[tmtalpey]

Re: Final Drive Gears - Change??? (23109VC)

It's not impossible, but it might as well be. You'd need to change out both front and rear differentials, and probably rejigger a bunch of electronics settings.

The easiest way to change your effective final drive ratio is to alter the wheel/tire diameter. I considered that in my V50 but concluded there is not enough vertical clearance from the spring seat on the strut to the top of the front tires to make a significant difference.

My V50 has a 4.00:1 ratio and I toyed with the idea of achieving 3.77:1 as on the R. Interestingly, a 235/50-18 tire would exactly reproduce the existing sidewall of my stock 205/55-16's, and bring the final drive to exactly 3.77:1. Oh, well, in addition to hitting the strut they'd probably rub, too.

Tom.

 

[tmtalpey]

Re: Final Drive Gears - Change??? (JimLill)

Maybe - I doubt the front diff is interchangeable though, being embedded in the trans and all. The rear is probably a straight swap.

In the 04 and 05, the GT final drive is 2.65:1, in the 06 it's 3.33:1. MT final drive is always 3.77:1. That's quite a jump!

Tom.

 

[tmtalpey]

Re: (23109VC)

You want a shorter ratio? Hey I'll swap you the 4.00 gears from my V50! (same trans

)

Smaller tires would be the way for you to go, I think. You'd need to drop about 6% total circumference, which might be possible on 17's with some radical 35's or 40's...

Don't jump to the conclusion you'll get more acceleration though. You might be rewarded with wheelspin.

Tom.

 

[tmtalpey]

Re: (JimLill)

Or don't want!

Personally I think the R will light up its tires with that much mechanical advantage on the wheels. OTOH, my V50 doesn't do it... has less torque than R though.

I poked around a little and I'm wondering if the rear differential might not need changing. It all depends on whether the angle gear gets final drive output, or gear output (i.e. takeoff ahead of or after front differential).

If it's after the final drive, then only the front differential gearset needs changing. Not that it's a huge help, because the AWD final drive physical configuration is different internally from FWD. But, I can say that most manual AWD Volvo's are 4.00:1, and most FWD are 3.77:1. In other words, the R is "special" in that it has the taller 3.77:1 ratio, with AWD. I think this is because of the extra power.

All this might lend options to parts swapping, since there exist both AWD and FWD cars with otherwise similar drivetrains. But, even if it can be done, there's the matter of programming the rest of the car to match. The speedo/odo would change of course, but the brake (traction) and chassis modules need to know the ratio as well. It won't be easy.

Tom.

 

[tmtalpey]

Re: (JimLill)

Quote, originally posted by JimLill »

the prop shaft runs at the trasnmission output speed... so you need 2 gearsets

That's what I thought until I noticed the (rear) final drive is the same part # between MT and GT. Not conclusive, of course.

Johann - my V50 AWD has the M66 and a 4.00:1 gearset, verified with wheel speeds. So it exists.

Tom.

 

[tmtalpey]

Re: (pie_ya)

Benefits:
- more torque on the road (quicker takeoff)
- quicker turbo spool (torque available earlier)
- shorter ratios (tighter powerband gearing)

Drawbacks:
- more torque on the road (wheelspin)
- quicker turbo spool (on/off behavior)
- shorter ratios (more shifting)
- reduced top speed
- reduced fuel economy
- need for other adjustments

It would completely change the car, that's for sure. Whether for the better, that's unclear. This is why I suggested prototyping it with smaller tires first.

I was considering the reverse, taller gearing, primarily for the fuel economy. The V50 T5 FWD gets significantly better fuel economy than the AWD, and it isn't (all) the additional weight and rotating mass. Just a thought experiment for now however.

Tom.

 

[tmtalpey]

Re: (23109VC)

Quote, originally posted by 23109VC »

If I can change my gears at a reasonable price, and gain acceleration that would be as if I had added 30-40 hp....I'd be all over it.

And I agree with you and say again, change your tires for ones that reduce the circumference by 6% and you can see for yourself. While it doesn't solve the problem of recalibrating the car, it's a) relatively inexpensive (compared to rebuilding whole drivetrains) and b) reversible.

Just a suggestion! Of course, the car might look a little silly, but actually the wheels would be lighter, and if it goes!? Well, it would prove quite a lot...

Tom.