RPM vs. Gear Ratio

[JJRJR]

Hey guys, trying to decide what rear gears to get. Is there a mathematical formula out there to give me an idea of what RPM's the motor will run at various MPH?

I'd like to get the highest gear I can, but want to be able to live with highway cruising as well. I'm thinking if the engine is working at about 50% (3,200 RPM) at 65 MPH or so, then I can live with that, but wanted to try out different gears in a formula.

Thanks,
John

 

[CompSyn]

Play around with this: Visual RPM, Speed, and Gear Ratio Calculator - LINK

 

[sixgunrunner68]

My car is a four speed with 4.30 gears. 60mph = 3000rpms. It's not very highway friendly. Starts to drone on you a little. :cents: don't get me wrong,I love them. There won't be any cross country touring though.

 

[JJRJR]

That link is flat out awesome, thank you so much. Yea, it's looking like anything above a 3.55 the highway isn't so much fun. Here iin South Florida, driving at 75 to 80 is more likely on most of the highways. With the 3.55, it'll turn 3,500 @ 80 mph. I suppose I can live with that.

Those with the 3.55; how is the low end with that gear? I hear they are the best all around gear for this set up.

Thanks,

John

 

[JJRJR]

Wow, playing with that link shows me that this thing will have nothing for top end highway running. At 5,800 RPM it'll go about 132 MPH with the 3.55's. Not that I plan on that very often, but I gotta think those little 5.0 mustangs will go faster than that at lower RPM?

What is the realistic redline for this build? I'm thinking 6500 max. It's a 383 that will have about 485 HP and 510 or so of TQ. I'll have to keep my racing from light to light. LOL.
John

 

[mac]

i have 3:54 now and the overall performance is very good. if i was considering more track testing, i would go with 4:11. my first RR had 4:10 and trying to drive on the highway at 60 mph was not fun for any distance. :cents:

 

[69hemibeep]

3;55 in mine with F70 15s and handle highway speeds pretty well, 80 is opening allot of carburetor especially on my car. I think a 3;73 might start to be a push.

 

[JJRJR]

Thanks guys, sounds like the 3.55's is where I wanna be. Best of both worlds.

Best,

John

 

[69hemibeep]

Thanks guys, sounds like the 3.55's is where I wanna be. Best of both worlds.

Best,

John

To answer your noise question. They are quiet.

 

[sixgunrunner68]

I like the 3.73s for highway. They'll work.I wouldn't even waste the time or money to go from 3.23 to 3.55.

 

[69hemibeep]

I like the 3.73s for highway. They'll work.I wouldn't even waste the time or money to go from 3.23 to 3.55.

3.91s aren't much different that 3.73s :devil: He's talking 80mph cruise.

 

[A31PKG]

... but I gotta think those little 5.0 mustangs will go faster than that at lower RPM?...

True, but remember those 'stangs have an extra gear (or two) in the tranny...I remember my wife's ol' 5.0 would do 60-65 all day at around 1500 RPM.

My 3:91's cruise nice at 55 MPH +/- at 2500 RPM +/-...

 

[JJRJR]

Yea, it's crazy. Had to drive wy wife's VW into work this morning. I wanted to help clean out her spark plugs, so did 100 for a couple seconds. I don't think it ever got over 3,200 RPM. 270 HP and really nice top end.

 

[sixgunrunner68]

I like the 3.73s for highway. They'll work.I wouldn't even waste the time or money to go from 3.23 to 3.55.

3.91s aren't much different that 3.73s :devil: He's talking 80mph cruise.

Might as well just get 4.10s then. What the hell.

 

[69hemibeep]

I like the 3.73s for highway. They'll work.I wouldn't even waste the time or money to go from 3.23 to 3.55.

3.91s aren't much different that 3.73s :devil: He's talking 80mph cruise.

Might as well just get 4.10s then. What the hell.

And a Gear Vendors OD

 

[JJRJR]

That would be amazing, but too much money at this point. Maybe someday in a land far, far away. . .

LOL

 

[JJRJR]

Now that you mentioned Gear Vendors, I read on their website a bit; sounds pretty amazing. Does anyone have one? How is the install? Seems if $2,800 is the only cost plus installation, it changes the car in a major way.

John

 

[andy69]

So what gear ratio is std on 83/4 rear running 383 with A727 auto

 

[mcmopar]

That link is flat out awesome, thank you so much. Yea, it's looking like anything above a 3.55 the highway isn't so much fun. Here iin South Florida, driving at 75 to 80 is more likely on most of the highways. With the 3.55, it'll turn 3,500 @ 80 mph. I suppose I can live with that.

Those with the 3.55; how is the low end with that gear? I hear they are the best all around gear for this set up.

Thanks,

John

The 3.55's I have are more than ample enough to spin the 275-60R/15's I've got out back and I can loaf around town at 30-35 mph in 4th gear, too. 3.55 is a great all-around gear and better with your/my setup than 3.23's. I had 3.23's in mine for a little while and it lugged off the line but when I put the 3.55's back in that problem was solved.