49 replies to this topic

[CodyWayne718]

Old thread I know. I'm good at that. Trying to find the 3.73s on tousley and this is all I can find http://www.tousleyfo...ponent=GEAR KIT

Is that what I need? It doesn't say what ratio they are so I assume stock.

[2010KonaBlueGT]

CodyWayne718, on 26 May 2012 - 11:24 PM, said:

Old thread I know. I'm good at that. Trying to find the 3.73s on tousley and this is all I can find http://www.tousleyfo...nent=GEAR%20KIT
Is that what I need? It doesn't say what ratio they are so I assume stock.

No, this is what you need:

P/N: M-4209-88373

Description: 8.8" 3.73 Ring Gear And Pinion

http://fordracingpar...tKeyField=13230

Call Steve or Mike at Tousley and order that part number along with a Installation kit, listed on the above page.

The instructions are also linked on the page I provided the link to.


Phill

[wingsnut]

At stock power level 3:73's are great, just be prepared to spend some coin to get it to hook if you add goodies under the hood. As stated above and nobody really believes me when I tell them I am getting just as good if not better fuel mileage with TVS, VMP tune and 3:73's as I did completely stock.

[SSGT500]

The first mod that I did to my 07 GT500 was a 3.73 gear.  That's probably why I'm still on the original clutch.  I was very disappointed that Ford built these cars with a 3.31 gear.  Then they wondered why they had clutch problems.  Since changing the gears, I've gone to a smaller tire that gives me an effective 3.90 ratio.  That feels really good.  The car is easy to launch on the street and feels great on the track.  My favorite place for FRPP parts is Buy Ford Racing.com.  They have 3.73s for $139 including shipping.
http://www.buyfordra...INION-SETS.html

[rdrawkit]

All purpose gear is the 3:73...Great with stock set-up or stage 1/2 setups....So easily to drive and great on the highway .....I'm running stock wheel size and nitto 555 all around....no complaints....

[Albino500]

3.73:1 are the way to go IMO. The important thing is to buy the installation kit also and take it to the installer - if they say that they don't need it - RUN don't just walk away !

[frazierfreud]

I've considered 3.73 gears. Just worried about traction. I hook nicely with drag radials with my stock 3.31 gears.  I am just concerned that I couldn't floor it in second gear without losing traction. Plus, I am considering going with a regular street tire instead of drag radials...this would probably assure me of not keeping traction with a 3.73

[rdrawkit]

Traction and 3:73 gears can be a problem...I learned how to feather the launch with nitto tires and 2nd grabs very nicley and I'm gone....

[CodyWayne718]

Would this install kit be alright?

http://www.americanm...moinkit8re.html

Or should I get the one from the above post for the 2012? The one at AM is just so cheap...... get what ya pay for, I know. That's why I'm asking first :-) Thanks

[CodyWayne718]

I've got the feeling that's not the install kit I need. Is it? There's like 5 different install kits!

[svt2010]

Does anyone make a 3.90 gear for the 8.8 rear in out cars?

[Albino500]

svt2010, on 02 June 2012 - 04:52 AM, said:

Does anyone make a 3.90 gear for the 8.8 rear in out cars?

Yes

[2010KonaBlueGT]

CodyWayne718, on 01 June 2012 - 08:04 PM, said:

I've got the feeling that's not the install kit I need. Is it? There's like 5 different install kits!

Ford Racing offers 3 levels of install kit. The one you cited is identical to the lowest end FRPP kit at the very same price. All it includes is the shims, pinion seal, crush sleeve and gasket.

Another includes bearings. I can't remember what the third one includes but if you follow the link to the Ford Racing gear, the 3 kits are listed near the bottom of the page.


Phill

[CodyWayne718]

So which one should I go with? Car has 18k miles on it. Thanks guys

[2010KonaBlueGT]

CodyWayne718, on 02 June 2012 - 01:52 PM, said:

So which one should I go with? Car has 18k miles on it. Thanks guys

I have a complete Snap-On puller set and bearing grips and caps to install so I can get away with using the basic kit without bearings. I can pull the bearings without destroying them, not sure if you can or not.

If you can pull the side/carrier bearings and the pinion bearing off without damage, you don't need bearings. Simple as that (well, unless your bearings are bad). If you can't, you do (need bearings). The Level 3 kit includes axle bearings so if you want to pull them and replace them, that'd be the kit for you. With only 18K miles on the car, your axle bearings should be fine.

SO....if you can pull the diff. bearings, get the 1st (L1) install kit. If you need diff. bearings, get the L2 kit. If you want or need axle bearings, L3 kit.


Phill

[Albino500]

I'll go with door (I mean kit) #2 Phill - - A WINNER !

