[mlee]

Originally Posted by BMWM.D.

This is why I mentioned possible false knock. I’ve heard of it happening to people from very minor exhaust modifications. The knock sensors on the gen V motors are very sensitive.

Definitely seen that and this is 3" as well, but then fit and finish of Corsa is as good as it gets and the double helix keeps things nice and tight too.

I read the title and thought we were going to see a dyno compare. Even if there was power decrease in a catback I seriously doubt it could be felt.

Definitley interested in hearing the sound video. Had my eye on this exact system.

I'm pretty good at the garage door down sneaking out, but @ 4:30 am you can hear crickets. Glad I have good neighbors.

[soceur77]

I too just installed a xpipe and catback and felt like I loss power....lazy was the exact word I would use as well. I did notice when in manual mode I allow the gears to wind out more than when I was stock. The only way I can describe it is for most of us im sure can tell when to switch gears by sound alone, when it was stock anything over 3krpm sounded like I was trying to race, now 3k seems tame and ill switch gears or even leave it in gear in certain circumstances if that makes sense. But yea my car def feel slower at low to mid speeds.

[Rlhay2]

For those that installed the Corsa double-X themselves: Can the stock exhaust be removed with a Sawzall or is the chain style pipe cutter necessary?

[Stealth7]

I think the increased flow causes some lack of back pressure resistance and that is what is probably being felt. this does not, however, mean that there is less power, especially horse power. I will report once my system is installed.

[Can'tHave2MuchHP]

Originally Posted by Rlhay2

For those that installed the Corsa double-X themselves: Can the stock exhaust be removed with a Sawzall or is the chain style pipe cutter necessary?

You could use a sawzall if you're careful. If you loosen clamps and let it hang with something to support the back, it would be very simple. Measure twice, cut once obviously.

[Mark114]

Originally Posted by Stealth7

I think the increased flow causes some lack of back pressure resistance and that is what is probably being felt. this does not, however, mean that there is less power, especially horse power. I will report once my system is installed.

I've read other threads that adding headers to the ZL1 reduces back pressure and therefore reduces boost pressure in the intake. If that is true then maybe there is a slight performance loss or maybe the power curve is changed? It would be interesting to see if you notice any difference in boost pressure after installing the exhaust on your ZL1.

[Can'tHave2MuchHP]

Originally Posted by Mark114

I've read other threads that adding headers to the ZL1 reduces back pressure and therefore reduces boost pressure in the intake. If that is true then maybe there is a slight performance loss or maybe the power curve is changed? It would be interesting to see if you notice any difference in boost pressure after installing the exhaust on your ZL1.

No. This is probably the biggest misconception that I see on any boost topic. The mentality that lower boost pressure = less/loss of power. NOT TRUE. Adding better flowing parts to your ZL1 or any boost engine that lowers the PSI on the gauge doesn't mean anything except internal engine pressure was lowered which is ALWAYS a good thing. The same amount of air is being sucked in and forced into the engine as before, it's just under slightly (Usually max of 1-2 PSI) less pressure once inside of the engine and exiting. Again, this is only helpful.

To demonstrate, let's say 1 PSI of boost is equal to 20 RWHP. If you put headers on your ZL1 and drop 2 PSI, does that mean you lost 40 RWHP? No. In fact, tune the car so it's running right and the car will probably pick up 40-50 RWHP. You just made your engine more efficient. There is NO downside to headers besides cost and under-hood heat (not an issue on these modern vehicles with proper fitment).

The most that could be happening in this case is loss of back pressure which will pick up peak HP but possibly lose some low end torque (marginal at best). If there really is something slower about these exhaust-modified cars, then it's something else such as knock sensors being tripped or something...

[TRZ06]

Originally Posted by Can'tHave2MuchHP

No. This is probably the biggest misconception that I see on any boost topic. The mentality that lower boost pressure = less/loss of power. NOT TRUE. Adding better flowing parts to your ZL1 or any boost engine that lowers the PSI on the gauge doesn't mean anything except internal engine pressure was lowered which is ALWAYS a good thing. The same amount of air is being sucked in and forced into the engine as before, it's just under slightly (Usually max of 1-2 PSI) less pressure once inside of the engine and exiting. Again, this is only helpful.

To demonstrate, let's say 1 PSI of boost is equal to 20 RWHP. If you put headers on your ZL1 and drop 2 PSI, does that mean you lost 40 RWHP? No. In fact, tune the car so it's running right and the car will probably pick up 40-50 RWHP. You just made your engine more efficient. There is NO downside to headers besides cost and under-hood heat (not an issue on these modern vehicles with proper fitment).

The most that could be happening in this case is loss of back pressure which will pick up peak HP but possibly lose some low end torque (marginal at best). If there really is something slower about these exhaust-modified cars, then it's something else such as knock sensors being tripped or something...

That makes sense to me.

The internal comb. engine is really just a pump. Move as much air/fuel in as you can, exit as much spent fuel/air as you can at the other end.

Someone should do a before and after dyno.