Engineer hp and torque graphs and tires

[wanderer]

hey everyone, I’m looking for an engine torque and horsepower chart that plots RPMs versus horsepower and torque when I’m trying to figure out is if I switch from 35 inch tires to 37 inch tires and I have a 456 gear ratio what will be the change in my RPMs on the larger tire at a 70 miles an hour in eighth gear
Assuming I can still pull eighth
I know they used to have these charts out for the JK 3.8 motor but I haven’t seen an accurate one for the newest version of the 3.6 my Jeep for what it’s worth is a 2024 Rubicon X
The second part of this inquiry is I’m on BFG 35 which I know or a small 35. I’m thinking I wanna try something different. I still want basically an all-terrain. I’d like it to be as quiet as reasonable but still a good off-road tire for most conditions I know there’s compromises I’ve been thinking about going with Thompson maybe COOPER or Nittos or toyos maybe even Patagonia

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[jadmt]

https://purperformance.com/p-29669-rpm-calculator.html

your 8th is 0.67 to 1 so just plug in your tire sizes to compare. rough guess tho around 150rpm difference give or take between a 35 ko2 which would be like 33.5 and most 37's which would be around 36"

 

[TrustWonUSA]

What would be a good RPM to shoot for at 70mph

 

[jadmt]

What would be a good RPM to shoot for at 70mph

2000 give or take feels good to me.

 

[2nd 392]

What would be a good RPM to shoot for at 70mph

1,943 RPM 4.56’s -37’s at 65 is 1804 RPM divide by 13 X 14 = 1943 at 70. 36’s are 1854 at 65- 1997 at 70. If the chart in the gears/axles section is for true size and you have BFG’s, likely about split the difference.

 

[wanderer]

So
What would be the hp and torque loss at a150 rpm less ?

 

[2nd 392]

So
What would be the hp and torque loss at a150 rpm less ?

Does this help ?

I would want at least 4.88 to bring the RPM up to 2079 at 70, 5.13’s wouldn’t hurt at 2186 RPM, well into the torque curve. …. Of course, chart numbers and tires vary but ballpark.

at the wheel dyno graph IIRC, I can’t be more specific, but that engine likes to rev.
Edit- 37’s are all heavy AF except for KO2’s, the only C I’m aware of.

 

[Twisted10]

my 392 w/ 4.56's doesnt care about the 38's.. hope that helps...

 

[TrustWonUSA]

Does this help ?

I would want at least 4.88 to bring the RPM up to 2079 at 70, 5.13’s wouldn’t hurt at 2186 RPM, well into the torque curve. …. Of course, chart numbers and tires vary but ballpark.

at the wheel dyno graph IIRC, I can’t be more specific, but that engine likes to rev.
Edit- 37’s are all heavy AF except for KO2’s, the only C I’m aware of.

I have the 4.88’s with the 315’s in the v6 Auto. Tonight at 62mph I was right on 2K rpm

 

[2nd 392]

I have the 4.88’s with the 315’s in the v6 Auto. Tonight at 62mph I was right on 2K rpm

The chart shows 2041 at 65, so it’s reasonably close considering tire variance. ie- the Interco 35’s on my PU are true 35’s, no squat. The Toyo C’s on the Jeep are ~34.5 iirc and do squat. I don’t recall the Jeep, but it was still reasonably close to the numbers when I checked after getting 4.56’s/35’s.

 

[azjl#3]

Impressively steep torque rise brought to you by vanos.

I sort of think your measuring with a micrometer and cutting with a chain saw. Little wind, incline, extra weight, the plan goes out the window

 

[Ratbert]

What would be a good RPM to shoot for at 70mph

Define "good". Best mileage at 70? Best acceleration from 70 to 100+? Best engine braking? Best towing? Something else?

Note that "best" can vary by engine and is impacted by transmission gears, diff gears, and tire size. Additionally, things like weight, aerodynamics, altitude, road grade, etc. impact what might be considered "best" in any given situation.

 

[wanderer]

Mainly i was trying to see what the hp and torque values drop to when the toms drop as a result of going to a lsrger tire size so far it looks like the drop in rom is around 150
Now to plot it and see what that means in terms of hp and torque

i ask the owner of shift auto about going to 37! And he said not a problem at all

 

[azjl#3]

I think it is mostly moot as what gear is this happening in, 8;7;6?

the tranny does a real nice job doing what it needs to do to get what you want.

 

[TrustWonUSA]

Define "good". Best mileage at 70? Best acceleration from 70 to 100+? Best engine braking? Best towing? Something else?

Note that "best" can vary by engine and is impacted by transmission gears, diff gears, and tire size. Additionally, things like weight, aerodynamics, altitude, road grade, etc. impact what might be considered "best" in any given situation.

Goooood point

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