Revving high reduces fuel consumption?

[tehsocks]

Hey, i have an 85 camaro (v8 5.0L 305ci) NOT an economical car by any means but its fun to see what it can do.

It can do consistent 30's on the highways and thats good. but thats aside the point.

I recently installed a vacuum gauge (hooked upto manifold vacuum), and my understanding is that when i have most vacuum im using the least amount of gas, correct?

Well I find that when im idling i have 22, and when i put my car into OD and start driving around, when i accelerate my vacuum goes all the way down to 14-16ish. and its horrible. But if i put it in 1st, rev to 3500rpm, and cruise around in 2nd at 3000-4000rpm. I have 22-24 vacuum.

And when i let off the accelerator in 2 or 1 my vacuum goes off the scale high which i also assume is good. But this doesnt make sense to me. I thought OD was the most economical thing you could do. But thats not what im getting from my gauge.

Ive tried doing this for about 100km's on this tank and i seem to be getting my normal gas mileage, so it doesnt seem to be using any more, and doesnt seem to be using any less.

But am i correct, is this how i read teh vacuum gauge, and does this seem odd to any of you? Ive never heard of revving high to get good mileage before.

(redline is 5000rpm)

[diesel_john]

Welcome, best mileage, of course usually is in OD. The vacuum gage just helps you drive smoother once you get there. Current thinking is get into OD quickly but stay out of the power valve and cut the engine and coast whenever you can. You dig?

[JQmile]

If I'm thinking right, think of your engine as a giant air pump, because without fuel, that's what it is. When you're idling, your throttle valve is closed, and there is a restriction. When you are revved up, your throttle valve may be open slightly more to keep a steady 3000rpm, but your engine will be revving higher and creating more of a vacuum, hence your readings will be similar. In theory the higher revving engine should use more fuel, but probably not that much more. Remember that engines run based on air:fuel ratios, and with the throttle mostly closed the engine won't suck in that much air, so its fuel economy won't suffer. But it probably won't be any better either.

[tehsocks]

alright thanks,

im gonna try some more runs this weekend.

My current record is 13/32 (city/hwy)

[PaleMelanesian]

Good article on this subject: Autospeed - Brake Specific Fuel Consumption

[EXPIOWA]

If you want to have the best mileage shift early and use large throttle inputs. Its not the best thing for your engine but you will get the best mileage. Your car's engine will be more efficient if it does not have to work against a closed throttle butterfly while accelerating. It creates vacuum that works against your pistons as they suck air and fuel in. Its called pumping loss.

[bgd73]

common sense says no. But with fuel injection, anything could happen. we intervene every move of fuel air if it means being japanese, woops, I mean backwards. If this post gets deleted, could it say "deleted." That would be great.

A carb uses more as you rev more, that is nature. injection could pop an intake in your face before the guage doesn't decipher jack squat.

[taco]

is the fuel injected?

i was toying with me sg2 and found out that in 5th at 60mph puchin about 2100rpm on flat ground i was gettin 33mpg, then i down shifted to 3rd and it ran up to arun 4500 rpm and with foot control i got 32.5mpg, but minute movements of the foot had great loos of mpg as apposed to the 5th gear.

[Christ]

The primary difference in induction between fuel injection and carburetors is that in a carb, the air passing has a venturi effect that sucks fuel through the jets.

in fuel injection, this doesn't happen, instead, the ECU meters fuel by calculating airflow.

Other than that, there are no huge differences in the physical properties of a carb vs. a throttle body.

You could evidence this by the fact that all carbs have a throttle body in them. It's just a giant throttle body with a bunch more crap added to it.


"injection could pop an intake in your face before the guage doesn't decipher jack squat."

I'm not really sure that anyone on this board can decipher what this means.

"we intervene every move of fuel air if it means being japanese, woops, I mean backwards"

Or this.

[tehsocks]

It is a 4bbl Carb'd engine.