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

you should be able to get that intake temp down more with a good intercooler. also, volumetric efficiency is supposed to be near 100% under boost, or so I'm told. does the duratec engine hit maximum HP at 6000RPM?

http://www.squirrelpf.com/turbocalc/index.php is a nifty calculator.

150° intake temps is VERY hot. ping central.

i usually do 90-100 at the most for that calc.

which puts you to like 18psi.

Is the redline only 6K on those things? the higher the revs the less boost is needed really.

i also take VE out of the equation.

Not yet anyway.

I got the book from Braineack's link, but it's a PITA to read anyway because it appears to the victim of a really bad OCR scan conversion. lol.

I just wanted to see what it looked like to know if it was going to be something I would want to add to my personal library.

The good news is the answer is YES. I'm off to Amazon right now to order it. :)

-Trent

Try not! Do, or do not. There is no try. http://yodasdatapad.com/livingroom/f...ns/cw_yoda.jpg

I'm betting it won't be too hard to get the EMU running on an '06+ MX5. Has anybody found a place to look at the NC wiring diagrams on line? Yeah, it's a scary new design, but hey, it's got fuel injectors and ignition coils. Nothin' new there.

According to my tachometer, redline is 6650RPM.

Should I be using 14.7 for atmospheric pressure? Trying to find a turbo with a Pressure Ratio of 3.5 and an air flow of 33lb/minute is impossible!

Corky's supposedly got the engine management already figured out.

fuck news to me. COol though

Only if your turbo is too small.

You should be looking for a turbo with a pressure ratio around 2 with about 35-40 lbs/min of compressor flow.

Mark

I've spent over an hour playing on that site instead of working now. Are you trying to get me fired or something? :bigtu:

Braineack, if you dont mind could I also get a copy of that book?

Thanx
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I was impressed with your math skills, so I figured if you were gunna do the calculations anyway, you should have an automated system to do it for you.

just think of all the time i SAVED you, by not needed to do all the calculations by hand! just explain that to your boss if they ask about your productivity :-P

Tell you what if Andyfloyd's 2.0L BP can make 300 mustang whp at 17 psi with a 3271 i think a 3071 or similiar would be a pretty good match for you. Part of picking the right turbo is looking at what others have done with similiar products. Airbrush took a 01 with a 1.8 and made almost 300 whp at 14 psi, Y8's took a 2860 on his 99 1.8 and made 250 whp at 8psi. I dont know how if the NC motor has the effeciency in intake and head design but given that the base hp is about 40 more from the start i think with a turbo sized from 2860-3271 would be ideal for you. They should spool well and have the headway to hit 300 whp. The key here is maximing your BSFC with timming and cooling. The cooler the intake stream is the more power you can make with more timming, then the VE goes up and pretty soon you will be sitting at 110% + pretty easily.

3271 (journal bearing) is smaller/flows/costs less than the 3071 (ball bearing). Quickly glancing at the compressor maps, the 3271 looks to match the 2860RS in terms of "size". Without really looking into it, I feel that the 3076 would be nice on the NC.

Y8S used the 2876 not the 2860. At least at the last dyno day... I had a tick more hp than him (~240rwhp) but he was around 8psi with his 2876, i was at 13 with my 1544's.

How much boost is too much boost?

What's the limiting factor here? Obviously you can't take a 14:1 CR engine and push 100psi through it. Something will give. But what? The NC has a stock CR of 10.6:1 (10.8:1 depending on where you read). There's plenty of bottom end bits to soup it up, but what really is needed?

How does compression ratio fit into the whole turbo schema? It seems that 6-8psi is "safe" on my motor. More than that requires pistons/rods. Why?

Cooling and maximum cylinder pressures will tell the tale. Along with octane rating hell alot of alchohol V8's run high comp ratios to make up off boost HP on there 900+ hp cars.
Tim IDK i was just shooting of the top of my head i never could get the squirle perfomancechart for the 3271 to work for me. But i take what you say as truth as I :dunno: alot about garrets or turbos in general compared to you. I was just trying to give him a ballpark to play in.

I hear ya :bigtu: I actually don't use any programs even though I should. I just look at garretts maps directly and imagine lines thru them. Then make sure there's headroom.

here's how a 1.6L would look with a 2871 to make something around 300BHP @ 7K

http://www.boostedmiata.com/random/gt2871.jpg

Would that really produce 300BHP? A "GT28R" (Which I'm assuming is any of Garret's GT28xxR line?) on a 2.0L non-VVT Duratec produced only 190WHP@8psi. Granted, the engine doesn't have VVT, and has a 10:1 CR instead of a 10.8:1, but would those two things make up for the approximately 60WHP loss?

http://focussport.com/images/fsturbo_stock_vs_stg1.jpg

Dude look at the chart he is tracking around 2.25 PR or 18.3 psi wich i think is abit high but within reason.

the 28RS is a bit smaller than the 2871 too. but yes I'm displaying it at 18psi.


remember, you have to determine how much lb/min 300hp is.

I use HP x AFR x (BSFC/60)

or 300 x 12 x .00916 = 32 lb/min


so you know you at least need a turbo that makes 32 lb/min. Now look at the above map, at 32 lb/min & 7000RPM the thing is most efficient. Then you gotta figure you need X amount of PSI to make the goal. Which I determined on a 1.6L to be something close to 18psi. Then I can plot my map as I've done above.


this turbo could produce something like 350rwhp easy.



300BHP on teh GT28RS would look something like this.... about the most it can do:

http://www.squirrelpf.com/turbocalc/...&product_id=32

Read the thread before you post, then go buy the book instead of stealing it from Corky.

Oops... I was rereading the thread, and got Y8S's 1.8 mixed up somehow or another. I'd be ecstatic to replicate their results!