Rick that's fine... It is what it is. But if you ever get board... try the math out. Math has only ONE right answer...

No not just the shape... the shear SIZE and weight as well. I honestly feel you underestimate SHAPE/WEIGHT/GEARING/OVERDRIVES/TIRE HEIGHT!

You cant tell me that weight nor shape/size has no room in the equation? So by your advice... its just RPMs alone and nothing else is all you need to take into consideration when choosing a gear ratio?

So if your theory of gear ratios is true, a Corvette with 3.55 gears used with a .67 overdrive ratio that allows it to get 25MPG@60MPH should yield the same MPG in a 7,000lb Tow Truck with 3.55 gears used with a .67 overdrive ratio at the same speed... As long as the RPMs are the same?

Sure I used the extremes of both ends but its your theory... And FYI you would be lucky to get 8MPG@60MPH in that Tow truck with the same drive train... and ratios. .

Rick, I have a specific question for you...

Would you consider a 3.05 gear ratio with a turbo 400 transmission to be too steep of a gear ratio for a truck or even a car?

Or would you consider the 3.05 gear ratio a GRANNY gear? For most it would be considered a GRANNY GEAR by most people's standards...

I'm just wondering if you would consider it as such.

"AIR BLADE" ???

SPEED SAFE, AIR RAM

 

aaahahahahahaaaa I was thinking for just the rear diff. I totally forgot about the front diff! I'm so used to modding sports cars. I have never done a swap on a truck so I always think rear diff only. Well, for that matter $1500 is exactly the right number as I was half of that!....whooooops

Hey
atleast
I don't
post my threads
in this annoying
nature.
Actually
it's not only annoying,
but rather very irritating for
the need to keep on tapping the enter bar to bring the column down. WHY?????

 

Rick, the reason I asked you that specific question was because the 2003-2007 545RFE transmissions have a .75/.67 overdrive. This effectively changes the final gear ratios... Our trucks today have TALLER tires and steeper overdrives then ever before which lower the effective overall gear ratio even further. My point is the gearing is MATHEMATICALLY WRONG from the factory.

But when you take into consideration the overdrive ratios... they effectively give us a NEW Ratio other then what you physically have in the rear end. In other words, the OVERALL GEAR RATIO would be your rear gear ratio if you had a 1:1 none overdrive transmission such as the Turbo 400/350..

When in 3rd gear overdrive, our effective overall gear ratio becomes another gear entirely.

3.55 x .67 = 2.37 OVER ALL GEAR RATIO
3.92 x .67 = 2.62 OVER ALL GEAR RATIO
4.10 x .67 = 2.74 OVER ALL GEAR RATIO
4.56 x .67 = 3.05 OVER ALL GEAR RATIO

Again simple math shows us that we are clearly OVER DRIVEN from the factory...

Next time your going 35MPH shift into 6th gear and tell me how great your fuel economey is... But fight the urge to downshift to gain more POWER and better fuel economey... Hang out in a super low RPM and lug your engine down real good... this way you can experience what your truck is going through.

This is a good debate. If you feel I have offended you please don't take any of my comments offensive... I just want to help people understand the facts by sharing my experience and giving them the math to chose the most effective rear gear.

Again... do the math....

__________________________________________________ __________________
1) Find your (OGR) Overall Gear Ratio:
TRANS GEAR x REAR GEAR
__________________________________________________ __________________
2) Find your RPM's @ any speed:
SPEED x OGR x 336 / TIRE HEIGHT = RPM
__________________________________________________ __________________
Remember RPMs alone do NOT dictate fuel economey, its the load on the engine at any given RPM that has more to do with fuel economey then RPMs alone. This is why a smaller car can get better fuel economey with less RPM... they inherently have less load on the engine...

Keep in mind for the best OVERALL PERFORMANCE aim for 2100RPM's@60MPH this goes for both the 4.7L & 5.7L as both seem to get their best fuel economey in the 2,000 RPM ball park.


SPEED SAFE, AIR RAM

 

LOL ... I think he types on a "WORD" spread sheet or something for the spell check and then cuts and past it to the forum... perhaps this is why it comes out like it does... I never cared for it either... but he has been posting like that for many many YEARS... I would hate to think its intentional.

SPEED SAFE, AIR RAM

 

Sorry AIR RAM, my mind was somewhere else. Weight and aerodynamics have everything to do with it. Car companies work very hard to get low CDs to help their overall mileage. My Corvette with another 1,000 lbs. in it would get worse mileage. The engine would have to put out more energy to get to speed and to go up any inclines. Also if I increased the coefficient of drag on the Corvette by 50% the mileage would obviously suffer.

As you know energy equals mass times velocity. So to maintain a given velocity it takes (x) amount of energy. The shape, weight and mechanical efficiency of said vehicle are the variables. My point being it takes slightly more energy due to less mechanical efficiency (piston drag, higher gear speeds etc.). Also because more air has to be moved through the engine at higher RPMs more fuel has to be used to maintain the proper air fuel mixture hence slightly lower mileage.

I heartily endorse 4:56s for all. I do think it would help around town MPG in stop and go situations given the mechanical advantage to get such a behemoth underway.

Re: "Would you consider a 3.05 gear ratio with a turbo 400 transmission to be too steep of a gear ratio for a truck or even a car?"... GM is putting 2:50 somethings in the new 6 speed auto C6 Corvettes so I have no idea what is considered a granny gear anymore. A common performance upgrade on the C5 auto's is putting 3:42s in place of the 2:73s that came stock in them.

I love higher gears to me it makes a car or truck a lot more fun to drive. If you don't suffer any major economic penalty from them then more power to ya. (pun intended)

See ya AIR RAM

Rick

 

Sorry to wind you up even more Air_Ram but...............Jaguars over here and several other car manufacturers who you probably haven't heard of, did have overdrives in their gearboxs in the 70's..............60's ..................and for that matter 50's over here in the UK LOL wink wink.
Al.

 

There is a SAE paper from U,K. authors where they fitted two overdrives in series and drove the vehicles in many different conditions to find the best MPH/rpm ratios for fuel economy in 'real world' conditions

 

To those interested in the subject
after reading about the use
in post #8 above
of 3.08 and 3.15 differentials
in the GM and Ford pickups
go to the opposite extreme (and opposite side of the Earth)
and find out what
diff ratios (very high) and overdrive gear ratios (very low)
were selected by
Japanese engineers for use in the
Toyota Tundra 5.7 and the Honda Ridgeline

It is also worth reading about
the German/American effort
between BorgWarner and VW
that resulted in the shaft-within-a-shaft
automated manual transmission

If you want both best possible acceleration
and best possible fuel economy
with a 'conventional engine'
at least 6 speed transmissions are needed
and 8 speeds can still give a bit of gain

Engines with variable valve timing and lift
plus specially coated bores & low tension rings
can perhaps get by
with less number of gears

 

Perhaps "some people' should look in the mirror

If you want to do that $30,000 bet
between you and me
on a Math test
I would be willing to change the bet
so that you put up $30,000
and I put up $90,000

What is the opposite of ASSUMING ?

Testing !

Especially testing when we use the knowledge
from our fathers and grandfathers
to do the
BEST POSSIBLE TEST IN THE LEAST TIME FOR THE LEAST MONEY.

If you are reading this
and speak English
as your 'mother language'
you should be especially proud
that English speaking people
have led the world
in creating good testing methods

 

Hank I would take up on your offer in a heart beat! You clearly have NO CLUE on the subject and can only look back to the old school train of thought and use the answers they derived with yesterdays math... Back when overdrives did not exist. I challenge you to do some math TODAY to support your ideas... ON YOUR OWN... try it, its fun!

Im glad you did agree that with your cut & past quote "the best MPH/rpm ratios for fuel economy in 'real world' conditions" which only backs up every point I have been making. And you where too blind to even see that... In one sentence, it sums up all my post ever made on the subject!

That statement alone supports that you can NOT chose the gear ratio based on RPMS ALONE... which cleary you feel is the all that matters in choosing a gear ratio.

The difference between you and me is experience. You have none and I have a great deal more... Not only that... but my experience is CURRENT and not DATED as yours is if you have any at all.

Hank, there nothing wrong with getting old... you just need to know when to step aside when you don't understand and when to put the guns down when you clearly are out gunned!

SPEED SAFE, AIR RAM