RaverRacerX

could always use the best of both worlds and do a rotrex setup=)

vwdave

I doubt you'll run across it, but find a G60 Corrado with a Bahn Brennar Lyshom supercharger. My best friend and I have 5 VW's between us. 2 are swap cars, 3 are SC/Turbo. So, we got a broad range. Anyways......

That car makes 20psi of boost. It fricken HOWLS. It sounds like a old fire engine. I will try to get audio at some point.

84CamaroSS

So what your saying is just to stick with the procharger P1SC. Actually looked at the STS turbo and was interested but i would still want a flowmaster o nit so you cant hear that turbo whine.

87CIZ

iTrader: (8)

i think about every person running a RMT isn't running any kind of muffler. I could be mistaken though...

and this is hilarious talking about i know a guy who, no you dont you just think you know and that "knowing someone" justifies that. I bought a radiator from Kenwood does that mean I know everything i need to know about building my turbo engine?

79vette

As far as if TurboTPI is lying about his numbers, I Have personally witnessed his car do 10's at the Track and have looked closely under his hood. All his claims are true.

I myself Had built a single turbo 350 and have had good results with it running a very tame cam.

As far as you wanting to use a flowmaster after the RMT, I wouldnt reccomend it. Flowmasters are not the best choice because they dont flow as well as other mufflers out there that do a better job quieting things down. Hooker aerochambers come to my mind.

dsw12387

In case you haven't noticed most high horsepower, street driven cars are turbos

TurboedTPI

Thanks man. I havent talked to you since that day at the track, hows your car doing?

383backinblack

there are tons of people making that much power, and more with single centrifugal blowers......on engines smaller than 400ci

like has already been said this argument is nothing more than a pissing contest.

as for the superchargers being a "package deal" the fact that they come in a "kit" doesnt mean anything......i've had to fabricate more parts for my car than i can even remember......although if you're using a street oriented kit they're not as bad pretty bolt on and go in comparison.

once you get to the stage where its time to make big power, no matter what method you use you're not going to save any money anyplace, and you're going to have to build just about everything from scratch.......believe me.

TurboedTPI

I agree 100%.

Orr89RocZ

iTrader: (20)

what do you guys consider big power? i call that about 650whp and up. maybe even 700+whp

383backinblack

in the 800-1000 hp range.......running deep into the 9s

79vette

After grenading my stock bottom end sbc with the turbo, only because of my mechanical advance got unlocked, I got a hell of a deal on a 496 shortblock. So For now I am going to put the turbo sbc on hold and run with a N/A bigblock with maybe a little spray. I will go back to playing with turbo's again the future.

TurboedTPI

Cool. I'll be looking for you at the next RSD's this summer. I'll check out the car. Good luck.

rmmstnr

It annoys me how people often people go on about how "dem roots things only be puttin out 50% efficiency" when repeated tests hve shown that properly done setups can reach efficiency ratings of up to 90%. just like with turbos, a blower must be designed to work with the engine and tune setup, otherwise also like a turbo, you will have an inefficient setup that doesn't work to your needs. blower sizes and drives must be setup correctly with your engine and desired results and are quite often much cheaper, easier, and less time consuming to employ.

to further increase efficiency by keeping the unit free of the engine's heat, somebody could make a carbon-fiber, phenolic or whatever material spacer to insulate the supercharger from the intake. a design could also be incorperated into the spacer to reduce the turbulence found in the intake caused by the design of the roots supercharger to increase efficiency by an even greater margin

while twin turbos are an incredible way to achieve high hp #'s and still get relatively good gas mileage, nobody seems to take into an account that there are two units, and that this on it's own is a big advantage (two smaller units waste less energy than one big one), one I'd like to see on a procharger setup. are there any dual procharger vids or stats out there? I honestly don't know, but it can't be a new idea, and I just know it's been done

in closing: I'm not a supercharger or turbo zealot, I just thought superchargers could use some support here. this was targeted towards nobody and is simply in hopes that people will agree that different power adders work best for different applications or different methods

D's89IROCZ

I don't know about the rest of you , but I would like to see a 90 % efficiency roots setup please

Orr89RocZ

iTrader: (20)

those kenne bell twin screw blowers with the water cooler are pretty efficient but i dont know the rating on them

vwdave

I must admit, that would be interesting.

