Measuring Engine Health By Vaccuum
 

I am curious about doing this. I have read several posts of people who claim anywhere from 18 to 20HG at idle.

However, I get several different reading off of my PFC, and my boost guage as well. Which is most accurate?

1. When I start my car cold my PFC reads 479 mmHG (18.8 HG at idle)

2. However when warm my car seems to drop to 379 mmHG on the PFC (15 HG at idle)

My engine idles at 1K does this affect the result?

I have a single turbo, with a streetport. Does this affect results?

I always have my boost controller on. Does this affect the result? (electronics should be off to measure? )

How much, if any, do these things affect the test by. E.G. does having a streetport = a 1HG loss at idle?

Help always appreciated :)

Porting will effect vac at idle so take that into account but having a higher idle will increase your vac. With a street port 18" of Hg is alot of vacuum and 15" sounds alot better. There was a post in one of the sections about how much vacuum people were pulling and what your getting stounds about right. I get ~400 with a similar set up.

~Luke

Having good compression is a must , the port timming does affect the vacuum .Stock timming will have the highest vacuum , the more agressive timming will lower the vacuum .The same with the cam timming on a piston engine .With a very high idle, with the throttle plate open the vacuum number will be lower than with a lower idle with the plate closed .The electronic controller should have the wastgate closed at idle so that should not affect the idle or vacuum .So what affects vacuum, Two things are compression and port timming .We are not considering leaks and other failures .

Re: Measuring Engine Health By Vaccuum
 

My engine idles at 1K does this affect the result?

Yes; most people base the "healthy" reading of 16+ on the 750/800 RPM idle.

I have a single turbo, with a streetport. Does this affect results?

Streetporting will affect results; will lower the "healty" number.

I always have my boost controller on. Does this affect the result? (electronics should be off to measure? )

No.

How much, if any, do these things affect the test by. E.G. does having a streetport = a 1HG loss at idle?

If your idle was at 750 with a streetport (and depends on level of porting), you probably will see anywhere from 11-14 inHG on a "healthy" ported engine. Add another 1 to 2 inHG if your idle is at 1000.

I have my PFC set at 850 idle, and I see 16 inHG in vacuum, whereas when I had it set to 750 it was around 15.

Now this "healthy" engine doesn't mean that your engine is perfect, just that most, maybe all the rotor seals are intact. It does not tell you if your coolant seals are bad.

Their are too many variables here to make a difinitive chart of health vs not healthy... I figure as long as i have all my apex's its healthy!

Thats my point. There really do seem to be a ton of variables to consider, and I do not know if they really matter.

My compression test came out at between 120 and 125 on all rotor faces. My car idles perfectly, and is like a sprung monkey on crack, when I get on the throttle. :p: however my HG reading is 15.

You are fine, vacumm on my pfc is 370-400 on my pfc with idle at 800 rpm. But like athiun said, it doesn't tell the condition of your water seals.