Turbo Restrictors and Air Cavitation....

[myne]

Dont want to sound rude, but just as a point, you/we are sort of thinking wrong.
You're thinking in terms of vacuum and pressure. Positive and negative.
We should be thinking about ALL engines in terms of absolute pressure. There's only ever positive pressure in an engine, because absolute pressure has no negative.

So when you say "Thinkin about that further tho, without a restrictor inplace, i dont think a BOV could do anything but limit outlet pressure - ie inlet is at ATM pressure so can go no higher." you're sort of letting that positive and negative thing trip you up.

It should work the same way regardless of restrictor, it just might not be needed because the pressure before the turbo shouldnt ever drop too much below 14psi(absolute).

The air will get hotter doing that, but there's no reason you couldnt plumb it in after the intercooler.

As for shaft speed, there are 3 ways I can think of that could possibly slow it down
- more resistance at the inlet (more air, air with more opposing energy [eg aim a small jet of air opposite to the turbine rotation])
- less airflow through the exhaust (wastegate, some sort of variable restrictor after the turbine to reduce flow)
- Brake the shaft. EG small electric motor as part of the shaft, some sort of controlable oil path that is used purely for slowing it down, Tiny centrifugal weights like a dizzy

That'd require it to be part of the turbo's original design though.

Anyhow, I'm hung over right now, so I might not be making that much sense. Twas a good night but

[mic*]

Myne,

I agree on the absolute pressure principal. That was Stu's lesson at the start...

What i meant is that with a restrictor in place, the maximum pressure at the restrictor is 14 psi-ish, allbeit with a lot of airflow. After the restrictor, the vessel diameter increases and there must be a velocity drop, but since the air is being drawn thru rather than blown thru, i would think there could be a slight absolute pressure drop here too.

Imagine a TB if it was just a ring that could somehow choke a pipe... You would still get an absolute pressure drop (commonly called vacuum)

[oldcorollas]

Imagine a TB if it was just a ring that could somehow choke a pipe... You would still get an absolute pressure drop (commonly called vacuum)

like a carby?

[takai]

like a carby?

Or slide throttles.

[gixer]

I have done alot of flow bench testing with a front runner IPRA team here in South Oz, we have lots of data from testing, when we run an engine on the engine dyno we also use an airflow meter to measure the amount of air the motor is using, from this we know a hp/cfm figure for a particular motor, hence most of the time we can just flow the restrictors which usually fall within a small cfm band(depending on profile etc) and approximate hp for a given engine type, some motors are better than others. BDA's are much better than YB motors with regards to bhp/cfm, and SR nissan motors come up good as well, rotary engines are shocking with a very high cfm per bhp ratio, hence why a turbo rotaries are not common in IPRA. Now I know there are a lot of specifics between engines , I am just stating a few of our findings.

As regards eldo's car, sure it does well but it's FAR off the lap record held by Adam Allen, I know exactly what adams restrictor flows and what his motor puts out both in torque and bhp, his fastest lap time is a 1.15.4 at Mallala.

[gixer]

Oh with regards the comments of pressure drop between the turbo compressor and restrictor......go measure it!!! you will be very suprised

[pilot]

Back in the old F1 turbo days, throttles were installed before the compresor. What I could know about that is that it was done to achieve turbine acceleration due to lack of charge on it (the throttle acts as a restrictor).

[takai]

As regards eldo's car, sure it does well but it's FAR off the lap record held by Adam Allen, I know exactly what adams restrictor flows and what his motor puts out both in torque and bhp, his fastest lap time is a 1.15.4 at Mallala.

Yeah, i was more making the point that the weight of a V8 is an inherent limiting factor, that and reliablity. I think in the last round all of the V8s retired with failures of some form (engine, gearbox and diff from memory).

With the information im just as interested in the theoretical physics side of things as the overall power output. At least the theoretical physics gives me a headache trying to understand it rather than a headache from listening to the other research scientists here at work crapping on about useless stuff.

[kingmick]

the V8 have this problem because of money! trying to get close to the HP we do without spending the same money. if we put on of our V8's into an IP car it wouldnt be beaten unless it had a really bad setup and tactics. HP dosnt always win but it does in most cases.

dont worry ask around and you will get it right Takai, the knowledge has been around for years.

[Ben Wilson]

rotary engines are shocking with a very high cfm per bhp ratio

Interesting, I would have thought that with a rotaries 'long slow' inlet pulses that they would work well with a restrictor. Do you think that it's just typical rotary inefficiency, or is the pulsing of a conventional motor creating some useful harmonics in there? Do different cams/cam timing make a real difference to the ratio?

[kingmick]

with the turbo rotaries its the volume of air needed. you can make better power atmo without the Restrictors because you can go higher in revs, were a turbo one would be a choked chicken. comes down to rotaries making power later.

[gixer]

actually takai i just heard what eldo did at the last meet and very good!!! was suprised when heard how fast he run...few aero aids!!!

generally a 4v motor will do 1bhp per cfm while a rotary will use 2cfm to make 1bhp, i remember using the airflow meter on a PP 13b and to make 320bhp it used 600cfm of air!!! so as you could imagine turbo rotor thru a restrictor is not going to produce much, say the restrictor passes 350cfm of air and rotor uses roughly 2 cfm to make 1bhp, as for making power later you can get a turbo rotor to produce very high torque at low rpm

[kingmick]

but then the rotor is just doing things like a V8 so you might aswell have a V8. they have used turbo low reving rotors on aircraft but for racing it really defeats the purpose of having a rotor that revs low.

[Ben Wilson]

actually takai i just heard what eldo did at the last meet and very good!!! was suprised when heard how fast he run...few aero aids!!!

generally a 4v motor will do 1bhp per cfm while a rotary will use 2cfm to make 1bhp, i remember using the airflow meter on a PP 13b and to make 320bhp it used 600cfm of air!!! so as you could imagine turbo rotor thru a restrictor is not going to produce much, say the restrictor passes 350cfm of air and rotor uses roughly 2 cfm to make 1bhp, as for making power later you can get a turbo rotor to produce very high torque at low rpm

I suppose that makes sense, they use a huge amount of fuel and still ran at much the same mixtures so they must use a huge amount of air as well...

[myne]

Has to be to do with the way they work, the fact that the exploding charge exerts force in BOTH directions, but due to the inertia, spark timing etc, it averages more force in one direction.
Whereas with a simple piston motor, the force can only go one way.