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Idakota
Dodge Dakota
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1/24/2005
17:37:22
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 Subject: 4.7 low end power
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I have an 03 4.7 with a volant intake, ho cams, magnaflow muffler, superchips programmer, and most recently a 70mm F&B throttle body. After installing the throttle body it seemed like I lost a little power in the lower rpms and gained a lot in the upper. What do I need to do to get the low end back up? I was thinking a high flow cat and a new y-pipe? Any ideas or suggestions?
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DanK
Dodge Dakota
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1/24/2005
17:42:43
| RE: 4.7 low end power
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Longer intake path between TB and intake valves.
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Idakota
Dodge Dakota
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1/24/2005
20:26:41
| RE: 4.7 low end power
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Are you suggesting a different intake manifold? Which one would you suggest? Do you think that is a better solution than a hiflo cat and y-pipe? Any other suggestions?
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DanK
Dodge Dakota
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1/24/2005
20:43:31
| RE: 4.7 low end power
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No need to change the intake manifold. Those HO cams did more to raise the RPM of the power and torque peak than any intake mod (short of a one-off custom built) will be able to overcome.
Take a real good look at your Y-pipe, where the two pipes are merged into one. That should answer the question as to what's next.
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Idakota
Dodge Dakota
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1/24/2005
22:28:07
| RE: 4.7 low end power
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Thanks for the info Dank. I've heard the y-pipe is very restrictive as well as the cat. With my mods, what kind of gains can I expect from freeing up the exhaust a bit? High end or low end power?
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DanK
Dodge Dakota
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1/25/2005
01:09:49
| RE: 4.7 low end power
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Here's my recommendation, sprinkled with opinion and observation from my experiences, but understand other peoples' opinions will vary about my next few statements, based on their experiences with engine types, sizes and exhaust configurations.
If you replace the Y-pipe, stay with the original size pipes from the exhaust manifold to the muffler if you can, just use a better "collector" section where the two pipes come together. Freeing up the exhaust in this small way may not give you noticeable, seat-of-the-pants gratification, but it's still a positive change for your engine: it will breathe easier, with slight increase in gas mileage, and a better exhaust note.
Too large a pipe does not maintain the flow rate necessary to help with exhaust gas extraction. That's why you may have read or heard that full dual exhaust sometimes slightly reduces the apparent hp/torque of the 4.7 engine.
Too small a pipe has just the opposite effect, but only in a very narrow rpm range way down low, and once the revs pick up, you will have excessive back pressure, noticeably reduced power, and higher under-hood temperatures.
It's hard to "tune" the exhaust of the 4.7 because of the firing order: odd and even cylinder firing does not alternate. By that I mean the exhaust pulses in the left exhaust pipe are not equally spaced in time, and neither are the right side's. And since one of the pipes crosses to the other, the exhaust pulses in the tailpipe are still not evenly spaced in time, because they travel vastly different lengths of pipe to get to the Y connection.
Food for thought: This non-alternating firing order is fairly prevalent in V8 engines. Ever wonder why an "H-pipe" or "X-pipe" works the way it does on dual exhaust setups? Hint: unevenly spaced exhaust pulses.
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Idakota
Dodge Dakota
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1/25/2005
02:07:57
| RE: 4.7 low end power
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I am planning on keeping the stock sizes on the pipes. The length of the pipes will be a bit shorter than stock because I'm going to dump it right after the muffler. Does anyone know what size y-pipe replaces the stock one? I think it is 2.25 inch inlets with 2.5 inch outlet. Does that sound right? This is what I am looking at getting http://www.justmagnaflow.com/Hardware/SmoothPipeTransitions_ypipe_0000.jpg
Thanks again.
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Pittdawg
Dodge Dakota
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1/25/2005
02:32:50
| RE: 4.7 low end power
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I just had that y-collector installed a few days ago, I highly recommend it, basically as DanK said, not a drastic increase in power but it definately feels peppier, have yet to check the mileage though. I'm not gonna check it till the next tank, I've been gettin into it way too much for a reading.
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Idakota
Dodge Dakota
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1/25/2005
23:34:48
| RE: 4.7 low end power
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Thanks pittdawg, do you know the measurments of your y-collector? I want to make sure I get the right one. Thanks.
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Pittdawg
Dodge Dakota
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1/27/2005
18:30:42
| RE: 4.7 low end power
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dual 2.25 into single 2.5
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Idakota
Dodge Dakota
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1/27/2005
20:38:29
| RE: 4.7 low end power
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Thanks!
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