Can someone explain to me how to read a turbo flow chart or point me to a website that explains it.

I was looking at these http://www.turbofast.com.au/FlowTO4E.html


Thanks,
Mike

 

Back when I was 16 (I'm 19 now) used to know how to read one by just glancing at one if it was appropriate or not for the engine... I haven't even looked at many in the past couple years so I'm out of touch... I better pay attention to this thread

 

the best way to understand is to get the book "maximum boost" by Corky Bell.

now here is my abriged version. if you need more, just ask.

first, here is a handy dandy equasion I cooked up a while ago to get all your information in the right format:

Litres x 61(CID) x RPM x .5 x Volumetric Efficiency
------------------------------------------------- = Result x Pressure Ratio = CFM Flow x 0.0756 = Pounds of air per Minute ( Lb / Min )
1728

I made that originally for piston engines, and I forgot what that .5 is for, so someone check it.

the number on the left is the absolute pressure in BAR. The number on the bottom is the amount of air flowing through in lbs/min (pounds of air per minute)

the "territory" map shows you the efficiency of the turbo. the "higher" it is, the more efficient, and the numbers show you what percentage. if you go too far to the left, you will cross the surge limit, and your pooped out. too far to the right, and the efficiency get so bad, guess what... your pooped!!! you need to make a couple graph points, at redline, 300 rpm above redline (just in case), at 85% of the redline, and at 75% of the redline. you should get a good line to show you where the efficiency lies. try to keep it as "high" on the map as possible. its best to have the peak efficiency around 85% of the redline, on average. you will have to decide for yourself where exactly you want it. then, you pick your turbo.

thats the abriged version.

 

Thanks a lot sinfestboy. I will study the maps some more and I will probably have more questions.

MIke

 

Thanks, it's all come back to me now

 

Actually, Corky Bell's "Supercharged!" book is more up to date. You can read up on the centrifugal supercharger to get some good turbocharger info. If you only get one book, then I would get this one. Of course, it's probably best to get both, although they cover about 75% of the same material. If I remember correctly, the "Maximum Boost" book doesn't cover the LBS/MIN charts, although it has a fantastic explanation of "AR Ratio".

The 0.5 is for 4-stroke piston engines. The 0.5 value (aka 1/2) represents the fact that 4-stroke piston engines only fire 1/2 of their pistons (ie rated displacement) for each revolution of the output shaft. For rotary engines and 2-stroke piston engines, you need to either take the 0.5 out of the equation, or double the engine's rated displacement when using it in the formula. This is because rotary engines and 2-stroke piston engines fire ALL of their rated displacement for each revolution of the output shaft.

As great as Corky Bell's books are, they do have some errors. One of them is his incorrect conversion of PSI to BARS. Fortunately, the books use PSI for all the equations. Anyway, FYI, the Pressure Ratio does NOT = Absolute Pressure in BARS. If you really want to convert to BARS so you can compare with non-Americans, then just use a web-based converter like this:
http://www.sciencemadesimple.com/conversions.html

This web page shows how to read the compressor maps, although it has some mathematical errors.
http://www.gnttype.org/techarea/turbo/turboflow.html

 

see:http://www.se-rx7.com/gallery/maps.html I used some "ballpark" math to plot BHP v. PSI. They should do for making comparisons.

Disclaimer: I used the "rule of thumb" from innovativeturbo.com to figure BPH as a function of Mass Air, and a simple conversion for figuring PSIG from PR. VE changes over the RPM range, so in reality, there should be a scatterplot over the graph.

 

Hi all,

Just wanted to say that this information is fantastic!


I have a question though, I have heard that when purchasing a Turbo for a Rotary, you have to take the HP figure given, and divide it by 2.

i.e. A GT35/40 Turbo has a HP rating of 700hp. Now if you put that onto a Piston engine, that is what it will make. But on a rotary at around 1BAR it will make approx. 350-400 - why is this?

 

Evil, how do you know what your VE is at any given RPM? Stock, Street and Bridgeported.

 

You should check out this months Turbo magazine. They go into this pretty well.

 

Will do. But is'nt it different for just about every motor depending on what setup you have? Esp. Piston vs. Rotary?

 

The divide by 2 rule is used when computing the airflow requirements of the engine at a given rpm, and this applies to 4-stroke piston engines, not rotary engines. If you are using a formula that is intended for 4-stroke piston engines, then you need to multiply the result by 2 for it to work with rotary engines and 2-stroke piston engines. See my previous post for more details.

The HP figure will correspond to a rotary engine the same as a piston engine, although there are quite a few other factors involved in choosing a turbo besides the turbo's max HP rating. Also, the HP figure isn't necessarily accurate because it is based on the turbo's max airflow rate, and it assumes:
1) Your engine will allow the turbo to reach this max airflow rate, which it may or may not, which depends a lot on the turbine and AR ratio.
2) A given BSFC (ie HP vs. amount of fuel) which your engine may or may not mimic since this is based on efficiency.
3) A given air/fuel ratio, which may be richer or leaner than your actual ratio.
4) An airflow rate and pressure just after the turbo, and doesn't take into account the pressure drop as the air flows through the plumbing into the intake manifold where the boost gauge reads the pressure.

If you look at a compressor map, you will notice that both pressure and airflow rate are factors. Rotary engines have different airflow requirements at different rpms, and they also tend to have a higher redline. It is quite possible for a turbo that is intended for a piston engine to run out of steam at the rotary engine's high-rpm airflow requirements. Also note that those GT turbo maps are based on a diesel engine, and those maps are very basic. The regular compressor maps on the Turbonetics site are much better.
http://www.turboneticsinc.com/index01.html

I don't know, but I plan on logging some good info in the near future. I tried with a dyno and EMS datalogging, but I ran into a roadblock because I didn't take accurate fuel pressure readings. The thing is, VE will change with RPM and load, so there isn't just one VE number, there are a countless number of VE numbers. It's kinda like torque or hp, where it varies a lot, so most people just state the max of each, even though this doesn't tell you the whole story.

VE will be slightly different even between similar engines, such as one person's stock 13B NA vs. another person's stock 13B NA, as it depends on wear, deposits, and other factors. The closer the engines are to each other, the closer the VE plots will be.

 

Wonderful information!

I will need to take time out to digest it all - thanks very muchly.

.ps Evil A - any chance if getting you on our Forum here in the UK? www.mazdarotaryclub.com? knowledge of yours is rare in these parts!

Thanks so much again.

 

Thank you, but knowledge like mine isn't rare in your parts, you just don't have many people on your forum yet. Most of the information I gave you is standard fare for an American public school 12th grade (age 17-18) auto shop course. You will have much more knowledgeable people on your UK forum once your membership increases. In the mean time, feel free to ask anything you like on this forum. We even have some engineers and professional racers on this forum who can answer the more difficult questions.

These books help explain turbos. You may even have them in your public library.
http://www.amazon.com/exec/obidos/tg...qid=1046904212
http://www.amazon.com/exec/obidos/tg...l/-/0895861356