2.5 vs 3 inch downpipe again?
Jan 13, 2005, 11:18 AM
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2.5 vs 3 inch downpipe again?
I know that there has been a lot of discussion regarding the merits of a 2.5 vs 3 inch downpipe.
I am, however not planning to mod my car much and would prefer not to have to deal with fitment problems, rattles, hot oil pans, tiebars etc.
My question is, would there be any concerns linking a 2.5 inch downpipe to a 3 inch hi-flo cat and 3 inch catback?
If there is a little loss in high end power, I'm prepared to accept that, but are there other issues that might crop up?
I am, however not planning to mod my car much and would prefer not to have to deal with fitment problems, rattles, hot oil pans, tiebars etc.
My question is, would there be any concerns linking a 2.5 inch downpipe to a 3 inch hi-flo cat and 3 inch catback?
If there is a little loss in high end power, I'm prepared to accept that, but are there other issues that might crop up?
Jan 13, 2005, 01:20 PM
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Originally Posted by nataku_CT9A
the 2.75 is the best you can get for your car if you have stock turbo
Last edited by TC4G63; Jan 13, 2005 at 01:27 PM.
Jan 13, 2005, 01:26 PM
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Originally Posted by DarrenJ
I know that there has been a lot of discussion regarding the merits of a 2.5 vs 3 inch downpipe.
I am, however not planning to mod my car much and would prefer not to have to deal with fitment problems, rattles, hot oil pans, tiebars etc.
My question is, would there be any concerns linking a 2.5 inch downpipe to a 3 inch hi-flo cat and 3 inch catback?
If there is a little loss in high end power, I'm prepared to accept that, but are there other issues that might crop up?
I am, however not planning to mod my car much and would prefer not to have to deal with fitment problems, rattles, hot oil pans, tiebars etc.
My question is, would there be any concerns linking a 2.5 inch downpipe to a 3 inch hi-flo cat and 3 inch catback?
If there is a little loss in high end power, I'm prepared to accept that, but are there other issues that might crop up?
BTW - hot oil pans wouldn't be an issue for you if you aren't going to really mod your evo or do some serious racing.
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Jan 13, 2005, 03:56 PM
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Originally Posted by 4-BNGR
Find the Buschur thread on this topic. He's done dyno comparisons of both...
The big restrictions are the turbo housing and catalytic,
The big restrictions are the turbo housing and catalytic,
Jan 13, 2005, 04:01 PM
#9
How is 3" exhaust alone gonna make more power and more torque than 2.75" exhaust?
you need 3" intake in order for you to take full advantage of 3" exhaust. And you need an a/f tunning in order for you to take full advantage of the intake.
I'd say just get 3" just in case you're going to do intake mod, then you don't need to mod later on.
you need 3" intake in order for you to take full advantage of 3" exhaust. And you need an a/f tunning in order for you to take full advantage of the intake.
I'd say just get 3" just in case you're going to do intake mod, then you don't need to mod later on.
Jan 13, 2005, 09:39 PM
#10
Less restriction will ALWAYS make more power on a turbo car. You may not FULLY utilize it but it will make more power. There is NO reason power wise to get anything smaller than 3" Most 3" DO have SLIGHT fitment problems (DAMN near rubbing on the oilpan or the tie-bars but its not that bad). If you are honestly that concerned about a tiny rub when going over speedbumps then get a 2.75". But 3" really doesnt have any fitment problems on all the DP's Ive seen or used. Get 3" so you dont sell the 2.75 later 
Trust me on that one.
Trust me on that one.
Jan 13, 2005, 09:41 PM
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With the size of the oil cooler the EVO runs, I doubt overly hot oil will be a problem. Not to mention that unless your sitting still, there is air flowing through the engine compartment, so its not like the heat from the DP is sitting there boiling the oil.
Last edited by 1.8t; Jan 13, 2005 at 09:43 PM.
Jan 14, 2005, 01:35 PM
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Originally Posted by 1.8t
With the size of the oil cooler the EVO runs, I doubt overly hot oil will be a problem. Not to mention that unless your sitting still, there is air flowing through the engine compartment, so its not like the heat from the DP is sitting there boiling the oil.
Back on-topic I keep hearing that 2.75" will optimize the torque down low and still give a good flow increase. Despite this thought I still bought 3" turbo back from BR.
Jan 14, 2005, 01:58 PM
#14
I don't think you guy's have searched....
To keep the exhaust velocity up you need to go from smaller diameter to larger diameter as the exhaust gas cools and expands.
Asuming a 3" cat back, the folowing is true:
The exit hole of the stock o2 housing is 2.5" and the stock cat is 2.5".
If you keep these two items (or add 2.5" hi-flow cat or 2.5"delete), a 2.5" dp. will flow better than a 3" dp.
Keeping the stock o2 and jumping to 3"dp. with a 3" hi-flow or delete will out flow the above set up.
The most power will come from a 3" o2> 3" dp>3" hi-flo/delete.
If this is incorrect please speak up, as this is what I have read from the discussions on this board.
To keep the exhaust velocity up you need to go from smaller diameter to larger diameter as the exhaust gas cools and expands.
Asuming a 3" cat back, the folowing is true:
The exit hole of the stock o2 housing is 2.5" and the stock cat is 2.5".
If you keep these two items (or add 2.5" hi-flow cat or 2.5"delete), a 2.5" dp. will flow better than a 3" dp.
Keeping the stock o2 and jumping to 3"dp. with a 3" hi-flow or delete will out flow the above set up.
The most power will come from a 3" o2> 3" dp>3" hi-flo/delete.
If this is incorrect please speak up, as this is what I have read from the discussions on this board.
Jan 14, 2005, 02:17 PM
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Originally Posted by TrinaBabe
(DAMN near rubbing on the oilpan or the tie-bars but its not that bad).