i have an 86 f150 with a stock 302 with a rv cam n long tube headers. im thinkin of goin true duals but not sure yet but am leanin far into it. anyway my other problem is im still not sure if i want bullets or flowmasters 40 series. i want a high velocity exhaust system so the gases flow out quickly to produce lower end torque but am not sure wat size i want. im thinkin bout goin down to 2 inch off the headers into the mufflers n all the way back to 3 or 3.5 inch tips exitin out the rear under the bumper. any other suggestions would b appreciated. thanks

 

personally recommend running a true dual setup with 2 1/4" piping.

 

I agree for dual applications more than 99% say 2.25 or 2.5 piping single would be 3-3.5 inch flowmaster 40s sound good check out my thread called Exhaust clips on the forum here dynomax bullets are really loud snappy

 

I do not recommend the dual exhaust unless you will be doing cams as well. I would go with 2.25" single and a straight through muffler. That should give you loads of torque without penalizing the top end over stock.

 

Duals will be fine regardless of cam choice. 2.25" duals like someone already said and you will be fine. 2.25 single? He might as well keep the stock system.

 

Not if you are tuning it for torque. Just think about it, do you ever have exhaust from both banks flowing down the pipe at the exact same time? You sure don't at the headers, and if you keep the length on the pipes before the y as close to the same length as possible, you won't at the y-pipe. The general rule of thumb is to use the smallest pipe that will handle the airflow of the motor. 2.25" will efficiently support 350 cfm @ 1 psi. The maximum theoretical airflow of a 5.0L under nearly perfect circumstances that never ever ever happen in real life is 349, which is just shy of what this pipe will flow. Since you do most of your driving between 1200 - 2800 RPM, your maximum airflow under day to day conditions will be around 220 CFM. If you run dual 2.25" pipes, you are running an exhaust that will efficiently support 700 CFM of total engine output in motor that maxes out at just less than half that. The velocity penalty is huge. If you wanted to run dual 2.00". you might be in the right ballpark, but dual 2.25 is what you would put on a 460.

If you want maximum power, your efforts are best focused on ensuring that unnecessary restrictions are eliminated and that the exhaust is as balanced as possible, e.i. try to make each side of the y-pipe as close to the same length as possible, minimize the number and severity of bends if that can be helped, and use a straight through free flowing muffler. The y-pipe needs to have a smooth transition, and it wouldn't hurt if you had some type of merge collector on the headers. A merge collector at the y-pipe would be a neat idea too, though I haven't met anyone who has tried it.

 

Torque?? Where?? redline?? Idle? Need a little more info there pal. You cant just say "tuning for torque" without saying WHERE. What if I was tuning for max midrange torque? Same rule apply? You know horsepower is a by-product of torque, right? Guess Im tuning for both.


Whats your point? We are talking about duals.

Prove it. Rules of thumbs are worthless because every engine and the environment it runs in are different. Wanna put that pipe on a race 302? Or even one with good heads/cam? Guess the solid low end gains my 4 cylinder Contour made on the dyno with 2.25" pipe is all wrong. 2.0L, WAAAAAYY smaller than a 302.

LOL!!
No, I dont drive a Peterbilt. I also dont believe in lugging the vehicle I am driving. What if max torque is made at 3500RPM?? You would hardly ever see it.

You are speaking about a perfect situation. This world, and the world our vehicles run in is not perfect. There are too many times that your logic has been proven wrong on the dyno. If for no other reason than to plan for possible future engine mods, I will always buy the bigger pipe, rather than hope that the soda straw exhaust will not need replacing when I throw a better intake/carb on the engine because it no longer flows where the engine is happy.

My point is this-- DUAL PIPES ARE NO BETTER/WORSE THAN SINGLE IF THEY ARE BOTH DESIGNED FOR THE ENGINE COMBINATION AND WILL NOT MAKE MORE/LESS POWER THAN THE OTHER.

Im tired of seeing you constantly saying that duals are no good. Its interesting that you are nowhere to be found when someone posts about their new dual exhaust system and how happy they are with it.

.

 

how do u run ur duals? ive heard of ppl runnin the right side all the way back n haveing the left with the bends while on the other hand ive heard of ppl runnin the left side out the right in the rear n the right out the left in the rear. wat would b better? to me, runnin out the opposite side as wat it comes off the motor would b better for flow cus there closer to the same length. wat are ur takes on this?

 

Bear River makes this statement and argument without any experience or background except he tuned up his Mazda or whatever it was, and sells cat converters. Some working knowledge of exhaust systems, hands on, would be helpful. jd

 

I do not personally install exhaust components, but as I am in the business, I deal with people who do every single day. I am very closely affiliated with a customer of mine who has a performance dyno. Yes, he installs duals, and he does exhaust all day every day. But he doesn't have duals on his personal truck. I asked him why, he says that the difference in peak performance was indistiguishable for everyday use. He is not opposed to installing what the customer wants, but if the customer doesn't know what they want, he always recommends the single. I can repeat this story minus the dyno referring to at least 50 other exhaust mechanics that I service across 3 states. But I figured if a guy with a performance dyno doesn't install a dual exahust on his daily driver, even though he could easily afford to, then maybe he knows something.

This same individual does have duals on his 1968 Hemi, but it is also a drag racer, and it has performance cams, it has been bored out, port matched, and host of electrical and fuel system modifications, and has been tuned to make the quarter mile as quickly as possible.

