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!

Read This.

http://en.wikipedia.org/wiki/Centrifugal_compressor

Then ask specific questions

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.

seriously how? Send it to me por favor

I'd also love a copy of that, if you wouldn't mind.

And thanks for the great post!

fine....

I am so going to abuse my companies printer right now.

well, thanks a lot braineack. my productivity at work for the rest of the day just went to shit. lol.

HAHA, Braineack is keeping a list of everyone who is stealing corkys book, then kicking them off miataturbo!

get those pirates braineack! getem!

Well, if you do steal his book, hopefully he'll impress you enough to buy something from him, ehh?

hahah. im the one who uploaded it.

hey i found it online over a year ago...it's not like any of you guys couldn't. ;)

I dunno, I'd be scared of posting said materials online in a place where corky frequents. If it was me, I would ask corky for his blessing. its like the godfather, you don't go and disrespect him.

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.

Hey brain can we ban each other?

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.

well fine then.

just say its for personal backup like NES games and stuff

hey, i really do have the paperback.

Just finished reading the TurboByGarrett link. (thanks!)

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?

No. You can get that power with lower PSI but more CFM.

PS. Don't bother with a '08, sorry, as far as I know there is no solution for fuel/timing