MoTech Swapped LS3 on the Dyno - JKowners.com : Jeep Wrangler JK Forum
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post #1 of 27 Old 10-11-2017, 07:32 PM Thread Starter
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MoTech Swapped LS3 on the Dyno

Took the Jeep to KC Maxx Performance today for a little dyno tuning. MoTech did the original swap a couple years ago and tuned it pretty conservatively. I recently did some work replacing the intake tube and updated the tune with HP Tuners using the timing, air, and fuel tables from a 2013 Camaro SS LS3. I wanted Ryan (KC Maxx) to verify my work and make sure I didn't have any risk of detonation or lean AFRs. They were great to work with. I captured some of the dyno pulls on video and posted it to YouTube for your viewing pleasure. He did all the pulls in 3rd gear to keep the drive shaft and tire speed safe. It shouldn't affect the final dyno numbers too much.


<iframe width="560" height="315" src="https://www.youtube.com/embed/FoO05hdvnh4" frameborder="0" allowfullscreen></iframe>
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post #2 of 27 Old 10-12-2017, 05:37 AM
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345 HP?

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post #3 of 27 Old 10-12-2017, 06:06 AM Thread Starter
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345 HP?
Yeah. It's definitely not breaking any records, but I'm happy with it. My intent wasn't to brag about a power monster, but to share a real-world verified number. I think it's fine when you consider it was a third gear pull, driveline loss, and the 35" tires. I'm not sure what the typical driveline loss is with the 6l80 and Jeep transfer case? The wheel and tire combo is about 100 lbs per corner, so it takes a little power to get them spun up. It drives great on the road and feels like plenty of power to me. Especially when you consider the original 3.6 made 285hp at the crank. I'm not sure what that would have been at the tire...

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post #4 of 27 Old 10-12-2017, 07:02 AM
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~14% powertrain loss. I would say that number is high.


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post #5 of 27 Old 10-12-2017, 07:43 AM
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~14% powertrain loss. I would say that number is high.
For an auto trans... hardly. The old standard used to be about 20% for an auto trans. These days the transmissions are more efficient and the loss is less but 14% is great considering.


To put it into perspective my 525hp crate engine came out to 360ish hp iirc. My rolling stock is 140lbs per corner and the looser converter soaks up a bit of power itself.

I don't think folks put enough thought into how much a heavy wheel / tire setup affects performance.
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post #6 of 27 Old 10-12-2017, 08:07 AM Thread Starter
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For an auto trans... hardly. The old standard used to be about 20% for an auto trans. These days the transmissions are more efficient and the loss is less but 14% is great considering.


To put it into perspective my 525hp crate engine came out to 360ish hp iirc. My rolling stock is 140lbs per corner and the looser converter soaks up a bit of power itself.

I don't think folks put enough thought into how much a heavy wheel / tire setup affects performance.
Doing the math, and assuming that my motor is making the advertised 430hp at the crank, 345hp is right at 80% of the crank figure. That means the 20% loss figure would be right on.
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post #7 of 27 Old 10-12-2017, 08:10 AM
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What GM ecu did you use?

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post #8 of 27 Old 10-12-2017, 08:18 AM Thread Starter
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What GM ecu did you use?

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E38. I think that's what Robbie suggests for all of his Gen IV swaps. Does Jon at RPM give you more flexibility regarding the GM ECU?
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post #9 of 27 Old 10-12-2017, 08:19 AM
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For an auto trans... hardly. The old standard used to be about 20% for an auto trans. These days the transmissions are more efficient and the loss is less but 14% is great considering.


To put it into perspective my 525hp crate engine came out to 360ish hp iirc. My rolling stock is 140lbs per corner and the looser converter soaks up a bit of power itself.

I don't think folks put enough thought into how much a heavy wheel / tire setup affects performance.
No I meant having only 15% powertrain loss is low in this situation. The old 15-20% "rule of thumb" comes from the performance world so 2 wheel drive, performance tires etc... My stock JK had close to 50% powertrain loss

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Doing the math, and assuming that my motor is making the advertised 430hp at the crank, 345hp is right at 80% of the crank figure. That means the 20% loss figure would be right on.
Sorry I did the math assuming a 400 hp crank rating. 20% is going in the right direction but I still think its more than that in a JK with a t case, larger drive shaft, larger axle components and big tires to spin.


