I'm adding a Pypes catted X pipe to the stock manifolds this week, should I re tune with the Xcal II? more importantly, will this mod effect my A/F ratio? because it's perfect right now and that is really not something I want to mess with. Thanks
Ha Dunno how i missed that. If you have a wideband just check that at WOT - or put it on a dyno and see how the a/f line looks. My friend put on a slightly smaller pulley and headers/mid pipe and the plugs were basically white. That's one way to tell, just take a look after you go full throttle - turn the engine off asap so that idle doesn't clean them off. Then wait for the engine to cool to take plug out/back in.
I'd suspect it's a tid bit more lean, but not the 2% increment you'd use on the tuner.
That will be a good mod. I have the 42lb injectors and no FMU. The car drives great and gets good gas mileage. My tuner said FMU's give a funky "surge" which causes driveability problems, so he talks people out of them.
I also saw a 97 Cobra with a Vortec and an FMU on the dyno and it had slight break up problems and it backfired really bad, which shot a flame out of the exhaust. My other friend has an FMU on his 95GT and the diaphram in there cracked twice giving his car problems as well. It stranded us both times and fouled the plugs.