I own a historic supercharger of somewhat unknown origin. There are no concrete specifications for this supercharger. I am wondering how I would go about testing it's boost pressure prior to running it on the engine. Some anecdotal information states it may put out 1 bar of pressure (14.5psi), but that is doubtful. That said 1 bar would likely cause a catastrophic event for my engine which I would prefer to avoid. I engineered the engine for a much smaller blower that was due to put out ~6psi, but as fate would have it I ended up with this much larger supercharger. Any ideas on how I could rig a bench test to check the output of this beast? I guess if it is technically infeasible then I might have to look at some boost relief valve.
It is technically infeasible. Post some details of the blower and the engine, boost from a positive displacement blower is not that hard to calculate.
Not enough information. A pressure gauge is easy enough. The tricky bit is matching the output volume to the engine's needs. If it was a blow through it might be possible to rig a blowoff valve to limit pressure. If it is belt driven you might try an undersize drive pulley for a start and if you want more pressure, get a bigger pulley. We don't know if it is centrifugal or positive displacement, blow through or draw through, on top of the intake, beside, or even in front of the engine. But the drive ratio and/or a valve are the first things that come to mind.
In order to test a blower with something like an electric motor, you would need a motor that put out as a blower at boost uses on a motor. Lets say a blower uses 25hp on an engine to make 5 lbs of boost, you might need a way to reproduce the actual power and speed it would turn on an engine. I rebuild the VR57 blowers that were used on '57 Fords and TBirds and always bolted them on my car and took a test drive to determine if they worked properly. It is a risky and pain to test them that way. I know some supercharger rebuilders have an engine on a test stand to test An experienced supercharger builder knows what specs to set one up and really do not need to test one they ave built.
I was a bit nervous about posting this question. My query was more from a theoretical standpoint, to give me an idea as to what is possible from a bench test perspective. I could not see in my own mind how it was possible to test on the bench, so out to the HAMB it went for some expert opinion. I wanted to avoid getting into the blower specifics as it will no doubt draw some other technical questions (such as how boost can be that high etc.). Needless to say it is from a 1980's championship winning WRC team out of Europe. There are only two known (there may be many more unknown) examples of this exact unit in the world. No one that I know of has specifications for this exact unit. There were multiple variations and I have never seen any published information on rotor measurements, displacement etc. Some conflicting information, but nothing exact. The unit is belt driven. The different pulleys are a good idea to keep the boost down. The manifold also has a boost relief in the event of a backfire. I was however hoping for an off-engine bench test. The more I think about it I can't see how it would be possible.
You could do it if you had a flow bench. Drive the blower at different speeds and measure the output. Calculate from that, what drive ratio you would need to give the required boost on your engine.
Mechanical blower '80s WRC - Lancia 037 Volumex? Who else ran a mechanical blower? I think that if it's a positive-displacement blower (and those were, right?) and doesn't leak too much then boost ought to be a function of output vs engine capacity, of course calculating it to closer than an approximation is going to be way beyond me...but if you know the output per revolution and the RPM you intend to spin it at and the capacity of the engine you intend to bolt it to with some fudge-factor for VE...and you know it was bolted to a 2-liter engine originally, so...if you want less boost from a positive-displacement blower you spin it slower, which will also help your one-off bit of unobtanium last longer. Other blower designs e.g. centrifugal will be a different story and harder to model.
The Jalopy Journal
