I do experience lag at low RPM's and I believe my mechanic simply added a straight pipe where the muffler originally belonged. Will this have produce problems with my engine in the future??Barmats said:There shouldn't be any change in low-rpm torque or engine response if the stock tubing size was retained. If you went with a larger diameter tube to fill the space where #7 and #8 were, this will negatively affect flow and scavenging. If flow is reduced by using larger diameter tubing (or adding resistance in the system with diferent components), spent exhaust gases will not evacuate from the cylinders as effectively as in the stock setup. This will definitely affect low-rpm response.
Even though LR apparently spent considerable time tuning the exhaust system (and making it sound weak and anemic), it is very likely a very efficient configuration designed to maximize engine power across the rpm range while reducing sound levels. This has nothing to do with backpressure, which is something you do not want in an exhaust system. Although some backpressure exists in all exhaust systems, backpressure = restriction. Maximizing flow with straight-through mufflers and the use of an X-pipe (many high-efficiency mufflers have an X-pipe built in to their internal construction) will generally improve scavenging, which should at the very least retain stock power levels across the rpm range. It has been my experience that just adding an X-pipe to a stock dual exhaust system (assuming it didn't have one in the first place) will improve scavenging (opposing pulses through the X-pipe generate negative pressure which helps "pull" the alternate bank of exhaust gases through) and can result in a slight performance and mpg boost. However, any mpg improvement is often negated by the right foot pressing harder on the skinny pedal if for no other reason than to just feel that newfound power. And if it sounds better, too... well then all the more reason to press harder!
lets say I just decide to install two aftermarket mufflers instead, will i still get that same raw sound and will this lag still occur?Barmats said:It shouldn't cause engine problems, but may indeed be the reason you've lost a bit of low-end grunt. If you can get under the vehicle and measure the outside diameter of the stock pipe, then compare it to the newly-added pipe, that should tell you if a larger diameter pipe was added. If it was, I would take it back and have them replace it with the stock diameter size.
You could also ask the mechanic what size pipe he used, but he may not know, or may tell you what he thinks you want to hear. Especially if you tell him why you're asking.