also, a steady state dyno should give you the same number regardless of gear ratio. If it's not, then something is ****ed up.
I agree, quarter times are indeed not run on mustang dyno's. They do however put a load (there that darn term is again) on the rollers to simulate the proper mass of the vehicle, wind resistance etc. ...therefore making them much more accurate than the likes of a dynojet. The mustang dyno in turbo apps will show a broader torque/hp curve due to the roller loading than a comparable dynojet. In the same token, a lower (numerical) gear will load the engine more...thereby allowing the turbo's to spool quicker. The end result again is a broader torque/hp curve than higher (numerical) gearset.

Quote:
A transient dyno with the proper weight and drag coefficients in it should give you a pretty good idea of how the car will perform. Getting that data plugged in can be quite troublesome though. Even the EPA doesn't hit it spot on when they made us do our testing. That's why real world MPG is different from EPA estimated MPG.
I'm not quite sure how this fit's in with the subject...so for now I'll just call it chewbacca.

Quote:
Having said all of that, making "boost" quicker does not translate directly into having a faster car.
A broader torque/hp curve with the same peak number certainly would translate into have a faster car.
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post #21 of 60 Old 02-15-2007, 04:56 PM
 
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One advantage I have noticed in my own car is that with the turbo, I made full power/torque very early in the RPM range. So revving the engine to redline as fast as possible really isn't as big of a concern. A turbo car wil usually make good power from about 3500-redline, so with the longer gears, the longer you can hold each gear, the faster it will go.

The difference is that all motor/supercharged applications will not usually make full power until they are reaching close to redline, so it's more important to get the RPMs shooting up to make power. With the turbo it's just not as important...even though you don't want too long of a gear with the turbo either.

The turbo just lets you run a little longer gears since it makes power differently.



Also...I have run 3.31 gears in my turbo '94 cobra and they were MUCH better than the 4.10s and 3.73s that I had in there in the first place with the turbo.
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post #22 of 60 Old 02-15-2007, 05:24 PM
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I've seen a couple of threads on turbomustangs.com, can't seem to find them now. Sweet Fairmont though, any pics!
tks, heres my buildup
https://www.corral.net/forums/showthread.php?t=858235

i have 3.73's now and cannot see how going to 3.27's will make me quicker. the only time i plan on being at low rpm is when i'm at the starting line. i've set my shift limit to 6k so i should have to run a 28" tire in the 1/4 as i'm expecting to run at least 125 traps. in the 1/8th i expect 3.73's would work great and that a 4.10 would be even better.

does anybody have any times showing their times improved going to a higher gear?

1982 Ford Fairmont Futura H/C/I, fuel injected and turbocharged [email protected]
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post #23 of 60 Old 02-15-2007, 06:18 PM
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tks, heres my buildup
https://www.corral.net/forums/showthread.php?t=858235

i have 3.73's now and cannot see how going to 3.27's will make me quicker. the only time i plan on being at low rpm is when i'm at the starting line. i've set my shift limit to 6k so i should have to run a 28" tire in the 1/4 as i'm expecting to run at least 125 traps. in the 1/8th i expect 3.73's would work great and that a 4.10 would be even better.

does anybody have any times showing their times improved going to a higher gear?
After doing a couple of quick searches over on tm, here are a few that I found. There are far more threads like these however.

http://www.turbomustangs.com/smf/ind...?topic=29243.0

http://www.turbomustangs.com/smf/index.php?topic=9083.0

http://www.turbomustangs.com/smf/ind...?topic=27095.0
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post #24 of 60 Old 02-15-2007, 08:12 PM
 
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tks, heres my buildup
https://www.corral.net/forums/showthread.php?t=858235

i have 3.73's now and cannot see how going to 3.27's will make me quicker. the only time i plan on being at low rpm is when i'm at the starting line. i've set my shift limit to 6k so i should have to run a 28" tire in the 1/4 as i'm expecting to run at least 125 traps. in the 1/8th i expect 3.73's would work great and that a 4.10 would be even better.

does anybody have any times showing their times improved going to a higher gear?
That's a pretty ignorant way to look at it. Just because you can't "see" how it would work, so then it must not...and if you ran a 4.10, I guarantee you'd go slower.

Look over at turbomustangs.com if you want more examples of what gears are preferred by people who have tested and tried a lot more combos than you have.

The biggest gears that most guy liek to run are 3.55s...

