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Comparison of turbo to supercharger

Ray said:
... a SC is RPM driven, making MAX HP at MAX RPM.
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Statements like this make it seem like an SC doesn't reach full boost levels until the top of the rpm range. Properly done a SC should be producing desired boost psi much ealier in the rev range. The same way a turbo will make desired boost at 3k rpm or earlier then bleed off the excess, a SC system does the same, doesn't it?
 
If you're talking about an eaton then yes, you will build boost instantly and in a linear fashion.

The vortech is centri. charger and builds boost in the upper RPM ranges, once it gets a'movin. In fact I think the vortech only builds boost at WOT too.... but I may have mis read that somewhere
 
with the Centrifugal, the "boost level" is based on the pulley size. it is rated at a certain psi at x rpm. If you aren't running that speed on the pulley, then you won't get that PSI. right?
 
The way I interpreted all the SC info I've come across, the centrifugal SC unit is essentially a belt driven turbo. Anything you do with a turbo, you can do with the centrifugal, I recon. Design the turbo by sizing your exhaust turbine & compressor to give desired psi at 3k rpm, or in the case of SC change the SC compressor and/or pulley to give desired psi at 3k rpm and in both cases bleed off the excess. Benefit to the SC is slightly less lag as it's belt driven.

Just because the Vortec kit produced a more linear power curve does not mean all SC kits will be designed like that. Frankly I think Vortec was being conservative in their compressor spec in order to minimize tuning requirements and maximize reliability of the whole car, not just their kit, and in doing so they sacrificed some power. A side benefit was keeping traction a little easier.
 
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BWHAAHAHAHAHA you just said "vortec" and "reliability" in the same sentence.


I'm just playin' man. I was just laughing because of the first release's near 100% failure rate. It doesn't have ANYTHING to do with the current kit, or planned kit.
 
umm yeah i dont like to go over 5 partially because my lights blink and it misses haha but normally dont go past 5 for daily driving because it eats gas and strains the engine
 
'scuse my noob question

whats wrong with (assuming before the maf) to just have the S/C make boost to a desired level and be vented to the atmosphere (again, before the maf) and maintain peak pressure without over boosting?
 
Nothings wrong with that but the more boost you pump out of a supercharger the faster it's spinning meaning it takes more power to drive it so you would essentially be wasting engine power down low to drive the supercharger. I'm not sure how much power these head units take to drive so it may be negligible.
 
Ray said:
BWHAAHAHAHAHA you just said "vortec" and "reliability" in the same sentence.


I'm just playin' man. I was just laughing because of the first release's near 100% failure rate. It doesn't have ANYTHING to do with the current kit, or planned kit.
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No harm done, it wasn't my design (was kinda funny 'cause I didn't quite feel right about it when I typed it. :laugh: ).
 
TourDeForce said:
Statements like this make it seem like an SC doesn't reach full boost levels until the top of the rpm range. Properly done a SC should be producing desired boost psi much ealier in the rev range. The same way a turbo will make desired boost at 3k rpm or earlier then bleed off the excess, a SC system does the same, doesn't it?
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Nope. A roots type blower builds boost in the screws and it comes out at high pressure even at low rpms. The centrifugal blower builds boost like a turbo in that it backs up in the engine and the turbo/cent-blower just pushes against it till the pressure rises so high it can't push any more (but that never happens on a vortech anyway).

The cent-blower suffers because the boost is rpm dependent and it doesn't build significant boost until late in the rpm range.

Look at all the vortec dyno graphs and you'll see that it really takes to about 5000rpm (engine) before the torque begins to rise significantly above a stock torque curve. That is when you are building 3-4psi. It continues to build boost till redline, usually about 7psi by 7000+rpm on the normal vortecs.

Then you have to consider how much torque is pulled off the engine by the rotating assembly anyway. It can be as much as 25HP lost at the top end.
So you've got to make 2-3psi just to break even when factoring the parasitic loads. However the vortech does a good job of making power with the boost it does make because it is cooler and pretty efficient. So you really want to tach the motor out to make the most of it.
You want to get that 7psi by say 6000rpm and you want to ride that motor to 7500rpm to really make peak HP numbers.
 
warmonger said:
Nope. A roots type blower builds boost in the screws and it comes out at high pressure even at low rpms. The centrifugal blower builds boost like a turbo in that it backs up in the engine and the turbo/cent-blower just pushes against it till the pressure rises so high it can't push any more (but that never happens on a vortech anyway).

