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Re: IS THERE A DIFFERENCE IN BOOST??
[Re: HotRodDave]
#553364
12/15/09 01:21 AM
12/15/09 01:21 AM
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DakFink
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There are so many variables and tangents  Being a roots guy,I figure a 1071 will produce more power than a 6 or 871 at the same boost level due to the different overdrive % needed to make the same boost.Now what determines the limit of max usable boost level?The point where more boost does not produce more power  
When your blown engine blows!
Some diesels in tractor pulling and such are stacking turbos and makeing enough boost to run your 3/4 inch impact off the manifold 
The more air you get in the more fuel you can burn.
Ever see a Diesel Blow!!! NOT PRETTY!! Seen a few pics where the block was literally split in 1/2 front to rear right through the middle..
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Re: IS THERE A DIFFERENCE IN BOOST??
[Re: Dos Snails]
#553365
12/15/09 01:48 AM
12/15/09 01:48 AM
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DakFink
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Now what determines the limit of max usable boost level?The point where more boost does not produce more power
Right at the point that you starting heating up the air to make pressure then you go backward..After that it's what the fuel can support.. 
Both of those could be overcome!!
Intercoolers and Bigger fuel delivery (Bigger Carb or Bigger Injectors)or different fuel.
What can't be overcome is the size of the ports once they are set and displacement. At some point there has to be a pressure that just over saturates the port and cylinder to the extent it doesn't allow any more fuel and air in?? In effect raising the Boost (back) pressure but not raising the output.
I know the Diesel and Import guys run extremely high boost (Diesel=60-120psi, Import 30-45psi) and make respectable power but not what you would think for those pressures due to the fact their head flows suck.
DSM (eclipse and Evos) good example. A highly ported head may flow 230-250cfm and they max lift at just over 0.400". With that being said they still have been known to make 900-1100hp but it takes 30-50psi boost.
So honestly the only limiting factor that would say where more Boost would finally quit making more power would be your port/valve size and maybe cylinder/chamber size. At some point you can't get all that Fuel/Air down the hall and through the door to the Chamber.
Fuel type, heat, fuel delivery, timing, etc. can all be worked with and over-come to accommodate the boost levels. Port size, Valve Size, and Cylinder displacement can not once the engine is built.
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Re: IS THERE A DIFFERENCE IN BOOST??
[Re: jcc]
#553368
12/16/09 01:14 AM
12/16/09 01:14 AM
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DakFink
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The better the port design the more air will actually get into the CC.
And Port designs for the high boost numbers in the 50-100psi range require how much difference of design then a NA motor? Since most air is already at 14.7psi.?
That's the reason for the Large Boost Numbers, The port designs are really poor!! Not a lot is actually getting down the port and into the cylinder. Most of it is just backing up in the intake.
Boost is really just a reference of BackPressure in the intake. It does not tell you what is getting into the cylinders.
Good example: several years back when Superchargers on Magnum motors was in it's infancy. We built a 408cui Magnum with out of the box R/T 2.02 heads. Put a Vortech S/C on it and set it up for 12psi boost. We made about 300 rwhp on the dyno. A few months later the same engine was tore down just to see if there were any issues? While it was down the heads were ported, intake was ported and larger TB was used. Everything else remained the same. When we put it all back together and set-up for 12psi boost we could barely get 8psi but we got another 50-60hp.
Big BOOST numbers are only impressive if your not familiar with the engine architecture.
60-120psi on a Race Diesel is expected, 30-50psi on a race-import is expected, 20-32psi on a turbo dragster is expected. Now if you tell me your running 80psi Boost on a Twin Turbo Hemi, and making 3000-4000hp. I am impressed!! BUt if your running 80psi on the same set-up and tell me your making 1000hp not impressed!!
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Re: IS THERE A DIFFERENCE IN BOOST??
