4.10 gears with a supercharger ?

F

fastblueroush

New Member
Apr 2, 2008
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#1
My car has a supercharger and - was wondering if 4.10 gears are a good idea? I pretty much just want them for "fun factor" and basically just drive around town and do some highway driving.

Almost all I hear is they are great with naturally aspirated, but wanted to know if they are OK with a supercharged motor.

How many RPM's at 55, 70, 90 MPH?

I have a 5 speed with short-throw shifter and upgraded performance clutch.
 

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#6
Yeah, that's not a twin screw, but it is a positive displacement blower. (roots)

Like steedman07 said, 4.10's with a centrifugal and 3.73's with a roots or twin screw if you plan on street driving.
 
#8
Thanks for clarifying that. Pretty new to the Mustang thing, but am having a ton of fun. Kind of a dig on the Roush blower eh? Listen, I'm 40 and just having a blast going fast again. I'm pretty stuck on doing the 4.10's just for the fun factor, but if you guys really know than I'm interested in hearing more. Here in Minnesota over 100 mph and you lose your liscense for 6 months, so I'm just interested in getting there as fast and loud as I can.

I'm probably never going to go to a drag strip, so are you really sure the 4.10's are WRONG for street use?

I don't want to be overreving on the highway, but I hear tons of conflicting information that I might even get BETTER MPG (Even though I don't really care about that) with 4.10 gears.

So is what you guys are saying that if I'm in 5th gear doing 70 and I want to drop down to blow someone away that I won't have much left because the RPM's will jump up so high?

Legitimately also, will I really be losing 1st gear or do I just need to get good at feathering in the clutch at launch so I don't totally smoke them before shifting into 2nd?

I WANT TO HEAR FROM ALL YOU GUYS WITH EXPERIENCE !!!!!!!!!!!!!!!!

Thanks
 
#9
fastblueroush said:
I'm probably never going to go to a drag strip, so are you really sure the 4.10's are WRONG for street use?

I don't want to be overreving on the highway, but I hear tons of conflicting information that I might even get BETTER MPG (Even though I don't really care about that) with 4.10 gears.

So is what you guys are saying that if I'm in 5th gear doing 70 and I want to drop down to blow someone away that I won't have much left because the RPM's will jump up so high?

Legitimately also, will I really be losing 1st gear or do I just need to get good at feathering in the clutch at launch so I don't totally smoke them before shifting into 2nd?

I WANT TO HEAR FROM ALL YOU GUYS WITH EXPERIENCE !!!!!!!!!!!!!!!!

Thanks
Click to expand...

If you don't plan on driving it a ton or in bad weather, 4.10s can work! Just get a taller(28"+)rear drag radial that will increase your traction and have fun! HEAVYGT sure does:rock:
 
#10
A taller rear tire will just change the gear ratio. For example, if you had 4.10's and the 28.8'' Nitto drag radials (which look too tall anyway) you'd actually make the 4.10's seem closer to 3.90's.

Fastblueroush, I have a Whipple twin screw and had 4.10's because before the Whipple I had a Procharger centrifugal blower for 2 years. After the Whipple install I removed the 4.10's and went back to 3.55's. With street tires ( and 4.10's) at 75 mph if I downshifted in cool weather to 4th gear aggressively the rear tires would spin out of control to the point where I had to let off the gas. It wouldn't have been like that in the summer, but that's no exaggeration when it was about 45 degrees out. After having the 3.55's in the car for the winter I'm sure 3.73's will be the sure thing for the street once summer arrives. I'll be installing them soon. The 4.10's were fine with my Procharger because it wasn't in boost until the motor started to rev. With that Roush blower you are kind of in no man's land. You are still in the upper 300's as far as rear wheel horsepower so 4.10's will ruin 1st gear at wide open throttle, but 2nd gear won't be so bad. I'm at about 470 rwhp which is about 100 hp more so maybe 4.10's will be ok for you. Just don't plan on any traction in 1st gear and maybe even part of 2nd gear. Keep in mind I have no traction in 1st or 2nd gear with 3.55's right now at 470 rwhp. With that Roush blower you are at about 370-380 rwhp with the standard tune and pulley.

One more thing....4.10's always felt like 1st gear was a bit short in length even while driving totally normal on the street. After feeling that and the 3.55's I feel as though the 3.73's are the ultimate street gear with a positive displacement blower. 4.10's would be a must at the track with drag radials though.
 
