Wastegate Exhaust System?

[CDW6212R]

The goal is to remove restrictions(H/X pipes), so if they don't do that clearly, don't do it for performance. The space around the front and rear of the exhaust is so tight that you can't gain anything there with cross overs. As soon as the cat pipes meet on the right side, that's a good place to do something with them. But it is tight there still until the pipes get past the trans cross member. There isn't a magic thing to do. Concentrate on the headers and cat pipes themselves if better performance(and economy) is the goal.

 

[2000StreetRod]

Crossover performance theory

According to what I've been reading, the advantage of an X or H pipe is to use the flow of one bank pipe to help scavange cylinders on the opposite bank. Exhaust occurs in pulses associated with each cylinder. There is a high pressure area at the leading edge of the pulse and a partial vacuum at the trailing edge. As the pulse flows thru the exhaust system it widens and softens becoming more of a stream. When the pulse passes thru the honeycomb of the catalytic converter there is significant softening and lengthening.

A crossover also reduces the sound intensity of the exhaust. My Sport has the equivalent of a crossover inside the muffler but I suspect its only advantage is noise reduction.

I'm wondering if compact, high flow cats could fit on either side of the transmission just aft of an H pipe. I've found compact, high flow cats with built-in pre and post O2 sensor bungs. With a crossover reducing sound levels I could have a higher flow muffler and still not be too loud. Being an engineer, I prefer a symmetrical exhaust system which will be hard to achieve with a single tail pipe on the right side. They DynoMax VT muffler is starting to look more desireable if I can fit two of them staggered with equal length inlet pipes coming from the cats. The outputs would feed a 2.5 inch Y pipe which should be adequate for less than 300 rwhp.

 

[CDW6212R]

Work on the location of the cats, everything has said they have to be very close to the engine. I've wondered about the affect of moving them down stream. If you can find support for moving them back a little, then what you are thinking may be good.

The only way a cross over can be flow effective is if it's very close to the header collectors. Your first paragraph about that is correct, but it can not work if the cross over is too far behind the collectors. The stock location around the trans cross member is way too far back. That is why in mine I'm only really concerned about increasing flow beyond that point.

Think of the exhaust flow, the whole exhaust, in two ways. First concentrate on the flow(scavenging) from the heads to beyond the collectors, and cross over if it's right behind those. That is the only place where scavenging will take place. After that try to have the exhaust not become smaller or slow down at any point. You want the back half of the exhaust to create as little back pressure as possible. The more back pressure is created by restrictions, the less airflow there will be, less power and less fuel(in general). That's where the fine line is between max power and fuel economy. It's a similar concept to the EGR system. More EGR means less airflow in, and less fuel, potentially more efficiency. Take away the EGR and you get more air flow, and fuel usage. That's at part throttle though, and so small that power and fuel consumption with or without EGR is not much different. Keep at it Dale, I applaud your efforts.

 

[2000StreetRod]

Cat efficiency

I believe the reason there is emphasis on the cats being close to the engine is because they are more efficient at higher temperatures. Some members paint their headers black or purchase black ones. Black headers radiate heat better than light colored headers. I painted my exhaust manifolds silver to reduce heat radiation. I've realized the importance of retaining exhaust heat. Cool exhaust is denser than hot exhaust and the velocity decreases accordingly. I finally understand what hunterdan was trying to explain to me that velocity is more important than back pressure.

I've found some dyno results comparing an X pipe to an H pipe with mufflers on the same vehicle vs open headers/collectors. With the optimum implementation there was very little difference in rwhp but a huge difference in decibels.

An X pipe would be very difficult to implement near the engine and I just don't like the idea of both banks of the exhaust having to flow thru the single X junction. At some pipe length and engine rpm an exhaust pulse from both banks could arrive at the same time and experience restriction. I think having two pipe diameters in the H configuration will be less restrictive. There are H pipe fittings that have equal diameters in all three directions.

 

[CDW6212R]

Remember that the only goal for the exhaust is to exit the gases as effectively as possible. So what matters is mass of air flow, not just velocity. Whether you heat or or cool it, the point is simply to get it out. Back pressure is a measurement of restriction, that is very important.

