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post #21 of 36 Old April 11th, 2015, 04:48 AM
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unless you're planning on adding boost in the future just do the 4.10
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post #22 of 36 Old April 11th, 2015, 09:45 AM
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Quote:
Originally Posted by Freaks89 View Post
I've been contemplating the idea of running 4.30s on my 99 GT auto.

It's my dd and I think that I will be doing cams and nitrous, SC and turbo is too expensive for me.

I recently did a fluid change on my diff and oil came out all glittery, I have to rebuild it anyways, anyone has ever ran 4.30s on a 99 gt auto?
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Originally Posted by Freaks89 View Post
Ohhhh, didn't thought about it, thanks!

I was under the impression that you could even run 4.56 on an auto.
People who are sitting their cars up for the Eighth mile track sometime go to 4.30s. I've see people comment on 4.56s but I don't recall any forum member actually running them. I have know guys with track only cars with them.

Here is the problem with an auto. It only has three drive gears and an overdrive (a gear with a gear ratio higher than 1.00:1). First has a high 2.84:1 gear ratio. For comparison manual transmissions have a 3.38:1 first. Second is a fairly high 1.55 compared to a manual transmissions 2.00. To get that jackrabbit start that most people want it is generally thought that 4.10s are needed for an automatic.

But there is a price to pay. An auto also has the lowest overdrive gear of any of our transmissions. It's 0.70:1. A 2002-2004 manual transmission's overdrive is a higher 0.62:1. That means that an auto's highway rpm are going to be a lot higher. At 70 mph with 4.10 gears and standard size tires an auto will be spinning the motor around 2700 rpm. A manual transmission will be spinning it around 2400 rpm.

The reason the Eighth mile guys can get away with lower gears is because they don't run out of gear on the short track. On a quarter mile track you have to worry about running out of gear in drive (third for an auto, fourth for a manual transmission) and shifting into overdrive. A lot of us don't mind pushing our motors a little into the red. With 4.10s 6000 rpm gets you 108 mph. With 4.56s you would be running 97 mph. A lot of naturally aspirated cars trap faster than that.

Almost any power adder pushes the limits of the 4.10/stock size tire in the quarter mile. For example, I trap at 111 mph. At 6000 rpm the speed is 108. I can spin the motor higher, go to a higher gear, or run larger diameter rear tires to water down the gear. A lot of dedicated drag racers choose to go to a larger rear tire with a softer sidewall. It gives them more grip during launches. My car is a daily driver in rain and sometimes snow. I also drive a lot of interstate miles and my T-45 has a lower overdrive gear than the later T-3650s. I chose a higher 3.73 gear.

Lower gears will overall make an auto quicker. But if you are a roll racer they actually make an auto accelerate slower between 65-80. This is because of the large step between second and drive. With stock gears an auto will downshift to second at 65 mph and run up to 80 mph before shifting into drive. With 4.10 gears it can't shift to second at 65 mph because the rpm in second would be too high. The overall gear ratio of the drive train is the transmission gear ratio times the differential gear ratio. Second with 3.27s has a lower overall gear ratio (5.07:1) than third with 4.10s (4.10:1).

So basically it boils down to this. The gear you choose depends upon how you use your car.

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post #23 of 36 Old April 11th, 2015, 12:49 PM
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Quote:
Originally Posted by Eagle2000GT View Post
People who are sitting their cars up for the Eighth mile track sometime go to 4.30s. I've see people comment on 4.56s but I don't recall any forum member actually running them. I have know guys with track only cars with them.

Here is the problem with an auto. It only has three drive gears and an overdrive (a gear with a gear ratio higher than 1.00:1). First has a high 2.84:1 gear ratio. For comparison manual transmissions have a 3.38:1 first. Second is a fairly high 1.55 compared to a manual transmissions 2.00. To get that jackrabbit start that most people want it is generally thought that 4.10s are needed for an automatic.

But there is a price to pay. An auto also has the lowest overdrive gear of any of our transmissions. It's 0.70:1. A 2002-2004 manual transmission's overdrive is a higher 0.62:1. That means that an auto's highway rpm are going to be a lot higher. At 70 mph with 4.10 gears and standard size tires an auto will be spinning the motor around 2700 rpm. A manual transmission will be spinning it around 2400 rpm.

The reason the Eighth mile guys can get away with lower gears is because they don't run out of gear on the short track. On a quarter mile track you have to worry about running out of gear in drive (third for an auto, fourth for a manual transmission) and shifting into overdrive. A lot of us don't mind pushing our motors a little into the red. With 4.10s 6000 rpm gets you 108 mph. With 4.56s you would be running 97 mph. A lot of naturally aspirated cars trap faster than that.

