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Old 12-28-2011, 08:44 PM   #1 (permalink)
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Vacume guage

Hi all, names spencer, new to this forum and new to all forums... I have a 93 tercel... I call it my green turd. I just put in a vacume gauge and was wondering why it says good economy when the rpms are high and poor when the rpms are low?

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Old 12-29-2011, 03:37 AM   #2 (permalink)
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An engine is typically most efficient running around 80% load at the RPM it produces peak torque at (most power per amount of fuel). Unfortunately, most cars have very over-sized engines and can't run at the optimal rpm at that load because they accelerate quickly out of it.

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Old 12-29-2011, 09:05 AM   #3 (permalink)
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The people who make those things simply don't know what they are doing.
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Old 12-29-2011, 09:39 AM   #4 (permalink)
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Vacuum also depends on the load on the engine; not just the RPM.
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Old 12-30-2011, 08:51 PM   #5 (permalink)
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My dad used to put vacuum gauges in his cars - 1970s Toyota - and they properly indicated efficient and inefficient driving (regarding consumption, not HP for the gallon).

Mind you, they liked engine braking (going all in the dark green) even though that's somewhat inefficient
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Old 12-31-2011, 06:01 PM   #6 (permalink)
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Thanks for the advice... So my goal it to not bury the needle? But when is a good time to shift? To soon and there is too much load...not soon enough and there is too much rpm...? Also I have open up my exhaust... No cat and no muffler...is that too much? I can't tell because I've been doing to many mods to quick to tell what is better. Im only on my third tank since I've found out about hypermilling. In three weeks I've done a list of mods
1. Driving behavior
2. Kill switch
3. Full grill block
4. Side mirrors delete
5. Hot air intake
6. Pizza pan wheel covers
7. Weight reduction (still plenty to go) strip it all
8. No ac or power steering
9. Light seals
10. Vacume gauge
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Old 01-01-2012, 10:12 AM   #7 (permalink)
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Quote:
Originally Posted by SpencersGreenTurd View Post
Thanks for the advice... So my goal it to not bury the needle? But when is a good time to shift? To soon and there is too much load...not soon enough and there is too much rpm...?
The vac gauge always indicated rather poor results when accelerating.
Even on slow accelerations it'd quickly slip over to the bad side.
I tried to keep the needle out of the red end during acceleration - it went from dark green, light green, yellow, orange, red - and I definitely tried to keep it from hitting the bottom peg.

Try to find the point on the gas pedal where pressing it down further doesn't give extra acceleration, then back off and try to stay away a bit from that point.

Acceleration is always a loss, so try to avoid it as much as possible - unless you're going for Pulse & Glide.
The gain of not slowing down, is in not having to accelerate again.
When you have to, accelerate at lower rpm with a good bit of throttle and get it over with quickly - but not flat out or pedal to the metal.

Low(ish) rpm and rather high load puts the engine in it's most efficient operating area - best Brake (HP) Specific Fuel Consumption or BSFC - where it produces most HP for the fuel it gets.
That's most efficient at converting fuel to power - but it's not giving the best mileage !

At cruising speed, your engine is far from operating at its most efficient. Fortunately, it also needs to produce so little power to maintain speed that fuel consumption over distance becomes good.

Quote:
Also I have open up my exhaust... No cat and no muffler...is that too much?
Probably too loud too

That's a performance mod.
To be effective it needs to be matched on the air intake and fuel supply end as well ... effective at delivering power and power/gallon but not fuel economy.
Most of the time you don't need much power anyway.

Quote:
I can't tell because I've been doing to many mods to quick to tell what is better.
You should see your average improve considerably in short time though.
Finetuning parts of the driving can come later.
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Old 01-01-2012, 05:26 PM   #8 (permalink)
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Thanks...that great stuff. I look forward to the challenges of this new hobby!

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