Need help...Can someone explain advantages/disadvantages of rear end gearing

[innrkid]

I am sure there is a thread somewhere...can somebody take the time to explain what performance enhancements could be expected from 3:73 or 4:10 or whatever. Will 3:73 cause a higher rpm at normal highway speeds? I just never took the time to really understand the advantages/disadvantages. Thanks

[Markass]

3:73
Pros:
Quicker acceleration than stock
Higher top speed than 4:10s
Better fuel economy than 4:10s

Cons:
Worse fuel economy than stock
Lower top speed than stock

4:10s
Quicker acceleration than stock and 3:73s

Cons:
Worse fuel economy than 3:73s or stock
Lower top speed than 3:73s or stock

In short: If you have a manual, get 3:73s, if you have an automatic, get 4:10s, unless you plan on supercharging the car then go with 3:73s.

[MattP 343]

You may even want to consider 3.90s

[05-1947]

Originally Posted by Markass

3:73
Pros:
Quicker acceleration than stock
Higher top speed than 4:10s
Better fuel economy than 4:10s

Cons:
Worse fuel economy than stock
Lower top speed than stock

4:10s
Quicker acceleration than stock and 3:73s

Cons:
Worse fuel economy than 3:73s or stock
Lower top speed than 3:73s or stock

In short: If you have a manual, get 3:73s, if you have an automatic, get 4:10s, unless you plan on supercharging the car then go with 3:73s.

I don't agree with the "in short" because I would not waste the money changing from the 3.55 to 3.73's.

Pro's:

Lot more fun to drive
Feels like you added 50hp

Cons:

Spending $550-$600

Your 427R will be lethal with the gears. Just get them

[Markass]

Originally Posted by 05-1947

I don't agree with the "in short" because I would not waste the money changing from the 3.55 to 3.73's.

Pro's:

Lot more fun to drive
Feels like you added 50hp

Cons:

Spending $550-$600

Your 427R will be lethal with the gears. Just get them

3.55 to 3.73 is quite noticable. Maybe not like jumping to 4.10, but in a manual you lose a lot on the top end, unless you are in an auto and in that case it needs that extra gearing to help pull it along.

Since he/she seems to be concerned with the extra RPMs, this is why I'm saying that for the best all around in a manny tranny, the 3.73s rather than the 4.10s because especially on the highway you're not at such a higher rev wasting fuel, but still have a large gain over the 3.55s. Unless you're doing a lot of racing, stick with the 3.73s.

In a blown application, 4.10s would be pointless. Period.

[MattP 343]

I think with a centri. blower and a set of DRs...410s would feel awesome!

[innrkid]

Originally Posted by 05-1947

I don't agree with the "in short" because I would not waste the money changing from the 3.55 to 3.73's.

Pro's:

Lot more fun to drive
Feels like you added 50hp

Cons:

Spending $550-$600

Your 427R will be lethal with the gears. Just get them

Let me see if I have this right...the car comes stock with 3.55's (?) So if I get 4.10's it will give me a quicker low end, less top end (like how much?) 3.73's would be middle ground (?)
The car is a stock 427R with no post delivery performance mods. It is supercharged and a manual tranny.
thanks guys...I appreciate the advice.

[DevilSun]

Originally Posted by innrkid

can somebody take the time to explain what performance enhancements could be expected from 3:73 or 4:10 or whatever.

You'll be spinning the rear-axle 4.10 times for every driveshaft rotation...if you can keep the traction tire-wise (fairly easy thing to do normally) you get into the power quicker so to speak.

Will 3:73 cause a higher rpm at normal highway speeds?

Yep, same as above...the higher gear will yield you less mpg by at least a little because 75mph at 3.55 is not the same rpm as 75mph at 3.73 is not the same rpm at 75mph at 4.10

Never fear the gear IMO. I don't think you can go wrong with any of the following 3.73, 3.90, 4.10. A little also depends what you want to do with the car...for all out drag racing, go even higher...4.30 or whatever. But for road racing you may want to stay at 3.90 or below...if you want all out excellent highway milage, stick with the 3.55s. Sick car btw

[MattP 343]

I didnt realize you had a supercharger...I would go with either 3.73s or 3.90

[EX1]

i have 4.30s in my N/A car and i love em, but you have a s/c so of course ppl are going to have different opinions. This is my genral rule...... if you plan on racing like 0-100 (hints 1/4 miles) then go 4.10 or 4.30. If u plan on a lot of highway driving or looking for more of a top speed car like 130mph+ then go a little lower like 3.90s. I personally couldnt feel anything when i went from 3.55 to 3.73 so i jumped up to 4.30s. In my opinion, i think you should go ATLEAST 3.90.

[divemaster03]

Bottom line...you will be doing much more normal driving than racing. 3.73 or 3.90 are your most sensible options.

[05-1947]

Originally Posted by Markass

3.55 to 3.73 is quite noticable. Maybe not like jumping to 4.10, but in a manual you lose a lot on the top end, unless you are in an auto and in that case it needs that extra gearing to help pull it along.

