I was wondering what values I should use for the BSFC and airflow (lbs/min) of both the 13B-RE and S5 13bt motors at say... 480rwhp (~550bhp?)?

 

According to this site http://www.maxcooper.com/rx7/how-to/...tem/calcs.html which many people use as a guidline for rotary fuel calculations, these are the values to go by. Try playing around with this calculator, it's pretty slick.

0.55 - stock rotary na
0.64 - stock rotary turbo
0.62 - modified rotary turbo
0.64 - super modified rotary turbo

I'm not really sure where 480 rwhp would fit, but I would say 0.63

Check out what RC Engineering has to say regarding fuel injector sizing, pressure, bsfc, etc at http://www.rceng.com/technical.htm

 

Thanks!

Now how do I calculate the approximate airflow of a streetported 13bt or 13bre to plot on a compressor map?

 

The formulas on this link are correct as far as I can tell, but there are a few math errors in the examples.
http://www.gnttype.org/techarea/turbo/turboflow.html

Note that you need to double a rotary engine's displacement when working with airflow formulas intended for 4-stroke piston engines. This is because rotary engines and 2-stroke piston engines fire their entire rated displacement for each rotation of the output shaft, while a 4-stroke piston engine only fires half.

Also note that the BSFC will be higher if you are running very rich mixtures, and the efficiency of the turbo, intercooler, and other factors will also affect BSFC.

 

http://www.turbofast.com.au/turbomap.html

this link is helpful, but use about 85% of hp cals, due to high bsfc and for fd. also use evil's link to get proper pressure ratio, to use other maps. use 3" bore, 3.9 stroke, an 4 cyl's.

I have a more detailed excel spreadsheet for determining map points for different brand turbos, at dif ambient temp and press. will send if interested.

 

Wow thanks for all that info! I'll be quite occupied with those two links for awhile... Thanks!

 

as to airflow... it is commonly assumed that the rotary requires 1.92 cfm to make 1 rear wheel hp. i have used this figure and it appears to be correct. therefore if you are talking 480 rwhp you need 922 cfm or 63.7 lb/min.
howard coleman

 

The descriptions with the BSFC values on the drop down list on my fuel calcs page aren't very descriptive. I didn't really understand what affected the BSFC at the time that I made the page or I would have done a better job on that part. The caculations aren't affected by my lousy descriptions, however, so you will get good numbers if you input a sane BSFC estimate. But the page just doesn't help you much in choosing a sane value.

I did do research in choosing which values to list, so I think they are a representative range of sane values for these cars (turbo rotaries). The research was based on looking at the stock car (HP versus fuel system components and reported max duty cycles) and a bunch of other modified cars. The page just doesn't help you choose a spot within the range very effectively.

If you run really rich, that will tend to put you at the higher end of the scale. Other things like the efficiency of your intake and exhaust systems (and the turbo that ties them together) and porting seem like they may also affect the BSFC. The richness of the stock fuel system (with the stock intake/exhaust) results in a high BSFC. A car with porting that works effectively at the power peak, and some free-flowing intake, exhaust, and turbo parts combined with a well controlled mixture (that isn't too rich) will probably land you near the lower end of the scale (0.60). I imagine all kinds of other things like operating temperature, etc. may also affect BSFC in reality.

The calculations page was designed primarily to help select fuel system components. It may be worth trying a few different BSFC values to make sure your intended injectors, etc. are up to the task even if you can't accurately predict the BSFC beforehand. Tuning with a wideband (or however you want to get the mixture right) should always be performed on a high-HP car after you upgrade. Perhaps you could note the injector duty cycle at the power peak and HP and feed that back into the form to estimate your car's BSFC. I'd love to hear about it if someone has a good estimate for their BSFC using this method or another.

-Max

 

this may be of no help at all but looking at a dyno sheet from one of my normally apirated bridge-ported daryl drummond motors i have the following BSFCs

uncorrected (for std temp and pressure):

6500 .707
7000 .631
7500 .625
8000 .598
8500 .583
9000 .583 peak hp
9500 .591
10,000 .590

corrected:

6500 .643
7000 .575
7500 .569
8000 .541
8500 .528
9000 .526
9500 .532
10000 .530

obviously additional BFSC would need to be added to cool things a bit. my motor made peak hp at 1750 degrees 6 inches from the exhaust port and turbo'd motors would probably melt at that egt. i will bet there is some kind of multiplier for a turbo'd motor though.
howard coleman

 

what would a half bport fall under?