switch527 Posted December 20, 2017 Report Share Posted December 20, 2017 Hey guys, Just got back from the dyno after my magnaflow catback was installed and I lost 20hp and 25lbft. Before this I had the catted downpipes, 3 bar, and the livernois tune and it mad 390hp and 450tq. After the catback I'm at 370 and 425....anyone have any ideas on this? I'm not sure where I went wrong here. Quote Link to comment Share on other sites More sharing options...
mjhpadi Posted December 20, 2017 Report Share Posted December 20, 2017 Apparently you reduced back pressure with the catback and this caused a loss of power. I had the same thing happen with my 98 F-150. Never knew the newer engines required a certain amount of back pressure to perform correctly. It also may be you just need the tune to be customize to take in the catback. SHOdded 1 Quote Link to comment Share on other sites More sharing options...
switch527 Posted December 20, 2017 Author Report Share Posted December 20, 2017 I suppose the backpressure thing is possible, but from what I have read on the forums it shouldn't have had any negative effect. Lots of people have full exhaust including downpipes and it doesn't rob any power. I'm going to attempt to reflash the tune and see if that helps while I try and find a place for custom dyno tuning in Denver. Quote Link to comment Share on other sites More sharing options...
tss Posted December 21, 2017 Report Share Posted December 21, 2017 Unfortunately I also feel the back pressure may be a culprit, or lack thereof. SHOdded 1 Quote Link to comment Share on other sites More sharing options...
Limited02 Posted December 21, 2017 Report Share Posted December 21, 2017 I’m going to disagree about the reduced back pressure causing power loss. Turbo engines don’t really need back pressure after the turbos as it becomes a restriction. There are too many variables that could be causing your power loss and the fact that you didn’t do it on the same day as the factory exhaust, I wouldn’t read into it too much. SHOdded 1 Quote Link to comment Share on other sites More sharing options...
mjhpadi Posted January 19, 2018 Report Share Posted January 19, 2018 I believe you are incorrect about not needing back pressure. We have heard too many times that the modern engines and computers need back pressure to work correctly. Not sure I understand it, but seems to hold true. There has been too many times that people have reduced back pressure in several different engines and have seen performance decrease. Kinda like that none of the aftermarket CAIs work to improve performance. The best track times always come with the stock air box..... tss 1 Quote Link to comment Share on other sites More sharing options...
mval Posted January 19, 2018 Report Share Posted January 19, 2018 strange, all i know is when i put my borla cbacks on it had no effect on power & really not a lot of change in sound. tough to make a 6 sound like an 8 unless you start removing resonators or other exhaust parts. as when i was looking, now ages again neither magnaflow or borla had an atak version for the sho like they had for other cars. SHOdded 1 Quote Link to comment Share on other sites More sharing options...
JimC Posted January 21, 2018 Report Share Posted January 21, 2018 It's not back pressure - it is scavenging. When you change the exhaust you often affect the scavenging effect which means you are not getting the spend gasses out of the cylinder properly. Back pressure is bad for an engine, and it is often a mis-use of the terms when what you are really after is the scavenging effect. Back pressure means you have a restriction in the flow. Think of it like a garden hose that is now attached to a fire hose. You can't get the fluid out of the garden hose fast enough to fill the firehose, but that isn't a back pressure problem it is a problem that you can't scavenge the fluid out of the garden hose quick enough. Now attach the garden hose to a straw. That is back pressure due to the restriction --- and eventually the garden hose will rupture from the back pressure. Quote Link to comment Share on other sites More sharing options...
brucelinc Posted January 22, 2018 Report Share Posted January 22, 2018 JimC, what you say makes some sense but what it the answer to the power loss and how can the OP correct it? Or, is there NO power loss and just a difference in testing??? Quote Link to comment Share on other sites More sharing options...
JimC Posted January 25, 2018 Report Share Posted January 25, 2018 You have to balance the exhaust system - changing the pipes can alter the scavenging. So a performance shop that understands how it all works and can determine the proper size pipe and mufflers can help balance it. What all was changed OP to your system? Quote Link to comment Share on other sites More sharing options...
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