I'm trying to design an exhaust system for my Y-Block 1964 F250. I've got headers but that's it so far. I don't require cats for NH inspection (antiques are exempt). I'm planning on using 1 7/8 pipe duals exhuast. I hope to get a mellow tone that still growls when I want it to. I'm not sure if I want to put an h-pipe in at this point.
I've been told that I should miss-match the muffler sizes and that will prevent the drone at certain rpms. But does that mean one muffler should be longer than the other, or larger diameter, or two different models of muffler? I'm confused.
Can someone give me a clear desciption of what you would recommend for an exhaust system to make my y-block sound like music. Thanks

 

If you want quit, with a little bit of growl, I've heard really good things about the Flowmaster Hushpower series. Why are you wanting to run such a small pipe? I would at least want to run a 2 1/4.

 

This is a small engine in a heavy truck, and you don't want to kill low end torque with large pipes.

Keep the two sides matched for the same reason.

All exhausts drone at steady speeds. It is the noise level that makes the droning irritating. If you use quiet mufflers, then you don't notice the droning as much.

Sound is an individual preference. I can't stand Flowmaster mufflers. They have a hollow, tinny sound that I don't care for, plus they are highly overrated and overpriced. jd

 

Torque in this heavy truck is more important than HP, so that's why I was advised to use smaller pipes. I never liked flowmasters either, but I heard clip of their Hushpower II's and was impressed. A bit pricey, though.

Question, using smaller pipes will make the sound louder? If so, I might take this into account when buying a muffler that might be fine on my FE 390 galaxy, but could be too loud on this truck.

 

I agree with the smaller pipes, though I would avoid the dual exhaust entirely and go with a single 2.5" instead. Better torque, better fuel economy, and less expensive, and you will only need one muffler. Unless the engine has been modified for the drag strip, I don't think the dual exhaust will give you any real gains over stock.

If you want a performance sound but a quieter tone, I think our 50 series meets that criteria, and is a lot less expensive than a flowmaster. We have sound sample on our website of a 4.0L V6 with our 50 series. The buzzing sound is not the actual exhaust sound, but rather distortion within our microphone (The mic we used does not like low frequency tones, we will be getting a new sample with better equipment soon.)

 

I was actually considering single exhaust for keeping things simpler and less money, but I did'nt know it could actually improve torque and fuel economy!? Everyone always goes for duals thinking we are helping the motor breath better, but it's not always the case.

Anyone else with opinions on single vs. dual exhaust for a stock truck like mine?

 

You are constantly saying this, and I disagree. Do you have any data to support your claims of the single pipe?
Do you ever make a post that isn't a commercial. I realize you are a sponsor, but I sometimes think your post are geared to try to sell your products, such as the above dual pipe statement. jd

 

Don't you think I could just as well sell two mufflers as one? I could make more money by selling more parts for more elaborate exhaust systems. I have several of my local customers who have access to performance dynos, and we are going to be sponsoring a 1968 Hemi Cuda on the drag strip next year. Dual exhausts rarely perform better than the factory exhaust, and often have significant torque penalties in the low end. Most of the torque curves shown on various internet sites have lot of other modification than just dual exhausts, many are ported, bored, and otherwise modified engines that are built up to drag race. These kind of tunes are designed to produce lots of power at high rpms and win races on the track. But they are not suitable for street use. Dual exhausts are also really easy to mess, up especially considering that dual 2.25" pipe is larger than 3" pipe. It is very easy to make it overly large and not realize that you have.

When one tunes a vehicle to be driven on the street, one want the exhaust gases to achieve a certain velocity. When this velocity is reached, the exhaust begins to create vacuum in the opposite bank. This draws the exhaust gases out and helps to scavenge the exhaust gases from the cylinders. Larger pipes require a greater volume of airflow to create this effect. Simply having a larger exhaust does not mean the engine will automatically improve its airflow to supply this volume. The engine has to increase its rpm to supply the required volume. So the end result is an increase in horsepower, but the powerband has shifter with the torque curves occurring at higher rpms than previously.

The vacuum effect I have described above is known as the venturi effect. in an exhaust system these principles are not so simple as they are in other systems, since exhaust gases move in pulses. This is important, so I will come back to it later. But let me explain somewhat the effect that is occurring here. If you take a soda straw, and place it in a glass of water or any other liquid, and you blow across it, what happens? The water gets drawn up the tube correct? The same thing applies to other tubes including exhaust tubing.

