In following with what Ron and Hass have been experimenting with I installed two Ebay 50mm blow off valves,
They were only a piss ant $ 35. each. I've spent more than that on lunch before. I dismantled them and they are a good quaility unit with a solid brass piston with 2 o-rings on each piston. A V band flange with a stainless vband clamp.
I have it piped so I can vent to atmosphere and just let the boost blow the valve open for a low boost # or close a 1/8" ball valve and it will operate just like a normal blow off valve that is open with manifold vaccuum and closed with boost to get a high boost number.
It came with 2 springs in it and I removed the heavier one to test it with. It was just vented to atmosphere. It made 6.5 # boost and held that number steady. What's surprising is that the wastegates were set for 15# boost so they never opened. The compressor tube boost control did the whole job. It worked real well. I added back in the 2nd spring to test again with next time.
Some interesting things to learn here. With the normal boost which is at 23# since I relocated the wastegates the header backpressure was at 18# which is real efficient.
With the wastegates not opening and just relying on the blow off valves it showed 11# header backpressure. For operating at the lower boost I should back the wastegates down to about 5#.
Now that I have tested it I am going to get one of those cheap solenoids like Hass found on Ebay and that will let me control it on the fly and have total boost control.
For a racer this could use a timer to switch between the high boost number and the low boost number just like they do with nitrous. A flick of the switch could bring on 800 hp that doesn't cost squat.
Here's my datalog,
The added control over this monster is excellent. I could run the bitch on pump gas if I wanted to.
I was pretty amazed that it still pulled those 60% gears to 5800 rpm with only 6.5# boost and the rpm was still climbing on the datalog. I'm curious to see what it would top out at with such low boost.
It was certainly less of a thrill ride to me at low boost but someone who hadnt' ridden in it at high boost would probably still be impressed.