You aren't going to gain much from exhaust on your car. The only option that might not be detrimental is a set of headers from PPE as all other options are sized larger for the IS350. You will probably be better off saving the money you would put into your IS250 to get a more sporty car.

 

Unless you have a custom set of short tube headers made, your only opinion are long tube headers.

What I would like to see if a set of unequal length headers and see how it sounds. I wonder if PPE ever made a set to try.

 

 

Unequal Tube length has minimal impact on this engine as the firing order is from side to side, 1 2 3 4 5 6. To benefit from equal length primaries 1 & 2 need a common collector as does 3 & 4 and 5 & 6 which won't happen in this chassis.

You stand to gain more from removing the actual restrictions like sharp bends, flattened pipes, and bad splits like the Y pipe to the muffler.

That said if you throw on some fleabay cheapo headers and primary CATs that flow well, you might be ok from 3,500 RPM up. And its cheap enough that you're not out much if it doesn't work. Perhaps write them and see what size the primary pipes are but their unequal length is not a show stopper. What they do need is a way longer collector due to the firing order having the banks split by 1 3 5 / 2 4 6. This could offer some scavange effect but they likely need to be some 18 to 22" long for this to benefit. So your only gain is reduced restrictions vs scavenging gains.

JM2C...