Dynoing with Open Rear End - Please Report

CumminsBeast

CumminsBeast

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Dec 20, 2008
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I'm planning on visiting the dyno in the next couple months and I have a concern over being able to hook up on the rollers. One stupid thing about my truck that I absolutely hate is that it has an open rear end instead of a limited slip differential. Every time I take off if I'm not locked in 4wd, if I get on it any at all, all I get it one spinning rear tire. I'm worried I'll just burn that one off when I hit the dyno instead of hooking up.

I should be somewhere around 550 hp, so has anyone else on here dynoed with an open rear end? Please report here on the result, good or not.
 
find a aam rear out of wrecked truck with the limited slip and problem would be solved it wouldn't be that hard to swap axles with the same gear ratio. you just have to unhook the drive shaft, u bolts, speed sensor and break lines. shouldn't take more than 2-3 hours to do the swap
 
i agree find a wreck and put in that limited slip, or eaton just came out with a new truetrac limited slip. for 03 to 07. 1-800-328-3850 or www.eatonperfomance.com i think on the rollers you will be fine cause of ur wheel speed.
 
I might be wrong but I think both rollers are on the same shaft so it should not be a problem
 
hoffscummins said:
i dont have any problems on the dyno with my open rear end
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How much HP you runnin? Also, should I dyno in 4th or 3rd? I've been told in 3rd gear you can achieve lockup by putting it in Tow/Haul mode? Since I don't have the lockup controller hooked up, would this be my best option?
 
SKYNYRD said:
find a aam rear out of wrecked truck with the limited slip and problem would be solved it wouldn't be that hard to swap axles with the same gear ratio. you just have to unhook the drive shaft, u bolts, speed sensor and break lines. shouldn't take more than 2-3 hours to do the swap
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I've thought about this. I'm in the process of hunting one up. I'd actually like to go down to a 4:10 rear end because the 35's have got me geared up waaay too high. By the way, is aam the manufacturer of our trucks differentials? I've looked online to try and find a limited slip conversion/ring and pinion combo and can't find it.
 
I doubt you will have any traction problems if you are strapped down properly.
 
CumminsBeast said:
I've thought about this. I'm in the process of hunting one up. I'd actually like to go down to a 4:10 rear end because the 35's have got me geared up waaay too high. By the way, is aam the manufacturer of our trucks differentials? I've looked online to try and find a limited slip conversion/ring and pinion combo and can't find it.
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i'm running 35's with my 3.73's with no issues at all really i still get a good pull out of the hole and good over all speed. i have an aam rear with 3.73 limited slip but have already worked a deal with another member on here for a 5.9 short block but if the deal falls thru i'll let you know.

this is my timesheets running with 35's and 3.73's with a TC lock up it will cut my times down some since it wasn't locking up til around 90mph
timeslips.jpg
 
SKYNYRD said:
i'm running 35's with my 3.73's with no issues at all really i still get a good pull out of the hole and good over all speed. i have an aam rear with 3.73 limited slip but have already worked a deal with another member on here for a 5.9 short block but if the deal falls thru i'll let you know.

this is my timesheets running with 35's and 3.73's with a TC lock up it will cut my times down some since it wasn't locking up til around 90mph
timeslips.jpg
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I feel like my truck is geared way too high with the 35's. I figured I might get better times with the 4:10's.

I've been told that lockup converter makes more of a difference than that. I was told that it makes more of a 0.4 to 0.5 difference, which I thought was pretty optimistic.

Does second and third gears feel much stronger with the lockup? I feel like my truck hauls pretty good after lockup is achieved in fourth.
 
when i had my lock up on my 05 it really kicked it in the pants and threw you back in the seat so yeah 0.4 to 0.5 difference seems reasonable a little light.
 
SKYNYRD said:
when i had my lock up on my 05 it really kicked it in the pants and threw you back in the seat so yeah 0.4 to 0.5 difference seems reasonable a little light.
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But from the looks of the slips, 0.04 seems more like what you gained instead of 0.4.???
 
jordanjames81 said:
use your smarty to change tire size in the ecm. get a lockup switch its worth it.
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I've changed the tire size with Smarty. Question though, is there a good way to lock up in third without the switch? I think I posted above where one guy on here said you can achieve lockup in 3rd if in Tow/Haul. I've not verified this.
 
CumminsBeast said:
But from the looks of the slips, 0.04 seems more like what you gained instead of 0.4.???
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both of those slips were without a lock up the lock up is sitting in the box behind my seat waiting to be installed once my knee heals from my surgery.
 
SKYNYRD said:
both of those slips were without a lock up the lock up is sitting in the box behind my seat waiting to be installed once my knee heals from my surgery.
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Which lockup did you go with? I tried installing my Co-Pilot with splice connectors and it didn't really work. I'd be interested to see how the splicing into that short little PCM harness goes without using those types of connectors. I'd like to find a better way.
 
mine is a on a toggle switch witha .30 ohm resisantor in it. on the black with orange wire on middle plug in on the firewall on passanger side.
 
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