http://www.landiss.com/mphvrpm.htm

if you have Excel down load this and try it out

is this a good way to do it ?

i tried to set this up for my truck but i dont know my gear ratios for my c6 tranny.

figured i was going about 88 mph at 3500 rpm does anyne else get this number ?
and what are my gear ratios ?
and any help modifying this setup i linked to let me know.

 

Drive always is 1:1

I get 89mph figuring your tire diameter is 31.73".

Barry

 

I get 87.96 at 3500. Pretty close. 75.4 mph at 3000. 62.83 at 2500. Normally, 235-85's are about 31.7 inches tall, but I calc at 31.5 just to amount for a little wear, and tire squat. My truck also seems to calculate closer to 4.56 than a 4.10. Not sure why, except for tranny slippage, and likely some error in my speedo. But my VIN says 4.10. I doubt it's been changed. I think most of these puter programs are a bit lenient as far as revs per mph. I wouldn't be surprised if your actual speed at 3500 is slightly lower than calculated. MK

 

Recalculating with 5% torque converter slippage and 31.5" tire

84mph

 

You could be loosing a couple hundred rpms through the tranny. I know on my powerstroke it drops 200rpm when the convertor locks up. Or you just might have 4.56s. You can pop the back cover off and the tooth count is stamped into the outside of the ring gear. It will read something like 41-10. That would be 4.1 (divide the smaller number into the larger)

 

Yeah I was thinking about that much loss through the torque converer since he doesn't have a lock-up.

 

thanks, did anyone download that excel link and see that spreadsheet. i figured my high gear was 1.1 was wondering what the first two were. to further my question out what is about peak rpm for a setup such as mine ?

 

1st = 2.46
2nd = 1.46

Are you asking what your redline is?

Barry

 

I use a different program. Your max horsepower rpm is on the VIN. Being a V8, it's probably 4000-4400 rpm or so range. Also, they will state the original stock horsepower at that rpm. Fer instance, my original 300 six was rated at 139 hp at 3600 according to the VIN.
As far as best cruise rpm, guess it depends on the needs. But usually you want to stay within the "max" torque rpm. Fer instance my 300 shows max net torque from 1400-2100. Max gross torque 1400-2400 rpm. I've never known why a difference in rpm's between the two... But anyway, you can see that a low cruise rpm is good if you run a 300. You'll have plenty of torque even at fairly low rpms. It would be preferable not to cruise over 2400 or so with a 300, but not always possible if low geared. The V8's will usually have the torque peaks about in the same upper teens, lower-mid twenties rpm range. Thats where you really want to cruise at. The lower end for best MPG. IE: cruising at 1800 -2000 *should* work out real nice with my 300 if I wanted good mpg on the road, but still have enough torque to make it up a grade. Unfortunately, I don't have an overdrive, and with the 4.10 I seem to turn 2700-2800 at 55-60 mph. But I wonder about the accuracy of the tach and speedo. For a tach, I'm using an engine analyser that I keep down on the floor by the shifter. It *should* be fairly accurate, and has low/high rpm scales, but hard to tell. My speedo seems to read a tad less than what I'm really doing. I need to do a good GPS test on mine... MK

 

>>are you gonna run your truck's speakers thru it?
I don't really have any at this point, except some small box speakers I keep nearly under the seats just for my delco AM-FM. I run my 706 into the speaker that is in the dash. That gets the sound up at ear level so the road noise doesn't drown it out. For music, I'd need to get a 2nd power amp to run after the sound card amp, and a decent set of speakers. I don't know where to mount them. The thought of cutting round holes in my so far unmolested door panels doesn't appeal to me. I may go with some dash or headliner level drivers for mids-hi end, and go with a subwoofer under the seat for low end. If I could get rid of the gas tank, it would leave room for speakers behind the seat. Mounting speakers in these trucks is a pain if you don't want to cut anything... BTW, once I did that, my 706 audio could also run through that system. I run all the same mess here in the house. I often use the 706 in the house , and use it like a computer radio. My sound card audio goes out to a kenwood integrated audio amp and speakers. Using a CI-V converter, I can control and program the radio by the puter if I want to. MK

 

I tried out the excel download - It's pretty easy to use. It saves you the trouble of figuring out your wheel diameter. You just plug in your tire size (mine are 235 75/R15), your gear ratios (I got mine for my NP-435 from the Novak site), and your rear axle ratio (it's a '67 Ford 9" inch, got the ratio of 3.70 from another site, I forget which but I can look it up), and the results seemed to match up pretty well with what I found from my speedo and tach.

At 2800 RPM in 4th I'm doing just over 60 MPH according to my speedo (in another thread I said I was doing close to 3000 RPM at 55 mph but I wasn't reading the tach right - there's two needles and I looked at the wrong one). The Excel program says I should be doing about 64MPH, so out a bit but not surprising given all the sources of error.

In 2nd at 3000 RPM I'm at 20 MPH which is exactly what the Excel thing says.

It's a bit of a pain figuring out the exact RPM vs. MPH in the Excel spreadsheet for values that aren't even - the results are displayed as a graph and the MPH increment by 10 and the RPM by a 1000 so if you want to figure out MPH at say 2700 RPM you have to guess where that is between 2000 and 3000 RPM and then guess where the result is for the MPH if it's not on the 50 MPH or 60 MPH line.

I don't know if that made sense. You kinda have to see the Excel spreadsheet to understand. Anyway, the formulas in there can probably be adapted to allow you to figure out exact values for any RPM or MPH inputs (I'm going to play with them a bit and see).

Hope that's useful.

 

cool, being my speedo is non working this helps out alot. i just like to kinda know how fast i am going just for the sake if i see a cop i wanna make sure i am at least close to the speed limit. you guys been a big help

 

if you get that excel spreadsheet dialed in for fords let me know, i been playing with it too and my tewaks usually result in having to start over lol.

 

I use one that has many different calculators on one page. I also have a few others. But I usually use the one with all the programs. It has calculators for many different angles of RPM vs rev's. speedo converters, crawl speed converter, tire converter, etc, etc...Even has an ohms law converter. I forgot where I got it at...I saved the page and run it off my drive. It's javascript. Eangel sounds like he turns about the same revs I do. Pretty close anyway...I notice my 16 inch tires with the 4.10 end up turning pretty close to 15 inch tires with a 3.70. Friend of mine has a 74 f-100 with 15's and a 3.70...So have another truck to compare with. The 235/75-15 is appx 28.87 inches dia. My 235/85-16's are 31.7. Or new anyway... MK

 

For better acuracy you should actually measure the diameter of the tire. I have seen almost 2 inches difference in 235s just from one tread design to another in Firestone tires ( no I don't run them ) So just taking a generic height from the calculator leaves a few percent margin of error.