The cent-blower suffers because the boost is rpm dependent and it doesn't build significant boost until late in the rpm range.

Look at all the vortec dyno graphs and you'll see that it really takes to about 5000rpm (engine) before the torque begins to rise significantly above a stock torque curve. That is when you are building 3-4psi. It continues to build boost till redline, usually about 7psi by 7000+rpm on the normal vortecs.

Then you have to consider how much torque is pulled off the engine by the rotating assembly anyway. It can be as much as 25HP lost at the top end.
So you've got to make 2-3psi just to break even when factoring the parasitic loads. However the vortech does a good job of making power with the boost it does make because it is cooler and pretty efficient. So you really want to tach the motor out to make the most of it.
You want to get that 7psi by say 6000rpm and you want to ride that motor to 7500rpm to really make peak HP numbers.
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So if I pick a larger SC blower I still can't make 7psi at 3k rpm?? I would think you can. Like I said, the Vortec is not all centrifugal superchargers. You can alter the blower specs to produce what you want, can't you??
 
TourDeForce said:
So if I pick a larger SC blower I still can't make 7psi at 3k rpm?? I would think you can. Like I said, the Vortec is not all centrifugal superchargers. You can alter the blower specs to produce what you want, can't you??
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Vortech only builds centrifugal superchargers.

And you can't alter the boost lvl's as you are saying. You can put a smaller diameter pulley which will in return build boost quicker, but will have more boost on top end.

The increase of the pulley and psi is different for each application. Then again it has to do with tubing and cfm from the housing itself. So if you get a larger supercharger, the turbine is huge. That will take it longer to produce power, which will only hurt your lower rpm range.

But overall yes you can get certain superchargers for specific applications. Vortech superchargers are meant for top end boost. Very little boost is created at low RPMS. That is why for low end boost, roots type blowers work great. Look at wars thread^^

As stated many times in this thread. It is belt driven. so the belt must spin that pulley enough times for the turbines to produce enough pressure. It will then help create enough pressure to fill the cylinders up with more air then it would in stock form.

We are trying to sqeeze in as much air as we can into those cylyinders before those valves close. At low rpms that supercharger is spinning very little. Too little to create enough pressure to gain much hp.

So there is very little u can do to a supecharger to change its rev's without hurting ur car up top aka blowing up the motor.
Too small of a pulley will build pressure sooner, but too much pressure in higher rpms can make car goo boom lol.
 
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Right!

And don't forget that the smaller that pulley you run into mechanical issues of belt-grip. Theoretically it's great to say a 1.5" pulley might spin the SC to some theoretical 50K rpm, but getting the grip with a standard rib belt when the actual surface area of the pulley touching the belt is getting smaller is another story. The force to turn the SC goes up as the rpm and boost climb making it like the belt will slip under heavy boost in higher rpms.

The only way might be an intermediate gear system off the main belt that consequently spins a larger SC drive pulley faster than what the main belt would have.
 
Another supercharger postivie is a possible carb cert for those in emissions states. I was searching vortechs site and this is what they say about carb certs:

icn_link.gif
Are Vortech supercharger systems emissions legal?
Unless otherwise noted, all Vortech supercharger systems are 50-state emission legal. The California Air Resource Exemption Number of each Vortech supercharger is stamped on the serial number identification tag. You can also check the Internet for the latest exemption numbers at http://www.arb.ca.gov/msprog/aftermk...es/devices.htm (after selecting this web site, select the device type "supercharger system").
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I'm sure the carb cert was intended for there original kit but how would a emissions tech now the difference between my kit and the orinial vortech kit unless they had seen one on a cougar before. I'd still recommend to pull it off as it only takes about 30min to an hour to unhook it all and put it back to stock.
 
Harrry said:
Vortech only builds centrifugal superchargers.