Almost any power adder pushes the limits of the 4.10/stock size tire in the quarter mile. For example, I trap at 111 mph. At 6000 rpm the speed is 108. I can spin the motor higher, go to a higher gear, or run larger diameter rear tires to water down the gear. A lot of dedicated drag racers choose to go to a larger rear tire with a softer sidewall. It gives them more grip during launches. My car is a daily driver in rain and sometimes snow. I also drive a lot of interstate miles and my T-45 has a lower overdrive gear than the later T-3650s. I chose a higher 3.73 gear.

Lower gears will overall make an auto quicker. But if you are a roll racer they actually make an auto accelerate slower between 65-80. This is because of the large step between second and drive. With stock gears an auto will downshift to second at 65 mph and run up to 80 mph before shifting into drive. With 4.10 gears it can't shift to second at 65 mph because the rpm in second would be too high. The overall gear ratio of the drive train is the transmission gear ratio times the differential gear ratio. Second with 3.27s has a lower overall gear ratio (5.07:1) than third with 4.10s (4.10:1).

So basically it boils down to this. The gear you choose depends upon how you use your car.
^Good info in this post.^

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post #24 of 36 Old April 11th, 2015, 01:41 PM
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Originally Posted by 4eyedcoupe View Post
^Good info in this post.^
I agree, very high info density rate in that post.

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post #25 of 36 Old April 23rd, 2015, 10:40 PM
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4.10's FTW!!!
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post #26 of 36 Old April 23rd, 2015, 11:14 PM
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I went with 3.73 and I don't really regret it. I do a decent amount of highway driving and i think if i had any more gear the exhaust note would be so bad i would want to beat my head in with a framing hammer, waffle masher head preferred. i guess that could be my exhaust choice issues as well.

4.10's ...pull like hell, where'd first gear go? that's what i have ascertained from my personal search.
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post #27 of 36 Old April 24th, 2015, 03:51 AM
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First gear was left behind in the smoke from the peelout

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post #28 of 36 Old April 24th, 2015, 10:45 AM
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Originally Posted by JustinG60 View Post
I went with 3.73 and I don't really regret it. I do a decent amount of highway driving and i think if i had any more gear the exhaust note would be so bad i would want to beat my head in with a framing hammer, waffle masher head preferred. i guess that could be my exhaust choice issues as well.

4.10's ...pull like hell, where'd first gear go? that's what i have ascertained from my personal search.
Quote:
Originally Posted by hwang21 View Post
First gear was left behind in the smoke from the peelout
Set up your suspension right and it'll hook pretty well. Problem is guys just slap 4.10's in a car with a stock suspension and expect first to hook when even the stock 3.27's don't.I loved my 4.10's when my car was NA making 340 WHP. I'm going to 3.73's now that I'm looking to go boosted with loads more power.
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post #29 of 36 Old April 24th, 2015, 12:03 PM
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Tires are important. But there is a big difference between hooking with hot drag radials on a prepped sticky surface and hooking with cold tires on the street. All the suspension work in the world will not make street tires hook. Besides the more you do to your suspension the greater the NVH. I hated my control arms when I first put the in. They transmit every road and gear noise directly into the cab. I've gotten use to it and now just dislike them a lot. They make my daily drive less enjoyable but aren't worth the trouble of replacing them.

4.10 advocates love their 4.10s. To them there is no other gear and they often mindlessly repeat the "Don't Fear the Gear" slogan. I have even seen advocates say its the perfect gear for boost. Really?

And they have recommendations for running 4.10s even when its inappropriate. They say "run a 28 inch tire" and "take off in second." I always wondered why. While this advice might be appropriate for a track/street car rarely driven on the street I have to question why anyone would set up a daily driver so that it is hard to drive on their daily commute? This makes no sense at all and this is way a lot of people have tried 4.10 gears only to take them out and put in 3.73s.

You need to pick the gear that best fits how you use your car. The mistake the "Don't Fear the Gear" advocates make is they assume the way they use their car is the only way to use a car.

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post #30 of 36 Old April 24th, 2015, 03:47 PM
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You can make street tires hook pretty hard if you set the car up right, if you can't you're doing something wrong. The NVH really isn't that bad either, it's a Muscle car, not a Cadillac.

I personally loved my 4.10's for daily commuting. City mileage went up and when in traffic I didn't have to keep clutching the car. I just let it roll real slow in first. Can't do that with the 3.27's or 3.73's as much.

