The 'Holy Grail' is a short lived thing, though. As one increases boost levels, eventually the exhbp to intbp ratio will work back up from favorable to 1:1 again, and higher ratios as boost levels are further increased. I know that in my case, at 28 psi boost I am still at a very favorable .90:1 exhbp to intbp ratio. :biggrin:
The Only 3300 lb. Buick V6 in the 8s using...
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turbobitt
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- Feb 14, 2002
Your scenario is not sound. The only thing you can do is minimize pumping loss but not create power through positive pumping. You are missing a key elment - Compression stroke.
Yes, atmosphere is acting on all undersides of pistons but it is still the pressure differential across all of them that creates the pumping loss. Point being if you had equal crankcase pressure as boost pressure, then the engine would truley think it's NA, not just the valvetrain. The majority of pumping loss accurs on the compressiion stroke and regardless, there is always a negative loss since this has the highest pressure differential.
Need more explaining ??
Allan G.
Well, I'm not going to go into this any further. I think I presented enough information to get people to take a closer look at this. Though this is not very useful to most, because this is such an extreme tuning situation that most would not bother pursuing, I think most can still find it interesting to imagine the hp that is still on the table that is rarely tapped into by the vast majority of turbo enthusiasts.Your scenario is not sound. The only thing you can do is minimize pumping loss but not create power through positive pumping. You are missing a key elment - Compression stroke.
Yes, atmosphere is acting on all undersides of pistons but it is still the pressure differential across all of them that creates the pumping loss. Point being if you had equal crankcase pressure as boost pressure, then the engine would truley think it's NA, not just the valvetrain. The majority of pumping loss accurs on the compressiion stroke and regardless, there is always a negative loss since this has the highest pressure differential.
Need more explaining ??
Allan G.
Allan. Study the different pressures that are occurring against the top sides of the pistons at each degree of rotation through the 4 stroke cycle. There are certain positions during the stroke of a piston where particular pressures will have much more leverage advantage on the crankshaft than at other piston positions during the 4 stroke cycle. Compression forces are the highest, but really start to work against the piston close to TDC where leverage advantage against the crankshaft is the least. An EA sim really helps you study this more accurately, than simply trying to imagine this in your head.
turbobitt
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- Feb 14, 2002
Don,
I really don't have to imagine this since every dyno test I ever run was baslined with friction power. Our dyno used a huge electric motor to drive or resist power.
I would agree on one thing though is that back pressure is an untapped power source. I know my combination takes advantage of this.
Allan G.
Friction losses is a completely different area of engine power loss than pumping work losses that are occurring during actual live engine operation.
The same as the amount of engine power lost through the cooling system (engine thermal efficiency) is different from friction losses, or pumping work losses, or mechanical losses.
A sophisticated engine dyno that can take cylinder pressure traces of all cylinders of the engine, relate the individual cylinder pressure traces to their specific crankshaft angles and piston position, include crankcase pressure, and with the right software, should be able to overlap all the cylinders for each degree of crankshaft rotation and calculate some interesting engine pumping work (hp) figures.
This would be the same thing that my EA sim is doing, but the difference would be that instead of using computer simulated pressure input for calculating the pumping work (hp) figure, actual real world cylinder pressure measurements would be used for the calculation.
This would be the same thing that my EA sim is doing, but the difference would be that instead of using computer simulated pressure input for calculating the pumping work (hp) figure, actual real world cylinder pressure measurements would be used for the calculation.
turbobitt
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- Feb 14, 2002
I did some checking and a negative number under the calculation result for pumping work expressed as hp indicates the amount of brake horsepower that is reduced due to the work an engine must do to pull a fresh charge into the cylinder and push the exhaust charge out. The calculation only takes into account the exhaust stroke from bdc to the start of the compression stroke at bdc. So the compression and the power stroke is not included in the calculation.
What will contribute to higher pumping work hp loss is restriction to taking in the intake charge and restriction to expelling the exhaust charge. Pressure levels of the intake and exhaust sides will change the resulting losses.
In a supercharger application, it is possible to see a positive number for pumping work, but the hp to drive the compressor is not taken into account for the pumping loss calculation. There is a separate calculation result that shows the hp lost to driving the compressor, supercharger or turbocharger.
It looks like I was incorrect with the idea that pumping work was adding hp in my case. Although, the level of pumping losses in my case is lower than it would be even at a 1:1 exhbp to intbp ratio.
Sorry for causing any confusion, fellas. For those that tried to correct me, you were right. I now have to think it would be too hard to get the exhbp to intbp ratio low enough in a turbocharger application to get a positive pumping work result.
The difference in the level of pumping work loss between 1.5:1 and .9:1 exhbp to intbp ratios is not very impressive, according to the sim. So lower pumping work losses due to lower exhaust backpressure does not appear to be the magic bullet.
What will contribute to higher pumping work hp loss is restriction to taking in the intake charge and restriction to expelling the exhaust charge. Pressure levels of the intake and exhaust sides will change the resulting losses.