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post #10 of 27 Old 10-12-2017, 08:33 AM
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No I meant having only 15% powertrain loss is low in this situation. The old 15-20% "rule of thumb" comes from the performance world so 2 wheel drive, performance tires etc... My stock JK had close to 50% powertrain loss



Sorry I did the math assuming a 400 hp crank rating. 20% is going in the right direction but I still think its more than that in a JK with a t case, larger drive shaft, larger axle components and big tires to spin.
Ahh, gotcha. The t-case when in 2wd really isnt contributing negatively to performance. There is a small bit of rotational mass there but it's not much and you aren't driving the chain.



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post #11 of 27 Old 10-12-2017, 08:41 AM
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E38. I think that's what Robbie suggests for all of his Gen IV swaps. Does Jon at RPM give you more flexibility regarding the GM ECU?
I'm running an e38 as well. I asked because the e38 can be run with flex fuel. All you have to do is get the sensor and plumb it inline one of the fuel lines and wire in the 3 wire pigtail. Only 1 of the wires actually goes to the ecu, the other 2 are power and ground.

The benefit here is that while it's fairly inefficient because it's 85% ethanol.... It's flippin 105 octane. You can get at least a 30hp wheel increase just running straight e85. So you install the sensor and go back to your tuner to have it setup and now that the sensor is there it will adjust your tune for e85 when it is present. The cool part is that it will detect % of e85 and adjust accordingly. Obviously the best gains will be from running straight e85 but you can run any blend in between and not screw anything up.

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post #12 of 27 Old 10-12-2017, 08:49 AM Thread Starter
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Thanks for the info. I didn't realize that e85 was 105 octane. That explains why so many guys run it at the track.
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post #13 of 27 Old 10-12-2017, 08:52 AM
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Thanks for the info. I didn't realize that e85 was 105 octane. That explains why so many guys run it at the track.
Yep, so for $100ish said and done you can get another 30ish rwhp. Also it comes with that nice sweet smell that burning high octane fuel makes.

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post #14 of 27 Old 10-12-2017, 10:05 AM
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Yeah. It's definitely not breaking any records, but I'm happy with it. My intent wasn't to brag about a power monster, but to share a real-world verified number. I think it's fine when you consider it was a third gear pull, driveline loss, and the 35" tires. I'm not sure what the typical driveline loss is with the 6l80 and Jeep transfer case? The wheel and tire combo is about 100 lbs per corner, so it takes a little power to get them spun up. It drives great on the road and feels like plenty of power to me. Especially when you consider the original 3.6 made 285hp at the crank. I'm not sure what that would have been at the tire...
I'm sure you still have some more ponies to unlock if you wanted to but it's plenty of power for a JK! My LS2 pulled 324 at the wheel in 3rd gear (6L80E) and 37s on a 20" wheel. My dyno guy figured closer to 30% drivetrain loss (He tunes a lot of hotrods and 4x4s around here).


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post #15 of 27 Old 10-12-2017, 04:57 PM Thread Starter
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I don't think folks put enough thought into how much a heavy wheel / tire setup affects performance.
That's a good point. It would be interesting to do an experiment comparing dyno pulls with a heavy set of off road tires vs stock size tires. If someone had convenient and cheap access to a dyno, and a set of stock-size tires, it could be done. I've read a lot regarding powertrain loss from the mechanical bits, but not much to address how tires affect the numbers.
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post #16 of 27 Old 10-12-2017, 05:08 PM
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That's a good point. It would be interesting to do an experiment comparing dyno pulls with a heavy set of off road tires vs stock size tires. If someone had convenient and cheap access to a dyno, and a set of stock-size tires, it could be done. I've read a lot regarding powertrain loss from the mechanical bits, but not much to address how tires affect the numbers.
It's exactly why racers use as light of wheel, tire, and brake setups that will still hold up.

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post #17 of 27 Old 10-12-2017, 08:28 PM
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That's a good point. It would be interesting to do an experiment comparing dyno pulls with a heavy set of off road tires vs stock size tires. If someone had convenient and cheap access to a dyno, and a set of stock-size tires, it could be done. I've read a lot regarding powertrain loss from the mechanical bits, but not much to address how tires affect the numbers.
You'd also have to change the rearend gears to go with the change in tire size if you wanted accurate data for different wheel/tire weights. 28" tall tires and 5.13 gears would skew the numbers a bit. Would be fun to do burnouts though.

