c'mon wrondayJ, you gotta tell us what your doin to your truck! The suspense is killing me!!

oh by the way, for those who are interested and don't think I'm a liar...My gas mileage before the 4.10s was about 15-17mpg. I just filled up at Texaco with 437.5 miles on the tripometer. I put 26.854 gallons of 93 in, so that comes to .....

16.291800104267520667312132270798 mpg

Not bad for having 4.10s and, I didn't take it easy on the truck(getting stuck at red lights is more fun now)

 

xlt sport did u recalibrate ur speedo after ur gear change ? u might be registering more miles than ur actually putting on ur truck , and giving u a false mpg

 

That's a good point...No I haven't. I know my speedometer is off but I didn't now that it affected my odometer as well. Are you sure that it affects the odometer?

 

POSITIVE!!!

Your adding milage that your not puttin on your truck

 

I mpg is roughly 14.010948089670067773888433752886. This is just an estimate I arrived at with the help of Talley.

I knew it was too good to be true....

 

Man, I'd love to spill the beans right here and now, but I test and tune alot and sometimes things might seem great at first, then after a couple hundred miles they aren't so rosey, or the effect isn't worth the effort. Plus, there are more than a few members out there that simply love testing my credibility. So before I spout off about the gains and benefits of any modification that I produce or endorse. . .I make sure I test the living daylights out of it and have some form of physical proof ready to help back-up my words.

But this next round of mods is nearly complete so it won't be long before I break out with the goods. Us automatic boys are gonna even the perverbial scales a bit. And I promise, there won't be any 'suprises' to encounter when performing the mods.

I can squeek out a little bit of info though. . .I can torque up right now and hold the RPM's at 2500, then drop the brake and flat boogie off the line. And the second gear chirp NEVER leaves a dry eye in the house. And get this. . .Total cost so far for ALL the mods I've got into this automatic- less than $300. (You don't have to change the converter unless you go over 2750 stall) The last piece to the puzzle is the traction control device. I am fond of slapper style bars, and need to test some sets to see if they perform on these trucks as they claim. I like Jay Lincolns Truck Traks, and Lakewood now has bars for our trucks. I don't like spinning my tires at all- even for fun. You gotta hook and book. . .or else sit back and read your opponents bumpersticker. So lemmie test some bars and then I'll give ya'll the skinny on how to shock the hell out of a 5-speed.

 

Alright...looking forward to it J

 

oh god!!! im really getting ancey now!!!!!!

Keep us posted

 

WrongdayJ:

Push of button ends all! hehe.

btw, I am going with JDM Traction bars. I have personally drove a "L" with cal-tracs and then with the JDM bars and ther is a BIG difference!

Pricey but well worth it. The JDM is the bars for me. Which is my next mod!!! Just gotta save for two weeks

 

I read that some of you recommended upgrading to 4.10's to help improve the "60-90 mph" acceleration. I was under the impression that 4.10 will make you quicker of the line, but not once you're at highway speed. The 3.08's however from what I understand will help more with a 60-90, but be a dog off the line.


When I had my '88 F-150 5.0, it had 3.55's, and my good buddy had an almost identical truck with 3.08's. I could smash him of the line every time, but cruising down the interstate, if he wanted around me, I couldn't stop him.

 

Hi, just thought I'd thow my 2 cents in as I understand it. Gears allow you to multiply the torque to the rear wheels. So with 4.10 versus 3.55, you're going to increase the you torque multiplication by like 15%. That 15% is at all RPMS, from 1RPM to redline. You notice great gains from 0-60 because you get into the powerband of the motor faster, and the increase in torque really helps to get a heavy truck moving.

At speed you still have the increase in torque, so the gears don't hurt in that regard. But what does make a difference when you're trying to compare 60-90 acceleration times is where the gear change put you RPM-wise at those speeds. For normal everyday stomping the accelerator around 60ish and running it up to around 90-ish, I think the 4.10s will be better because I'm betting at much over 60 even with 3.55s the auto transmission is only going to kick down to 3rd and I know with 4.10s it will only kick down to 3rd. In 3rd gear with 3.55s a 60-90 run will be between 2300-3500 RPMS. While a 3rd gear with 4.10s runs will be between 2700-4100 RPMS. The 4.10 are in a better powerband in 3rd gear and you have that 15% torque multiplication also.

Now on the other side of the coin if you were to pull it down into 2nd gear at 60 you can almost make the run up to 90 entirely in 2nd gear with 3.55s(90 works out to just over 5500RPM). In 2nd, you gain the multiplication of the 1.55:1 second gear. With 4.10s if you pull it down to 2nd you'll quickly be shifting to 3rd, you lose the 2nd gear advantage, but you still have your 15% advantage in 3rd.

So the moral of the story is dang this can get complicated quick. I personally say get gears, gears, and more gears. I'm running 4.30s with 31.5" tall tires(pretty much equals 4.10s and 30" tires) and can't wait for these tires to wear out so that I can get some shorter ones. But that brings in rotational mass which is best left for another day...

 

Okay,

Gears are not about torque this and hosepower that the engine is the only place were torque and horspower are prodused. Gears are for the sole purpous of letting the engine spin within its powerband while at a given speed. it really doesn't have anything to do with torque multiplication. The gears in the rear end are designed to work together with the gears in the tranny, and the size tire on the vehichle to offer a desired performance out of a given engine at a desired speed.

