Explanation Of Vaccuum

[SRT-4_&_NeonACR]

Quote: Originally Posted by SynthRocker

Great explanation.

So if your at WOT in a F/I car, then vaccum should read -? If 0 vaccum is atmospheric pressure and a turbo buts more pressure in.

Or am I thinking/going about this all wrong? lol

If you're asking what a true vacuum gauge would read while under boost then the answer is "0", but only because a "vacuum only" gauge can't read pressure, it only reads from 30in hg to 0in hg of vacuum. If you did have a vac gauge that read "pressure" as a negative number then the answer would be yes. However, when looking at a combined vac/boost gauge (like ours) think of a vac reading as a negative number (in relation to atmospheric pressure), and boost as a positive number. The only problem is, vac and boost are on two differnt scales... 10in hg vac is not -10psi (more like -5psi).

What ever you do though, don't confuse all vac readings for meaning there is an absence of air pressure. Only a reading of 30in hg. vac could be said to be void of air since normal atmospheric pressure is roughly 30in hg (therefore 30in hg of vac = 0 pressure). For example, a reading of say... 20in hg vacuum (our car at idle) is actually 10in hg. of pressure on an absolute pressure gauge. Our gauge simply tells us the difference in pressure in the manifold compared to the pressure outside (assuming at sea level). A reading on the vac side means the pressure is lower in the manifold, a reading on the boost side means the pressure is higher. This all then relates to how much air is entering the engine.

If you want to compare the vac readings to boost readings, think in absolute pressure.


Here's a typical boost guage:


Here's what it would say in absolute pressure (I rounded it off):

[AnotherNeon]

Quote: Originally Posted by Solace64

Out of all the animations I think I've seen on how an engine works, that just might be the best one.

[silver_s2]

Quote: Originally Posted by AnotherNeon

Quote: Originally Posted by Solace64

Out of all the animations I think I've seen on how an engine works, that just might be the best one.

did you do that yourself...if so i'd like a PM how...been wondering how to make animated gif's out of video files


and agreed that is the best video representation of an engine.....i saw some flash animations on howstuffworks.com
another good site for explanations on turbo and n/a engine working

[SRTVITO]

thanks guys I think I got it now

[kidbattle]

word up

[Socboy3000]

Excellent Video

[SRT-4_&_NeonACR]

Here's a great vid explaining VVT, and how it switches from "non overlap" cam timing to overlap cam timing, and demonstrates exhaust scavenging with some reversion into the intake. On a normally aspirated car this would have the benefit of bringing in more air, however on a f/i car this would only work to slow down the intake charge (almost like reducing boost would).

http://www.youtube.com/watch?v=9A6S1NUjg_A

[Socboy3000]

^^^^^ Very interesting

[MDRACER]

For any newbies reading this you need to know that f/i is not fuel injection, it is forced induction- either turbocharged, supercharged or both together. You might ask "why would you do both?" Detroit Diesel 8V71 2-stroke diesels in some applications had both. This is beyond the scope of this discussion, if you would like to know more about this, pm me and I will tell you about it. I'll give you a hint- those motors have both ports in the cylinders and exhaust valves. By the way, I own an 8V71- unfortunately no turbo but a huge supercharger that puts out4-5 psi (gauge). Dr. Mike

[pyro530]

Quote: Originally Posted by ac_srt4

this will explain how an engine works. as you can see the air (blue) is being sucked into the combustion chamber
http://www.metacafe.com/watch/169155/deutz_engine

What is Deutz?
I always thought the fuel injector sprayed as the intake valve opened.

[Corey_1986_2005]

I just purchased my SRT-4 Saturday. Im new to the Forum and not sure of how it fully works yet, but my question to you is.. At an idle my car reads 20 on the vaccum side. Im betting i have a bad vaccum leak but cant find any places to get a SRT-4 Diagram on vaccum lines. Do you have any helpful ideas? thanks for your time,

Mods I have
Needs Wings Down pipe
Needs Wings Delete
Borla CatBack
Mopar Cold Air Intake
Stage 2 with Toys

[Corey_1986_2005]

I just bought my 2004 SRT-4 Saturday, the Delership took the Intercooler sprayer sysetem and button along with the Pod The toys Sit in. I still have my Dial a Boost and 100+ octain were can i get a Toys pod and the full Intercooler System?

Also At Idle and while driving my car Reads 20 on the vaccume side. Yet if i get into it i can get 15-16psi of boost on #3 on my dial boost gauge. Where can i get info on the Vaccume Lines to fix this or is this a comman problem?

Mods
Stage 2 with Toys
Needs Wings Down pipe and Delete
Borla Cat Back
Mopar Cold Air

[stowaway]

at idle 20 in/hg is just where you want it to be.

[mrkodi]

Quote: Originally Posted by Corners

Quote: Originally Posted by 16g4g63

I'm currently in college for engineering and am taking a fluid dynamics class. According to the professor, as I understand it, vac pressure can not be greater than the atmospheric pressure. I was wondering how my boost gage can read 21 psi vac at idle when the atmospheric pressure is 14.7 psi.

Well, first off, you need to read your guage again. The stock guage reads inHg (inches of mercury) for a vacuum, and psig (psi guage) for positive pressure. I'd suggest you get your fluids book out and review the whole gauge vs. absolute pressure.

I'm a licensed ME and I specialize in thermal fluids design, and I can tell your professor is right IF you assume atmospheric pressure in psia (psi abolsute). If you're using psig, atmospheric pressure is 0. Just make sure you know the difference between psia, psig, and psid (that's absolute, guage, and differential), and you're good to go.

God Damn I feel stupid as hell right now.

[westrock]

Quote: Originally Posted by ac_srt4

our engine is four stroke engine:
1. air/fuel mixture intake
2. compresion of air/fuel mixture
3. ignite by spark plug and explosion
4. exhaust the waste

Suck
Squish
Bang
Blow

thats how I rememberd it