Vacuum gauge and BSFC chart - few questions

[RRC]

Hi Ecomodders!

I have installed vacuum gauge in my car Skoda Felicia since there is only old ODB version and I'm unable to use SG.
VG works like a charm so far but I have a few questions about optimal range of vacuum during acceleration.
I have found BSFC chart for my car. It's chart for 1.3L MPI engine (50kW):


So from this chart it looks like the less fuel I burn if I'll accelerate with 100% throtle between 2300-2700 rpm, so for my car on selected gears it will be:

Gear --- Speed for 2300 rpm --- Speed for 2700 rpm
1 ------- 10 mph (17 kph) -------- 12 mph (20 kph)
2 ------- 19 mph (30 kph) -------- 22 mph (35 kph)
3 ------- 28 mph (45 kph) -------- 33 mph (53 kph)
4 ------- 38 mph (62 kph) -------- 45 mph (72 kph)
5 ------- 50 mph (80 kph) -------- 58 mph (93 kph)

And here are a questions
- how should I accelerate to use less fuel? Start from 10 to 5 In/Hg and then when I get during acceleration 2300 rpm press throtle little more?
- what numbers should shows me my vacuum gauge when I will be between 2300-2700 rpm, should it be 10 to 5 In/Hg or maybe 5 to 0 In/Hg?

I've also noticed that this engine burn less fuel (I'm not 100% sure but the vacuum gauge shows then 19-18 In/Hg) when I'm doing 30mph on 3rd gear (about 2600 rpm) than on the 4rd gear (about 1900 rpm) (then vacumm gauge shows about 16-15 In/Hg) on the flat road and with steady foot.


Thanks,
Peter.

[krrcan]

I drive the same car, and I would also like to know more.

[kafer65]

If you use 100% of your throttle to get full load to the engine your intake vacuum should approach zero. Conversely, if the throttle is not being used to put a load on the engine you should see close to the maximum vacuum you normally read like when you are at an idle coasting down a hill. Many throttle plates are not linear. A small movement from zero may be a larger movement of the throttle plate at the beginning than at 2/3 to full throttle.

[cbaber]

The first thing is that higher vacuum doesn't always mean you are burning less fuel. It's a way to measure engine load. For example when you said you can drive at 18-19 inHg in 3rd gear or 15-15 inHg in 4th gear, the lower RPM gear (4th) will be getting better fuel economy at the same speed, even though the engine load is higher. 5th gear would be even better if the engine has the power to lug it along at those low speeds. You could see this if you had a MPGuino or SG with instant MPG readout.

You generally never want to accelerate at full throttle. Most cars will go into open loop mode, enriching the fuel mixture to protect the engine. I would say you should accelerate from 2000 RPM to 2700 RPM at about 5-10 inHg. Roughly 80-90% engine load.

[kennybobby]

Looks like a good find on the chart and a good strategy. i would accelerate with vacuum in the 3 to 6 range up to 2700 to 3000 rpm before shifting such that the revs don't drop too far below the first torque peak (at 2300) after the shift, until getting up to cruising speed, then shift into 5th gear and pulse and glide and stay off the brakes...

This approach minimizes the time of the acceleration phase yet operates in the most fuel efficient range while accelerating. 5th gear cruise runs at lowest rpm for the speed and uses less fuel regardless of the reading on the vacuum gage. Other folks like to accelerate slower or shift sooner, so you could experiment with different launch schemes and measure the fuel usage. i've had 20% improvement using this technique, ymmv.

[krrcan]

I would need some strategy that doesn't utlize the vacuum meter. Since I don't have such fitted.

[gone-ot]

Originally Posted by krrcan

I would need some strategy that doesn't utlize the vacuum meter. Since I don't have such fitted.

RULE-of-THUMB: shift at ~70% of TORQUE peak RPM, using no more than 3/4 full throttle, to get there.

...prior posting: http://ecomodder.com/forum/showthrea...tml#post374549

[bestclimb]

you can feel under load where adding throttle does not add acceleration. Find that point then reduce throttle a little bit more. As RPM goes up you can add a little more throttle to keep the engine just under the point where adding throttle does not add power.