And you can't alter the boost lvl's as you are saying. You can put a smaller diameter pulley which will in return build boost quicker, but will have more boost on top end. lol.
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So you're sayin' that centrifugal SCs only come in one size? You can get different size turbo blowers, yes? Why not a SC unit?

Maybe you're suggesting that with 'x' pulley I won't get more boost no matter what size SC blower I have?

Are you guys also saying that a turbo spins at the same speed with the engine at 3k rpm as it does at 6k? I think not. The excess boost is just bypassed or blown off, I thought. My point is you should be able to do that with a SC as well.

Maybe I've got more reading to do, or I'm not explaining myself very well... Maybe both. :shrug:
 
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TourDeForce said:
So you're sayin' that centrifugal SCs only come in one size? You can get different size turbo blowers, yes? Why not a SC unit?

Maybe you're suggesting that with 'x' pulley I won't get more boost no matter what size SC blower I have?

Are you guys also saying that a turbo spins at the same speed with the engine at 3k rpm as it does at 6k? I think not. The excess boost is just bypassed or blown off, I thought. My point is you should be able to do that with a SC as well.

Maybe I've got more reading to do, or I'm not explaining myself very well... Maybe both. :shrug:
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NO.
The centrifugal superchargers need VERY big blowers because the bigger ones are more efficient and can move more at at low impeller speeds. This is when you look at a turbo map for the RPM numbers and try to size a compressor based on the theoretical RPM you can turn it at. You will see that only really big compressors can produce enough airflow at low impeller speeds(rpm) to satisfy the engine. e.g. T66 compressor.

Now a turbo spins the compressor a lot faster because it relies on the pressure and velocity of the hot gasses. It can spin many thousands of rpms at moderate amount of exhaust pressure. The more exhaust flow the faster the turbo spins, its just you can spin a turbine much much faster with the exhaust pressure than you can gear a Centrfugal blower to spin.
This gives you all kinds of options as far as sizing.

So assuming you want full boost by 3000K rpm then you size the turbine correctly to spin the required rpm that produces that level of boost out of the compressor. Then you just bypass the turbine with any excess exhaust not needed to maintain that turbine/compressor rpm.
So to answer you last question....YES. Optimally your turbo will spin close to the same rpm from 3000 to 6000 rpm because of proper exhaust housing size and proper wastegate operation. Now if you are using pressure to control the wategate then your turbine/compressor rpm will increase a bit to continue to supply enough air to maintain a constant boost pressure across the rpm range, but not a huge change like you find in a centrifugal supercharger.
This means your boost pressure is exactly constant at whatever level you were after, consequently your torque output of the motor is a flat because the cylinders are filled with all the air they need.
 
OK, got it. For some reason I get it in my head that this is a simple math problem. Seems to me there's a way around this with a large SC pully & some gearing. Paxton or Procharger does that I think.... Should reduce the overall rpm range of the blower vs engine speed, but provide more consistant boost levels across the rpm range.
 
The supercharger I used in this kit can push out more than enough air (800cfm) so you wouldn't have to ever worry about switching to a different blower. You only switch pullies to increase boost. With the way I have my kit setup I'm running a pulley stacked on a stock pulley so swapping that pulley for a smaller size will increase boost levels without having to switch to a tiny pulley on the supercharger which may cause belt grip issues.

You could setup a boost controller on a supercharger and bleed off the extra boost to keep the boost constant throughout most of the rev range. You would run a small pulley to get more boost down low and then bleed off the boost up top to a user set level. The only reason you may not want to do that is because you would essentially be wasting energy driving the supercharger harder at upper rpms because you are bleeding the extra boost off but the amount wasted needs to be determined. You could do it this way to get more tq down low.
 
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Excellent explanation. :cool:
Were I using a supercharger that is exactly how I would do it. Size the pulley to maintain the boost I want to reach by some specified RPM so I don't waste energy at higher rpms, and then use a ball and spring to bleed any excess if I can't handle more boost than that.
Blackcoog if your pulley system works as well as it sounds then your kit will be far more effective than the original Vortech kit! I really can't wait to see the results!
 
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