Turbo vs Superchargers

I have a good question what is better a TURBO…or a SUPERCHARGER?

Define better.

My understanding is that a supercharger gives better performance at low rpm’s (good for off the line acceleration) and overall more power boost that a turbocharger.

I believe however that a supercharger puts more strain on the engine possibly causing failure and is more prone itself to breakdown.

I’m sure some of the local gearheads will be along to correct me if I’m off base here.

Supercharger adds significantly more horsepower.

The primary difference between the two: Supercharger is belt driven and turbocharger is powered by outgoing exhaust.

The similarity: Both devices are used to cool the intake air so that the air expands faster in the combustion chamber.

I concur w/ zoid , who simul-posted with me.

Superchargers tend to fail more often, but are however easier to replace once they have failed.

AFAIK, neither device does any cooling of the intake unless there is an “intercooler” present.

What they BOTH do is take big fistfuls of air and ram it down the engine’s throat (basically, they pressurize the intake system). The difference is in how they do it…

A supercharger is a mechanically-driven device…it’s “slaved” off the engine mechanically, usually by some kind of belt drive (there are different types). The advantage is that the power boost is immediately available off-idle. The disadvantage is that it takes power to actually turn the mechanism itself, so there’s some parasitic power loss.

Turbos are spun by the outgoing exhaust. The driving force is essentially “free”. They take some time to spool up, though, so the power is not immediately available (this is what’s referred to as “turbo lag” or “boost lag”). Since the actual compression ratio of a turbocharged engine is often lower than a non-boosted engine, this means that turbocharged engines can suffer from a lack of performance at low RPMs. Not always, but typically.

As to which produces more power, there’s a lot of variables to be considered. It’s entirely possible that a turbocharged engine would produce more power that an identically-sized supercharged engine, depending on the amount of boost the turbo was supplying.

I believe you are mistaken. An INTERCOOLER cools the incoming air, making it denser, providing more oxygen for combustion in the same volume of air.

Turbos and superchargers force air into the engine at higher than ambient air pressure. They do not cool the incoming air. So instead of the engine sucking in air, the turbo or supercharger is forcing air into the engine. Blowing rather than sucking. Which is why you’ll often hear a supercharger referred to as a “blower”.

As an aside, I have a turbocharged Nissan 300ZX. There’s a boost gauge on there that shows whether the engine is “blowing” or “sucking”. The gauge goes up to a positive 7 psi, although I don’t think it’s ever been above +6 psi, all the way down to a negative 7 psi. I’m not sure if this is measured relative to ambient air pressure or measured absolutely. Does anyone know?

One thing I’m not sure of is with which you’ll get more horsepower. If I recall correctly, most race cars, I’m pretty sure about Indy cars anyways, use turbos rather than superchargers. Someone with more expertise will be along shortly to give a defenite answer though.

Nice simulpost Cow!

Short answer: It depends.

First of all, there is some terminology that needs to be worked out. A “supercharger” is a device for forcing air into an engine. Superchargers usually come in two forms: Exhaust driven, and mechanical.

The exhaust driven supercharger drives its compressor with a turbine wheel mounted in the engine exhaust stream. It’s a turbo-supercharger, usually shortened to just turbocharger.

A mechanical supercharger can be belt or gear driven, directly off the engine.

There are several advantages and disadvantages to each:
[li]The turbocharger can produce varied boost levels independent of engine RPM, its boost is regulated by a valve which diverts exhaust gas past the turbine wheel.[/li][li]The turbocharger has to spool up, resulting in a short lag in boost pressure. The mechanical supercharger doesn’t have this.[/li][li]The mechanical supercharger uses some engine power to generate boost. The turbocharger usually takes a little less, as SOME of the energy is uses would have just been wasted anyway, BUT[/li][li]It’s a lot harder to have an effective tuned exhaust system with a turbocharger. You can get some serious gains with a tuned exhaust system.[/li][li]A mechanical supercharger tends to heat the air less. While both systems heat the intake charge due to compression, the turbo unit itself runs hotter to begin with.[/li][li]The mechanical supercharger is usually easier to implement. A turbo requires a custom exhaust as well as intake system. Plus, it requires a wastegate to divert the exhaust gas, plus various controllers. Turbochargers are also more likely to be intercooled.[/li][/ul]
I’m sure there’s more, that’s just a list off the top of my head.

Neither method is better than the other. It simply depends on the application.

The more operative question is: What are the vehicle variables to consider when deciding on whether to install a TC or a SC?

Both are superchargers. And both are used in all applications. For example, the WWII Republic P-47 had a turbo driven supercharger while the North American P-51 used a mechanically driven one. Both were high altitude fighters.

AdmiralQ: If you are reading negative psi it will be relative to ambeint pressure. If it was absolute 0psi would be a perfect vacuum.