Edited by Albino500, 02 June 2012 - 03:16 PM.

[corepuncher]

I have 3.73's, and they are NOT right for my car.  I am looking to go MUCH lower.

I have a 2011 GT500 SVT.  When it was bone stock, the gears were PERFECT!  It would barely scratch the tires in 1st and going into 2nd.

However, now I have a TVS supercharger, and about 170 more hp and torque than stock.  Not balanced any longer. In fact, I have to get to 3rd gear before I can safely go WOT in the power band.

Not only is wheel spin a problem, but just 1st gear in general, the engine is always racing and it seems I have to shift into second 2 seconds after I leave my driveway.

Therefore, I"m going to pick a rear end ratio that reduces wheel spin and increases gas mileage for daily driving.

My choices are 3.55, 3.31, 3.27, 3.15, 3.08.   Which one is best?

I did some calculations.

First, compare to the 2013 which already comes with a TVS. Ford does a good job optimizing, so lets trust them:
Factor in a different 1st gear: Rear ratio X 1st gear = 8.8 for 2013.
My current setup = 11.08 for my 2011.
A 20.5% difference in torque. So what rear end ratio would I need to mimik the 2013 (get an 8.8?):
8.805/11.078 * 3.73 = 2.96.  

Second, since I liked the way it behaved stock...lets compare the torque ratios and reduce 3.73 by that amount (no need to multiply by 1st gear ratio...they are the same):
Stock Torque:  510
My Dyno:  602

510/602 X 3.73 = 3.16.  Ahh...that would suggest 3.15 rear end.

One last benchmark...I found an equation to estimate when tires will break loose at a given torque:
Using a typical 0.7 friction coefficient, I get 464 ft/lbs.  Sticky tires with a 0.8 would yield 530 ft/lbs.
464/602 * 3.73 = 2.87
530/602 * 3.73 = 3.28

So using three different benchmarks:
Range: 2.87 to 3.28
Average of all 4: 3.07
I trust the 2 - real world measurements better than uncertain friction coefficient, so average of those two: 3.06

Now, the 3.08 would seem the winner using the averages.  HOWEVER...this means if I ever get stickier tires, I have left acceleration on the table.

Therefore, I think the optimum choice would be the 3.15. It also happens to be same ratio of when my car was stock, and I LOVED how it accerated...only slight spin.

(3.73 - 3.15)/3.73 =  15.5 % decrease in overall RPM's across the spectrum.  This should result in that same increase in gas mileage...as RPM's are basically proportional to gas usage (ignoring external factors).
That means a nice 2 mpg gain city, 3 mpg gain highway.

One last thing I have to consider...6th gear.  All the other gears' shift points are effectively moved up...but the buck stops with 6th.

At 75 mph I currently am at about 1725 RPM.  If I go with 3.15's, it will drop to 1457.  That should still be fine for interstate...super OD!

I think this all makes sense, please let me know if you find an error, thanks.  Now...time for shopping!  Black Friday in effect.

Edited by corepuncher, 23 November 2012 - 01:11 PM.

[HARLEYDEALER]

This link is very helpful, when choosing the right gear, I rather be a tat lower, then taller. But it's up to you and your driving style and how you want your car to react. Bill     http://www.currieent...hCalculator.htm

[Albino500]

corepuncher - JMO - tire diameter and coefficient of friction factor need be looked at more and one can only guess at driving style . My guess at this point would be to suggest a 3.27:1 rearend ratio to establish what you are after. Run the numbers and see what you think. Good luck and enjoy the ride.

Edited by Albino500, 29 November 2012 - 07:41 AM.

[corepuncher]

Thanks for your replies. I have ordered the 3.15 gears, along with a new girdle (hope it does not make me look fat)

Since my 1st gear is a 2.97, it really raps up fast.  I decided to use the 2013 as a baseline since it has the same TVS as mine. 2013 has 2.66 1st gear.

One thing I did not take into account, the 2013 might have more torque than mine, since it's a 5.8 liter.  Spec sheet says 631...my dyno said 602.  At first I was thinking that is at the crank but actually I think torque numbers do NOT get reduced like HP does (from engine to wheels)?  Can someone verify this?

If that is the case, I need to re-factor for the 2013 comparison.

So before, I got an equivalent 2.96 rear end.  But multiplying by 631/602 = 3.10.  So it appears the 3.15 I got is just right...a tiny bit shorter which is good.

Again, this is a daily driving car, so I'll never have slicks on it. And if I did, I'd have to get a new driveshaft anyway.

Now, I just need to find a place to install it.  I would try myself but my friend said he had trouble with noise and such. Is there some tutorial that is very precise, would I need any special tools to get aligned properly, or do they just snap into place?