Final Drive gears??

[Nigelr32]

I am building a forged engine with around 500hp, so am going to be using a SC sequential 'box. Obviously, I will get a choice of ratios with the 'box, but am still wondering, should i change the diff gears??

As an Engineer I can see the benefit in having higher ratios, as the propshaft will get spinning faster, but am not convinced I'm right??

Any advice from those in the know will be appreciated.

[stevesnj]

Ummm the extra torque created will trash your U-Joints, Driveshaft final drive gears and drive axles.

[kodyo]

I wouldn't put higher ratio gears in if you are planning on putting a turbo/SC in, you will top out on that gear too quickly. Most people who go that route actually get a lower ratio.

[humfrz]

I reckon that would depend on what you're going to do with the car ......


humfrz

[KoolBRZ]

Originally Posted by Nigelr32

I am building a forged engine with around 500hp, so am going to be using a SC sequential 'box. Obviously, I will get a choice of ratios with the 'box, but am still wondering, should i change the diff gears??

As an Engineer I can see the benefit in having higher ratios, as the propshaft will get spinning faster, but am not convinced I'm right??

Any advice from those in the know will be appreciated.

That all depends on the ratios in the gearbox. Why don't you just install it first, then change the final drive to suit the gearbox? Remember, the lower the FD ratio, the more torque is put on the drive train, the higher the ratio, the more torque is put on the axles and wheels. Do you need top speed, or top acceleration? That sequential gearbox will give phenomenal acceleration with a high ratio FD because it will make the gearbox a close-ratio gearbox.

[gramicci101]

Originally Posted by KoolBRZ

That sequential gearbox will give phenomenal acceleration with a high ratio FD because it will make the gearbox a close-ratio gearbox.

Are you really saying that changing the ring and pinion in the differential will make the gear ratios in the transmission closer to each other? Do you think before you speak, or do you just open your mouth and roll with whatever comes out? Why don't you try to sell him on removing the left swaybar and welding the header closed too?

[Ultramaroon]

Originally Posted by KoolBRZ

Remember, the lower the FD ratio, the more torque is put on the drive train...

Care to elaborate on this?

[Apoc]

Originally Posted by Ultramaroon

Care to elaborate on this?

I am still amazed at his ability to spew out completely backward shit.

[gramicci101]

Originally Posted by Nigelr32

I am building a forged engine with around 500hp, so am going to be using a SC sequential 'box. Obviously, I will get a choice of ratios with the 'box, but am still wondering, should i change the diff gears??

As an Engineer I can see the benefit in having higher ratios, as the propshaft will get spinning faster, but am not convinced I'm right??

Any advice from those in the know will be appreciated.

I assume you'll have some sort of forced induction, since you'll be pushing around 500hp? In that case, you'll benefit more from lowering the ring and pinion ratio, so you can stay in your power band longer before having to shift. Definitely do as @stevesnj suggested and beef up the rest of the drivetrain back there so you don't lose an axle or cv joint or something like that.

[cdrazic93]

Originally Posted by KoolBRZ

Remember, the lower the FD ratio, the more torque is put on the drive train, the higher the ratio, the more torque is put on the axles and wheels.

[cdrazic93]

Originally Posted by gramicci101

suggested and beef up the rest of the drivetrain back there so you don't lose an axle or cv joint or something like that.

this.

I would reccomend 3.73 FD, replace the drive shaft, axles, I would look into FBM's Ford 8.8 rear end. IS300 diff would be a good thought.

[KoolBRZ]

Originally Posted by gramicci101

Are you really saying that changing the ring and pinion in the differential will make the gear ratios in the transmission closer to each other? Do you think before you speak, or do you just open your mouth and roll with whatever comes out? Why don't you try to sell him on removing the left swaybar and welding the header closed too?

Yes it actually does. While it doesn't change the gears themselves, it does change the spread between the gears. The gearbox isn't used by itself. It works BETWEEN the engine and the differential. The gear spread, which is the difference between close ratio and wide ratio gearboxes, is dramatically affected by the FD ratio.

In simple words, the redline speeds in 1st thru 6th with a lower FD ratio will be further apart, in other words, a wider spread. For example;

4:10 ratio lower = farther apart
1st=38 MPH @ 6966 RPMs
2nd=63 MPH @ 6969 RPMs
3rd=89 MPH @ 6933 RPMs
1st - 2nd, 25 MPH. 2nd - 3rd, 26 MPH

5:10 ratio higher = closer together
1st=30 MPH @ 6841 RPMs
2nd=50 MPH @ 6880 RPMs
3rd=72 MPH @ 6977 RPMs
1st - 2nd, 20 MPH. 2nd - 3rd, 22 MPH
If you're shifting closer together, it's the same as saying it has a closer ratio between gears.

[KoolBRZ]

Originally Posted by Ultramaroon

Care to elaborate on this?

I just did.

[KoolBRZ]

Originally Posted by Apoc

I am still amazed at his ability to spew out completely backward shit.

Think before you speak. I've actually changed my FD. Have you? Any idiot can spew insults. I back up what I say with fact. Care to dispute that?