Straight Piping the 4.7 - Jeep Commander Forums: Jeep Commander Forum
Exhaust Questions or advice about exhaust systems? This is the place...

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post #1 of 12 (permalink) Old 10-07-2015, 10:56 PM Thread Starter
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Straight Piping the 4.7

I currently have a Flowmaster Super 10 on my Commander. Sounds amazing but lately I've been having the itch to straight pipe it. Had anyone done this? If so how bad is the interior drone?
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post #2 of 12 (permalink) Old 10-08-2015, 11:09 PM
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Had a straight pipe before I replaced it with Magnaflow. Honestly it very irritating specially in long drives. Plus it may decrease the horse power if not properly tuned.

Last edited by jeepdriver11; 10-10-2015 at 07:55 PM.
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post #3 of 12 (permalink) Old 10-09-2015, 04:29 AM
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A dude here done the straight pipe, highly noticeable sound difference but not sure of the performance.
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post #4 of 12 (permalink) Old 10-09-2015, 11:30 AM
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IMHO it will sound like crap, and you'll annoy people.

Maybe I'm just old. Get off my lawn!
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post #5 of 12 (permalink) Old 10-10-2015, 12:35 AM
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A Straight pipe exhaust will cause you to lose engine back pressure, which in turn will cause you to lose power & gas mileage - I wouldn't recommend it.

Of course, if you just want it to be louder and that's all you are looking for, then go for it.


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Last edited by Big Blue; 10-10-2015 at 12:51 AM.
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post #6 of 12 (permalink) Old 10-10-2015, 07:56 PM
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I agree no back pressure= bad fuel consumption and performance.
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post #7 of 12 (permalink) Old 10-11-2015, 02:11 AM Thread Starter
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Appreciate the feedback guys. Commanders already suck on mpg as it is and my Super 10 sounds great. I'll just stick with what I currently have.
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post #8 of 12 (permalink) Old 10-11-2015, 10:16 AM
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Originally Posted by BurghXK View Post
Appreciate the feedback guys. Commanders already suck on mpg as it is and my Super 10 sounds great. I'll just stick with what I currently have.
It's not just Commanders - most Jeep vehicles are notoriously lacking in the MPG dept.

Case in point, I had a 2008 Jeep Grand Cherokee Rocky Mountain Edition with a 3.7L V-6 and believe it or not, I get the same MPG with my Commander with the 4.7L Flex Fuel V-8, even slightly better on the Highway.

In your situation, I would be more concerned about the loss of engine back pressure and the resulting loss of HP you would experience going with a straight pipe, than the MPG's.

You already modified your exhaust to improve it and seem pretty happy with it.

There's an old saying, "If it ain't broke, don't fix it"


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Last edited by Big Blue; 10-11-2015 at 10:20 AM.
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post #9 of 12 (permalink) Old 10-11-2015, 12:26 PM
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Straight Pipe It? As in straight pipe from the Catalytic Converter Back -OR- straight pipe from the exhaust manifold back?

Keep a few things in mind. Engines are coming pretty well designed and optimized off the factory floor. I would NOT assume that its like the 70's were the designs had huge compromises to keep costs and prices down.

You can't flow out more from the engine, than you can flow in and vice-a-versa. So concentrating freeing up the exhaust while the choke point in air-flow through the motor is the intake system, its NOT going to get you anything at all, mileage or power.

Keep in mind as well, the engine is a balanced system, freeing up the exhaust more than will help, usually doesn't "hurt", but disrupt the balance to much, you'll hurt it instead of improve it, or just make no difference at all.

The old carbuerated engines, needed a strong vacuum signal through the intake and carb, reducing the back pressure too much would reduce that vacuum signal going through the intake. EFI, that is NOT usually a problem, but two things can happen, free up that exhaust too much, it might go outside the EFI's calibration far enough it can't adjust to the changes and loose power and economy. OR, since the EFI has to maintain emissions standards, the exhaust changes are screwing up emissions and thus the EFI is adjusting in response to that.

Regardless, there is enough testimonials here that its pretty clear straight pipes on a Commander, like a lot of modern vehicles, hurt more than it helps.

All Jeeps have bad fuel efficiency? Ummm, Renegade, Patriot, Compass, the new Cherokee? That all have decent fuel efficiency they are also heavily criticized for being "soft" Jeeps that based on on-road car platforms will some improvements to suspension and drivetrain to provide better off-road ability that falls short of traditional Jeep ability.

A couple of things to keep in mind;

The WK and XK are based on the same platform, in fact they are both WK platforms and XK is more a body code/designation. They were built on the same assembly line. So similar mileage between the very similar vehicles should NOT be surprising.

Today's car manufacturers are massively regulated, there are thousands of regs and standards that the vehicles must meet. Crash standards and Mandated Safety Equipment that increase vehicle weight significantly and mandatory emissions standards that significantly reduces engine fuel efficiency.

To build a body with sufficient off-road strength and a 4WD/AWD drivetrain only adds to the weight and drags down the fuel efficiency even more. The more fuel efficient Jeeps suffering in off-road ability is good evidence of that concept.

V6's making the same mileage as the V8's, lets keep in mind a lot of work has gone into making engines more efficient, only to be dragged down by emission standards. What you're really seeing is as efficient as possible engines, and it takes that much fuel to move a vehicle of that weight, while staying under pollution standards, regardless of the number of the cylinders.


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Last edited by Mongo; 10-11-2015 at 12:29 PM.
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post #10 of 12 (permalink) Old 10-11-2015, 02:03 PM
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Quote:
Originally Posted by Mongo View Post
Straight Pipe It? As in straight pipe from the Catalytic Converter Back -OR- straight pipe from the exhaust manifold back?

All Jeeps have bad fuel efficiency? Ummm, Renegade, Patriot, Compass, the new Cherokee? That all have decent fuel efficiency they are also heavily criticized for being "soft" Jeeps that based on on-road car platforms will some improvements to suspension and drivetrain to provide better off-road ability that falls short of traditional Jeep ability.

A couple of things to keep in mind;

The WK and XK are based on the same platform, in fact they are both WK platforms and XK is more a body code/designation. They were built on the same assembly line. So similar mileage between the very similar vehicles should NOT be surprising.
I supposed I should have been more specific as I was not referring to the new little tiny/hybrid, half-a$$ed SUV's that Jeep has come out with in the last few years (Compass, Patriot, Cherokee & Renegades) - they are not true, legit 4x4's in my opinion. I was referring to Commanders, Grand Cherokees & all of the various Wranglers/Rubicons - and yes, they are all absolutely notorious for not getting great gas mileage.

I am also well aware that Commanders & Cherokees are built on the same assembly line and that Commanders are essentially the same platform & use a lot of the same components that Grand Cherokees do - that's why I bought one in the first place. Now that being said, I don't really see where that has any bearing on this discussion.

Anytime I see a 4.7L 8 cylinder engine that puts out 305 HP & 334ft lbs of Torque which is 95 more HP and 100ft lbs more torque than the 3.7L 6 cylinder engine that was made the same year and it gets the same or slightly better gas mileage than the V-6 does, I will continue to be surprised.

That just defies conventional wisdom.


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Last edited by Big Blue; 10-13-2015 at 09:03 AM.
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