First, I'm comfortable with the specifics of forced induction, especially turbos (I've got a friend a Supra and nother with a Nissan 300ZX TT). After I got done doing the pulley mod, they were interested in how superchargers worked -- and they asked me a lot of questions. While I could explain how it worked off the crankshafts drive belt to compress air and build boost, there were some things I couldn't explain....

-- I was told the reason why its a 15% reduction pulley is: at the redline of the car, the supercharger, with the smaller pulley, is also spinning at its redline (near 18K) . But I thought SC's are always supposed to produce a conisistant amount of boost, hence why they don't have the notorious turbo lag especially present with larger turbos. So, how can the SC produce a consistant amount of boost at varying RPMS, dispite the change in speed of the crankshaft?

Can someone please explain the theroy behind the supercharger or point me to a good website. I really want to know this a little better.

Thanks,
Erik

 

SCs produce increasing boost up to max rotation speed, similar to turbos. It's just that SCs don't have to wait for exhaust gases to build enough pressure to spool them up like turbos do.
this site or this site may help.
BTW, the MCS has an Eaton SC, similar to the M45 design.
_________________
[img]albums/album25/ama.gif[/img]VinceAndJessica.com
Alta pulley, Stebro exhaust, Pipercross intake, Progress rear anti-sway bar.

 

In a previous post (worth a look)
RandyBMC wrote:
The supercharger is a compressor that is turned by a belt from the crank on the engine. As the belt turns, the compressor blades are turned and compress the intake charge - providing a "boosted" intake charge. This is commonly referred to as forced induction (turbos are another way of forcing induction using exhaust gasses rather than a crank belt). The smaller the pulley on the supercharger, the faster it turns relative to the crank pulley. If you spin the supercharger faster, the blades spin faster, and the intake charge is compressed more, providing more boost. The more boost you make, the more horsepower the motor makes. That's the reason people are doing the "pulley".

see
https://www.northamericanmotoring.co...amp;topic=8885

I got this by searching for "supercharger" with author RandyBMC.
There are tons of very good posts in the past. Took me about 2 months to go through a bunch of them before I made my first ever post.

 

To add to minihune's statement just incase you didnt know, not trying to make you look dumb.

If the air is denser then more air gets into the engine which requires more feul (14:1 ratio a/f) which creates more sparks which means more power.

That is way oversimplified but I think it's right.

 

THe supercharger pulley is driven off of a belt from the engine. So, yes, the supercharger is always working and always providing at least SOME boost. HOWEVER, the higher the RPMs, the higher the boost. That's why the MCS, even with the pulley reduction which adds good low-end torque, is still at its best at high RPMs. A supercharger is still better than a turbo at low RPMs b/c it is providing SOME boost while a turbo provides NONE. A turbo provides no boost whatsoever until you hit a certain RPM level say 3000 or 3500. THen a turbo is spooled up by the exhaust gases and provides boost rapidly. SO you go from no boost to a very fast buildup of high boost. Hence the reason turbos "lag" and then take off. Zero boost to lots of boost. Also, if you're not at WOT or close to it in a turbo, there aren't a lot of exhaust gases (from less fuel being burned) so there isn't a lot of boost. WHereas in the supercharger, again the boost is dependent on the engine RPMs so there is always a lot of boost at higher RPMs - even if there is very little throttle. This also makes it a bit more responsive at higher speeds and RPMs also if you're going from partial throttle to full throttle. Hope that helps!

 

>>If the air is denser then more air gets into the engine which requires more feul (14:1 ratio a/f) which creates more sparks which means more power.

more fuel creates more sparks, eh?
Don't the spark plugs create the spark and the fuel is ignited by the spark? Sorry, had to pick.

 

ha ha, thats what I meant orbhot!

 

I have a coworker who has a turbo Lotus Esprit. He says he has to manage it when he is in the corners. If he doesn't watch out the turbo will kick in and start the rear wheel spinning!!

 

Some people should read this book:

http://www.bentleypublishers.com/pro...amp;subject=24

 

Umm. The blower is not a compressor, despite what mercedes (Kompressor) or randy wants you to believe. There is NO compression that occurs inside the blower. Eaton makes positive displacement blowers, and thats what it does, displaces air.

--
Cheese

 

A supercharger displaces free air when is pulls a certain amount of air at a given RPM and pushes it back out into free air. If you take a cubic foot of free air from the inlet of the supercharger and force it in a combustion chamber thats a 1/4 of a cubic foot, THATS COMPRESSSION!.

