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Discussion Starter · #1 · (Edited)
Interesting topic! Have heard about exhaust reverson and back pressure on turbocharged motors, but have never seen it discussed. Hoping for some feed back to help me understand the topic better!??
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I am somewhat familiar with the difference between reversion and scavenging type headers on motorcycles from my track days with my KZ 1000 when I used to drag race it. I had a Vance and HInes 4 into 1 header on it that did very well at the WOT used in drag racing since it is a scavenge style system that is designed for WOT use but not so much for lower rpm street riding. When I quit racing and put my bike back on the street, I noticed that my low-end torque just did not seem as strong as I felt it should be and the bike was very hyper once I hit 7000 rpm range when it came up on the cams. The issue with the Vance&Hines is that it over scavenges at rpms below 7000 so it is actually sucking raw fuel out past the exhaust valve until the motor hit the 7000-rpm mark due to cam duration and overlap.

I found an old Warrior reversion header on eBay that is a 4 into 1 into 2 style that I put on my bike and immediately noticed my low end (2500 to 7000 rpms) was much stronger than with the Vance and Hines header. The bike would now light the tire up at 4000 rpm in the lower gears with just a twist of the throttle without clutching whereas with the Vance& Hines it would not do that at all without clutching. But the big plus was with the Warrior header I lost no top end power at the 7000- 10,000 rpms where it was up on the cams in the rpm range, I used in drag racing. So, I kind of had the best of both from the reversion header versus the scavenge header.

I much prefer the reversion style headers on a street vehicle over scavenge headers which are truly designed for WOT throttle uses. Of course, all that also depends on the cam profiles used and their duration/overlaps. It is just so much of an overall well-matched combo of parts to get the most from any engine.

I would also be interested in info from more educated folks than me on these subjects.

BD
 
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Agree it should be reversion not revision since what the exhaust is doing is reversing its direction of flow due to the rapid changes in pressure pulses within the exhaust system close to the exhaust port/header interfaces. That is why aftermarket headers are generally equal length rubes to try to minimize the reversion affect as compared to factory manifold/headers that can have varying length/combined runner/tubes.

Reversion occurs more at lower rpms with cams that have a lot of duration and overlaps since the exhaust valves are still open partially when the intake starts to open and that can allow positive pressure pulse from other cylinders to force burned exhaust gasses back into cylinders that still have the exhaust valve open thereby diluting the incoming intake charge with burned spent gasses. It is less of an issue once the engine rpms reach the point that the cam duration/overlap is happening faster than the exhaust pulses can force burned gasses back into adjacent cylinders, it what is commonly referred to getting up on the cam.

Conversely you can have the opposite effect occur if your header design tends to over scavenge at lower rpms by actually creating an opposite type of pressure pulse that is a negative pulse drawing the incoming intake charge in and right out past the still partially open exhaust valve thereby reducing the incoming intake charge versus diluting it with burned gasses. Again, it is less of an issue at higher rpms when there is less time for the pressure pulse to act on adjacent cylinders.

It is why the cam is always referred to as the heart of an engine because a poorly matched cam profile to intake and exhaust system can make or break the performance and power band the engine runs best at for its intended usages. It all has to be closely matched to create a well-balanced air pump which is all any ICE engine really is, we just add combustible mixture into the air stream to make it an engine.

For an example using a Harley V twin motor that you see mostly with two separate pipes referred to as drag pipes with one off each cylinder. They sound great and powerful but in reality, they kill all the low-end torque of the big v twins since the extreme pressure waves create a lot of reversion in the pipes that hamper good cylinder filling until you reach the upper rpms ranges of 4500 rpm and above. They are called drag pipes for a reason meaning they only perform best at WOT high rpm drag racing engine speeds. Put a 2 onto 1 header on a V twin like a thunder header and you suddenly have a whole different running engine that has gobs of low-end torque with very little to no loss of high rpm power.

