Exhaust Back pressure

[CommVTS]

Sounds good man, all i'm doing to mine now is a chip then saving for LS1.

 

[HamaTime™]

What chip are you getting mate? I'm going for a Delcowizzid tune (guy off this forum). What were you thinking of?

 

[feistl]

Back pressure is bad in any situation. It just loads up the engine and makes it work harder.

Exhaust velocity is what you need. Extractors achieve this better than any exhaust system on it's own can. The reason they are called extractors is they 'extract' exhaust gas from the cylinders. As each exhaust pulse travels down the header tube it creates a low pressure point behind it, as this pulse passes through the collector it draws the next pulse in the firing order out of it's header tube. All these pulses need to maintain a certain velocity as they travel along the exhaust system to help draw the next pulse along behind it.

Once the exhaust gas cools it takes up less space, so to keep the velocity going, you will need to reduce the size of the exhaust pipe the further you go from the engine. Too small and it creates a restriction thus causing back pressure. Too large and the cooler exhaust loses velocity and the pulses behind it bank up and end up pushing the exhaust out, this is back pressure too.

A 2 1/2" cat back system really needs a smaller tail pipe to maintain good velocity and reduce back pressure. People confuse back pressure with velocity, thinking that they are adding back pressure and increasing engine performance, but what they are doing (sometimes) is keeping velocity.

Restricting the exhaust can give the impression of more power, but all you are doing is throwing in more fuel so it feels like there is an increase in performance.

Wow great post mate.

Little off topic, but would my exhaust be causing a restriction?

Its a 6.3L LS1 with Pacemaker Extractors 4 into 1s (3") with a 3" section into dual high flow cats (4.5" body, 100cpsi) then going back into a 2.5 twin system (full stainless steel). I was worried that it was 2.5" after the cats, but by this post would that be an advantage?

Engine is making around 330rwkw. Is it worth upgrading to dual 3" system?

Cheers

(Sorry for hijacking)

 

[Not_An_Abba_Fan]

Wow great post mate.

Little off topic, but would my exhaust be causing a restriction?

Its a 6.3L LS1 with Pacemaker Extractors 4 into 1s (3") with a 3" section into dual high flow cats (4.5" body, 100cpsi) then going back into a 2.5 twin system (full stainless steel). I was worried that it was 2.5" after the cats, but by this post would that be an advantage?

Engine is making around 330rwkw. Is it worth upgrading to dual 3" system?

Cheers

(Sorry for hijacking)

If you want good dyno figures put the 3" twin on as dynos like a big exhaust. For street drivability and punch off the line, keep your 2 1/2".

You will find your top end improve a bit with the 3" but you will lose low end torque as what you are doing is losing a bit of exhaust velocity. I would keep what you have.