Not saying it won't work with 3.73s or 4.10s, but it will go faster with a 3.55, 3.31, etc.
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post #25 of 60 Old 02-15-2007, 09:23 PM
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ignorant?
internet is full of people who go by what they read, all i want is an example. i don't care about dyno #'s or buttometer, i'm talking about the track.

can u guarantee i will go faster with less gear? i will do the swap when the tracks open in 3 weeks if you'll pay for the gear if its not faster.

i have an aod and make instant 10psi as soon as i go wot. my cam makes power and pulls effortlessly to 6k+. if i had a stock cam that pulled to 5200 then of course it would make more sense to run less gear. johnboy who is on this site and tm runs 4.10 very sucessfully till he sold/traded the car.

i'm not saying i know it will be faster with my 3.73's, but i want more than somebody telling me because tm says so or another site.

have you tested your car with different gears at the track? what where the differences.

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post #26 of 60 Old 02-15-2007, 10:14 PM
 
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ignorant?
internet is full of people who go by what they read, all i want is an example. i don't care about dyno #'s or buttometer, i'm talking about the track.

can u guarantee i will go faster with less gear? i will do the swap when the tracks open in 3 weeks if you'll pay for the gear if its not faster.

i have an aod and make instant 10psi as soon as i go wot. my cam makes power and pulls effortlessly to 6k+. if i had a stock cam that pulled to 5200 then of course it would make more sense to run less gear. johnboy who is on this site and tm runs 4.10 very sucessfully till he sold/traded the car.

i'm not saying i know it will be faster with my 3.73's, but i want more than somebody telling me because tm says so or another site.

have you tested your car with different gears at the track? what where the differences.
I gave you an example of a car that went faster when going from 4.102 and 3.73 where I was usually around a 12.3 and after going to a 3.31 I ran a best of 11.9.

The way a turbocharged engine makes power is much different than most superchargers and most definately an all motor setup. Like said above, they usually have to be spinning to max RPM to make a lot of power, so the best way to do that is to rev the engine faster in order to keep the RPMs up higher.

With a turbo car it makes **** loads of power at a little lower of an RPM so you can run longer gears and go faster with them. Otherwise you'll build up boost and then bam it's time to shift again and you are back at building boost back up before you know it.

No one said having gears that lasted forever would go faster. But to a certain point you can run a longer gear and go faster. Not saying go as high (numerically low) as you can go like some 2.70s or whatever. But typically a 3.73 and 4.10 can be toomuch for a turbo car and something around a 3.55 or 3.31 is a little better suited and usually improves times at the track.

And you keep talking about revving to 6K...you act like you're revving it to the moon and want shorter gears for that reason.

I will tell you now that if you swap them out for a 3.55 and compare that to a run with the 4.10s you will find it'll run faster with the 3.55s and maybe you'll change your mind that 4.10s are the right choice for your low revving turbo setup...

Last edited by red1994turbocobra; 02-15-2007 at 10:17 PM.
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post #27 of 60 Old 02-15-2007, 11:30 PM
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Quote:
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I gave you an example of a car that went faster when going from 4.102 and 3.73 where I was usually around a 12.3 and after going to a 3.31 I ran a best of 11.9.

The way a turbocharged engine makes power is much different than most superchargers and most definately an all motor setup. Like said above, they usually have to be spinning to max RPM to make a lot of power, so the best way to do that is to rev the engine faster in order to keep the RPMs up higher.

With a turbo car it makes **** loads of power at a little lower of an RPM so you can run longer gears and go faster with them. Otherwise you'll build up boost and then bam it's time to shift again and you are back at building boost back up before you know it.

No one said having gears that lasted forever would go faster. But to a certain point you can run a longer gear and go faster. Not saying go as high (numerically low) as you can go like some 2.70s or whatever. But typically a 3.73 and 4.10 can be toomuch for a turbo car and something around a 3.55 or 3.31 is a little better suited and usually improves times at the track.

And you keep talking about revving to 6K...you act like you're revving it to the moon and want shorter gears for that reason.

I will tell you now that if you swap them out for a 3.55 and compare that to a run with the 4.10s you will find it'll run faster with the 3.55s and maybe you'll change your mind that 4.10s are the right choice for your low revving turbo setup...
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post #28 of 60 Old 02-16-2007, 12:43 AM
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i guess we will see ricky. and if you are right it won't hurt my feelings.

my goal is to run 6.8 in the 1/8 and 10.8 in the quarter with 3.73's and a little turbo. if i cant hit the # with 10psi maybe i'll try a different gear. i've got 3 weeks till the tracks open back up.

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post #29 of 60 Old 02-16-2007, 04:55 AM
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Depends on transmission??
The quicker I get into second gear the faster my run in both mph and E.T..
My car is heavy compared to Mustangs...It doesn't pull hard till 3 rd gear.If I try too hard it just smokes the tyres... 3800 Lb & 3.27... M/T street radial..
An auto wuld give better 60 ft times.. But its not a trailor or drag car...

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post #30 of 60 Old 02-16-2007, 07:18 AM
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Question

4.10 with Powerglide here..

