How to adjust for minimum Brake Specific Fuel Consumption?

[neil]

How do you adjust the spark and fuel to obtain minimum BSFC without an attending loss in power? Combustion efficiency is maximized when BSFC is minimum.
BSFC and maximum torque should occur at or near the same RPM.
Is this the same or similar process to the Auto VE process?
Is there a graph for the LS1 engine showing BMEP - Brake Mean Effective Pressure against engine speed?

Regards,

Neil.

[vzsv8]

Presumably you are chasing better fuel consumption. BMEP has a little to do with it, unfortunatly, you have chosen a car that really never needs to operate a large throttle openings. At low throttle openings the BMEP curve takes on a flat shape, so you may as well go for low revs and an egg on the accelerator. This means that it will never get near its best BMEP, this is more relevent for Toyotas etc. Or a NASCAR, which I believe are more efficient than a Toyota Pius.

Your best BMEP is going to be around 4500rpm at WOT, expensive both in fuel and fines.

I am experimenting with lean cruise at the moment and so far what I have found is that best economy is at around 80kph, 16.5AFR and 40degrees of spark advance. I can get better than 7l/100km, but it is so mind numbing that i dont. Best real world is a end to end run up the F3 at 110kph and 9l/100km average on the trip computer (which is a little pessimestic).

Interestingly I could consistently get better fuel consumption than my old VX cruise control, but I cannot beat the VZ unit, I think its brain is bigger than mine. (NOTE personal PCM is < 1Mb )
Cheers, Steve

[neil]

Thanks Steve.
That's what I was hoping to do. I have a power switch on my WH Statesman and was intending utilizing it for a Power/Economy selector using the BSFC point as the switching point for the gearbox.
I thought that changing gears at a lower RPM point would place the engine under more load, therefore helping to minimize the BSFC.
Any thoughts on this subject would be greatly appreciated.

Regards,

Neil.

[vzsv8]

I have a generic set of curves for a petrol engine. The diagram comes from a text I 'liberated' from the internet, it runs to over 1100 pages but it does have a lot of theory. The basic problem is that the big dip in the BSFC curve that mirrors the torque curve is less pronounced at lass than WOT.
If you are interested in a looong read PM me, the book is 19.4Mb in size and was published in 2001 (13th edition), so a lot of it getting a little old.
Cheers, Steve

[joecar]

May I please have a link to that document...?

[vxchev8]

Neil try COS 5 to control AFR's at idle and normal driving area's. Fuel economy on a heavy car is hard to have.

[neil]

Thanks vxchev8. I am using Cos 3 at the moment and will try your suggestion.
I have been thinking about trying COS 5 for a while.
I think getting the A/F ratio and timing right and then setting up the transmission to change at the correct time is probably going to get the best results.

Regards Neil.