BSFC Numbers for Rotary

[NoDOHC]

If I can afford the dyno time, I would love to document a full BSFC curve. This issue with this is that drivetrain loss is a little funny at lower throttles (manifold pressures), as some of it drops with load (bearing and gear resistance) and some is fixed (windage and oil displacement). Still, this curve would be more useful than an actual engine BSFC curve to develop optimal mileage gearing....


More data would be awesome here, as I would not consider the number from a single engine a representative sample.

The data is easy to get, simply datalog injector on-time and engine speed during a dyno run and compare the graphs. You should have fuel pressure and manifold pressure to be really accurate.

With enough data, we could develop compression ratio comparisons (which should show lower BSFC with higher compression). Porting comparisons, aspiration comparisions, AFR comparisons (mostly done already by Kenichi Yamamoto) and ignition timing comparisons.

I wish I owned a dyno sometimes, I would get a lot more data if it didn't cost me $60 per hour to collect it.

[RICE RACING]

I have all these numbers for the 13B-REW & Cosmo in std form, street ported and various version of race porting, across all types of fuel mixture and ign timing values, (compression ratio's from 7.8:1 to 9.0:1) apex seals from 2mm to 3mm single piece and multi piece........... but it took me 15 years of work/learning to accumulate the data and not about to share it on the internet... sorry

One thing I will say! you must have the ability to measure the air mass flow rate, cause you will be surprised as to the ACTUAL volumetric efficiency of even a standard ported engine when free from OEM constraints (bolt on's)...... Wanted to add, be very careful making ASSumptions on fuel flow! (you actually need to test this). Also be even more careful relying on compressor maps (if you are doing turbo work!) you will see why when you start measuring turbine speed and trying to reconcile PR ratio's and calculated airflow rates! the more you get into this the more you see how many big fundamental mistakes you can make if using other peoples data/tables/figures.

I have never ever come across anyone (in performance game) who has accurate BSFC data that is believable (including some Racing Beat published articles on 12A Fuel injection V's Dellorto V's Holley set ups) and can be cross checked to other measures to be varified from modern rotary engines. There is plenty of very old texts that cover up to 1982/90 developments and some of those figures for BSFC on old 3mm two piece apex seals at heavy fuel mixtures in turbocharged application are flat out scary but again TOTALLY USELESS if you want to draw conclusions for your own stuff based on say a 13B-REW standard engine with associated bolt on's let alone tuning set up you have calibrated the engine too.

In short if you are doing it part time it will take you years to collect the data, you will need lots of equipment, and money and the qualifications in mechanical engineering (along with the interest to follow it through).

[RICE RACING]

Originally Posted by NoDOHC

If I can afford the dyno time, I would love to document a full BSFC curve. This issue with this is that drivetrain loss is a little funny at lower throttles (manifold pressures), as some of it drops with load (bearing and gear resistance) and some is fixed (windage and oil displacement). Still, this curve would be more useful than an actual engine BSFC curve to develop optimal mileage gearing....


More data would be awesome here, as I would not consider the number from a single engine a representative sample.

The data is easy to get, simply datalog injector on-time and engine speed during a dyno run and compare the graphs. You should have fuel pressure and manifold pressure to be really accurate.

With enough data, we could develop compression ratio comparisons (which should show lower BSFC with higher compression). Porting comparisons, aspiration comparisions, AFR comparisons (mostly done already by Kenichi Yamamoto) and ignition timing comparisons.

I wish I owned a dyno sometimes, I would get a lot more data if it didn't cost me $60 per hour to collect it.

What you really need is an engine dyno and a super accurate fast acting lab (not Leb!) spec scales) I did BSFC testing on our FSAE car engine and simple effective way to measure fuel flow was to have the whole fuel system sitting on the scales! this negated the need to have $20,000 worth of calibrated fuel flow sensors in both supply and return line to determine the exact fuel flow into the engine. these sensors are still only as good as the data they are calibrated too and only work on certain fuel types!

With 3 reference meters we could see air fuel ratio and thus determine air flow rate in the said engine, from this data we could then along with power on the brake (on equilibrium!) establish that correct output less intertial variances! (very important). The output fuel usage (by mass) was feed into a data logger and all the collections automated.

Seen all kinds of set ups, there are many ways to do it, but as anything in life lots of ways to do it incorrectly! Dealing in an Aeronautical and Mechanical Engineering lab even 4th year Thesis students tended to make some very fundamental mistakes and ASSumptions that they think would cut it in doing up a proper report.