Let me elaborate on this. Each port on the exhaust manifold leads the exhaust gases away from the motor and into the rest of the exhaust system. Now these gases have mass, and they are moving. As they pass through the collectors region (where the tubes from the separate ports come together) this motion creates relative vacuum in all the other exhaust ports. This vacuum creates an ideal condition for scavenging those ports and pulling the exhaust gases out as soon as the exhaust port opens. The gases do not back up into the other ports, even though vacuum would tend to make the gases want to (remember that fluids and gases will flow from higher pressure to lower pressure) but this doesn't happen because the motion or velocity of the gases prevents this. The air cannot just spontaneously stop or change direction. The faster it is moving the harder it is to stop.

Now as you increase the number of cylinders the effect becomes stronger, which is why a say a 4.0L V6 does not normally produce as much power as a 4.0L V8. This is an overly simplified explanation, but the reason for this, is that the extra cylinders creates more relative vacuum in the exhaust manifolds. The actual pressure or vacuum that forms is very difficult to measure, in part because is is a high stress high temperature area, the pulses move very fast, so fast test equipment would be needed, and most the available test equipment also somewhat alters the readings. We do however know the effect exists because it is possible to calculate its effect and verify the results.

So each collector create this vacuum in the collector because the gases are moving in pulses, and alternate as they pass through the collector creating vacuum that helps draw the next pulse out of the combustion chamber. The exact same effect also occurs as the gases combine into a single exhaust. if the system is set up properly the pulses from each bank will create vacuum in the opposite bank which helps enhance the effect. But a true dual exhaust system eliminates this last effect, making a v8 similar to two 4 cylinder motors connected to a common crankshaft. The exhaust exiting each bank no longer helps draw the gases out of the other bank. The result is a loss of this scavenging effect, especially at low RPMs. This in turn causes a direct loss in torque which is a function of volumetric efficiency. If less exhaust gas gets drawn out of the cylinder, then less clean fresh air can get drawn in during the intake stroke. This causes a loss of total efficiency. In addition, exceptionally well tuned systems can actually create enough vacuum to literally pull the piston upwards along its path, effectively removing all the spent exhaust gases from the chamber and transferring some of this force to the crankshaft.


It is important to realize that as the exhaust gases exit the exhaust port and flow into the manifold, they are still burning and expanding. This further increases the velocity, but about the time the end of the exhaust stoke is approaching the most of the gases have finished burning and are starting to cool. As they cool the gases tend to reduce in volume and pressure, which would enhance any scavenging effect. All the above mentioned effects would increase in intensity as a result of this effect. Also the very fact that the pressure of the gases has been reduced from the former combustion pressure to the 0-4 psi backpressure of the exhaust causes a rapid cooling to occur which further increases the effect.

So one may ask what happens if the systems such as manifolds, and exhaust tube are too large. The answer is really simple, the gases slow down very quickly after leaving the cylinder. Without the needed velocity, they do not create as strong of a vacuum effect and the advantages are lost.

Normally these effects do get stronger with increased velocity, but since all of this is happening inside a tube and there is still such a thing as friction, the exhaust tube itself will tend to slow the exhaust gases. so as the engines speed increases, and the velocity increase, the friction tends to produce more backpressure which directly counters the effect. So it really is a tradeoff. One can choose larger pipe that flows more freely and can handle a larger volume of air, but does not produce the needed velocity at low rpms, or a smaller system that quickly build the required velocity but may become somewhat restricted under the higher airflow conditions.

Now much of this is assuming that the valves themselves can flow much more air. A larger pipe may flow more freely, but the valves may not be capable of matching the airflow of the exhaust pipe, which is why more flow doesn't not always equal more power. Larger valves and modified ports can compensate for this, but the engines stroke tends to play into this as well. If the engine has large bore, there may be benefits from flow tuning. But if the engine has a longer stroke, it will tend to benefit more from high velocity tuning at lower rpms. Since most of todays trucks use stroked engines, the later tuning applies, but many of the older engines were bored designs which benefited from larger freer flowing valves and exhausts. Many of them achieved the needed torque at low RPMS by brute size. But longer stroke high velocity designs tend to produce more power at low rpms and also tend to get better fuel economy at low rpms.

