Rear mounted turbo?
04-30-2008, 02:34 AM
#42
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Which reminds me, rear turbo on a miata +1 for the bad idea. You mention not needing an intercooler because the charge air cools as it heads up to the motor anyways, but it also works against you because there is not a lot of exaust gasses to spool the turbo as is. Why let them cool that much before getting to the turbo? And throttle response will be *****
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04-30-2008, 03:08 AM
#45
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On another note, both throttle response and turbo lag will increase greatly by adding a lot more piping(although given a miata isn't THAT long, its still a good amount more piping).
Last edited by J.T.; 04-30-2008 at 03:36 AM. Reason: grammar >me
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04-30-2008, 10:42 AM
#47
JT and 18psi, how tough do you think it is for Subaru to switch the position of the intake and exhaust ports on the cylinder head.........not very. With that they could have drastically shortened exhaust manifolding and also run a front mounted intercooler very easily.
Even with all those advantages they still didnt do it. I think its beyond me and you to speculate why. I'll take Corky's approach and say that Subaru knows a thing or two more about turbocharging than any of us here. Hence nothing wrong in copying their layout and giving it a shot.
Speculating that one layout or the other is "*****" and "crap" without trying it, IMO, is stupid. But hey, no harm in following convention for the majority of us.
Even with all those advantages they still didnt do it. I think its beyond me and you to speculate why. I'll take Corky's approach and say that Subaru knows a thing or two more about turbocharging than any of us here. Hence nothing wrong in copying their layout and giving it a shot.
Speculating that one layout or the other is "*****" and "crap" without trying it, IMO, is stupid. But hey, no harm in following convention for the majority of us.
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04-30-2008, 10:43 AM
#48
Once the charge pipes is pressurized it has no affect, it may take a millisecond longer to pressurize in a rear mount situation. The delayed spool happens due to exhaust gases cooling of too much before reaching the turbo, loss of heat=loss of energy, so you need mroe exhausts gases to have same spool. End of story.
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04-30-2008, 12:41 PM
#49
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JT and 18psi, how tough do you think it is for Subaru to switch the position of the intake and exhaust ports on the cylinder head.........not very. With that they could have drastically shortened exhaust manifolding and also run a front mounted intercooler very easily.
Even with all those advantages they still didnt do it. I think its beyond me and you to speculate why. I'll take Corky's approach and say that Subaru knows a thing or two more about turbocharging than any of us here. Hence nothing wrong in copying their layout and giving it a shot.
Speculating that one layout or the other is "*****" and "crap" without trying it, IMO, is stupid. But hey, no harm in following convention for the majority of us.
Even with all those advantages they still didnt do it. I think its beyond me and you to speculate why. I'll take Corky's approach and say that Subaru knows a thing or two more about turbocharging than any of us here. Hence nothing wrong in copying their layout and giving it a shot.
Speculating that one layout or the other is "*****" and "crap" without trying it, IMO, is stupid. But hey, no harm in following convention for the majority of us.
I didnt say the setup was ***** or crap I said throttle response and or turbo response.
And to put the intake underneath would not work out too well, there isn't that much room under there(don't tell me there is I stand under them for 6+ hours a day. Plus where you gonna put the oil pan with that intake under there? It would likely take a strange setup with some really awkward super unequal runners. And 18psi knows a thing or two about subies too
Anyways, it might be able to be done with a dry sump system, but they weren't trying to make a super expensive supercar.
Once the charge pipes is pressurized it has no affect, it may take a millisecond longer to pressurize in a rear mount situation. The delayed spool happens due to exhaust gases cooling of too much before reaching the turbo, loss of heat=loss of energy, so you need mroe exhausts gases to have same spool. End of story.
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04-30-2008, 02:27 PM
#51
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The "next county" comment is directed specifically at speed-density based ECUs where no AFM/MAF is used.
Originally Posted by Corky Bell in Maximum Boost
It is distinctly possible to upset the basic throttle response if an engine is equipped with an airflow meter positioned too far from the throttle body, Opening the throttle causes a low-pressure pulse to be created that travels up*stream toward the airflow meter, The time it takes this pulse to reach the flow-meter and cause it to react is indeed the delay in throttle response. Typically, such a pulse must travel from the throttle body to the intercooler, through the intercooler, back to the turbo, then to the flowmeter, in order for the flowmeter to register a response. It is not until the flowmeter receives this pulse that the air/fuel ratio can change to account for new load conditions in the engine. I should point out that there are exceptions here, based on the style of throttle-position sensor with which the engine is equipped. Nonetheless, it is generally true that the farther the throttle is from the airflow meter, the poorer the throttle response. Thus, this path length should receive some consideration in the design process.