BD
 

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Discussion Starter · #5 ·
Watched a YouTube video posted by "Tuned by Nishan". He makes an interesting connection between Exhaust Reversion and Engine Detanation!?
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Watched a YouTube video posted by "Tuned by Nishan". He makes an interesting connection between Exhaust Reversion and Engine Detanation!?
View attachment 43284
I remember seeing a link for that video in another thread either on this forum or the 6G forum. He explains it very well and is a perfect example of poorly designed exhaust runner/manifold lengths that allow for different flow characteristics and backpressure levels between cylinders. I understand ford did it to try to keep the engine very compact and less costly to manufacture for the power level it was intended to operate at as a mass-produced vehicle.

It is undeniable proof that the stock engine indeed does have an upper power limit before you reach the point of ecoboom. Also even going with a built engine as he stated you can still find that upper limit as well. The only way to get past the reversion/detonations limit would be to design a head with equal length exhaust runner/external header style manifold that flowed equally from all cylinders, but then there will always be a limit you will reach where components fail.

I find it interesting that the intake on the eco is so very well designed with equal length runners and flow volumes, yet it seems they just forgot about the exhaust side and matching it to flow comparable if not better than the intake. You have to get air in and out equally to make big power and make it live a long life.

There is a very good series on motortrend TV titled "Engine Masters" that I have recorded every episode where they test every aspect of engine performance and components interactions on a dyno to show what works and what does not in making power or not and the effects that they have on many different engines brand and combos. It is hosted by David Frieberger , Steve Dulcich and Steve Brulle of Westech performance in California. Tons of very in-depth testing and useful info for the hot rodder. You can stream it on motortrend+.

BD
 

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Discussion Starter · #7 ·
Watched some YouTube videos concerning boost and back pressure. Does anyone monitor both thier boost and back pressure?
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Discussion Starter · #8 ·
Has anyone seen any data, as far as increased exhaust flow (boost vs back pressure, etc) between the stock Turbochargers and the Aftermarket Turbochargers??
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Watched some YouTube videos concerning boost and back pressure. Does anyone monitor both thier boost and back pressure?
View attachment 43296
Those are some very good informative videos for sure. I like the on the cheap backpressure gauge idea just not sure how long the tire pressure gauge will hold up unless the length of copper oil line allows the heat to cool enough so it does not melt/deform the rubber seals in gauge or melt solder on Bourdain tube in gauge that moves the needle. I guess if you used his trick with the steel wool in a brass tee fitting to dampen the flow it would reduce the heat enough.

Do our ecos have exhaust backpressure sensors in the system that we can see with the MX+ or Cobb? I know I have seen some PIDs for exhaust but never actually looked to see if they were reading temp or pressures.

BD
 

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Discussion Starter · #10 ·
Those are some very good informative videos for sure. I like the on the cheap backpressure gauge idea just not sure how long the tire pressure gauge will hold up unless the length of copper oil line allows the heat to cool enough so it does not melt/deform the rubber seals in gauge or melt solder on Bourdain tube in gauge that moves the needle. I guess if you used his trick with the steel wool in a brass tee fitting to dampen the flow it would reduce the heat enough.

Do our ecos have exhaust backpressure sensors in the system that we can see with the MX+ or Cobb? I know I have seen some PIDs for exhaust but never actually looked to see if they were reading temp or pressures.

BD
LOL... Yea, I liked the "cheap backpressure gauge idea and steel wool in a brass tee idea" also! I'd probably run a minimum of 5 to 10 feet of line into the cab and maybe a filter to the gauge.
I removed my Turbocharger and there were no sensors to disconnect, so I'd have to say no to any factory sensor or port. Don't know if the ECU and/or Cobb device has the ability to monitor exhaust back pressure...? I'll need to do some research.
Over the past 3 racing seasons, I've had help from an Ecoboost builder and Ecoboost tunner, and have been told that in order to get the results I want, I'll need to crank up my boost. But I've held firm to my old school training, my low HP numbers and high ETs are on me. But, I have successfully brought my car home in one piece... And that's almost as good as a win!
Next step, change the turbo and install a back pressure gauge!! After that I'll probably start working on rear end gearing and perhaps make a tire change.
 

