Gear heads...Please help!!

[Mark W]

You need to check your speedo! You're gonna get busted.

I'm running 39.5 boggers with 5.29s. Basically same setup that you have.

3500 rpm equals 76mph.

2500 rpm equals 55mph.


Determined by GPS and by simply running the numbers.


Mark...

 

[Denofearth]

I have been followed by my wife in her car and my speedo is almost bang on. I do have a 465 tranny, the gears might be different than yours. If i was doing 76 mph then the people passing me were doing 110 mph that is how fast it seems that they are going. I am telling you it feels like I am standing still.

 

[projektdotnet]

Friend runs 38.5s with a 700r4 and 4.11 axles with no speed issues...just takes a min to get up to speed...enjoii runs 36's with a 350 and 465 with 4.11 diffs no problems

 

[FJ40Jim]

something is wacked w/ the speedo or tach or???

5.29 gear x 39" tire x 60MPH = 2700RPM.
About the same as a stock cruiser w/ 4.11 & 29" tires.

 

[nuclearlemon]

drop down to a 4.88. i run 36's with 4.56, and 350/sm465 and can run 65, so 4.88 should be pretty good with 39s

 

[Degnol]

http://www.cosports.com/fwhldr/equipcalc.htm



If I entered the data correctly, you should be doing almost 66 mph at 3,000rpm


You try and see what you come up with.....I think Mark W is right.


Ed

 

[Degnol]

something is wacked w/ the speedo or tach or???

5.29 gear x 39" tire x 60MPH = 2700RPM.
About the same as a stock cruiser w/ 4.11 & 29" tires.

Like is your tach set for 8 cyl?

 

[Denofearth]

Are you taking in to concideration the 465 tranny? I don't have the stock tranny just the transfer case.

At 55 mph I am turning 3500rpm by my speedo and I did have my wife follow me and it is pretty close.

 

[Denofearth]

I did not know that it needed to be set for an 8 cyl?
and how would I do that?
I bought the tach before I switched the motor out.

 

[projektdotnet]

YMMV but the tach that is going to go into mine has a switch inside the housing that says 4-6-8 and you set it for your engine

 

[Degnol]

4th gear in most any transmission is 1:1

And reset your tach.

The numbers don't lie.

GL


Ed

 

[60/40GUY]

Are you taking in to concideration the 465 tranny? I don't have the stock tranny just the transfer case.

Unless it is an overdrive tranny, high gear is one to one output. So the tranny is a non issue in the equation. Something is not adding up.

 

[Denofearth]

Well that is very interesting. The engine does sound like the rpms are high @55 but i will look into the tach to see if there is a switch . Thanks again. So if the tach is wrong then i must be getting worst gas milage than when i had the 6 in it! That blows!

 

[Mark W]

Are you taking in to concideration the 465 tranny? I don't have the stock tranny just the transfer case.

At 55 mph I am turning 3500rpm by my speedo and I did have my wife follow me and it is pretty close.

Tranny doesn't matter. 4th gear is 1:1.

You do know that you speedo reads at the T/C? It is ahead of the diff. It will always think that you have stock gears (and tires). It is not an accurate way to determine your speed at all if you have modified the gearing and tires.


Mark...

 

[Denofearth]

Well I just got back from outside to check the tach. and I can't see any easy switch. so I went to the old tach and dwel meter to try and see exactly what the rpm is...Well I cant hook it up to the tbi (or I don't know how to) I can't find the coil on the engine?!

 

[Degnol]

Don't know what tach you have, but usually there are a couple of screws on the back of the mount and if you remove those, the selector switch is right there on the back of the tach itself, not the mounting. I think the tach reads the number of firings of the ignition and divides by the # of cylinders you've selected and counts that as revolutions, so if you have it set for 6 cylinders and you now have a V8, it will be reading rpms about 25% higher than it should, which pretty much matches your numbers.
I'm not entirely sure my theory is correct but I'll just bet that if your tach is selctable, and not all are, you've got it set for 6 cylinders.

GL

Ed

 

[Denofearth]

Thanks guys been great help!!
now to take the tach off the dash@#$%^& it aint going to be pretty!!
thanks

 

[Denofearth]

I have 37'tires and a fuel injected V8 350, 529 gears with 465 tranny. My problem is when I go on the Hi-way!!! I go slow! and the motor turns fast.. My RPM's @ 60 is about 3000!.

My question is this...If I put in 411's again what will my RPM's be turning @ 60.
If I put in 488's would it suite on hiway and good crawling ratios?
I am doing 70% on road (hi-way ) and 30 % off road. My very short 28" or so driveshaft cant be any shorter or on anymore of an angle.
I don't want to give up my crall ratio BUT this 3000 RPM can't be good on my new rebuilt motor. Any help (please with out sarcasm, I get enough from my wife!..he he) would be Great!!

Thanks, Den

 

[grant5127]

It's hard to have the best of both worlds.....Handy Chart.......

The chart is divided into three categories. The rpm highlighted in black are optimum for the tire size and ratio combination. These will most closely give you the best overall drivability. If you're looking for a ratio that will give better fuel economy for highway driving at the expense of some acceleration and overall performance, choose a ratio in the yellow shaded area. If you're looking for a ratio that will improve acceleration and towing power at the expense of some fuel economy, choose a ratio in the blue shaded area..........................

This chart is based on engine rpm at 65 mph with the transmission in a 1:1 gear ratio ............

note: provided for entertainment purposes only, actual experiences may vary.........

 

[Elbert]

either re-gear or consider going with a 5 speed trans or one of those overdrives. If you want super-low crawl speeds with a 4 speed trans you will have to give up top end. Can't you run something like 4.56 and go to low range off-road?