Milton Chadwate

In the process of having a full custom exhaust created for my C55 from the headers back. Will utilize 2.5'' inch piping throughout with 200 cell cats. Will try to utilize the existing mufflers (prefer the AMG tips and size).

Question:

Will the elimination of backpressure (significant considering what's in place) have any type of negative effect of the car's overall performance? Not sure if Mercedes designed the car with this type of free-flow in mind.

AcesHigh

No. If anything you will gain a decent amount of horsepower. Just keep the number of bends to a minimum, and be sure to get your ECU tuned to enjoy the full benefits of this mod...

BF_JC230

I think you will be just fine...that is one of the first things anyone with a domestic "muscle car" does...intake, exhaust...You may want to look into fire order and a double D cross pipe, cross pipe or X pipe for cross balancing...this is an exhaust I built with 2.5" stainless pipe and mandrel bent turns...Yes - Keep it simple and as smooth as possible...This is in my w123...
Jake

c3232c

The elimination of back pressure can hurt your low end torque, I have had 2 experiences where I have lost power going to a bigger exhaust, But where you are using the stock muffler I think you will be ok. Just my 002. Make sure and post your results after you drive it with the new exhaust

AcesHigh

You lose torque, but you do not lose "power". This is what happens when you free up the flow of air; in essence you are trading torque (the thing that throws you back in your seat) for power (the thing that makes your car move faster). You won't "feel" any faster when you do mods like CAI, headers, and exhaust but you will "be" faster.

c3232c

But on a heavy car torque is what gets it moving...

lkfoster

Who is doing the work? Last I heard a shop cannot legally remove a functional catalytic converter.

Vadim @ FD

Milton, you will not gain any power. Stock factory exhaust is very good.

To gain power on C55 you will need to start with headers and than do a true dual. There is about 15-20HP in headers and than another 5 HP in the rest of the exhaust. If you were to add a supercharger than upgrading stock exhaust will be worth more power.

Milton Chadwate

Not looking to do a SuperCharger. That's cheating in my book. Looking for true engineering power, no power adders. Thought is to create the first true DTM Mercedes, based on the popular DTM Mercedes AMG raced in Europe. Want it to be all motor. Naturally aspirated with a rev capacity of 9K. Granted this is going to cost me more than a small child. But hey, you only live once, and you have to spend it to make it.

Thought is to start off with a full capacity exhaust then look to rebuilding the motor, bottom-end and all. Want high compression with the sound to follow. No reason why all the Italians (Ferrari, Lamborghini, Maserati, Alfa Romeo 8C) should have all the fun.

JToups386

When you say you want high compression, you do realize our engine is already at 11:1 don't you?
I won't go into my dissertation about "back pressure" again. I've written enough about it in the past. I don't believe the theory about needing it. The engine is a big air pump. Get more air in, and out, as quickly and freely as possible.

As for your thoughts of rebuilding the engine, I'm not sure where you're going with that? It's a magnificently built engine already, and quite strong. The compression is already about as high as you can get away with on pump gas. You could possibly bump it up to 11:2 or 3-ish, but that's certainly not going to be justified in the cost. I was running 11:2 on my LS1 stroker, but had larger injectors to help compensate for the extra fuel needs therein.

I've been surprised no-one on this forum ever mentions having headwork done. Based on all my years of racing, the true power comes from opening up the heads. I've never seen the heads off of a C55, but I tend to believe there would be some power to be had by opening them up and smoothing them out. Same with the intake. This is a case where "old school" methods should make a difference, hence the "engine being an air pump" theory mentioned above. However, it too would be a very costly venture to do the heads on this car. I'd love to see those results if anyone has done it, or is going to do it! Maybe one day I will...

Vadim is correct about the exhaust. The headers are where the restriction is, however it's still hard to justify spending $3k+ for a gain of 15hp. We've dyno'd a C55 with the exhaust removed from the front of the resonator to the back. It only picked up 2rwhp across the curve, which shows the stock catback to be quite free flowing as is. The stock mufflers are superb for a factory muffler. Removing the resonator completely will at a minimum give you a much nicer rumble, but without being obnoxious. I still plan to do it to mine simply for the sound.

BF_JC230

I hear that...On a few cars I have worked on - and a lot of buddies cars...AFR heads always bring in extreme numbers!

Someone go get a CNC machine!
Jake

Vadim @ FD

JT: We talked about heads quiet a bit. Check out W211 E55 forums. The problem with 3-valve head is that it was designed for TQ and with twin plugs is very good for forced induction. It will just not flow enough air to support 9K rpm, no matter what you do to it.

c55asleep?

Headers and a full custom exhaust got me 16rwhp at about $3500 but then again this is not my C5 LOL. A shop here in Miami can do some head work for about $3000 and can get around 20ish rwhp but the down time of the car is really long (apx. 1 month), just to long for me. Nos always does the trick!!

JToups386

Thanks for the forum link. I'll check it out.
I'd still think there is some gain to be had, even if it's nominal. However, it all falls back to the whole "bang for the buck" scenario, whereas it certainly doesn't warrant spending $3k for headwork that may net out 15-20 peak hp up top by moving the power curve upwards, and therefore taking away some of the low-end torque which we obviously need to get the car moving from the start.

I've never dealt with a 3-valve head before, but I can certainly understand the challenges it would bring, as well as the 2 plug/cylinder combustion chamber design.

I'm still trying to adapt to the fact the C55 is just not nearly as 'mod-friendly' as other things I've owned. But then again it's not supposed to be the "race car"...

Thanks for the input.
J