Sound. That now makes sense to me! Was getting myself a bit confused over that
It's been a long debate about Rotrex SC efficiency and MAX boost for M54B25/B30 engines. Can anyone teach me how to read the chart for supercharger compressor on the example below, Rotrex C30-94?
C30-94 flow chart.jpg
Its not even max boost, its RPM. Calculated from crank/sc pulley size.
I would say that C30-94 is way to small for a 3.0l engine ...
please find attached a calculation for a 2.9 engine and the biggest Rotrex available - C38-81
If you have any questions about how was calculated - feel free to ask
Best, Bogdan
' 99 E36 316i Compact, 83kw
Here is a question I did not see answered. How do you read the maps if you are use two turbos? Would your values be halfed?
Heres what I have and why I am asking, my current build up is a Small Block Chevy 383, getting two turbos, one running off of each exhaust bank. I'll be running a max of 15 psi, and according to the Airflow Chart Def made, at 2k I will need 25lbs min, and up to 6k I will need 77lb min with a PR of ~2.1. Also, this is with it running at 80% VE.
So, for each turbo, the values I should be looking at will be 12.5lbs at 2k and 38.5lbs at 6k correct with a PR of ~1.5?
Or would I half the boost, and calculate each turbo running at 8psi which did come up with different numbers.
Also, I know a single turbo is more efficient, but this is the plan!
Pressure Ratio will be the same(i.e. boost pressure is the same at each turbo outlet), but you are correct in that total flow is cut in half for 2 turbos. 80% VE is pretty conservative for a turbo engine with a favorable intake/exhaust pressure ratio and a reasonably sized cam. At least it is that way with most modern 4V/cylinder heads. SBC's tend to have a more narrow efficiency window due to packaging/head constraints, but I'd still think you could get it a bit better than 80% at 6k RPM.
Twin turbos make a lot of sense for a V engine, so you'll get no arguments from me on your plan!
thanks for putting this together....gave me a good insight on how to read the maps....now i can go somewhere and work out how much power i want to make and what turbo to get
good stuff DEF!
Absolutely great info !! Thanks Def !
and the spreadsheet is really the best !
I guess it doesnt really matter for those of you who are running a turbo already , you can select a different sized one .......
But it would be very interesting to see some of the new turbos maps(comp wheels) in comparison ....
and then see when a bmw engine( not a 2.0 liter) will work with them
Thanks a lot Def, thats what I figured.
I figured I would go conservative with my numbers so that way I will be less likely to be disappointed or expect too much out of the engine.
I think I'll try to find a turbo that has a map that will fit in the ranges of 80% to 100% just to be safe, then afterwards play around with different turbos based on how well these work out.
If you have any tips or pointers I would greatly appreciate.
First off sorry for asking what will is probably a stupid question. Reading the first post and looking at the lines you have drawn on the compressor maps. I understand the horizontal lines are drawn at the desired pressure ratio and that you started off on the x axis with the corrected flow given at 2000rpm in your spread sheet. What i don't get is how you calculate at what gradient the line goes from the x axis to your pressure ratio line? Is it related to the constant speed lines or calculated through the turbine maps?
Can Someone Email The latest version of the spreadsheet to me? (after the data uplink ban)
Aetro4@gmail.com
Thanks
very nice write up.
Thanks!!!
"If you can leave black marks from the time you exit a corner till the time you brake for the next turn, then you have enough horsepower." --Mark Donohue
Wtf
Sorry but i can't understand it......
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