Increasing Exhaust Diameter
Thread Starter
Drifting
Joined: Nov 2002
Posts: 1,455
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From: East TN
Increasing Exhaust Diameter
I was wondering how my setup is going to affect performance. I have 1 3/4 EM LT headers going into some EM 2.5 inch extensions that are coupled into some 2.5 inch RT cats. The cats meet up with a 3 inch magnaflow X pipe and finally some 3 inch magnaflow mufflers.
Does increasing the diameter like this from 1.75-->2.5--> 3 inch make any difference in performance...will I loose some low end torque by doing this? Would it be better to keep the same diameter all the way through or does it not make a noticeable difference?
Does increasing the diameter like this from 1.75-->2.5--> 3 inch make any difference in performance...will I loose some low end torque by doing this? Would it be better to keep the same diameter all the way through or does it not make a noticeable difference?
Team Owner
Joined: Dec 2000
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From: SE NY
Cruise-In II Veteran
The individual 1 3/4" header tubes merge into the larger exhaust pipe at the collector; this is where the tuning occurs which provides the scavenging pulses.
Beyond that it really doesn't matter if you increase exhaust pipe size as the engine only "sees" the smallest pipe, in this case 2 1/2". Some may argue that the gasses will lose velocity when going into the larger pipe but that is inconsequential to performance as volume of gas flow will remain constant.
We are concerned with air velocity in two places: 1) in the intake for the ram air effect to increase VE and maintain low end torque and 2) in the exhaust tubes to maximize scavenging effects.
Beyond that it really doesn't matter if you increase exhaust pipe size as the engine only "sees" the smallest pipe, in this case 2 1/2". Some may argue that the gasses will lose velocity when going into the larger pipe but that is inconsequential to performance as volume of gas flow will remain constant.
We are concerned with air velocity in two places: 1) in the intake for the ram air effect to increase VE and maintain low end torque and 2) in the exhaust tubes to maximize scavenging effects.
Team Owner
Joined: Sep 2001
Posts: 62,097
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From: Athens AL
C7 of the Year - Unmodified Finalist 2021
C4 of Year Finalist (performance mods) 2019
Yes, it makes a difference in flow velocity, which directly impacts performance. Ideally you would like the pipe size to slightly decrease along the exhaust's path.
Increasing tube size slightly improves top-end, while cutting low-end a little.
Its doubtful that youll notice it, but it would show on a dyno.
Increasing tube size slightly improves top-end, while cutting low-end a little.
Its doubtful that youll notice it, but it would show on a dyno.
Team Owner
Joined: May 2002
Posts: 24,337
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From: San Diego , CA Double Yellow DirtBags 1985..Z51..6-speed
The 1-3/4 to 2.5" is actually a reduction. As the exhast gasses cool, you want smaller pipes to keep the velocity up.
So, the 3" xpipe back is oversized. I don't think it's hurting you much though, but it defeats the point of having an xpipe.
So, the 3" xpipe back is oversized. I don't think it's hurting you much though, but it defeats the point of having an xpipe.
