I was playing around in excel and decided to make a rotary-specific horsepower estimator tool.

It is based off of 2 sites:
http://www.gnttype.org/techarea/turbo/turboflow.html
http://www.turbobygarrett.com/turbob...o_tech103.html

About ports:
I've added porting. 5% increase in capacity for medium streetports, and 10% for large streetports. These values, however arbitrary, seem to correspond very well with dyno results.
Notice 400 rwhp can be had with stock ports at 16 psi. You would need to flow 47 lbs/min at 7500 rpm. Look around for compressor maps that have a high efficiency (75% and above) at 2.37 P2/P1 and 47 lbs/min.
A medium streetport gives 400 rwhp at 14.7 psi and 7000 rpm. Look for compressors efficient at 2.2 P2/P1 and 47 lbs/min.
A large streetport gives 400 rwhp at 14.7 psi at 6500 rpm. Same ideal compressor rules apply as for medium ports.

About boost pressures:
14.7 psi is default wastegate spring pressure.
16 psi (~1.1 bar) is the limit on pump gas. Exceed at your own risk.
19 psi (~1.2 bar) is just to show what gains can be expected by a 0.1 bar increase.

Finally, the dyno charts. Compare predicted 19 psi results with Jason's (RX7store) 19 psi large streetport dyno.

 

What do I open the XLS file with?

 

Doesn't Microsoft Excel work?

 

i think that the accuracy of the chart is pretty good but not to 99%. I think there might be more factors that play into the actual numbers like heat exchange efficiency, which can increase or decrease those numbers dramatically. and this is with a 11.0 AFR across the board which may be different per engine as not every identical setup will preform identically. But i think you got the idea of it. Pretty good chart i might add. Definitely shows a large portion of the bigger picture when figuring out accurate HP numbers.

 

Yes, it's an interesting chart and it does do a good job of showing the effects of porting. Of course real dyno charts would drop off after a certain RPM depending on porting, exhaust, A/R etc.. instead of continuing to clime. Maybe is there a way to stop the climb in power at certain rpms depending on an estimation of port characteristics and their rpm power shift?

 

I believe the climb will stop once you get out of the efficiency range of the turbo. This is just dependent on the selected turbo.

For example, a 62-series turbo would flow maybe 60 lbs/min. It will peak at whatever rpm 60 lbs/min occurs and stabilize or drop beyond that, as efficiency of the turbo decreases. It's best left to the end-user to look at compressor maps to figure when the decline begins.

Theoretically though, if your turbo could flow as efficiently at the low end as at the high end, your curve should look like the one I made.

 

The turbo doesn't know the rpm of the engine. it just receives exhaust gases and spins. The engine has a sweet spot where it is most efficient at consuming air, this point is most dependent on the engine porting, the exhaust size and restrictions, turbine housing size, the intake/exhaust manifolds, the throttle body. etc etc. After this point of peak volumetric efficiency the engine doesn't breath as easily and doesn't make as much power even if the turbo can still efficiently move more air.

 

what about for a peripheral port?

 

And Bridgeporting

 

I think the VE's change too dramatically with bridgeporting and especially peripheral porting for the usual equations to work.

But hey, you can just add say 15% increase in chamber volume for bridgeporting and maybe 20% for peripheral port, and adjust the VE's to scale higher. I think above 6000 rpm bridgeporting and peripheral porting have >100% VE.

 

Need more data to know where this "sweet spot" is. I've set it to 6500 rpm or so in my excel sheets. I think it would be pushed up more depending porting. Perhaps around 7500 for a large streetport, 8000 for a HBP, 8500 for BP, 9000 for PP?

 

You can tell where the sweet spot is by looking at the base map fuel curve of individual maps. It will be where the most fuel is needed to keep the AFR's consistent. (provided the map is tuned correctly) This sweet spot is where peak torque is produced, but HP will still go up after the sweet spot because RPM's are a multiplier. HP = RPM x TORQUE ÷ 5252. Some engines make more torque then HP because the peak torque is made well below 5252 RPMs. The higher up in the RPMS peak torque is made, the more HP you will have.

I think your guesses on ports and where they would peak in terms of HP are about right. I couldn't say for all of them individually but stock and large street port are close to those. Each setup will vary depending on the rest of the system too. For instance a smaller A/R housing (.82) would start falling off more in the upper RPMS compared to a larger A/R housing such as a 1.32 especially at higher boost pressures. And lots of other factors would also effect this.

http://www.catenet.net/dyno.php is a site with a LOT of mostly all RX7 dyno sheets that you can compare to one another. Unfortunately there isn't many that actually claim to be half bridges or full brides, and I saw only one P port on a NA. Most of them are either not stated, stock or street port, without stating how large.

In the end it would be very difficult to account for every difference between setups, but you have made a good tool that illustrate the differences that porting generally will have on power output.

 

Well.. that was the idea. To capture some of the most important factors to consider when trying to attain a specific hp goal. To show that it's really just airflow, BSFC, and efficiency at the end of the day.

Everything else is just to support that required engine airflow. People don't realise what they're supposed to be doing when selecting a turbo, which really bothers me. Or fuelling setup either.

 

Lol. Yeah it only bothers me when ignorance is forced on me, or false information is brought up as a fact from a person that don't know the first thing about it. Other then that, people that don't know and at least admit to it is fine with me. They can continue to not know, i won't lose any sleep and won't respect them any less.

 

Lifelong learning anyone? Gahahaha.