Velocity means nothing if the mass of air is not considered. You can cut the pipe sizes in half or more, and thus greatly increase the velocity. But did that help or not? The gas temps went way up, and expanded, taking up more space. The result is tons of back pressure, high velocity, and thus less airflow. Airflow is the only goal, and it's the velocity of mass(both).

Once you realize that an exhaust is dealing with a combination of air mass, and velocity, then you can begin to build a great system.

I've been speaking about airflow and power, not sound. The "X" and "H" pipes as they are being installed(too far back, poor transitions) do more for sound, and usually nothing for power. I'm going to rely on two mufflers and full length tail pipes for sound control. If it isn't quiet enough I'll add resonating pipes to each tail pipe.

 

[2000StreetRod]

Pipe diameters

My SOHC V6 exhaust pipe outside diameters range from as little as 1 7/8 inches for the downpipe between the manifold and the catalytic converter to 2 1/2 inches between the muffler and the resonator. The input to the muffler is 2 1/4 inches. The tail pipe is only 2 inches in diameter.

I suspect that a constant diameter of 2 1/4 inches from the manifold output to the muffler inlet would significantly improve exhaust flow.

 

[CDW6212R]

Increase all of it, and try to keep it the same throughout. You have a tuner, so correcting the A/F ratio is not hard for you.

 

[2000StreetRod]

Dynomax VT muffler

I recently read some 2010 dated negative reviews of the Dynomax VT muffler. At idle and lower engine speeds the butterfly valve partially opens and closes rapidly generating a loud rattle. The rattle is loud enough to be obvious. In my application it might be detected by the knock sensor and result in retarding the ignition advance. Even though Dynomax came out with an early fix of adding some padding to the valve there were still rattle reports in 2012. Like so many new ideas, the VT sounded good in theory but is lacking in implementation.

 

[CDW6212R]

I had an Edelbrock "chambered" muffler installed, I forgot the name of it. I only paid to have one crush bent 2.5" tail pipe. That muffler wasn't too loud, and it sounded good for a V6.

If I had a flasher and the software already to do the vehicle PCM programming, I'd open the exhaust a lot and see what is gained. The 4.0 isn't as big as a 5.0, but it still needs more than the small 2.125" restrictive resonator and single 2.25" tail pipe. At a minimum if tuning was going to be done, I'd make it at least dual 2.5" pipes, end to end(collectors to tips). It's free power, and economy, after the project cost.

 

[2000StreetRod]

no pre-cat H or X pipe

The cats are now 13 years old and probably need replacement before long so I've resumed investigating exhaust configuration options.

I'm no longer considering a pre-cat H or X pipe for two reasons. The main reason is there's no room for either. The other reason is any pre-cat cross flow might affect the fuel trims for each bank.

As I mentioned previously, currently the greatest flow restriction is in the downpipes where the bend is. I think the manifold outlet diameter is 2.25 inches but the bend in the downpipe narrows to a diameter of 1 7/8 inches. Replacing the stock downpipes with less restrictive formed ones and installing high flow cats containing inlet and outlet O2 sensor bungs should be a priority.

The stock dual input single output muffler configuration provides space efficient and economic cross flow capability. Replacing the stock three pass muffler with a dual mode muffler is desirable. The Corvette bi-mode muffler is not suitable because it has a single inlet and dual outlets. Maybe there's something else available.

 

[CDW6212R]

I agree about the cat pipes, they are not that big, and there are pinch points, like the 302 has 2.125" collector outlets(the ball socket end).

Think of the whole engine as 80% as big as a typical Mustang 302, plus almost 20% more rpm, which equates to almost the same needs for exhaust flow.

Stock 302 Mustangs come with true dual 2.25" exhausts, end to end(collector to tips), two mufflers and tail pipes. If you only use one muffler, it needs to be at least twice the area size of two 2.25" pipes(stock Mustang).

