I have a 1985 f150 with a 5.0 EFI and i was wondering what is the best setup for mpg and low end torque. Things such as long tube vs shorties, primary pipe size colector size and flange thinkness. My main concern is exhaust velocity. i dont want anything slowing it down. Also i want to install a tachometer, if anyone has done it, help is greatly appreciated.

 

Aftermarket tachs are pretty easy to install.

As far as headers go, do a little research on websites like Summit or Jegs. They will give you a little clue. One thing to keep in mind is that you can actually lose torque with a higher flowing exhaust and no engine mods.

As far as hp improvements go, shorty headers improve least, equal length shorties mid range, and long tube the most.

Also, if exhaust flow is your main concern then you may want to look at more than just headers. High flow cats, mufflers, mandrel bent tubes, etc. all inprove flow.

Alright, enough rambling...

 

How do you lose torque in higher flowing exhaust?

 

Larger diameter piping reduces backpressure and can cause reduced torque. Usually low end torque. Here are a few explanations:

backpressure

Aftermarket exhaust parts - Wikipedia, the free encyclopedia
(Look Under "Performance" section)

torque affected by exhaust velocity - Car Forums and Automotive Chat

 

reducing backpressure doesnt reduce torque, and why are we talkin bout larger pipe? i asked why a high flowing exhaust reduces torque

 

Let's differentiate between the generic term high flow and fast flowing.

A high flowing exhaust on its own doesn't necessarily reduce torque. However, a common thing to do to improve exhaust flow is to increase pipe diameter. Going with too large of a diameter is bad for low end torque because it reduces exhaust velocity (no back pressure and slow flow).

However, improving the velocity (fast flowing) of the exhaust gas can reduce back pressure, but can also have no negative effect on torque. A fast-moving but free-flowing gas column in the exhaust helps create a rarefaction or a negative pressure wave behind the exhaust simulating back pressure.

With that said, if you want to improve mpg drive slower. If you want more power and torque an exhaust alone isn't going to quench your thirst.

 

If its high velocity, then it wouldnt be a wide pipe, or high flow because it would be slower to move all that air right?

 

If you want high velocity at all rpm ranges, then smaller diameter free-flowing pipes are what you want. The down side of this is that a smaller pipe can only move so much exhaust, so if you are at WOT you could be restricted especially if you have engine mods for more power.

On the other hand, larger free-flowing pipes will give you the best flow at WOT, but can cause a loss of torque at the low end because of the slower moving gases and lack of back pressure.

If your focus is on just the headers, just about any aftermarket header is better than a cast stock manifold. If you are looking at the whole exhaust then you need to decide what your future plans for the vehicle are. If you just want to improve the exhaust gas velocity with your current setup then maybe something like a high flow cat is what you want.

 

Well as far as modding my engine i have only put cold air and maybe a diff throttle body and intake in the future, my questions is, im not goin to do much more than that so i just didnt know if there was a way to get the best velocity at all rpm range which you clarified to smaler pipe correct?

 

Correct. I think that if you stuck with the same sized pipes you have - maybe even a 1/2in larger in diameter - with a more free flowing system (i.e. mandral bent pipes, high flow cats, high flow mufflers, headers, etc.) you would be fine for what you have and may do.