How important is backpressure for the 4.0?

[Diesel Ranger]

Just from reading stuff around the site, how imortant is back pressure to the 4.0, like what would happen performance wise if a person strait piped one?

 

[JohnnyO]

what would happen performance wise if a person strait piped one?

It would be a lot louder but not much faster.
It isn't so much the backpressure, but too big a pipe will slow down the exhaust gas velocity which helps pull the exhaust out of the cylinders. Ranger engines, even a 4.0, simply aren't that big and don't flow that much air. This is why a CAI, headers, cat-back exhaust, don't make a lot of difference until you're spinning some higher rpm's. On mine I picked up 3 mpg on the highway with the exhaust but city mpg is no different.

 

[gw33gp]

The only important thing about back pressure in any engine is to make sure you never have back pressure. Back pressure is not good for any engine.

JohnnyO is right, exhaust velocity or lack of it is what most consider lack of back pressure. If you open your exhaust too much, you slow down the velocity so much that you can actually get reversion (momentary reverse flow of exhaust gasses) in the pulses of exhaust flow. This is a bad thing and has a similar effect of too small exhaust pipe.

There is an optimum size pipe for each engine in combination with how it is going to be used.

 

[Hahnsb2]

The only important thing about back pressure in any engine is to make sure you never have back pressure. Back pressure is not good for any engine.

Except 2-strokes

 

[gw33gp]

I wasn't thinking about 2-strokes. I don't know that much about them. You could be right and yes, they are engines too.

 

[Yellowsplash]

Here we go again with another one of these threads....

Backpressure=BAD
Scavenging=GOOD

The biggest pipe isnt always the better....Its a matter of velocity and the scavenging effect!

 

[RavoHimself]

what exactly are you trying to get out of straight piping the exhaust. more power? louder?
on my brothers ranger we gutted the second cat, put a thrush muffler and made a 6" exhaust tip. when it starts up it idles low around 500 and the thing sounds like it has a V8 under the hood. obviously with less restriction from the second cat it has more airflow and it is a lot louder and beefier

 

[feellnfroggy]

If you straight pipe, I would go more than 1 5/8-2 inch pipe. Even this might be too big. Run it all the way out, no turn downs or side exhaust with this method. A mild amount of backpressure is good other wise there would be nothing to push the piston down. So you need a little backpressure and you need scanvenging, scavenging helps the velocity of the exhaust gases which if allowed to move too slowly will cause backpressure. It will be Loud, I recommend at least a cherry bomb of some sort or some kinda glasspacks. If you go the route of headers, the rule of thumb is Long tubes help torque and shortys help hp.

 

[85_Ranger4x4]

Back pressure pushes the piston down?

Here all this time I thought it was another cylinder firing and turning the crankshaft which pulled the piston down...

Forget about backpressure altogether, the only thing that matters is velocity. Too big and your exhaust pulses get lost on the way out, too small and they can't get out fast enough.

 

[scheetz21]

Back pressure pushes the piston down?

Here all this time I thought it was another cylinder firing and turning the crankshaft which pulled the piston down...

Forget about backpressure altogether, the only thing that matters is velocity. Too big and your exhaust pulses get lost on the way out, too small and they can't get out fast enough.

your right other cylinders firing and the counter balance on the crank keeps it revolving.. that guy doesn't know what hes talking about. you can run a engine with no exhaust at all..except might burn up an exhaust valve ppl say. lol

 

[85_Ranger4x4]

your right other cylinders firing and the counter balance on the crank keeps it revolving.. that guy doesn't know what hes talking about. you can run a engine with no exhaust at all..except might burn up an exhaust valve ppl say. lol

Two of my tractors essentially have a 2' long straight thru muffler stuck in the exhaust manifold... and will plow as long as you can stand to drive them without valve damage. I even ran straight pipes in my younger days with no ill effects (to the tractor)