A turbo is driven by the exhaust gas leaving the engine. It does require engine power to drive it it is just harder to measure the a supercharger. The exhaust impeller of the turbo creates a restriction in the exhaust and will cause backpressure to increase (the amount of pressure in the exhaust manifold). The pistions have to force the exhaust out under that pressure which requires horsepower. A turbo will have some lag between when the go pedal is pushed and when it starts building boost. They are getting better with the vairiable geometry turbos but still not as good as a supercharger. Depending on apllication turbos will be equiped with a wastegate that allows exhaust to by pass the impeller to prevent to much boost being generated.

A supercharger is belt driven. I don’t work with superchargers so I don’t know much about them. They don’t have the lag that a turbo has but have to be designed not to allow an overboost condition at high rpms.

They both heat the incomming air since they are compressing it. From what I have seen superchargers are normally used when they want a torque increas for better off the line acceleration while turbo chargers are used if you want a power increase in the higher rpm range of the engine

Yes, they are both superchargers, as I pointed out in my post. However, just because both are used in all applications doesn’t mean one isn’t better suited for a particular application than the other.

For instance, you pointed out that some aircraft use turbos, and others use mechanical superchargers. With a mechanical supercharger, you start having problems with running out of boost at high altitudes, which of course led to two-speed superchargers and the like. But with a turbo, you can vary the boost independent of the RPM. The turbo nowadays is (arguably) the better system for aircraft.

Besides, have you ever seen a normalizing system for aircraft that was mechanically driven? I never have. Turbo-normalizing is very popular, though.

On the other hand, a drag car needs a lot of boost right away, with no lag. You see a lot more of those with mechanical superchargers, although there is no reason you couldn’t use a turbo.

The OP asked which was better. The answer depends on what you’re trying to accomplish.

Hey, I’m not arguing with you or crictizing in any way.

Just the same, I’m not sure that the boost available in a turbo system is entirely independent of engine rpm. At low rpm less exhaust mass/sec is being discharged. Doesn’t that mean less energy is available to drive the turbo?

I understand, sorry about that. I thought I might have been unclear in my first post. :slight_smile:

Yessir, you are correct, of course. I didn’t mention it because I thought it might be getting a little too in-depth. I typed up a lot of stuff, but I felt like I was going on and on about it.

P.S. When I go back and look at my posts later, they always read to me as being snarky. Purely unintentional.

Which brings up an interesting aspect of this discussion, and maybe a slight hijack…

The aircraft applications mentioned are not really meant to INCREASE power, but to MAINTAIN power in the presence of decreased atmospheric pressure (high altitude = lower pressure). Not that that invalidates anything posted here, it’s just interesting. Just another application of some pretty cool technology.

It’s fairly amazing how cheap and small this stuff has gotten. Okay, so I’m old…but I remember Roots-type blowers that stuck up out of the hoods of funny cars and were a defining feature of Top Fuel dragsters…and now, I find that I can purchase an entire Roots-type blower kit that fits under the hood of my S-10. Ain’t technology wunnerful.

Along the same lines, there are now two-stage turbo systems designed to address the lag problems. Along with lighter components (less mass = less time to spool up), the usual lag is becoming negligible. See also, Volvo’s “low pressure turbo”.

There’s some pretty good turbo information on HowStuffWorks.com (I’d provide the link, but I’m on a slow dial-up and I’m appallingly lazy).

Are there DIY supercharger kits for many types of street cars? Could someone with a basic knowledge of cars and a little help install one himself? What would the dangers be?

There are quite a few that provide boost above standard pressure, too. I occasionally get some time in a Cessna 404, which has a manifold pressure redline of 42 in/Hg. That’s a fair amount of boost over ambient, and results in 350hp per side.

In school, we were taught some slightly different airplane terminology for forced-induction systems:

Supercharger: Any device which boosts manifold pressure over 30 in/Hg.
Turbo-supercharger: Turbine-driven supercharger
Turbocharger: turbine driven system to maintain 30 in/Hg up to a critical altitude. An engine equipped with one of these would be considered turbo-normalized.

Now, these definitions don’t exactly jive with what I hear outside of school. I suspect they are outdated.

Yes, there are several companies that make bolt-on supercharging systems, such as Vortech and Paxton. The kits I’ve seen were relatively straightforward to install. The main risk is overboosting, which could result in detonation and a destroyed engine. Most of the bolt-on kits are pretty well thought out, though.

Cardinal, I helped a buddy of mine put a supercharger on his truck. It was pretty straightforward. If I remember correctly, it basically involved bolting on another pulley on the front of the engine tor drive the supercharger, removing the existing air intake assembly, bolting the supercharger on the included mounting brackets, attaching the supplied intake assembly, then putting the belt on. Plus lots of little things I don’t remember right now. It took us the better part of a day, but most of this time was spent trying to get our hands in tight places. Of course we found a way to screw it up though…but it involved the higher pressure fuel pump that came with the supercharger (we installed it backwards!). We took it to a shop, they had it fixed in about 15 minutes. The kit my buddy bought was about $3000 or so. Check out www.superchargersonline.com if you want to know more.