is there any point in running 3" exhaust from my bell 2.5" dp? - Miata Turbo Forum - Boost cars, acquire cats.

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Old 07-07-2007, 12:14 PM   #1
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Default is there any point in running 3" exhaust from my bell 2.5" dp?

If its already bottle necked there, will the 3" from the dp back help at all? I know bigger is better in this respect, but its not going to get any better with this dp...right?

I'm looking at the 3" enthuza w/cat.
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Old 07-07-2007, 12:20 PM   #2
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i thought the bell dps were 2.75" but anyway it can't hurt, only reason not to go 3" would be for noise, but with a proper muffler and a resonator should be decently quiet
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Old 07-07-2007, 12:24 PM   #3
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Quote:
Originally Posted by Mach929 View Post
i thought the bell dps were 2.75" but anyway it can't hurt, only reason not to go 3" would be for noise, but with a proper muffler and a resonator should be decently quiet
64mm i.d.
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Old 07-07-2007, 02:48 PM   #4
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pipe size is measured by OD...

and go with the 3". less back pressure downstream is still good.
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Old 07-07-2007, 08:14 PM   #5
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If Enthuza's 3" fits without banging into anything and isn't too loud for you, they I agree with Y8S, 3" instead of 2.5" post turbo should give you a hp or two.
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Old 07-07-2007, 09:27 PM   #6
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do it!
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Old 07-08-2007, 12:52 AM   #7
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3" is the hotness....2.5" is so 2003.
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Old 07-08-2007, 01:08 AM   #8
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so a 2.5" ID is a what OD?
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Old 07-08-2007, 01:10 AM   #9
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about 2.75 I think.

But yeah 3" is the only way to go if you're turbo, not much louder than 2.5" and it's just so hot and gives you some more horses
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Old 07-08-2007, 01:15 AM   #10
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do it!
its done. Now I just have to pick up my $350 torsen swap, then decide if I need the 57mm rad or not...then there is nothing I need to buy.
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Old 07-08-2007, 02:33 PM   #11
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Quote:
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2.5" is so 2003.

clearly
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Old 07-08-2007, 04:53 PM   #12
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Has anyone dyno'd a car swapping a 3" for 2.5"? I just got my 2.5" and it looks huge for our tiny motors. Just wondering if the gain is proven or theory.

Not only do I drive a Miata, now I have to feel even less manly with my little 2.5" exhaust.
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Old 07-08-2007, 05:43 PM   #13
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Quote:
Originally Posted by RusMan View Post
about 2.75 I think.

But yeah 3" is the only way to go if you're turbo, not much louder than 2.5" and it's just so hot and gives you some more horses
oh... so i guess i have 2.5" ID Turbo Back
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Old 07-08-2007, 06:30 PM   #14
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FM, BEGi, and their supporters have always said it doesn't make any difference, but BEGi's new DP is a 2.75".... it probably isn't necessary on little turbos like the Greddy turbo and the gt2554r, but any bigger, and I'd run a 3".
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