Your in the same boat as me parish8!

I just posted this on the FSC site to get some feedback on staying with my old 3.73 gears or upgrading to 4.10 4.56 gears....

Not as many tech heads over there though Let's see how you guys do with this

"550+HP! 3.73, 4.10 or 4.56 gears?

Need some imput to make a good decision here guys!

What I have: 5100lb K1500 3dr truck with vortech supercharged 383 with 550+HP/600TQ, Super built 4L60E 2500 stall with 3.73 gears in it now with 1/2 worn 33x12.50x15" C-rated tall tires (actual 32" tall now) They only weight 65lbs total with the weld wheels Ed Wright programing with no TC lockup in 3rd gear at WOT.

I will not be driving it everyday (once or twice a week) as I use to but I drive 30 miles to work and spend 80% on the freeway about 50/50 on the weekend. I don't tow anything and go off road once or twice a year otherwise it's on the pavement.

Will be installing my upgrade 14 bolt 9.5" in the rear, but will keep the stock 8.2" diff up front.

Options: (your vote?)

1. install the used 3.73 gears I have now into the 14 bolt to match the front gears...this would keep my rpms at about 2,000 at 70mph on the freeway.

2. Swap out both gear sets to 4.10 gears...10% more torque to the rear end and a reduction of 10% stress on the trans and driveline. Also what brand gears?...Richmond does not make any 14 SF FF gear sets!

3. Swap out both gear sets to 4.56 gears....22% more torque to the rear end and a reduction of 20% stress on the trans and driveline. I could also upgrade to 35" tires as I do have the room for them (3" body lift, 2" suspension lift) Disadvantage: More wheel spin, more strees on R&P/Axles, Less MPG...who cares!

4. None of the above?

I have Ed Wright programing to match the supercharger but I also have a Hypertech with SC module...Ed told me that I could use this to adjust the gears and shift points, but not to use it for reprograming the fuel or timing...BTW got it used on ebay for $84 I also know that the engine torque converter will have less stall with the 4.10/4.56 grears so I need to know before I upgrade this as well while the engine is still out as I can get to both the TC and front diff rear easy

What do you gears heads think?

Goal is to have a super fast lifted street truck that will run 12's without NOS Also wanted to be able to run slicks at the track (reason for bigger rear end) Now what about 4HI launches on the street?...I'm thinking the lower gears would also make everything hold up better as the truck would acell faster...now I need to worry about the axles as that is where the extra stress would be...hmmm?"

Ken

P.S. I also move the GP tranny deal over there as well...sorry about that John...guess I need to read the fine print sometimes

 

Also for you guys trying to figure out the difference in two gear sizes or tires...this is about the best one out there!

http://www.smokemup.com/auto_math/mph_range2.php

Ken

 

Transmission Ratios:
1st: 2.48 2nd: 1.48 3rd: 1 4th: 0.75

Tire Diameter 1: 31 inches
Rear Gear Ratio 1: 4.10:1
MPH
RPM 1st 2nd 3rd 4th 5th 6th
1000 9 15 22 29 0 0
1500 13 22 32 43 0 0
2000 17 29 43 58 0 0
2500 22 36 54 72 0 0
3000 26 44 65 86 0 0
3500 30 51 76 101 0 0
4000 35 58 86 115 0 0
4500 39 66 97 130 0 0
5000 44 73 108 144 0 0
5500 48 80 119 158 0 0
6000 52 88 130 173 0 0
6500 57 95 140 187 0 0
7000 61 102 151 202 0 0
7500 65 109 162 216 0 0
8000 70 117 173 230 0 0

Tire Diameter 2: 31 inches
Rear Gear Ratio 2: 4.56:1
MPH
RPM 1st 2nd 3rd 4th 5th 6th
1000 8 13 19 26 0 0
1500 12 20 29 39 0 0
2000 16 26 39 52 0 0
2500 20 33 49 65 0 0
3000 23 39 58 78 0 0
3500 27 46 68 91 0 0
4000 31 52 78 104 0 0
4500 35 59 87 116 0 0
5000 39 66 97 129 0 0
5500 43 72 107 142 0 0
6000 47 79 116 155 0 0
6500 51 85 126 168 0 0
7000 55 92 136 181 0 0
7500 59 98 146 194 0 0
8000 63 105 155 207 0 0

Ken

 

When you launch in 4HI it's locked in for the duration of the run as the applied power will not let it disconnect esp. on a automatic vehicle Would be cool if it could release after the first 60 feet Takes another 5% of the power to run 4HI! When I made my 14.10 run at Carlsbad I would of been in the high 13's with some slicks....but was afraid the 10 bolt would scatter

Very important that all four tires are close (1/32) to the same size or there will be binding...I've launched in 4HI over a hundred times on the street with no problems...just don't do it around a corner AWD would be another approach but not to sure the viscus coupler would hold up!

Ken

Ken

 

on my 1500 i was able to shift out of 4hi when at full throttle. i was starting to get really bad vibrations once i got over 100mph in the 1/4 while in 4wd so i just tried it one day and it sliped right out. i always put it in 4hi right after the run to give it pleanty of time to fully engauge and once i ran and was up to about 60mph i hit the 2hi button and it came right out, no more vibration.

 

I have a manual shift on the fly transfercase...and I always shifted it back to 2WD when I got past 30mph...so maybe the whine I hear is the front diff still engaged? Never got any bad vibrations but I was only getting up to 95mph in the 1/4 mile.

Also did some figuring...compared to the stock 3.73 gears and 4.56 gears I would have 1524 lbs more torque going to the rear wheels in first gear! Anyone know if they make chromemoly 4340 axles for the 14 bolt 9.5"? Parish8 another good reason to go to a FF 14 bolt in a new truck as the stock axles could handle this with no problems!

Ken

 

Ken - Is the 9.5" a FF? I thought only the 10.5" in the HD's was.

I would say to set a target rpm that you want to shift at and figure what MPH you think you might run at the track. Then figure your gear ratio out so that you are at peak or just a little above it by the 1320 mark.

PS - Thanks for understanding about me deleting that other thread.

John

 

someone asked a ?? RPM @ ?? MPH question....
with 4.10's and stock height tires (245/75's or 29.5's) I turn 3000@90 mph in OD.....4.56's and 31's would turn just about the same in OD

 

MY mileage on the street stayed the same and on the freeway i lost about 1 or 2 if im driving fast


Id go with the 4.56s if you have 33s because the 4.10s will belike going back to a stock size tire, If you get the 4.56, you will have an increase in overrall ratio, where as with the 4.10, it will be more like stock

 

I think we both need to go with option three

Last thing I am concerned about is how much weaker will the pinion gear be... 4.10 vs 4.56 as the 4.56 will have less total tooth contact as the pinion circomfrence will be less...I would not worry about this on a 14 bolt 10.5" R&P FF but not to sure on a 9.5" SF 14 bolt.

Ken