That's all stock figures, not upgraded high performance levels. Dual 2.5" pipes do not hurt, and most modified Mustangs have at least that. So nothing would be lost by upgrading to at least dual 2.5" pipes, front to back.

I'm not going to modify my 99 SOHC truck more, since I don't need it for work any longer. But for my 302 truck I'm skipping the 2.5" level, and going for 3", dual. I'm not saying try 3", but I would definitely go to 2.5" if I was doing a 4.0 SOHC truck.

What exhaust do the late model 4.0 SOHC Mustangs have in them, the total area from collectors back, how many mufflers etc? That would be a good minimum to work towards.

 

[2000StreetRod]

1/3 pass muffler

In an earlier post I mentioned it might be possible to modify a three pass muffler by adding an inlet that allows one pass: Modified 3 pass muffler? . In searching for a dual mode muffler I found that for a brief period in 1969 & 1970, GTO buyers were able to purchase an option known as “Vacuum Operated Exhaust”. Waldron's Exhaust sells a direct replacement for that muffler system. They call it driver controlled exhaust (DCE) and have a patent on it.

Unfortunately, the vacuum motor requires a minimum vacuum of at least 14 inches of mercury. Forced induction engines would probably need a vacuum pump. Also, the DCE muffler only has a single inlet.

Dynomax makes an Ultra-Flo X muffler that come with dual inlets and outlets of 2 1/4, 2 1/2 or 3 inch diameters. The internal cross pipe has a diameter of 3 inches.

. I haven't found any specs on the flow or the noise level yet but I suspect they are loud.

I'm considering the 2 1/2 diameter model with 2 1/4 to 2 1/2 adapters installed on the outputs of the cats and equal length 2 1/2 inch dia. pipes to the muffler inlets. One muffler outlet would go thru an electrically controlled cutout valve and then thru a tailpipe over the axle with no resonator. This would be the high flow performance (loud) path that would be blocked below a to-be-determined engine speed (maybe 3,000 rpm). The other muffler outlet would go to a small muffler (to reduce noise level) and then thru another over the axle tailpipe next to the high flow one. I might try using the stock resonator and 2 inch diameter tailpipe to see if its quiet enough.

I'll work on a block diagram and will add it when done.

 

[CDW6212R]

That's a lot of work while leaving some basic principles behind. More muffler volume(total internal volume of all mufflers), results in lower sound levels than smaller or less muffler volumes(for the same muffler model or type).

Why not lay out a largest mufflers you can find system, with the biggest pipes(less restriction, and end with tail pipes that fit and are not too big at the end(the ricer cars with huge tips(loud)).

There are 1/4 wave calculations that can help you to make pipe branches that dead end, and those cancel some droning. There is a big old thread on the Corral about those pipes, with many examples that show that it works. Each car is different, so it isn't as simple as copying someone else's pipe length/size.

Give the exhaust enough flow space, good mufflers that you like, and tips sized for your taste(not too big), and you should have a quiet enough result.

 

[2000StreetRod]

Some Ultra Flo X specs

I found some specifications on the Ultra Flo X muffler. The overall length is 25 inches and the shell length is 20 inches. The Part Number for the 2.5 inch port muffler is 17553.

PN Sound Flow Loss free HP
17552 Sport 1200 545
17553 Sport 1300 590
17554 Sport 1400 636
17555 Sport 1450 659

The sound level for a 370 HP Mustang:

Borla XS, 80db at idle, 90db at 2,000 rpm, 110db at WOT.
Magnaflow, 82db at idle, 91 at 2,000 rpm, 114db at WOT.
Flowmaster, 82db at idle, 93 at 2,000 rpm, 115db at WOT.
Dynomax UltraFlo, 83db at idle, 94 at 2,000 rpm, 113db at WOT.
Borla XR1, 83db at idle, 96db at 2,000 rpm, 118db at WOT.
No Muffler, 91db at idle, 103db at 2,000 rpm, MAX. (120+db).

 

[JCase]

Not trying to ruin a completely reasonable conversation on how to over-engineer a basic aspect of a combustion engine...but...why not just install some electric cutouts on what you have now? That way you get the quiet daily driver mannerisms AND the "all out" performance your looking for at the flip of a switch.

