keep blowing valve cover gaskets

[billy4hp]

Re: keep blowing valve cover gaskets

How can a cylinder at 5000 rpm that is drawing in more fuel and air not have a higher pressure than a cylinder at 600 rpm?

Off topic... But that is completely not true in naturally asperated engines.
Compression ratio is constant in NA engines, but cyl PSI is certainly not... need a supercharger or turbo for that.

Read about doing a static vs dynamic compression test and you'll see what i'm talking about.



It draws more fuel and air because your making RPMS.

But in fact if you break it down, the higher the RPMS go, the lower the cylinder psi goes per stroke.

It's all about volumetric efficiency[/QUOTE]

JustJason,

I don't know what your trying state part of your argument is what I stated in my post...

I tried to explain something in simple terms and your trying to use you internet skills to explain something you have seem to have only read about... I used the 5000 rpm figure as just a number, sure if the engine is so inefficient at this rpm it could have a very low cylinder pressure but it would have to be a real turd...

If you want to get all fancy, are you talking about cylinder pressure before or after maximum BMEP has occured?

Volumetric efficiency is just that efficiency so I don't know why you pulled that out onto the table...

Or should we just help the OP get his valvecover sealed up...

If you look at my original post I also indicated that I went on a mini thread hijack and helped the original poster...

I see a trend in this I/O forum that the old guard around here have a "my way or the highway" attitude... Believe it or not there are people outside of Iboats.com that might have a clue on how things work...

With that said there are plenty of folks around here that know how to fix it all so everyone here have fun... I have a boat to go use....

 

[JustJason]

Re: keep blowing valve cover gaskets

If you want to launch the spaceshuttle over it, let's start a different thread..

Not trying to launch the spaceshuttle over it. I just don't like it when folks put out mis-information. And what you wrote was completely wrong. All of it was wrong, I only touched on part of it.

If you draw in more air and fuel in a given space the pressure will increase vs. less air and fuel in a given space. Simple physics...

You seem to be missing the concept of RPMS.
An engine draws in more air and fuel per revolution at idle rpms.
An engine draws in less air and fuel per revolution at high rpms.
But since we are talking physics, what I wrote was wrong to because an engine doesn't draw (or suck in) in any air at all. Air is forced in by atmospheric pressure differential.

Just sayin....

 

[billy4hp]

Re: keep blowing valve cover gaskets

Not trying to launch the spaceshuttle over it. I just don't like it when folks put out mis-information. And what you wrote was completely wrong. All of it was wrong, I only touched on part of it.



You seem to be missing the concept of RPMS.
An engine draws in more air and fuel per revolution at idle rpms.
An engine draws in less air and fuel per revolution at high rpms.
But since we are talking physics, what I wrote was wrong to because an engine doesn't draw (or suck in) in any air at all. Air is forced in by atmospheric pressure differential.

Just sayin....

Okay using "draws in" is my snafu.... I tried to state something simply for the average person to understand...


So if what I wrote is wrong, all wrong... Pick me apart... I am a big boy and can take it...

Please explain to me oh wise one about cylinder pressure in a internal combustion engine. I would also like to know how volumetric efficiencey comes in play.

What I am saying is if you have more stuff in a given cylinder, when you squeeze it you will have more pressure than if you have less stuff in the same cylinder.

 

[JustJason]

Re: keep blowing valve cover gaskets

your trying to use you internet skills to explain something you have seem to have only read about

While i'm not going to insult you, I see that you also used your interwebz skills to edit your post #21 so people can't see what you originally wrote, and just added some junk that you probably got from wikipedia.

So if what I wrote is wrong, all wrong... Pick me apart... I am a big boy and can take it...

Alright man... but only because you asked for it.

I won't bother repeat what I already wrote, I'll just add to it.

