Hey guys. I'm working on tuning my Valiant. It has a warmed up Slant with a newer Holley 390 (8007) and the Offy intake. I want to put a vacuum gauge in the car so I can tune it more effectively and see how the car does under driving conditions.

I've heard very mixed things about where to get the vacuum reading on the Slant. The Holley has a non-ported nipple at the base of the carb that pulls a pretty solid vacuum. I also have a bung on the #6 cylinder arm of the Offy I can tie into. I've heard good and bad things about pulling off either location, but haven't really found anything definitive. Any advice you could offer would be greatly appreciated.

Thanks!

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Chuck and the Flying Valiant

Non-ported vac at the base of the carb, or even better there should be a 1/8 NPT port in the intake on the driver side face, just below the carb base. Get a hose nipple to NPT at the hardware store. #6 runner should be fine too, but maybe will fluctuate more.

Lou

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Home of Slant6-powered fun machines since 1988

I added a vacuum gauge when I re-newest the 83 D150.
Agree it is a helpful tuning tool. My set up draws vacuum from the tree at #6 intake port.
No issues with unexpectedly fluctuations.
I used standard rubber vacuum line, has been around 5 years and 30k miles and working fine.

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Doo Ron Ron and the Duke of Earl are friends of mine.....
https://www.youtube.com/watch?v=uX8Nj8ABEI8

On Holleys you want to use the port under the primary bowl... The reason for this is it sees what the carb will be
be directly sensing... and will have the direct bearing on your throttle plate position (which is important if the carb is not quite right
for your engine the readings can show if it's too big or too small), and will also help you directly determine what power valve to pick...

Thanks! I figured that I could use that port but I wanted to be sure. If that doesn't work, I'll try Lou's thing with the bung, but I'd imagine it would be almost the same thing.

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Chuck and the Flying Valiant