Each gearset has its place. IMO a NA car, 4.10's all day long street or strip. Biggest point here that can be seen, is to each their own. Take the words from everyone and decide what gear is best for your ride/preference.
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post #31 of 36 Old April 24th, 2015, 04:42 PM
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My 4.10s on DD use is not bad at all...My ride is pretty rough due to my suspension setup but I didn't buy a Mustang for the comfort. Maybe Im young and dumb but if you are an NA/Bolt-on GT, 4.10s are the minimum for rear gear. You do lose top end but I don't spend a lot of time above 100mph anyway (who does on the street) so I could care less about top end.

I hook decently well with my sucky A/S tires and 4.10s...you just learn your car.

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post #32 of 36 Old April 24th, 2015, 07:15 PM
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Love my 4.10's.
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post #33 of 36 Old April 24th, 2015, 08:11 PM
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Originally Posted by GBPackerFan View Post
My 4.10s on DD use is not bad at all...You do lose top end but I don't spend a lot of time above 100mph anyway
Actually, there is a lot of evidence that says you will gain a couple of miles per hour top end with 4.10s. The first four gears (three in an automatic) are rev limited meaning you run out of rpm before you run out of horsepower so you are still accelerating when you reach redline. Overdrive is power limited meaning that you stop accelerating before you get to redline. The faster you go, the more power you need to overcome increasing levels of wind resistence and friction.

A stock GT has around 225-230 rwhp. But that is peak horsepower at 5200 rpm. When you shift into overdrive at redline rpm the engine drops back to around 3600 rpm where the stock motor has around 170 rwhp. The car will be running around 130 mph which, according to CliffyK's charts requires 140 rwhp to maintain. Since you have 170 the car still accelerates. Somewhere around 145 mph the car will stop accelerating. The motor has reached 4000 rpm where it has around 185-190 rwhp. Cliff's calculations state that it requires 190 rwhp run 145 mph.

If you put in 4.10 gears then at 145 mph the engine is spinning at near 5000 rpm where it has 215-220 rwhp. With 4.10 gear the car will keep accelerating to somewhere around 152 mph so instead of loosing top end you actually gain. Forum members have stated this actually happened to their cars. Check out Cliff's calculators. PaladinMicro

You have to have a dyno sheet in order to calculate top speed with different gears for modified applications. I did this for my car. With 3.73 gears my car runs out of power just as it is hitting redline which according to the calculations is 185 mph. I will never know if this is true or not because my car is neither rev limited or power limited, its driver limited.

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post #34 of 36 Old April 26th, 2015, 01:13 AM
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Yea I definitely would not go 150mph+ in my stock suspension vert, I already feel like my car is gonna lift off the ground at like 140mph lol. I also don't really see the point of going for top speed. It has so few uses in a DD car. Acceleration>top speed imo lol

But that is interesting that our theoretical top speed is actually higher on 4.10 than 3.27. Good info Eagle +rep

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post #35 of 36 Old April 27th, 2015, 11:30 AM
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3.73 and 4.10s are very similar
You will probably enjoy the 4.10s over the 3.73s IMO
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post #36 of 36 Old April 27th, 2015, 04:43 PM
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Quote:
Originally Posted by Eagle2000GT View Post
Actually, there is a lot of evidence that says you will gain a couple of miles per hour top end with 4.10s. The first four gears (three in an automatic) are rev limited meaning you run out of rpm before you run out of horsepower so you are still accelerating when you reach redline. Overdrive is power limited meaning that you stop accelerating before you get to redline. The faster you go, the more power you need to overcome increasing levels of wind resistence and friction.

A stock GT has around 225-230 rwhp. But that is peak horsepower at 5200 rpm. When you shift into overdrive at redline rpm the engine drops back to around 3600 rpm where the stock motor has around 170 rwhp. The car will be running around 130 mph which, according to CliffyK's charts requires 140 rwhp to maintain. Since you have 170 the car still accelerates. Somewhere around 145 mph the car will stop accelerating. The motor has reached 4000 rpm where it has around 185-190 rwhp. Cliff's calculations state that it requires 190 rwhp run 145 mph.

If you put in 4.10 gears then at 145 mph the engine is spinning at near 5000 rpm where it has 215-220 rwhp. With 4.10 gear the car will keep accelerating to somewhere around 152 mph so instead of loosing top end you actually gain. Forum members have stated this actually happened to their cars. Check out Cliff's calculators. PaladinMicro

You have to have a dyno sheet in order to calculate top speed with different gears for modified applications. I did this for my car. With 3.73 gears my car runs out of power just as it is hitting redline which according to the calculations is 185 mph. I will never know if this is true or not because my car is neither rev limited or power limited, its driver limited.
All true if you use 5th gear full throttle...which I don't and never did before the 4.10. I, personally, have lost top speed now only wringing out 4th gear. Technically I haven't but again, I only max out 4th (both before and after the gear swap).

I visit Cliff's site often...good info on there.

Good info nonetheless.

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