Why bigger turbos make more HP at the same PSI....
04-25-07, 01:52 PM
#76
development
Originally Posted by NissanConvert
Okay- my hang up the "everything remaining the same" has become clear.
<snip>
- suddenly the fog drifted away and everything became clear.
<snip>
- suddenly the fog drifted away and everything became clear.
Oh and everything DaveW has stated...I showed with post #8
https://www.rx7club.com/showpost.php...07&postcount=8
and post #17
https://www.rx7club.com/showpost.php...5&postcount=17
and
at Last edited by dgeesaman : 1 Day Ago at 07:00 AM. Reason: nobody misspells Obi-Wan Kenobi and gets away with it!! for post #8
04-25-07, 01:54 PM
#77
Racecar - Formula 2000
Originally Posted by dubulup
Oh and everything DaveW has stated...I showed with post #8
https://www.rx7club.com/showpost.php...07&postcount=8
and post #17
https://www.rx7club.com/showpost.php...5&postcount=17
https://www.rx7club.com/showpost.php...07&postcount=8
and post #17
https://www.rx7club.com/showpost.php...5&postcount=17
Dave
04-25-07, 01:56 PM
#78
Originally Posted by DaveW
OK. I read it. How does anything there contradict what I said above?
Dave
Dave
and your example is wrong. Actually you can slap on a smaller compressor wheel, turn up the boost a notch, cool to the same temp with some magic intercooler and move less air. lol . think about it.
Boost is not flow.
04-25-07, 01:59 PM
#79
Please somebody help!!!
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Originally Posted by wanklin
Not quite, the larger surface area of the t04 compressor wheel would move more air. Your frankenturbo would in theory become more efficient as it would create 10PSI boost at a lower rotational speed (= less heat).
Originally Posted by wanklin
In theory yes, but you'd be introducing lag and other variables.
04-25-07, 02:00 PM
#80
Racecar - Formula 2000
Originally Posted by wanklin
You are talking in absolutes as if the exhaust was pulling the air from the compressor. The turbo is pushing the air and the exhaust is restricting that movement, not the other way around. during the exaust phase the gas is pushed out by the face of the rotor, during the intake phase the rotor face moves away from the housing and creates a vacuum. At this instant that 10lbs boost is diluted as that fixed volume of air between the turbo and rotor face is spread accross a larger volume of area. Once this occurs the exhaust port has already been isolated from the intake and the only thing forcing air into the engine is rotor movement and the compressor wheel IOW: Flow.
and your example is wrong. Actually you can slap on a smaller compressor wheel, turn up the boost a notch, cool to the same temp with some magic intercooler and move less air. lol . think about it.
Boost is not flow.
and your example is wrong. Actually you can slap on a smaller compressor wheel, turn up the boost a notch, cool to the same temp with some magic intercooler and move less air. lol . think about it.
Boost is not flow.
I call for a truce.
Dave
04-25-07, 02:01 PM
#81
development
Originally Posted by DaveW
Sorry - I said I didn't thoroughly read the entire thread and I might be repetitive...
Dave
Dave
04-25-07, 02:02 PM
#82
Originally Posted by NissanConvert
The figures i have heard *third party information alert* are that for every ~7° (don't know Fahrenheit or Celsius- I assume F) you reduce the temperature of the intake charge you gain ~1hp. so i think the increase in flow would be the greater power gainer.
I didn't say that it would be as fast or enjoyable but at a given RPM it would produce the same amount of power.
04-25-07, 02:09 PM
#87
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Originally Posted by dubulup
it was the exhibits...wasn't it
Originally Posted by wanklin
Boost is not flow.
The flaw in that thought process is that the flow increases due to a reduction in back-pressure & temperature.
& neither is CFM
gosh, I'm such an idiot
04-25-07, 02:22 PM
#89
but if you pressurize a void to a given pressure at a given temperature, then equalize that void with a new void the total volume of the combined void will remain the same regardless of how large the compressor is. The *only* variable will be how fast the void fills up again.
The flaw in that thought process is that the flow increases due to a reduction in back-pressure & temperature.
& neither is CFM
The flaw in that thought process is that the flow increases due to a reduction in back-pressure & temperature.
& neither is CFM
The exhaust ports is isolated from the intake port for 90% of the intake phase. I don't understand how you think a reduction in backpressure is doing anything once the exhausting rotor face is isolated?
Yes decreased backpressure will help the rotors face to expell more expended gas - and that help with VE, but that's it. IOW, decreasing back pressure just clears out more room for the next intake phase so that the compressor wheel can cram more air in.
A better flowing wheel will cram more air in. And if the air is colder, well then that's all the better....
Last edited by wanklin; 04-25-07 at 02:43 PM.
04-25-07, 02:59 PM
#90
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Originally Posted by wanklin
Yes decreased backpressure will help the rotors face to expell more expended gas - and that help with VE, but that's it. IOW, decreasing back pressure just clears out more room for the next intake phase so that the compressor wheel can cram more air in.
A better flowing wheel will cram more air in. And if the air is colder, well then that's all the better....
A better flowing wheel will cram more air in. And if the air is colder, well then that's all the better....
04-25-07, 03:04 PM
#91
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Originally Posted by NissanConvert
So if for example we put a 1" diaphragm in the exhaust the power lost would be due to lost volumetric efficiency, you'd still be able to make boost, and the total engine flow would not be affected?
04-25-07, 03:16 PM
#92
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Originally Posted by Fritz Flynn
I can see you are not grasping this info but hopefully one day you'll enjoy a single turbo FD and won't have to stress about it any more
Originally Posted by NissanConvert
Okay- my hang up the "everything remaining the same" has become clear. Because not only the manifold changes (increasing flow) but the turbine side also changes (increasing flow) so the all things staying the same (in abstract) would be:
Putting t04r compressors on the stock twins turbines (& manifold) @ 10psi is going to make nearly identical HP at a given RPM.
