This may be one of those posts that only the engineers can love

I'm going through the usual exercise of considering the options and picking one for my EBC setup and external wastegate. I have built and tuned a 2-port before so I am directly familiar with that setup. I have also watched the usual vids and read the usual posts about 3-port and 4-port setups, including pros and cons.

I am considering a 4-port setup because I want to run a light wastegate spring; my car will be really traction limited in 1st through 3 gears (road racing) and I want to run very low boost in those gears. In first and second my target boost will be really low. Therefore I could see needing a boost range from 5-15 psi depending on the gear.

FWIW I will be controlling EBC with a MaxxECU Race and obtaining boost pressure at the compressor exit. This is on a 5.7L LS1 with a single 7875 and a 50mm WG.

I know about this setup below (posted here) and a youtube vid on the same. The thing is, those sources only talk about venting the line to the top port. To me it seems the bottom needs to be vented as well since there is no way for pressure to bleed from the bottom while there is equal pressure in the source line.



So, looking at alternatives, basically there are a couple of ways I can see to achieve the '4-port effect'. Either use the above 3-port version WITH a small leak in the TOP AND BOTTOM port hoses, or use a 4-port as usual.

So why choose one over the other?

From what I am reading some say the 4-port setups are very sensitive to duty cycle, or put another way, less stable. This makes sense to me because the vent (4th port) is huge compared to a small hole in the line(s) of the 3-port version, and therefore the net force of the wastegate diaphragm can change more rapidly. Perhaps this sensitivity can be tweaked with a restriction on the 4th port so it is not as touchy. See what I mean?

Here is a diagram showing what I am describing... In either setup, the leaks are adjusted in size to increase (larger leak) or decrease (smaller leak) the response rate of the system as the MAC opens and closes, thus making it more tunable... stability vs. response. The leaks would just be small orifices that would be adjustable (permanently) by drilling or whatever other means.



So, for example, by using the traditional 4-port setup, one can get the larger range of minimum to maximum boost. By adjusting the size of the orifice in the small leak, one can reduce the 'inherent' instability of the 4-port.

 

OK so perhaps this post needs an executive summary...

Why not vent both dome tubes on a 'pseudo 3 port'?
Are 4-port EBC wastegate systems generally manageable or really touchy to control? They seem to have a reputation for the latter.
Has anyone tried damping a 4-port system mechanically with an orifice at the vent port?

 

The lower port isn't air tight, no need for vent. Many top ports aren't either. in that case also no vent is needed. Configured like above, I have 7 (gate pressure) to 30+ with a 3 port.

 

With a MaxxECU and closed loop PID boost control just get the 4 port and dial it in.

 

Thanks. That is the direction I am headed in.

FWIW I have only dealt with IWGs until now and assumed (incorrectly) that the EWGs had sealed vacuum chambers as well.