No, boost is NOT boost. PSI in and of itself is useless. They're all compressors, with varying volumetric efficiencies and adiabatic efficiencies. The turbo's generally have a pretty good efficiency (around 74%), where-as roots blowers are down around 54% or lower! (The camden was 41%! YIKES!) Whipple blowers are great because they're up around turbos (70-72% or higher), but they draw a lot of power off of the engine, and they aren't as modular as a turbo (where you can adjust boost with a wastegate, etc).

 

Excuse my ignorance......but what "efficiency" are you talking about?
I was just saying that you can blow a motor with a turbo
just like you can blow one with a SC.

Boost is Boost.

How you get the boost is what separates a turbo from a supercharger.

 

Whoa there, Deena's car is a LOT different!!

She's using s4 TII rotors, 8.5:1 freaking compression! And also TII irons rather than n/a, supercharging from that is different than supercharging from n/a rotors. It'd be different if she had used n/a rotors.

 

That's not exactly turboing an n/a... that's doing a damn engine swap.

Add up the freaking dollars you'd spend on the engine, shipping (if you have to), misc stuff for install, new exhaust, other parts you might need, ecu/harness if you're going to do that, plus additional mods that you keep talking about. Now take that and get a standalone, good turbo, put it on your n/a with proper intercooling, fuel, and tuning, and you'll have MORE power than the TII swap...

Uhhh, the supercharged vert did NOT do 187rwhp... Pianoprodigy, if I'm thinking about who you are, did 230 at the wheels. https://www.rx7club.com/2nd-generation-specific-1986-1992-17/230-whp-supercharged-vert-complete-dyno-car-video-sc-comparisons-431570/

That was a 65rwhp increase from before the charger, and only at 6psi.

 

I already mentioned the efficiencies.

Boost != boost.

6psi on a blower is extremely different than 6psi on a turbo. Why? Because 2psi of that could be from the heat the blower puts off alone, where-as a turbo would be denser air, thus making more power, at the same boost...

 

6 psi @ 240 degrees (ie roots blower) does not contain as much oxygen as 6 psi at 180 degrees (ie. turbo).

 

In terms of power boost does not always equal boost. Most importantly is that a supercharger runs off the crank (or e-shaft in this case) so it saps engine power to turn it. BUT a turbo also requires some engine power to operate. A turbo causes backpressure, so the exhaust has a much harder time escaping the motor, and the motor has to use some power to push the exhaust past the turbo's impeller. However, this loss of power is less dramatic than a superchargers power draw, as a turbo also uses the thermal energy from the hot exhaust to power it. If you have two identical motors running the same boost at the same intake air temperature, one with a supercharger and one with a turbo and they both have the same efficiency, then the turbo motor WILL be more powerful. There are advantages and disadvantages of both, and it's up to the owner to decide what's best. For autocross, a supercharger is generally better, as it will have boost right out of the corners at low revs, whereas if you never get down on revs like in road racing or drag racing a turbo is often better, and for street driving it's personal preference.

 

I'm not sure i follow, do you mean to say that the expanding exhaust gas pushes against the rotor and the impellor while it expands, doing work on both? I could see how that would work, although only to the point where the blowdown cycle has an increasing chamber volume. Once the rotor has to push out the gases through the impeller, the rotor would be doing work on the gases which do work on the impeller, so the impeller steals energy from the rotor (and eshaft).

Anywhere I can research this identical motor, identical boost test you mention? It seems reasonable.

 

Well still, there would be a substaintal (omg I can't spell) difference I know, even in boost response. But with the ITB and a few various other things, wouldn't you think she'd be at least pushing past PianoProdigy's car? (Who did a very fine build FYI).

 

It'd still suck even if she had N/A rotors, because she'd be damn near detonating that thing with how much heat it cranks out ontop of the higher compression.

These threads are rather pointless though, everybody thinks PSI means everything, and it's always a bunch of inexperienced(read none) people rambling on about it.

 

not a pointless thread at all, i actually learned something, so thanks for debating...

most people on this forum already believe turbocharging offers the best performance in most cases. And now you have helped to explain why. I would still like to know a bit more though. Why exactly is the compressed air from a supercharger so much hotter than that from a turbocharger?

 

It has less adiabatic efficiency, so it generates more heat in compressing than say a turbo would (again, like 52% vs 74% or so)

 

Roots blowers don't normally use intercoolers either, sometimes they use air to water "aftercoolers" which don't cool as well as air to air intercoolers, unless you fill their fluid reservoir with ice water, which will only stay cold for a little while.

But yeah, what he said ^ Turbos and twin screw superchargers will make the same boost as a roots blower but at a lower temperature. Air temp always rises when air is compressed: Pressure * Volume = Number of moles of gas * constant * Temperature, or Pv=nRt for short (the ideal gas law, very fundamental equation in chemistry and physics).

Problem with roots blowers is the air is beating back and fourth out the discharge port because the blowers don't actually compress the air, they just move it like a giant air pump. Turbos and twin screw chargers actually compress the air and then spit it out. This allow it to come out smoothly into the intercooler pipes, which would have pressurized air in them already.

 

Have you seen those peltier Air/Water coolers? I've used peltiers a lot, but I can't imagine the power draw required to cool efficiently... Any thoughts?

 

Lol, are they like an AC unit that is for the intake air? I've always wondered about a setup like that, lol. I think I'll stick with a good fmic and traditional setup for a while, maybe CO2 spraying on the fmic if I get desperate to hit 12's.

 

No, it uses the Peltier effect, where it transfers heat from one side of a plate to the other, I commonly use them in computers to cool CPU's (I've had athlons running sub-freezing using them), but those were almost a 250watt draw, lol. And they're very unreliable, but I saw some intercoolers using them the other day, and I thought it was pretty interesting. As long as you can keep the water relatively cooled, even at room temp, they work well.

 

I haven't seen identical motor tests, but damn near. I'm fairly well versed on forced induction miata's (my dad's is turbocharged), and there are many different turbo and supercharger kits. The turbo's will make a little more peak power (not a lot typically for similiar setups), but the supercharged ones have better low end power. I think what the aftermarket needs is a fusion of technology. We need a centrifugal supercharger for it's high efficiency with a continuously variable transmission for good low end boost and easy electronic boost control. I figure you could use compressed air from the supercharger to power the CVT and use an electronic boost controller so that you could get full boost at half the RPM's of a non CVT system and then keep it there right up untill redline. Also changing boost could be as simple as pressing a few buttons, no pulley changes needed. The CVT centrifugal blower part has been done before, now all we need to do is get someone like Vortech to make a modern one that'd fir our cars. If this was available, it'd be my first choice for forced induction, as I've always liked the idea of a centrifugal blower, but didn't like the idea of little low end gain.

 

A twin-screw is just as efficient as a centriugal... The problems with them is the static drive, a variable drive would be nice, but then you're mimicing a turbo anyway.

The best supercharger for the FC is the twin-screw, hands down it's been proven over and over again. How can you have a similarly setup turbo vs supercharger setup? It doesn't much exist. Even the stock turbo's make more power throughout the ENTIRE powerband than the Camden units, and pretty much the same as the paxton setups. Considering most dyno's start at 2K rpm, if you compare most recent supercharged dyno's versus others, you'll see often that the turbo is making just as much torque already, and it just goes up from there, instead of staying flat.