Fitting a vacuum gauge

[disco2hse]

I am going to install a vacuum gauge into my Stage 1 V8. I have SU carbs, so what vacuum pipe is the best one to cut into for the gauge?

There is one that appears to come off the inlet manifold on the rear end of the engine. It looks like goes down by the gearbox so I think that is the CDL pipe.

[Mrs Bingham]

I'm sure there will be many opinions on this subject but if you plan to have a vacuum gauge for any other reason than a decorative item then ideally you need two - one for each carb and the vacuum take off should be taken as close to each carb as possible using one way valves where necessary. Using the pipe you suggest will operate a gauge just fine but it will provide little in the way of accuracy when using the info for tuning.

[disco2hse]

I don't agree. Air moves pretty quickly and in a negative pressure, even more so. A gauge is slower, it is mechanical. There is no practical value in situating gauges next to the nearest device unless they are on different lines. Then all that is going to tell you is how far out of tune each carb is.

The gauge is not for tuning but for economy, performance and engine monitoring.

The purpose of my question is not to debate this with you but to identify which line to use.

[disco2hse]

OK, so that pipe was not a good choice

It seems to read only constant vacuum and about 10-12 inHg. It also raises (lowers?) vacuum at a slow rate. Not sure if that might be due to leaks since I have not fully installed the gauge yet.

Other choices?

[disco2hse]

I hang my head in shame. The pipe was buckled behind the dash. Untwisted and the gauge sprang to life. Not too happy with the idle but that is probably because I don't the right cam shafts fitted at the moment.

Now the next problem: See new thread.