The Only 3300 lb. Buick V6 in the 8s using...

[Alky V6]

2-3 years ago I did not realize it until I started monitoring it and tuning more and more cars. Now I hate to tune a car that doesn't monitor it. I do know how much there is to gain which is why I have stated numerous times this is why you can run the et's you do with your heads. I don't think many others realize just how much power an engine can gain. The only reason most of us class racers can't capitilize on it is because of the limits of the class, in order to have parity between all power adder types.

The new HP turbo's from Precision are making the rules makers go back to work because you now have 94mm turbo's capable of power it took a 106mm to accomplish just 4 years ago.

Did you realize, though, that you could actually create hp from engine pumping work alone with the right exhbp to intbp ratio?

 

[its2qik]

Did you realize, though, that you could actually create hp from engine pumping work alone with the right exhbp to intbp ratio?

Don, I learned this a few years ago myself. As a result, I engineered some small jet engines that fit right into the ends of my tailpipes. They actually create horsepower by sucking the exhaust out the pipes. I will be marketing them very soon.

 

[Dusty Bradford]

we're just picking up two hundred more horsepower throughout the RPM band, collectively (averaged), but this pickup in horsepower due to reduced exhaust pressure also raises naturally aspirated horsepower at the same time, it has to...

I'm confused here. What do you mean by averaged hp? I'm talking a 2000hp engine now making 2200hp just by dropping back pressure. It's easy to assume Don has gained over 100hp from his bp being so low...maybe more.

I'm also confused by reducing back pressure on an n/a engine. An n/a engine doesn't have back pressure. Sure you can play with step headers and collector design to gain 10-20hp from scavenging on an n/a engine but that is nothing compared to dropping back pressure on a turbo engine. We're talking over 10% gain.

 

[Dusty Bradford]

Did you realize, though, that you could actually create hp from engine pumping work alone with the right exhbp to intbp ratio?

I wouldn't have called it creating hp. Boost also creates hp. Anyime back pressure is lowered while still maintaing the same boost, the car will run faster.

 

[Alky V6]

I wouldn't have called it creating hp. Boost also creates hp. Anyime back pressure is lowered while still maintaing the same boost, the car will run faster.

Think of it this way. You gave an example of how exhaust back pressure can cause pumping work losses by hooking up shop air to the exhaust manifold. As you decrease the amount of shop air pressure in your example, the pumping losses decrease. All the way to the point where both intake and exhaust are both at atmospheric pressure.
Now take that shop air and now hook it up to the intake side and begin increasing the pressure on the piston through the intake side. Forgetting for the moment that boost pressure will also be involved.

With the shop air on the exhaust side of one piston positioned to try to expel exhaust gasses, and atmospheric pressure working on another piston that is positioned to receive intake air, the pressure differential between the two pistons is working against the engine trying to rotate in the preferred direction. You have pumping losses in this instance.
Switch it around where now the piston that is trying to expel exhaust gasses is now seeing a lower pressure than the piston that is receiving intake air pressure, you can see that now the pressure differential between the two pistons is attempting to push the one piston, attempting to intake air, in the engine rotation direction that is desireable. In this scenario, you are actually creating hp, from the pressure differential, alone. You have negative pumping losses. Or, actually pumping gains, which means instead of having net hp losses due to pumping work, you have a net gain in horsepower due to pumping work.

 

[Alky V6]

I'm confused here. What do you mean by averaged hp? I'm talking a 2000hp engine now making 2200hp just by dropping back pressure. It's easy to assume Don has gained over 100hp from his bp being so low...maybe more.

I'm also confused by reducing back pressure on an n/a engine. An n/a engine doesn't have back pressure. Sure you can play with step headers and collector design to gain 10-20hp from scavenging on an n/a engine but that is nothing compared to dropping back pressure on a turbo engine. We're talking over 10% gain.

You can increase the power of an engine that is at an idle by sucking on the exhaust pipe. That's why it's not a good idea to work on dialing in your fuel table when there is a fume collector stuck to the end of the exhaust pipe.

 

[Street Lethal]

I'm confused here. What do you mean by averaged hp? I'm talking a 2000hp engine now making 2200hp just by dropping back pressure. It's easy to assume Don has gained over 100hp from his bp being so low...maybe more.

I understand what you are saying, and I realized by my explanation I said it in a confusing way. The turbo being used in the equation is capable of 2200-HP to begin with, but because of back pressure, it is being restricted as to realizing it's full potential. Being in a restricted state (meaning too high of backpressure), we're leaving horsepower on the table, and all we're doing by eliminating backpressure is unleashing it, not necessarily creating more than what the turbo is capable of producing to begin with, but maximizing it...

