1/4 mile gearing

[Dogeexpress]

I've been debating this swap for awhile now. So let's cut to it. A 3.21 8spd rear end swapped to a 3.92 rear is it worth it? Or is this running out of gear at the top end going to be an issue?

 

[Booms]

I have a 3.92 8 speed.....You will never run out of gear in the 1/4 mile. I came from a 3.21 6 speed and the difference is night and day.

 

[R/T_Fire]

I've been debating this swap for awhile now. So let's cut to it. A 3.21 8spd rear end swapped to a 3.92 rear is it worth it? Or is this running out of gear at the top end going to be an issue?

I have 4.10's in my truck and hit the line at about 92-97mph and have much much more with the 545 trans. Granted I'm stock and running low 14's but the truck has so much more in it. It is still governed at 106mph and off the track it still wants to go more and pulls all the way to the governor.
I'm not sure the final gear ration of the 8speed to the 545 but I assume they should be similar.

You wont loose any top end due to high RPM I assume is what you mean. My power band is between 3600-5000ish rpm so its right in the prime for me. From my experience your good. but I'm sure some with more track experience with these trucks can chime in with better info

 

[sicmadek]

I have 3.92 6 spd and a 2800 stall. I pulled a 1.78 60' with a slight scratch off the line. im happy with my setup. Thad tried 4.10 in his 8 spd and it wasnt so peachy with 28" slicks. He just swapped back to 3.21 to try out the slicks this sunday.

 

[thad8403]

I'll let you know tomorrow if you should make the switch. 4.10s and 3.92s are pretty much the same. I have a 14 ram crew cab. Ran a 13.33 @102 with tune, 4.10s, ram air, jba long tubes no cats, and 28" slicks. First and second gear were useless with the slicks. If you're racing with 20s you'll be fine with 3.92s.

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[Dogeexpress]

Just got the oem 3.92 gears ordered from moes, should probably hold off on installing until I get a limited slip in.

 

[Kotta390]

I'll let you know tomorrow if you should make the switch. 4.10s and 3.92s are pretty much the same. I have a 14 ram crew cab. Ran a 13.33 @102 with tune, 4.10s, ram air, jba long tubes no cats, and 28" slicks. First and second gear were useless with the slicks. If you're racing with 20s you'll be fine with 3.92s.

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Useless as in couldn't hook up or the gearing was too short?

 

[thad8403]

Useless as in couldn't hook up or the gearing was too short?

It dead hooked Gears were way too short

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[Kotta390]

It dead hooked Gears were way too short

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I can see that. If you are to run a 3.92 gear I would never recommend running a 28" tire with these new 8 speeds. Does nobody make a 31" slick or drag radial?

 

[thad8403]

I can see that. If you are to run a 3.92 gear I would never recommend running a 28" tire with these new 8 speeds. Does nobody make a 31" slick or drag radial?

I went to the track today with the same set up and went 13.19 at 103.29 with 3.21s

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[Kotta390]

I went to the track today with the same set up and went 13.19 at 103.29 with 3.21s

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Very nice. The 3.92s are really nice for the 33" tires but with such a short slick it is overkill and you just proved that.

 

[Dogeexpress]

So could anyone tell me what kind if any performance gain ill see from this swap? I'm cutting a 14.2 now hoping to get somewhere near the high 13's

 

[R/T_Fire]

Depending on trans gearing (assuming you have the 8 speed or 6 speed? ) you should see better 60' and 300' times really. and as pointed out tire diameter plays a factor in that also with the rear gear ratio. To much gear IE 4:10's for a small diameter tire equals more wheel spin which is slower 60'-300'-1/4".

I'm curious as to the difference in drive with more trans gears. cause there is a huge dead spot in my set up (Stock R/T) anything above 3rd gear truck is not very responsive till higher RPm's. But I think a Torq converter will solve that issue somewhat.

 

[Geo2slow4u]

I have a 8spd with 3.92's I agree 1 and 2nd seems useless. My 1st to 2nd shift and 2nd to 3rd shift seem annoyingly slow. Truck feels like it falls on it face for a second on both of those shifts. Anyone else's truck feel like that?

 

[Revo]

I have a 8spd with 3.92's I agree 1 and 2nd seems useless. My 1st to 2nd shift and 2nd to 3rd shift seem annoyingly slow. Truck feels like it falls on it face for a second on both of those shifts. Anyone else's truck feel like that?

I feel that w/ 3.21s. Every gear after that is smooth and firm as can be. Currently have mine getting swapped to 3.92s as I write this, doubtful that I'll see a change in those shift points.

 

[Kotta390]

I have a 8spd with 3.92's I agree 1 and 2nd seems useless. My 1st to 2nd shift and 2nd to 3rd shift seem annoyingly slow. Truck feels like it falls on it face for a second on both of those shifts. Anyone else's truck feel like that?

The shift itself is actually not slow at all, it is very quick!!

It's the torque management doing that. Recently I have been playing around with the tuning on our trucks (well not me, but a buddy of mine), and he has seen multiple logs where it will decrease timing up to, IIRC, 21 degrees between shifts and the later shifts in the truck will be a little less abrupt on timing pulled. Also the throttle body closes too in some cases.

 

[sicmadek]

The shift itself is actually not slow at all, it is very quick!!

It's the torque management doing that. Recently I have been playing around with the tuning on our trucks (well not me, but a buddy of mine), and he has seen multiple logs where it will decrease timing up to, IIRC, 21 degrees between shifts and the later shifts in the truck will be a little less abrupt on timing pulled. Also the throttle body closes too in some cases.

I believe they call it recovery timing.

 

[R/T_Fire]

The shift itself is actually not slow at all, it is very quick!!

It's the torque management doing that. Recently I have been playing around with the tuning on our trucks (well not me, but a buddy of mine), and he has seen multiple logs where it will decrease timing up to, IIRC, 21 degrees between shifts and the later shifts in the truck will be a little less abrupt on timing pulled. Also the throttle body closes too in some cases.

Didn't Think of that.. Question, does torq management control the traction control system? Cause with my truck (granted whole different world being 4x2 but) from the seat of the pants it feels like it wants to go but like the trans is slipping or something is holding it back. I engage tow haul and this is reduced. ships are firmer and more responsive to throttle changes, while not in tow haul it seems lost and slips..

 

[Kotta390]

I think the TC system is seperate from what I recall. I had my TC turned off permanently and it didn't affect the shifting at all.