My car has run a best of 6.06 @ 113 mph..

I doubt I would go faster with a 3.27 gear...

I have 3.55 gears to try out but I don't think they will make the car faster either..

My car runs 6.20s @ 110 on 10 lbs. of boost and 93 octane..

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post #31 of 60 Old 02-16-2007, 10:55 AM
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Don't be fooled too much by the guys at turbo mustang.

My assessment is that the cam and intake were too small for the engine speed they were running with the bigger gear, and they as much as admit that in their posts. By reducing the size of the gear, they were able to run a higher volumetric efficiency and thus the average HP during the run was increased, making the car go more faster. It's also useful to note that the more power you make, the faster the car will go, which in turn necessitates the use of a numerically smaller gear if the engine has a constant redline speed. That's just simple math.

Hitting the right drag coefficient on a mustang dyno (or any other electrical resistance type) is damn near impossible. You can get close, and as such is helpful, but I would not hang my hat on it. That is the point I was trying to make. It's decent enough for back to back comparisons, but I would not try to translate that into real world performance.

Here's another little tid-bit of info. The longer you stay in any one gear, the better the torque curve will look. That absolutely does not mean the car will run faster. It probably doesn't even mean you've changed the transient response of the engine. You've just changed the boost level you see in each gear.

Also if you're loosing boost between shifts you need to stop granny shifting. That skinny pedal should be matted the entire time. Even on a synchronized transmission. Just stab the clutch and grab the next gear. If you don't break at least a couple of shift forks on a stock shifter, you're probably not doing it right.

"Let the little children come to me, and do not hinder them, for the kingdom of God belongs to such as these." - Mark 10:14-15

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April 28th 2009
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post #32 of 60 Old 02-16-2007, 11:43 AM
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Go with 3.27's. 3.73 is way too much gear for a turbo car. If you plan to run a 26'' tall tire 3.27's will keep you in the powerband longer.
Tell that to my 10-sec GT.....

Sorry, I don't have any data about swapping from a different set of gears, just offering up my combo and particular experience. Currently goes through the traps right at 6k in "D" (Gainesville)

Everything just happens to work well together for my application. That's why I can run 10.97 with only 407 rwhp. That's not to say I couldn't pick up a little more by swapping to 3.27's, but I'm currently working the interior. For now, the drivetrain is right where I want it for performance (until it's time to shoot for the mid-low 10's )

BTW, I used to have a T-5 and she ran 118mph. I switched to the Art-Carr AOD and "smaller" E-cam and picked up almost 4.5 mph in the 1/4. I love my manual VB "auto."

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1990 Mustang GT (93 Cobra Clone) HOK KandyTangerine. October 2008 MM&FF Feature Car
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post #33 of 60 Old 02-16-2007, 12:10 PM
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Originally Posted by ATOMonkey View Post
Don't be fooled too much by the guys at turbo mustang.
What's to be fooled by? It by far the largest resource we have in the mustang community with real world examples.


Quote:
My assessment is that the cam and intake were too small for the engine speed they were running with the bigger gear, and they as much as admit that in their posts. By reducing the size of the gear, they were able to run a higher volumetric efficiency and thus the average HP during the run was increased, making the car go more faster. It's also useful to note that the more power you make, the faster the car will go, which in turn necessitates the use of a numerically smaller gear if the engine has a constant redline speed. That's just simple math.
I'm not quite sure what your talking about here…as you give no reference to what your assessing.


Quote:
Here's another little tid-bit of info. The longer you stay in any one gear, the better the torque curve will look. That absolutely does not mean the car will run faster. It probably doesn't even mean you've changed the transient response of the engine. You've just changed the boost level you see in each gear.
I have no idea where your going with this. In N/A form, if you dyno in 4th gear the torque curves should be nearly identical between different rear end gear sets. In turbo form you will get a broader torque curve with lower numerical gears as your loading the engine more. Haven't we already been down this road before?
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post #34 of 60 Old 02-16-2007, 12:20 PM
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I now feel a need to clarify that not all combo's are the same…and it's not always the case that lower numerical gears are better. My intent was to alert people that in turbo applications conventional wisdom does not apply on many things. Rear end gears happens to be one of them. If your 100% content with your current gears…good for you! Don't however rule out the possibility that what's good for the goose may not be good for the gander.
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post #35 of 60 Old 02-16-2007, 01:07 PM
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Though I dont own a turbo car I could see how a 3:27 would be faster on the street or at the track in street trim, mainly because of the traction issues associated with a steeper gear and the short time between gear changes. But when you talking a slicked car with AOD tranny that has no traction issues I would think a stepper gear may be faster. I know sometimes my car would be faster with a longer gearing with constant shifting and the back end all over the place.
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