Supercharging Versus Turbo Charging

You know this gives me an idea. (Tim you out there?)

GRM should take a Miata do a base line test of an AX and a Drag strip

Then put a turbo on it (with IC). Set it for say 8PSI of boost. Take the car to a dyno and get a tune on it that is reasonable. What I call a street tune. And then take it to take a drag strip run and an AX run.

Then take the same car and put a supercharger with the same IC on it set it to 8PSI and repeat the tune and the tests

Have multiple drivers run the car with each setup up.

I would want the drivers opinion BEFORE they know the times. This is what I call the "fun factor"

And then again after they know the times.

With a little pre planing you could make the interchange from turbo to supercharger a bolt on deal so the swap could be made quickley so the tests would occur in similar weather conditions. May be have a portable dyno at the track so when you make the swap you can verify that things are proper before the runs.

Anyway it would be an interesting article to see the build options and then the results and here what the drivers think before thy know the times (But dyno results)

Also, anyone wanting to see how turbos can be superior to superchargers in an autocross situation just needs to ask DILYSIdave, or whatever his name is, about turbos and throttle response.

I am very happy with my supercharger, particularly the torque "curve". And the fact that it has an water-to-air intercooler makes it even better.

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

I would guess that this is not a sizing issue at all, but rather a cost issue. Two of the biggest things that will help a turbo spool quickly and with lower exhaust flow (ie: at lower rpm), is the type of bearing used, and whether it has variable vane geometry. An expensive turbo will have fancy bearings (ball bearing, etc), variable geometry, or both, but the cheap turbos that come on things like the WRX have journal bearings and static geometry because it's cheap.

No, it's sizing.

Everybody that owns one of the factory Suzuki turbo 3's complains about how small the turbo is, but nobody complains about lag. That's because they sized it correctly.

dean1484 wrote: You know this gives me an idea. (Tim you out there?) GRM should take a Miata do a base line test of an AX and a Drag strip Then put a turbo on it (with IC). Set it for say 8PSI of boost. Take the car to a dyno and get a tune on it that is reasonable. What I call a street tune. And then take it to take a drag strip run and an AX run. Then take the same car and put a supercharger with the same IC on it set it to 8PSI and repeat the tune and the tests Have multiple drivers run the car with each setup up. I would want the drivers opinion BEFORE they know the times. This is what I call the "fun factor" And then again after they know the times. With a little pre planing you could make the interchange from turbo to supercharger a bolt on deal so the swap could be made quickley so the tests would occur in similar weather conditions. May be have a portable dyno at the track so when you make the swap you can verify that things are proper before the runs. Anyway it would be an interesting article to see the build options and then the results and here what the drivers think before thy know the times (But dyno results)

I've actually done a similar test - Janel's 1.6 came with an M45 supercharger running at raised boost. I spent some time making it work as well as I could, then I swapped it out for a small turbo. Same engine management. No IC on the SC, but it would have been undriveable if it had one.

Boost was very similar - the "big boost kit" on the SC put out something like 8 psi on the gauge, and that's about where I ran the little GT2554 turbo. I forget the boost level on the super exactly, but it wasn't something I could control so I didn't pay much attention.

At the time, our autoxes were run at 8000' which exaggerates turbo lag. Janel immediately preferred the turbo on the autox course. She's by no means a hotshot autoxer, but she also doesn't have a lot of seat time in different cars to teach her to adapt to different engine types.

The dyno told a pretty compelling story. The dyno was at 5000', which delays the onset of full boost for the turbo somewhat, showing more advantage to the supercharger at low RPM. http://flyinmiata.com/tech/dyno_runs/M45_vs_VoodooII_1.6.pdf

Janel does miss the whine of the blower, though.

Here's where we get into implementation. That M45 is a little blower. On a 1.8, the differences would have been bigger as the "big boost kit" would mostly just mean more hot air. An MP62 on a custom intake manifold might have been a different story, particularly for driveability and certainly for power levels. I'm not anti-super, we use them on our NC kits because they suit the nature of the engine well. But that's on an intake manifold with an integrated A/W intercooler, not something you're going to cobble up at home easily.

A swap is not going to happen at the track. You're better off looking at the weather report and testing one day, swapping the next and returning the third.

Keith Tanner wrote: No IC on the SC, but it would have been undriveable if it had one.

How does having an intercooler on a supercharger setup (is it this supercharger setup in particular?) make a car undriveable?

Some day I'll get a handle on forced induction, but all too frequently it seems like the concerns that come up are out of left field...

In reply to ransom:

I think he means there would be too much torque/power and make the vehicle hard to drive from wheelspin. Less intake heat means more power, more compression of air (boost) means more heat.

Zomby Woof wrote: No, it's sizing. Everybody that owns one of the factory Suzuki turbo 3's complains about how small the turbo is, but nobody complains about lag. That's because they sized it correctly.

Agree.

Sizing as a science has advanced in the past 20 years.

Zomby Woof wrote: No, it's sizing. Everybody that owns one of the factory Suzuki turbo 3's complains about how small the turbo is, but nobody complains about lag. That's because they sized it correctly.

exactly.

FWIW, to follow up on what Zomby posts- there's a lot more in sizing a turbo than there is a supercharger. You have two fans to design, two housings, two inlets and outlets, and two different points of those two fans.

In addition to having the right map in a good dynamic range, you also have to make sure the extremes are not crossed- since turbo surge is not a good thing to deal with. And altitude is a major PITA, since turbos work on pressure ratio, so if you can get 2:1- then you can get 28psi at sea level, but more like 20psi in Denver.