I have provided independantly verifiable links to information supporting my claims, and folks have yet to counter claims that are verifiable. I have provided mathematic prove showing dual exhausts have more surface area to slow the exahust down, and are often too large for the engines they are matched with. I have shown independantly verifiable information showig the strength of collectors, such as those found on headers. In all out horsepower, like that found in drag racing, exhaust scavenging is not really an important factor. But in a street vehicle, it is everything.

If a y-pipe is restrictive, that why use a collector on a header, why not run a seperate system off each port. Any of you would agree that would be disastrous. So why are you so objected to a single exhaust. That y-pipe if properly designed and positions, creates additional scavenging effect which in turn produces additional horsepower, not less.

The reason a large pipe may offer some benefits, is because there are 3 distinct stages that occur during the exhaust stroke. Increaseing pipe size enhances one of those stages, but penalizes the other two. The other two represent a larger portion of real power in everyday driving. I may not be doing the installation, but that doesn't mean I don't know exactly what I am talking about.

And on a final note, how many people on this forum, who have dual exhausts can prove they have more power than before. Do they feel they have more power? Do they sound like they have more power? Do they win races against comparable vehicles with comparable modifications? Do they have dynos tests showing their actual horsepower to the wheels, versus comparable modified vehicles.

I don't know about you, but it seems to me that most of the exahust modification people install on their trucks have absolutely nothing to do with power. Its all about sound. If it sounds louder, and in general makes more noise, and sounds like it is more powerful, then you are happy. From this perspective, duals are better. Duals sound awesome. They even sound more powerful. But I have yet to ever see a stock motor running duals that was actually more powerful than a stock vehicle running a performance single exhaust.

Pray tell, why would automotive manufacturers run h-pipes and x pipes on performance cars when they could save money and run true duals? And why does the trend away from true duals get more popular with automakers in recent years, when they could save money? It is because through years of careful research, they have found that these minor modifications could dramatically improve performance and yield greater returns, without penalizing emissions, without making the vehicle overly loud, and often increaseing fuel economy. Its funny how they go through the effort of doing all this just to slap some crappy restrictive muffler, on there. But in many cases, all you need to do to get more power out of your vehicle, is to replace just the muffler.

 

Good God, man. You give me a headache. All these claims that you make about single being better than duals, and duals will make less power, and you contridict YOURSELF!! And to hear this kind of claim from a dyno operator is shady itself. Any dyno operator knows its all about the power UNDER THE CURVE, not peak power. Peak power is for dyno queens, not drivers, or even race cars.

Not saying your friends know nothing, but I know several "mechanics" that claim you need lots of backpressure to keep an engine from blowing up. Just being a mechanic does not mean they are experts or even generally know what they are talking about. Also, do you know how many posts there are where someone "claims" they know all these guys that will agree with them??


"Just ask my friend!! Im right!!" Doesnt work for me.

No, you constantly claim there are tons of people that think the same way you do. Lots of people honestly think that the Tornado they just put in their intake makes them 30 HP and gives 40 MPG. Think its true?


See above.

LOL!!! In an all out attempt for big power, you use everything at your disposal to make that power, INCLUDING exhaust scavanging. Think those pipes under a NASCAR chassis have no thought put into them?

You talk about scavenging a lot, do you realise its in use with duals too? Here is the part about scavenging I dont think you know. You dont want max velocity/scavenging at low RPM. As soon as the engine revs above that point, the exhaust becomes a RESTRICTION, and can no longer support good flow. At low RPM, an engine doesnt need maximum scavenging to make power. And if the air/fuel is getting diluted THAT much with left over exhaust to really hurt power, then an exhaust system is the least of your worries. You want the engine to not breathe above 3000 RPM??


Never said it was. Factory pipes?? Some are VERY restrictive.

Just like a well designed dual exhaust system will.

If you have been around a dyno like you claim (or "know" someone who is) then you would know that 2 vehicles, no matter how "similar" will never dyno the same. That would be a terrible way to compare anything. Even running on a dyno on different days will screw up any comparision. How do I know? Because I HAVE RUN ON THE DYNO PLENTY OF TIMES. Both the truck and the car. The car is more fun though.

I agreee most are setup for better/more sound, not power.

What??? I currently run true duals WITH an X pipe. They are not exclusive. True duals means at no point does the exhaust merge into a single pipe.


Because single exhaust is cheaper, lighter, and easier to package. Dont think the factory spends too much time trying to get the best exhaust setup.

 

ok so im goin to run true duals with an H pipe with flowmaster 40's. im gunna run 2.25 all the way back to 3 inch tips. now the question is, how do i route the duals? do i have the drivers side exit out the passenger side and visa versa or have the driver side exit out the drivers side? either way its goin to end up under the rear bumper.

 

Perhaps I should emphasize what this individual asked for. He wants a high velocity system, not an overly large dual exhaust system. If this individual ran dual 2" pipe all the way back, that would be ideal for what he is looking for, Or take the two 2" off the headpipes and y it tegether into 2.25" pipe. Either arrangement can flow more air @1 psi than the engine can, and therefore, won't be restrictive.

The main key is to make sure the muffler can flow the required volume of air. If he goes with just about any performance muffler, excluding a louvered glasspack, this goal will be achieved.

 

but with the 2 inch duals wont that become restictive with the rv cam in there n shorter lifters and different heads? im thinkin that 2.25 will b wat i run

 

Yes it should become a restriction as the engine revs up. 2.25" would be my vote.