optimal revolutions watcher .. a sort of

[seifrob]

Browsing on the internet stumbled across this:

Otáčkoměr. Well, I know it's in Czech and very few would understand (if any), so here is uncle Google's help: english version (google translate), and french version (human translated)

It's an electronic device showing optimal/suboptimal/too high revolutions using series of two rotating lights. I like the idea it is visible even with one's peripheral vision.

The page itself is quite old, the contraption also - probably more than ten years. Anyway, I find it interesting idea.

What do you think?

[RobertISaar]

interesting idea, but RPM alone won't guide you to better fuel efficiency.

my torque peaks at 4000 RPM, which is where BSFC(fuel used per unit of power produced) is at it's best.

i could either stay in 2nd gear to run 60MPH and be at 4000RPM or be in 4th at slightly less than 1800RPM, it should be quite obvious which one will result in better fuel economy/less wear/etc.

[gone-ot]

...what we REALLY could use is a real-time BSFC gauge, meter, lamp, or ...

[RobertISaar]

calculated on-the-fly or calculated/estimated beforehand?

[gone-ot]

...real-time...

[RobertISaar]

well, to do that, you would need to be able to measure torque while driving..... not sure how to do that with a FWD vehicle. there are U-joints out there for RWD vehicles to have what is essentially a full-time dyno while driving. not sure of their accuracy though.

[gone-ot]

Originally Posted by RobertISaar

well, to do that, you would need to be able to measure torque while driving..... not sure how to do that with a FWD vehicle. there are U-joints out there for RWD vehicles to have what is essentially a full-time dyno while driving. not sure of their accuracy though.

...just adapt the same technology as currently in use with the "in-wheel" Tire Pressure Monitoring System (TPMS) units.

[ever_green]

Originally Posted by RobertISaar

my torque peaks at 4000 RPM, which is where BSFC(fuel used per unit of power produced) is at it's best.

Optimal BSFC is not always where the peak torque is produced, contrary to popular belief. also for city driving, driving with load did not change my overall MPG significantly. That is, i used +80% engine load during acceleration and shifted at 2500rpm. what helped me the most was pulse and glide. interestingly enough the BSFC for my car indicates a wide BSFC sweet spot of 1500-4000rpm at 85% load. however in practice shifting at 3500-4000rpm with 80% increased my trip consumption and got me a speeding ticket for me i just take it easy on the throttle and shift at 2k rpm.

this is a BSFC for a honda s2000 which makes peak torque at ~6500rpm yet it gets best BSFC at 3000 rpm...get what i mean?

[gone-ot]

...it's an exercise in finding & maintaining a minimum BSFC value.

...it's NOT a new concept, it's been around on aircraft engines since the 1930's!

...lookup BMEP gauge for aircraft engines.

...and, it's exactly the same priniciple and result with automotive engines.

[ever_green]

oh i forgot to say, there is a quick way to measure your BSFC. what i did was i recorded a WOT run with my scangauge displaying the GPH gauge. I took the maximum number it reported, which i think it was 12gal and multiplied it roughly by 6 to get the pounds of fuel burnt per hour. then i divided that number by the horsepower (170) and i got 0.42. Subaru claims a 0.418 lb/ps/hr for my car i think.

fairly accurate