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Wastegate Exhaust System?

2000StreetRod

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Year, Model & Trim Level
00 Sport FI, 03 Ltd V8
I've been told that the full potential of intake improvements (free flow air filter, larger MAF & throttle body) will not be achieved without reducing the exhaust restrictions on my SOHC V6. I've also read numerous threads emphasizing the need to retain exhaust back pressure to maintain low end torque.

Does anyone have an idea of how much back pressure in psi is needed?

I've been trying to dream up a way to have low restriction at high rpms and still have good torque at low rpms. One idea is to incorporate a wastegate in the exhaust system. The wastegate spring could be selected for the pressure needed to maintain torque. When the pressure is exceeded the excess could be vented to a high flow/low restriction muffler/tailpipe. With the proper pressure setting, during normal driving the stock (quiet) exhaust path would muffle all of the exhaust. During high performance driving the high flow (loud) exhaust path would supplement the stock path.

What are your reactions?
 



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This is a very interesting idea. I don't know much about wastegates. They do sell electronic exhaust cutouts that you could install. You would then need a way to control it so it would open up at a given throttle position. There are probably other ways to control a cutout but they would be more complex.

I thought I heard that the VW R32 has an exhaust system that is nice and quiet but once you punch it it opens up and goes through different routing to be louder. I think it is vacuum controlled. You could look into how that system works.

http://www.youtube.com/watch?v=BQUE271zAbw

I would try to look into how that system works and see if you could make something similar.
 






This is a very interesting idea. I don't know much about wastegates. They do sell electronic exhaust cutouts that you could install. You would then need a way to control it so it would open up at a given throttle position. There are probably other ways to control a cutout but they would be more complex.

I thought I heard that the VW R32 has an exhaust system that is nice and quiet but once you punch it it opens up and goes through different routing to be louder. I think it is vacuum controlled. You could look into how that system works.

Thanks for your input. I never thought of an electronically controlled cutout. It could be vented to a high flow muffler to reduce the noise and harshness. A commercially available one is probably either wide open or closed. I need something variable (from slightly open to full open) to maintain a constant back pressure. I would want it controlled by back pressure instead of throttle position.

Most external wastegates on turbo systems are set to open at a specific pressure (psi). The simple ones have a calibrated spring (for example 12 psi) that open when the pressure is exceeded. The lowest pressure I've seen advertised is about 5 psi which may be too much for my application.

I'll try to find out about the VW R32.
 






PowerStroke Waste Gate Exhaust

I recently did some searching on the internet and learned that the Ford PowerStroke has an exhaust back pressure sensor that provides data to the powertrain control module (PCM). The PCM remotely controls exhaust back pressure via the waste gate to help warmup after a cold start. The system is somewhat complicated and based on user reports has some reliability problems.

I also learned that Ferrari has a exhaust back pressure relief system for high performance situations.
 






Heat riser valve exhaust control

Here's an alternative to using a wastegate or electrically controlled cutout to relieve excess back pressure while maintaining adequate back pressure for good torque - a vacuum actuated heat riser valve. Ford used them on their V8 engines in the early and mid 1980s. The valve could open a high flow exhaust path when high performance is requested by the driver. I just bought one on eBay for $20 to experiment with.

I have not yet heard from anyone how much back pressure (in psi) an SOHC V6 needs to supply good torque. Does anyone know?
 






Here's an alternative to using a wastegate or electrically controlled cutout to relieve excess back pressure while maintaining adequate back pressure for good torque - a vacuum actuated heat riser valve. Ford used them on their V8 engines in the early and mid 1980s. The valve could open a high flow exhaust path when high performance is requested by the driver. I just bought one on eBay for $20 to experiment with.

I have not yet heard from anyone how much back pressure (in psi) an SOHC V6 needs to supply good torque. Does anyone know?

