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Is It Possible To Have A 3" Exhaust And Still Make Power?

Mid_Nite_R33
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Brezza Proficient

Brezza

Posted
Posted

ive got a r32 GTR with trust front pipes, not sure on the diameter? but its around 2.25 ot 2.5" to a 3"decat and a 3" custom cat back with one 3.5" muffler, which is the oval type, not sure about the brand off the top of my head? all stailness too

but its quiet in low to mid range, but in top end it screams.

never had any issues from the cops with it being too loud, its a deeper note than with a cannon.

i got 319rwkw @ 18psi

so 3" is okay for over 300kw, maybe not totally ideal?? but it does the job and keeps the sound low.

Harey Veteran

Harey

Posted
Posted (edited)
Personally I think the greatest gains are from being larger in the first 1/3 to 1/2 of the exhaust system .

The gasses are pretty hot out of the turbo on full load so giving them some volume to expand into seems to work .

The gasses cool and contract (increase in density) quite quickly and you can afford to go a bit smaller in tube size toward the rear half of the exhaust system . Usually the cat and mufflers are back there anyway so 3.25 or 3" mufflers should be reasonably easy to fit .

Cheers A .

+1

Except for the comment about the cat. I think the cat is very important. After all it is the second component in the line after the dump pipe. I think it is a lot more important than the mufflers.

Edited by Harey
Harey Veteran

Harey

Posted
Posted (edited)
ive got a r32 GTR with trust front pipes, not sure on the diameter? but its around 2.25 ot 2.5" to a 3"decat and a 3" custom cat back with one 3.5" muffler, which is the oval type, not sure about the brand off the top of my head? all stailness too

but its quiet in low to mid range, but in top end it screams.

never had any issues from the cops with it being too loud, its a deeper note than with a cannon.

i got 319rwkw @ 18psi

so 3" is okay for over 300kw, maybe not totally ideal?? but it does the job and keeps the sound low.

2.5" cross sectional area = 19.63 cubic inches

2.25" cross sectional area = 15.90 cubic inches

3" cross sectional area = 28.27 cubic inches

3" < 2 * 2.5"

28.27 < 39.27

3" ~= 2* 2.25"

28.27 ~= 31.81

So if your dump pipes are 2.25" then I think the 3" decat pipe is fine. However, if the dump pipes are 2.5" then the 3" decat pipe is quite a drop in size.

The only real life test would be to drop the decat pipe and see.

Edited by Harey
discopotato03 Grand Master

discopotato03

Posted
Posted

My maths work like this .

Area of a circle is Pi x radius squared so ...

2.25" = 3.976 square inches .

2.50" = 4.909 square inches .

3.00" = 7.068 square inches .

Tube is usually measured in OD and last time I measured 2.25 and 2.5" exhaust tube had a wall thickness of ~ 1.9mm and 3" ~ 1.6mm .

You're only going to get exhaust pulses one at a time from each dump so its not like a constant flow from both at the same time .

A .

Harey Veteran

Harey

Posted
Posted
My maths work like this .

Area of a circle is Pi x radius squared so ...

2.25" = 3.976 square inches .

2.50" = 4.909 square inches .

3.00" = 7.068 square inches .

Tube is usually measured in OD and last time I measured 2.25 and 2.5" exhaust tube had a wall thickness of ~ 1.9mm and 3" ~ 1.6mm .

You're only going to get exhaust pulses one at a time from each dump so its not like a constant flow from both at the same time .

A .

So a 3" pipe has a thinner wall??

R31Nismoid Grand Master

R31Nismoid

Posted
Posted

I've never seen a skyline pass with 1 mufflers + hod-dog.

You need two mufflers and that means using the space where you'd put a hot-dog, for as big of a muffler as possible.

EPA reporting works on suspicion only, there is no fact when the Police report you.

They just have to "think" you are illegal, which is utter bullshit to be honest, but thats life... Next time i get reported and i pass im going to take the cops to court adn try my luck :blink:

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