Supercharging Versus Turbo Charging

While it's true that turbo affects crank HP due to backpressure, it's also true that on a street car, turbo allows you to run less muffler than on a super.
This can bring total backpressure effect on crank HP to near equal levels between super and turbo.

Here's a link that shows HP needed to drive the M62 at various RPM and pressure, it's a tiny graph on the lower left side (strangely, the Eaton site used to have this graph, but no more):

http://www.capa.com.au/eaton_m62data.htm

And here's the efficiency map for M62, note the max efficiency island at 66%, spans a fairly narrow range of RPM and pressure ratio. This is important since the super RPM is fixed WRT the engine RPM.

http://www.eaton.com/ecm/groups/public/@pub/@eaton/@per/documents/content/ct_128484.gif

Mind you, I like supers.
I have an M45 that will find it's way onto my street car.
But I also have a T-25 that will find it's way onto my street car.

The plan is to contrast/compare ( a 'blow off' ?)

It is interesting to note what manufacturers use what solution. From memory:

Porsche: iconically turbo.
MB: was supercharger, now turbo.
BMW: turbos on M cars! That's not what you'd expect, really. Ford: both. Mini: super, then turbo
VW: turbo, then twin charge
(pretty much all of Japan) turbo Aston Martin: super - I don't think they've ever done turbos, have they?

I thought there was one that had started with turbos and moved to superchargers, but it's not coming to mind.

I absolutely hate superchargers on anything that doesn't displace at least 3.0 liters or more. Such a waste on a little motor. Turbo would be the way to go on a 924.

I'd rather have a supercharger. Less heat under the hood, no complex exhaust work, and less cooling/oiling issues. I like the "bigger engine" feel of them.

Superchargers only make sense if running a miller cycle. That's my opinion and I am unanimous in it.

Most S/Cs don't put out more than 8psi.. 12 at those levels, heating the air is nowhere near as bad as on a turbocharged car

That doesnt make any sense. Supercharger selection is fairly narrow, especially if you want cheap and used. Turbo selection is wide friggin open. I dont think there is ANY situation where you couldnt find a turbo that had better adiabatic efficiency at a given PR than the best supercharger available. I think if you just make a random selection of whatever cheap superchargers and turbos are available locally, its even MORE likely the turbo will beat the SC heat-wise. This is BEFORE we talk about intercooling.

Old roots SCs are notoriously bad about putting crazy heat into the intake air. Sure, at very low boost it's not going to be a major issue with either turbo or SC, but to say an SC puts out cooler air at ANY pr is misleading.

That's my opinion and I am unanimous in it.

LOL

My personal opinion in this specific scenario is the supercharger. The install will be easier, and the car will be easier to drive through corners with the more linear power delivery of the SC. Since neither setup is going to make the car crazy fast, i think those are the most important issues in this scenario. I still agree with Keith's and others' statements that a properly sized, installed, and managed turbo setup can do 95% of everything a roots blower can and beat it in many ways, but in this scenario of this car, these install issues, and these specific used blowers, i think the SC wins. My .02

Keith Tanner wrote: I thought there was one that had started with turbos and moved to superchargers, but it's not coming to mind.

Audi sort-of has. The "3.0T" engine in the A6 & current S4 is a supercharger, not a turbo. The "2.0T" and S6 motor are still turbo, though.

Everything has it's trade offs.

And how you ballace the trade offs change a lot if you are making a custom fit, a kit, or production.

IMHO, for a highly loaded production set up- turbo is the easiest to deal with.

I like the elegance of turbos, but for an application where it's street and autocross, I don't like the idea of having that lag between dipping into the throttle and having boost.

All I've got to go on is my stock WRX, but I assume Subaru did a decent job of sizing the turbo, and the stock turbo isn't some oversized monster that's trading lag for giant boost.

When enjoyment at less than peak power and/or immediate and predictable response are the goals, a supercharger makes more sense to me. If I am convinced otherwise before the 2002 actually gets built, then it'll get a turbo. But I'd be really bummed if it had that "softness" in short throttle applications that the WRX has while you wait for the turbo to spool...

crazycanadian wrote: I'll trade you that M62 hybrid for the Thuderbird M90 I have... :) I need something shorter for my application...

I have one of those on the shelf as well

ransom wrote: I like the elegance of turbos, but for an application where it's street and autocross, I don't like the idea of having that lag between dipping into the throttle and having boost.

It's not 1977 anymore- sizing and tuning for lag is pretty easy.

alfadriver wrote: It's not 1977 anymore- sizing and tuning for lag is pretty easy.

Direct injection and electronic throttle also do a great job of covering up lag. They're not running engines under vacuum very much anymore.

