3.54 Final Drive Swap Review

KusoSama

My friend, Andrew Larson, and I were looking to swap out our final drive gears and finally did it. 3.69 to help him enter his powerband earlier for drifting and 3.54 to lengthen the shift points of the 370z.

Much to everyone's advice against it saying it wouldn't net any noticeable difference...
We've found out otherwise.

The swap went extremely well and have found out that a 3.54 in a 370z, makes the car feel like it's a much smoother accelerating ride and still can pack a punch if you put it in it's powerband. I'll be updating this post with the speeds I reach for high speed cruising.

5th Gear:

2500RPM = 55 MPH

3000RPM = 65 MPH

3500RPM = 75 MPH

6th Gear:

2500RPM = 68 MPH

3000RPM = 82 MPH

3500RPM = MPH << Still waiting for that time when I could test this now...

Negatives:

Cruise Control is no longer working. Not a problem since my foot still works.

Honorable Mentions:

Andrew Larson: For your hardwork and the 350z Final Drive

IntecRacing: For the use of your facilities and all the help you provide during my project.

I'll be more than happy to update the original post if any questions come up that everyone should benefit from.

kevin.z

What is the rationale for 3.54 gear? why didnt u go for the NA-optimal 4.08 drive? Any butt dyno gains?

thanks!
kev

KusoSama

Biggest reason was to lengthen the time between shifts. Final drive won't change the HP/TQ ratings of the car it either reduces/increases time in/out of powerband.

**EDIT** This is based on what I know about how the final drive works. If someone knows more about the mathematical specifics, I'm all ears.

The OE 3.69 got me into my powerband quick but that's not so good for me since I deal with a TON of traffic. So I'm usually sitting in 1st a lot.

A 4.08 would shorten that up even more. It's great if you want quick acceleration but you'll be sitting at much higher RPM at 75MPH in 6th. I am usually hovering around 2500-2600RPM for 75MPH in 6th which is only the beginning of the powerband. Also I do plan on going FI with my car so lengthening my gears will be nice when dealing with immense power.

As for the "butt dyno", I have to say my car now is deceptively fast. I say this because the MPH creeps up on you quick and you don't even notice it. Though what's nice is once I'm around 2500RPM, I can still pull pretty good because of the "less work to do more" gearing.

I forgot to mention in my OP but my car presently has a CEL and needs a tune. That'll be done this coming Tuesday so I'll be updating the speed info.

kevin.z

cool thanks! reps to you

SPOHN

I wonder what the exact reasoning for cruise control no longer working? It's understandable, just wondering the cause.

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KusoSama

Thank you very much!

The first install caused an overheating condition because of some excessive torque on the U-Joint Nut. So the oddly chosen plastic cables that are connected were melted a bit and possibly damaged. Until I swap those out I won't know if that's the true cause for the loss of Cruise Control or not, but presently we feel that's the most likely cause.

I've seen VDC kick in so that system wasn't affected.

track370

hey KusoSama,

what do you mean "less work to do more gearing"?

Changing final drive won't change your engine HP or Torque numbers, it only has an effect on what is after the final drive and that is what is important to most people or drivers because that is what you feel. Final drive has an enormous effect on wheel horsepower and acceleration ("pull"), not sure if your comment was referring to the former or latter.

By going from a 3.69 to a 3.54 drive you have simply just decreased your wheel torque by about 4% across your entire powerband. Since horsepower is simply a function of engine rpm and torque, you have decreased that as well. In terms of pull, as you mentioned, it is torque that is doing the work to accelerate you, so since you have decreased that, with all other variables aside you will accelerate or "pull" 4% slower than a car with 3.69 gears at a given rpm (as long as you are not in a powerband where you are traction limited, because then you will obviously be accelerating at the same rate which is limited by your tire). However with that effect you gain longer gear ratios and higher top speed.

It all depends on personal preference, if you don't mind losing acceleration for having to shift less then you did the right thing. Or like you said if you plan on doing FI and boosting to a point where the amount of added torque makes daily driving difficult or increases torque beyond your traction limit, then you went the right way. However, if you want more acceleration and can afford to, then you would want to go the opposite way. Its all personal preference which may be greatly effected by what you use the car for (DD, track, drag, etc).

I personally would go the other way if anything, not being traction limited for the majority of 2nd gear, I would appreciate a bit more acceleration at the sacrifice of shifting slightly sooner Especially because that additional torque will be apparent in every gear after that also, and I won't be doing any performance mods that will significantly increase my torque curve. But then again I DD my z so i wouldn't go drastically higher due to the effect on fuel economy, shifting, etc.

-Matt

KusoSama

My ultimate goal is to supercharge my Z so I definitely am doing this to soften it out to be smoother.

As far as numbers go. I pulled a baseline of 280rwhp today and was tuned to 299rwhp. Despite the decreased final drive ratio. I still have great pull when I need it with a quick downshift thanks to SRM but the ability to high speed cruise with little effort at the engine.

A buddy of mine talked with me a bit about my change and we came to the same 4% degradation of available power at a given RPM like you have explained very well. Considering how much this car has before FI... I'm glad I have gone this route.

Thank you very much for the insight. +Rep for you sir.

jnaut

OP is ur car auto or manual?

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Best 1/4 mile 12.24 Best mph 114.5_______

red6spd

Good question. And if it is a stick have you had any problems with the SRM?????????

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2010 Base+Sport 6spd: Stillen G3, FI Non-Resonated CBE, FI Non-Resonated Test Pipes, UpRev Tuned, Custom 24R Oil Cooler, JDM Rear Fog-OEM Harness.
???Whp ???WTQ (Will find out come spring time)

jnaut

all autos will lose cruise control, if you alter rear axle ratio. wakes me wonder what he has and if you have an auto then you went from a 3.3 ratio to a 3.5. just curious

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Best 1/4 mile 12.24 Best mph 114.5_______

KusoSama

What is this "AUTO" you speak of? HEHE!

Definitely got a manual which is why I went from 3.69 to 3.54 FD ratio.

After the tune and removal of the CEL I was getting... Works amazing. My Uprev tune also got rid of any throttle position issues I was having.

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K&N Drop-in Filters || Invidia Gemini CBE || ERZ High Flow Cats || Uprev || 3.54 Final Drive

Flyboy

How far off is your Speedo?

KusoSama

I've not scientifically measured it yet but perception feels like it's showing 2MPH higher than before.

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K&N Drop-in Filters || Invidia Gemini CBE || ERZ High Flow Cats || Uprev || 3.54 Final Drive

jnaut

The speedo shouldnt be off as its gets it signal through the abs sensors.

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Best 1/4 mile 12.24 Best mph 114.5_______