Kvin C Posted December 17, 2010 Report Share Posted December 17, 2010 Although a very happy user and a disciple of the 4.10 rear gear in my SGT, I am curious as to why the 3.90 rear is not more poular today. As evidenced by many posts here, a lot of guys "fear the gear" and, while cognizant that the 3.73 is a marginal improvement over their stock 3.55 (at least in an N/A application) , are clearly hesitant to make the larger leap to 4.10s. As a pimply-faced teen in the 'sixties, I recall the 3.90 to be the hot set-up! Why has the 3.90 fallen out of favor? (And I realize that non-FRPP gears have a "whiney" rep, isn't that more a function of the manufacturer rather than the ratio itself?) Just curious..... Link to comment Share on other sites More sharing options...
jmn444 Posted December 17, 2010 Report Share Posted December 17, 2010 I have 3.80's in my '68 with a T-5 trans and like it... But LOVE my 3.55's in the SGT! Link to comment Share on other sites More sharing options...
slbgtsc Posted December 17, 2010 Report Share Posted December 17, 2010 I have 3.80's in my '68 with a T-5 trans and like it... But LOVE my 3.55's in the SGT! I went 3.73's because I thought with a roots SC'r 4.10's might be a little deep, and everything I read on the 3.90's was they were considerably louder. This includes two setup locally on GT500's the owners love them but they are much louder than 3.73's/4.10's. My "guess" is the manufacturer or cut must have something to do with it. I've seen a lot of 3.90's in 9" rearends with out complaint of noise? Link to comment Share on other sites More sharing options...
BAD500Chris Posted December 17, 2010 Report Share Posted December 17, 2010 And I realize that non-FRPP gears have a "whiney" rep This seems to be why. I would have actually gone with 3.90s if FRPP made some. Instead I went with 4.10s Link to comment Share on other sites More sharing options...
shelbytexan Posted December 17, 2010 Report Share Posted December 17, 2010 I believe the 390's are the best ratio and you would certainly feel a difference compared to the 373's as they are to close to the 355's but i went with the 410's on account of noise. The 390's are considered foreign gears and the cut on the gears do create more noise than others. I am now s/c'd and still love the 410's. If i were to go down in gears now, i would do 373's as they are noticeably higher in ratio than the 410's but i will probably just stay where i'm at. The 410's are the only way to go if n/a. Link to comment Share on other sites More sharing options...
kahmann Posted December 17, 2010 Report Share Posted December 17, 2010 I intend on swapping to 3.90's within the next couple weeks. The 4.10's are too much gear for my setup. I'll let ya know what I think of the change. Link to comment Share on other sites More sharing options...
ilmor Posted December 17, 2010 Report Share Posted December 17, 2010 Seems like a 3:90 would be a popular compromise...I wonder why Ford Racing does not sell this? Link to comment Share on other sites More sharing options...
speedyburd33 Posted December 17, 2010 Report Share Posted December 17, 2010 I would have gone with 3.90's if FRPP had them too. I am very happy with my 3.73's for now though. Link to comment Share on other sites More sharing options...
shelbytexan Posted December 17, 2010 Report Share Posted December 17, 2010 Motive is the only one i know that makes the 390's but there may be others. I would have gone with 390's also if Ford Racing had made them but i really don't care for the noise that supposely goes with them. I guess i could get some louder mufflers. Link to comment Share on other sites More sharing options...
rush_junky Posted December 17, 2010 Report Share Posted December 17, 2010 I would have gone with 3.90's if FRPP had them too. I am very happy with my 3.73's for now though. +1 Link to comment Share on other sites More sharing options...
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