One of the benefits of the turbo is that it makes boost early, then regulates it through out the rev range. This is done with a waste gate / blow off valve right?

Why then can you run the ati with a 12lb pulley, and regulate it down to say 8 or less, so that instead of getting target boost at 6000 rpms we get it say at 3000-4000...

Or am I not understanding the principles. :crazy:

Brian :jester

 

Ive thought of that exact same thing. All you would have to do is install a relief valve or wastegate. Im sure its very easy to set up. Just need to get the part and install it. I dont see any reason why it wouldnt work.

 

I'm no expert, but I have thought about trying this too, and have even seen some supercharged systems with a manual purge valve.

Again I'm no expert on the subject, but in thinking about the issue I came up with a few potential problems.

- Turbos open the wastegates, which basically bypass the compressor. This is not possible on a supercharger.

- Purging air after the compressor does not necessarily lower the parasitic effect of the supercharger. Not an issue with the way turbos do it.

- Purging air after the compressor on a push based setup may cause strange airflow issues for the MAF when the throttle plate is open. Blow off valve works because throttle plate is closed. Problems with a pull based setup would be worse.

I'm sure others will chime in and clear this up, but these are just a few of the potential issue I was concerned with.

 

Might be possible.
MAF issues with being over-rich losing metered air.
Increased load on engine at all times.

 

My though was to put the relief valve, just before the intercooler. Thus the MAF hasn't metered any air that will be purged.

 

Not knowing much about it I can't add too much. I will say however, the advantages to such a setup would be great. Having the ability to drop just a little boost ( couple PSI ) for around town while still running higher for race days would be nice. Not really what the original post was about though.

On the other hand, if you are going all out with a SC setup, you would also setup your motor for optimum performance at whatever boost level you choose. Lowering boost on such a setup while maintaining the same parisitic loss, would kind of kill the whole idea. Just my uninformed .02 :D

:cheers:


[Modified by sirchman, 9:37 PM 12/10/2002]

 

Wastegates bypass exhaust energy around the turbine, not the compressor. The wastegate slows down the turbine before the compressor produces more than the preset boost limit, not after the boost is already made. A blow off valve does that by releasing boost pressure between the compressor and the throttlebody, as well as protecting the compressor from reversion damage.


[Modified by Monty, 4:01 PM 12/10/2002]

 

Yes, my description of how the wate gate works was very poor. I should have said that opening them basically slows down the compressor instead of bypassing the compressor.

So anyway, a turbo has a tubine driving the compressor, which can be slowed down with increasing engine speed by opening a waste gate. This results in control of the compressor speed. A supercharger has a direct belt driven pulley that drives the compressor, this does not allow for compressor speed to slow as engine speed increases (unless you count the nice belt slipage feature some people have :lol:).

I'm assuming tubos strikly use the wastegate to control boost when the thottle plate is open. Is this true? Has anyone seen a blow off valve work to control boost when the thottle is open?

 

I have thought of similar ideas over the years for superchargers. A couple past ideas that come to mind are,
1) An intake bypass that would have a Y-tube in it right after the supercharger outlet. One of the y-tube inlet ends would come from the supercharger and one would come from a filter. A gate controlled by a manual lever could select the intake inlet. In open mode it would be a NA engine, and in the closed mode the inlet would go through the supercharger.
2) Some sort of an electric controlled clutch that could be switched on or off from within the car. Both would probably not work for different reasons.

I have a third idea that would be a compromise but I think it could work. The only problem would be that it would require some engineering on the supercharger manufacturers part. The idea I had would include adding a second gear ratio in the supercharger transmission that could be run off of a boost controller. You would set it up to shift gears at some controlled level. You could even use a off the shelf boost controller if designed correctly.
What do you think, does this idea have some validity?


[Modified by MXRACER, 6:07 AM 12/11/2002]


[Modified by MXRACER, 2:15 PM 12/11/2002]

 

Just like above a wastegate is controlled on the exhaust side of the turbo. No possible way for a wastegate to work on a supercharger. As for blow-off valves, they are designed to relieve pressure when the throttle valve/plate is closed. This prevents compressor surge from damaging the compressor impellor. Blow-off valves are and can be used on supercharger applications but for that purpose only. Attempting to control boost via a blow-off valve will not work. Venting air to the atmosphere after measured by the maf sensor will result in severe richness. Not only will the boost level be lower, the volume of air will also be reduced dramatically.

There are products out there call pop-off valves but they are designed to prevent an overboost situation and protect your engine from damage.

The best method you can use is to properly size your compressor with your given hp request and engine size. Also depends on how much rpm you are spinning. There are several types of compressor trims which will result in very different power bands and hp output.
:cheers:

 

Some systems, like the ATI are push based. So the air is metered after the blow off valve.

I still don't think it will work properly without some significant engineering.