I have a 92 f 150 300 6 cid. Was wondering if I installed a larger exhaust, would that increase my mpg any? If so does anyone have an idea about how much more mpg? And what if I removed the cat? Would that help any?????

 

You exhaust needs to be matched to the application. gut feel is that a 3 inch exhaust would not help. A free flowing exhaust would work better maybe. Free flowing and 3 inch are not necessarily the same. You have a lot of constriction in the muffler and cats. You probably also have restriction in the exhaust manifold. You probably do not have bad restriction in the exhaust pipes but maybe could use a step up.

If you are talking 3 inch duals, almost certainly that would be too much for your truck unless it was heavily modified. A single 3 inch pipe might be OK for your truck. You have to look at the overal picture and determine what kind of driving you do. A competent exhaust shop should be able to give you good recommendations, if you have a clear picture of what you want.

If I wanted to improve the mileage the following might do the trick. Easy... Cat back exhaust system, either small duals or a large single. Medium(depends) headers, probably small tube. Harder A good cam, RV types usually improve your lkow end torque which usually helps mileage.

I keep saying depends and probably. This is because I don't know about your truck and driving style. If your engine has excellent breathing, high compression and a hot cam and you regularly run to say 6,000 RPM, then a big exhaust may be for you. If you do a lot of around town driving, light load, low # gears, low RPM etc, small pipes would probably work better.

Good Luck,

Jim Henderson

 

Hi Jim,
I'm about to install a Magnaflow muffler on my truck, I just wanted to know if it's worth increasing the pipe size from the last cat to the tailpipe from 2 1/4 to 2 1/2?

Would there be really any improvement or is it just not worth the money?
I just do around the town driving on the weekends, I want some sound in the exterior but not in the cab!

 

Not knowing your truck model that well, I have to make an educated guess.

With the new muffler, if the extra cost isn't high, I would go ahead and do the slightly larger pipe from cat to tail pipe, ie the "cat back". This usually gives most engines a bit better performance and economy. Depending on the model Magnaflow, you will get a nice mellow tone or a real brappy sound. Usually the longer mufflers are quiter and mellower. The short ones are louder and more brappy sounding.

A wild guestimate would be that a single 3 inch pipe would be about max for your setup. Back when I did some hotrodding, dual 3 inchers were appropriate fora 400+ cube engine turning high RPM. A 300 cube 6 banger is not likely to need that kind of exhaust. So 2.5 sounds about right.

Your cats will keep the backpressure in your system so I think they will be the limiting factor on performance until you modify your engine and or add headers.

Best bet is to go with a muffler shop that you have heard good things about and tell them what you plan to fdo and they can tell you what will work best for you. Since they put you onto the moderately larger pipe it sounds like they may be doing a good job of fitting you and your truck to an exhaust system that will work for you.

Good Luck,

Jim Henderson