In a supercharger application, it is possible to see a positive number for pumping work, but the hp to drive the compressor is not taken into account for the pumping loss calculation. There is a separate calculation result that shows the hp lost to driving the compressor, supercharger or turbocharger.
It looks like I was incorrect with the idea that pumping work was adding hp in my case. Although, the level of pumping losses in my case is lower than it would be even at a 1:1 exhbp to intbp ratio.
Sorry for causing any confusion, fellas. For those that tried to correct me, you were right. I now have to think it would be too hard to get the exhbp to intbp ratio low enough in a turbocharger application to get a positive pumping work result.
The difference in the level of pumping work loss between 1.5:1 and .9:1 exhbp to intbp ratios is not very impressive, according to the sim. So lower pumping work losses due to lower exhaust backpressure does not appear to be the magic bullet.
I would imagine that the VE, evacuation of trapped exhaust gases during intake and exhaust overlap, short circuiting, crossover, or effective increase in intake duration flow as you put it, would have to improve in a situation where exhaust backpressure is relatively lowered. Especially if you're dealing with a camshaft in a turbocharged application that is spec'd more closely to what you might use in a naturally aspirated application. A good amount of overlap.
Pressure pulse tuning a turbocharged engine. Not a new idea. Enjoy.
Turbo F1 engines - How they started, part 1 - YouTube
http://youtu.be/gqfVAGOaGEc
Turbo F1 engines - How they started, part 1 - YouTube
http://youtu.be/gqfVAGOaGEc
Wise guy.
You must really hate making french fries and burgers.
Do you kick your dog around when you get home too?
Frychild. In case you don't know this, anyone can slow down any turbo car by lowering the boost level, or using too small a tire, or running on a bad track surface. It's kinda like slowing the cooking time of a hamburger patty by lowering the grill heat by using the knob on the side of the grill that controls the electricity or the gas. You know the one I'm talking about? Or, have you not gotten to that level of training, yet?
But how do you slow a 91mm into the 8.70s when you're still using 30+psi and W tires??
Oh yeah, pressure pulse tuning!
I'm using 30 out of 45 available to me, if the heads don't stop me first. It's like the marks on that dial on the grill that controls the heat. I'm a little past halfway turning the knob up to full heat.But how do you slow a 91mm into the 8.70s when you're still using 30+psi and W tires??
Oh yeah, pressure pulse tuning!
I suppose you think that 30 psi is the max on a turbo application. Maybe that's how it works with centrifugal superchargers?
I know 30 psi must seem like a whole bunch to you. Heck, those french fry holders only hold,... what? 20 fries?
Just FYI, I stopped using superchargers in 2004 and have been using turbos since then. 30psi is enough to not be stuck in the 8.70s with a 91mm
What is your infatuation with my job? Do you want me to get you an application? I can talk to the boss and see if I can get you in if you're that interested.
Relax Mr. Genius engine theory master. You don't have to go back and edit every post
There won't be a test on this. It's only the Internet, calm down!Maybe you should go back to superchargers. You sure are having a hard time grasping my combination.Just FYI, I stopped using superchargers in 2004 and have been using turbos since then. 30psi is enough to not be stuck in the 8.70s with a 91mm
What is your infatuation with my job? Do you want me to get you an application? I can talk to the boss and see if I can get you in if you're that interested.
Relax Mr. Genius engine theory master. You don't have to go back and edit every post
About your profession, I love the McRib, and the Big Mac! French fries aren't bad, either. So what?!
About editing posts, I like to add neat stuff to a post when it comes to mind. Does it bother you? It shoudn't. The more I can add to a post in hopes of helping you, the better. Right?
Once you learn enough from me, maybe you can get a better job. Move up in the world. That would be good, right?
No need to go back to superchargers, I've been going way faster than you with less turbo, less tire, no nitrous, and gasoline for years LOL!
Glad you like what McDonalds makes, just not sure why you keep bringing it up. I'm not ashamed of it in the least, it's an honest living!
And as for me learning from you??? HAHAH!!!
Seriously man thanks a ton because I don't often actually LAUGH OUT LOUD but you seem to be good at making me do it. Keep it up, please!!
Why don't you tell us a little about your stock or Stage I headed Buick V6? I'd like to know how much faster you've been going for years now with a V6. Curious minds want to know.No need to go back to superchargers, I've been going way faster than you with less turbo, less tire, no nitrous, and gasoline for years LOL!
Glad you like what McDonalds makes, just not sure why you keep bringing it up. I'm not ashamed of it in the least, it's an honest living!
And as for me learning from you??? HAHAH!!!
Seriously man thanks a ton because I don't often actually LAUGH OUT LOUD but you seem to be good at making me do it. Keep it up, please!!
When you laughed, did vanilla shake squeeze out of your nostrils.
That's what I was shooting for.- Status