PS - The 3.5 Ecoboost engine? The exhaust manifold outlets look about the same size as half of a Lancer Evo outlet. TINY. Barely fit my thumb in there. And those are 400hp engines.

In reply to alfadriver:

But I'm driving a 2012 Subaru, not a '77 anything, and I find it annoyingly laggy... Unless there's something else going on (I'm under the impression that Subaru limits boost in first and second gear, but I don't know how quickly they allow the limited boost to build, or whether they also tie it to RPM, creating a softer delivery) I'm not sure what other conclusion to arrive at besides turbos having some amount of inherent lag...

Anyhow, while I'll happily admit that my experience is very limited, the only experience I have is a stock production vehicle which I'd assume would be tuned much more for driveability than peak power, and yet it feels soft and annoyingly laggy to me.

FWIW, on a road course, I don't think it would be nearly as annoying. But for street and autocross where I frequently want power for a short duration, but I want it right now, and I want exactly as much as I'm expecting for a given throttle movement, it seems suboptimal...

I would love to drive a car that shows me that Subaru is simply giving me the wrong impression of turbos with their boost-limiting mapping or something, but I can't jump to that conclusion...

ransom wrote: I would *love* to drive a car that shows me that Subaru is simply giving me the wrong impression of turbos with their boost-limiting mapping or something, but I can't jump to that conclusion...

Drive an STU prepped STi? I've driven a few, and they have power right now. The 2.0 STX WRX I used to codrive did have some lag, but I really didn't find it annoying - especially on the street. Autocrossing it, you just had to learn to put your foot down a second earlier.

there's a guy on the 924board that has a car running both, its pretty cool.

the 2.5is pretty truckish, so something to help it at the mid-high end of the power curve might make sense, a turbo tends to provide this iver a blower.

ransom wrote: In reply to alfadriver: But I'm driving a 2012 Subaru, not a '77 anything, and I find it annoyingly laggy...

Well, there's your problem...

Really, it's not that hard to size it right. Why Subaru has problems? I don't know.

In reply to alfadriver:

Earnestly, is that a problem?

Like I said, it's my only frame of reference, and it's affecting other decisions (specifically, do I turbocharge or supercharge the M42 in the 2002?)...

ProDarwin wrote: Drive an STU prepped STi? I've driven a few, and they have power right now. The 2.0 STX WRX I used to codrive did have some lag, but I really didn't find it annoying - especially on the street. Autocrossing it, you just had to learn to put your foot down a second earlier.

What about the STU STi made the power instant?

As far as putting my foot down early and waiting for the power, it may be an effective technique, but when it comes to building a car I drive for the joy of the feel of driving (and maybe possibly a plastic trophy), that's really not a behavior I want... That's not how I want the car to feel.

crankwalk wrote: I absolutely hate superchargers on anything that doesn't displace at least 3.0 liters or more. Such a waste on a little motor. Turbo would be the way to go on a 924.

Come take a ride in my blown 1.8 Miata. Throttle response is right now , it pulls like a little locomotive until I shift at 6500, and it's putting something well north of 230 hp on the ground... On a stock bottom end. I don't see the "waste" you're referring to.

On another note, I've driven several stock WRXs while looking for purchases. I'm fairly underwhelmed by the driving experience. It was kind of fun to keep it simmering along on the open road, but anywhere that traffic exists, it's pretty annoying to fall outof boost all the time.

In reply to Duke:

It's nice to know I'm not crazy!

Coming from owning a M62 supercharged car, that blower will handle 21psi before bearing issues, granted you're talking about alot of heat at that point....but my car had a w2a intercooler setup. If packaging is the biggest issue for you, go s/c. It can always be changed later. If you're good with welding aluminum, you could probably remote mount the m62 and run a Vortech charge cooler box before the intake manifold.

Don't look at the amount of boost a supercharger can provide before failure, look at power output. Well, more accurately blower speed - but that's going to tied to power outlet. The amount of boost produced by an MP62 is going to depend on the relationship between the speed of the engine and the speed of the blower and the size of the engine. So 21 psi on a small engine is going to involve lower blower speeds than 21 psi on a big engine. The redline of the car will be a factor as well.

We used to see this on some of our supercharged twin-screw cars - the blower didn't really work well until it was at about 15 psi, but on our 2.0 engines that was enough to put the bearings at risk. We lost a few. 1.8 cars didn't have as many problems because the blower wasn't spinning as fast for the same 15 psi.

There are a lot of versions of it I suppose, the supercharged ecotec guys were actually maxing out the intercooling systems instead of bearing issues. ours were 1L on a 2L engine.

mad_machine wrote: And I would not call Superchargers "redneck" MB used them quite successfully for a long time

There are rednecks in Germany too. Just sayin'