There is legitimacy to the admistrator's argument. First off you lose a little low end torque by going with bigger pipe, the back pressure we're all talking about won't occur until you get up in the RPM range, so the low end grunt dosen't need the big pipes, and it's here when the engine is moving slow that you can have the problems Milion is talking about, however if this guy wants a loud truck, he's gonna need more than 1 3/4''. Peak horsepower and torque are generated at the upper end of the range, so it's here that bigger pipes make sense. Having smaller pipes here run you into the problems you're talking about kens; but at the low RPM's there is a need for some backpressure. Oh, and snag, a good set of headers should get you the backpressure you need to keep everything stable. I think that's what you're talking about with the hookers, which will be more than safe. I'd go with flowmasters for the mufflers, but I think that any of the major brands should be fine here, it's just a matter of taste and price.

 

Thanks amish. I appreciate everyone's help on this one.

 

Such as? I will stay with the previous comments I made, because they all add up to efficiency, and that equals power. Low RPM, high RPM, it doesnt matter.

I still cant figure out how people think that restricting flow, (and of course, that restricts power) will equal a better running engine. Put a dual 3" exhaust system on a 289, guess how much torque is "lost"? 5, mabye 8 ft/lbs at most. But guess what? Its not lost, its a little higher in the powerband, in the midrange, where it can be just as useful. Backpressure DOES NOT equal torque. For all the people that want torque all through the powerband, look at some dyno graphs with different systems. They are all over the net. A restrictive exhaust will cause torque to fall flat sooner or later, but much sooner than most people think.

Velocity is everything, backpressure is worthless. Get the highest velocity system you can afford, and guess what? There is little to NO backpressure there. A properly designed exhaust system will INCREASE torque, and that increases horsepower over a stock system. The only thing that was reduced was backpressure. Build an exhaust with even moderate backpressure, and your engine will never realise its full potential. Period.

To the person that started this thread, do some research on your own about the whole thing. You will find that even rock crawlers and pullers, that need all the torque they can get, will have free flowing systems.

 

IMO, Magnaflow. Straight through flow is always better than baffled. However, if you want loud, better stay with FM. MF are usually pretty mellow.

Cylinder scavenging- If exhaust velocity is high, (meaning no restriction) the exhaust pulses will flow well enough that they form a suction, or vacuum behind each other. This vacuum will help the cylinders empty when the exhaust valve opens. This leaves more room for the air/fuel mixture for the upcoming stroke. Having too small of a pipe you will never have the best velocity. On the other hand, too big of a pipe will cause the same thing. You will have the exhaust slowing down due to the pulses cooling and losing speed.

More air/fuel= more horsepower

Since horsepower is measured from torque, that goes up also. Hope this helps.

 

Wow! Thanks for explaining that for me, ken. I had no idea. I'm just a tinkerer. I've never had the cash to put into my old truck till now and I have to educate myself! I've always heard the tagline "let it breathe". I also remember from the 70s (before the environmental movement) that running straight pipes was always better. So, I assumed that the less restriction you have in your exhaust, the better. I suppose according to your explanation, that is true! Since I'm just starting to do work like this to my truck, I'm looking for what works. I'm not particular about sound or looks, I just want the function. I think I'll go with the Magnaflow, since they should be a little cheaper, and perform better with less restriction. Besides, it's always a treat to have someone ask what size V8 I've got, then pop the hood for my I-6! They're always shocked!

 

Wow ken.......Thats a lot of info. Thanks. I'll look around for my best combo of price and power.

 

RED77F100 and snagmaster86-

Glad I can help, thats what I am here for, we can all learn from each other
Good luck to both of you in your exhaust search.

 

