in a quest to find the impossible....a turbo small enough to fit on the greddy manifold yet large enough for 9-11psi of boost all the way to 9000rpm with as little lag as a t618z....i've lost myself in an orgy of excel sheets and compressor maps. i've calculated out how the motor flows air through the RPM band at WOT, but I know that's only part of the solution.

but first a basic, probably dumb, question about compressor maps. the CFM numbers at the bottom...if an engine flows 400cfm NA at WOT and redline does it still flow 400 cfm at a PR of say...1.75? seems to me that it would...

turbine maps...a compressor's only half the equation. why is there so little attention given to turbine maps? they look so uncomplicated in comparison to a compressor map.

how can you calculate lag with a compressor map? it's clear that a gt30r can flow 400cfm at 11psi but where's it going to reach target boost? does it involve the use of a turbine map?

other than using a canscan tool, is there any way i can calculate airflow and thus plot points at part throttle and cruise?

...anyway im not so concerned about the size aspect of this or really anything specificly related to X turbo on Y motor. i'm open to suggestions for turbos that may fit my "mild boost, high flow" goal, but please dont provide that without any sort of evidence supporting the claim. i'm looking for useable power that can still scream all the way to 9000. dyno queens excite me about as much as the fat girl at a party, which aint much at all.

 

great????
bump

beers

 

The way to read a comp map is that the cfm is what is going into the compressor. The CFM going out is going to weigh more but still be writen as CFM. This winds up being very confusing so the better way to work with these things is by mass meaning lbs/min.
Rule of thumb for a good piston engine is 10HP per Lbs/min. In the case of this engine it is about 30% maybe more. Use 7HP for your calcs.

The turbine side is not as much of a problem as the vcompressor. Utilizing the energy already in the air and defusing it allows the energy to always be pulling away from the surface of the blade. This gives stable aerodynamic actions. It is easy to get high efficency from this operation. Thus there is wide usage of a given design because there is a broad operating band.

When selecting a compressor you must look at your off design operation. This means that your target point of X psi at x CFM is only a small part of the operating time. Most of your driving will be somewhere else on the graph. Because of this it is more difficult to find a good blower for street use then race use where the operating range is small.

Pick a few points of operation and plot those on several graphs. You might find that the blower you first pick might not be the best for street usage. It would be better to choose for better off peak then just have a great peak operation.

Remember that your wastegate is going to put you at X psi wth lots of different flows. So look at that pressure with many different flows and see where it puts you. For sure don't let it put you into surge. Have fun.

 

thanks richard

 

Richard I think you got something backwards. Don't you mean use 10 lbs for the rotary vs 7 lbs for a piston engine?

 

As usaual I left out some word or two. I forgot the word "less."
However the statment is correct. One pound of air in a good piston engine will give you 10BHP. In a rotary from my experiance so far with the dyno and other data I would say to use 7 BHP for a Lb of air per min time.

Perfect air can be converted to CFM by dividing the Lbs/min by .076. But it isn't a perfect world so you might try using .073+/-