2.5" bore vs 3" bore

[Dean Mac]

Ktec's KTR Pro CAT Back Exhaust has a 2.5" bore, and the Milltek CAT Back Exhaust has 3" bore.

With the bore being larger on the Milltek...could you argue that the performance will be greater, when compared to the Ktecs 2.5" bore, due to the exhaust gases being released more efficiently...

Will the sound be amplified on the Milltek with it being a larger bore?

Apologies if this question has been asked. :blowup:

 

[shakey_hand_man]

I'm surprised if it is 3", but a 2.5" bore system can flow efficiently at over 300bhp

for Normally Aspirated -back pressure is key to optimise torque and power. The akrapovic is 2.5" but gives a very widespread torque and power increase, by managing the back pressure not to low for low engine speeds and not too restrictive at high engine speeds.

If a system were to have a very low back pressure then you would normally lose low end torque, but make good power at top end...


i don't know the exact pros and cons to back pressure affecting engine scavenge, but someone else may be able to help
-Andy

 

[ryan197]

miltek aint 3" bore

 

[Dean Mac]

miltek aint 3" bore

I see. My mistake. It has 3" tailpipes though...

 

[Foxspeed]

I'm surprised if it is 3", but a 2.5" bore system can flow efficiently at over 300bhp

for Normally Aspirated -back pressure is key to optimise torque and power. The akrapovic is 2.5" but gives a very widespread torque and power increase, by managing the back pressure not to low for low engine speeds and not too restrictive at high engine speeds.

If a system were to have a very low back pressure then you would normally lose low end torque, but make good power at top end...


i don't know the exact pros and cons to back pressure affecting engine scavenge, but someone else may be able to help
-Andy

back pressure in the exhaust bit of a myth - you want the gases removed as easily as possible - if not you are using engine power to do it...

modern exhaust have a massive restriction its called the catalytic converter - they are designed and fuelled to work with this "back pressure" in the system thats why once removed they seem to lose or flat spot as the fueling etc is wrong..

the pinicle of engines - f1 dont use any restrictions in their systems and usually run a 4-1 manifold which produces better top end power/torque

only 2-strokes use a form of back pressure in the exhaust

the 2.5 exhaust is plenty and to be honest its not all about pipe diameter!

 

[Willis]

back pressure in the exhaust bit of a myth - you want the gases removed as easily as possible - if not you are using engine power to do it...

modern exhaust have a massive restriction its called the catalytic converter - they are designed and fuelled to work with this "back pressure" in the system thats why once removed they seem to lose or flat spot as the fueling etc is wrong..

the pinicle of engines - f1 dont use any restrictions in their systems and usually run a 4-1 manifold which produces better top end power/torque

only 2-strokes use a form of back pressure in the exhaust

the 2.5 exhaust is plenty and to be honest its not all about pipe diameter!

+1.

A degree of back pressure is beneficial in the manifold to aid scavenging (from what I've read) but beyond that the less the better. Bigger pipes do not always mean bigger power and 2.5" is more than adequate for a 2.0 NA engine running ~100BHP/Litre, infact it's more than adequate for most of the FI engine'd cars on here too.

 

[Dean Mac]

Great replies...

So, no cat = power gains?

As long as the ktec cat back exhaust enhances power in some way, and graces my presence with PHAT exhaust melodies, then I'm all goooood

 

[Willis]

So, no cat = power gains?

Not without a Remap, you'll get more rasp but that's about it.

These aren't easy engines to get more power from, Cat-Back will probably give you 4-5BHP without a Remap. With a Decat, Remap and Cat-Back then you'll be lucky to see an extra 10-12BHP peak... You're looking at around £100 per 1 BHP extra on these. It's not the best bang per buck ratio!!!

 

[shakey_hand_man]

With a zero back pressure system the peak power and torque would be the highest achievable, but the car would be down on low end torque.

Sorry this is an example of what I meant, (not a Clio but an N/A 370z) The engine is down on power and torque up to about 3250rpm over the standard (more restrictive system):

Website for the image: http://www.zshop.ca/parts/370z-ap-catback-exhuast/ the last sentence also

 

[Foxspeed]

not mapped or fuelled to suit the new exhaust then...

 

[shakey_hand_man]

not mapped or fuelled to suit the new exhaust then...

probably not :jase2: