I am looking at the turbo maps and I have no idea what they mean by surge limit can someone fill me in on this.

 

That's the minimum a compressor can flow for a given speed. If you try to flow less than that, the flow becomes unstable and it flutters, or "surges". Not good.

Compressors surge when you shut the throttle quickly, too. The turbo is still spinning fast but it can't produce the flow because the output is too restricted. BOV's vent the compressor outlet so it can flow more and not surge.

 

this is what I found on how to read compressor maps.

airflow+(2/1000)*0.9*(R/E)*S*(303/360)*146.5

R = engine rpm
E = none turbo HP ( I assume 120hp)
S = boost pressure + 1 bar


this should give a rough estamet.
can someone give a better way of doing it??
I got 35lbs/min on a 2 rotor.

 

I've never seen how to read a compressor map based on non-turbo HP, so I couldn't help you there.

In fact, I'm trying to decipher that formula... it just doesn't make sense to me. Hmm... Is it trying to calculate airflow directly, by calculating V.E.? Interesting...

 

I got an easy way, get your compressor rating in lbs/hr
if you have a 55lb/hr comp wheel rule of thumb says its good for 550hp ON A PISTON engine usually DOHC, highly efficient.

so basically lb/hr X 10 = max hp from comp wheel. 10hp per pound. you can go higher if you run very high compression ratios. the max I've done is 11hp/lb of air

remember this is a rule of thumb so there are far too many variables to use this as the bible, but I use it to give me a good indication of where I want to be. I have yet to find the perfect turbo on the first shot, I've always had to resize. If you spin at super high RPM's this goes out the window. Also if you start running higher than 30psi this formula is usually useless too. But it works to give you a general idea of what your wheel is good for. We tried an 88lb/hr wheel with a turbine that was too small (TV-51 1.09 AR), the car would just buck. full boost in first gear, wouldn't go past 4000rpm. The worst compressor surge I'd ever seen. And this ladies and gentleman was a mamoth turbo.

For rotaries, this is highly arguable also, but due to the inefficiencies of the combustion chamber design, plus your porting (major factor) I like to estimate 25 percent less. ie only 75 percent of the power making it. so that same 55lb/hr wheel making 550hp on your 4cyl DOHC honda @ 30psi, will make about 400-440 on you rotary.

for example a 60 trim comp wheel will make about 475-500 whp on a highly tuned 2.0L DOHC 4 banger. On a mild port rotary this thing can't do better than 400-425 whp.

 

wow thanks

 

That would be one tiny wheel - I am sure you mean lbs/min...


Bernd

 

Bernd,

your right I screwed the pooch on that one, let me fix that.