Only 6100 ft-lbs output-torque for short duration on a 9.75" rear??? That seems quite low to me. A stock 5.4 on a '09 make 395 ft-lbs on E-85. Now with the 4.17:1 1st gear in the 6-speed and a 3.73:1 rear, this makes 395*4.17*3.73 = 6144 ft-lbs (over spec). That doesn't even include the 2.5x torque converter multiplication on output torque when stomping the gas off the line (especially with a tune that removes the "drive-line shock management" from the computer). (The 5.4 has near peak torque at stall speed.) This results in ~15360 ft-lbs of torque on the axle - way over spec. With 4-low, it doesn't take much gas in first gear to greatly exceed this number as well. Now my tires break loose if I stomp it off the line (with a custom tune), but I am way over 6100 ft-lbs output before they spin. Thoughts?

 

your math eludes me.

tell me what my truck will be doing with the 4r70w,436hp/475tq (wheels) and 3.73 ratio in the sterling 10.5?

 

Yeah im confused. Does the torque converter multiply 2.5 on the 09s? I know the older 5.4's TC multiplied 1.9:1.

I know that up until now ive been considering a 6.8 swap with my 4.88's and 35's everyone has i've talked to (here and mechanic) has said the 9.75 would be the way to go..the 6.8 is 425lbft, idk what to multiply together but that seems like it would be too much for a 9.75 rear..with what you just said.

I wanna do a 5.4 swap. Stil using 4six converter. I mean im rough on my transmission and i expect it to give out before then even with hte 4six. ill just have to get my 4r70w built like klitch^. Anyway back on topic,5.4, that way i believe my 8.8 is plenty strong enuf for that. I heard thatifixed the main weak spot with the auburn locker. I don't kno exactly how to calculate that. 350 lbft on 99+ 5.4, and the gots intake and LT's during install. 370, 375lbft 4.88's 35's. I'll be alright with the 8.8 won't I? It isn't rly that weak of a rear from what i hear. I've heard of probs on very high hp cars..

 

2.5x torque converter multiplication was just an estimate. If it is 1.9x, it is still way more torque than the output rating for a 9.75" rear according to the post I referenced. As far as the math goes, it is just multiplying the torque by the gear ratio for each step of the way.

more details using 1.9x and let's say that the 5.4 only makes 300 ft-lbs at the stall speed (~2000 RPM) - it makes more though. Since some torque is lost in the drive-train, I will stick to this conservative number.

300 ft-lbs output from the engine with a 1.9x torque converter multiplier (when the vehicle is taking off from a stop) = 570 ft-lbs on the transmission-side of the torque converter. 570 ft-lbs * 4.17 (first gear ratio) = 2377 ft-lbs on the output side of the transmission. 2377 * 3.73 rear gear ratio = 8866 ft-lbs at the axle. This is way over the 6100 ft-lb number given above. My stock 32" tires will break loose around this point, but those running larger tires (e.g. 35") will most likely not. They will have the full 8866 ft-lbs of torque on their axles - much more for those that went with shorter gears. With the 6.2L engine available on the '09 raptor, it will easily exceed 10,000 ft-lbs. Something doesn't seem right here. Ford wouldn't release a vehicle where the rear can be subjected to way more torque than its rated maximum.

In 4-wheel-low, you multiple by the transfer case ratio. 8866 ft-lbs * 2.64 = 23,406 ft-lbs. Now, one doesn't normally tromp the gas in 4 wheel low, and the tires will break loose well before this axle torque is reached; otherwise, something would most likely break.

 

Ive been having similar problems with what sounds like my rear diff. every once in a while it'll make a nasty popping sound while going down the road. I usually stop and back up a little ways and take off again and will stop.. any ideas?

 

With your math and my dyno number I'd be only 9560 to the rear. if torque converter multiplier is 1.9

So Opt A: 475 x 1.9 = 902, first is 2.84 so = 2563, multiplied by 3.73 ratio is the 9560 I mentioned before


if I use a speculated 2.2 converter multplication factor as some sources say the converter is
Opt B: is 11069

I dont understand how I blew apart a 8.8 so many times if I'm under the continuous duty. Even with those numbers, my 10.5 is under par, which is total BS because the 7.3s were 500tq stock.