[Re: DakFink]
#553369
12/16/09 09:16 AM
12/16/09 09:16 AM
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Joined: Dec 2003
Posts: 22,697
Bitopia
jcc
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Good points, but let me refine my question, does air under say at 60 psi flow different, and require a different design, then air on a NA motor? Not really asking about the volume, more does it behave differently, have different dynamics, and are they linaer differences, etc?
Reality check, that half the population is smarter then 50% of the people and it's a constantly contested fact.
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Re: IS THERE A DIFFERENCE IN BOOST??
[Re: hemi-itis]
#553372
12/17/09 12:09 AM
12/17/09 12:09 AM
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Joined: Oct 2007
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New York
polyspheric
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At 15 lbs of boost or 1 bar (however you wish to make it) you will effectively double horsepowerThis has been repeated to death, and it's still not true. Yes, alllll the magazines have printed it, it's even on some blower websites. It's that annoying "thermodynamic ratio of heats" thingy. In brief: 1. no compressor is 100% efficient (although a good cooler can reduce charge temp below intake temp) 2. the gas expands and loses density just by virtue of being compressed 3. the difference in delivery volume between 2 pressures is the square root of their ratio. 14.7 ambient + 14.7 boost (assuming perfect, no temp, no para loss) is about +41%. (14.7 + 14.7)/14.7 = 2 2^.5 = 1.414, or 141.4% of original charge mass. More info? Read my article: http://victorylibrary.com/supercharger/super-c.htm
Boffin Emeritus
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Re: IS THERE A DIFFERENCE IN BOOST??
[Re: Duner]
#553374
12/17/09 11:24 AM
12/17/09 11:24 AM
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Joined: Oct 2004
Posts: 8,165
Left Coast
BobR
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Quote:
Interesting.
I don't doubt your math, but it really seems like the addition of 1 bar of boost doubles the hp. Or at least that's what my results have pointed to.
I have rear wheel dyno pulls on the same vehicle on the same dyno - both with and without boost, with no other changes other than the addition of a Vortech SC and my home-built air/water intercooler. I got right at 300rwhp without the blower and 582rwhp with the blower - at a max peak of 16 psi boost. (it was more like a spike to 16 psi, mainly 14-15 psi the whole pulls) According to your math I should only be at 480rwhp?
What other factors could fit the results? Was the transmission just eating that much power that now with the increase the "robbed" power remains a fixed number and not a percentage? I know the blower was eating a bunch of power (125hp?) - since swapping to a turbo from the blower resulted in an 8 mph gain and a second quicker on actually less boost. I haven't had the turbo setup on the dyno.
All of this doesn't quite add up unless it's a matter of the parasitic losses being fixed numbers and not percentages. Am I screwing up the math by being able to get the intake charge temps below ambient? Why would my results be different than the math says it's supposed to be?
Perfect example of real world vs theory. Sometimes it goes the other way, as well. The 1 bar thing is a useful rule of thumb for planning only. There are too many variables to put a lot of faith in either rules of thumb or complex calculations.
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Re: IS THERE A DIFFERENCE IN BOOST??
[Re: Duner]
#553376
12/17/09 01:36 PM
12/17/09 01:36 PM
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BobR
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I completely agree. Every time I do some change and figure "the math" - it NEVER matches my timeslip results. (usually under-performs according to the math) So far, all I can ever safely rely on is the timeslips. All of my "shoulda, woulda, coulda" never works out.
On our Procharged Mustang deal. It took until that last 2 races before we actually realized the performance we apsired to when we visualized the combination. Getting parts to work together at maximum efficiency is very challenging-especially the lower the predicted ET is.
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Re: IS THERE A DIFFERENCE IN BOOST??
[Re: bigtimeauto]
#553378
12/17/09 06:29 PM
12/17/09 06:29 PM
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Posts: 3,619
Norwich CT USA
Defbob
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Is 15 lbs of boost the same if it is produced by supercharger,procharger or turbo? 
