Shiftpoints
 

I put a vacuum gauge on my car a while back. I have noticed that vacuum stays around 19 very high into the gear. I don't have a tach but my rpm's seem very high. I am just curious if there should be a drop in vacuum at high rpm. At what point should I shift to the next gear? When I can go to the next gear with a high vacuum?

I am driving a 1963 Chevrolet Bel-Air with a 3spd transmission and a 6-cylinder engine for reference. I usually shift to second at 15 or so and third at 30-35.

Thanks for any advice you can offer.

Fourthbean

Vacuum depends on the amount of throttle opening at a given rpm. If the throttle position stays constant and rpms go up, vacuum goes up too. At lower rpms it takes less throttle to change the vacuum to a lower value. I usually only pay the most attention to my vacuum gauge under cruising conditions. More vacuum is better while cruising, less vacuum means you have it throttled more so you are using more fuel. As far as shift points, I usually shift as early as possible for the driving conditions I'm in. More throttle and lower rpms while accelerating seems to work for my FE. It may be different for different engines. Hope this helps a little :) .

jwxr7 -

I agree with this.

Fourthbean, maybe you could find the "lug zone" for each gear (when the car starts to buck). Once you know that, you can "know your bottom" and adjust your driving accordingly. The closer you shift to the "lug zone", the slower you'll have to accelerate, so you will always have to be making context driving choices.

Does that make sense?

CarloSW2

Alright, this next tank I will shift a whole lot earlier then. When you say buck, is that the car bucking or the engine bucking? Because my car doesn't buck in third gear till I get down to maybe 15-20mph. Third gear is my top gear btw. And second gear is fine down to 15 or so.

Fourthbean -

When I say buck is when I feel the car "buck". I can drive in 5th down to maybe below 25 MPH, but at that speed it is almost impossible for my car to accelerate on command without shuddering. When I reach above 30 MPH, then I can accelerate moderately on the flat. Soooooooo, below 30 in 5th gear is when I am approching the lug zone.

PS - I think that the "lug zone" can also be define as being when the car's RPMs in gear start to go below the car's normal idle RPM. In this case the engine is being forced below the lowest RPM it is willing to go and starts to lug.

CarloSW2

That makes sense. Thanks for the tips. I am currently at 380 miles on this tank and my needle just passed the halfway mark today. With the accuracy of my gas meter as it is I should still be able to go another 50 or more miles. Which should equate to around 24 miles per gallon :). I am headed for 30, not sure if I will make it or not. But if I do I can say my car gets the same gas mileage as my brothers civic, should have some people scratching their heads on that one!