4.10 to 3.55 swap for $85 -- worth it? (Rear only)

[chris142]

With stock tire size and comparable setup to mine? You used to have 4.10's?

No never had 4.10s. Buy its a given that 4.10 will pull better than 3.5.

 

[The_Josh_Bear]

How about taller rubber?

Yeah I know I've been looking around at it... ive heard 305/75R-16 fits stock without rubbing just a little bumper adjustment but hard size to find. 315/75 is easier to find but I dont want to deal with rubbing. So I'd have to run 285/75-16 which is only about 5% bigger. I may run them anyway, ha!

Bigger tires do look way better on these rigs, I'll never dispute that!

I need tires anyway, and thought pretty hard about getting taller tires. But even with 315/75's it's a 9% increase according to a tire calculator online, 3.55's are a 13.4% increase in speed at the same RPM.
Bigger tires also make more rotational inertia to get going, but changing gears doesn't change that variable.

But all that said it's a simple way to lower revolutions per mile for sure.

 

[nj_m715]

how bad do you need 4x4?
swap it out, try it out, then change the front or change back to stock
look for the gears and have someone install them
local guy in my old jeep club set up gears for 80 bucks

 

[Clb]

you did the math, Well done, so you have a firm grasp of your situation and needs, what about just a r\p swap in the front, Or ya could ship a center section?
Just thinking here.

 

[The_Josh_Bear]

how bad do you need 4x4?
swap it out, try it out, then change the front or change back to stock
look for the gears and have someone install them
local guy in my old jeep club set up gears for 80 bucks

This is good thinking, that's my thinking too for now. I'll grab the axle tomorrow and go from there. I *might* be able to swing by a wrecker that has 2 D50's listed on Car-parts.com because as it happens, the guy with the axle is in the same area. Pretty sweet!
$80 to set up gears is amazing. I would be all over that, it's like a 6 hour process if you don't do it often. I want a TruTrack something fierce in my Sterling 10.25 so I'll still have to figure that out some day.

you did the math, Well done, so you have a firm grasp of your situation and needs, what about just a r\p swap in the front, Or ya could ship a center section?
Just thinking here.

Thanks! My thoughts were exactly that of finding used gears for the front. But late last night I remembered the above site and I'll call them this morning, rolling in a complete D50 should be easier than splitting the case and doing gears for the first time... oh and they are listed for about $300 so I call that a win any day.

 

[Thewespaul]

3.55 to 4.10 makes a good difference in towing ability with a na truck, but once you got turbo intercooler, you’ve got plenty of power to get up to speed. Interesting note, although taller tires will usually read less power on a dyno, 3.55 gears will typically read more power than 4.10s.

 

[The_Josh_Bear]

3.55 to 4.10 makes a good difference in towing ability with a na truck, but once you got turbo intercooler, you’ve got plenty of power to get up to speed. Interesting note, although taller tires will usually read less power on a dyno, 3.55 gears will typically read more power than 4.10s.

I'm pumped for the swap now that I have the power!
That's really interesting about the dyno, I wonder why. Rolling resistance? But that doesnt say anything about 4.10 vs 3.55. Huh.

 

[Macrobb]

I'm pumped for the swap now that I have the power!
That's really interesting about the dyno, I wonder why. Rolling resistance? But that doesnt say anything about 4.10 vs 3.55. Huh.

It's because the MPH of the rollers needs to change further from 2k to redline. It takes longer, which gives your turbo more time to spool up.
It's going to really depend on the turbo, though - I'd expect a non-wastegated turbo to have this more than a wastegated(smaller) turbo.

Personally, I found that with Banks Sidewinder turbo, zf5 and 4.10s, I got the best dyno numbers in 4th. This reduced gear losses evidently. The difference was like 10HP though.

 

[79jasper]

With all this discussion (and some on another forum where this was mentioned) apparently you cant get 4.10 gears in liberalfornia.... (maybe just after a certain year of production, they consider it no different than tampering with exhaust/emissions equipment)
Don't believe it, do a search. Lol I was about to call a guy out, but wanted to have all the facts first. Glad I researched it.

Sent from my SM-N960U using Tapatalk

 

[Thewespaul]

It doesn’t really matter if the engine is turbo or not, a stock Prius would see a power change with a gear set change, here’s a great explanation stolen from an ls forum I snoop on.

"Higher ratio gears will give you lower chassis dyno numbers for a strange, but logical reason. In essence, the DynoJet calculates hp based on the time it takes to spin up the 2800lb roller assembly. It's basically work divided by time and rpm. Think about this: If you car is at idle in neutral and you stab the throttle, it will take time to accelerate to redline...let's say 1.1 seconds. Now let's say it takes 8.2 seconds for your car to accelerate the DynoJet from low speed to top speed with 3.23 gears and 7.3 seconds with 3.73 gears. Dyno printout says 355 rwhp with 3.23 gears and 346 rwhp with 3.73 gears...why?

Think aabout this: In the 8.2 seconds it takes to spin the rollers with 3.23 gears, it would still take the motor about 1.1 seconds to overcome its own inertia (idle to redline). There's about 13.4% of the work used just to accelerate the motoritself. With 3.73 gears, the time to reach redline decreases to 7.3 seconds. Divide the 1.1 seconds into the 7.3 seconds and you will see that overcoming the internal engine inertia costs 15.1% of the work with 3.73 gears. There is less hp available during this time period to spin the rollers so the DynoJet will read a slightly lower hp figure.