I'm also confused by reducing back pressure on an n/a engine. An n/a engine doesn't have back pressure. Sure you can play with step headers and collector design to gain 10-20hp from scavenging on an n/a engine but that is nothing compared to dropping back pressure on a turbo engine. We're talking over 10% gain.

Wouldn't it be the same difference, but on a smaller (vacuum) scale? Meaning, if we open up the exhaust ports, and run longtube headers, the naturally aspirated engine is less restricted, and can spin more freely. It wouldn't be as significant of an increase of horsepower as on the boost side of the spectrum of course, but still the same principle would apply though, no? There is roughly 6.802% of air in every pound of boost, and at 15psi, we're looking at about 100%. How could decreasing backpressure allow for more air at, for example, 15psi? The extra horsepower is realized throughout the RPM, no? Meaning in areas under the curve, and just after peak, horsepower is raised as apart of the average throughout the whole entire spectrum. If horsepower is raised during peak, then that just means the turbo was being restricted and we helped maximize for what it was already designed to do, but by no means did we exceed it though...

 

[Alky V6]

I understand what you are saying, and I realized by my explanation I said it in a confusing way. The turbo being used in the equation is capable of 2200-HP to begin with, but because of back pressure, it is being restricted as to realizing it's full potential. Being in a restricted state (meaning too high of backpressure), we're leaving horsepower on the table, and all we're doing by eliminating backpressure is unleashing it, not necessarily creating more than what the turbo is capable of producing to begin with, but maximizing it...



Wouldn't it be the same difference, but on a smaller (vacuum) scale? Meaning, if we open up the exhaust ports, and run longtube headers, the naturally aspirated engine is less restricted, and can spin more freely. It wouldn't be as significant of an increase of horsepower as on the boost side of the spectrum of course, but still the same principle would apply though, no? There is roughly 6.802% of air in every pound of boost, and at 15psi, we're looking at about 100%. How could decreasing backpressure allow for more air at, for example, 15psi? The extra horsepower is realized throughout the RPM, no? Meaning in areas under the curve, and just after peak, horsepower is raised as apart of the average throughout the whole entire spectrum. If horsepower is raised during peak, then that just means the turbo was being restricted and we helped maximize for what it was already designed to do, but by no means did we exceed it though...

Mmm. Close.
It's not that you're restricting the turbo with the high exhaust backpressure. It's more like you're restricting the engine from being able to rotate more freely, eating up horsepower.

On the second reply. The affect or hp gain that you would expect when pressure pulse tuning a naturally aspirated engine is scaled similarly as boost levels are increased. In other words, if a naturally aspirated engine saw a gain of 20 hp due to pressure pulse tuning at one atmosphere, you wouldn't expect only a 20 hp increase from pressure pulse tuning with the engine operating at more than one atmosphere.

 

[Street Lethal]

Mmm. Close. It's not that you're restricting the turbo with the high exhaust backpressure. It's more like you're restricting the engine from being able to rotate more freely, eating up horsepower.

On the second reply. The affect or hp gain that you would expect when pressure pulse tuning a naturally aspirated engine is scaled similarly as boost levels are increased. In other words, if a naturally aspirated engine saw a gain of 20 hp due to pressure pulse tuning at one atmosphere, you wouldn't expect only a 20 hp increase from pressure pulse tuning with the engine operating at more than one atmosphere.

Here is a better explanation. Lets say theoretically we dyno a 3.8 engine at 300-FWHP natually aspirated with open headers. Now, we throw on a turbo, at 0-psi of boost the engine will no longer see 300-FWHP because the turbine becomes a restriction in the exhaust, so let's just say it now embellishes 250-FWHP because of the backpressure caused by the turbo restriction which is now at a 2:1 ratio. Still at 0-psi, if we eliminate backpressure down to say 1:1 by opening up the exhaust housing, the engine will read higher than 250-FWHP, slowly making it's way back to the 300-FWHP number because it is being allowed to flow again. So we're not really creating more horsepower, we're just allowing the engine to realize it's potential. As power increases on the boost side, it has no choice but to increase on the vacuum side, again not as substantial on the vacuum side though, but it does increase, it has to. 15-psi will always double the amount of air entering the engine at 0" of vacuum, and if we make more power at 15-psi because of reduced backpressure, that is because engine horsepower also increased at 0" of vacuum. It has to. So ultimately, the potential power is already there to be discovered, we're just untapping it because of the turbine restriction, but it was always there though nonetheless...