Conversely putting a stock twin compressor on a t04r turbine (& manifold) could make more power (in theory) than the stock twins because of the reduction in back pressure from the new manifold and turbine.
Apples to oranges- suddenly the fog drifted away and everything became clear.
Putting t04r compressors on the stock twins turbines (& manifold) @ 10psi is going to make nearly identical HP at a given RPM.
Conversely putting a stock twin compressor on a t04r turbine (& manifold) could make more power (in theory) than the stock twins because of the reduction in back pressure from the new manifold and turbine.
Apples to oranges- suddenly the fog drifted away and everything became clear.
04-25-07, 03:18 PM
#93
Originally Posted by kashent
Ergh. I'm sorry, this thread is getting ridiculous. Let's break the problem down into a few easy to understand parts.
1) Flow through the engine - THIS IS THE ONLY MEASURE OF VOLUME THAT MATTERS. PERIOD. Not the CFM of the turbo, nothing else.
(snip)
1) Flow through the engine - THIS IS THE ONLY MEASURE OF VOLUME THAT MATTERS. PERIOD. Not the CFM of the turbo, nothing else.
(snip)
-Max
04-25-07, 03:19 PM
#94
2/4 wheel cornering fiend
Originally Posted by NissanConvert
Okay- my hang up the "everything remaining the same" has become clear. Because not only the manifold changes (increasing flow) but the turbine side also changes (increasing flow) so the all things staying the same (in abstract) would be: Putting t04r compressors on the stock twins turbines (& manifold) @ 10psi is going to make nearly identical HP at a given RPM.
Originally Posted by NissanConvert
The figures i have heard *third party information alert* are that for every ~7° (don't know Fahrenheit or Celsius- I assume F) you reduce the temperature of the intake charge you gain ~1hp. so i think the increase in flow would be the greater power gainer.
04-25-07, 03:32 PM
#96
Originally Posted by NissanConvert
The figures i have heard *third party information alert* are that for every ~7° (don't know Fahrenheit or Celsius- I assume F) you reduce the temperature of the intake charge you gain ~1hp. so i think the increase in flow would be the greater power gainer.
-Max
04-25-07, 03:35 PM
#98
Here's another post that matches my understanding, and is very succinct:
Here are some of my own ramblings about the pressure issue (ignoring temp) that relate to this topic as well:
http://maxcooper.com/rx7/how-to/fuel_system/why.html
-Max
Originally Posted by DaveW
I have not read all the posts on this, so this may be repetitive...
Two thoughts about how a larger turbo (or turbos) can result in more HP at the same boost level:
1. A larger turbo will have more flow area, so exhaust can exit with less backpressure at the exhaust port. Even at the same boost level, the lower backpressure at the exhaust port will raise HP.
2. A larger turbo will likely be more efficient at high flow/HP, generating less heat in the compressed air at the same boost level, resulting (even with an intercooler) in a denser intake charge, and raising HP. This increase in efficiency would further reduce backpressure.
Dave
Two thoughts about how a larger turbo (or turbos) can result in more HP at the same boost level:
1. A larger turbo will have more flow area, so exhaust can exit with less backpressure at the exhaust port. Even at the same boost level, the lower backpressure at the exhaust port will raise HP.
2. A larger turbo will likely be more efficient at high flow/HP, generating less heat in the compressed air at the same boost level, resulting (even with an intercooler) in a denser intake charge, and raising HP. This increase in efficiency would further reduce backpressure.
Dave
http://maxcooper.com/rx7/how-to/fuel_system/why.html
-Max
04-25-07, 03:45 PM
#99
Nice write-up with which I think we all agree, but it seems that everyone ignores that period of time when the exhaust becomes isolated from the intake tract.... My stance is that flow does matter in this window of time.
Please read posts 68, 78 and 89.
Rob
Please read posts 68, 78 and 89.
Rob
04-25-07, 04:47 PM
#100
If one turbo flowed more (meaning actually delivered more air, not just capability) than another during the post-exhaust-port-close period, the boost pressure in the manifold would change. The scenario we are considering dictates a constant boost pressure, which is both realistic and reasonable. So, the difference in compressor flow capabilities doesn't have the effect that you think it does. If backpressure, boost pressure, and intake temps were somehow equalized, a big turbo would NOT put more air into the combustion chambers than a small turbo. (However, in reality the big turbo will need to flow more, since the backpressure is lower, allowing more flow for a given boost pressure.)
Also consider that even when the exhaust port closes, the amount of backpressure still has a lasting effect. A lot of backpressure is like leaving a pet elephant in a room. A little backpressure is like leaving a pet mouse in the room. Even after the pet owner has left, you still have to deal with their pet. You can fit more stuff into the room with a mouse than you can into the room with an elephant.
Big turbos make more power because they offer less backpressure (which in turn increases the flow at a given boost pressure) and have more efficient compressors (more oxygen molecules for a given volume).
-Max
Also consider that even when the exhaust port closes, the amount of backpressure still has a lasting effect. A lot of backpressure is like leaving a pet elephant in a room. A little backpressure is like leaving a pet mouse in the room. Even after the pet owner has left, you still have to deal with their pet. You can fit more stuff into the room with a mouse than you can into the room with an elephant.
Big turbos make more power because they offer less backpressure (which in turn increases the flow at a given boost pressure) and have more efficient compressors (more oxygen molecules for a given volume).
-Max