One has to know the point of the project as well- a turbo for a pick up is WAAAY differen than one needed to do a 1/4mile.

But that's just being accurate for what you are making.

ransom wrote:

Keith Tanner wrote: No IC on the SC, but it would have been undriveable if it had one.

How does having an intercooler on a supercharger setup (is it *this* supercharger setup in particular?) make a car undriveable? Some day I'll get a handle on forced induction, but all too frequently it seems like the concerns that come up are out of left field...

On a supercharger, the throttle is before the supercharger. This means that any intercooler is part of the throttled volume. With the supercharger mounted separately from the intake manifold (ie, a "hot side" install on a Miata with the SC on the other side of the engine), you've got increased throttled volume. This means difficulty in getting the idle to behave, as the little idle speed controller can't cope. In particular, the engine speed will drop dramatically as the car tries to come to idle. Add the extra drag from the blower and it's even more exaggerated. The extra volume from an air/air IC makes this a lot worse.

Of course, you notice this idle droop as you drive around the city or in traffic. It's not a concern on the autox course (other than the tendency to stall as you come up to the line) or on the highway (until you hit the off-ramp). But it's annoying as hell. I was having enough trouble getting the car to drive properly without the IC. You'll find that a lot of cars with aftermarket superchargers on the hot side tend to run high idle to work around this.

A supercharger built into the intake manifold is a whole lot better, as the throttled volume can be kept down. On a turbo car, the throttle is in the factory location.

Why not put the throttle body post-SC? Partly because you would need a massive blow-off valve to dump pressure when you close the throttle, superchargers can't back-flow like a turbo can. I've actually seen someone blow an intercooler apart. Also, the noise levels have to be heard to be believed. They scream all the time. It sounds cool on a YouTube video but that's about it.

Note that I am discussing positive displacement superchargers here. Centrifugals are just like a turbo when it comes to throttle body placement.

Making a Miata with an M45 hard to drive due to excessive wheelspin. That's funny. Maybe if you used space savers for tires.

In reply to Keith Tanner:

Keith There are production set ups that have the throttle downstream of the blower. The SuperCoupe comes to mind right away- with blow off valve and everything.

There are trade offs with the blower before or after the throttle- it's how one wishes to deal with the problems each set up generates.

I also have an Eaton Bypass Valve to go along with my suppercharger.

Like this.

This is a must have if you are doing a "blow through" setup

Actually, they're kind of a "must have" regardless. They're actually built into a number of MP62s. They're not for blowoff purposes, they're to bypass the blower when you're operating in vacuum. I'm referring to the big pressure spike you get when you slam the throttle closed on a supercharger that's frantically pumping air into the intake system.

I seem to recall those Eaton parts having trouble when they see boost, the actuator is designed to see vacuum only (between throttle body and super). I've seen someone try to use them in a turbo application, and the actuators failed regularly.

Alfadriver, that's really interesting. I didn't know that. Every aftermarket attempt I've seen has ended poorly. A production setup would be able to deal with the noise thanks to a baffled airbox.

This is the replacement part used on many C230's

Very intresting discussion everyone!!!!

most intercooled S/C setups I have seen use water to air intercooling with the cooler part built into the intake so that it adds the least amount of air volume

My vote is to twin charge it.

dean1484 wrote: This is the replacement part used on many C230's

And a bunch of other applications. It's pretty generic. Is the C230 set up with the throttle downstream of the blower?

mad_machine wrote: most intercooled S/C setups I have seen use water to air intercooling with the cooler part built into the intake so that it adds the least amount of air volume

The Manic Miata has a cold-side SC with an air-to-air intercooler. The idle does droop a just little when you come to a stop, but just a touch. It will idle like a kitten at around 750 all day long.

Duke wrote:

mad_machine wrote: most intercooled S/C setups I have seen use water to air intercooling with the cooler part built into the intake so that it adds the least amount of air volume

The Manic Miata has a cold-side SC with an air-to-air intercooler. The idle does droop a just little when you come to a stop, but just a touch. It will idle like a kitten at around 750 all day long.

Several aftermarket superchargers available for Mustangs have both an air-to-water intercooler and utilize water cooling of the blower itself, as well.

mad_machine wrote: most intercooled S/C setups I have seen use water to air intercooling with the cooler part built into the intake so that it adds the least amount of air volume

That is the way mine is set up. It uses its own radiator, water pump and expansion tank. The SC is an Eaton M62 and it does have the vacuum bypass built-in. Then intake runners end up being ~1/2 the length of the ones in the stock NA manifold. You can see pics of the complete setup on page 14 here. Focus Powerworks SC Manual

Twin Charge it.

Keith Tanner wrote: Alfadriver, that's really interesting. I didn't know that. Every aftermarket attempt I've seen has ended poorly. A production setup would be able to deal with the noise thanks to a baffled airbox.

Doesn't surprise me- a lot of the solution depends on what you are doing. If you are an OEM, the decisions are a lot different than any aftermarket. And if you are Eaton making a kit for a Mustang, it's different than what FM will do, just for the market, let alone the resources available.

Where an OEM would come up with a fancy fix to make sure the response and driveability would be spot on, Eaton may choose something different, since they have deep pockets, but don't worry about driveability as much. And FM would choose something different with less resources and different view on driveability.

If I were to do another challenge, I've gone back and forth on the blower v. turbo set up. I know that my trade offs for a weekend would not even be close for the trade offs for a vehicle liftetime- so my solutions are different even IF I had the resources.

Realistically, there's almost no right answer. Just one that is right enough for the situation.

The correct answer is compound turbo setup.