Turbo calculator spreadsheet in Downloads> Programs secti

[BrianC72bgt]

I put together a simple spreadsheet based on the formulas found on the turbobygarrett site to help in the selection of the right size turbo for a particular HP target on an engine of a specific size and volumetric efficiency.

http://60degreev6.com/discussion/dload.php?action=category&cat_id=6

All ot the Items in Blue can be adjusted to find the specs of the "right" turbo for your application. This is all the stuff you have to do first before you look at the turbo maps. I made some starting assumptions about the efficiency of my pushrod 3.4 and my tuning ability - you will see what they are and can adjust them if you think your tuning ability or engine's efficiency is better or worse than mine.

I welcome any corrections or suggestions for changes to this simple sheet.

Regards,

Brian C.

[bszopi]

Looks like a pretty cool and simple program. Thanks for sharing!

[BrianC72bgt]

I've been stalled on my project for a while...converting a 72mgb-gt with an iron head 3.4..with plans for twin T25, T28 or 2 small T3s...so I was poking around at trying to size turbos a while back, but life has been otherwise busy. So, I'll try and get back to this little program and maybe build in some map plotting capabilities and data points at different rpm.

The tricky bit is properly interpreting this info after mapping it on the available compressor graphs, making some assumptions about the turbine side and then, ultimately, picking the "right" one. Corky Bell's Maximum Boost covers it, but fairly briefly. I would really love to see a tutorial by someone who really knew his (or her) stuff do a bunch of different engines and walk you through three or 4 candidates for each application. That would be really helpful to the unwashed masses like myself.

Regards,

Brian C.

[bszopi]

I haven't dabbled much into turbos, so I don't know all the ins and outs of what exactly going into one of the graphs (although I have seen a few). What would obviously be ideal would be the ability to enter a couple variables for a certain turbo, and have excel create the turbo map. If anyone knows about what makes up the map, I would probably be willing to help out in trying to get the graph/map created. I've done a little dabbling in excel (ok, so I've gone to the extreme on a couple programs at work, including graphing the impedance of electrical conductor vs length of the conductor, and being able to alter the graph automatically by changing the ambient temperature or magnetic flux created by bundling multiple conductors together). If it was possible to just plug in the AR values of the compressor, etc a create a map for any turbo, the program could become extremely useful.

Damn you... Now I'm going to have to start researching some of this more....

[BrianC72bgt]

bszopi,

Unfortunately, I don't think the turbo maps themselves are capable of duplication by entering a few simple equations. However, what would be very useful is if the Mfrs made excel map files of their turbpos available and then you could do your maths and plot directly to their graphs. However, it is not really a big deal to simply print out their charts and plot a few points and then connect the dots.

Understand that all we are looking at is the compressor side. The equations I used are designed to compute what Air flow and compressor ratio is ideal for a given engine with a known HP target and redline. The things I am not sure of on the compressor side are:

(1) Do you alter the compressor ratio when computing discharge at lower engine rpm speeds or do you use the one computed at max engine rpm for all instances.

(2) Also, at what low rpm engine point do you draw the plot line back down to the XY intercept (0,0). Seems to me that even though some formulas are being applied that a lot is being left to constants and rules of thumb. Not ideal...

Here is how Corky Bell puts it in Maximum Boost,"The surge charachteristics of the compressor with regard to the application must also be examined before finalizing a selection. This can be approximated in a simple manner. Assume that the desired pressure ratio is reached at 50% of the redline rpm and plot this point on the compressor map....Then draw a line from this point to a point of PR = 1 and CFM = 20% of maximum....It is imperative that this line lie completely to the right of the line on the (compressor) flow map called the surge limit."

I am sure that this method is pretty damn close, and he clearly knows of what he speaks, so I guess that is more than adequate for now. There does seem to be a real lack of detailed discussion on selection of the turbine side of the turbo with the available info dummed down to: smaller ratio = faster spoolup and limited top performance with large ratios= slow spoolup and ultimate top end power.

Hmmm... I guess it does come down to experience and some Trial and error. Thats great if you've got the money to get it wrong and then try again...

Regards,

Brian C.