IF you disconnect the line directly at the wastgate port then there isn't a boost reference. Therefore no pressure differential and no spring activation. The wastegate will stay, for the most part, shut.

 

Charlie brown,
An engine doesn't breathe air in. Especially under boost. It is pressurized regardless of boost pressure or atmospheric pressure.
If the air was to "back up" then you would see a restriction somewhere. If there were a restriction then the turbo may continue to boost 30 psi at redline or close to it. As an engines rpm increases the amount of air being processed decreases after peak torque. That would definately decrease the life of the little turbo.
You are right that the turbo will push a certain amount of CFM, BUT what does cubic feet per minute have to with compressor efficiency?
Timing is timing. There is an ideal figure for every load and rpm. It doesnt matter if it is "retarded" or advanced. It is a figure that is calculated to provide the most amount of power without sacrificing reliability in the quality of fuel being used. Advanced timing does NOT give you more power. The proper timing lead (whatever number that may be) along with the proper parts of air and fuel do.

 

This seems strange on the surface because the action of pistons provides the 'breathing', but in fact good inertia tuning on a N/A engine does create intake pressure, albeit small.


This statement is somewhat misleading because the mass of air passing through the engine reaches a maximum at peak hp. I think what you meant to say is that Ve decreases after the torque peak, and the mass of air processed per revolution decreases from that point onward.


Good point. Sufficient timing such that peak cylinder pressure occurs 10-15 deg ATDC is optimum. Advancing the timing further does not enhance power and only increases the possibility of detonation.

 

Ok, that makes sense. I know the original post was in reference to the strength of the stock internals. Have you been running 33psi on the stock turbo for 60k miles, or was that just for testing? I'd be surprised if the turbo lasted that long, running so hot.

 

There are other ways to reach that amount of boost besides upgrading your injectors... stock injectors + C16 or methanol will do it as well.

 

that 24-25 psi.. just pump gas right.. with alky its more like 27-28

 

One can run as much boost as he likes (e.g. 30 psi spikes) with the stock injectors, so long as the hp level at that point does not exceed the injectors' max flow rate.

 

I hope this isn't too OT for this thread, but does anyone have a compressor map for the 16g? I'm interested to see what the flow rates are at 30#

 

You are correct in saying that the cylinders are filled via boost pressure and not vacuum created by a downward traveling piston. However, the boost pressure measured at the intake manifold is the pressurized air that wasn't able to get into the cylinders. An engine with higher VE can flow more air at a lower boost pressure than an engine with low VE at high boost pressures. Assuming that the dynamic pressure at BDC before compression is the same as the reference pressure measured at the intake manifold can be and often times is a bad assumption...

- Steve

 

If you search around you'll find them...

 

damn, busted for being lazy

 

At 4k rpm (around where you're going to see that boost spike), a 2.0L engine running around 100% Ve will use around 400cfm.

Assuming we use the compressor map for the 'Large' 16G turbo (?), the outer window of turbo efficiency works out to around 29psi from ~350-400cfm.

 

You are correct the action of the pistons do create the "breathing". But it is how the meaning is interpreted. The downward mechanical action of the piston, conrod assembly creates negative pressure in the bore. The atmospheric pressure behind the valve is what PUSHES the mixture into the cylinder. That is what I am trying to convey. There is always some sort of pressure. whether it is atmospheric or above doesn't matter.
You are also correct that I should have raised the point of max VE. Mass air will peak at peak HP but that is a multiplication of rpm and cam profile.
Thank you for helping to clear up some of my thoughts.

 

No it has not been only for testing. The stock turbo has been holding up very well up to now.

 

The change in octane does not increase the amount of fuel. Maybe just your detonation point. The stock injectors at 33 psi and peak torque do not supply enough fuel for more than a 12.5:1 A/F ratio. If that seems safe for the 4G63 in its current production for you then fine.... I choose to go a little richer.