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Mr.H
Dodge Dakota
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8/13/2003
11:29:41
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 Subject: Off with 3rd Cat on 01' 4.7. No power??
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7 months ago I had straight-pipes installed just behind the 3rd cat to have the cool-looking tips. Since I lowered my truck 3" in the rear, the pipes were stupidly routed right over the diff. case where the speedo. sender connects and when it bottomed it broke the sender or melted the wires, I'm not sure which.
I finally got around to pulling the exhaust out and cut it off before the 3rd cat to go ahead and get rid of it as well.
Now my exhaust is open just behind the y-pipe and it's stupid loud but seems to have lost TONS of power. What's my solution????
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.alex.
Dodge Dakota
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8/13/2003
11:33:27
|  RE: Off with 3rd Cat on 01' 4.7. No power??
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Message:
Well, if you're running an open y-pipe, I guess it is pretty loud. I bet it makes good power up around 5500 though.
Try running a few things here:
True dual pipes 2.5" from the exhaust manifolds all the way back. No 3rd cat.
Then add a 70 mm or 72 mm TB.
Then add HO cams & HO intake.
Be sure you have a cool air tube or get rid of the factory air hat in some manner.
Ditch the clutch fan, too.
Oh yeah... dont' forget the Kenne Bell computer flash.
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Demon Dakota
DakotaEnthusiast
8/13/2003
20:07:02
| RE: Off with 3rd Cat on 01' 4.7. No power??
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Message:
You need to stuff as much air into the engine as you can before really opening up the exhaust (cams, intake, TB, intake...). If you do them all about the same time, you'll get plenty more usable low end power than stock.
K&N Drop in AF (CAI during summer months)
True Dual exhaust and removed third cat
HO Cams & HO Intake
FASTMAN 70mm TB
Autolite 3923 Plugs
TPS @ .76 VDC
IAT Adjuster Mod
14.52@94.2 MPH at Silver Dollar Raceway
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Kyle
Dodge Dakota
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8/14/2003
01:18:32
| RE: Off with 3rd Cat on 01' 4.7. No power??
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Message:
You probably lost some back pressure from removing the third cat. Go with Demon's idea, slam it with air and it will create more back pressure trying to get all that air out.
http://home.comcast.net/~dakota2001cc4x4/
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Jacque
Dodge Dakota
JOIN HERE
8/16/2003
14:53:53
| RE: Off with 3rd Cat on 01' 4.7. No power??
IP: Logged
Message:
You need to add some exhaust pipe to get it to run right. You cut off too much exhaust pipe and know the engine can get the exhaust out of the engine. Every engine combination wants a specific length of exhaust to run its best. To find out what it wants you can simply experiment with different lengths of exhaust pipe til you find what it likes. You don't want to be short of the ideal length because it want run the best that it can. You can take various lengths of pipe from a muffler shop and open one end each so you can slip them on together forming different lengths until you find what it wants. You can make up these sections of pipe in 2 1/2 inch or 3 inch if you like.
There is a computer program called pipemax that can tell you exactly what you need; the length and size of the exhaust pipe. The guy that designed and sells the program phone number is 1-337-893-1541. He can answer any of your questions you have. The computer program is helpful in designing headers and collector length also. It is very accurate. A friend of mine has a car that runs in the 8's that added 9 inches to his collector length because the computer program said that was the ideal collector length and went a 1/10 faster in the quarter.
So at the very least add a couple foot of exhaust pipe and see how it runs.
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Demon Dakota
DakotaEnthusiast
8/17/2003
11:03:22
| RE: Off with 3rd Cat on 01' 4.7. No power??
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Message:
If you go with true duals, don't go larger than 2.5" piping. Anything larger than that for you would be overkill and would probably result in a slight loss of performance. I assume you're going the true dual route (since you removed you third cat), but if you're not and are planning on sticking with a single exhaust, then use 3" pipe from the Y back. The best overall length for the duals seems to be equal length with the exits run out the rear (for slightly higher TQ peak). If you want the RPM to spool up faster with a higher HP rating, do a right side exhaust exit in front of the rear wheel (or dump it under the bed before the rear axle).
K&N Drop in AF (CAI during summer months)
True Dual exhaust and removed third cat
HO Cams & HO Intake
FASTMAN 70mm TB
Autolite 3923 Plugs
TPS @ .76 VDC
IAT Adjuster Mod
14.52@94.2 MPH at Silver Dollar Raceway
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Mr.H
Dodge Dakota
JOIN HERE
8/18/2003
11:46:28
|  RE: Off with 3rd Cat on 01' 4.7. No power??
IP: Logged
Message:
Well,
After $146 I now have a single 2.5 dynomax dumped before the rear axle.
It sounds way better and seems to have gained power all the way through the powerband considerably.
Thanks for the advice.
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