Since he/she seems to be concerned with the extra RPMs, this is why I'm saying that for the best all around in a manny tranny, the 3.73s rather than the 4.10s because especially on the highway you're not at such a higher rev wasting fuel, but still have a large gain over the 3.55s. Unless you're doing a lot of racing, stick with the 3.73s.

In a blown application, 4.10s would be pointless. Period.

Do you drive an 05+? I have multiple friends with superchargers that have 4.10's. The 427R is stout but it isn't exactly a powerhouse either.

the 3.73s rather than the 4.10s because especially on the highway you're not at such a higher rev wasting fuel, but still have a large gain over the 3.55s. Unless you're doing a lot of racing, stick with the 3.73s.

The difference is about 200rpms, so fuel should not be an issue. If it was then he would not have bought a 48k+ car.

INNRKID,

Get yourself some 4.10's and it will put a smile on your face, or you could go with the 3.73's but I am telling you that you probably will not be able to tell a difference.

You can go to many other sites to see that almost everyone with a poweradder and 5spd are using 4.10's. (in the 05+ bodystyle)

[innrkid]

Thanks everybody....
One of things I have noted in the 427R is that @ 60 mph it's turning 1900-2000 rpm's which is no problem....other than the damn off road exhaust they put on drones....and I mean rattle your head drone. I don't want to change the exhaust because in every other category it is perfect...but the drone drowns out the stereo!
So, If I put 3.73's in I am hoping that the rpm's would actually increase a little...say, to the 2200 to 2300 range which is a drivable sound. On the other hand I don't want 60 mph to be turning 2500+.
Thanks again...you guys have been great.

Oh yeah, somebody mentioned wheel spin could be controlled...could you expand?

[NorCalRoush2]

Innrkid,
Is this your daily driver? That should be a part of your decision too. You got to remember that a lot of fnsweeters dont drive there cars everyday. So you will get a lot of people telling you they put 4.10's in there roushes, this will give you great power but low top end speed and bad gas mileage.

When I supercharged my roush I went up from 3.27's to 3.55's. The difference was noticeable and with the blower you dont need much to get you up and moving.

It really depends on what you are looking for. If you like top speed (100+) and you think your acceleration is pretty good already, then a change to something like 3.73's is probably in order.

If you are just going to drag the 427 and think your acceleration is lacking, then go with 4.10's. Just realize you are not going to have a top end.

Just know the higher you go in the gears the more power you will get but at the expense of top speed. Also the higher your gears the quicker you will be shifting.

Bottom line, with that supercharger on that thing you will not need much in the aspect of gearing to get up and going. 4.10's are great on a N/A car, but on a supercharged car its just too much.

[05-1947]

On the other hand I don't want 60 mph to be turning 2500+.

With my 4.10's I am turning 2500rpms at 75mph in 5th.

[UIN2IT]

I am glad this topic came up...gears are on teh Christmas list adn I needed info on teh purchase.

I am running all N/A (plan to stay that way)
I do not have the need to go 130+ mph (No speed limit is that high, and I do not Road Race)
I DO however care about low mpg...I do not want a Cty: 15mpg car!

I want to go 3.90 (kinda best of both worlds) although I have heard some really bad things about MOTIVE GEARS! Whining and such...that is what makes me start to second guess the decision. Its too bad FRPP do not make a 3.90 setup!!

Recommendations!?

[05-1947]

Originally Posted by MY6SRB

I am glad this topic came up...gears are on teh Christmas list adn I needed info on teh purchase.

I am running all N/A (plan to stay that way)
I do not have the need to go 130+ mph (No speed limit is that high, and I do not Road Race)
I DO however care about low mpg...I do not want a Cty: 15mpg car!

I want to go 3.90 (kinda best of both worlds) although I have heard some really bad things about MOTIVE GEARS! Whining and such...that is what makes me start to second guess the decision. Its too bad FRPP do not make a 3.90 setup!!

Recommendations!?

I wanted 3.90's as well, but felt the same way.

[Markass]

Originally Posted by MY6SRB

Recommendations!?

3.73s.

[Vistablue06Roush]

I agree wth 05-1947 that 4.10 are the way to go. I have the S/C and in no way is it to much of a gear. These Mod. Motors are made for bigger gears. Im still getting 20 mpg so i didnt loose much in the mpg catagory.

The 3.73 isnt going to make that big of a change for your buck. A 4.10 will really wake that 427 right up! As far as loosing your top end, dont worry about that unless you want 140 mph or up. I can hit 120 with ease and there's more in it. The 4.10 is a Blast! Wouldnt change a thing--

[05-1947]

Originally Posted by Vistablue06Roush

I agree wth 05-1947 that 4.10 are the way to go. I have the S/C and in no way is it to much of a gear. These Mod. Motors are made for bigger gears. Im still getting 20 mpg so i didnt loose much in the mpg catagory.

The 3.73 isnt going to make that big of a change for your buck. A 4.10 will really wake that 427 right up! As far as loosing your top end, dont worry about that unless you want 140 mph or up. I can hit 120 with ease and there's more in it. The 4.10 is a Blast! Wouldnt change a thing--

I agree, topping out 4th around 110-120 is plenty for me.