Quote:
Originally Posted by bigbrian
If you are simply bolting on catless DPs w/o a tune you are not going to get additional power out of them. The exhaust will sound a lot better but that is about it.
Brian
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I would not think that the difference in changing DPs would be much (w/ or w/o CAT) without some kind of tune (flash or kit) to boost performance. But I would have thought that the ECU would learn it was freer flowing just a little. Maybe not enough to notice but at least some - couple of hp maybe, and possibly a few more. To see any appreciable difference you'd have to do something to get more air into the engine.
It's getting air into an engine that's tough. Fuel is a liquid and much denser, plus you only need about 1/12th (+/- a bit) as much fuel as you do air (by mass). Getting fuel in is easy in comparison. Then it's getting the burnt stuff out that's the trick. Anything that impedes air going in or coming out is going to cost performance. Everyone around here seems so keen on the exhaust sound. I agree that a good sound is really a nice feature of any exhaust system, but to me it's free flowing that is the key. One that does that well will sound just fine to me.
There's not much you can do to get more air in. You are pretty much limited by the volumetric efficiency of the engine; in other words the mechanical parts on the engine - cam (lift and duration), cam timing (advance/retard off TDC), larger ports and polish and match, intake and exhaust tuning. All of those things are fixed unless you want to get into some engine building, not to mention that they are also already done extremely well on the M6 motor. No, there are only a couple of reasonably viable routes to go. Of the easy ways I can think of, make the air colder is one - water, water/meth, straight meth and/or gasoline injection into the intake system at high boost will help cool things down quite a bit. A bigger and/or more efficient intercooler setup can cool the intake air down too. More boost is another and probably the easiest one of the options - up to a point, you need to watch where you are running on the compressor and turbine maps (don't over drive them or run them in really inefficient areas of operation - too much temperature increase). A bigger turbo can help as well (what you do when you are running them beyond their design capabilities) but generally you are after a lot more air flow and more boost (lots more hp) with this change. This is just trying to gain even more horsepower by pushing a lot more air into the engine at the upper boost and RPM end of things - you need to maintain a sufficient compressor efficiency up there to actually achieve additional air into the engine and/or to keep that air at a decent temperature so that the added boost doesn't cause some self ignition (knock). Sometimes though, if you are not careful about the design and turbo selection (compressor and turbine size and trim, and wg bypass sizing) you can give up a bit of performance and response on the low end with this route. After any of these you really need some kind of a tune to take full advantage of the benefit(s) those mods offer.
What I wonder though is how much does removing the CAT material gain you over having a freer flowing but CATed DP. Let's say you are going to change the DP (maybe other bolt-ons too) and do something for a tune as well. How much does the race CAT DP help and how much more will the CAT-less DP benefit? The CATed DPs are about a grand more than a CAT-less one. That's sure a lot to pay for something that is going to slow you down some but will also not give you any CELs. I am just wondering how much slower.