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Three Inch Exhaust - Can it work on N/A??

pulpmelon_R

pulpmelon_R

Messages
227
Afternoon all

I wanted to draw on any experience on the forum of those that are currently running, tested or are thinking of trying out a 76mm exhaust on a NASP K20?

It seems to be common law in the USA with all of their K-swapped eg's and ek's along with the K-native RSX to run a 3"er after fitting the usual bolt-ons (intake, header, RBC, etc etc)

Is this something we in the UK are overlooking??

Many thanks
 
Basically is it worth running a 3" exhaust system on a NA setup.

Most systems are around the 2.5" mark, so would you see any decent gains by changing to a 3".
 
Didn't G run a Skunk2 one for a while on his EP3?? I'm sure it was designed to be run on N/A though, but he did say it would work better on Boosted/Charged engines.
 
CPL are making one this weekend for a K swapped EK, the pics are on their facebook, im sure their will be results out once mapped
 
I thought the risk was that using a 70mm bore exhaust with a NA engine would cause a drop in torque due to a decrease in backpower?
 
stoneyni said:
CPL are making one this weekend for a K swapped EK, the pics are on their facebook, im sure their will be results out once mapped
Click to expand...

Will keep an eye on that one.

It's interesting that the general opinion is negative. There's quite a lot of discussion on the topic, with some 'back to backs' on 8thcivic.com that suggest 2.5" to 3" is worth 5 -7hp?
 
Read the sticky on the k20... 2.5" has been found to be optimal for the k20, any bigger or smaller will see power and torque drop

3" is ideal for fi cars which also nof course are remapped

Remember the the US k20 variant is a slightly different beast to the ukdm one
 
Hi Mjhamilton.

The K20a2 in the USDM RSX is the exact same engine as the ep3, the only minor differences are in the ECU (USDM runs a wideband o2 sensor) and the final drive ratio in the gearbox is longer (4.4 as opposed the 4.7 in the UKDM ep).

Also I think that sticky info is a few years old now, the boundaries have been pushed to the point that we have 9 second all motor K-series cars on the quarter mile (running open header I might add).

I guess I just wanted to challenge what seems to be a closed case in most people’s mind, and try out something that is unorthodox!
 
pulpmelon_R said:
Hi Mjhamilton.

The K20a2 in the USDM RSX is the exact same engine as the ep3, the only minor differences are in the ECU (USDM runs a wideband o2 sensor) and the final drive ratio in the gearbox is longer (4.4 as opposed the 4.7 in the UKDM ep).

Also I think that sticky info is a few years old now, the boundaries have been pushed to the point that we have 9 second all motor K-series cars on the quarter mile (running open header I might add).

I guess I just wanted to challenge what seems to be a closed case in most people’s mind, and try out something that is unorthodox!
Click to expand...

You are right.. But I did say it was a variant of the k20 which is true... Different mapping and management systems make for a different engine experience even as you correctly point out the mechanicals are the same
 
After some research i'm confident that it's worth a shot.

TDI-N have the ability to fabricate headers, exhausts and and custom pieces for engine swaps and turbo kits, I have asked them to make up a 3" header back system for next week. We will do a before and after dyno run to prove / disprove the performance gains of a big exhaust on an N/A k20!
 
If you buy the corect bolt on's to accomodate the 3" exhaust I suppose you could see benifits over having a 2.5' system.

Good on you for trying mind, deeps pockets I hope.

Mugen did a test on the F20 showing that the optimal average size for NA tunes was 72mm IIRC (I'll see if I can dig out the page), goes to show that the tunning houses plough plenty of R&D into their work to make the best possible aftermarket performance parts. Perhaps thats a sign that the anything towards 3" is a move in the wrong direction.
 
Ped said:
Will you need to get a port and polish to mate nicely a 3inch header?
Click to expand...

I say header back, because I dont have a cat.

Its probably a good idea to illustrate that i'm not suggesting that you slap a 3" exhaust on a stock CTR to make power!

My spec list:
3" injen intake with BPI velocity stack
70mm throttle
Skunk2 IM
Prayoonto stage 2 cams
supertech flat face valves
spoon skinny head gasket
piper header
piper 2.5" exhaust
kpro

Makes 270hp @ tdi-north
 
rm cya said:
3" works well. with just bolt ons aswel.
Click to expand...

This is what most of the US based forums are saying.

To reference Suits post about mugen, if they settled on 72mm for the F20's ideal exhaust. A K20 with bolt-ons and cams should love 76mm.

But hey I guess we'll find out next week.
 
So your keeping your OEM Exhaust manifold/Cat? The Manifold does most of the improved power when replaced and mapped. Catbacks sound good and in theory let out a few bhp. But and improvement on a 2.5 up to a 3 will be zero if not lose some need back pressure?
 
Surely if your looking to get the most power from your mods you won't be keeping your manifold and cat. That will be swapped out for a race header then a 3" catback fitted.

But if all your after is induction and exhaust... Then yeah settle for either just a generic catback/backbox.
 
pulpmelon_R said:
I say header back, because I dont have a cat.

Its probably a good idea to illustrate that i'm not suggesting that you slap a 3" exhaust on a stock CTR to make power!

My spec list:
3" injen intake with BPI velocity stack
70mm throttle
Skunk2 IM
Prayoonto stage 2 cams
supertech flat face valves
spoon skinny head gasket
piper header
piper 2.5" exhaust
kpro

Makes 270hp @ tdi-north
Click to expand...

Ped said:
So your keeping your OEM Exhaust manifold/Cat? The Manifold does most of the improved power when replaced and mapped. Catbacks sound good and in theory let out a few bhp. But and improvement on a 2.5 up to a 3 will be zero if not lose some need back pressure?
Click to expand...

rm cya said:
Surely if your looking to get the most power from your mods you won't be keeping your manifold and cat. That will be swapped out for a race header then a 3" catback fitted.

But if all your after is induction and exhaust... Then yeah settle for either just a generic catback/backbox.
Click to expand...

He's already said he has a Piper header fellas.
 
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