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Discussion Starter · #1 · (Edited)
hi everyone i have a 99 mustang v6 and i recently add mac long tubes headers and i have gt take off tails whit flow 40s but not sure what size piping should i go whit them, im ready to have a shop customize the true duals but not sure about the piping size, does anybody has an advise ill appreciated it. thanks in advanced.
 

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2.25" piping is fine for bolt-ons and such but if you plan on forced induction or H/C/I go with 2.5"
 

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Honestly I'd go with 2.5 if you plan on any mods, even without FI you'll make enough power to not make the larger size harmful. Most sixxers with aftermarket exhaust have 2.5". Most (or all) shops, especially the simple muffler shops or whatever will always say 2.25" because that's stock.
 

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I got a question. Does it pay to get mandrel bent exhaust, or just the regular shop bent ones? I just was curious. Im sure you will get better flow with the mandrel bends but is it worth it to pay more?
 

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Mandrel bending is definitely worth it, you get better sound and flow.

OP, I don't think you will be able to use the longtubes if you go FI either, so keep that in mind.
 

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alright thanks. and i believe you can use lts if you go supercharger. you cant with a turbo cuz you will need turbo manifolds.
 

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Discussion Starter · #9 ·
thanks guys the reason i wanted to ask too is because i read on another forum that 2.5 piping make your car loose some torque in the 94 -98, but i have a 99 if that make any difference? but if you guys use it and had no problems then i guess that's the way to go.
 

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with 2.5" piping and hi flow or no cats you will lose some backpreassure. With normals cats you shouldnt see too much difference.

You can use LTs with any type of FI except turbo.
 

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i have 2.25 without any cats and an X pipe with flowmaster 40's and i love it. it is a little high pitched but it flows just enough to keep some back pressure for the low end and still flow at the top.
 

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I mean i dont want to be some old man or something but i dont understand taking the cats out. I understand maybe the front set cuz our cars have two. But for the little difference in sound and the itsy bitsy freed up power supposidly it aint worth it to kill the enviornment. I mean if it is a track only car then go ahead. But otherwise i think we should try to save the planet for our kids and their kids. just my opinion, since the gain in sound and performance is minimal.
 

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i've heard that 6ers sound like **** with cats off. i think i read it on the super six website. cant remember where exactly
 

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ha ok sure the planet might be messed up but it just seems dumb to remove the cats unless your running a turbo. if you want the sound of catless car put some cutouts before the cats so you can switch back and forth. that way at least it is not always catless.
 

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ha ok sure the planet might be messed up but it just seems dumb to remove the cats unless your running a turbo. if you want the sound of catless car put some cutouts before the cats so you can switch back and forth. that way at least it is not always catless.
but then you cant run no cats with mufflers.
 

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Discussion Starter · #17 ·
ok so what setup will be the best 1= 2,5 whit cats and flowmasters 40s( beacuse whit out the cats will be lost of back pressure) or 2= 2.25 whit out cats and the flowmasters 40s (remember i already install the macs long tubes) i just want to get sound and performance. i have a cai and 70mm tb. or maybe the 2.5 whit hi flows cats?
 

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as long as he has some type of muffler then he won't have any problem even with no cats..
Ok well I have the same LTs he has, with 2.5" piping and MAC mufflers. I do notice backpreassure loss. Now maybe its the MAC mufflers, dont know for sure. And I DO have hi flow cats.

So I can say with 80% certainty that without cats he would have some backpreassure issues.
 

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def. 2.5" piping. The back pressure loss without cats will be negligible. Most people in non-emissions states go without cats, that's for a reason.
 
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