Teach me about turbos!
#1
Teach me about turbos!
I understand the basic concepts of turbocharging a vehicle. I don't, however, understand why some turbos are better for certain applications than others.
What makes a turbo spool up quicker?
What is the limiting factor on a turbo's output?
Would a 1.6L daily driver require a different turbo than a 2.0L autocross car? And why?
What is a compressor map, how do you read them, and what's so great about them?
Thanks in advance, and if you've got any off-site links or books to recommend, I'd appreciate those as well!
What makes a turbo spool up quicker?
What is the limiting factor on a turbo's output?
Would a 1.6L daily driver require a different turbo than a 2.0L autocross car? And why?
What is a compressor map, how do you read them, and what's so great about them?
Thanks in advance, and if you've got any off-site links or books to recommend, I'd appreciate those as well!
#4
Boost Czar
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Join Date: May 2005
Location: Chantilly, VA
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Typically it's the size of the turbine wheel itself and the A/R of the housing.
if the airflow of the exhaust is not enough to spin the turbine fast enough, obviously it wont produce boost.
the size of the compressor wheel and turbine flow.
if the compressor wheel can only support 20 lb/min (180BHP) efficiently, dont expect more than that from it. After that point it will start blowing hot air and your torque will drop.
likewise, if the turbine side is too small and your engine expells greater CFMs than wheel can flow, your boost will acutally drop as well as your torque.
the same wheel with a bigger housing may not have any problems.
yes, the spool and flow charateristics are substantially different. the 1.6L might want a GT2554 sized turbo, the 2.0L maybe a GT2560.
the compressor map shows how the wheel produces boost.
the x-axis shows how much airflow volume it can flow
the y-axis shows how much boost it can flow. 14.7psi + 14.7 / 14.7 = 2PR
is island shows the heat efficiency. the drop off point is 60%, anything past that will just be hot air.
to read a map:
determine the amount of airflow volume (lb/min) you need to make a certain amount of power (fairly direct relationship)
example:
200BHP x 12AFR x .00916 = 22 lb/min
so for 200BHP you need about 22 lb/min of airflow.
look at your map, find 22 lb/min. you want to make sure that your turbo can at least support that.
now you gotta determine how much boost it may require to make 22 lb/min
easiest way:
200BHP/120BHP = 1.66PR
1.66 * 14.7 - 14.7 = roughly 9.7psi
hard way:
(lb/min x 639.6 x (450 + intake temp) / RPM/2 x C.I.) - 14.7
22 x 639.6 x 550 / 3500 x 97.7 = 22.6psia - 14.7 = 8psi
so now plot that mark, 22 lb/min and 8-9-10psi. how does that mark look? good efficiency? off the chart?
i suggest you read turbobygarrett.com tech 101 102 and 103....this could go on forever.
fwiw, i have corky's book in a word doc.
if the airflow of the exhaust is not enough to spin the turbine fast enough, obviously it wont produce boost.
the size of the compressor wheel and turbine flow.
if the compressor wheel can only support 20 lb/min (180BHP) efficiently, dont expect more than that from it. After that point it will start blowing hot air and your torque will drop.
likewise, if the turbine side is too small and your engine expells greater CFMs than wheel can flow, your boost will acutally drop as well as your torque.
the same wheel with a bigger housing may not have any problems.
the compressor map shows how the wheel produces boost.
the x-axis shows how much airflow volume it can flow
the y-axis shows how much boost it can flow. 14.7psi + 14.7 / 14.7 = 2PR
is island shows the heat efficiency. the drop off point is 60%, anything past that will just be hot air.
to read a map:
determine the amount of airflow volume (lb/min) you need to make a certain amount of power (fairly direct relationship)
example:
200BHP x 12AFR x .00916 = 22 lb/min
so for 200BHP you need about 22 lb/min of airflow.
look at your map, find 22 lb/min. you want to make sure that your turbo can at least support that.
now you gotta determine how much boost it may require to make 22 lb/min
easiest way:
200BHP/120BHP = 1.66PR
1.66 * 14.7 - 14.7 = roughly 9.7psi
hard way:
(lb/min x 639.6 x (450 + intake temp) / RPM/2 x C.I.) - 14.7
22 x 639.6 x 550 / 3500 x 97.7 = 22.6psia - 14.7 = 8psi
so now plot that mark, 22 lb/min and 8-9-10psi. how does that mark look? good efficiency? off the chart?
i suggest you read turbobygarrett.com tech 101 102 and 103....this could go on forever.
fwiw, i have corky's book in a word doc.
Last edited by Braineack; 10-18-2007 at 03:31 PM.
#13
Boost Czar
iTrader: (62)
Join Date: May 2005
Location: Chantilly, VA
Posts: 79,501
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if he hurries up and finally publishes revision 2 that's already written, then he shouldn't have a problem :gay:
besides, we have like 10 members that will actually read this thread and download it and I've already boughten it and it's already been in publication for over 10 years and if you do a google search you'll find the site I originally got it from.
besides, we have like 10 members that will actually read this thread and download it and I've already boughten it and it's already been in publication for over 10 years and if you do a google search you'll find the site I originally got it from.
#15
Boost Pope
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Join Date: Sep 2005
Location: Chicago. (The less-murder part.)
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Honestly, this is one of those rare occasions when I gotta speak against the family. Corky is, well, he's The Man. I'll be the first to admit to being a torrent freak, I haven't payed for an OS in about two decades, and I even use downloaded copies of factory service manuals. But stealing Maximum Boost... It ain't right.
#19
I've got an '08 MX-5.
Assumptions:
· Horsepower Target: 300BHP
· Air/Fuel Ratio: 12
· BSFC: 0.55
· Wa: 33 lb/min
· Intake Manifold Temp: 150F
· Volumetric Efficiency: .95
· RPM: 6000
· Displacement: 2.0L
· Atmospheric pressure: 12psi (Denver)
(33*639.6*(460+150))/(.95*(6000/2)*122) = 12875148/347700 = 37psia
37psia - 12psi = 25psig
So I'd need to hit 25psi of boost to achieve 300 flywheel horsepower, right?