[wanab5150]

I think I remember the same back in the 60's where the vacuum gauge was used on older engines for diagnosis purposes. My dad used to use one before newer tech. In the case of a new engine I don't see how it would help tuning.

While advancing the timing will cause the idle (and vacuum) to rise, and retarding the timing will cause the engine to idle down and the vacuum to decrease, the timing set by Roush is their idea of optimum. I would think with the R&D Roush has put into these engines, and the thousands of them that are on the streets, the timing should not be messed with. The 427R engine puts out around 550HP. Bumping the timing up 5 degrees might give it a few more HP, but I'll bet it will rattle like a jar full of marbles as a result. Possibly if you want to run octane booster you may kill the pinging, but that's not what the engine was designed for. It's and everyday 550HP engine with a 24,000 mile warranty. I think if Roush had an idea you were tuning a warranted engine out of spec, you could use the warranty paperwork in the bathroom. So, I'm still curious how he does it.