Back pressure is not the best term to be using. You want exhaust velocity and volume. Your goal is to find the pipe size and muffler that gives you the best exhaust velocity without sacrificing volume. When you go to a larger pipe, you are increasing the volume, but the velocity is going to slow down, this can affect your torque. The larger pipe kind of acts like a radiator, there is more surface area for the exhaust gases to cool down, therefore slow down. The hotter you can keep the exhaust gases, the faster they will flow. The term back pressure can relate to the exhaust velocity because the smaller, more restrictive stock pipes help to retain exhaust velocity, which is why it sometimes stock seems to have more low end torque. My suggestion, find the muffler of your choice, and go with a single 2.5" pipe. Then either have the pipes coated with some kind of ceramic coating to retain heat, or have the pipes wrapped with header wrap. On my frontier, I wrapped my pipes coming from the cats going in to the muffler, and then the muffler. The result, after the pipes heated up and everything was at normal operating temp, low end torque was noticeably better than before. Nothing big, but still noticeable. Plus this helps to keep heat away from the passenger compartment. I think that if you wrapped the pipes going to the muffler, and the tail pipe, and if you had a good quality muffler you could wrap that and have some decent results. You would maintain a good exhaust velocity, and have the volume to have good higher rpm gains.

Dan
 






...You want exhaust velocity and volume. Your goal is to find the pipe size and muffler that gives you the best exhaust velocity without sacrificing volume. ...My suggestion, find the muffler of your choice, and go with a single 2.5" pipe. ...
Dan

Thanks for your response!

I notice that you used to have a Sport. Are you recommending a 2.5 inch diameter system based on your experience with a SOHC? I have a catalytic converter for each bank of cylinders. The output of each "cat" connects to a dual input/single output muffler. Should I stay with that configuration or combine each "cat" output in a "Y" prior to the muffler?

Do you think a powered exhaust extractor would improve low end torque and high performance?
 






I had an OHV in my sport, and used 2.5" pipe with no real ill side effects. It doesn't really make a difference if you use the y-pipe or a dual inlet muffler, as the dual inlet muffler will act like a y-pipe any way, and it will save space underneath. Not sure on the extractors, or what you are referring to. If it is a fan of sorts that fits in the exhaust, I would drop that idea as it would probably cause a restriction at higher rpms. But I would seriously look at the Aeroturbine mufflers. Their concept looks really interesting and they do sound really good.
http://www.aeroexhaust.com/dual_stainless_muffler_156.html
That has a 3" outlet, but I'm sure adapters could be used to knock it down to 2.5".

Dan
 






Progressive exhaust system

Due to some recent PMs from forum members I have resumed my investigation of revising my exhaust system. I spoke with the exhaust technician who installed my wideband O2 sensor about the possibility of having two mufflers and tailpipes. He told me I could probably fit two mufflers but two tailpipes would not fit under the existing heat shields. So I'm considering a single 3 inch diameter tailpipe with the output of each muffler combining via a "Y" connector. The drawing below is a block diagram of a possible configuration.
dual.jpg

The proposed plan is to activate (open) the vacuum controlled crossover valve at 3,000 rpm. For lower engine speeds all exhaust will flow thru the high flow muffler. The right bank will get to the left muffler via the "X" pipe which also balances the exhaust between the two banks in the same way as a cross pipe. Above 3,000 rpm the more direct flow will be thru the very high flow muffler. Some flow will still go thru the left muffler with the exhaust taking the path of least resistance. The two flows will combine with the "Y" pipe and exit via a 3 inch diameter tailpipe.

One of my concerns is if the manifold vacuum will be adequate to keep the valve open from 3,000 to 6,000+ rpm. However, vacuum activators were used on the SOHC variable induction system (variable length intake runners) on the 97 and 98 SOHC engines so that should not be a problem.

Another concern is finding the right length and shape mufflers to fit in the space available. I wish that 32 inch glass pack mufflers were still available because that might be a candidate for the left (high flow) muffler with an 18 inch long one for the right (very high flow) muffler. I don't want a loud exhaust below 3,000 rpm. I have to do a lot of muffler research in the future.

I will probably not implement my exhaust modification until the stock cats start showing signs of deterioration. My current odometer is 151,000 miles so that time will probably come fairly soon. That way I will feel justified in purchasing high flow cats as part of the modification.

Any comments?
 






