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Over the weekend I learned how sensitive our cars are with reduction of flow in exhaust. Had my street tail pipes on, and got dinked for 96.5 db (MRLS). Stuck my MC baffled tail pipes on, and was at 89 db. Sounds good right? Wrong! The previous event, I had a slight hesitation around 5k and up, going up the hill, and through front straight. Figured plugs might be tired, and extra boost is overwhelming spark. Didn’t get to plugs, and car had felt really good on drive to track. Next session with baffles, immediately notice my “hesitation”. So I end up short shifting the rest of Saturday, and most of Sunday. Last session Sunday afternoon, I figured I’d pull baffles, and see if I can get by sound. Immediately felt like I replaced 50 ponies, nursed it up the hill past sound (at 89 db), and ran my personal best pal time. The baffles I had been using are more so, spark arrester, than a muffler. Wouldn’t have thought it would have had such an impact on boost.
Just so I understand (since I do not remember what baffles you are running and if they are more restrictive than the stock pipes, or they are part of the custom crossover?) is that a more open exhaust downstream of the cats felt like more power and less hesitation, or do I have it backwards?
This is what I was using. Just a bolt, and nut, holding them in end of straight 997 tips I made. Cans are pretty much free of any packing, and no cats.
I was just stunned, that such a small amount of restriction, made such a noticeable loss in power. Easily at least 25-30+ hp loss, because it felt like 50 hp.
I guess it makes sense - probably the turbos naturally give the engine all the back pressure it needs, so anything downstream of the turbo should be as free-flowing as possible - less resistance in this area, it allows for more pressure differential across the turbo and thus better spin up and higher flow. I went with this theory when I built by exhaust, using 3" tubing right through to the mufflers - but I need to finish that system, I go to 2.5" tubing after that since I am using gutted mufflers. Yet another project on the list ... ;-)
02-28-2018, 12:26 PM
Back pressure