Boost is a measurement of restriction so technicly yes. But the intake air temps will be all different
well if your going to add little footnotes to the answer let's not forget to note that boost produced from a turbo does not take any HP away . A blower robs 10% or more
Well if your gonna add stuff in add it all in. a turbo doesn't *take* power away like a blower BUT due to the bottleneck of the exhaust flowing it does hamper it from making all it can.
Have a spare 4cyl in the trunk to operate the turbo 
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Re: IS THERE A DIFFERENCE IN BOOST??
[Re: Kam*Kuda]
#553380
12/17/09 09:46 PM
12/17/09 09:46 PM
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Joined: Oct 2004
Posts: 8,165
Left Coast
BobR
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You are correct. At some point making more pressure takes away more power than it adds. The same principles to making power apply to N/A engines and boosted engines. This is especially true on an all out racing effort. The better the port design the more air will actually get into the CC. Boost numbers are just a reference point for us. Better heads and intake will mean lower peak boost numbers but more power.
I think this is a very important point.
A turbo or blower will be able to move a certain cfm of air. A more efficient engine will be able to use that air
(ie volumetric efficiency)
The boost measured at the intake is residual air
If the an engine having 15 pounds in the intake and this engine was improved (ie better cam, heads etc) it would likely produce more power and have less PSI in the intake. The CFM of the blower would more effectively be utilized.
Does this seem correct 
If the restriction is in the delivery path rather than the combustion chamber filling completely then backing up this is absolutely correct. A PERFECT environment is where there is ZERO restriction until the boosted air completely fills the combustion and pressurizes it to the indicated boost pressure level. Picture your combustion chamber as a small compressor tank that contains, say, 35 pounds of pressure. In this environment adding boost pressure would likely add power but there is rapidly diminishing returns as the compressed air heats. Most, if not all, boosted engines are not perfect environments so the boost tends to back up at restrictions and not in the combustion chamber. In this case adding more pounds may not result in a power increase-only hotter air and more power being scavenged by the blower working harder and more inefficiently. On our Procharger we can change the overdriven potential with a 10 minute gear swap. Through a lot of testing we have found the sweet spot from where the best power is made. Turning it faster from this sweet spot results in less power.
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Re: IS THERE A DIFFERENCE IN BOOST??
[Re: BobR]
#553381
12/18/09 12:18 AM
12/18/09 12:18 AM
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Joined: Oct 2007
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New York
polyspheric
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"real world vs. theory"?
Not quite. That's not a theory (global warming is a theory, Darwin is a theory), it's that quite different thing: a fact.
There is no more "real world" than fact. Facts are still there even if no one believes them, they cannot be discussed (if I give up or change my mind, the gas laws are still the same way they've been for about 6 billion years).
Far too frequently, what people describe as theory (meaning "someone made that up, and it has nothing to do with actual parts"), what they're really telling me is "I can't distinguish between an opinion I disagree with (a theory), and a fact that I don't understand".
Attacking physics on the basis that someone who claimed to be well educated was wrong ("You sound like a guy I went to school with, always reading books - and couldn't make change for a dollar") is the same as "someone I know went to a doctor, and died anyway, therefore medicine doesn't exist".
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Re: IS THERE A DIFFERENCE IN BOOST??
[Re: polyspheric]
#553382
12/18/09 12:25 AM
12/18/09 12:25 AM
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Joined: Nov 2003
Posts: 1,969
Chandler, AZ
Duner
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Quote:
"real world vs. theory"?
Not quite. That's not a theory (global warming is a theory, Darwin is a theory), it's that quite different thing: a fact.
There is no more "real world" than fact. Facts are still there even if no one believes them, they cannot be discussed (if I give up or change my mind, the gas laws are still the same way they've been for about 6 billion years).
Far too frequently, what people describe as theory (meaning "someone made that up, and it has nothing to do with actual parts"), what they're really telling me is "I can't distinguish between an opinion I disagree with (a theory), and a fact that I don't understand".