The MINI is 1.6 liters. For a 4 cycle engine, for every 2 revolutions, the intake
sucks in 1.6 liters of air. If you stick a supercharger in the inlet, you know through the ratio that it spins more than the engine RPM how much additional volume your going to send through the engrine (boost pressure). This is a constant. As the engine RPM increases so does the amount of air that it has to draw. The engine is really a positive displacement pump.

A turbo charger is not driven directly off of the engine. As engine RPM goes up, the amount of exhaust gas increases, driving the turbo charger faster, creating more boost until the pop off valve opens, letting the excess air vent to atmosphere. At low RPM, there isn't enough air flow to spin the turbo very fast (thats known as turbo lag).

The supercharger is more linear in control and response, but consumes more HP to operate. Dragsters and funny cars use superchargers because they need the power right now and have the HP to give.

 

>>Umm. The blower is not a compressor, despite what mercedes (Kompressor) or randy wants you to believe. There is NO compression that occurs inside the blower. Eaton makes positive displacement blowers, and thats what it does, displaces air.
>>
>>--
>>Cheese
>>


yeah this is what I thought too. but, I guess the main difference between a positive displacement blowers, centrifugal blowers, and turbos is where the compression of the air actually takes place.

Here's some good articles on the different types of forced induction components out there....

http://www.superchargersonline.com/content.asp?id=22
http://www.motorsportsdigest.com/forced1.htm
http://www.motorsportsdigest.com/forced2.htm
http://www.motorsportsdigest.com/forced3.htm

 

I hate to be picky, . . . but . . . . .
Turbos DO create significant boost at low rpm's In fact, this is what they're known for. Have you ever seen a supercharged deisel? (I haven't, but I have heard of it) Have you ever seen a turbo charged deisel (I see them all the time). Don't most deisels red line in the neighborhood of 3,500 rpm?
The only thing a turbo needs to spool up is exhaust back pressure. It does not need high rpm's
If you have an opportunity to drive a VW 1.8T, get the rpm's real low (around 1,500) and floor it! You can hear the turbo start screaming, and then you feel the boost. All before the tach gets anywhere near 2,000.

Just my $0.02

 

You can size a turbo to work well in any RPM window you'd like.... just dont make it too wide. Most CI engines dont have a high redlines. CI engines have a lot more junk in the CC than SI engines. The CR in a diesel is ~22:1 compared to the 8:1 in the S.

--
Cheese

 

True,
You can also design a supercharger to work well in any RPM window you'd like.
But turbos are inherently less efficient at higher rpm's due to increased exhaust restrictions.
Also, efficieny and effectiveness of a forced induction system is not dependant on the method of ignition. (CI or SI)
Compression ratio is a whole other can of worms. But irrelevant to this discussion.

 

>>I hate to be picky, . . . but . . . . .
>>Turbos DO create significant boost at low rpm's In fact, this is what they're known for. Have you ever seen a supercharged deisel? (I haven't, but I have heard of it) Have you ever seen a turbo charged deisel (I see them all the time). Don't most deisels red line in the neighborhood of 3,500 rpm?
>>The only thing a turbo needs to spool up is exhaust back pressure. It does not need high rpm's
>>If you have an opportunity to drive a VW 1.8T, get the rpm's real low (around 1,500) and floor it! You can hear the turbo start screaming, and then you feel the boost. All before the tach gets anywhere near 2,000.
>>
>>Just my $0.02
>>


Yes, obviously, this is true. This is also the logic behind TWIN turbos. One smaller turbo that spools up quickly for low RPM power but low overall boost and a larger turbo for higher RPM with lots of overall boost. Most cars, however, have one turbo and it takes until 3000 RPM usually to get enough exhaust gases to start building boost.

 

I'm sorry that I can't convince any of you guys. I've often found it difficult to do so on forums like these. Rather than argue eternally about such a subject, I will just reitterate my original point.
Without comparing turbos to turbo, or SC's to SC's. My point is that turbos are less efficient at higher RPMs than SC's. period.

You guys can make arguments about CR's spark methods, number and size of turbos, etc. etc. etc. No of this argues my original point.

I suggest you do some technical research on the subject. Not just rely on general knowledge that you've learned throughout the years.

Of course, what the hell would I know. I'm only an engineer.

Best regards,
"The Bean"

 

I don't know if anyone is disagreeing with you on this point. I know I'm not. But as
I reread your posts, it seems that the point you were trying to make is that turbos are well known for making significant boost at low RPMs. And in MOST (but not all) cases, this isn't the case.