opinions on 3.90 to 3.55 swap...

[Foxfan88]

as you guys know i am adding a SC trim vortech to my car here in a few weeks and i am quite sure its going to create traction issues. my car isnt doing to bad now in the 90+ degree temps it will hook up a little better, once it cools off it goes back to frying the tires in 1st and getting squally in 2nd. with a supercharger i only see that intensifying that.

i have a 3.90 gear now, i have considered stepping to a higher ratio like 3.55 to give the car a little more street manners, i'd rather have some fun and hook up rather than having to spin tires, fight to control the car and waste rubber on the street. i am sure i would still spin with 3.55s but it wouldnt be so bad and each gear would last alot longer, that car NOW feels like it runs out of steam fast due to the low gearing it gets to topping out 4th gear rather quickly.

only thing i fear is swapping down to 3.55s would have a bad affect of SOTP but i am guessing the SC will totally cover that up. i also think that with a higher gear the engine would stay in boost a little longer rather than building up to peak boost quickly then shifting and having boost go down some.

i like to take the car to the track and wouldnt really care if i lost a tenth or two, for some better street driving, that is where the car is driven 90% of the time lol.

i just fear with 3.90s and the SC the tachs just going to fly up way to fast to have any fun on the street.

anyone done any swapping from a low gear to a higher gear for the same reasons i am discussing? and thoughts?

 

[blackened88lx]

I would definitely suggest it.

 

[Blk91stang]

I have 3:55's with a Sc-Trim right now and the car is driven on the street more than at the track (sees track time a few times a year)

I was making 405rwhp and running 114mph in the 1/4 and wish I would have some 3.73's in the back or 3.90's to get out of the hole better and keep the tach screaming at the top end (I think i go through the traps around 5,300)

With my current transmission overdrive (G-Force T-5), I only see around 2,200rpms doing 80 mph with the 3.55's and 26" tires.

I say keep the 3.90's and see how you do after the supercharger is installed. You dont want to have to do the job twice because you may have made a bad choice.

27" tires will help if you dont already have them. Will theoretically drop your 3.90's to around a 3.77 which would give you around 200 more rpms at the end of the track if needed.

Just my .02

 

[ninety15.0]

I would also say its not a bad idea to wait. I think you are going to have big traction issues either way. My brother has 3.55's in his car and i have 3.73's in my car, the difference is minimal....and makes me wish that i went with 3.55's just for the extra couple hundred cruising rpm's that he gets on the highway. I think a swap from 3.90's to 3.55's will not be nearly as detrimental as you think and the blower will more than make up for it. But wait and see if the car will light em up in 3rd after the blower install!

 

[Foxfan88]

yeah i will wait and see how she acts with the blower with 3.90s and go from there. i am running a 27" tall tire now, it goes pretty good on the highway. only spins 2000 at 65 mph. which isnt too bad.