i have a 1997 5.4L f150. i just put a flowmaster on my ford and i noticed that i seem to have lost power... i was told that if i put what i believe is called a Butterfly Valve on my exhaust i could set it to the backpressure that i needed... have any of you guys heard of doing this??

 

Umm I wouldnt make your exhaust more restrictive to gain back pressure, I would instead do something to the engine to gain the low end torque back, which is all you would loose with a free'r flowing exhaust. I have heard switching to a electric fan will get you noicible improvement, but I have no hands on experience of this. Also sometimes just getting the truck tuned with a predator or something does wonders.

Welcome to the forum, im sure youll get some other opinions, which may suit you better than my opinion, which will cost you some cash.

 

Once again!!!! You do NOT lose torq or HP with a free flowing exhaust. We have proved that on the dyno again and again. The Butt-o-meter will lie to you. We have NEVER seen a car or truck lose power with an open exhaust. EVERY one gained HP. If backpressure gained HP then Top Fuel would run mufflers.

 

Could that be that on most application Flowmasters are proven to be more restrictive than a stock muffler? Put a dynomax superturbo on it or something. Flowmasters were/are designed for sound. Ironically, flow was never considered.

 

He is talking about low end torque not top end like your talking about, and btw thats what I was talking about when I made that post. You are right when you say you will gain torque or horsepower overall, but typically only at the top end unless your running a turbo or blower, or your exhaust is way too small for the engine in general(ie. 1in diameter exhaust on a 4.6L v8) .

 

From a stock application, ANYTHING you do to get into and out of it will alter the powerband further up.

That said, just a muffler shouldn't be hugely noticeable one way or the other, but Flowmasters do have a reputation for just noise, not power.

 

Yeah I agree, I am surprised he felt anything with the flowmaster

 

Putting a butterfly valve on your exhaust??? I don't claim to know it all - but I ain't never heard of doing that to improve performance. Sounds like a nightmare to set up and to dial in.

The only thing I can recall in this line of thinking, IIRC, was a heat-sensitive spring-loaded valve device used on some vee engines to help with warming the engine up way back in the early days of emission controls.

Engines really are nothing more than internally-fueled air pumps - so backpressure is a consideration when the engineers make all their calculations and do the trade-offs between material and installation costs, performance, and other target criteria.

However, considering the performance vein alone - it would seem that the easier that exhaust gas can exit, the easier it will be to get more air in. More air allows for more fuel - thus more power. Then one gets into the crazy stuff like cam lobe timing - a free-er flowing exhaust may enable the use of shorter duration and smaller lift lobes, etc. Just speculating here - this is way beyond my expertise.

If anything - I wonder if the new setup is somehow more restrictive than stock - thus increasing the backpressure???

 

As others mentioned, some back pressure can be a good thing, especially if you want/need low end torque. Ever ride a Harley with open pipes? They're awful around town, in that they loose all of the grunt the HDs are know for. The same goes for street cars. Sure the total HP and Torque numbers will be up with less back pressure, but that doesn't say WHERE the peak figures are. What's more important than the maximum figure is the curve. Getting the right power at the right RPM is much more important than simplying getting it at maximum RPM. In a truck, give me torque at low RPM! (just look at the figures on the Super Duty Trucks)

 

Take a look at the corvette Z06 or the new ZR1. They both use one.