What RPM's

FordTruck · Post by **FordTruck** » Thu Jun 11, 2009 4:13 pm

What RPM's do your trucks run at between 30-45mph??
My trucks got a 302 with a C6 combo and I think 3:50 or 3:55 and it runs between if I rember correctly about 2000-2500 at about 40. That just seems high to me and I was wondering what may cause that or is that about normal?

SteveC · Post by **SteveC** » Thu Jun 11, 2009 4:36 pm

my 67 with a 352 np435 and 4.11 gears runs around 2500-2800 at 55-60
of course tire size plays into this equation as well

miner3do · Post by **miner3do** » Thu Jun 11, 2009 4:40 pm

mines a 390 with a four speed and at 45 mph im at 2000

FordTruck · Post by **FordTruck** » Thu Jun 11, 2009 4:47 pm

Thanks for the imput guys.
If it matters the trucks got 235/75R/15's on it.

green68250 · Post by **green68250** » Thu Jun 11, 2009 8:53 pm

That does seem high for that gear ratio and that size of tire. I know my F-250 with a c6 and 4.10's will do 65-70 at around 3 grand, I would say shes around 1800 to 2000 at 40mph.

Fordnatic · Post by **Fordnatic** » Fri Jun 12, 2009 12:07 am

2400 @ 60 with 3.50's and 31' (tall) tires
2400 @ 60 with 4.10's and 35" (tall) tires
are what my two F100's run.

So, yes tire size makes a big diff. There is a calculation page here: http://www.angelfire.com/fl/procrastination/rear.html

mrtleavitt · Post by **mrtleavitt** » Fri Jun 12, 2009 9:01 am

My truck runs 1600 rpm @ 35 mph. 390 w/ T19 4 speed and 31 inch tires. That's as high as you'd every want to go with gearing imo.

FordTruck · Post by **FordTruck** » Fri Jun 12, 2009 9:18 am

Thanks for all theimput guys so it sounds like it may be running a little bit high. What could cause that? I'm pretty shure its shifting into 3rd becasue 1st&2nd shift really soon.

SteveC · Post by **SteveC** » Fri Jun 12, 2009 11:21 am

are you sure of the ratio in the rear end?? could it have been changed?

FordTruck · Post by **FordTruck** » Fri Jun 12, 2009 1:12 pm

SteveC wrote:are you sure of the ratio in the rear end?? could it have been changed?

I'm pretty shure that's right because that's what the tag on the rear end said. I'll have to try and find that tag again just to make shure I got it right.

FordTruck · Post by **FordTruck** » Fri Jun 12, 2009 1:34 pm

Here's the numbers off of the rear end tag.
WDM-T 9N?
3.50 8 7 311A

Fordnatic · Post by **Fordnatic** » Fri Jun 12, 2009 5:16 pm

It's common to change the gears, so the tag may not be correct. Just use the formula on the link I posted and see what you get.

FordTruck · Post by **FordTruck** » Sat Jun 13, 2009 2:28 pm

Fordnatic wrote:It's common to change the gears, so the tag may not be correct. Just use the formula on the link I posted and see what you get.

I checked it and the link matches what the trucks doing. Just 3 grand seems like alot of RPM's for that speed. But its a small block so I guess it can handle the revs.

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