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Discussion Starter · #1 ·
I've been toying with the idea of having a custom exhaust put under my car, but not for the same reasons as most. This idea is for my autocross car, and I'm looking to dump some pounds off the car...took the stock Y-pipe and flowmaster catback off today, and it's pretty heavy. So here's my idea: replace the Y-pipe with a catless setup w/ two 2.25-inch pipes into a midmount Magnaflow and a single 2.5-inch pipe out, leading back to exit in the stock location on the driver side (as on the V6 cars). Now contrary to what my profile says, I don't live in CA anymore, so smog testing isn't a problem. Does this sound like a decent setup, or will I just be hemorrhaging power in the name of saving 20-30 pounds? With 145,000 miles on the car, the stock cats are pretty choked up anyway, so let me know what you think.
 

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why not dump the exhaust earlier as well to save on weight? and yea cats and mufflers were heavier than i thought so that could save a lil weight i guess.

since your autocrossing i would focus on removing weight more from the front and not the rear. drop in an explorer motor already and be done with it lol. did you re-locate the battery yet?
 

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Discussion Starter · #4 ·
why not dump the exhaust earlier as well to save on weight? and yea cats and mufflers were heavier than i thought so that could save a lil weight i guess.

since your autocrossing i would focus on removing weight more from the front and not the rear. drop in an explorer motor already and be done with it lol. did you re-locate the battery yet?
An Explorer motor is in my plans, just not this second. Rather than relocate the battery, I'll probably just use a Dyna-Batt or similarly small battery to save the weight of the cables, new battery box, etc. I would prefer to save more weight from the front of the car, but the way our cars are built means that it's easier (and cheaper) to shave weight off the rear of the car. So for now, that will do.

Carbon fiber? We may have just found something that material isn't good for.
 

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PostSkank
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you could always just exit out the center in the rear. As long as the single pipe you use from the "3rd cat" back has a cross section comparable to that of the 2.25 pipes you have up front, I dont think you'll sacrifice much at all.


A 3" pipe is just short of having twice the cross sectional area as two 2.25" pipes :zdunno:


And since weight is the concern, I was bored enough to do some math:
it seems 16 gauge 2.25" pipe will weigh in at about 1.220lb/ft, 2.5" pipe at 1.355lb/ft, and 3" at 1.627lb/ft (unless I botched my equation somewhere). Which gives you a difference of .272lb/ft between 2.5" pipe and 3" pipe (still assuming 16 gauge).

I don't know how much pipe length you can shave off from exiting straight out the tail opposed to the stock V6 DS location, but I would be willing to bet you could come out ahead on weight by going straight out the back with 3" (as opposed to 2.5" in the V6 location), and eliminate some bends in the process.

Going from dual 2.25" pipes to single 2.5" pipe (assuming the same pipe length) will see a loss of 1.085lb/ft (44% weight loss), and a loss of 3.043in^2 cross sectional area (a 38% loss).

Going from dual 2.25" pipe to single 3" pipe (again, assuming the same pipe length) will see a loss of .813lb/ft (33% weight loss), and a loss of only .883in^2 of cross sectional area (only 11% cross sectional area loss).


lord I hope I didn't botch that up anywhere in there.




PS. anyone know anything about the relationship between cross sectional area and flow rates?
 

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Discussion Starter · #7 ·
you could always just exit out the center in the rear. As long as the single pipe you use from the "3rd cat" back has a cross section comparable to that of the 2.25 pipes you have up front, I dont think you'll sacrifice much at all.


A 3" pipe is just short of having twice the cross sectional area as two 2.25" pipes :zdunno:


And since weight is the concern, I was bored enough to do some math:
it seems 16 gauge 2.25" pipe will weigh in at about 1.220lb/ft, 2.5" pipe at 1.355lb/ft, and 3" at 1.627lb/ft (unless I botched my equation somewhere). Which gives you a difference of .272lb/ft between 2.5" pipe and 3" pipe (still assuming 16 gauge).

I don't know how much pipe length you can shave off from exiting straight out the tail opposed to the stock V6 DS location, but I would be willing to bet you could come out ahead on weight by going straight out the back with 3" (as opposed to 2.5" in the V6 location), and eliminate some bends in the process.

Going from dual 2.25" pipes to single 2.5" pipe (assuming the same pipe length) will see a loss of 1.085lb/ft (44% weight loss), and a loss of 3.043in^2 cross sectional area (a 38% loss).

Going from dual 2.25" pipe to single 3" pipe (again, assuming the same pipe length) will see a loss of .813lb/ft (33% weight loss), and a loss of only .883in^2 of cross sectional area (only 11% cross sectional area loss).


lord I hope I didn't botch that up anywhere in there.




PS. anyone know anything about the relationship between cross sectional area and flow rates?
I did a little of the same math not too long ago. Dual 2.25 into 3-inch would be best, I think, but I also have to use a muffler design that's actually commercially available. Magnaflow doesn't make such a muffler, or if they do, I missed it. I think the bulk of the weight savings, too, will come not from eliminating one of the pipes (though that will help) but from eliminating three cats and one muffler.

Now if the dual 2.25 in pipes were merged into a 3-inch pipe prior to meeting the muffler, I could go with a single 3-inch in/single 3-inch out muffler.
 

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Discussion Starter · #9 ·
I'm not entirely sure if you're just playing or mocking my idea, but if it's the latter, I don't see what's so ridiculous about wanting to eliminate one muffler and three cats that represent probably 20 pounds or more of unneeded weight.
 

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I'm not entirely sure if you're just playing or mocking my idea, but if it's the latter, I don't see what's so ridiculous about wanting to eliminate one muffler and three cats that represent probably 20 pounds or more of unneeded weight.

im just jokin bro......nothing went wrong today and I just ordered a new set of tires.
 

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Is the magnaflow stuff pretty quiet?


Russ
 

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those were standardd turbo mufflers but you would need a fuel cell too lol
 

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I'm liking the idea of routing the dual 2.25" pipes into a midmount muffler as early as possible, and running single 3" straight out the back (well, as straight as our fuel tanks allow). I may mess with that myself when I get home.... should sound pretty "unique" as well ;)
 

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