Advice/discussion needed: DTTs. re-gear also?

[sota]

So I'm making this the year I **** and get off the pot with this. I'm installing DTTs front and rear. What I need to decide is, do I re-gear or not. Being it's a v6 stick drive train I have the 3.55 gears from the factory. The biggest issue is, I have to decide whether to go with 3.73s or 4.10s, since they use the same DTT part number, and the 3.55's do not. I'm worried about effecting the fuel economy (which has a long term rating of 18.278mpg over 2,580 days and 41,630.40 miles... I did say long term ) but i'm also envious of people getting 20s and better consistently.

I'm currently running MOABs with 245/70R16's as listed in my sig, and i've considered next go-around going with 235/75.
Full 4X Guard armor is planned and the backbone plus winch is getting integrated into the front.

As most of you know I plow and I tow a car trailer occasionally, so factor that all into the equation.

So given all that is and all that is planned, what say the intelligentsia about what would make the most sense in terms of gears.

 

[u2slow]

So I'm making this the year I **** and get off the pot with this. I'm installing DTTs front and rear. What I need to decide is, do I re-gear or not. Being it's a v6 stick drive train I have the 3.55 gears from the factory. The biggest issue is, I have to decide whether to go with 3.73s or 4.10s, since they use the same DTT part number, and the 3.55's do not. I'm worried about effecting the fuel economy (which has a long term rating of 18.278mpg over 2,580 days and 41,630.40 miles... I did say long term ) but i'm also envious of people getting 20s and better consistently.

I'm currently running MOABs with 245/70R16's as listed in my sig, and i've considered next go-around going with 235/75.
Full 4X Guard armor is planned and the backbone plus winch is getting integrated into the front.

As most of you know I plow and I tow a car trailer occasionally, so factor that all into the equation.

I'd want at least the 245/75R16E for towing... so that's more gear needed right off the bat. So go 3.73+. Cheap/used 3.73s gears (or diffs) are usually easy to find. Even if you go to 4.10 later, the DTT still works.

I put a No-spin (lunchbox) in so I didn't have to worry about future ratio decisions. Haven't towed other that moving a few things around the yard. No plowing either.

 

[tommudd]

If only running 29-29.5 inch tire, 3.73s should help you

 

[HoosierJeeper]

I'm thinking 3:73s too, that's the same improvement that an auto gets from 3:73 to 4:10, which is perfect for that size and 4:56 is probably a little short for optimal highway cruising, as 4:10 would be for a stick.

Reading between the lines: I don't want you to get 4:10s bc I probably need them more.

 

[sota]

If only running 29-29.5 inch tire, 3.73s should help you

Yea I don't see me getting crazy with tall tires or anything nutty like that. I treat it like a pack mule, so other than towing and plowing and hauling heavy things, it's I guess closer to a "mall crawler" than anything else. I'm hoping to eventually do some off-roading, but it won't be anything too bizarre or extreme.

R&P	Gear	rpm @ mph:		@ rpm:	3000
3.55	Ratio	65		shift drops to	speed
1	4.46	-			-	17
2	2.61	-			1756	28
3	1.72	4522			1977	43
4	1.25	3287			2180	59
5	1.00	2629			2400	74
6	0.84	2209			2520	88

R&P	Gear	rpm @ mph:		@ rpm:	3000
3.73	Ratio	65		shift drops to	speed
1	4.46	-			-	16
2	2.61	-			1756	27
3	1.72	4752			1977	41
4	1.25	3453			2180	56
5	1.00	2763			2400	71
6	0.84	2321			2520	84

R&P	Gear	rpm @ mph:		@ rpm:	3000
4.10	Ratio	65		shift drops to	speed
1	4.46	-			-	14
2	2.61	-			1756	25
3	1.72	5223			1977	37
4	1.25	3796			2180	51
5	1.00	3037			2400	64
6	0.84	2551			2520	76

So there's the hard numbers for things. I'd lose the ability to cruise comfortably at 90mph, but then I don't do that that often.

Tommudd: so you're thinking I should error on the side of caution and go for 3.73's instead of all out for 4.10's?

Funny fact: she's pretty damn stable at 100mph. I mean you still feel that she's a big girl, but it still handled fine at that speed.

 

[tommudd]

My 04 with over 4 inches of lift was stable as well at 100 on the wide open roads
but...
If you would be going to 245-75-16s/265-70-16s I would do 4.10s
but with the sizes you mention stick to 3.73s IMO

 

[sota]

Thanks. After going through this, my un-experienced self is saying "3.73 passes the 'smell' test better than 4.10 does right now." I appreciate your confirmation bias.