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LOL... Yea, I liked the "cheap backpressure gauge idea and steel wool in a brass tee idea" also! I'd probably run a minimum of 5 to 10 feet of line into the cab and maybe a filter to the gauge.
I removed my Turbocharger and there were no sensors to disconnect, so I'd have to say no to any factory sensor or port. Don't know if the ECU and/or Cobb device has the ability to monitor exhaust back pressure...? I'll need to do some research.
Over the past 3 racing seasons, I've had help from an Ecoboost builder and Ecoboost tunner, and have been told that in order to get the results I want, I'll need to crank up my boost. But I've held firm to my old school training, my low HP numbers and high ETs are on me. But, I have successfully brought my car home in one piece... And that's almost as good as a win!
Next step, change the turbo and install a back pressure gauge!! After that I'll probably start working on rear end gearing and perhaps make a tire change.

Yes, he has some good shade tree old skool tricks up his sleeve for sure. I agree on the 5-10 feet of copper line and actually I have one of those line kits somewhere in the garage I had bought to replace the plastic line on my 78 Datsun pickup back in 08 when I was working on the engine and carbs to get it back on the road but never finished it, still have it sitting on the side of the garage. It was a fun little truck with 2.0L 4 banger with twin SU carb setup off a 60s MG sports car, small cam and header it would run mid 14s in the 1/4 with a powerband of 4-7500 rpm and go thru the traps in 3rd gear. Truck only weighs 2200 LBs. Datsun back in the 70s made all kinds of performance parts for their L20b motors so the truck has a factory dual carb intake and peanut chamber cylinder high compression head on it that's worth way more than the truck ever will be since they are no longer made at all.

Yea I know there is no backpressure line/gauge anywhere on the turbo so was thinking it may have an inferred reading that could be seen with a cobb or MX+ based on the waste gate control sensor inputs to the PCM, I will do some research as well.

I agree on not turning up the boost to much and end up with a blown motor as a result, 3 seasons on the same motor is doing very well and for sure as good as wins indeed. I think rear gears and tires would be the best bang for the buck till you are ready to go big turbo and should get you in the12s pretty easy.

BD
 
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Discussion Starter · #13 ·
Currently looking for a spacer to install between my new Turbocharger turbine housing and engine cylinder head. Thick enough to place a tap in to add a backpressure gauge.
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Currently looking for a spacer to install between my new Turbocharger turbine housing and engine cylinder head. Thick enough to place a tap in to add a backpressure gauge. View attachment 43318
I like the ingenuity of using a pressure gauge in place of the tire pressure gauge from above video.

Why do you want a spacer between the turbo and head versus just drilling and tapping into the side of the turbo exhaust housing that bolts to the head itself. Just pack the inside of the housing with rags/paper towels very tightly do that any fillings/chips from drilling and tapping will be captured and can be vacuumed out easily before they make it to the impeller. You could even tape up the top if the rags/paper towels to the side of housing to add more protection as well.

BD
 

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Discussion Starter · #15 ·
I like the ingenuity of using a pressure gauge in place of the tire pressure gauge from above video.

Why do you want a spacer between the turbo and head versus just drilling and tapping into the side of the turbo exhaust housing that bolts to the head itself. Just pack the inside of the housing with rags/paper towels very tightly do that any fillings/chips from drilling and tapping will be captured and can be vacuumed out easily before they make it to the impeller. You could even tape up the top if the rags/paper towels to the side of housing to add more protection as well.