 

start simple, check u-joints.

 

Those axle capacity numbers are direct from the manufacturer. Remember they have a safety factor built into them. Those specs used to be easily available online at the Visteon site but are now gone because they don't operate the Sterling axle plant any more (Ford took it back over). I don't have a current chart from Ford, but I have seen the current 10.5 specs (from Ford) and they match my Visteon chart from '03.

Anyway, you are forgetting one thing... traction torque. Tires, ground conditions and engine torque almost never combine to give you that much traction torque. In other words, the tires break loose long before the something in the drivetrain does. You'd be very surprised at how little torque tires can support in most conditions.

You can get a rough approximation of traction torque (slip torque) using the following formula:

weight on axle x coefficient of friction x rolling radius/12= slip torque (lbs-ft)

My own F150 HD with perfect traction for example:

2433 x 1.0 x 15.65/12= 3173.03 lbs ft

With typical traction

2433 x 0.7 x 15.65/12= 2221.12 lbs-ft

COF is highly variable and a combo of tires and ground condition. With the best and most sticky street tires combined with the best pavement, you might reach 0.8 or 0.9. Most times, you will be hard pressed to see 0.6 or 0.7. Those are also researched numbers. With racing tires and on a dragstrip, you can exceed "perfect" traction of 1.0.

Also, the driveline torque (output torque) you guys are using are missing an efficiency factor. You guys are showing the theoretical output. Friction losses, realworld engine performance, etc. reduce the actual figure. Commonly, 85% (0.85) is used but if you have very slippery oil in the drivetrain and a fresh engine, you can use 0.90. Also, engineers don't commonly use converter ratio, which changes constantly and by the second. The Dana engineer I queried called it "soft" torque. At the time I'm not sure I understood all the rest of the stuff he told me, so I won't try to relate it.

 

Jim Allen,

Good points.

Looking at it from a raw acceleration point-of-view, the numbers look more reasonable.

My truck can accelerate at about ~0.6 G (0-20 in about 1.5 seconds) when taking off. Since my truck weighs just over 6200 lbs with me in it, the forward force is 6200 lbs * 0.6 G = 3720 lbs (simplifying by assuming a constant force from 0-20). My tires are 32" tall, so the moment-arm is 16" long. The torque on my axles is 3720 lbs * 16/12' = 4960 ft-lbs. That is with the 3.55 rear. if I had the 3.73, it should be about 5211 ft-lbs - still withing spec. When trying to take off faster (which I can now that I have a custom tune), my tires do indeed break loose. I still think there may be an issue with the many people that have put taller tires on with shorter gears. If one has 4.88 gears with tall tires, they can hit 6800 ft-lbs - if their tires don't spin. Your point that there is a safety margin built-in should still cover this.

 

Well, I'm so sorry to hear about your gears. Hate that for ya!!
I am about to do the gears in my 06 screw I'm going to 4.56-- 8.8 front and 9.75 rear. I'm running a 35in tire on my 3.73's right now, yuck. And I'm about to get my 38's but I don't think that I really want to go to 4.88's. Any pointers to do this the right way? Best type for the money and where to get them and the kit to put them on??

 

I think here in the next week or so im purchasing traction bars, it kills me i can't get a good launch.. So with traction bars, less wheelspin(traction torque i guess) it'll translate to more torque thru the rearend im sure my improved 8.8 will handle it, when i do a 5.4 swap alot more torque, traction bars, 35's, 4.88's. Will I be risking a break again if i don't step up to a stronger axle(9.75)? Should i still go ahead and plan to swap axles?(As a must)

 

where are you gettting the bars from?

 

I haven't even rly looked into them yet lol... Maybe skyjacker or rcd..

 

i was thinking about buying some from broncobeater on lrodder. although he isnt sure if they will fit a 4x4, but i dont see why not.

http://www.lightningrodder.com/forum...ad.php?t=56440

 

Yea you'll need them forsure! Idk I've never looked at the leaves in a lightning.. Unless the width is different idk why they wouldn't eork either..