#11
I have 4.10's with my twin screw Whipple supercharger and love it. First gear is useless if I stomp on it, but first gear is worthless with pretty much any supercharger. Also, you don't NEED a drag radial, I don't know why people are saying you do. I dont have them and my car is fine. I have the Nitto 555r 295/45/18 out back with 4.10's which makes my effective gearing a 3.92.

Just get a taller tire (28.3" or so in the back 295/45) and it would work great. I got stuck in rain today picking up tile and my car was 100% fine. No freak outs or anything.
 
#12
Anthony and Hobo -

That's the kind of feedback I was looking for - THANKS

I want others real world experience on this topic also. I know you guys love to talk about your cars. My install is only days away and I want to hear more.

4.10 or 3.73 with a Roush Charger ??????????

Anthony -- You were pretty right on with RWHP - I had pulls of 384 RWHP on the dyno, so mine definitely is in the 100 hp less than yours, so I am still thinking 4.10's.

I do put my car away in winter (just drove it last night in 40 degree weather cause I could't wait any longer to get it out of storage and it was noticeable the lack of grip with cold roads. I don't drive it in rain or very bad weather, pretty much just warm and dry. (In MN 40 degrees qualifies for warm after seeing 40 inches of snow and -25 this year.) I can't wait to get the work done, but want to make the best decision.


I have BF Goodrich G-Force KD's on which are 275/40zr 18 on all 4 corners.

I don't plan on getting new tires as these are basically new. Hobo - you figured out effective gear ratio with your tire size. How could I calculate effective gear size with my tire size?

It's a 2006 Roush stage 1 Manual 5 speed with SC added, and Stage 2 suspension going on with the new gear set along with off-road Roush exhaust and anti-wheel hop kit.

Thanks for all your guys information!!
 
#13
Get the 4.10's with your roushcharger. It will make it feel faster with the 384rwhp.

To calculate your effective gearing take the stock tire height (27.1) and divde that by the new tire height (for me, 28.3 from Nitto's site). Take that answer and multiply it by the gears you have in the car (3.55, 3.73, 4.10, etc...) to get your new gear ratio.

So:
(27.1)/(28.3) = 0.9579....
(0.9579...)*(4.10) = 3.926...
Effective gearing = ~3.93

Note that a smaller tire than stock will INCREASE your effective gearing and a larger tire from stock will DECREASE your effective gearing :nice:

Your new effective gearing:
(27.1)/(26.66) = 1.0165...
(1.0165...)*(3.73) = ~3.79
(1.0165...)*(4.10) = ~4.17

There you go! Hope it helps! :nice:
 
#14
I can give you some perspective from first hand experience as I've switched from 3.55 to 4.10 and back to 3.55. Your initial question about 4.10s with a supercharger is extremely valid, as that is the reason I'm back with 3.55s. I had the 4.10s in before getting my twin screw SC and LOVED them. It was so much fun. Then when I got the SC and still had the 4.10s the fun factor went even higher... The combination of the gears and the power was unreal. It was still completely driveable on the street as long as I kept my foot out of it (yeah right!)

The problem came in when I would drop the hammer and go full throttle... The RPMs would jump up to 7000 almost instantly, which really scared me a lot. I mean, the power of it all really amazed me, but realistically, it was only a matter of time before something would go BOOM. So I really evaluated it for a long time and opted to put the 3.55s back in.

The first thing I noticed with the 3.55s back was "holy cow.. I have 1st gear again!" which was nice, because with the 4.10s it was like having a 4 (or even 3) speed with how quickly the shifts were going. I will be the first to admit that the fun factor may have gone down ever so slightly with the 3.55s but believe me when I tell you the car can still fry the hides off through the gears with the SC.

So the choice is really up to you - I just wanted to share my experience with the exact situation you are inquiring about.

:nice:
 
#18
4.10's with your Roush blower will be fine. Just don't think you'll get any full throttle 1st gear. I guess I say go for it. If I had about a 100 rwhp less I think I would be ok with the 4.10's. You sound like that's what you want, so I think you should get the 4.10 gears. Nothing's perfect....there's always a small price for everything. If 3.73's are perfect for my Whipple car at about 100 rwhp more, then I see no reason why you wouldn't be happy with 4.10's. I'll have a major loss of traction with the 3.73's too, so join the club. At least you're not gonna complain the tires won't break loose.
 
#19
What about 3.90's are those a good combo for some freeway driving and mainly street.....? IM looking at getting them when my K.B. comes in will it hurt me on the freeway part alot, I have an auto
 
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