3.73 gear swap to 4.09

7904 Views 5 Replies 4 Participants Last post by midnitejam, Dec 14, 2017

midnitejam

Discussion Starter · Dec 12, 2017

I have already attempted to post this thread, but I don't think the post was successful. So, here goes with my 2nd attempt to post........

Has anyone swapped out the 3.73 gears to the 4.09's in the gt 350? Were there any issues?

I was told that a different set of gears in conjunction with the flat-plane Voodoo engine wasn't recommended because of possible cabin noise, excessive vibration, and cabin drone. I was told that the engineers jumped through hoops to tune out the resonance, vibration, and drone that is inherent with the flat-plane engine and that 4.09 gears might make the car crazy. And that the inter-cooler differential might not function with the bigger gears.

I would have more pleasure driving my GT 350 if it had the 4.09 gear set. I enjoy inter-city cruising (red light-to-red light) and the sound of down shifts and up shifts. 35 mph is the usual speed limit in city driving. The red-line shift from 1st to 2nd occurs at aprox 60 mph with the 3.73 gears......that's considerable jail residency if caught.

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GreyGhost

· #2 · Dec 12, 2017

midnitejam said:
I have already attempted to post this thread, but I don't think the post was successful. So, here goes with my 2nd attempt to post........

Has anyone swapped out the 3.73 gears to the 4.09's in the gt 350? Were there any issues?

I was told that a different set of gears in conjunction with the flat-plane Voodoo engine wasn't recommended because of possible cabin noise, excessive vibration, and cabin drone. I was told that the engineers jumped through hoops to tune out the resonance, vibration, and drone that is inherent with the flat-plane engine and that 4.09 gears might make the car crazy. And that the inter-cooler differential might not function with the bigger gears.

I would have more pleasure driving my GT 350 if it had the 4.09 gear set. I enjoy inter-city cruising (red light-to-red light) and the sound of down shifts and up shifts. 35 mph is the usual speed limit in city driving. The red-line shift from 1st to 2nd occurs at aprox 60 mph with the 3.73 gears......that's considerable jail residency if caught.

As already replied before, I think you're making a mistake. The 410's are gonna make 1st gear virtually useless. The higher rpm limit will help make the pace of shifts more to what people are normally used to in terms of shift cadence (I can't tell you how many vids I've watched of people short shifting a 350 just because they're used to the timing of gear runout in other v8's).

It helps that the 350 has a good overdrive and I'm assuming fuel economy isn't a concern.

But without a solid axle and fat tires to take advantage, I think all you're going to do is create a spin monster where 1st gear either must be skipped or half pedaled/clutch feathered and you'll have to do the same in 2nd to avoid rolling the tires over.

I guess what I'm saying is that unless you're going to improve the suspension/tire, swapping out gears is just going to make an awfully difficult car to drive.

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Gamecock

· #3 · Dec 12, 2017

3.73 to 4.09 (never heard of a 4.09) is less than 10% change. I don't think you'll have much trouble, but I don't see what the point is.

I took my 2001 Bullitt from 3.27 to 4.10, a 20% change. It was transformational. But it has 265hp vs the GT350's 526. I don't see the GT350 needing to be transformed.

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GT_Dave

· #4 · Dec 13, 2017

For the street and my DD activity, I can't justify a 4.09 gear. But for autocross, I would think a 4.09 gear would make much better use of the time I spend in 2nd gear.

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midnitejam

Discussion Starter · #5 · Dec 14, 2017

GreyGhost said:
As already replied before, I think you're making a mistake. The 410's are gonna make 1st gear virtually useless. The higher rpm limit will help make the pace of shifts more to what people are normally used to in terms of shift cadence (I can't tell you how many vids I've watched of people short shifting a 350 just because they're used to the timing of gear runout in other v8's).

It helps that the 350 has a good overdrive and I'm assuming fuel economy isn't a concern.

But without a solid axle and fat tires to take advantage, I think all you're going to do is create a spin monster where 1st gear either must be skipped or half pedaled/clutch feathered and you'll have to do the same in 2nd to avoid rolling the tires over.

I guess what I'm saying is that unless you're going to improve the suspension/tire, swapping out gears is just going to make an awfully difficult car to drive.

My driving in the GT-350 will be a an occasional week-end warrior and inter-city cruising. I love red light to red light driving. The sound of a sports car running through the gears is music to my ears. Obviously the most of my driving enjoyment is in the streets where the speed limit is 35 mph.......currently, red-line in 1st is 60(?) mph.
The flat-plane-Crank engine is just beginning to breathe at 30 mph.

GT 350's 1st gear is 330.1 and there's three more gears before 5th gear which is the final 1:1 drive.

I have a 1998 WS6 T/A with Moser 4.56's and that is ideal for me. With a red-line of 72k rpm I don't even shift out of 4th at the end of the 1/4

My only concern with the 4.09 swap is whining.

When my GT-350 comes out of winter Storage in March/May it will probably be wearing 315 MT's or 325's if they will fit.

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midnitejam

Discussion Starter · #6 · Dec 14, 2017

Gamecock said:
3.73 to 4.09 (never heard of a 4.09) is less than 10% change. I don't think you'll have much trouble, but I don't see what the point is.

I took my 2001 Bullitt from 3.27 to 4.10, a 20% change. It was transformational. But it has 265hp vs the GT350's 526. I don't see the GT350 needing to be transformed.

The GT-350 is a step down from my current WS6 T/A which has 590 hp with Moser 9-inch 4.56's and a detroit locker. It is a perfect street/strip application except for gear whine.

The 4.09 gear set is the only set available above the 3.73's. Ford Performance (Ford Sanctioned) offers the 4.09 gear set dealer installed.

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