Nistune Forums

just an idea is it possible to gauge HP bassed on airflow... of course there is alot needed to take into consideration but as an idea... a lot of people say that the standard sr20 AFM is only good for 250rwhp or 200 RWKW

or is that based on fact or just an assumption... cause if it is fact maybe we can calculate power with it..

i dont know think you can draw HP conclusions solely from airflow, but it could be somewhat of an indication

The max figures for most common AFMs (eg CA18, SR20, Z32 etc) are more accurate than others in the list which havent been flow tested (so a best fit approach against known flow rates was used)

We know for example with an RB30 AFM we know this maxes out about 200rwkw and Z32 AFM maxes out just over 300rwkw based from peoples logs of AFM voltage and dyno results

However given this you have to remember that the air flow is not linear, and you are getting close to the top last few points on the VQ map when you are close to maxing it out

for the Z32 I once programmed something that was able to calculate semi accurate BHP/dyno printouts, using constants like VQMAP & kval (injectorsize) and logfiles of the RPM, AFM voltage and injector dutycycle.

But using these variables makes it very car/engine specific.

Also to make it more accurate you need to know the VE of the engine, but for the Z32 it worked pretty well and gave a rough idea of how much power a car made.

There's also a formula that is able to calculate pretty accurate results using aerodynamic drag variables and acceleration (using rpm and gear/diff coefficients), but I was never able to find the exact formula.

-Eric

AFAIK, I would be more interested in fuel consumption (instant, average), average speed during a trip... It has been done in ECUTalk.

A HP gauge based on airflow and/or fuel consumption would not be accurate, because it would mean that whatever your tuning is, you get the same energy with the same volume of fuel and/or air. When you tune your ECU, you try to get more HP with the same boost. Or you try to get more HP with more boost w/o detonation by adding fuel to lower internal temperatures. Or you use race fuel or water injection...

All these mods will have an effet on the airflow vs HP ratio.

You would better estimate HP by measuring an acceleration, if you know the SCx and weight of your car. I have a french software, Powerdyn, which does that very well. My SBC i-color has an embedded dyno, but it's really unaccurate.

does anyone know the calcualtions for trip computing. I have to do some research on this

It would have to be based from current speed and injection pulsewidth for specfiied CC injectors (flow rate * current injection opening time) to work out the instant consumption

Then based from distance (derived from speed over elapsed time) should be able to work out how many litres used

Matt, you could ask to Peter Collins at ECUTalk. I hope there's nothing secret in his formula. You Australians are great guys (Nistune, PLMS, TechEdge, ECUTalk...), you should work together

Yes, I presume that :
Current Fuel Consumption = Total Injectors Flow Rate * Current Injection Opening Time

The sampling rate of this measure should be as high as possible, then you do an integral of the samples every, say, 1 second. You have Fuel Consumption (liters) for 1 second

Do the same with speed and you have samples for the Distance (km) every seconds.

Gas Mileage (liters/100km) = Fuel Consumption (liters) / Distance (km) * 100

Refresh the gauge every seconds and do another integral for trip values : total Distance and total Fuel Consumption since the beginning of the trip, so you can display average Gas Mileage.

Hey Matt you could reverse engineer the R31 Silhouette trip computer!

yeah i know! i've fitted one of those to my current car. it takes an injection pulsewidth output from the RB30 ECU and works out the immediate injection and then the injection per km/h from speedo

however it also uses current fuel tank usage and uses that for fuel left on the computer also

i'll have to try out the calcs and see if they work