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Anyone have an idea of the typical HP increase with running straight pipes from a stock header, no cat, no muffler on a 460 out of a 95 f250?
 

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Not much. You'll gain a bunch of exhaust decibles, though, and be setting off the CEL.

The electronics/computer in those trucks is very sensitive to exhaust system changes (i.e. gutting or removing the catalytic converter). I'd either leave the stocker on it or put a high-flow cat on it.

Ford didn't leave a great deal on the table. It's not in their best interest to sell vehicles that they choke and make as unefficient as possible. That said, they do have to walk something of a fine line between producing vehicles that make adequate power for the masses, deliver decent fuel economy and are relatively quiet and refined.

The return on investment is debateable (realistically it's not big gains for the dollars spent), but the most improvement you'll see on the exhaust side is ditching the stock cast iron manifolds and installing long tube headers matched with a high flow catalytic converter (or converters and a cross-over pipe if you want to run duals) and high-flow muffler.
 

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You actually need a certain amount of back pressure. You will actually most likely have worse performance, gas milage, and it sounds like crap IMO. I would look into some after market long tube header that are as close to equal length as possible. I would also look at running a muffler like dynomax that allows the system to breathe, but not to much. I run pacesetter long tubes with a pacesetter y pipe to a dynomax muffler that has dual 2-1/2 outs.
 

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You actually need a certain amount of back pressure. You will actually most likely have worse performance, gas milage, and it sounds like crap IMO. I would look into some after market long tube header that are as close to equal length as possible. I would also look at running a muffler like dynomax that allows the system to breathe, but not to much. I run pacesetter long tubes with a pacesetter y pipe to a dynomax muffler that has dual 2-1/2 outs.
x2
 

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Not Much

Swapped out stock exh. for straights w/glasspaks on many Ford products. Very little gain when done as a single upgrade. Sounds faster but... that's mostly what you get. And Critters is right. You'll get tired of it and so will your neighbors. Better results were realized when this type of mod follows some level of build. And you do need back pressure. True straight duals let too much out.
For those in the know, how neccessary/beneficial is a crossover?
 

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Try telling somebody running a double A fueler that he needs back pressure!! I think this line of thinking comes from the 2 cycle crowd.
I have a 4.3 S10 that I ran duals on with cherry bombs but no converter and an O2 cheater and it makes lots more power and an extra 5 miles per gallon. It takes about two power pole lengths less distance to go 0 to 100 mph so I can't see it making less difference on a 460!!
 

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First of all, no engine needs ANY amount of backpressure.

Proper scavenging at given engine operating ranges/speeds (read: rpm) is what many folks confuse as "backpressure" and, hence, there's this great misconception that engines need a certain amount of backpressure. This is not accurate AT ALL. A relatively restrictive exhaust scavenges better at lower engine speeds than does a large, open exhaust. Conversely, that smaller/more restrictive exhaust may impede exhaust flow at elevated rpms, limiting the engine's performance. Exhaust systems are complex in terms of building/tuning one to work optimum for a given engine and it's performance spectrum.



Secondly, if your S10 picked up 5 mpg by removing the catalytic converter and whatever else you did, that catalytic converter must have been plugged up and/or something else was wrong with the exhaust system.

I am highly suspect of your claim of an increase of 5 mpg but whatever...IF the truck really did pick up 5 mpg, something was clogged/plugged. There's no way in God's green earth that GM engineered, produced and sold a product that instantly gave up 5 mpg when it's in their corporate interest (due to CAFE standards) to produce, within reason and within certain utilty/usefulness specifications, vehicles that are as efficient as possible WHILE being EPA emissions legal.


Go ahead and straight pipe that 460 and prove us all wrong. I'll bet you'll pick up 200 horsepower and 20 mpg.
 

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The factory has to meet smog regs first then they work on mileage and the other subtleties. The O2 cheater replaces the one behind the converter and tells the computer what it wants to hear so it's not trying to make up for the converter that isn't there any more. Mind you, you could get in a heap of do-do if they caught you using one in some jurisdictions.
As for the mileage increase, going from 22 to 26.4 is a 20% increase. If a 460 starts at 10, then 12 is a 20% increase. Take a 460 with a 2.5" single plus cat and go to 2.5" duals with no cat and I'd bet you'd top that increase. As for power, 10% on a 4.3 is around 18 where on a 460 it's over 30.
Oh, and by the way, I've run vehicles with dual straight pipes and it's a bit much for noise, especially in crowded areas.
 
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