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3 inch exhaust with n/a set up

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DaveJMK

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12
What's the general feeling about a 3 inch exhaust with a naturally aspirated set up?

Haven't got itb's or cams, but will have a toda header, 70mm rbc inlet Manifold, 70 skunk2 throttle body and injen cai intake and k100.

Will it make much more gains over a spoon b pipe or is it not really worth considering?

Thanks all
 
Well proven the K20 loves to breath heavily and 3 inch exhausts make good gains in power.
However, they're more noisy and can hang low. Get one made extremely well so it's as quiet and close to the floor as possible if you want half a chance of getting on track with noise limits and over the occasional speed bump.


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Thanks guys.

So do you think a Spoon B pipe will be sufficient should I decide to go for cams or itb's at a later date?
 
Unless you replace the exhaust manifold and cat too (or decat) with a similar diameter piping you're in exactly the same place since the mani and cat would be the choke-point.

For up to 230hp or so 2.5" is fine, if you're wanting more than that then you have other issues to worry about. Getting beyond 230hp from a 2.0L NA engine is going to get very costly though.

3" exhaust is overkill unless you're planning forced-induction.
 
To chip in with the above a 3" on K20s will make more power but at the cost of drone.
The difference isn't huge until you get into ITBs and cam territory where a 3" will certainly make the most out of them.

This is assuming the system also has an adtermarket header as OEM are easily the bottleneck.
 
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I have pretty much similar mods with 3" cat back and manifold made by solid fab. Mapped for 248.4hp and 175.5lft


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Good info thanks all.

What about that Smokehoes EP3 though. That's running cams and itb's using only a HKS Hi Power Catback. That car still makes 300bhp without using a 3" exhaust.

Thoughts
 
DaveJMK said:
Good info thanks all.

What about that Smokehoes EP3 though. That's running cams and itb's using only a HKS Hi Power Catback. That car still makes 300bhp without using a 3" exhaust.

Thoughts
Click to expand...
Take them figures with a pinch of salt. Also I think it's got a fully built engine with a slightly higher displacement.
 
DaveJMK said:
I think it may be a 2.1ltr engine actually. Would you still argue those figures despite this?
Click to expand...

It probably did make them figures on a dyno or very close to it. That set up was built a long time ago and I don't think this side of the world had recognised the potential of 3inch exhaust systems on the K20. It only had a HKS rear exhaust box. Centre section was 2 1/2 inch.
Also the smokehoes car was more of a 'scene' vehicle. Queer windscreen stickers and drive by YouTube videos rather than being used for what it looks to be built for. Sure the spec list is great for a magazine feature. Same vehicle with 60bhp less but more focused on handling set up would be a much better vehicle and quicker overall.
 
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