kens, I'm not in disagreement that the larger the pipe, the better the flow in general, but there are many exceptions to this rule. Like in the case of a ford 7.3l Diesel or cummins turbo diesel running 5'' pipes. The reason that they don't run sixes? It ends up that in the fives the exhaust flows out where in the sixes the exaust cyclones around the circumference of the pipe. Ends up in this case that the bigger pipes meant less flow. Just bolting on bigger pipes will not always increase exhaust flow. The second problem with bigger pipes is that they are harder to route, avoiding the brake and gas lines and whatnot. I know that any competent exhaust guy can get the job done, but it means more money. Plus you have to think of the diminishing returns. The three's may loosen up what five more horspower than the 2.5's, and for what? extra money, more hassle. Third, there is a major reason for backpressure. If you do not have any backpressure, it can hurt the motor. This is the reason for headers, if you didn't need the backpressure, then why not just make four pipes on the right and left had sides of the motor with three inch openings that dump right at the ground. you'd be heard, and you'd have all the flow you could ask for. So why don't we all do this? Well first of all the police would be on us in a new york minute, and second we would find incredible wear on the exhaust valves of the engine. oh, and if you don't have any backpressure, how can you get the "pulses" that create scavenging? Lastly, the amount of flow that you get the gains from in the three inch as opposed to the two and a half, is minimal at the peak of the horesposer and torque range. This is four to six thousand rpm, which a daily driver will more than likely hit five times in all the years that you own the truck. Having that pipe under your truck may give you the extra 2 or 3 horses, but in my book, it just dosen't make a whole lotta sense.

 

Whoa now, I never said to go as big as you can. And you are right, there are exceptions to the rule. But at least a size bigger than stock will almost always give an improvement. Its all about the cost to the factory, or in some cases, what they happen to have around or can get cheaply. A great flowing exhuast will never appear on most factory trucks, because there is always an increase in noise. Good flowing mufflers just dont muffle as good as a huge, 50 lb box o' baffles like most stock mufflers, thats something most people dont want. Thats why there are people like us talking about making what the factory gave us better.


Thats ok, we are not in disagreement. Thats why in my post I said its just as bad to go too big also

Sorry, but thats basically an old wives tale. Just like breaking an engine in easy and oil changes every 3K. Even my '64 can go much longer than 3K on an oil change. Oil analysis proved that. The newer trucks can go far longer. But thats not the point of this discussion. Making your engine more efficient is never bad and will never hurt it.


Cops, yes. Valve wear, not gonna happen. Tell that to all the guys on this site alone running straights. IMO, thats on the verge of becoming an old wives tale. There is just no 100% proof that it causes damage. 1 person might say their valves went bad the second they installed a larger better flowing exhaust, but what kind of condition was the engine in, in the first place? In the '50s and 60s the common thing was to take the mufflers off and run straights, sometimes just the headers and nothing else, all year long. But I have never heard of a huge problem of dead valves back then either. I remember talking with my Dad who could not think of anyone back then NOT running straights, even some old folk Sorry, but history has my side on that one.


The force of the exhaust being pushed out of the cylinders creats the pulses, it has nothing to do with backpressure. Each pulse is the exhaust from a single cylinder moving through the pipe. With even moderate backpressure, the pulses cant get out of each others way, making the engine work harder to force them out the tailpipe. Would you rather run the marathon breathing through a 1/2" straw or a 2" straw?

I agree completely, however, it depends on the engine, the exhaust setup, and all kinds of other factors. A single 2.5" pipe would not be enough for a big block with simple bolt ons like an intake manifold, carb, bigger cam, and headers. Going to 3" would make a huge improvement. Throwing a 3" on a 302 or an inline 6 would not give you those numbers, though. All depends on application.


I agree to a point. Big time generalization. Depends on the driver, and what the truck is used for.
I ran my Y block to redline all the time when I drove it in high school, it sounded great.

I will agree that 2-3 horses on the top end would not even be noticable, but then I never told anyone to go throw a 3" pipe on their truck without asking a few questions first

 

sorry for getting on ya, I thought you were one of those "bigger is always better" people. They get me a little hot under the collar sometimes.
I always thought that scavenging was best created by an h or x pipe. the cylinders firing in opposition caused the scavenging, but I guess you could get some with straight duals as well. The thing I was trying to say with the some backpressure for scavenging pulses is kinda along the lines of the diesels argument. If the exhaust dosen't fill the tube, but rather cyclones along the walls or breaks up, then you don't have the fluid seal that causes the vacuum.
and come to think of it I think you're probably right about the exhaust valves being a wives tale, the people that tell me about that hapening always seem to have it happen to their wives cousin's friend or something. guess I shouldn't have shot from the hip of that one.
the guy that posted this one has a 351 not sure windsor or cleveland, but I was banking on windsor (it's the more popular) and therefore small block. Only so much air that you can flow through a small block, I guess with forced induction you could have a justification for 3'', but stock or even slightly modified I don't see enough hp gains to make it worth it.

 

I agree on all points.

Yes, an X or H pipe wil help out a lot, especially on the low end. I forgot about that.