Holden 304 manifold vacuum inches of water

[Wade]

Anyone know what inches of water the 5 litres generally run at? Hooked the magnehelic up and was pegged at 50 which is as high as my gauge goes.

[Wade]

Never mind, brain fart moment. Converted kpa over to inches of water

[Deuce]

Never mind, brain fart moment. Converted kpa over to inches of water

Very good.
I was going to question weather inches of water changes based on the internal diameter of the tube filled with water to measure the inches.
Therefore someone else's measurements would be irrelevant to you unless they were using the same machine to run tests.
You can buy/make a calibration plate to help standardize your measurements.

[brindo]

Inches of water or inches of mercury?
Anything over 17” Hg at idle is good but completely dependant on the camshaft.

[vlad01]

Whats that in Kpa absolute?

I'd say anything from 20-40Kpa is pretty typical for a healthy OEM engine of this era but depends on exact cam and other config. I can't recall what the V8 ones are, but the V6 is normally around 20-30 Kpa iirc, the v8 one shouldn't be too different.


If it's high like 40+ then a tune issue, other problems or the cam is bigger than stock, but I recall you said it was stock?

[Wade]

I tried using this but no good

[Wade]

Then ended up using this. Leaned idle afr’s out and then adjusted timing and ended up getting 20 in-hg

[vlad01]

I see that one has the Kpa in negative instead of absolute, so you'd have to invert the scale if comparing to TP if you decide to use Kpa.

20" in Hg looks to be about 30Kpa absolute, so looks all good to me.