When an engine is equipped with a speed density type of EFI system, wherein no airflow meter is utilized, or a blow-through carbureted turbo system, the length of the intake tract tan extend into the next county with no negative re*sults insofar as throttle response is concerned.
The overall problem in designing an intercooler system, then, lies in maximizing the ability of the system to remove heat from the compressed air while not adversely affecting boost pressure, losing throttle response, or contributing to any delay in boost rise.
When an engine is equipped with a speed density type of EFI system, wherein no airflow meter is utilized, or a blow-through carbureted turbo system, the length of the intake tract tan extend into the next county with no negative re*sults insofar as throttle response is concerned.
The overall problem in designing an intercooler system, then, lies in maximizing the ability of the system to remove heat from the compressed air while not adversely affecting boost pressure, losing throttle response, or contributing to any delay in boost rise.
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04-30-2008, 02:38 PM
#52
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The "next county" comment is directed specifically at speed-density based ECUs where no AFM/MAF is used.
Originally Posted by Corky Bell in Maximum Boost
It is distinctly possible to upset the basic throttle response if an engine is equipped with an airflow meter positioned too far from the throttle body, Opening the throttle causes a low-pressure pulse to be created that travels up*stream toward the airflow meter, The time it takes this pulse to reach the flow-meter and cause it to react is indeed the delay in throttle response. Typically, such a pulse must travel from the throttle body to the intercooler, through the intercooler, back to the turbo, then to the flowmeter, in order for the flowmeter to register a response. It is not until the flowmeter receives this pulse that the air/fuel ratio can change to account for new load conditions in the engine. I should point out that there are exceptions here, based on the style of throttle-position sensor with which the engine is equipped. Nonetheless, it is generally true that the farther the throttle is from the airflow meter, the poorer the throttle response. Thus, this path length should receive some consideration in the design process.
When an engine is equipped with a speed density type of EFI system, wherein no airflow meter is utilized, or a blow-through carbureted turbo system, the length of the intake tract tan extend into the next county with no negative re*sults insofar as throttle response is concerned.
The overall problem in designing an intercooler system, then, lies in maximizing the ability of the system to remove heat from the compressed air while not adversely affecting boost pressure, losing throttle response, or contributing to any delay in boost rise.
It is distinctly possible to upset the basic throttle response if an engine is equipped with an airflow meter positioned too far from the throttle body, Opening the throttle causes a low-pressure pulse to be created that travels up*stream toward the airflow meter, The time it takes this pulse to reach the flow-meter and cause it to react is indeed the delay in throttle response. Typically, such a pulse must travel from the throttle body to the intercooler, through the intercooler, back to the turbo, then to the flowmeter, in order for the flowmeter to register a response. It is not until the flowmeter receives this pulse that the air/fuel ratio can change to account for new load conditions in the engine. I should point out that there are exceptions here, based on the style of throttle-position sensor with which the engine is equipped. Nonetheless, it is generally true that the farther the throttle is from the airflow meter, the poorer the throttle response. Thus, this path length should receive some consideration in the design process.
When an engine is equipped with a speed density type of EFI system, wherein no airflow meter is utilized, or a blow-through carbureted turbo system, the length of the intake tract tan extend into the next county with no negative re*sults insofar as throttle response is concerned.
The overall problem in designing an intercooler system, then, lies in maximizing the ability of the system to remove heat from the compressed air while not adversely affecting boost pressure, losing throttle response, or contributing to any delay in boost rise.
Thank you. Exactly what I've been trying to say, but couldn't find the passage. And anyways, when your out of boost and driving on the street your engine will be acting like a non turbo motor anyways.
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04-30-2008, 02:57 PM
#53
Actually, the quoted passage disagrees with what you said:
Because everyone who is making decent power here runs a speed-density system, not the AFM.
BTW I wasnt alluding to you when I made that "*****" and "crap" statement.
The point is, unless someone tries this setup (near the cat, not near the muffler), speculating on its performance is of no consequence.
BTW I wasnt alluding to you when I made that "*****" and "crap" statement.
The point is, unless someone tries this setup (near the cat, not near the muffler), speculating on its performance is of no consequence.
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04-30-2008, 04:35 PM
#59
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he tried to convince us rear mounting is superior in ever aspect. so i got tired of it and banned him.
I did love his comments like (from his tuning video on youtube) "ran autotune on spark map last night, so that's worked out" 3:00
watch at the end in "boost" slowest 15psi ive ever seen, in matters of spool and speed of car.
I did love his comments like (from his tuning video on youtube) "ran autotune on spark map last night, so that's worked out" 3:00
watch at the end in "boost" slowest 15psi ive ever seen, in matters of spool and speed of car.
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