MyE28.com

Does anyone have any performance curves for the M30B34 8:1 engine other than just the stock power/torque curves? I'm doing some calcs for a blower install and I need the actual air flow OR volumetric efficiency curve. Either will do as one can be easily calculated from the other.

Any other thermodynamic data for this engine would be useful too. Hoping someone can help.

Cheers!

Can't you calculate air flow by using the basic numbers that we all know about the 3.4? 92mm bore, 86mm stroke, 6 cylinders, 46mm diameter intake valves, 38mm diameter exhaust valves, etc? Or is it still more complicated than that? I'm actually curious to see!

Yep I can and have. In fact it's easier than that cause all you need to know is the displacement. Since the engine pumps the design displacement once every 2 revolutions you get theoretical airflow = RPM x displacement / 2 (in litres/minute if you put the displacement in litres).

However you need to take into account the fact that the engine isn't 100% volumetric efficient. This is because intake drag causes a pressure drop and the intake charge therefore has a density ratio less than 1. Also there is leakage past the piston rings and this causes a further reduction in actual pumped volume. So the actual pumped volume is less than theoretical. Volumetric efficiency = actual pumped volume / theoretical pumped volume.

For doing rough calcs you can assume a volumetric efficiency figure. I've read that 80% is a good value for 2-valve engines and ~88% can be used for 4-valve engines. But each engine differs and the figure is also rpm dependent.

It's important for me to know 'cause then I can select a compressor and drive ratio that will give the power output that I'm after but without over boosting.

While I'm at it does anyone have the power and torque curves for this engine? My manual only gives the curves for the high comp engine and all the charts I've seen online are for the high comp engine. I've generated a new power and torque curve by taking the curves for the high comp engine and multiplying them by the ratios on the maximum powers (218/186 = 0.85). This will be near enough at the top end but the low and mid range will differ and this is the area that I'm most interested in.

Of course a curve for engine airflow (cfm or litres/min V. rpm) will tell me the same thing and the volumetric efficiency curve. Hoping someone has this info out there!

Edit: of course I should add that the stock air flow / volumetric efficiency won't actually be 100% accurate for my engine because of significant changes made to the intake layout (removing AFM, longer air piping runs, installing an intercooler, using a different air filter etc). When I think about it though... the longer air pipe runs would be offset largely by making them larger bore... the installation of the intercooler would be offset to a degree by the removal of the AFM... and the air filter should increase flow a bit. So overall the stock air flow or V.E. curve should be close enough to the modified engine when running normally aspirtated, so they will still be useful.

how is the air flow curve measured? I'm assuming this can be somewhat easily done with an engine out if you have the equipment to do it, but do most say engine rebuilders have that capacity or is it a more specialize thing that only say high performance race shops would have? Just curious because it would be something interesting to have done when I reubuild my M30 B35 in the next year or two.

Actually,
You can so it by measureing the AFM and temp sensor and calculate the air mass. With my 179 ECU and live data aquisition you can get the AFM in mg/ms(milligrams/millisecond) and temp readings from the IAT sensor and calculate the air mass ingested say during a dyno run. You can do this with any ECU that gives live data(OBD-I/II). Thats harder with the 059 as theres no live data, so you need some other form of data aquisition.

RussC

There are a number of ways to measure it as you have both pointed out. I'm sure that most good dyno shops would be able to use add-on instrumentation to measure the air flow directly.

Russ I hadn't actually thought of your idea and that'd probably be the easiest to do. These days you can get basic multi channel stand alone data loggers for under $100 and something like this would do the job. Just log the AFM and air temp voltages while you do a WOT run from idle to the red line. You'd also have to get an RPM signal on the log.

To make use of this you'd then need the transfer function of the AFM to calculate air flow from the voltage signal. And also the characteristics of the air temp sensor - I don't even know what this is - RTD / thermocouple / NTC thermistor???