 

[Alky V6]

Here is a better explanation. Lets say theoretically we dyno a 3.8 engine at 300-FWHP natually aspirated with open headers. Now, we throw on a turbo, at 0-psi of boost the engine will no longer see 300-FWHP because the turbine becomes a restriction in the exhaust, so let's just say it now embellishes 250-FWHP because of the backpressure caused by the turbo restriction which is now at a 2:1 ratio. Still at 0-psi, if we eliminate backpressure down to say 1:1 by opening up the exhaust housing, the engine will read higher than 250-FWHP, slowly making it's way back to the 300-FWHP number because it is being allowed to flow again. So we're not really creating more horsepower, we're just allowing the engine to realize it's potential. As power increases on the boost side, it has no choice but to increase on the vacuum side, again not as substantial on the vacuum side though, but it does increase, it has to. 15-psi will always double the amount of air entering the engine at 0" of vacuum, and if we make more power at 15-psi because of reduced backpressure, that is because engine horsepower also increased at 0" of vacuum. It has to. So ultimately, the potential power is already there to be discovered, we're just untapping it because of the turbine restriction, but it was always there though nonetheless...

I think you're still missing one very important point. This is a point that is not discussed much, but I have been trying to get across through the last few posts. When the exhbp to intbp ratio becomes better than 1:1, such as 0.900:1.000, you can have a situation where hp is being created not by the air/fuel mixture, but by pumping work of the engine.

 

[Alky V6]

It would be like having a naturally aspirated engine in a closed off engine dyno cell. The intake air would be at atmospheric from a source outside the dyno cell room. But,... the area where the exhaust from the engine is being routed to is pumped down to a pressure level that is below the intake source air pressure. It is a form of supercharging. The intake air is at a higher pressure than the exhaust side.
You just created hp out of thin air by changing the pressure differential between the intake and the exhaust side. Of course, there would also be some amount of hp increase from the better VE that would also result.
The piston had to work less when attempting to expel the exhaust gasses. Or, another way to look at it, the intake side had more intake air pressure acting on the piston during the intake stroke helping to push the piston down the bore.

 

[Alky V6]

Clear as mud, right?

 

[Alky V6]

Look at an extreme example. A supercharged engine at WOT has very little exhaust backpressure. Imagine taking away the parasitic drag of having to turn the supercharger. A supercharged engine has an extreme pressure differential across a piston on intake and a piston on the exhaust stroke. But, the drag of running the supercharger and the efficiency of some superchargers keep the gains in check when comparing to a turbocharged application.

And, exhaust backpressure in a turbocharged application keeps gains in check through pumping losses. Take away the pumping losses. Don't just neutralize the pumping losses, but begin to have the pumping work of the engine work for you.

 

[Alky V6]

Is any of this soaking in?

 

[Alky V6]

Do any of you need another example?

 

[Dusty Bradford]

Here is a better explanation. Lets say theoretically we dyno a 3.8 engine at 300-FWHP natually aspirated with open headers. Now, we throw on a turbo, at 0-psi of boost the engine will no longer see 300-FWHP because the turbine becomes a restriction in the exhaust, so let's just say it now embellishes 250-FWHP because of the backpressure caused by the turbo restriction which is now at a 2:1 ratio. Still at 0-psi, if we eliminate backpressure down to say 1:1 by opening up the exhaust housing, the engine will read higher than 250-FWHP, slowly making it's way back to the 300-FWHP number because it is being allowed to flow again. So we're not really creating more horsepower, we're just allowing the engine to realize it's potential. As power increases on the boost side, it has no choice but to increase on the vacuum side, again not as substantial on the vacuum side though, but it does increase, it has to. 15-psi will always double the amount of air entering the engine at 0" of vacuum, and if we make more power at 15-psi because of reduced backpressure, that is because engine horsepower also increased at 0" of vacuum. It has to. So ultimately, the potential power is already there to be discovered, we're just untapping it because of the turbine restriction, but it was always there though nonetheless...

You do understand a turbo doesn't automatically go to 2:1 ratio unless your maxing it out. Just take a 70mm on a stock block. At 10psi it may be .9:1, 20 psi may be 1:1 and then at 30psi it could be 2:1. To get the bp less than the intake will require a super sized turbo or twins. In pretty much every case when you size a turbo to accomplish this you will need nitrous to get it going. Just like running a T6 80mm on a stock block combo. It may make killer power up top but will be a dog without nitrous assist.

None of this is applicable to a class racer with turbo limits.

 

[turbobitt]

Do any of you need another example?

This doesn't work like you think.

You are not considering that the crankcase is still at or near atmosphere and there is still exhaust backpressure regardless of how more or less than boost pressure. Pumping losses are still there and not "generating power". Still a high pressure differential across the piston top and bottom in favor of pumping loss.

