drive pressure

[Rodram2002]

Wow, so it was choking it on the exhaust side and not the compressor.
That helps me alot.:thankyou2:

 

[Ph4tty]

My precious 64 lol.

 

[NoSeeUm]

Now picture 100 psi of back pressure typical to some twins, the pressure venting into the manifold you speak of is more like a 100 psi pressure vessel with the spring pressure trying to pull the valve closed.

Now lets say you have a 2" diam valve.
(pie)* r2= 3.14 x 100 psi is 314 lbs holding the valve open against a 60 lb spring. Give or take a little.

Gotcha, thought of that.

Two things:
1) You have 100 psi inside the cylinder also. That cancels out the 100 psi in the exhaust manifold. Net pressure force on the valve is zero (depending upon the relative surface areas of the cylinder vice exhaust sides of the valve).
2) You have the valve return spring laying down its 2 cents.

As soon as the intake valve opens, 100 psi is now filling the cylinder. It is seems unlikely to me that at any time the cylinder pressure drops much below drive or boost pressure. If they are equal it would seem to be only more true. Remember the engine in the pressured room example from above.

I can see how if drive exceeds boost by a wide margin, (of for an example of a worst case = exhaust brake) that cylinder pressure could actually vent into the intake manifold right as the intake valve opens. In essence you would now have some what of an un-intentional "un-cooled EGR like phenomenom" going on. Going back to our original drive pressure discussion I could see how that could also rob some Hp as well as cause elevated EGT's.

This rapid de-pressuration into the intake manifold could be what you are talking about?

If so then possibly:
Drive = 100
Boost = 65
(pie)* r2 = 3.14 x 35 psi is 110 lbs

That be enough?

Just confused, thanks;
Jim

 

[NoSeeUm]

FWIW I burnt up the tubing on my first drive pressure gauge hook up. I needed a bit more copper tubing to cool things down..... wned:

Jim