Hemi 5.7 power - Jeep Commander Forums: Jeep Commander Forum
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post #1 of 10 (permalink) Old 03-01-2011, 11:46 PM Thread Starter
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Hemi 5.7 power

Does anyone know why the hemi makes less power in our Jeep's than in other Chrysler vehicles? Is it mechanical (ie camshaft) or a different software tune?
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post #2 of 10 (permalink) Old 03-02-2011, 12:00 AM
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If you pop the hood on my jeep and pop the hood on a charger same exact motor. I know every year it seems the Hemi makes more power which might be a number of factors obviously. But 06 Commander and 06 Charger, Challenger, 300, Magnum I assume is tune. I didnt mention Ram because I think it is a different motor. I am not a mechanic. I just know it looks different.
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post #3 of 10 (permalink) Old 03-02-2011, 12:14 AM
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Torque or HP? (I haven't compared numbers)
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post #4 of 10 (permalink) Old 03-02-2011, 12:26 AM Thread Starter
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Both

Both HP and Torque.

Here is what I asked the superchips guys (I have a flashpaq)

**

I noticed that the Hemi in my Commander differs in power output from the one in the 300C I had. In the 300C Chrysler spec was 340hp (250KW) and 390 ftlb tourqe. In the commander it is rated 322Hp (240KW) and 375 ft-lb. Why the difference and where is the Flashpaq 91 tune on this scale? It would seem that 18HP and 15 ft-lb must be there for the taking? I thought perhaps it was an axel limitation as in theory the commander can put all of that on one wheel. Does the SC tune deliver more than a stock 300c tune?

cheers


SC Response 1

**

5.7L Commander stock has 236hp and 258torque to the wheel.
tuned=252hp 284 peak torque

5.7L 300C stock= 272hp and 300ftlbs
tuned= 285hp and 314.7ftlbs

**

When I asked them if they new why they said they dont tear down the engines just tune them.
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post #5 of 10 (permalink) Old 03-02-2011, 12:37 AM
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I wonder if those are at the wheel numbers? I can imagine that the transfer case of a 4wd has a greater loss than a 2wd.. Just guessing.
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post #6 of 10 (permalink) Old 03-02-2011, 04:30 AM Thread Starter
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Power

Superchips numbers at wheels. Chrysler numbers at flywheel.
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post #7 of 10 (permalink) Old 03-02-2011, 05:46 AM
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Quote:
Originally Posted by hoaxci5 View Post
I wonder if those are at the wheel numbers? I can imagine that the transfer case of a 4wd has a greater loss than a 2wd.. Just guessing.
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Originally Posted by andrewturnbukk View Post
Superchips numbers at wheels. Chrysler numbers at flywheel.
I was thinking the same thing as Hoax... I thought flywheel HP was "old school", but maybe that was flywheel with no accessories on the motor on a test stand (back in the 1960's?).

Oh well... either way, it could just be a matter of de-tuning the motor to protect the transfer case from damage (over-kill safety factor maybe?).
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post #8 of 10 (permalink) Old 03-02-2011, 10:40 AM
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So did the newer jeeps get new transmissions or transfer cases that can take the extra HP?
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post #9 of 10 (permalink) Old 03-02-2011, 05:47 PM
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Join Date: Dec 2010
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Quote:
Originally Posted by Chuck1026 View Post
I was thinking the same thing as Hoax... I thought flywheel HP was "old school", but maybe that was flywheel with no accessories on the motor on a test stand (back in the 1960's?).
Oh well... either way, it could just be a matter of de-tuning the motor to protect the transfer case from damage (over-kill safety factor maybe?).
Mfr's can't test like they did in the 60's with no accessories. They have to test in the same condition they are on the street.

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So did the newer jeeps get new transmissions or transfer cases that can take the extra HP?
The Jeep drivetrain can take a lot more power than is being thrown at it with a stock motor. No modifications were needed with the minor power bumps.

It's more likely a question of fuel mileage and emissions. Other things that can affect the HP and TQ would be space in the engine bay, exhaust dimensions and cams and other aspects tuned for car driving vs. truck driving (different peak power bands).
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post #10 of 10 (permalink) Old 03-02-2011, 08:23 PM
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Lots of things go into vehicle tuning....


I have not heard of any major internal differences between teh Jeeps and the 300C variations... but I would fully expect tuning differences.

The cars are going to be tuned for a more sporty higher reving feel and shifts, whereas a $45k Jeep is going to be tuned for some level of smoothness, but also torque to pull more load, tow etc. Not to mention different packaging constraints for intake/exhaust/cooling etc.


As far as factory vs measured hp #s? Factor test is 'bench' horsepower if you will. SAE certified testing conditions, but with accessories, exhaust etc... Dyno numbers are power measured after parasitic losses in the driveline (torque convert, trans, differential, etc etc) and often depend on teh equipment used to measure (dynojets vs Mustang, entered load parameters etc on the dyno setup)

So yeah... Only real way to know is find a Chrysler powertrain Engineer.
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