I'd keep your car as is until you have another dyno done. Once that is out of the way, get those secondary cats out. You removed the primary cats, but now the restriction is on the secondaries.

 

Honestly, I would expect that the stock long and short term fuel trims would produce a very lean A/F mixture if the headers were installed then immediately dyno'ed without any significant mileage. Furthermore, I would expect the power curve to change significantly as well. The fact that it didn't change much implies to me that the A/F didn't change much, so I wouldn't expect there to be much gain in a week either. I hope I'm wrong though since I would love to buy a good set of headers.

 

Thanks for weighing the stock manifolds, but did they weigh 25 lbs EACH, or 25 lbs TOTAL?

 

could you actually run around with both your primary and secondary cats removed and still have an exhaust that belongs on a luxury car? i know the point and purpose of this project is performance primarily, but i'm curious if an aftermarket exhaust that removes the secondary cats with just resonators and the mufflers would be really loud

 

25 lbs total

 

Toptier, thanks for all your efforts keeping us all informed. I hope the power gain is much more significant down the road as predicted.

 

come IS350 guys.... any update on how the headers are doing.. cars getting any faster?

 

The sound wouldn't be the problem with a catless exhaust. You would absolutely HATE the constant buildup of black soot on the back 1/4 of your car. You will also not like the black cloud that you will leave behind when you punch it after a couple hundred miles of conservative driving.

 

Wow. I'm surprised that they are that light. Does anyone know what the Mazzuri headers weigh?

 

I got 250 miles on the car now, and it feels faster. I don't know if it's just me wishing it is or if it actually is. But we will find out later this week when I get it dyno'd.

 

The Mazzuri's felt lighter then the stock

 

The OEM exhuast and y-pipe with the secondaries is more than likely the cause of the restriction now. The dyno shows the torque increasing and then leveling opff at the higher RPMs. I think this vehicle needs an exhaust (full header back) to see the real gains.

But it needs to be driven for a couple of days until the trims adjust themselves. Before it goes to the dyno.

 

the IS250 showed great gains still using the stock exhaust.. so the IS350 should as well

oh and toptier.. you need to check on a drag strip around you.. if you see some good gains on the dyno.. who knows.. you might be able to pull the fastest time at the track..

 

In my experience, bolt ons tend to show better gains BEFORE the fuel trims settle since the ECU will want to run richer than optimum once they do settle.

 

I won't be seeing any good times up here at a mile high