373 gear ratio

[KEH]

Where should the vacuum gauge be attached; at the carb or the intake manifold?

[RON WOODGEARD]

Originally Posted by 67ChevyRedneck

That's the second or third time someone has mentioned figuring mileage with a vacuum gage. I know what its for and I believe, can't remember exactly, but I think a 350 should pull between 12-16" at idle speeds. SO, what are good and bad readings going down the road??? If this really helps I might add a vacuum gage to my cluster....

Take it at the Intake,,Manifold Port that goes to the Power Brakes. When your engine is operating at it's peak mileage it will also be at the peak Vacuum Reading.

I used to have a 64 El-camino with a 283-/308 gears/ Powerglide tranny.. I took a trip from Washington to California, I forgot the mileage that I was getting, But it wasn't too bad.. ( or so I thought) Going through southern Oregon Northern California, I got in behind a 18 wheeler that was running Fast. I pulled in behind and stayed there getting close to 100 MPH. for a long way ( No Andy, I didn't have a camera :p ) My mileage Jumped up a BUNCH ??? I had put in a Console from a 63/64 Pontiac Grand Prix.. It had the Factory Vacuum Gauge.
I took notice that the vacuum gauge was reading more vacuum ?? Then When I got back to Earthly speeds in Sacramento, Again watching the Vacuum gauge I noticed that the vacuum increased when I put the Tranny into low gear while driving in Town traffic at respective speed.

Moral of this story ? You need to find the operating Efficient RPM of your engine at what speed you intend to run it the most. One way is to install a Vacuum gauge, and going down the road a slower then normal Speed, change gears in the tranny and see where you get the highest reading and at what RPM. This is where you want it running, for where you do your major driving. Or take it out on the highway and stand on it in high gear watching the Gauge, again, when the vacuum reaches it's highest reading, (slower speed or faster) that's where you want your final rear end gearing set to at the speed your going to 'normally drive.'

There's a couple of ways to do this to set it permanently. But the most feasible is Rear end Gearing, and tire size.

PS: I traded the Camino off before I had a chance to change the gearing...

[RON WOODGEARD]

One more thing

For you guys running High gears ( 307s and the such) try dropping the tranny into a lower gear in town and see what your mileage does.

It'll be working your engine at a better efficiency instead of Lugging it..


Yea, I Know !! It doesn't set right in the head, but Do it.

[FirstGen]

just get a freakin six speed guys! come on get with the program

[68CST327]

If only there was a way to get those new fancy 5-speed auto transmissions in our trucks...

[FirstGen]

where there is a will, there is a way...

[Gary]

Ok currently I have a 700r4 and 3.08, that pick you showed Longhorn_Man of you doing 60? at that rpm I'd be going 75 or maybe a hair faster.

Now - my rearend isn't posi or limited slip, just one tire pulling and with that much oomph I want to have both tires be "useful" so I'm thinking to upgrade the rear end with new however, I kinda like the fact that highway driving isn't a high RPM on the motor but maybe what I'm seeing now isn't high ENOUGH. So all you fellas with way more knowledge than me, should I go 3.73 on my rear? maybe 3.42 I see thrown around? or stick with 3.08?

[chickenwing]

With 3:08's I'd probably run around in 3rd. Saving the overdrive till I got up to freeway speeds. I don't have a technical explanation for the word lugging. I understand it is bad though.