Its not a limit, the 22psi, just a guesstimate of a good number to run the SC at. It would support more boost if you needed it to!
With some seriously good intercooling, you might squeeze 30psi out of it on the 2.2 usefully.
Its pretty easy working out how to size an SC for an engine really. To get a ballpark figure just find how much air your engine is needing at a certain rpm:
(engine volume x rpm x volumetric effciency)/2
then the boost in psi you want is:
{[(SC displacement x drive ratio x rpm) / engine airflow] - 1 } x 14.7
Just change the drive ratio until you get the boost you want. If you needed say 1.5 drive ratio, your SC pulley should be 2/3rd size of the crank pulley.
The method above does not take into account SC efficiency (how much it heats the air) or heating due to compression of the air, but if you have a good intercooler (80% eff) you are still in the ballpark for sizing and drive ratio as long as you are running the SC in the right airflow range. You can check if you are by looking at the SC map like this one for the newer versions of the m112:
http://www.eaton.com/ecm/groups/public/@pub/@eaton/@per/documents/content/ct_128487.gifOne other way to check simply if you have the right SC is to see what it's max rpm is at the engine max rpm. Most wont withstand 14000 rpm (especially not the big ones), and if its not getting to 10000rpm its a bit oversized.
Most SC applications have an drive ratio of around 1.5, some have less but then don't have a great bottom end. Because the range of the usable boost on any SC engine needs to be the same as engine rpm range, they run right up to the inefficient high rpm's. This is when a turbo is ALOT better. Some engines like big V8's dont really need to much of a hand at the bottom end and can have low drive ratios nearer to 1, but its a waste of power driving the SC.
The bypass valve for the SC is so that the air is bypassed around the SC when you don't want it i.e. at low throttle openings. In a petrol car that is very important to avoid running lean. On a diesel you can worry less about it but you should really still have something in place. Alot dont though. It's because the SC is just a positive displacement pump and always puts out the same pressure ratio, not like a turbo which is load dependant (only spools up when you put your foot down). As diesels always run lean and dont have a throttle, you can just about get away with not having a valve for bypass if the boost controlling valve is set up correctly.
Anyway, a simple turbo into SC with big intercooler setup and external wastegate valve to control boost would make one quick 1.9 aaz!! It would be quick off the line and really torquey. It might be a bit *** to drive round town but good on the strip!!
Topic: how does an LDA work if you have a supercharger? (Read 5523 times)
