An Engineer's Ultimate Guide To 3.21 VS 3.92 Axle Ratio

[theblet]

Or the little blonde chick driving the truck with 3:21 gears would hit a slight head wind and BOOM. Dead in her tracks.

How can she drive while giving me head?

 

[theblet]

These trucks will be aero limited before they hit 8th gear. So any advantage you think you have by being in a lower gear doesn't matter as much. There will be a time when both trucks will be in the same gear at the same speed as the 3.92 trucks reaches top of gear and 3.21 trucks has to shift into next higher gear, losing any advantage it may have had. You can't change the rules of physics

You must have a really nice wind tunnel

 

[BowDown]

These trucks will be aero limited before they hit 8th gear. So any advantage you think you have by being in a lower gear doesn't matter as much. There will be a time when both trucks will be in the same gear at the same speed as the 3.92 trucks reaches top of gear and 3.21 trucks has to shift into next higher gear, losing any advantage it may have had. You can't change the rules of physics

They will be aero limiteong before they hit 8th gear which is exactly why the 3:92 wouldn't have an advantage.
The 3:21 truck can always match the 3:92 geared truck by being 1 trans gear down, look at the gear chart

 

[BowDown]

How can she drive while giving me head?

They like "mud holes", remember... he can't answer that

 

[HSKR R/T]

They will be aero limiteong before they hit 8th gear which is exactly why the 3:92 wouldn't have an advantage.
The 3:21 truck can always match the 3:92 geared truck by being 1 trans gear down, look at the gear chart

Idid look at the chart. Maybe you should look at it again, re-read my reply, and try again

 

[Ramjack]

Since you don't k ow what the aero limited top speed is, once again, you are just assuming the 3.21 truck would be a gear lower. Depending on the speed and shift points, there is a distinct possibility the 3.92 could be hitting top speed at the top of 6th where the 3.21 would have to shift into 6th because it had too much RPM in 5th due to higher gear ratio

Assuming the two trucks are otherwise equal, the only thing that matters is which truck is running closer to the peak hp RPM when it "tops out" (w/o speed limiter). That is the truck that is overcoming the most drag and is therefore going the fastest. I have no idea which axle ratio that would be. The latest 5.7's peak at 5600rpm, right? So whichever truck tops out (drag-limited) nearest 5600 is going the fastest. Granted, there is an unknown here because we don't know whether the 5.7 generates more hp at 5500 v 5700 (5600+/-100), or 5300 vs 5900 (5600+/-300), etc. Can we even exceed 5600rpm w/o a tune, even in a locked gear?

 

[ferraiolo1]

I love how people still take this debate seriously lol.


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[Mountain Whiskey]

I love how people still take this debate seriously lol.


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This thread is just one giant Troll. It is hilarious!

 

[theblet]

I’m having a great time

 

[Eighty]

Assuming the two trucks are otherwise equal, the only thing that matters is which truck is running closer to the peak hp RPM when it "tops out" (w/o speed limiter). That is the truck that is overcoming the most drag and is therefore going the fastest. I have no idea which axle ratio that would be. The latest 5.7's peak at 5600rpm, right? So whichever truck tops out (drag-limited) nearest 5600 is going the fastest. Granted, there is an unknown here because we don't know whether the 5.7 generates more hp at 5500 v 5700 (5600+/-100), or 5300 vs 5900 (5600+/-300), etc. Can we even exceed 5600rpm w/o a tune, even in a locked gear?

The 5.7 Hemi is limited at 6400 rpm, which is also its peak HP range. At least, according to the 2021 specs

edit: my bad, wrong engine. Peak HP at 5600 and limited at 5800 rpm.

 

[Ramjack]

The 5.7 Hemi is limited at 6400 rpm, which is also its peak HP range. At least, according to the 2021 specs

I believe that is the 6.4, not the 5.7.

 

[Eighty]

I believe that is the 6.4, not the 5.7.

Actually it’s the Pentastar. But I just caught that and edited the post.

 

[Ramjack]

I believe that is the 6.4, not the 5.7. Our trucks would not shift at 5500-ish if the power peak was at 6400.

5.7 crate engine:


6.4 crate engine:

 

[Eighty]

5.7 crate engine:
View attachment 120433

6.4 crate engine:
View attachment 120434

ok we are both right.

 

[Eighty]

Now for the record, you could buy a real engine that peaks at 6100 rpm and produces 702 hp.

 

[Ramjack]

ok we are both right.
View attachment 120435

Hey, where did you find that spec sheet?

 

[TNRamGuy]

Don't tell me this thread is going to start using facts and people are going to start agreeing on things. That sucks

 

[Mountain Whiskey]

Don't tell me this thread is going to start using facts and people are going to start agreeing on things. That sucks

 

[Eighty]

Hey, where did you find that spec sheet?

I just googled “Ram max RPM” and found it.

https://s3.amazonaws.com/chryslermedia.iconicweb.com/mediasite/specs/2021_RAM_1500_SPo67hu6voh18mm7gihlqgenf6cf.pdf

 

[BowDown]

5.7 crate engine:
View attachment 120433

6.4 crate engine:
View attachment 120434

Those numbers aren't for production engines, those don't have VVT