6BT, CUCV Axled M715 Build

[Mikel]

This part I get. This is general rule type stuff... Changing final drive ratio whether done by changing ring and pinion, changing tire size, adding OD, or a combo of all of the above will always effect engine RPM. This part is clear as a bell...



This is the where I get confused. Let's apply this to three different vehicles, all with the same driveline from trans to tires. If we assume 4.56 gear ratio, a .73 overdrive final drive trans, and 38" tires, one truck has a 4BT, one with a 6BT, and one with a 6.5 detroit. Wouldn't all 3 engines have different RPM at the 65MPH? Since the calculator uses a small block Chev gasser as it's base example, if I'm I'm correct, what math do we use in conjunction with that calculator to account for the differenmce in engines? If I'm not correct, maybe some more experts can chime in to explain it to my dumb ass, because I'm

Engine RPM's are determined by speed, tire size and gear ratios. Nothing else. You can put a Yugo engine, or a Cadillac V16 in your M715, that it will turn at the same RPMs if those variables are kept the same

You will want to optimize gearing to run the engine at the RPM range that it is most efficient in.

[brute4c]

Gas engine and diesel engines rpm range is vastly different one to the other.
Gas engines do vary some...like say a 230 that has trouble doing 5000 rpms and a properly built 289 with its short stroke and lots of oil flow work turning 9000 or better.
Diesels too...some big diesels stop under 2000 rpms while others go to over 4000.

Just trying to find a reason they chose that particular engine...


As Mikel said...if you keep all the other variables the same after the motor, then the motor will have to turn X number of rpms to get to a given speed...the question then is, will the selected engine achieve that RPM for long periods safely.

[Barrman]

We got the front end spring perches tached on Friday. We also put the cab on the frame. Or rather, the cab is sitting on the frame. Students are working on it as I type, so I can't take a picture. The front axle is off again so we can weld all the perches up real good and paint everything again.

I have only been around 1 or 2 spring over trucks in the past and forgot how tall they are. The top of the door is right at my eye level. That is with 32" tall tires. This thing is going to be a tall truck when it is done.

[ryanroo]

We got the front end spring perches tached on Friday. We also put the cab on the frame. Or rather, the cab is sitting on the frame. Students are working on it as I type, so I can't take a picture. The front axle is off again so we can weld all the perches up real good and paint everything again.

I have only been around 1 or 2 spring over trucks in the past and forgot how tall they are. The top of the door is right at my eye level. That is with 32" tall tires. This thing is going to be a tall truck when it is done.

that is tall. but with big tires it will be cool.

mine is spring over and i would say its only an inch or two taller than a stock truck if that. it is on a 31ish inch tire right now.

Ryan

[randyscycle]

I was figuring on doing a springover on the stock axles and 38's. I didn't think it would put the door up that high. I better get my tape measure out and recheck before I do it!

[Hammer]

I have only been around 1 or 2 spring over trucks in the past and forgot how tall they are. The top of the door is right at my eye level. That is with 32" tall tires. This thing is going to be a tall truck when it is done.

How tall are you?
I am 6'1", and when I had 44" tires on my M715 with SOA, the door handle was pretty much shoulder height to me. I would stick my hand straight out and grab the handle.

[Hammer]

I was figuring on doing a springover on the stock axles and 38's. I didn't think it would put the door up that high. I better get my tape measure out and recheck before I do it!

Why SOA for only 38" tires? Most of them fit ok stock.

[brute4c]

39.5's look like stock tires on a spring over truck...roughly...

[Barrman]

I will measure it once we get the axle back on and sitting on the tires again.

[Barrman]

The top of the door is 60". The tires are 32" tall. Here is how the truck looked yesterday afternoon:
[IMG][/IMG]

We had a change of engines over the last week. Sermis got ahold of a 1997 6BT that has an SAE #3 bell with an Allison auto. The Allison is not an OD. However, he had a 3053A OD from a M35 that will bolt right up. The '97 also has bell housing motor mounts. Here is the '97 with the 5 speed bolted to it:
[IMG][/IMG]

Notice the very wide bellhousing with with the mounts? Here is how far it would go on the truck:
[IMG][/IMG]

[IMG][/IMG]

A 6-8" body lift would be needed to clear everything. Or, the throttle pedal could be move about a foot toward the drivers seat.

My students just pulled it back out, verified that the Getrag really is an OD 5 speed. It is, seems really deep too like around .68 or so by twisting the shafts and counting the turns and are now putting the 1992 6bt in the truck. Pictures will follow.