In the simplest of terms, this increase in pressures is what makes your exhaust louder as rpm increases

Increase of pressure in what? Your not increasing your engines internal pressure. But because you are pumping the exhaust out faster than the mufflers can discharge it, you are increasing the pressure in the exhaust system. Another reason the exhaust gets louder is because of the frequency of the soundwave inside of the exhaust changes with RPM. Controlling that frequency, or sound/pressure pulse, can be usefull in making more HP via exhaust scavaging. Exhaust scavaging helps increase the overall volumetric efficiency (VE) of an engine, but i'll touch on that later on.

In the simplest of terms, this increase in pressures is what makes your exhaust louder as rpm increases, requires a increase in ignition timing to burn all that extra fuel and air

What? Again, per stroke the engine burns less fuel and air at HIGH rpms. You increase (or advance) ignition timing because fuel burns at a constant rate regardless of RPM. If you don't light the fire earlier, you don't burn as much fuel. If your not burning fuel, your not makeing power. If you take any engine and rev the snot out of it without advancing the timing, nothing bad or catastrophic happens... the engine just doesn't make any power.

At idle a relatively low amount of fuel and air comes in the cylinder

Relatively??? Relative to what? Relative to high rpm instead of idle speeds? Again, at idle, cylinder compression is the highest it's going to get. Air enters the engine, any engine, at a fixed rate. It's called atmospheric pressure (atmo). You can't change that unless you mechanically pump in air via a turbo or supercharger. Even then, because of lag, SC's and turbos really don't effect idle pressures. They compensate for the inherent drop of pressure at higher rpms. At 5000 RPMS, the engine is spinning faster, but the air is still entering at a fixed rate, therefore pressures are lower.

Ever pump up a bike tire with a manual pump? The faster you stroke the pump the quicker the tire inflates due to the increase in pressure (and this increase in pressure is what makes your arms tired faster).

Nooooo... The tire pumps up faster because your effectively increasing the RPMS of your tire pump by pushing faster. In fact, the faster you pump the less air you'll get, per stroke, out of the pump. Unless of course you turbo'd your bike pump or found another way to increase it's VE to 101% or higher.

Any easier way to check for excessive ring clearance is to do a dry compression test then do a wet compression test by squirting in a bit of engine oil into the cylinder being tested.

Eagh.... the only thing wet compression tests are good for is loading up a compression gauge full of oil and blowing the face off it. Really you want to do a leakdown test. But thats only my opinion on that matter.

all the spark plugs removed or with the throttle at WOT for his compression test we are all just guessing..

Eagh... I know that's how they do it by the book. But do a compression test with the throttle plates closed and only 1 plug out at a time. The numbers don't change that much.

I would also like to know how volumetric efficiencey comes in play.

Volumetric efficiencey is everything when building a motor, especially a high performance engine. In fact VE is the only really tell the difference between 2 different motors.

Lets take 2 hypothetical engines.
Engine A. 3.0 liter displacement. 5000 Max RPMS. 225 Max Hp
Engine B. 3.0 liter displacement. 5000 Max RPMS. 300 Max Hp

So why does engine A make 75HP per liter, while engine B makes 100HP per liter??
VE is your answer.

It's more complicated than this. But the down and dirty way to know what your engine compression should be when testing is to look up the compression ratio and multiply that number by atmosphereic pressure.

So....
8.5 to 1 with atmo at 14.6 would yeild you 124.1psi
10 to 1 would be 146psi.

But I have an engine in my own personal car, that I know for a fact has an 11 to 1 compression ratio, yet when I compression test it I get 210psi.
If i'm using my own down and dirty math, I should get 160.6 psi. So why the difference? It's VE.
I have a tuned, ported and polished intake, tuned exhaust using scavaging to help me pull a little more air into those cylinders, Quad cam motor with tons of valve lift and valve overlap. So much so that If my timing belt skipped 1 tooth i'd smash the valves and ruin the engine.
But I am getting 240HP out of a 2.5 liter engine, or 96HP per liter. Because volumetrically it is very efficient.

If you would like to debate this further, or actually learn something, please start a new thread in non-boating tech topics called "launching the spaceshuttle" (i'll find it) and i'll be happy to meet you there. Otherwise i'm done with this thread.