First gear is too tall. Should I make it taller? Nitrous guys, help!

FastDriver

My dad had a bra
SN Certified Technician
Sep 5, 2001
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I've had these discussions before with guys trying to pick the right gearing in T56s. Lots of folks like the tall 2.66 first, because of the short ratios, but the problem is that it leads to situations like the one I'm in, a first world problem to be sure.

I got this trans from my best friend for a good deal, and decided to put it in Black Jack so that I could eventually spray and put sticky tires on the car.

With the 3.35 first in the T5, the car would 60' as low as 1.83 on stock size Goodyear all-seasons, leaving off of near idle. I'd just do my best to get the clutch out smoothly and let the super short gear to all the work.

Now, after having Black Jack out at the 1/8 event at Foxtoberfest, I've learned that it wants to leave off of the limiter. On Nittos, which aren't fantastic Drag Radials but are still far better than the previous Goodyears, a 6k RPM launch took me to a 1.86 best. I attribute the need for the launch RPM to this 25% difference in Gear Ratio.

So, here's the crux of it, I'm installing a 150-200 shot of nitrous, and because it's still 1:1 in 4th with my 4.10s, it still runs out of gear at ~109 mph. Beer math says that I might be running over 120 in the 1/4. 3.73s would be about perfect for that, but I'm concerned that it'll launch like a dog. Will nitrous make up the difference on the launch, and allow me to prevent bogging? Santa brought me an Eaton Detroit TrueTrac for xMas, and I was thinking I'd do the gears while in there.

Wish my best friend listened when I advised the 2.97 first gear, wide-ratio, T56.
 
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Depends on when you hit the juice. Also depends on if it is a progressive shot or all in on the hit.
Nitrous will provide a huge torque spike on the hit. That would solve a potential bog and create a possible traction issue.
 
Santa brought me an Eaton Detroit TrueTrac for xMas,
Merry Christmas.... Remember to use GL-4 gear oil in it.....
DSCF0740.jpg
 
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Depends on when you hit the juice. Also depends on if it is a progressive shot or all in on the hit.
Nitrous will provide a huge torque spike on the hit. That would solve a potential bog and create a possible traction issue.
It's an all in one hit. I have some safeties in place, including a window switch that I'm thinking I'll set at 3.5k, a WOT switch off of the TPS sensor, and a hobbes FP switch. But it should cut straight in with everything.
 
Plates systems are pretty violent when they hit vs a fogger system or at least in my experience. So if you are going to launch with the nitrous then expect the hit to be pretty quick unless you opt for a progressive timer which IMO is the way to go as it greatly reduces the shock to the drive line.

So one rule of thumb when looking at a first gear ratio and rear end gears is try and get to a final drive ratio of 10 when multiplying the first gear ratio times the rear end gear ratio. For the most part anything over 10 makes first gear useless as you will have to shift out of it as soon as you launch if you don't bang the limiter before that. So for example: 2.66 x 3.73 = 9.92 or 2.97 x 3.73 = 11.07

My T-Bird has a Tremec TKO circa 1998 in it. First gear is 3.27 and the rear end is 4.11 which is a 13.44 final drive ratio which I can personally tell you sucks as first gear is useless especially with the 351. I would like to pull the 4.11's and go to 3.31's to get a final drive ratio of 10.82 and the NX fogger system will be usable in first. This will give the 0.68 fifth gear a much better highway cruising rpm as well.
 
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Plates systems are pretty violent when they hit vs a fogger system or at least in my experience. So if you are going to launch with the nitrous then expect the hit to be pretty quick unless you opt for a progressive timer which IMO is the way to go as it greatly reduces the shock to the drive line.

So one rule of thumb when looking at a first gear ratio and rear end gears is try and get to a final drive ratio of 10 when multiplying the first gear ratio times the rear end gear ratio. For the most part anything over 10 makes first gear useless as you will have to shift out of it as soon as you launch if you don't bang the limiter before that. So for example: 2.66 x 3.73 = 9.92 or 2.97 x 3.73 = 11.07

My T-Bird has a Tremec TKO circa 1998 in it. First gear is 3.27 and the rear end is 4.11 which is a 13.44 final drive ratio which I can personally tell you sucks as first gear is useless especially with the 351. I would like to pull the 4.11's and go to 3.31's to get a final drive ratio of 10.82 and the NX fogger system will be usable in first. This will give the 0.68 fifth gear a much better highway cruising rpm as well.

Based on what I'm reading, the only option is to go progressive nitrous on the launch. Then, I can have a taller first gear that won't bog, so long as I'm spraying.

I think my next step, after a dyno tune to check on output, and adjustment to get to my hp goal and ensure safe AFRs, is to get myself to a track and see how the car does. If I can hook and launch at 5k RPM or less, then I can safely drop to 3.73s without getting a progressive. If I can't hook on the spray, I need to decide if I'm going to keep 4.10s and run N/A through 1st, or spend the money for the gears + the progressive system.

Thanks for helping me think through this, fellas!
 
You need good fuel. Nitrous is an accelerant. It makes the air/fuel burn much faster, which can lead to detonation.
Some race fuels are rated for Nitrous, such as C-16.
You say that you have a WOT switch off of the TP sensor, so I assume EFI. If so, is this a wet or dry system?
 
I know several guys running wet nitrous setups upstream of the throttle body but I will say that I think a plate between the upper and lower are better and foggers are even better.

NX has a plate system that goes between the TB and the upper that looks pretty sweet.


Progressive timer:

 
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