Drag racers use a lower rear end (numerically higher) so that the engine is in the powerband right off the line(and the engines are built to have a much broader powerband). But, if you gear to low, you'll put the engine at too high of an RMP and end up on the other side of the powerband. (which is why some race in the 1/8th mile circut instead of the 1/4 mile)

The powerband has a curved shape, it goes up to a point, then comes back down. so lets take the case of the 3.55 vs. the 4.10 on an otherwise identical truck. The 4.10s will blow the 3.55 off the line every time (pending a traction aid device), but remember, the 4.2's peak power output comes right around 4000 RMP. the 4.10's will max out the powerband just about the time the 3.55s are just getting into the heart of it. thus, the truck with the 4.10's cannot accelerate, while the 3.55 passes by.

this is why police cars use high geared rears, with a built up engine that produces more low end torque. You can always beat a police car off the line, but you'll never out run one.

so, the answer to the original question is yes, gears. the question that remains is what size gears? if your just out looking to race from the line, go with 4.10s. heck go with 4.30s if you don't care about gas, or top end speed, or if you want bigger tires (if your racing, I doubt that you would). If you want to race from a roll, then 3.73s would be great, they'd also allow for better towing and hauling. If you want all around drivabillity, and don't tow heavy loads often, and accept that a V6 F-150 is not an L, then let the other guy pass you and keep the 3.55s. 3.08s are for highway crusers, and higher gas mileage. The 4.2 doesn't have the power needed to take 3.08s to high speeds like the police interceptor does.

 

gears are a tricky thing...one minute you say ..yeah I get it, and the next minute your not so sure....That's me anyway.

All I know is that I can't go back to the 3.55s on this automatic.

 

Gears _are_ about torque multiplication. That is the entire point of gears. We all know that HP = (T*RPM)/5252, so take a theoritical torque of 300 ft lbs at 3500 rpm.

HP = 300 * 3500 / 5252 = 199.8 HP @ 3500 RPM

Remember that number we'll use it later to check a calculation...

Now my hypothosis is that your rear gears multiply the torque from the motor to the wheels. We'll leave out the actual diameter of the tires since they only act to change the final ratio and can be considered a constant that can be ignored. So these figures are actually the torque your rear axle is seeing. I say that in a 1:1 3rd gear on the transmission, a 3.55 gear ration will multiply torque 3.55 times and a 4.10 ratio wil multiply torque 4.1 times. So I say in the first example the rear axle sees 1065 ft lbs of torque(300*3.55) and that the second example sees 1230 ft lbs(300*4.1).


As a proof we must figure the RPM of the rear axle and use that with the known 199.8 HP @ 3500 RPM to calculate the torque. Now for a truck with 3.55 gears you factor in the gear reduction of 3.55:1 at that 3500 rpm. 3500/3.55 = 985.9 RPMs. That is the speed the rear axle is turning. 4.10s give your 3500/4.10= 853.6 RPMs. So plugging that into our equation that I'll now solve for T.

T= (HP*5252)/RPM

T=(199.8 * 5252)/985.9 = 1064.3 ft lbs.
T=(199.8 * 5252)/853.6 = 1229.3 ft lbs.

Pretty much what we hypothosised they would be. I had problems wrapping my head around this concept of gears multiplying torque but not affecting horsepower until I sat down and worked this all out and it finally clicked for me. It's all just math, the gears slow down the RPMs of the axle(wheels), yet your HP and torque from the motor stay the same thus the torque on the axle must increase. So it's quite a bit more than simply getting you and keeping you in your vehicle's powerband(although that is a great deal of it also). The whole concept follows basic laws of physics that can't be ignored...

 

Now as for top speed and fuel economy. On most of our trucks top speed is a mute point. Drag is going to be the limiting factor before gear ratio in most cases. 4.30s with 30" tires will reach 140 @4700 RPMs. I'm not going to have the kind of power to reach that anytime soon.

As for mileage, you will sacrifice a some on the highway, but it's not as bad as everyone makes it out to be. I went from 3.55s to 4.30s with a 31.5" tire. Before the swap I would get a low of around 14 mixed hwy/city with alot of WOT bursts. Normally averaged around 15-16 mixed driving. All hwy I could get 20 driving fairly decent. After gears mixed driving stayed around the same actually closer to 16 most of the time. All hwy(actually interstate usually around 73mph) I recently averaged 18 mpg. Driving normal highways at 55 it creeps closer to 19. This is with a 4.6, but I can't see how the 4.2 with a little less torque that likes to rev would be much different. That's why I'm a big proponent of gears. Overdrive transmissions are wonderful inventions, might as well take advantage of them...

While I'm thinking about it I want to expound on the "race" a couple posts up between 3.55s and 4.10s. Yes the 4.10s will beat the 3.55s off the line every time. Yes the 4.10s runs out of breath as the 3.55s come into it's power. But no the 3.55s don't pass the 4.10s up at this point because the 4.10's shift into second gear. Yes the 3.55s will pull a little during and right after the shift, but now the 4.10s are in the powerband again and pulling hard while the 3.55s have to shift and lose any ground they made up. This process will continue with the 4.10s pulling for the remainder of 2nd, losng a little on the shift to 3rd, etc, etc until drag eventually stops the acceleration of both of them. Which by the way will stop the acceleration of the 3.55 geared truck slightly before it stops the acceleration of the 4.10 geared truck because the 4.10 geared truck puts more torque to the rear wheels.