The amount of boost an engine makes is determined by how much air it can ingest compared to how much air the SC can output. Volume has no effect on the final boost level. Volume does, however, affect how long it takes to reach the final boost level. In the case of the spacer you added, it would only take a fraction of a second to overcome the increased volume. Unless you're using it to add meth or N2O, the spacer provides no real performance benefit. I would take it off.

 

dBomm
Very well written dBomm..)

On a high performance NA engine, there is a relationship to the
size / volume of the engine, versus the size / volume of the plenum.

Do you feel there is still a relationship to the volume of the engine,
versus the volume of the plenum, on an FI engine?

Also;
Have you given any consideration to pulses within the intake tract
and / or plenums chambers with regard to FI applications.

Cheers,
The Duck

 

The original idea behind the spacer is to allow the air to turn less abruptly, thereby increasing airflow (mass) into the engine.

 

Agreed - the lid spacer - theoretically - allows the air an easier path to follow, supposedly by making the turns the air must make less "sharp". If you really want to optimize the SC, just go with the ZL1 lid swap - that's proven by GM engineering to address the optimization of the flow path thru the lid area as well as improve heat exchange.

I'd just eat the lid spacer and go ZL1 lid...it's a much more proven part swap.

 

Agreed.

 

I run both the spacer and a ZL1 lid...

 

I'm planning on adding nitrous spray bars in a couple weeks, at which point I'll remove the spacer and also stop by the dealership to address the darn isolator rattle (or something). Hitting the 1/4 mi. track this spring and want to show up with my A game.

It does make the whine more apparent under light throttle, but I was confused on why it made the same boost pressure I thought it would at least reduce. I have seen 10 on my digital gauge sometimes. If it makes up for it that easily, isn't there anything I can do to exploit that phenomenon and get more airflow? I'm talking without changing pullies. should I be wanting to go up or down with boost pressure with only minor bolt-ons?

 

Boost is a function of airflow and restriction.

Once you get this concept, and I am really not trying to be condescending or suggesting you don't get the idea, so please don't take it that way, then increasing flow or decreasing resistance after the blower's rotors will decrease boost.

Doing the same prior to the rotors will increase boost.

This assumes everything else is constant (weather being a big one, and perhaps less obvious).

 

The scenario of air making less-abrupt turns to increase flow works on NA carbureted manifolds, but not on boosted manifolds. Boosted manifolds have totally different airflow dynamics.

With a NA manifold, the air that enters is immediately directed towards the runner that has an open intake valve. So it's pretty much a direct stream from the inlet to the valve. The smoother this path is, the better the air will flow. Airflow into the manifold can only be as much as the engine is capable of ingesting - no more.

With a boosted manifold, more air is forced in than the engine is capable of ingesting. This air doesn't flow in a stream towards a valve. It spreads out, pushing against other air molecules trying to equalize pressure throughout the plenum volume. When an intake valve opens, air rushes into that runner from all directions immediately surrounding the runner opening. Then air from other parts of the plenum backfill the air that went into the runner. And then this air is backfilled from air exiting the IC brick, etc. There's always the need to equalize pressure, and this occurs from air movement in the plenum, independent of direction.

Look at the tight spacing from the top of the brick to the lid. Visualize the path from the center of the brick to the open sections of the plenum. Does that look conducive to high airflow? And by raising the brick wrt the runner openings, you're actually increasing the abruptness of the turn the air must make.

 

Thanks for the input everyone. Admittedly I did get lost in the last few posts but what I took out of this is the boost is only a measurement and things will change and somewhat compensate. The same amount of restriction is met (psi) and I only increased the available volume for the cylinders to draw the air from, which makes it easier for the engine to breathe? Since it is the same restriction, the engine is doing less work reaching the same boost level and the engine compensates for it very quickly. Where is the limitation of increasing the volume beyond reasonable aka too much air volume/much less boost?


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