3.9 Gears Help?
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Joined: Oct 2005
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From: Spring, TX
3.9 Gears Help?
I've done some research and looked at comparo charts & etc but I'm not understanding how a 3.9 gear helps? From what I've read it looks like it slows you down. Like a bit more technical detail other than it help you.
They work as a TQ multiplier. This can greatly help in 1/4mile ET's but it will reduce the trap speed slightly.
It basically takes your transmission gear set down a notch.
You can think of it like this:
1st gear is now 0.5gear
2nd gear is now 1st gear
and so on.
This helps in the most critical phase of a 1/4 mile race. (Launch and 60MPH times.)
It gets you moving faster at the very beginning of the race.
If you can get an extra 3-4 MPH out of your launch, you will carry that additional 3-4 mph throughout the duration of the race. And 3-4 MPH for ~13.5 seconds equates to a lot of distance and time.
How far will you go at 3-4 MPH for 13.5 seconds?
This is the 3.9 gear advantage.
It basically takes your transmission gear set down a notch.
You can think of it like this:
1st gear is now 0.5gear
2nd gear is now 1st gear
and so on.
This helps in the most critical phase of a 1/4 mile race. (Launch and 60MPH times.)
It gets you moving faster at the very beginning of the race.
If you can get an extra 3-4 MPH out of your launch, you will carry that additional 3-4 mph throughout the duration of the race. And 3-4 MPH for ~13.5 seconds equates to a lot of distance and time.
How far will you go at 3-4 MPH for 13.5 seconds?
This is the 3.9 gear advantage.
Last edited by Hydrazine; Dec 16, 2006 at 02:37 PM.
As Hydrazine said, it's going to multiply the amount of torque at the wheels. It will also alter the over-all gear ratio of your car, so your top speed would come down a hair, but you'll reach the end of each gear faster.
As far as track days goes, it could help by keeping your car in the powerband a little better and applying more torque to the wheels. It could hurt in some areas though because you'll have to waste time on a shift where before you didn't have to. As an example, you might come into turn one at PMI faster because of the gearing, but at turn three you might not be able to take it in second like normal and have to shift into third. So, there could be a trade off depending on the track. It will help in acceleration, but will cut the speed you can hit in each gear. Of course, Robert, with your UTEC you have a higher limiter to offset the loss.
Will
As far as track days goes, it could help by keeping your car in the powerband a little better and applying more torque to the wheels. It could hurt in some areas though because you'll have to waste time on a shift where before you didn't have to. As an example, you might come into turn one at PMI faster because of the gearing, but at turn three you might not be able to take it in second like normal and have to shift into third. So, there could be a trade off depending on the track. It will help in acceleration, but will cut the speed you can hit in each gear. Of course, Robert, with your UTEC you have a higher limiter to offset the loss.
Will
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Thread Starter
Joined: Oct 2005
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From: Spring, TX
So this might be a wise investment. Considering N/A is most likely my route or 350whp S/C, I might do this w/ the Quiafe in the future. Mmmm? What to do... What to do.
Originally Posted by Robert_K
So this might be a wise investment. Considering N/A is most likely my route or 350whp S/C, I might do this w/ the Quiafe in the future. Mmmm? What to do... What to do.
(I know, I know, living vicariously.... )Will
Thread Starter
Joined: Oct 2005
Posts: 12,390
Likes: 101
From: Spring, TX
Originally Posted by Resolute
I think you're on the right track, and I recommend the swap no matter which way you go since you already have the higher rev limit. What you need to do is have Rick's wife snag another Central 20 3.9 for you before she leave's Japan, LOL. And you already know how I feel on the Quaiffe. All that's left is to buy 'em and let me test drive it (I know, I know, living vicariously.... )
Will
(I know, I know, living vicariously.... )Will
I wish I could get it from Rick but I don't have the $$$ right now. Why I started researching. March is 3 months away (New Job) and than hopefully we'll get started. 
I have the gears and love them. Every gear feels much more powerful and responsive than it did before. The main downside to the shorter gearing is when you have to be in a taller gear than you did before at a given speed.
I'm not familar with the real word speeds for the 6MT... so for example, say with the 3.5 at 80 mph you used to be in 3rd gear at 5500 rpm. Now after the 3.9, at 80 mph, you need to be in 4th at 4000 rpm. The 3.5 will actually accelerate more quickly than the 3.9 because its still in 3rd which puts more power to the wheels than 4th. However, once the car with the 3.5 shifts to 4th, the car with the 3.9 will have a much greater advantage.
Probably the best way to explain it is try and draw it out. This isn't accurate for real world, but just an example of the concept. Basically, from the the start, the 3.9 car will have the advantage all the way through first. When it shifts to second, the 3.5 car will still be first and pulling more strongly. Once that car has to hit 2nd, the 3.9 car will be pulling more strongly in 2nd. This will go back and forth until the 3.9 car maxes out in 6th and the 3.5 car can still pull, ultimately going faster.
The real question is, does the increased acceleration offset the loss when you have to shift? I think anybody who has done the gear swap would argue yes, but there really hasn't been enough conclusive testing to say definitely one way or another.
And yes, do it with the Quaife. Love mine!
I'm not familar with the real word speeds for the 6MT... so for example, say with the 3.5 at 80 mph you used to be in 3rd gear at 5500 rpm. Now after the 3.9, at 80 mph, you need to be in 4th at 4000 rpm. The 3.5 will actually accelerate more quickly than the 3.9 because its still in 3rd which puts more power to the wheels than 4th. However, once the car with the 3.5 shifts to 4th, the car with the 3.9 will have a much greater advantage.
