BigTex Posted December 11, 2003 Report Share Posted December 11, 2003 With all the talk about electic cutouts, I thought I'd share my recent experience on this issue. Watch / listen to my video at the track. I have two flowtech cutouts in place of the stock catalytic converters, basically making them almost open headers. I uncorked them at the track. They are extremely loud in the cab, and sound great outside at full throttle. You'll get lots of lookers checking out your truck. http://www.z71.net/1382b.mpg Like I said, that is with the cutouts open. Prior to going to the track, I had used LS1 Edit to tune my truck and had it running great. At the track when I logged my runs with autotap, my air / fuel mix went way off. I had my truck tuned well to run with the cutouts closed (13:1 A/F), but with them opened at the track, I was super rich (~11.5:1). I made no real changes in the tune before the track run. My timing typically climbs up to about 28*, but it barely got into the 20s that night. I can normally log MAF flow readings up to 44#s, but that night, I was lucky to see 39#s. The more air and fuel you get in the combustion chamber, the more power you make (think of a supercharger). That means I was using roughly 15% less intake air. Could that mean that I was actually down 15% in power due to the less airflow and over rich tune? probably.... Honestly, my runs that night, including my 13.8 N/A run, were disappointing. I was expecting to see mid 13s NA after dropping a little weight. Anyway, back to the topic, I think my poor performance was due to the cutouts really hurting my tune and ET (huge drop in exhaust backpressure and no scavaging). These effects may be less if the cutouts are farther back in the exhaust system (near the muffler). This would give you a little more back pressure and hopefully not throw off your tune much. I wanted to preserve the back half of my exhaust for the quiet muffler and sleeper look, but be able to open the cutouts when needed and gain power. I saw the exact opposite results, ran great through stock muffler and poor with cutouts open. At this point, I'm going to take off the cutouts and replace everything with high flow mandrel bent exhaust and probably a better flowing muffler. Then I can get the truck tuned correctly for street and track with no exhaust variables. Its my opinion (now) that a good full exhaust system with an X pipe for scavaging will make more power all around. I do think that cutouts with a tuned vehicle can make a higher peak HP number, but the power below the peak will be better on the good full exhaust (minimal crimps in pipe, mandrel bent tube, X pipe, good muffler). If you plan on running electric cutouts, get your truck tuned well with the cutouts opened. I think I would have been OK if I had tuned it before with the opened cutouts. Of course this makes your tune not optimal with the cutouts closed, but thats why you'd have the electric openers. When I say "tune" I'm referring to the wide open performance mode only (air / fuel, timing, knock, etc...). Daily driving wouldn't be changed. Any thoughts? Anyone with real world experience logging the effects of an open VS closed exhaust? Richard *** At this point, I think I could run a 13.5 through the stock muffler, but it may hold me back more than I think. Hopefully I'll be able to test that theory soon. I sure wish that both outlet pipes were open in the stock muffler, and I'd keep it for sure. Link to comment Share on other sites More sharing options...
Fun Guy Posted December 11, 2003 Report Share Posted December 11, 2003 Link doesn't appear to be working. Link to comment Share on other sites More sharing options...
BigTex Posted December 11, 2003 Author Report Share Posted December 11, 2003 Fixed the link. Link to comment Share on other sites More sharing options...
GEAR M UP Posted December 11, 2003 Report Share Posted December 11, 2003 Big Tex....that sounds bad azz......Not a bad time and Mph..... Link to comment Share on other sites More sharing options...
m396 #00-011 Posted December 12, 2003 Report Share Posted December 12, 2003 Ah come on, go out for a few hundred miles and tune it with the cut-outs open. Take some Excedrin first. Link to comment Share on other sites More sharing options...
BenKey Posted December 12, 2003 Report Share Posted December 12, 2003 Driving with open headers was not very popular through my town. I put my ASM headers on then drove to have the welding done. It was during the morning during heavy traffic. Lots of looks, especially from women and older people. Link to comment Share on other sites More sharing options...
Fun Guy Posted December 12, 2003 Report Share Posted December 12, 2003 Driving with open headers was not very popular through my town. I put my ASM headers on then drove to have the welding done. It was during the morning during heavy traffic. Lots of looks, especially from women and older people. Did you rev it up a few times, just for effect? My second car was a 1973 Olds Toronado with a 455ci motor. I bought if for $50 because a friend of mine was moving to Florida and his dad told him he couldn't bring the car with them. He got so angry he drove it out into the woods and bounced it off of 20 or so trees. Looked like hell. In the process of his joyride, he broke the exhaust off at the manifold, which is the condition it was in when I got it. Talk about LOUD!!! Link to comment Share on other sites More sharing options...
zippy Posted December 12, 2003 Report Share Posted December 12, 2003 i've driven many with open headers and although it's fun, it's not a real street set up. i only run at the track with the same exhaust i run on the street. i dial it in for that and feel if i need cutouts, i just need a better cat back system. Link to comment Share on other sites More sharing options...
marc_w Posted December 12, 2003 Report Share Posted December 12, 2003 Excellent post... I wanted to keep my stock system for keeping quiet on the street. I was hoping I'd be able to just pop open the cutouts, putt around the parking lot, and have the truck ready for a 'uncorked' run. I think I may end up with a larger sized Magnaflow, and leave the rest of the exhaust buttoned up. Link to comment Share on other sites More sharing options...
383ss Posted December 13, 2003 Report Share Posted December 13, 2003 putting the cutouts farther back would have helped a lot. the 02 sensors are in front of and behind where the cat was. with the cat out you should only be using the O2 sensor right in front of the cutout and have a dummy on the other one. the computer can't get a good reading of exhaust air with the cutout open and having ouside air so close. move the cutout way back towards the muffler and you should get good results but yes DO tune it with the cutouts open. Link to comment Share on other sites More sharing options...
2bseen Posted December 14, 2003 Report Share Posted December 14, 2003 Had the same problem on my hawk with trying to run open headers ran like sh/t and a/f was terrible. After I ran the y-pipe and put the cutout in rear ran great. For some reason you still get air to your o2 and screws everything up, change cutout to in front of muffler and see what your reading are. Link to comment Share on other sites More sharing options...
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