Is the LMR 4.10 Gear kit worth it?

[Dinadeira]

For context, I have a mostly stock 98 Cobra with about 120K miles on it, and I want to put in some 4.10 gears. In the future I do want to increase the engine power quite a bit with a blower.

For reference this is the kit I'm talking about: LMR 4.10 GEARS KIT

Looking at this kit and the price, I'm wondering if all the extra stuff in this kit is worth it? For example, does the new diff cover have any real benefit other than fluid changes? And do I really need to switch out my stock LS Differential if it has had no issues?

I could potentially just buy the 4.10 Gears and some hardened 28 spline axles (should work with stock I believe) for like half the price of the above kit.

What do you guys think? I would appreciate any advice

 

[RAU03MACH]

Personally I would get 4.10 or 373
Gears and shim kit only
Up to you

 

[Dinadeira]

Personally I would get 4.10 or 373
Gears and shim kit only
Up to you

That could work too, I'm vaguely worried I might break the axles though, lol. I was hoping to bring the car to a drag strip every once in a while, nothing serious though, like 95% street use.

 

[94IndyPace]

I would just throw a new clutch pack in your differential and new axles along with the gear set

 

[cobrajeff96]

You'd need significantly more power and/or grip to break the stock axles.

 

[badass98svt]

4.30s
Most people I know that did 4.10 in their 96-98 Cobra wished they had gone with 4.30s


I had 4.30s for years and was getting well over 20 mpg on the highway.

 

[Wmac]

That kit has everything that would be needed if you plan on some track time. Especially if you launch with some sticky tires.

Don't forget a driveshaft safety loop and torque box reinforcement.

 

[Dinadeira]

4.30s
Most people I know that did 4.10 in their 96-98 Cobra wished they had gone with 4.30s


I had 4.30s for years and was getting well over 20 mpg on the highway.

Hmm, I'm heavily considering it, it's just... I feel hesitant because I'm not sure how much of a difference it will really be, especially with the jump in price

 

[Dinadeira]

That kit has everything that would be needed if you plan on some track time. Especially if you launch with some sticky tires.

Don't forget a driveshaft safety loop and torque box reinforcement.

this is the first I heard of a driveshaft safety loop, thanks for the tip!

 

[badass98svt]

Hmm, I'm heavily considering it, it's just... I feel hesitant because I'm not sure how much of a difference it will really be, especially with the jump in price

4.30 for the win. They aren't that much more $$. Dont fear the gear

 

[cobrajeff96]

3.90 and higher is the N/A motor's dream gear. I personally run a 4.10 and couldn't be happier. Gonna stay N/A as long as I can, maybe forever.

 

[Terrorist 5.0]

I would stick with Ford Racing ring and pinions. Lots of reports of them fitting without any adjustment, and don’t have as many issues as other brands. I think 4.10 will be more than enough for a Cobra, but that’s my opinion. I personally don’t like anything more than a 3.55, GT or Cobra, as daily driving just gets annoying with all the noise.

 

[badass98svt]

I would stick with Ford Racing ring and pinions. Lots of reports of them fitting without any adjustment, and don’t have as many issues as other brands. I think 4.10 will be more than enough for a Cobra, but that’s my opinion. I personally don’t like anything more than a 3.55, GT or Cobra, as daily driving just gets annoying with all the noise.

3.55 in a 4V Cobra is absolutely pointless. The stock gear is 3.27. Maybe you're thinking a 94-95 Cobra, which would make more sense.
My 98 Cobra with a turbo has 3.55 and I wish I went with 3.73
I rocked 4.30s for 15 years+. It's an incredible gear for the 96-98 4V. Keeps you in the sweet spot in the upper RPMs when you want to be, or you can shift up another gear and drop the RPMs down low.
Around town you can cruise in 4th, rather than 3rd gear and do it a lower RPM too.

 

[GTamas]

Is there somewhere a good gear - rpm - speed calculator to show what would be the change in rpm @ speed between my stock gears and shorter ones?

 

[badass98svt]

Differential Gear Ratio Calculator | West Coast Differentials

Differential Gear Ratio Calculator Tools for Tire Diameter, RPM, and Gear Ratio from the technical experts at West Coast Differentials

differentials.com

 

[shovel]

When considering gear changes - especially with a manual - remember it's not only about your highway RPM it's also about how versatile each gear is. For example when driving in hills or in variable traffic if your rear end ratio is 20% higher then the range of road speeds (miles per hour) that each transmission gear is usable is 20% smaller. In other words you will need to shift more often the higher your rear end ratio.

Automatics of course shift for you and the torque converter makes that even more squishy so if you just like getting pushed back when you push the skinny pedal an auto and deep gears will get you there. After driving a lot of cars, regearing 2 other Mustangs (one of them twice for this very reason) I've decided to stick with 3.08 in my 94 manual GT. Not trying to talk anyone into or out of anything here, do whatever you want with your car.

 

[Dinadeira]

Well, I ended up ordering the 4.30 gears, hardened axles, and other supporting hardware/bearings/fluids instead of buying the LMR kit. It ended up being a little bit more expensive because of the gears, but that's fine because I felt like everything I bought was necessary for what I want.

I'm very excited to see how it turns out! I'll update what happens afterwards. The shop is gonna have a lot to install with what I bought and the subframe connectors I have waiting to be installed. Hopefully it all goes well! I would install it myself, but I'm in a very busy position in my life right now, and I don't really have the time to learn how to weld or to correctly measure/install gears. Maybe I'll learn in the future though.

Thanks everybody for the advice!

 

[Musturd]

The stock axles don’t snap that easily . I had countless mid to low 7 second 8th mile passes on my stock axles before finally snapping . On full slicks . I would go 3.90-4.10 personally in a 4v car

 

[Dinadeira]

The stock axles don’t snap that easily . I had countless mid to low 7 second 8th mile passes on my stock axles before finally snapping . On full slicks . I would go 3.90-4.10 personally in a 4v car

I understand about the stock axles, but I just want to play it safe. I'd rather replace them now and not worry about them, than for them to give out at some unknown point in the future. (I want to be able to beat on them a little without any worry)

And for the 4.30 vs 4.10 gears... well the general opinion seems pretty split. For my situation, this car is not my daily, but more of a fun weekend car. If I was daily-ing it, I'd probably go 4.10's, but since I'm not, I really wanna FEEL that extra torque when I do drive it! Worst case, if I decide to change it in the future, a 4.10 gear and pinion by itself is not very expensive

 

[Musturd]

I understand about the stock axles, but I just want to play it safe. I'd rather replace them now and not worry about them, than for them to give out at some unknown point in the future. (I want to be able to beat on them a little without any worry)

And for the 4.30 vs 4.10 gears... well the general opinion seems pretty split. For my situation, this car is not my daily, but more of a fun weekend car. If I was daily-ing it, I'd probably go 4.10's, but since I'm not, I really wanna FEEL that extra torque when I do drive it! Worst case, if I decide to change it in the future, a 4.10 gear and pinion by itself is not very expensive

By all means go ahead I’m just saying they lived fine behind a car with 500whp for hundreds of passes on slicks . I wouldn’t be scared to run 4.30’s by any means , I had 4.56’s in my car last year with a blower on 18psi . I went back down to 3.55’s as it’s all I had but will end up going to a 3.90 later .