Allan G.

 

[Dusty Bradford]

Think of it this way. You gave an example of how exhaust back pressure can cause pumping work losses by hooking up shop air to the exhaust manifold. As you decrease the amount of shop air pressure in your example, the pumping losses decrease. All the way to the point where both intake and exhaust are both at atmospheric pressure.
Now take that shop air and now hook it up to the intake side and begin increasing the pressure on the piston through the intake side. Forgetting for the moment that boost pressure will also be involved.

With the shop air on the exhaust side of one piston positioned to try to expel exhaust gasses, and atmospheric pressure working on another piston that is positioned to receive intake air, the pressure differential between the two pistons is working against the engine trying to rotate in the preferred direction. You have pumping losses in this instance.
Switch it around where now the piston that is trying to expel exhaust gasses is now seeing a lower pressure than the piston that is receiving intake air pressure, you can see that now the pressure differential between the two pistons is attempting to push the one piston, attempting to intake air, in the engine rotation direction that is desireable. In this scenario, you are actually creating hp, from the pressure differential, alone. You have negative pumping losses. Or, actually pumping gains, which means instead of having net hp losses due to pumping work, you have a net gain in horsepower due to pumping work.

I dont need any explanation Don. This is well known info in many of the turbo shops, it's just never discussed. The turbo companies recognized the advantage of lower back pressure years ago and began designing turbos to achieve this. They knew if they could design a turbo that would meet the compressor side requirements and would spool easily but lower back pressure they would own the the market. A perfect example was when Precision rolled out the Pro mod turbo line-up. These turbos quickly put a large gap between other turbo cars as well as the nitrous and blower cars. The rules commitees had to ban these units to maintain parity or limit them to smaller turbos.

 

[Alky V6]

This doesn't work like you think.

You are not considering that the crankcase is still at or near atmosphere and there is still exhaust backpressure regardless of how more or less than boost pressure. Pumping losses are still there and not "generating power". Still a high pressure differential across the piston top and bottom in favor of pumping loss.

Allan G.

Yes. Pumping losses are a little more involved, but my scenario is sound.
Crankcase pressure on the back side of the pistons is an equal pressure value against all the pistons. One piston is not seeing a greater or less crankcase pressure value over another. What is making the difference is the pressure differentials that are occurring against the tops of the pistons.

When you have one piston expelling exhaust gases, you also have another piston taking in an intake charge. You also have another piston on a power stroke and another on a compression stroke and other pistons in various positions of a particular stroke of the 4 stroke cycle. So yes, pumping losses are not as simple as the examples of just 2 pistons that I gave above.
While one piston is on its power stroke, that power stroke, along with any rotating inertia (flywheel affect) must be enough to overpower the resistance of another piston working to compress its charge in preparation for combustion, another piston working to expel exhaust gases against an exhaust backpressure, another piston working to intake an air/fuel charge under boost pressure, whatever other pistons in various positions of the 4 stroke cycle, and have extra power to make up for all the other types of parasitic losses, and still supply power to the ground. Moving the atmosphere around that is under the pistons does offer some pumping work resistance also. The major players in pumping work losses though, is the piston on its compression stroke, a piston at the beginning of its power stroke (still positioned btdc), and the piston working to expel exhaust gases.

The piston that is on its exhaust stroke can have its pumping work losses modified through manipulation of the exhaust backpressure value.
The piston that is at the beginning of its power stroke (still positioned btdc at ignition) can have its pumping work losses optimized by not using more ignition timing than is necessary. In fact, using a 'minimum best timing' value.
The piston that is on its compression stroke can have its pumping work losses modified by not using more boost than is necessary for a particular power output target.

 

[Alky V6]

I dont need any explanation Don. This is well known info in many of the turbo shops, it's just never discussed. The turbo companies recognized the advantage of lower back pressure years ago and began designing turbos to achieve this. They knew if they could design a turbo that would meet the compressor side requirements and would spool easily but lower back pressure they would own the the market. A perfect example was when Precision rolled out the Pro mod turbo line-up. These turbos quickly put a large gap between other turbo cars as well as the nitrous and blower cars. The rules commitees had to ban these units to maintain parity or limit them to smaller turbos.

This is interesting. I've never heard of this topic explained in detail from anyone. I had to figure it out for myself. Books did bring up the 'Holy Grail' of turbocharging, but simply left the definition at a "lower exhaust backpressure to intake boost pressure ratio". They would never go into detail about the swing in pumping losses from positive to negative. The sim did help show me that advantage, though. When I was aware enough to see it in the sim calculation results.