lol, nice one.

 

defanition of vaccum....


Manifold vacuum, or engine vacuum in an internal combustion engine is the difference in air pressure between the engine's intake manifold and Earth's atmosphere.

Manifold vacuum is an effect of choked flow through a throttle in the intake manifold of an engine. It is a measure of the amount of restriction of airflow through the engine, and hence of the unused power capacity in the engine. In some engines, the manifold vacuum is also used as an auxiliary power source to drive engine accessories. Manifold vacuum should not be confused with venturi vacuum, which is an effect that is exploited in carburetors to achieve a fixed mix ratio between fuel and air.

The rate of airflow through an internal combustion engine determines the amount of power the engine generates, and most engines are controlled by limiting that flow with a throttle that restricts intake airflow. Manifold vacuum is present in all naturally-aspirated engines that use throttles (including carbureted and fuel injected gasoline engines using the otto cycle or the two-stroke cycle. Diesel engines do not have throttle plates.).

The mass flow through the engine is determined by the rotation rate of the engine, multiplied by the displacement of the engine, and the density of the intake stream in the intake manifold. In most applications the rotation rate is set by the application (road speed in a car or machinery speed in other applications). The displacement is dependent on the engine geometry, which is generally not adjustable while the engine is in use (although a handful of models do have this feature. Restricting the input flow reduces the density (and hence pressure) in the intake manifold, reducing the amount of power that is produced. It is also a major source of engine drag, as the engine must pump material from the low-pressure intake manifold into the exhaust manifold (at ambient atmospheric pressure).

When the throttle is opened (in a car, the accelerator pedal is depressed), ambient air is free to fill the intake manifold, increasing the pressure (filling the vacuum). A carburetor or fuel injection system adds fuel to the airflow in the correct proportion, providing energy to the engine. When the throttle is opened all the way, the engine's air induction system is exposed to full atmospheric pressure, and maximum airflow through the engine is achieved. In a "naturally-aspirated" engine, total engine output is thus determined by the ambient barometric pressure. Superchargers and turbochargers can "boost" manifold pressure to above atmospheric pressure, usually by a maximum of 0.7 bar.

Some modern engines using the Atkinson cycle rely on variable valve timing to regulate mass flow through the engine, and hence have no throttle and no manifold vacuum at all. In those engines, mass flow is regulated by phasing the intake valve to change the effective displacement of the engine.



so if you have a boost gauge it will read - something for vacuum.

 

Ah i have an aftermarket boost gauge, its very nice, it goes up to just over .8 smooth but at idle its like minus 5 or something, What shoudl i be looking for????

mines a 92'

 

'minus 5 or something'? go look at your gauge and tell us exactly what it reads in----inches of mercury etc. If you're only seeing 5 inches of vacuum, then that is definitely a problem.

 

His might not be in "InHg", it could be Pa, atm, or some other measurement as "bloke" would seem to indicate that he isn't from the States.

 

Hence that's why he wrote:

 

What gauge are you talking about, if its not standard on the car i dont have one, apart from boost gauge, sorry,

 

at idle my boost gauge reads -5 or just a touch under, like 1/2 mmm, its by blitz

 

Right, but -5 what? is it x100 kg/cm^2? If so, you're sitting at -500, which if your idle is below 1000 then that's a very good value and your motor is fine. So, I ask again-----what are the units that your vacuum is measured in? I'd like to help you, but I need some basic information first

 

thats it mate its sits just below this value at 850rpm

So its ok? brilliant

I think i might spend my rebuild budget on a single turbo conversion

 

.....Or you could save your rebuild budget until you do need a rebuild, lol. A properly sorted single turbo conversion with good parts is going to run you $3000-$5000 just for the turbo kit, not including ecu, fuel, ic, etc.

Good to know that your motor is fine . Whoever performed the compression check didn't do it correctly.

 

he is from liverpool and even us brits cant understand what a scouser is saying half the time

 

Nice one kidda, i thought that southern bloke with the aphex twin hair was trying to have me off big time, you can imagine me driving home in a car id just spent my life savings on,
then something clicked

7.3 at 500rpm not 250 rpm

nooooooooooooooooooooooooooooooooooooooooooooooooo oooo!!!!!!!!

im from near liverpool and i sound nothing liek a scouser according to the 'real' scousers, as you can imagine i do an awsome impression of the real thing.

(y)

 

Just thinking how did he get it so wrong and how did the motor turn so fast though

Love the sleeve

 

All I want to know is, what the ??? is a scouser?

 

its slang for a resident of liverpool that will lift ur wallet and then make u think u gave him the wallet

 

my vac shows -4 mmhg is that good?

 

should be like-12

 

If your gauge is reading in mmHg, check to see if your numbers are in hundreds (i.e. -400 mmHg).

If it is in hundreds, multiply -400 by 0.0393701 and that will give you the inHg which is what most people use (which would be about -16 inHg).

 

it is measured in hundreds. At 900 to 1000 RPM it is measuring -400 mmHg thats -15.74 inHg. Im new to all of this and im very curious to know what that meens as far as the condition of the engine.

 

It doesn't mean anything as to the condition of the engine unless its also used in conjunction with a compression test (as well as taking into account other factors such as idle rpms, height related to sea level, etc).

Vacuum can give an indication if something is wrong, once establishing a baseline (i.e. you do a compression test, check your vacuum and your boost is fine). Once you have the baseline, you can then study your vacuum reading to see if something is wrong with the car. But, lower vacuum doesn't always mean the engine has a problem as it could be a simple vacuum leak.

 

i think this whole thread is retarded and the car doesn't even have a problem..

you're concerned about a 2 second cranking time to fire the engine? well, after 4 pages am i going to be the first to tell you that it is normal?

 

Mahjik Thanks for the info. I was just curious about the vacuum. Im still new to the rotorary engine and was curious. I just recently about 1500 miles ago got my FD back from the shop from being rebuilt.

 

I was concerned with the difference between my new rx and my old,

first the comp test scared me, 2nd the oil pressure reads generally lower than my last engine and thirdly the cranking time, its just my last fd gave an overall different performance,

checking the compression this weekend, hopefully this 'specialist' will give me something more accurate,

 

if you think your motors gone a compression test is about the only valid test.