Replace leaking manifold with headers?
After 15 pages I say THANK YOU Otto! Great info. Here's my conundrum:
I have a leaky mainfold/blown gasket on my completely stock '07 SuperCrew 5.4L Flexfuel. Rather than giving the Ford dealer ~$1000 to return it to stock on one side, I'd rather replace it all with something that works for me.
Here's what I'm going for which isn't really covered on this thread:
I mostly do daily commuting to my office job & occasionally do long haul towing with a 22' enclosed (~7000lbs total trailer weight).
I'd like to add some MPG's for daily driving and a few HP's/MPG's for towing at highway speed.
I don't care about sound & would prefer little increase in dB level.
I don't care about looks or where the exhaust exits.
You state that long tube headers with a straight through muffler are best so I got that. What about single vs. dual pipes before & after the muffler? Which configurations work best for the added HP/MPG I'm looking for giving no regard to looks/sound. If dual then use H/X pipe, I got that much, but over all would single before & after muffler be better/cheaper or not? Now if sound can be made better within the primary desires then that's fine, I'm not opposed so long as it doesn't get much louder than stock.
I'm thinking of perhaps springing for ceramic lined headers to keep engine comp temp down when towing. $$ is not the primary concern for me here, just the added MPG/HP & maintaining good towing characteristics.
Also since I'm having a local shop do the work with custom bent tubing, I'm a little concerned about the effect they will have on the ECM. What questions should I ask about O2 sensor placement in the new system? & what should I look for to be the right answers. Could you discuss this a bit?
Should I look for them to weld new cat's into the system or will the local shop likely eliminate this or try to reuse old (which seems wrong)?