2.5L exhaust system

[Slo Ranger Trk]

Hey all,
have a question about pipe diameter from the flex joint back ... i've noticed that at the flex-joint the pipe diameter reduces , so if i have the muffler shop fab a 3" pipe from the flex-joint back to the muffler , will that reduce back pressure and increase exhaust flow ? i'm using a flomaster turbo muffler w/a turn down @ the rear axle .. the muffler guy told me he could fab brackets that use the stock hangers and not create a mess ...
any input would be apricated and be a major help...
thanks all for your help,
mahalo, R

 

[Str8sixfan]

Your best bet is to get underneath with an accurate caliper to measure what the pipe diameter is before and after the reducer.

As far as pipe sizing goes, it's always a tricky trade off. Usually, if you're not pumping out 400+ Hp and crazy tq numbers, bigger isn't always better. For a 4cyl, you'll likely want a little back pressure to help with your low end tq, and 3" from the manifold all the way back likely wouldn't be the best set-up. However if you don't care about accelerating fast, and would rather go for MPGs, then an upgrade in pipe size might be a valid investment.

Ultimately, my advice is this: if you must increase your pipe size, don't go over 1/4" over stock. I'd have to take a look at my own truck, but I'm guessing your stock exhaust is either 2" or 2 1/4" exhaust. In which case, don't go over 2 1/4 or 2 1/2" exhaust. What you lose in the low end, you might notice you pick up in the high end, where it might be a little easier to pass people at highway speeds, but might struggle more going up hills on the highway.