Really there’s dozens of factors that also play into this, like rob said having more time to spool a turbo would benefit your torque figure, although a good operator and a loaded dyno should be able to set the dyno up that this shouldn’t matter as much. Another couple factors are rotating mass and frictional loss. A 3.55 gear set is smaller than a 4.10, so it’s less mass the engine has to perform work on, and less frictional loss to gear fluid.

Is this deep enough down the rabbit hole josh?

 

[Thewespaul]

It's because the MPH of the rollers needs to change further from 2k to redline. It takes longer, which gives your turbo more time to spool up.
It's going to really depend on the turbo, though - I'd expect a non-wastegated turbo to have this more than a wastegated(smaller) turbo.

Personally, I found that with Banks Sidewinder turbo, zf5 and 4.10s, I got the best dyno numbers in 4th. This reduced gear losses evidently. The difference was like 10HP though.

You always want to dyno a zf in fourth because that’s your 1:1 gear, you will get the most accurate reading there, although on an unloaded dyno you may see a slight improvement in 5th since you will have more load on the engine to spool the turbo, but also more frictional loss with the .7ish gearing

 

[Isaac Ristow]

I'm swapping my 83 from 3.54 to 4.10 for towing. Swapping from a t19 to a zf5 do I have overdrive. Swapped from a na 6.9 to a studded rebuilt 7.3 with a non gated rajay turbo kit. Planning on towing around 14,000lb quite a bit it's not going to be my daily driver I chose 4.10 for the pulling power

 

[david85]

I went from 4.10s to 3.08s and was very happy with the results, but I rarely tow more than 3500lbs. If I had to tow more than about 4000lbs consistently, I would consider swapping back to the 4.10s. I still have them in a box somewhere. Of course, I do have overdrive now. No way in hell would I ever go back to a C6/4.10 combo. Very reliable and cheap to maintain but horrendous fuel economy on the highway.

I made some excel spreadsheets that show how many of these various combinations can work, but it looks like OBN does not allow .xls files to be uploaded. In any case, here's what the ZF5 looks like with 3.55s vs 4.10s @ 70 MPH.

2300 isn't all that bad a cruising RPM at that speed. Although with a turbo, you can probably afford to bring it down to 2000 without much trouble. Best of all, you can still downshift to maintain speed if you really have to. 3000 RPM with 4.10s still gets to you 70 MPH.

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[The_Josh_Bear]

With all this discussion (and some on another forum where this was mentioned) apparently you cant get 4.10 gears in liberalfornia.... (maybe just after a certain year of production, they consider it no different than tampering with exhaust/emissions equipment)
Don't believe it, do a search. Lol I was about to call a guy out, but wanted to have all the facts first. Glad I researched it.

Sent from my SM-N960U using Tapatalk

That's funny, I should sell my 4.10 axle set to some guy in Cali, lol!

 

[The_Josh_Bear]

It's because the MPH of the rollers needs to change further from 2k to redline. It takes longer, which gives your turbo more time to spool up.
It's going to really depend on the turbo, though - I'd expect a non-wastegated turbo to have this more than a wastegated(smaller) turbo.

Personally, I found that with Banks Sidewinder turbo, zf5 and 4.10s, I got the best dyno numbers in 4th. This reduced gear losses evidently. The difference was like 10HP though.

Interesting, thanks for the insight. I always thought dynos were done in 4th anyways but I guess you can choose?

It doesn’t really matter if the engine is turbo or not, a stock Prius would see a power change with a gear set change, here’s a great explanation stolen from an ls forum I snoop on.

"Higher ratio gears will give you lower chassis dyno numbers for a strange, but logical reason. In essence, the DynoJet calculates hp based on the time it takes to spin up the 2800lb roller assembly. It's basically work divided by time and rpm. Think about this: If you car is at idle in neutral and you stab the throttle, it will take time to accelerate to redline...let's say 1.1 seconds. Now let's say it takes 8.2 seconds for your car to accelerate the DynoJet from low speed to top speed with 3.23 gears and 7.3 seconds with 3.73 gears. Dyno printout says 355 rwhp with 3.23 gears and 346 rwhp with 3.73 gears...why?

Think aabout this: In the 8.2 seconds it takes to spin the rollers with 3.23 gears, it would still take the motor about 1.1 seconds to overcome its own inertia (idle to redline). There's about 13.4% of the work used just to accelerate the motoritself. With 3.73 gears, the time to reach redline decreases to 7.3 seconds. Divide the 1.1 seconds into the 7.3 seconds and you will see that overcoming the internal engine inertia costs 15.1% of the work with 3.73 gears. There is less hp available during this time period to spin the rollers so the DynoJet will read a slightly lower hp figure.

Really there’s dozens of factors that also play into this, like rob said having more time to spool a turbo would benefit your torque figure, although a good operator and a loaded dyno should be able to set the dyno up that this shouldn’t matter as much. Another couple factors are rotating mass and frictional loss. A 3.55 gear set is smaller than a 4.10, so it’s less mass the engine has to perform work on, and less frictional loss to gear fluid.

Is this deep enough down the rabbit hole josh?

I would think the dyno software would have an input table for variables like final drive...but I've never even been on one before.
Haha I appreciate the info! Rabbit hole indeed but at the same time this is much more interesting than why I want to swap 4.10's for 3.55's.

You always want to dyno a zf in fourth because that’s your 1:1 gear, you will get the most accurate reading there, although on an unloaded dyno you may see a slight improvement in 5th since you will have more load on the engine to spool the turbo, but also more frictional loss with the .7ish gearing

That's what I've read many times, thanks for the confirmation.

-Joshua