FWIW, I must say this thread has been very entertaining.

 

[2000StreetRod]

cutouts

. . . why not just install some electric cutouts on what you have now? That way you get the quiet daily driver mannerisms AND the "all out" performance your looking for at the flip of a switch. . .

Cutouts before the stock muffler would be too loud and I want all of the exhaust to exit at the rear of the vehicle.

 

[JCase]

Sorry, please continue...

 

[CDW6212R]

I found some specifications on the Ultra Flo X muffler. The overall length is 25 inches and the shell length is 20 inches. The Part Number for the 2.5 inch port muffler is 17553.

PN Sound Flow Loss free HP
17552 Sport 1200 545
17553 Sport 1300 590
17554 Sport 1400 636
17555 Sport 1450 659

The sound level for a 370 HP Mustang:

Borla XS, 80db at idle, 90db at 2,000 rpm, 110db at WOT.
Magnaflow, 82db at idle, 91 at 2,000 rpm, 114db at WOT.
Flowmaster, 82db at idle, 93 at 2,000 rpm, 115db at WOT.
Dynomax UltraFlo, 83db at idle, 94 at 2,000 rpm, 113db at WOT.
Borla XR1, 83db at idle, 96db at 2,000 rpm, 118db at WOT.
No Muffler, 91db at idle, 103db at 2,000 rpm, MAX. (120+db).

Dale, I didn't intend to cloud your thread or contradict your posts. After I read my last post, it sounded mean, and I didn't intend that. I like just about every idea you have come up with, I agree with most of them.

I had those Edlebrock Ultra Flow mufflers on my first 86 Crown Vic, all 2.25" pipes. Those were no "quiet" mufflers, but they are on the lower side compared to a lot of others. I liked them, and I think they were among the first few mufflers made that were straight through, with the louvered pipes and packing etc. I don't know how long they would last, I sold the car with about 75k on them. They came out in SS later, which was kind of rare then.

I did choose those partly because they were 20" long, versus most 14" aftermarket mufflers. That was around 1994. Regards,

 

[2000StreetRod]

learning about cats

One problem with being a "senior citizen" is that a lot of my knowledge is based on old technology. The early catalytic converters were fairly restrictive to air flow so I've been focusing on "high flow" cats. However, after doing a little reading on the internet I've learned that cats manufactured since the 1990s flow very well. Some OEM cats on less expensive vehicles (such as Honda Civic) have only about 3% restriction compared to a straight thru pipe. I also incorrectly assumed that cats for large engines would be superior to those for small engines. After reading a good article about cats, I'm less concerned about using a small cat which will fit in the space available. A cat that's rated for at least 4.0 liters should be adequate even if I add forced induction later because only half the flow goes thru each cat. The article indicates that a metal core cat is superior to a ceramic core for flow (only slighlty better) and for high temperature robustness.

 

[CDW6212R]

One problem with being a "senior citizen" is that a lot of my knowledge is based on old technology. The early catalytic converters were fairly restrictive to air flow so I've been focusing on "high flow" cats. However, after doing a little reading on the internet I've learned that cats manufactured since the 1990s flow very well. Some OEM cats on less expensive vehicles (such as Honda Civic) have only about 3% restriction compared to a straight thru pipe. I also incorrectly assumed that cats for large engines would be superior to those for small engines. After reading a good article about cats, I'm less concerned about using a small cat which will fit in the space available. A cat that's rated for at least 4.0 liters should be adequate even if I add forced induction later because only half the flow goes thru each cat. The article indicates that a metal core cat is superior to a ceramic core for flow (only slighlty better) and for high temperature robustness.

I will let you lead the way for choosing cats, if you get to it this Spring. I will need to find a pair for a 3" cat pipe I'm going to make. The last time I looked they cost between about $50 and $200 from the aftermarket. It wasn't clear then which types or brands were better. I didn't find any comparison tests or reviews, evaluations etc. Hopefully that's what you did find.