Magnuson SC and proper gearing

[JeepLab]

You're correct. I spend most of my time on the highway (and mostly at or above 80 mph). My thought on going to 4.56 is because my auto trans is five speed. I would like all of my passing and acceleration at highway speed to be with a downshift to 4th gear. But to really "kick it in the guts" and push myself back in the seat I need to downshift to 3rd gear and let the motor spin up to 3,500 rpm and stand on it through 4,500 rpm and then either lift off the pedal to shift or use the auto-man to up-shift. I would hope that the lower gears would get the rpms up just enough to get have a bit more available power at the pedal in 4th gear.

So let me know if I get this right.

SC + AUTO + 35s + 4.10 gearing = highway passing in 4rd gear?

SC + AUTO + 35s + 4.56 gearing = highway passing in 3rd gear?

Now, this all brings further questioning

1. Is your speedo calibrated perfectly?

2. What is the RPM you cruise at if doing 80mph?

baumann, Ive read your posts a bunch of times now trying to get clear about how to help the OP in this thread. Since you have the auto with the mag and we dont, your experience above ours in this case because of your AUTO transmission.

I have the Mag S/C on my 2013 JKU with automatic trans. I have 35s and 4.10 gears. If I had it to do over I would get 4.56 gears.

Here is what I think about your situation, not Jt1911's.

I think are geared right. 4.10 for 35s with the SC is PERFECT gearing. If you had 4.56, you would feel overgeared. If you have never been overgeared, take it from me. It sucks. Do not feel like if you did it over again, you'd do it different. The grass is always greener on the other side of the fence. I promise, you are on the greener side of the fence. Being overgeared, turns your supercharged truck into a pig on the highway. I dont care how much horsepower you make.

If you had 4.56 with 35s on an Auto, you would be at 2700 RPM at 70 MPH! Your truck would struggle to get to 80, and would be gasping for air there at 3500 RPM. You would almost be forced to go to 37s.

Just my position. take it from a guy who geared twice.

[gbaumann]

[QUOTE=JeepLab;3125]So let me know if I get this right.

SC + AUTO + 35s + 4.10 gearing = highway passing in 4rd gear?

SC + AUTO + 35s + 4.56 gearing = highway passing in 3rd gear?

Now, this all brings further questioning

1. Is your speedo calibrated perfectly?

2. What is the RPM you cruise at if doing 80mph?

baumann, Ive read your posts a bunch of times now trying to get clear about how to help the OP in this thread. Since you have the auto with the mag and we dont, your experience above ours in this case because of your AUTO transmission.[QUOTE=JeepLab;3125]

OK.

SC + AUTO + 35s + 4.10 gearing = highway passing (65 mph to 80 mph) in 3rd gear. I use auto-man to go to 3rd and that lets me get the throttle open enough to get boost up. 4th gear is problematic when passing. Even in auto-man if I pass in 4th gear the trans will downshift when accelerator is depressed beyond a certain point. It won't stay in 4th. The downshift from 4th sometimes jumps two gears to 2nd! That's not safe for me or the motor. So to stay safe I go to 3rd. Yes, I can pass in 4th but it takes much more distance and not at all uphill. Again, there is probably more power available in 4th gear but I can't access it because opening the throttle enough to close the SC bypass and get into full boost will cause an unwanted downshift. I'm thinking that 4.56s will get rpms up in 4th a bit and reduce the downshifting. A better solution would be to get access to the transmission side of the PCM and reprogram automatic trans shift-points and keep my 4.10s. But I hear that's not going to happen for a long time if ever based on how difficult it is to crack Chrysler's PCM transmission programming.e

I'll record my rpms at 80 today and report back.

[gbaumann]

So let me know if I get this right.

SC + AUTO + 35s + 4.10 gearing = highway passing in 4rd gear?

SC + AUTO + 35s + 4.56 gearing = highway passing in 3rd gear?

Now, this all brings further questioning

1. Is your speedo calibrated perfectly?

2. What is the RPM you cruise at if doing 80mph?

baumann, Ive read your posts a bunch of times now trying to get clear about how to help the OP in this thread. Since you have the auto with the mag and we dont, your experience above ours in this case because of your AUTO transmission.



Here is what I think about your situation, not Jt1911's.

I think are geared right. 4.10 for 35s with the SC is PERFECT gearing. If you had 4.56, you would feel overgeared. If you have never been overgeared, take it from me. It sucks. Do not feel like if you did it over again, you'd do it different. The grass is always greener on the other side of the fence. I promise, you are on the greener side of the fence. Being overgeared, turns your supercharged truck into a pig on the highway. I dont care how much horsepower you make.

If you had 4.56 with 35s on an Auto, you would be at 2700 RPM at 70 MPH! Your truck would struggle to get to 80, and would be gasping for air there at 3500 RPM. You would almost be forced to go to 37s.

Just my position. take it from a guy who geared twice.

With 35s and 4.10 gearing with automatic trans I'm running around 2,700 (2,750?) at 80 mph. That's in 5th gear, of course.