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derek j.
Dodge Dakota
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6/16/2002
21:18:06
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 Subject: exhaust idea, need opinions
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after bolting on a 2.5 dynomax race bullet on my 2002 4.7 i lost some low end torque. i knew that would happen when i put it on. but i have an idea to get some torque back. there is no pipe after the muffler, just a turndown, so i weld an 1/8" steel plate over the end of the turndown outlet. then use a cutting torch and cut a hole at a starting point of about about 3/4" to increase the back pressure some. i can tune the torque by opening the hole up more. has anyone done this. i think it is a good idea but would like some of your opinions first. if it doesn't work, i go to autozone and get a new turndown and live with it.
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motorsportdak
Dodge Dakota
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6/16/2002
22:37:40
|  RE: exhaust idea, need opinions
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Sounds like it might work. You dont want to have too much back pressure though, So what you might want to look at is the restrictions that your OEM muffler has, compared to the dyno. So you can figure on a size of a cap that you need to put on there without having too much restriction. Instead of using a torch, id recommend drilling it out. Don't know what size bits you can get ahold of though. Make sure the hole's in the dead center as well.
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derek j.
Dodge Dakota
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6/17/2002
08:07:35
|  RE: exhaust idea, need opinions
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when i thought of it i couldn't find anything wrong with the THEORY, but we will see what happens. i have never heard of metal bits that are 3/4" or bigger so i just thought of doing some precision torch work the get right hole. i can always draw the hole on the metal then cut it out. anyone else have a comment or suggestion?
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MotorsportDak
Dodge Dakota
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6/17/2002
08:29:14
| RE: exhaust idea, need opinions
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I used to be a machinist and make parts all day long. 3/4" bit's were small. They are industrial bits though. I beleive we got them through Grainger or McMasters or something. If you have a steady hand and a hot hot flame, you can cut it by hand, just cut the whole a little smaller then you need, and use a demel tool with one of those drum sanders on it, and finish it up. That was you have a clean round hole.
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Bruce P
Dodge Dakota
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6/17/2002
22:54:53
| RE: exhaust idea, need opinions
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It is NOT the "backpressure" that is the problem.
When one adds a better-flowing exhaust to an enginem the VELOCITY of the exhaust gasses must be considerd.
Simply adding a better-flowing muffler and larger pipes is often NOT the right way to go. This is because the VELOCITY of the exhaust gasses SLOWS DOWN with larger pipes. This changes the scavenging (vacuum) on the exhaust valves at certain RPMs. We (the drivers) see this as reduced engine torque at lower RPMs.
Instead of adding backpressure to your engine by "plugging up" the exhaust tip. You would get better results adding a length of pipe after the muffler (no larger that 2.5") that will maintain the VELICOTY of the gasses within.
You may find that going with 2.5" on the 4.7L is too much for it to handle. Many folks have found that 2" all the way back does best for maintaining the low-RPM torque.
GENERAL RULE: Larger diamater pipes make HIGH-RPM power while smaller-diamator pipes make more low RPM power.
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hardbody
Dodge Dakota
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6/18/2002
00:15:59
| RE: exhaust idea, need opinions
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Your idea sounds like what Supertrapp has been doing for years tuneable mufflers
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Pistolero
Dodge Dakota
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6/18/2002
02:02:50
| RE: exhaust idea, need opinions
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If you still want to try the plate and hole thing, you could try a 3/4" radio chassis punch to make your hole. I use them all the time to make panels in which to mount microphone connectors. Most of the panels that I cut are aluminum, but I think they'll work in 1/8" steel. They're made by Greenlee. You drill a 3/8" pilot hole, then put the bolt through the hole with the cutting die on one side and the cup on the other. Tighten the bolt with a wrench, and it pulls the cutter through the plate, making a clean, burr free perfect hole.
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MotorsportDak
Dodge Dakota
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6/18/2002
08:05:51
| RE: exhaust idea, need opinions
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Pistolero, your in the audio install buisness?
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Pistolero
Dodge Dakota
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6/18/2002
16:04:12
| RE: exhaust idea, need opinions
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MotorsportDak, no, I'm not in the audio install business specifically...but, I've worked in the TV broadcasting and A-V fields as an engineer/tech since '73. I've often had to build a lot of "stuff" to get a certain job done. I'm the Video Engineering Specialist for a school district nowadays. Are you in the business or have an interest?
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MotorsportDak
Dodge Dakota
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6/18/2002
19:13:00
| RE: exhaust idea, need opinions
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I was guessing you had some relation to the audio buisness when you said you installed Mic plugs, guessings XLR? I've been in the audio/lighting buisness for almost 12 years now. I used to work with several audio company's, and a lighting company, but since the mixing and some of the installs were at night, I also had a full time day job that was more secure then the audio/lighting, work picked up, so I had to drop that, and work a hell of lot of overtime at my day job. But, I do mix and do lighting design on occassion for local school's with their theatrical productions, seeing as I can just walk in and do what I need at night etc.. But it's fun, I kinda miss doing it alot more.
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Eazy
Dodge Dakota
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6/18/2002
19:40:48
| RE: exhaust idea, need opinions
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Use a bi-metal holesaw.
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motorsportdak
Dodge Dakota
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6/18/2002
20:49:49
| RE: exhaust idea, need opinions
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bi metals are going for $9-11 for a 3/4" from Grainger
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