4.0 OHV 1994 True Duals?

[ridgerunner]

Got a guy who can make any exhaust I want for the Ranger. He made true duals for my 1990 F150 I6 300 for as little as $250. It picked up some extra HP according to my butt dyno. Would like true duals for the 4.0 what do ya think? Anything I should or should not do or watch out for?

 

[Haywire6000]

To my knowledge most EFI stuff doesn't true duals due to uneven back pressure on each bank... That's what I've been told though....

 

[Grey_04]

To my knowledge most EFI stuff doesn't true duals due to uneven back pressure on each bank... That's what I've been told though....

I've heard similar comments but wouldn't an " H " or an " X " pipe before the muffler or cats take care of this problem

 

[bobbywalter]

where i am from an h or x or any crossover is not "true duals" manifold out one side is a straight piped true dual.


but yeah, a x in there with reasonably sized pipe has potential to free up some power.

tuned it could be worth it.

 

[Goldmachine]

I also have the same year and engine size as the OP. What's a good exhaust that will get me some more power? And also will I gain more power with headers?

 

[85_Ranger4x4]

To put duals on your truck you will also have to put in two aftermarket cats to keep it legal.

Don't know if headers would be worth it.

True duals with no crossover did perk up my 2002 F-150.

 

[ridgerunner]

Exhaust getting louder now...still no sure what to have him build for me. Not worried about the CAT(s) here. My 90 F150 was EFI and had no CAT and power did go up. Also what size dia. pipe should he use?

 

[RonD]

Correct size and working Cat can't effect power, simply not possible, clogged Cat can, just like a clogged straight pipe can.

Stock exhaust systems take advantage of what was learned in racing engines, one of these things is "scavenging" exhaust systems.
When several cylinders will be hooked to one exhaust pipe you can create a LOW pressure at the exhaust valves using the Velocity of the exhaust.
The calculations for this is above my pay grade, I just know it works, lol.

The diameter of the exhaust pipes at the head and the length of that pipe and then the diameter of the Collector pipe(where that banks exhaust pipes connect) all determine when the LOWEST pressure will occur in the RPM band.
Most stock exhaust systems are set for mid-RPM range.
Most 3rd party headers are set up for low-RPM range
Racing headers are setup for high-RPM Range

You don't get more power, it just changes when the extra scavenged power will be available.
Scavenged power is from the crank using less power to push out exhaust, the lower pressure pulls it out, so crank has more power for the rear wheels.

From the collector back needs to be the same size or larger pipe, but there are also newer "H" or "X" exhaust system used on V engines with dual exhaust, basically a crossover pipe or pipes that add an extra scavenging ability because of the opposite exhaust pulses that exist on each bank.

The "Myth" of back pressure comes from factory(stock) scavenging exhaust systems.
People would determine that a "free flowing" exhaust would have to be better than a stock exhaust system.
So they would install larger pipes from the heads back.
Then on a test drive they found they LOST power, "WTF!!!"
So they would, incorrectly, think "this engine must need back pressure", opps, lol.

The larger pipes reduced the Velocity at the collector so there was little or no pressure drop at the exhaust valves, they lost the scavenged power with the "free flowing" exhaust, so their results were to be expected but their conclusion was incorrect

 

[ridgerunner]

Mkay...so U R telling me stay stock then or???

 

[adsm08]

No, he is not telling you to do anything. He is telling you that certain setups perform differently and then giving you information about the different performances. You need to make your own decision about what you do.

 

[RonD]

Yes, +1

Just saying there is a right way and a wrong way to setup your new exhaust system.
You need to decide what power band you want first, low, mid or high RPM.
Then build the system from there back to the single or dual tail pipes.

 

[ridgerunner]

OK. Looking to get more in the lower rpm band. Any thoughts?

 

[ridgerunner]

ok...I'm feelin' ya...I am thick sometimes lol