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Unread 05-01-2007, 05:21 AM   #1
djaychris
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Backpressure question

I'm thinking of putting a flowmaster 40 on my wrangler. I will be keeping the stock cat and manifold. I'm concerned about backpressure, as I don't want to loose my low end power. Does anybody know if the flowmaster 40 is too wide open for the wrangler? Also, does the 40 series have a tendency to drone loudly?

-Thanks
-Dan

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Unread 05-01-2007, 06:55 AM   #2
Rocky529
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The Flowmaster 40 is great and has no negatives about it.

It does not drone at all, at highway speeds, I can't even hear it. It is perfect for my liking.
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Unread 05-01-2007, 09:47 AM   #3
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Quote:
Originally Posted by Rocky529
The Flowmaster 40 is great and has no negatives about it.

It does not drone at all, at highway speeds, I can't even hear it. It is perfect for my liking.
X2 aggressive enough to like but not too loud.
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Unread 05-01-2007, 01:39 PM   #4
djaychris
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Thanks guys, thats what I'm leaning for. What size diameter did you go with, 2.25? Any power loss issues? It didn't make your gas mileage worse did it?

-Thanks
-Dan
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Unread 05-01-2007, 01:46 PM   #5
Rocky529
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Quote:
Originally Posted by djaychris
Thanks guys, thats what I'm leaning for. What size diameter did you go with, 2.25? Any power loss issues? It didn't make your gas mileage worse did it?

-Thanks
-Dan
I believe it is a 2.5" diameter and I recall the shop welding on adapters to fit my 2.25" pipe. I was watching from outside the garage so I can't be sure. Either way, I am using my stock 2.25" pipe... no need for a bigger diameter.

No, it didn't make my gas mileage worse. Don't worry about gas mileage, life is too short.
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2.25" Suspension Lift with Old Man Emu Shocks
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Spidertrax 1.25" Wheel Spacers - 32"x11.5" MT/R Tires
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Unread 05-01-2007, 01:57 PM   #6
djaychris
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Rocky,

Just curious, did you buy yours online? If so, what was the offset and/or part number? What kind of tip did you use? I don't want a tip that I'm going to have to clean constantly.

-Thanks
-dan
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Unread 05-01-2007, 01:59 PM   #7
Rocky529
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Quote:
Originally Posted by djaychris
Rocky,

Just curious, did you buy yours online? If so, what was the offset and/or part number? What kind of tip did you use? I don't want a tip that I'm going to have to clean constantly.

-Thanks
-dan
I had a local shop install mine. They had it on hand. I don't have any off-set measurements. I remember seeing them on this forum though so if you run a search for "Flowmaster 40", I'm sure you will find what you need in no time. I would have ordered it online and installed it myself except for the fact that I don't have a welder 'nor do I know how to weld. I couldn't say no when they charged my ~$115.

I did not want a chrome tip or anything of that nature. I left it completely stock. You can not tell I have a Flowmaster 40 unless you crawl under my Jeep and look... or of course if you open your ears and hear the sweet sound.
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2004 Jeep Wrangler Sport - 5 speed

Silver Metallic finish with black dual tops - Dana 44 Rear
2.25" Suspension Lift with Old Man Emu Shocks
Performance Accessories 1" Body Lift
Daystar 1" Motor Mount Lift
Spidertrax 1.25" Wheel Spacers - 32"x11.5" MT/R Tires
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Unread 05-01-2007, 02:07 PM   #8
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djaychris, clear your PM inbox.
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2004 Jeep Wrangler Sport - 5 speed

Silver Metallic finish with black dual tops - Dana 44 Rear
2.25" Suspension Lift with Old Man Emu Shocks
Performance Accessories 1" Body Lift
Daystar 1" Motor Mount Lift
Spidertrax 1.25" Wheel Spacers - 32"x11.5" MT/R Tires
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Unread 05-01-2007, 03:13 PM   #9
djaychris
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Thanks for the advice. My inbox is cleared for ya.

-Dan
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Unread 05-02-2007, 09:30 PM   #10
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Curious too about the specific backpressure question. This used to be discussed a lot on the forum: whether 2.25" was necessary to preserve backpressure (felt as low rpm torque) or whether you could open it up with 2.5" (for a little better high rpm hp performance) and still keep enough backpressure. Don't remember what they decided for the I6, but I remember that folks felt the fourbanger was better off with the smaller diameter. Because the I6 has a non-restrictive intake it stands to reason that it could take some opening up of the exhaust without losing bp (IIRC the 2.5 and the 4.0 use the same dia. exhaust).
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Unread 05-02-2007, 09:47 PM   #11
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I'm running a 2.5 inch pipe from the cat back and have felt no loss in low end torque.
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Unread 05-03-2007, 03:36 PM   #12
djaychris
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I'm probably going to stick with my factory plumbing for now, and just throw on a flowmaster with the stock tip.

-Dan
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[B][I]I promised the wife I'd keep it stock............I lied.[/I][/B]


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