 

[CzarKJ]

Having the 3.73 with the 5 speed I wish I had 4.10s. Wouldn't dare go up a tire size past 240/70/16.

 

[renegade 04]

If you want a fun liberty, and don't care about mpg then go 4.10 but if you are worried about mpg then go lower maybe even stay stock. If you want 3.73 then I could sell you for cheap my old front differential.

 

[u2slow]

Having the 3.73 with the 5 speed I wish I had 4.10s. Wouldn't dare go up a tire size past 240/70/16.

Can't even really compare the 5 and 6 speed. A 5-4 downshift on the 5spd is like a 6-4 shift on the 6.

A gear change that makes 1st gear redundant seems a waste.

 

[sota]

Can't even really compare the 5 and 6 speed. A 5-4 downshift on the 5spd is like a 6-4 shift on the 6.

A gear change that makes 1st gear redundant seems a waste.

well.....
I was working on an idea on how to make it so I could safely start off in 2nd gear instead of first, and either swap in the 5.01 1st gear ratio or get a trans with it already installed, along with some other changes. Basically, make it a 5spd with a LO gear for towing take off or plowing w/o using 4LO. 4.10 was definitely in the cards for that. I forget... did 4.56 gears fit in the pumpkins? I never ran the numbers for that.

ETA: looks like i'm SOL for 4.56 in the stock D30A up front. Rear can do it.

Anyone have a power band chart for the motor itself? I'm curious on something.

 

[u2slow]

If taking 1st gear out of the picture for regular driving....might as well go to 4.10. I believe 4.56+ ratios are why JBA made the steel D30 diff.

I have fullsize trucks for chores.

 

[sota]

It was just a crazy thought/idea I had at one time, and mentally kick around ever so often. If I ever found myself in possession of a spare NSG370 trans, time on my hands, and a beer or 3 to have someone "hold" I'd considered tearing one down and measuring some things to see if certain "ideas" were possible.

U2 is right though, a 6-5 downshift is damn near worthless most of the time, as it's only a 500rpm jump up if you're lucky, and usually by the time you realize you need the downshift it's too late so it's a 6-4 (engine note isn't as noticeable in this thing.) 6-4 happens a lot for me, and in general I find i'm skipping a lot of gears frequently. 3-6 and 4-6 occur a lot on the back roads when going from a stop. I get the feeling that something between 5 and 6 would be the better choice for a top gear in terms of engine speed, especially on the highway. I know, lots of random thoughts.

Still looking like 3.73 is the answer/compromise.

 

[u2slow]

U2 is right though, a 6-5 downshift is damn near worthless most of the time, as it's only a 500rpm jump up if you're lucky...

No - wrong idea. You're downshifting too late and missing the whole benefit of the close ratios. IMO, the best way to drive this trans is to realize you have two usable gears for any road speed. One for power, one for cruise.

 

[sota]

No - wrong idea. You're downshifting too late and missing the whole benefit of the close ratios. IMO, the best way to drive this trans is to realize you have two usable gears for any road speed. One for power, one for cruise.

My old brain just can't handle that, what with driving up to 5 different vehicles (4 of them stick) in a given day at times. I know i'm downshifting too late, since I'm not getting the "signals" i'm used to to tell me to do so. That also goes with my question of a power band chart for this motor, as the barely 500rpm change between 5 & 6 never seems to be enough, unless you're already up in 6th quite a bit.

 

[u2slow]

IMO, powerband starts at 2500rpm. If you roll into a highway grade doing less, you will be downshifting.

The louder muffler I put on gives better feedback on what the engine is doing.

 

[Cardhu]

all or nothing. 4.10s.

If your doing DTT's, your already replacing carrier. Unless your setting up used 3.73s to save some coin go all out.

If its too low with your current tires, go bigger. 265 something or bust.

 

[u2slow]

If its too low with your current tires, go bigger.

I like how you think :gr_grin:

 

[turblediesel]

I drove a lot of Italian cars with small engines and powerbands. The trick was to put the tach in the powerband sweetspot and stir the stick to keep it there. Double-clutching and rev-matching allowed for skipping as many downshifts as the road called for.

 

[sota]

I drove a lot of Italian cars with small engines and powerbands. The trick was to put the tach in the powerband sweetspot and stir the stick to keep it there. Double-clutching and rev-matching allowed for skipping as many downshifts as the road called for.

pretty much how i've driven every car I've ever owned.

problem with this thing is, with the )$(#$)#($ drive by wire I can't ever tell if I'm in/out of the power band, or if the computer is just being a ****. sometimes it goes like stink, other times not.

and cardhu... raises an interesting point