Anyone with a C20 running 700r4 with stock rear end?
 

Curious if anyone with a C20 has a 700r4 installed and still has there stock rear end? If you are which gears does your rear have. What are your rpm's at 65 mph?

Thanks, Matt

Re: Anyone with a C20 running 700r4 with stock rear end?
 

what year? The 60-62 have different rear ends than the 63-66 IIRC

Re: Anyone with a C20 running 700r4 with stock rear end?
 

Sorry, I have a 1965.

Re: Anyone with a C20 running 700r4 with stock rear end?
 

send me the following information:

1. your email address

2. current transmission

3. engine information

4. height of rear tire from ground to top of tire in inches.

5. rear axle ratio

I will send you back a custom spreadsheet that will show you how your truck will perform with a 700r4.......Kieth

my email kieth.ruleco@hotmail.com

send this info in a private message or to my email. :gmc2:

Re: Anyone with a C20 running 700r4 with stock rear end?
 

I have a direct-drive (1:1) SM420 and 32" 235/85r16 tires with 4.10 gears in my C-30 I drive daily. 65MPH is about 2,900RPM for me.

With a .70:1 OD, even with shorter 245/75r16 tires and 4.57 gears, 65MPH would only be 2,400RPM. Hard to believe anyone could be scared of running a 327 2,400RPM going down the highway.

Here's a link to the website I use. Just plug in axle ratio, tire revs per mile/tire size and your trans gearing, and it makes a list of all the speeds in 100RPM increments from 500 to redline. It also shows speeds in all the gears, which is kinda nice.

http://f-body.org/gears/

Re: Anyone with a C20 running 700r4 with stock rear end?
 

Thank you Email sent.






Thanks for the link. I currently have a 327/TH400/4.57 I have not installed the 700r4 yet. I'm just trying to plan my next move. If I need to start looking for a different rear-end to swap in or not. I tend to over think everything especially this time of year in Michigan with no garage to work in and being 9 degrees outside. I just sit inside and think.:lol:

Re: Anyone with a C20 running 700r4 with stock rear end?
 

This is a test, torque to ground, speed, different engines and transmissions, 1st chart 24" tire diameter:

Attachment 1223743


WONDER WHAT HAPPED TO THE QUALITY, I COPIED A FILE FROM A EXCELL SPREADSHEET INTO PAINT, SAVED IT AS A JPEG WONDER WHY IT IS BLURRY ? GUESS I WILL TRY TO SAVE IT AS A BMP AND SEE HOW THAT WORKS.....

Re: Anyone with a C20 running 700r4 with stock rear end?
 

THAT IS A GOOD WEBSITE BUT IT LEAVES TORQUE OUT OF THE EQUATION, YOU COULD GET A GREAT SPEED LINE AND THE TRUCK MIGHT NOT HAVE ENOUGH POWER TO GET OUT OF ITS OWN WAY. I WILL RUN A SPREADSHEET FOR YOUR TRUCK THAT WILL LET YOU COMPARE WHAT YOU HAVE NOW ALONGSIDE WHAT YOU WANT TO CHANGE TO.........AND YOU CAN ALSO LOOK AT HOW MUCH POWER THE TRUCK WILL HAVE (TORQUE) I USE 460 ft/lbs as a minimum number since that is what my truck has as far as torque to the ground........Kieth

HERE IS A SPREADSHEET ON YOUR TRUCK DID NOT KNOW IF YOUR 327 WAS A 2 BARRELL OR A 4 BARRELL PM ME IF YOU HAVE QUESTIONS...

Attachment 1223748


WELL THE BIT MAP FORMAT WAS NOT ANY BETTER WILL SEND YOU A EMAIL. KIETH

Re: Anyone with a C20 running 700r4 with stock rear end?
 

Not in the C and K 20/30's

The Eaton HO52/72 was used from the mid 50's thru '72

Re: Anyone with a C20 running 700r4 with stock rear end?
 

I think the 3/4-1 tons started using the Eaton rears all the way back in '47.

I have a question about the spreadsheet, Kieth. It doesn't show the actual torque curve for the engines, just peak numbers; is that just the condensed version? The torque curve is extremely important to consider when talking about real-world performance, especially when talking about the ability to pull tall gears.

Re: Anyone with a C20 running 700r4 with stock rear end?
 

Well you cannot get everything into 1 spreadsheet (and the torque values are not peak torque values just torque at the highest rated rpm), tried to make it where it was usable and peak torque numbers are not always available. We can get the top side torque numbers just by doing a little algebra since we know the hp and the top side rpm. Trying to show peak torque as well is darn near impossible.......but give it a whirl.
I just wanted to have something available to everyone that would even take torque within a usable range of speeds into consideration, I try to use comparison numbers that I know actually work compared to the torque values we calculate. We know that the real torque numbers will be higher all the way down to peak torque but since we are using the same range of values then it does give us something to go on.
No one will be unhappy if there truck performs better than expected.... Thanks for the comments and if you can come up with a better spreadsheet have at it, I still have not had the patience to go back in and add all the transmissions that I have found since doing the initial work.
Since I found a limited way to show the information on the forum I am going to work on improving the quality.........tried using a PDF format but the sheet is too large for the forum........hmm maybe we can take away the lines on the chart to save pixels.....maybe that will work.......will try it.....Kieth

ps I am not a engineer but have worked in mechanical and hydraulic power systems, excavator, dozers, and the application of gearboxes, winches, planetary track drives from 150 in/lbs to 400,000 ft lbs, and class 5, 6, 7, & 8 trucks.......just tried to put some information out there that could keep people from changing a lot of things around on their truck and then have it fall on its face or end up only going 50mph... You are correct that peak torque is a better way to compare towing performance and if anyone needs that done I can modify the spreadsheet to meet their requirements.... Kieth

Re: Anyone with a C20 running 700r4 with stock rear end?
 

A 700r4 would change your 4.57 to 3.20 ( 4.57x.7). It would allow you to keep your 3/4 ton a 3/4 ton.