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post #18 of 27 Old 10-12-2017, 08:55 PM
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Hi there, crate engine dyno'd @ 427 h/p & 463 F.P.T. Running TH400, 4:10 in one tons and 38's. I think my wife's Toyota Corolla might be faster on road. In 4wg low, it's a friggin' monster though.
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post #19 of 27 Old 10-13-2017, 06:07 AM
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That's a good point. It would be interesting to do an experiment comparing dyno pulls with a heavy set of off road tires vs stock size tires. If someone had convenient and cheap access to a dyno, and a set of stock-size tires, it could be done. I've read a lot regarding powertrain loss from the mechanical bits, but not much to address how tires affect the numbers.
I would try it if I could get stock wheels over my brakes. My dyno guy built a 72 Scout with an LS3 and he had around 40hp difference between 31" and 35" tires.


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post #20 of 27 Old 10-13-2017, 07:20 AM Thread Starter
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I would try it if I could get stock wheels over my brakes. My dyno guy built a 72 Scout with an LS3 and he had around 40hp difference between 31" and 35" tires.
That's crazy. I wouldn't have expected 40hp. Rolling resistance and the unsprung weight associated with heavy wheel/tire combos obviously kills fuel economy and overall power. I just didn't realize exactly how much! Thanks for sharing your tuner's observation.
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post #21 of 27 Old 10-13-2017, 09:42 AM
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My 5.3 LC9 with 118 pounds per corner of 37's (4.56 ) went from 235 hp to 274 with a dyno tune. Also much nicer than the 118 ish the 3.8 put out.
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Running 37's as a daily driver is dumb
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post #22 of 27 Old 10-15-2017, 05:44 AM
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I just had my bone stock 2014 L83, gen v 5.3 dynod and it came in at 270 hp with a tune. I was like what?? Th engine claims 355 hp!
So then the tech said it is normal for a car to loose about 20-25% hp, and then I dug up the RIPP video on dyno pulls for a stock 3.8 JK and a stock pentastar, which show a 35% calculated power loss from rated flywheel hp to rear wheel hp.
I don't feel so bad now, my 3.8 made about 135 whp, and the pentastar a whopping 180 whp, but at 5,000 rpm! Anyone care to rev their pentastar to 5k? I do know my V8 is limited to 5,5k revs.....

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post #23 of 27 Old 10-15-2017, 08:42 AM Thread Starter
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My 5.3 LC9 with 118 pounds per corner of 37's (4.56 ) went from 235 hp to 274 with a dyno tune. Also much nicer than the 118 ish the 3.8 put out.
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I just had my bone stock 2014 L83, gen v 5.3 dynod and it came in at 270 hp with a tune. I was like what?? Th engine claims 355 hp!
So then the tech said it is normal for a car to loose about 20-25% hp, and then I dug up the RIPP video on dyno pulls for a stock 3.8 JK and a stock pentastar, which show a 35% calculated power loss from rated flywheel hp to rear wheel hp.
I don't feel so bad now, my 3.8 made about 135 whp, and the pentastar a whopping 180 whp, but at 5,000 rpm! Anyone care to rev their pentastar to 5k? I do know my V8 is limited to 5,5k revs.....
Both of these 5.3s making in the neighborhood of 270hp to the tire makes this swap sound like a heck of a value. Sure, you get a little more power with the 6.0 and 6.2, but I imagine the 5.3 makes the Jeep seem plenty powerful at a much better price point for the swap. Dyno numbers are only an indicator, but I imagine the 5.3 probably has plenty of area under the curve (like most of the LS and LT motors) making it a great motor to have fun with on the street or trail.
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post #24 of 27 Old 10-15-2017, 09:21 AM
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I would talk to Robbie about engine choice. A gen 4 6.0 or 6.2 would have been a better choice. (He suggested it, but someone didn't listen.).
Big grades fully loaded in a 6000 lb jku are now doable with the 5.3, but not really awesome. The same grades doorless, topless and loaded with a backpack, a wife and two fishing rods are pretty easy.

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post #25 of 27 Old 11-07-2017, 06:34 AM
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Would love to see the results of a dyno-tuned 430hp LS3 with a Whipple SuperCharger, and maybe some Water-Methanol Injection.
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