Mattman928

Does anybody know what the lowest vacuum pressure is, if measured at the Mass Flow Sensor on a naturally aspirated 928 GT?

Has anyone attempted to mount a vacuum gauge in that area to measure the pressure?

jpitman2

Vacuum to measure engine efficiency is usually measured under the throttle plate. I suspect vacuum at the MAF would be very low, if any....
jp 83 Euro S AT 48k

928 Fool

Mattman,

In case anyone is looking at you confused, vacuum is the opposite of pressure. You have pressure, vacuum or static. Of course this is all relative, but normally pressure and vacuum are derived from static which depends on your altitude and current barometer. jpitman is correct, vacuum is barely present (at least readable) until you reach the throttle body. There you have your choice of ported or going deeper to read manifold vacuum. Why are you curious about vacuum at the air valve?

Kevin

Mattman928

I was curious about how efficient the design of the intake is? So many folks are supercharging their 928's to increase the amount of air entering the engine.

If there is a vacuum at the throttle body on a naturally aspirated engine, then theoretically there may be opportunity to remove / reduce some of the pressure drops naturally, and improve the performance of the engine.

2V4V

Matt,

Are you talking about at part throttle or WOT?

If you are talking about airflow through the throttle, yes there are some gains to be had - search for "euro intake' or 'euro throttle' in the archives.

In any engine scenario - forced or NA - the smallest point through which air has to pass is a restriction to the rest of the system, if you are talking in terms of raw flow. There are some times when you *might* want to flow at a less than 'highest achievable' rate - intake port speeds (at the valve) pop to mind.

Anyway, if you want to learn, go buy some tools. You need a coupla vacuum gauges and some fittings - dive in and measure.

Greg

Mattman928

That is the plan. I was just trying to size the vacuum gauge. I have a feel that a basic vacuum / boost gauge will work fine.

928 Fool

Mattman, this is kind of where the road forks and goes different directions. If you are interested in increased flow (volume) then you are going down the porting road or different runners, plenum and throttle body as was mentioned. This change you will see mostly at the top of your rpm range. If you have more cfm you will have more fuel which translates into more hp at the top end. Forced air on the other hand does not increase your flow, it provides you with an increase in charge density. This will increase throttle response and hp across the entire rpm range depending on the boost curve. It is like a garden hose, it will only flow a fixed amount of volume. You can increase pressure but you will still flow the same volume until you make a mod to increase volume. When I say a fork in the road I don't mean that you have to go one direction or the other. You can and many people do both. It just depends on what you want. Where do you want your hp gains and how many pennies do you want to spend. Have fun.

Kevin