Are shorty headers or long tubed headers better for my 98 z28. Plus how much of a difference is there between an offroad y pipe compared to a y pipe with high flow cats. I just want to know i will still be able to pass emissions. What would i need?

 

Where are from and how do they test cars in your area? Long tubes and an ORY will offer the most gains (around 20-30 hp depending on your other mods). If emission testing is a huge concern then MAC midlenths and high flow cats are a decent option. You can tune the PCM to "think" the car still has cats and not though a code, in some states (like mine) all they do is plug into the OBD II port and check for codes, no codes and you pass just fine.

 

Headers provide more power through two means. First, they provide a smoother path for the exhaust flow and make it easier for it to exit the engine: hence more power. All headers do this, but this adds only about 5-10 HP. Second, they "tune" the exhaust for a type of exhaust pressure resonance which actually assists the exhaust valve function within a certain RPM range usually a range from some RPM (say 3000) to about twice that RPM (say 6000) adding a further 15-20 HP.

This gets very complicated as to how and why this resonance works, but it really does work and on some gran prix racing engines, almost a third of the exhaust outlet timing in the power band is accomplished by header resonance, not valve action (one reason why a FI race car is dead meat if its headers break).

The overall engineering rule is::: the longer the length of the header tubes from flange to collector, the lower the RPM at which this tuning kicks in with added power, and the lower that RPM limit where it stops helping the engine. On a typical LS engine, headers about 28 inches long gradually kick in with this extra HP starting at about 3000 RPM, peaking at about 4500, and gradually stop providing that power gain beyond about twice that RPM (6000), by contrast, shorty headers (say 16 inch length, only kick in at much higher RPM, about 5500-6000, and would peak at about 8000 RPM, and would only stop providing gain at around 10000 RPM. But since the LS1 engine is typically only run to 6500, this means shorty headers provide only a little added power at the very top end RPM, so its not very usable.

It is also best not to get to wide of a tube, otherwise you kill low end torque: 1 3/4 inch is best unless you have a heavily modded engine at more than about 400 RWHP, then you want 1 7/8 tubes, and above about 800 HP you want 2 inch tubes.