Probably the best way to explain it is try and draw it out. This isn't accurate for real world, but just an example of the concept. Basically, from the the start, the 3.9 car will have the advantage all the way through first. When it shifts to second, the 3.5 car will still be first and pulling more strongly. Once that car has to hit 2nd, the 3.9 car will be pulling more strongly in 2nd. This will go back and forth until the 3.9 car maxes out in 6th and the 3.5 car can still pull, ultimately going faster.
Code:
0 30 60 90
3.9 1***********2------**********3------**********4------
3.5 1-----------******2----------*******3---------*******
And yes, do it with the Quaife. Love mine!
Last edited by helldorado; Dec 16, 2006 at 04:58 PM.
Thread Starter
Joined: Oct 2005
Posts: 12,390
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From: Spring, TX
I pretty much sold since I'm a TQ lover vs HP junkie. I'm not looking to break world speed records. I like to get out in front first on the street and that my goal. A better, streetable Z. I like to be at a light and put the traffic behind me. So the 3.9 is a great investment for me?
Also, are they all pretty much the same except for brand name? Is there one better than the other?
Also, are they all pretty much the same except for brand name? Is there one better than the other?
If you're NA, the 3.917 is a great mod; particularly for what you said your goals are. If you plan to go FI in the future, a low boost CSC setup would complement it best.
At any given speed, you're putting down 10% more torque to the wheels than you were before, without adding any additional stress to the engine to produce it.
I haven't heard of any major differences between 350EVO, Central 20 or Nismo aside from price. I had fitment issues with my 350EVO FD, so I had it swapped for the Nismo one because I needed it ASAP. If it wasn't for the fact my diff was already in pieces and the Central 20 was a 3 month wait, I probably would've opted for that. Its a good $700 cheaper than the Nismo piece.
At any given speed, you're putting down 10% more torque to the wheels than you were before, without adding any additional stress to the engine to produce it.
I haven't heard of any major differences between 350EVO, Central 20 or Nismo aside from price. I had fitment issues with my 350EVO FD, so I had it swapped for the Nismo one because I needed it ASAP. If it wasn't for the fact my diff was already in pieces and the Central 20 was a 3 month wait, I probably would've opted for that. Its a good $700 cheaper than the Nismo piece.
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From: san diego
helldorado??? are u boosting at all? cuz i have the TN kit and i want these gears. maybe its me but i dont feel 3.5 1st gear is very short. not saying 1st and 2nd in 3.5 is long but unless the 3.9 makes a incredible difference i see it being an advantage. i understand ull shift more often to get to a speed but to me thats the advantage. but i jus dont want with F/I my 1st and 2nd to go to ****
Originally Posted by helldorado
I have the gears and love them. Every gear feels much more powerful and responsive than it did before. The main downside to the shorter gearing is when you have to be in a taller gear than you did before at a given speed.
I'm not familar with the real word speeds for the 6MT... so for example, say with the 3.5 at 80 mph you used to be in 3rd gear at 5500 rpm. Now after the 3.9, at 80 mph, you need to be in 4th at 4000 rpm. The 3.5 will actually accelerate more quickly than the 3.9 because its still in 3rd which puts more power to the wheels than 4th. However, once the car with the 3.5 shifts to 4th, the car with the 3.9 will have a much greater advantage.
Probably the best way to explain it is try and draw it out. This isn't accurate for real world, but just an example of the concept. Basically, from the the start, the 3.9 car will have the advantage all the way through first. When it shifts to second, the 3.5 car will still be first and pulling more strongly. Once that car has to hit 2nd, the 3.9 car will be pulling more strongly in 2nd. This will go back and forth until the 3.9 car maxes out in 6th and the 3.5 car can still pull, ultimately going faster.
The real question is, does the increased acceleration offset the loss when you have to shift? I think anybody who has done the gear swap would argue yes, but there really hasn't been enough conclusive testing to say definitely one way or another.
And yes, do it with the Quaife. Love mine!
I'm not familar with the real word speeds for the 6MT... so for example, say with the 3.5 at 80 mph you used to be in 3rd gear at 5500 rpm. Now after the 3.9, at 80 mph, you need to be in 4th at 4000 rpm. The 3.5 will actually accelerate more quickly than the 3.9 because its still in 3rd which puts more power to the wheels than 4th. However, once the car with the 3.5 shifts to 4th, the car with the 3.9 will have a much greater advantage.
Probably the best way to explain it is try and draw it out. This isn't accurate for real world, but just an example of the concept. Basically, from the the start, the 3.9 car will have the advantage all the way through first. When it shifts to second, the 3.5 car will still be first and pulling more strongly. Once that car has to hit 2nd, the 3.9 car will be pulling more strongly in 2nd. This will go back and forth until the 3.9 car maxes out in 6th and the 3.5 car can still pull, ultimately going faster.
Code:
0 30 60 90
3.9 1***********2------**********3------**********4------
3.5 1-----------******2----------*******3---------*******
And yes, do it with the Quaife. Love mine!
Thread Starter
Joined: Oct 2005
Posts: 12,390
Likes: 101
From: Spring, TX
Originally Posted by Abishop
what is a Quaiffe?
Warning: Once you enter this site you'll most likely lose $1500.