BD
There's a good chance that is what I will probably do. However, I've also been thinking of adding a spacer already, in order to get the heat from the turbo away from the engine block. It will also give me nice flat surfaces to tap. May have to build one, maybe from a salvaged turbine housing!??
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There's a good chance that is what I will probably do. However, I've also been thinking of adding a spacer already, in order to get the heat from the turbo away from the engine block. It will also give me nice flat surfaces to tap. May have to build one, maybe from a salvaged turbine housing!??
View attachment 43319

I had thought about the salvage turbo housing as well but the issue I see with that is not sure if the thickness of the flange portion of the housing is thick enough to be able to drill and tap a 1/8"-27 pipe thread since it would need to be at a minimum of 3/8" thick due to the pipe thread drill size being 5/16" which would only be 1/16" worth of material on either side of the threaded hole to cut threads. Being cast iron it would be enough material if you can make sure the drilled hole is perfectly centered in the flange. The other issue would be you will have to open up the salvage turbo flange once you cut the main housing off so it's not the 2-twin scroll passageways but rather just one open common area, so you get a true backpressure reading from all 4 exhaust ports/channels.

I would need to see the inside of the housing to determine the best location for the backpressure tap to be installed so it gets combined reading from all exhaust flow out of the head versus just 2 of the cylinders.

The other issue I see with either a spacer or modified salvage housing flange in trying to get the turbo farther away from the head is the fitment of the coolant and oil pressure/drain lines back onto the turbo as I am not sure how much flexibility/clearance they have to be relocated 3/8 to 1/2" farther away from the head. I have not had any of that off yet to know if that could be issues or not, then there is the downpipe fitment as well to be considered. Things tend to have a snowball effect at times.

Just my thoughts on making sure the signal is the most accurate it can be.

BD
 
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Discussion Starter · #17 ·
I had thought about the salvage turbo housing as well but the issue I see with that is not sure if the thickness of the flange portion of the housing is thick enough to be able to drill and tap a 1/8"-27 pipe thread since it would need to be at a minimum of 3/8" thick due to the pipe thread drill size being 5/16" which would only be 1/16" worth of material on either side of the threaded hole to cut threads. Being cast iron it would be enough material if you can make sure the drilled hole is perfectly centered in the flange. The other issue would be you will have to open up the salvage turbo flange once you cut the main housing off so it's not the 2-twin scroll passageways but rather just one open common area, so you get a true backpressure reading from all 4 exhaust ports/channels.

I would need to see the inside of the housing to determine the best location for the backpressure tap to be installed so it gets combined reading from all exhaust flow out of the head versus just 2 of the cylinders.

The other issue I see with either a spacer or modified salvage housing flange in trying to get the turbo farther away from the head is the fitment of the coolant and oil pressure/drain lines back onto the turbo as I am not sure how much flexibility/clearance they have to be relocated 3/8 to 1/2" farther away from the head. I have not had any of that off yet to know if that could be issues or not, then there is the downpipe fitment as well to be considered. Things tend to have a snowball effect at times.

Just my thoughts on making sure the signal is the most accurate it can be.

BD
It's definitely a challenge! The coolant and oil inlet have a little flexibility, but the oil return line has very little forgiveness. I took some measurements and I think the flange is around 3/8" thick.? Which is not really enough to drill out and tap. Tig Welding 2 together will require all new oil/coolant lines, etc. So it may be best to just machine a new one from scrap or just drill and tap the housing itself!??
Thanks for the input!!
 
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It's definitely a challenge! The coolant and oil inlet have a little flexibility, but the oil return line has very little forgiveness. I took some measurements and I think the flange is around 3/8" thick.? Which is not really enough to drill out and tap. Tig Welding 2 together will require all new oil/coolant lines, etc. So it may be best to just machine a new one from scrap or just drill and tap the housing itself!??
Thanks for the input!!
I was afraid of some of those issue being real obstacles to using salvage housing or new spacer as well. 3/8" inch would be very borderline for thickness to drill and tap but could be done, just not sure if it may crack at thin area of the side of tapped hole from heat/cold cycles. Plus, even then you will only be reading two cylinders backpressure instead of all 4 so it would be best to tap housing where the 2 passages combine into one common flow passage.

If it was not a twin scroll it would not be so much of an issue.

BD
 
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