Hello every one I have a strange question for you Exhaust guys.
I was reading a article about headers and it was saying that with stock engines or even mildly moded engines that using true dual headers can make you lose up to 10+HP.
And they went on to say that its worse when using them with big blocks.
Is this true or a bunch of hooey?

 

i am sure that there are alot of variables that play into that such has long-tube or short-tube, FI or Carb, Cam and so fourth. i can see a for sure drop in economy with a stock motor and carb using long-tubes cause of the scavenge affect. but thats about it

 

Explain. The scavenging effect should be better with headers than manifolds.

Now, doing all that work and not retuning for the changes COULD lose you 10 hp. Not likely. Therefore its not the headers fault. I would say 99% of the time headers will give gains over stock manifolds.

Got a link to the article? I want to read it.

 

the scavenge effect will draw more air and along with that will come more fuel hence the decrease in mileage. i never said anything about power, but its all in the tuning don't forget to re-time when adding headers thats over looked alot and most just adjust the carb if that.

 

An engine that makes more power than stock will use less fuel at a given speed, due to not having to work as hard to maintain the given speed. Yes there are limits to this, but headers will not cross that line.

The engine will only use the amount of air/fuel needed to keep a certain speed or accelerate at a given rate. No engine will randomly use extra fuel just because its there.

Your way of thinking would be correct with an engine with lots of valve overlap. Most stock engines dont work that way.

 

That is unless the engine begins over-scavenging. In this case, the mixture fromt eh intake can be pulled right on through the cylinder and waste fuel. This would not cause a power loss however, just a decrease in economy due to the wasted fuel. It could cause a loss of power if the extra air that gets pulled through throws off a sensor. There are very few engines capable of over-scavenging, and most of them are highly sophisticated engines with a lot o overlap. On a stock engine, the worst a header will likely do is nothing. I do believe that in a lot of cases, true duals can be bad unless they are sized properly. It is easy to make them too large, and that can cause a loss of power in some parts of the powerband. As a whole though, the engine will produce more peak power.

 

One major thing to consider when reading these types of articles is WHO is writing it and what type of engine do they know anything about. Most likely if you read this in something like hotrod mag then they are talking about Chevy engines (according to them there isn't any other engine) and the problem is the dynamics of a stock set of heads are completely different between a chev engine and a ford engine. typically on most the Chev engines the INTAKE is the restriction thus increasing the exhaust flow at best does nothing. But on almost all the Ford engines it's the exhaust that is the restriction so at WORST it does nothing and almost always helps, and in the case of Fords Big blocks like it even more then small blocks.
To give you an idea how much different the two companies engines are in this regard. And why the BBC MAY actually lose some power with headers. The aftermarket ford Prostock style heads (A and C types of heads mainly) actually use BBC exhaust ports because the flow is so much better then the restrictive Ford type of ports. But the Ford intake ports even the stock passenger car style heads like the D0VE and D3VE heads unported flow as good as most of aftermarket BBC stuff does out of the box, and the CJ/SCJ ported will outflow even some of the best aftermarkt BBC heads.
So my guess would be what you read was just dealing with the Chev stuff like I said.

 

Well come to think of it I think it was from horsepower. So ya the only time they talk about fords is when they make fun of them...
So it really would be beneficial to get a good pair of headers. since i'm going to be getting a smaller cfm carb and gonna get a new intake and HEI for her.
cool thanks guys for your great info =)