Mates Rb25de

[chaser33sum]

Hey everyone

my mate is after an exhaust for his non turbo series one r33.

hes been told that a 2.25 inch system is ideal for his car.

would that size be too restricting and cause performance loss,

or on a non turbo application is it better to keep the exhaust piping larger

like a 3inch.?

cheers

[beamstas]

For non turbo you still want to keep some back pressure in your exhaust, so going to a 3" system you will lose power. 2.25" should be adequate.

[chaser33sum]

For non turbo you still want to keep some back pressure in your exhaust, so going to a 3" system you will lose power. 2.25" should be adequate.

cool thanks

[mad082]

also a 3" system on a NA car will be loud. like police hear you from 3 suburbs away and greet you with their night stick wrapped in course sand paper the give you a good reaming loud.

as for the ideal size, either 2.25" or 2.5" at the biggest would be good. unless he plans on doing track work, etc where he will be spending lots of time at high RPM he won't really notice the difference between 2.25" and 2.5".

to put it into perspective, a 4.0L falcon uses a 2.25" system as stock and 2.5" as a sports exhaust. so if they can flow enough air to work on a 4L engine reving to around 5000rpm, they should be fine on a 2.5L engine reving to around 7000rpm, as from an airflow point of view there isn't that much difference

[-Jimmy-]

I've got a 3" HKS Catback on my RB25DE and it's not loud at all.

Also got it dyno'd and reached 115rwkw.

It would be ideal to go for a smaller exhaust however I'm using what came with the car but I haven't seen any major disadvantages of having 3" and it certainly pulls hard.

Edited February 1, 2010 by -Jimmy-

[scathing]

I've got a 3" HKS Catback on my RB25DE and it's not loud at all.

Also got it dyno'd and reached 115rwkw.

It would be ideal to go for a smaller exhaust however I'm using what came with the car but I haven't seen any major disadvantages of having 3" and it certainly pulls hard.

What's it like in the midrange, compared to a car with a 2.25-2.5" exhaust?

On a street car having the car generating good power from 2000-4000RPM is better than making a bit of extra peak power at 5500-6000RPM.

[-Jimmy-]

From about 4k rpm onwards it pulls strongly, on a twisties run (for example old pac where I'm only using 2nd and 3rd) you can utilise all the power if you shift later in 2nd gear (almost on the limiter) and still be on the peak power when you shift into 3rd.

But it has it's ups and downs I guess. My bro's 34 with a 2.5" definitely is better down low.

[sh@un]

For non turbo you still want to keep some back pressure in your exhaust, so going to a 3" system you will lose power

it's really only the length of the primary pipes and the way they combine down that determines the cylinder-scavenging effect on NA engines. the system that would give the most power would be if the tuned-length extractors just exited out from the side near the front of the car. lowest back-pressure possible is the best scenario (it's just a pumping loss for the engine after all). i do realise that having to have a full ADR-legal exhaust system does present some issues regarding noise, cost, available space/ground clearance and to a lesser extent weight