Anyone want me to graph out their "sweet spot"?
 

Here's some examples:

http://i130.photobucket.com/albums/p...13speed355.jpg

http://i130.photobucket.com/albums/p...13speed373.jpg

http://i130.photobucket.com/albums/p.../direct279.jpg

http://i130.photobucket.com/albums/p.../direct264.jpg

I just used microsoft works spreadsheet, and created a graph out of the calculated values.

It takes me a matter of seconds to change two numbers, and it recalculates the whole graph.

What I need:

Differential gear ratio
Transmission final gear ratio, OR make and model #, I *NEED* the model number, as some transmissions have several different ratios(for example, eaton 10 speeds).

So as you can see from the graph, it's pretty easy to visualize where your sweet spot is, and to see how much of a difference a tire change would make.

I just realized I put the RPM and MPH labels in the wrong spots, we must have some damn FAST trucks!

It would be real interesting to see MPG graphed in as well. Might help keep a light foot :)

If engine manufacturers released a BSFC chart, I could.

Trans# FRO16210C
Rear Diff= 4.11
Tires= 22.5 not lopro
C12
I looked up trans once before and I think, if I read the
chart right the 10th gear was .73
My trach reads 1650 rpm's @ 65 mph
When you say sweet spot do you mean the best engine speed
to get the best mpg?? 8) 8)

http://i130.photobucket.com/albums/p...10speed411.jpg

Wow, that thing is really geared aggressive.

My dad's truck has 4.10s, but he runs tall 24.5's.

I don't know what cat recommends for your c12, what year is it, and is it multi-torque?

Cat recommends 1400 rpms at 65 mph for their c13, multitorque 1325 rpms at 65 mph, both with a max speed of 1500 at 65 mph.

I'd say to get good fuel mileage out of that thing, you shouldn't run a hair over 60!

Do you want me to expand the graph up?

Wish I knew my final drive. When my super 10 died for the 3rd time, I dug an old 9 speed out of the sand out back, turned the gears around in it and put it in. I have 3.58 rears and turn 1650 at 70mph with 24.5 low pro's.

Thanks Allen it looks pretty close, today I kept my foot out of it and held
it down to about 57 to 60 and your graph shows about what my tach was
reading. Yes you can expand it if it's not to much trouble. Diesel is $3.13 here and I been averaging about 5.3 to 5.8 but thats with a lot of stop and go and me running 65mph. My c12 is 2002 model truck I think it is mulity torque, but have never seen the boost gauge go above 22.5 psi. and it will only develope that much boost till it hits about 1400 to 1500 rpm's & up.

Can you get me a model # off the tranny? Or at least a make?

Are you sure 70 mph at 1650 is right? How accurate is your speedo?

Allan, can you explain why there's three lines. I don't understand that part.

If I ever get mine out of the shop I'll post my numbers. Maybe I'll stop by there today and grab the trans number.

The three lines show how a tire change would affect your RPMs.

22.5 Lo pros top line

11r22.5 and 24.5 lo pro middle line(both are same height)

11r24.5 bottom line.

Thanks Allan, I understand now. I'll post my numbers as soon as I can.

Could you run the graph for me Allan?

Cat C-15 475 motor
390 gear ratio
RTLO-18913A Eaton Fuller Trans 13 Speed

Thanks!

Allan, not to change the subject, but what do you think of these two things advertised to boost mpg? www.getliberator.com and http://specialtiesmg.com/jetstar.php

Straight through muffler yes, regardless of make.

Hydrogen injection? I haven't seen ANY evidence to prove it.

Hydrogen does make power, but the draw on your alternator will be greater then the energy you get from the hydrogen.

Didn't know Allan if you saw this or not?

yeah since I want to change fron 24.5lp to 24.5 tall rubber this would be great

C15-550 hp
3.36's rears
RTLO-18913A Eaton Fuller Trans 13 Speed

Yeah I did see it papa rick.

I'll do it after supper, it's more efficient to do 4-5 at once.

Ok, thanks Allan, Appreciate it!

Allen,
425 Cat 3406B
3.90 rears
18 sp. RTL0 14918b
24.5 tall

Thanks. :D

Alright that was one hell of a long supper! 2700 miles later(in 4 days).

I'm doing the graphs right now. I promise.

Mr. Sodbusters expanded graph:

http://i130.photobucket.com/albums/p...11expanded.jpg

Rosty and Papa rick(both have same specs):

http://i130.photobucket.com/albums/p...and18speed.jpg

Mr. Mike's "I don't know what tire to run" graph:

http://i130.photobucket.com/albums/p...33613speed.jpg

enjoy!

Also, how fast do you guys run, and what tires do you have?

Thanks Allen

Well I think that pretty much wraps up that decision.....thanks

So you're going with the taller rubber?

Do you travel at 68-70 a lot?

usually atleast 65 no more than 70-72

Well 65 is absolutely a perfect speed right now, but yeah if you want faster you should go with taller rubber.

If it were me, I'd just stay with that rubber, and run 64-65.

No tags off the tranny, been gone for years. Dug it out of the sand when the super 10 died. Pulled the bearings out and had Napa cross the numbers to rebuild it.

1650 at 70mph according to the gps and the tach.

Yeah I'm still trying to figure out what you have, do you at least have a make?

Unfortunately eaton 9 speeds have very many different final gears:

.73
.74
.76
.80
.83
1

Yeah, I think its an Eaton Fuller. I re-checked my rpm's last night and my post is correct. at 60 mph, I turn 1475 and at 94 mph she's screaming out 2350.

Damn slow truck.

Good news, slowed down to 55 mph mpg went from 5.5 mpg to 7.2 mpg :D
and the engine noise is quite now, after a while it does not seem your driving that slow. But here in Texas driving 55 makes alot of 4 wheelers mad. Those 4.11 gears and 22.5 tires suck out on the hwy. But need the gear when hauling sod, it is so heavy :cry: :cry: just filled up to check mpg and diesel was $3.359, there changing the everyday now. :cry: :cry:

I'll do a graph on friday when I get back.

I think it might be worth it for you to either swap that tranny, or maybe swap gears.

Unless you want to stick to 60.

I have a 13 speed, big bearing w/oil pump. It was rebuilt 2 years ago and never put in. I'm told it's a double-over - the high gear is against the dash. My 9 is the same way, but not double over??? Maybe that would make a difference? I've got 6 years on my clutch and thinking about replacing both pretty quick.

Allen, would you mind doing another graph for me using a smaller gear?
Here is the old specs
425 Cat 3406B
3.90 rears
18 sp. RTL0 14918b
24.5 tall

I'm wondering what the graph would look like with a 3.55 or perhaps something smaller like a 3.36? I was doing some research on this engine and I'm curious to see how much of a difference it would make.

My bad....I thought he was talking about something "kinky".... :shock: 8)

http://i130.photobucket.com/albums/p...13speed355.jpg

http://i130.photobucket.com/albums/p...33613speed.jpg

Both are the same for your application.

Thank you much Allen. :)

Wow, from that graph you can do 1,550mph at only 70rpm.