Are you planning on forced induction or Nitrous? Otherwise it IMO seems like a lot of work and money for a pretty minimal gain. That being said though it looks like it should work fairly good if you can get the valve to actuate when you want it to reliably.
 






no nitrous or blower

Are you planning on forced induction or Nitrous? Otherwise it IMO seems like a lot of work and money for a pretty minimal gain. That being said though it looks like it should work fairly good if you can get the valve to actuate when you want it to reliably.

When I was working on my intake modifications I kept getting advice from members to improve my exhaust. The logic was that air can't get in if it can't get out. Now that the basics of my intake system are implemented I'm thinking about the exhaust. I have no interest in nitrous or blowers because my main objective is to see what improvements I can achieve in fuel economy with less emphasis on power increase. Obviously since the very high flow path only opens above 3,000 rpm it's not going to improve fuel economy. But it should improve driving pleasure when I choose to utilize the capability.

I'm going to check my PCM to see if it still has the variable induction system capability that was on the SOHC in 97 and 98. If so, I'll use the PCM to activate a vacuum solenoid that controls the crossover valve.

I'm expecting at least an increase of 15 rwhp with the mod.
 






I honestly don't see how this is going to be very beneficial to you, if anything your just adding more weight your exhaust system and that may negate any improvements you may see. I really think your best bet would be to chose either a dynomax Ultraflow, or magnaflow muffler about 24" in length with 2.5" pipes and settle with that. Then if you really wanted, wrap the entire system with header wrap to retain all the heat within the pipes to keep your exhaust velocity as high as possible. Or even have your system coated with a hi-temp ceramic coating. I think this will give you the best balance with low end torque, and mileage and not sacrificing high end power at all. A 2.5" system should adequately flow enough for 250+ hp. With the system you described above, your adding a lot of bends, and possibly a lot of turbulence to the system. As well as creating a ton of potential problems. The 3" pipe will be overkill for you. If anything you still want to do something like this, I would install a set of exhaust cutouts that are electrically controlled. Then have them set up so that they open at either full throttle or somewhere like 2/3-3/4 throttle. But with doing so you are limited to space underneath. But I still stand by what I told you as being the best option for you and giving you the ultimate advantage to both mileage and hp increases without being overly complicated. Don't try to over-complicate something that is really only going to have a minimal impact on hp and mileage. The engine really only has a certain volumetric efficiency, to improve on that, your going to have to look at going internal and having a full CUSTOM tune done. Your idea has some merit, but it is not going to work well with a single exhaust system and the very limited space under the explorer.

Dan
 


















I appreciate your comments!

. . . I really think your best bet would be to chose either a dynomax Ultraflow, or magnaflow muffler about 24" in length with 2.5" pipes and settle with that. Then if you really wanted, wrap the entire system with header wrap to retain all the heat within the pipes to keep your exhaust velocity as high as possible. Or even have your system coated with a hi-temp ceramic coating. I think this will give you the best balance with low end torque, and mileage and not sacrificing high end power at all. A 2.5" system should adequately flow enough for 250+ hp. With the system you described above, your adding a lot of bends, and possibly a lot of turbulence to the system. As well as creating a ton of potential problems. The 3" pipe will be overkill for you. If anything you still want to do something like this, I would install a set of exhaust cutouts that are electrically controlled. Then have them set up so that they open at either full throttle or somewhere like 2/3-3/4 throttle. But with doing so you are limited to space underneath. But I still stand by what I told you as being the best option for you and giving you the ultimate advantage to both mileage and hp increases without being overly complicated. . . Dan

Dan, I appreciate your latest and previous posts. Thank you for taking the time!

I want to avoid a noisy muffler for normal driving but also want high performance when desired. There are few, if any, reasonably quiet high performance mufflers (if you know of one please tell me). That's why I started considering two mufflers.

It seems to me that "tuning" effects would be minimal downstream of the equalizer pipe between the two banks. It also seems that the closer the equalizer is to the exhaust ports the greater the "tuning" effect. The cats probably further reduce tuning effects. I suspect that past the post cat equalizer pipe low restriction is more important than exhaust velocity.