Many people refer to an engine as an air pump. As demonstrated in the above discussion this is simply not true. Firstly, allowing more air in does not mean that more air will flow into the engine. Truth be told, it doesn't allow more air to flow into a pump either. A pump suffers the same restrictions and laws of physics as an engine. Secondly, one could take a 4.0L engine and a 4.0L air pump, and find the engine may actually have a higher CFM rating than the pump due to the fact that the engine is burning a combustible and the resulting combustion results in a draw through the engines exhaust system that increases its volumetric efficiency.

The peak torque corresponds directly with the peak volumetric efficiency, the point at which each individual stroke displaces the maximum volume of air and produces the maximum amount of power per stroke as a result. This is the point where the exhaust induction (venturi effect, whatever you want to call it) is at its peak ( similar effect also occurs on the intake side as on the exhaust side, though the effect is much weaker). The peak hp output is a time/work ratio. At this RPM, the engine may be producing less power per stroke, but in any given period of time the engine is producing the most energy it can. It is also achieving its maximum CFM rating at this point. If you increase the engine speed beyond this point the motor will produce less power in a given time period.

Since the conditions that results in good low end torque are at odds with the conditions that result in result in top end horsepower, these two types of tuning are largely incompatible. You have to choose one or the other. There are tricks that can be done to increase both, via variable valve timing, multi-valve configurations, jet valves, and other methods to increase the power spread, these methods tend increase cost, decrease reliability, and increase mechanical complexity. They also fail to address the issues of exhaust size, and the fact that you cannot have a variable diameter exhaust system.

Now with this information I have hopefully enlightened someone, and have in some way provoked thought.

 

Way too many words, some of it to vague, some of it incorrect. There are many more simplistic explanations that are easier to understand through out the web.

But, you do not present one bit of data supporting your "dual exhaust isn't worthwhile" statements.

It's still a commercial no matter how many items you can or cannot sell. jd

 

I find this hard to believe in the thermal efficiency department not alone burnt exhaust valves this would create.

I was told once I had a burnt intake valves, learn something new every day I guess?

 

Some things are true whether you choose to believe them or not. That the still burning gases exit the open exhuast port is a fact, and an easily verifiable one. The exhaust valve opens before the power stroke ends.

Exhaust gases are not pushed out of the chamber by the upward motion of the piston, they are already gone by the time the piston starts moving up.

On the point of explaining exhaust scavenging, yes there are defiantely simpler ways it could have been stated, and I apologize for the lengthy article.

Now on the point of things being vague, could you point them out so they can be clarified?

And which items are incorrect, could you also point them out so they can be clarified.

And lastly, on the original topic, yes, I have heard of using different mufflers to reduce droning. In fact, on my parents van we have two differnt types of Magnaflows, and it helped reduce droning. A better combination is a Flowmaster Hushpower and large body Magnaflow behind it. But it does depends on the exhaust size and the type of vehicle, so what works well on one may sound terrible on another. Even with the 2 Mufflers on my parents van, it still drones at certain RPMs, while my van doesn't drone at all. Both Vans are Aerostars, my parents is a 3.0L extended, mine is a 4.0L extended.

I did not intend to stray away from this topic so I will be discussing this further here .

 

True. Remove your exhaust manifold and watch how far out the blue flames shoot.
Not true. The piston does expel the burned gasses. Not all of the gasses are expelled with the opening of the valve. That is why headers were designed. Does scavenging ring a bell?
As do all modified exhaust systems. You can change the note, but they will still drone. jd

 

Headers do improve the scavenging, but don't discount what I said entirely. If there was any pressure left in the cylinders at the end of the exhaust stroke, you would get a nasty backfire into the intake, because the intake port is already open. The improved scavenging will draw air through the chamber and get the intake gases moving through the intake port before the piston begins its downward motion.

When you improve this scavenging, you will get these gases moving more quickly and improve the efficiency of the intake phases. Some of the fuel/air mixture gets wasted, but it is a small price to pay for the overall improvement in performance and volumetric efficiency.

 

My reply and thoughts are posted at the dual vs single thread. No need repeating them here. jd