Looking to get no less than 450whp on 91 octane from a P31 PP C63.

The plan is ECU reflash, filters, Akrapovic slip-on mufflers and some type of headers that actually work. To this end the MHP Long Tube headers caught my attention.

Have MHP owners had ANY issues with these headers? Leaking, cracking, not fitting perfectly, excessive under-hood heat, etc? I would most likely ceramic coat mine.

Is it possible to run long tube headers and retain catalytic converters? Not for smog testing but I hate the smell of catless cars and I do have an conscience when it comes to OUR world/environment.

I had the MHP LT headers when I had my C Class. They are the best. Prior to going with MHP I had a diffrent tune and a diffrent set of headers. They were nothing compared to MHP. MHP's V3 tune and headers will give you 100 RWHP.

The headers will cancel out your primary cats automatically. So if your looking to keep your primary cats. MHP headers wont work, because the merge collecters will be in place of the primary cats. You can still keep your secondary cats though. Dont worry about the smell too much. Get
the headers dude, you will love your car.
Who cares about the smell, go catless, and wake up the neighbors

No problems, they remove the primary cats but u could always add cats were the miss go I believe Andy already has a package availible for that

Thanks for the info. It looks like the MHP long tubes (w/ceramic coating) and tune will give me the power I want while retaining one pair of cats.

Are drop-in filters the way to go or are there any good airbox mods, other than the ROW box?

Go with the TTM air box mod. Or if you really want HP gains, go with the renntech airboxed, good for 10 HP ,they really do give you gains. Stay away from carbonio intakes, they literally give you small gains.

As for the filters, go with pipercross, or BMC. that would be a good 5-8 HP gain

Hello.

what about the Renntech stage 2 performance kit:

http://www.renntechmercedes.com/www/node/199

better than MHP?

The MHP headers Are the best in biz rite now, Most power gains and best track results,
I think I was the 3th person to have the LT's from MHP
I had no fitment issues and I did the install with a friend took about 1 full day on jack stands,
I have the headers for almost 2 years now and so far no cracks or leaks besides what my welder F'ed up,
Good Luck with u build sound like you going to have a beast in your hands after.