Attacking physics on the basis that someone who claimed to be well educated was wrong ("You sound like a guy I went to school with, always reading books - and couldn't make change for a dollar") is the same as "someone I know went to a doctor, and died anyway, therefore medicine doesn't exist".
Nobody is attacking your numbers.
I'm just wondering what would cause my actual numbers to not match the physics model.
Is it an efficiency question? Or is it a fixed parasitic drag question? The "rule of thumb" started somewhere. Why does mine fall into the range of that working out?
Edit: I read your webpage on superchargers. Is this difference because of the efficiency difference between a carbed engine and a fuel injected engine? Would my fuel injected engine be coming closer to 100 efficiency with below ambient charge air temps? I don't want to argue - just figure out why it doesn't all match up.
Last edited by Duner; 12/18/09 01:05 AM.
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Re: IS THERE A DIFFERENCE IN BOOST??
[Re: polyspheric]
#553383
12/18/09 07:16 AM
12/18/09 07:16 AM
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Joined: Dec 2006
Posts: 506
Texas Afghanistan Iraq etc.
DakFink
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Quote:
"real world vs. theory"?
Not quite. That's not a theory (global warming is a theory, Darwin is a theory), it's that quite different thing: a fact.
There is no more "real world" than fact. Facts are still there even if no one believes them, they cannot be discussed (if I give up or change my mind, the gas laws are still the same way they've been for about 6 billion years).
Far too frequently, what people describe as theory (meaning "someone made that up, and it has nothing to do with actual parts"), what they're really telling me is "I can't distinguish between an opinion I disagree with (a theory), and a fact that I don't understand".
Attacking physics on the basis that someone who claimed to be well educated was wrong ("You sound like a guy I went to school with, always reading books - and couldn't make change for a dollar") is the same as "someone I know went to a doctor, and died anyway, therefore medicine doesn't exist".
I've known DUNER for a few years now and I wouldn't put him in the category of BookWorms that don't know how to make things work. He's the kind that runs the numbers just for the sake of running them and then goes to the track and see what he really has, whether the calculated numbers are right or wrong.
As far as your comment on theories!! You live your ever day life revolved around a theory. "ELECTRICITY" It is nothing but a theory. There are Hundreds of Laws and Formulas that explains how it works, but to this very day there is no Physical FACT that that they are 100% correct. Physicist and Chemist stil to this day do not no for sure whether electricity flow + to- or - to +. In the Navy's elctronics schools both theories are taught to cover all bases.
As for that article: Not too impressed. He states that Atmospere not Vacuum fills and engine and then immidiatelt starts talking about vacuum from the egine. (so which is is?) It is both. Vacuum and Pressure are both created by a difference in pressures. If an engine was only filled by atmosphereic pressure you probably wouldn't get muh if any air in the cylinder with the valves openeing and closing 1000's of time per minute. Now add the vacuum (difference in Pressure) that the cylinder creates as it makes a void on the down stroke and you will get some air forced into the cylinder as the valves open.
Exhaust Back Pressure: I am adressing this cause this is the second mention I have seen. Yes you will have more exhaust back pressure with a Turbo, BUT this will not effect the engines output as a Turbo Cam correctly designed does not let exhaust gasses get pushed back into the cylinder. In fact most turbo cams will make you wonder what the plans are because the specs are usually way smaller than a N/A or even a S/C for the same power levels.
ATMOSPERE: I'll address this one as well since that article wanted to get all Physics BUT left alot of details out. ATMOSPHERE= 14.7PSI or 1-BAR 0r 29.92 IN/HG @ sea-level on a Standard Day. Standard Day= 70*F and 70%.
I see what the article was getting at and I will agree that you get more bang for the Boost at 7,8,10,12 psi than 15psi. You can usually make about 50-60% extra HP @7-8 psi and about 70-80% @ 10-12. And you'll be lucky if you get into the 90% range solidly with 15% on most street engines. That is why they call it a Rule of Thumb, NOT a BOOST LAW of physics!!
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