3800 Engine cylinder pressure question

[98 TGP TOY]

Ok quick question.....if you are pushing 14 psi. Whats the pressure is in the cylinder before the valve closes? 12-13psi?


Any insight on this type of topic, good webpages, etc, is welcomed. Thanx

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[Royalgtp]

Wouldnt 14 psi be peak pressure when the vavles are closed and combustion is about to happen??

If they are partially open, wouldnt you either be gaining or losing pressure based on what stroke you are in they cycle?

 

[imported_Ron Vogel]

Good question, but in a perfect world, it should be 14 psi, as piston is at tdc, it should be well into the 200psi range.

 

[98 TGP TOY]

If they are partially open, wouldnt you either be gaining or losing pressure based on what stroke you are in they cycle?

Not sure what your saying. The M90 would be pushing enough air to keep the lower manifold at a *constant* 14 psi. The exhaust is always the low pressure side, so flow will always head that way. With overlap, some of the intake air will actually pass by the cylinder.

But more or less, im wondering what the pressure inside the cylinder is right when the intake valve closes....at the bottom of the stroke.

Good question, but in a perfect world, it should be 14 psi, as piston is at tdc, it should be well into the 200psi range.

Oh the perfect world and assumptions....an engineers world

I know with air compressors, they lose 2-3 psi across the valves, so Im assuming 1-2 with our engines...eh...time to hit up the search button.

 

[sr71_rgl]

I read on CGP one time that 10psi on a stock L67 is right around 18:1 CR. Does that help?

 

[98 TGP TOY]

It may....depends if I can find what equations they use for engines. I mean, i may mess around with some isentropic compression equations, but i dont know whats actually used with engines. Luckily my university has my back and they cancelled all of our internal combustion courses....whew dogded a bullet there


Ive just sort of got a crazy plan to write some really in depth articles about our cars analyzing/showing the numbers and calculations for our intercoolers, w/a injection, different power-adders, etc.

Im trying to get a lot of experience with engines in my own time and trying to build up a bit of a portfolio type of deal. I graduate in a year

Im just freaking out...

 

[98 TGP TOY]

Also, I was bored today during Econ 102 , i cant beleive thats a college course, anyways, i was bored so i ran some numbers that show why water injection is effective. I've yet to equate alky into the picture. Its nothing special, except I like seeing these things for myself

 

[imported_Ron Vogel]

Also a well designed exhaust system will produce 6-7 psi on the pipes. That will pull on the Ex valve and produce scavenging.

 

[Royalgtp]

I like my ECON class..........really I did... B)

 

[sweetness]

Originally posted by 98 TGP TOY@Apr 7 2005, 02:21 PM
Ok quick question.....if you are pushing 14 psi.  Whats the pressure is in the cylinder before the valve closes?  12-13psi?


Any insight on this type of topic, good webpages, etc, is welcomed.  Thanx

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My best guess would be that the pressure is related to the VE of your heads. More flow, more pressure. Less flow, less pressure. Kind of like a restirctor in the oil line for your turbo. Less of an opening, less oil pressure.



BC