I think I understand your emphasis on heat retention to maintain exhaust velocity and plan to use a wrap on the downpipes and downstream to include the equalizer pipe. I'm a little concerned that wrapping the downpipe upstream of the cat may increase the cat temperature and reduce its effectiveness and shorten its life. But if the new cats only last 100,000 miles instead of 200,000 miles they'll still probably last longer than I'll live.

I agree that a single 2.5 inch diameter pipe is adequate for 250 hp and I'm not anticipating more than 225 rwhp with my current and future mods. However, I like the concept of decreasing diameter for intake and increasing diameter for exhaust. I believe the downpipes are 2.25 inches in diameter and I think the smallest "X" pipe I can buy has a diameter of 2.5 inches. I'll stay with 2.5 inches diameter for both paths until the "Y" pipe which will go to 3 inches to match the tailpipe.

I considered an electric cutout instead of a vacuum valve but it is much more expensive. I bought a new Ford vacuum valve for an Econoline van for $20. I can buy a vacuum solenoid that will work with the PCM variable induction system output for less than $20. On the 97 and 98 models the PCM closes the solenoid/valve below 3,000 rpm and opens it above 3,600 rpm. I thought about using the WOT PCM signal to open the valve but wouldn't that defeat the idea that the SOHC has better torque with a smaller exhaust area?
 







Looking at your diagram, this will actually make things flow LESS. do some research on the late model Z06's, and how their dual mode exhaust is setup. That might give you an idea. Also, please do more research on how an exhaust system helps to make power. You're hung up on backpressure which is the wrong variable to focus on.
 






Bi-mode muffler

. . . do some research on the late model Z06's, and how their dual mode exhaust is setup. That might give you an idea. Also, please do more research on how an exhaust system helps to make power. You're hung up on backpressure which is the wrong variable to focus on.

I was able to find considerable information on the bi-mode mufflers but very little on the overall exhaust configuration. It appears to have an "H" pipe with a cat for each bank prior to the crossover. After the crossover each pipe feeds a bi-mode muffler with single inlet and dual outlets. One of the dual outlets has a vacuum actuated valve prior to the large diameter tip. When the valve is closed the exhaust is forced to take a longer and muffled path to the tip. When the valve is open it allows the exhaust to follow a straight thru short circuit to the tip but the longer path remains open.

The Corvette concept seems similar to the one I have proposed. The pipe diameter increases from front to back. The crossover is near the headers but still after the cats. The main difference is the valve is after the muffler on the Corvette vs ahead of the muffler on mine. Also, the Corvette has four tips vs one on mine.

I can't remember if the stock piping prior to the mufflers is 2.5 or 3.0 inches in diameter. I think it varied by year. The muffler outlets look to be only 2.5 inches in diameter feeding much larger diameter tips. The system appears to have little if any tuning downstream of the crossover and seems mainly designed to relieve back pressure and increase noise (attention).

As I recall from many years ago, tuning is timing exhaust pulse reflections to occur at the exhaust port of another cylinder at a specific time to extract waste gas from the cylinder and increase air flow. The engine speed range for the tuning to be effective is narrow. The exhaust pipes have to be equal length and a cylinder has to be paired with another according to firing order. The incorporation of cats and O2 sensors pretty much doomed the real tuning for street legal vehicles. The only factors that seem to be left are exhaust velocity and flow restriction. What else is there?
 






Good reading on exhaust design

The following link provides concise and informative data on designing high performance exhaust systems. Exhaust Science Demystified
In my opinion, it is worth reading several times to "digest" the content.
 






I was able to find considerable information on the bi-mode mufflers but very little on the overall exhaust configuration.

Exactly. They did it at the muffler. The Z06 was essentially a "spare no expense" car. If an arrangement such as the one you're suggesting was better....................wouldn't they have done it?
 



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PCM has no VIS output

Today I received a Ford book of wiring diagrams for the 2000 Explorer. PCM pin 46 that controlled the variable intake system on the 97 and 98 SOHCs is now used to illuminate a fuel cap off light in the instrument cluster. Too bad! I can think of two possible alternatives for a control signal for an exhaust flow valve. One is strictly rpm based that could be derived from the tachometer signal that goes to the instrument panel. The other is load based that could be derived from the MAF sensor output voltage.
 






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