Exhaust sizing
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Agree, 2.5 is what I would run. Thats what I have on my H/C 6.0.
There are several "Engine Masters" videos that test some exhaust sizes, manifolds, and mufflers, on youtube and the motortrend on demand app They never tested 2.0" because, well, no one runs pipe that small usually. At 600HP, there was, I think, a ~15HP drop from 3.0" to 2.5".. I would guess dropping to 2" on a 400HP motor (Which would pretty much be stock, if talking crank engine dyno HP), would be hurting probably 15-25hp over 2.5" (2.5" is ~55% bigger than 2.0", on paper).. Mufflers can have a big impact as well.
There are several "Engine Masters" videos that test some exhaust sizes, manifolds, and mufflers, on youtube and the motortrend on demand app They never tested 2.0" because, well, no one runs pipe that small usually. At 600HP, there was, I think, a ~15HP drop from 3.0" to 2.5".. I would guess dropping to 2" on a 400HP motor (Which would pretty much be stock, if talking crank engine dyno HP), would be hurting probably 15-25hp over 2.5" (2.5" is ~55% bigger than 2.0", on paper).. Mufflers can have a big impact as well.
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I did just about 400 at the crank (NOT at the wheels) on a 5.3 through a full 2.5" exhaust with knockoff flowmaster mufflers and less than 2" diameter in the crimped bends after the mufflers.
If those are 2" mandrel bends it'll be fine. If they are crimped, they will probably be necked down to 1.5" in some places.
If those are 2" mandrel bends it'll be fine. If they are crimped, they will probably be necked down to 1.5" in some places.
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From: Ohio
True, but a 2" full mandrel exhaust isn't likely to be any more restrictive than one that is 2.5" back to the edge of the floor pan and then 1 5/8" over the rear diff and out the back. I think he will be fine.
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Verdad Gallardo TECH Senior Member
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From: Central Cal.
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Also, its most important in the front section, up to the mufflers, where often some cooling has occurred. Its less critical on the size for the last few feet. So if you have an application where you want to keep a certain appearance, like stock exhaust tips on an old corvette or something, it'd likely not hurt much to go small at the end.
I thought about this but just the opposite, if 2.5" factory exhaust size is good for 550 plus HP on a CTS-V then would 2" be ok for 400HP CTS V8. Looks like mixed opinions. I think I will scab into the 2" for now then next year get the Chinese CTS-V 2.5" aftermarket on evil bay or find used CTS-V exhaust locally, i find used CTS-V exhaust everywhere but near me and shipping it cost more than the exhaust itself.
Besides that -- you have to look at the cross sectional area for an idea of flow comparison. Nominally, dual 2" pipes have 6.28 sq inches of cross sectional area. Dual 2.5" pipes have 9.81 sq inches of cross sectional area. So IF 550HP was non-restrictive with 2.5" duals, the Hp to area comparison would be 2" duals supporting 352 HP --- so even using your example, 2" would be restrictive.
Don't get me wrong -- you can do it. And I doubt you'd be leaving a huge amount on the table. But the engine output would benefit from having dual 2.5's compared to dual 2".
Last edited by Michael Yount; Oct 4, 2019 at 04:45 PM.
Ford uses 2.75" duals on the 440HP 5.0L Coyote. Just because the factory/GM used 2.5" piping on the 550HP motor doesn't mean that they didn't leave something on the table by not going bigger. They're trying to manage a myriad of conflicting variables when building a car like that -- managing space being a big piece of it.
Besides that -- you have to look at the cross sectional area for an idea of flow comparison. Nominally, dual 2" pipes have 6.28 sq inches of cross sectional area. Dual 2.5" pipes have 9.81 sq inches of cross sectional area. So IF 550HP was non-restrictive with 2.5" duals, the Hp to area comparison would be 2" duals supporting 352 HP --- so even using your example, 2" would be restrictive.
Don't get me wrong -- you can do it. And I doubt you'd be leaving a huge amount on the table. But the engine output would benefit from having dual 2.5's compared to dual 2".
Besides that -- you have to look at the cross sectional area for an idea of flow comparison. Nominally, dual 2" pipes have 6.28 sq inches of cross sectional area. Dual 2.5" pipes have 9.81 sq inches of cross sectional area. So IF 550HP was non-restrictive with 2.5" duals, the Hp to area comparison would be 2" duals supporting 352 HP --- so even using your example, 2" would be restrictive.
Don't get me wrong -- you can do it. And I doubt you'd be leaving a huge amount on the table. But the engine output would benefit from having dual 2.5's compared to dual 2".
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How is the car being used ?
Just a cruiser ? .....2" will be fine IF you had 600 (just don't expect max effort)
Street and strip, will be maxed out quick at the strip
Strip....no way would I do it.
My 2.5" American Thunder kit went 10.9's in a 3420# w/ me.... shows 400-450 @ the wheels depending on which calculator you use.
Just a cruiser ? .....2" will be fine IF you had 600 (just don't expect max effort)
Street and strip, will be maxed out quick at the strip
Strip....no way would I do it.
My 2.5" American Thunder kit went 10.9's in a 3420# w/ me.... shows 400-450 @ the wheels depending on which calculator you use.
How is the car being used ?
Just a cruiser ? .....2" will be fine IF you had 600 (just don't expect max effort)
Street and strip, will be maxed out quick at the strip
Strip....no way would I do it.
My 2.5" American Thunder kit went 10.9's in a 3420# w/ me.... shows 400-450 @ the wheels depending on which calculator you use.
Just a cruiser ? .....2" will be fine IF you had 600 (just don't expect max effort)
Street and strip, will be maxed out quick at the strip
Strip....no way would I do it.
My 2.5" American Thunder kit went 10.9's in a 3420# w/ me.... shows 400-450 @ the wheels depending on which calculator you use.