Intake/Exhaust Tubing Size

I am asking this question for a friend of mine. He has a 1996 Mazda B2300 (same as the 4 banger Ford Ranger). Anyway, he was wondering if we straight pipe the his exhaust from the cat back since he already has a header system to the cat, will it affect gas mileage?? I said that as long as we don't create too much back pressure and keep the Delta pressure high, that we won't have a problem. He may lose a little bit of torque at low rpms, but he will have the performance that he wants at higher rpms.

We were also going to put a new hoime-made intake set up on it....we were wondering what size we should do since we have to again worry about the back pressure vs. delat pressure issue. On the exhaust side, we were going to use 2.5" mandrel bent exhaust tubing, the same for the intake, but we wanted opinions on the size.

How much if any would this set up affect the gas mileage?>?>

I was also wondering if you can effectively alter the pressure in the exhaust system by changing the size of the intake tubing.

We are doing all of this in conjuction with porting and polishing the head on both intake and exhaust sides and port matching the head to the new intake. We are using a throttle body spacer and larger throttle body. This is a possible turbo (remote mount) application in the future so we did some work ahead of time.

Thanks for the input

http://www.grapeaperacing.com/GrapeApeRacing/tech/index.cfm

I'm shure you can find what your looking for in here about a custom intake and certain formulas for what you need.

but if you can make the intake manifold like the exhaust headers it would work in the same manner.. 1-2-4 to help low mid and high just size you plenums correctly with your main runner lenghts and diameters and you can get one mean intake system :)

don't use a remote mount turbo, it's already been discused that it doesn't worke well at all, the people who advertize it are just trying to get you to pay them, normal mounted turbos works a hell of alot better.

Save the money and put a turbocharger on it after the exhaust manifold where it's supposed to be instead and you will get the engine to perform better for less money.