JoBy

Those have high efficiency, but they are not roots blowers.

JoBy

Why do you think two smaller turbos are more efficient than one big one? The fact is that one big unit is more efficient than two smaller ones.

There are a few resons for using twins. It might be easier to place two small units than one big unit. You get a shorter more efficient exhaust header.

I know that there ar a few twin centrifugal supercharger builds.
Why would you do that?
1) One supercharger does not flow enough air to feed the engine.
You can use two superchargers and plumb them parallel.
They can now supply twice as much air, but the boost will be the same.

2) You want more boost.
You can plumb them in series to multiply boost. Two 8psi units will give you 19 psi in series. 8 psi boost = 1.5 pressure ratio. 1.5 * 1.5 = 2.25 pressure ratio = 19 psi boost. They will not be able to supply any more air then a single unit.

383backinblack

there's no reason to plumb a blower in series, because boost pressure is basically meaningless.......its only useful to tell you at what efficiency the individual system is running on a given engine.

boost is only a measure of pressure (restriction) and has nothing to do with airflow, so if you're not creating more airflow you will not make any more power regardless of pressure. Although, to be fair you may have just wrote that incorrectly, due to the fact that unless the motor is at maximum capacity due to camshaft or head restrictions (which is almost impossible) increasing the pressure WILL cause a net increase in volume at the combustion chamber, as more air will be able to enter the chamber in the same time period due to the increased pressure.

that being said, pressure and volume(flow) are independant of each other........my blower will flow 2000cfm at max output......thats enough to feed about 1300hp. on my motor, that might come close to 30psi of boost.

however on a well prepped big block (like a 540ci) it might only make 15psi (guess) but its still flowing the same air.

so aiming to only increase pressure would be pointless when you can have the same pressure, but increase the flow.....which would also eliminate a massive amount of heat, over double compressing the aircharge. Like i said before though, unless you are at the point where you NEED that pressure in order to force the engine to accept the airflow

BUT if you're at that point, its almost pointless to go that route.....you should get bigger heads and a bigger cam lol.........

the main reason for using 2 blowers, is if there isn't one blower that flows enough air (unlikely) or for show/cool factor reasons.......or if for some reason you believe that it would be more efficient, which might be true, as 2 blowers spinning at a lower RPM would provide more air at the same engine rpm as one blower........but more drag, etc etc etc.

its a never ending process, which only serves to reinforce the point that nothing is free......especially horsepower, you ahve to give something to get something......which is something that turbo guys forget all the time, with their "yo free horsEpOWerZ yO!"

turbos cost power just like a blower........the problem is because they're exhaust driven its nearly impossible to quantify how much power it takes to turn the turbo wheel, because it costs power by exhaust restriction not by direct drag on the engine.......a blower can be dynoed and measured to find out how much power it takes to turn it.

i love how the turbo guys always try and pass it off like turbo's don't cost anymore power.....they might be more efficient, they might not.......but they have their applications, just like blowers do.

Orr89RocZ

iTrader: (20)

i thought thats what a roots blower was? it has the screw like blades that mount over where the intake sits that suck air in, compress it and force it thru, just like a 6-71 or little weiland 144. Maybe i have it wrong?

JoBy

They may look similar on the outside.

This is good reading:
http://www.superchargersonline.com/content.asp?ID=76

JoBy

Are you saying that boost pressure is meaningless? Then why use a supercharger in the first place?

On a given engine boost has everything to do with airflow. You might have a small engine that is built to handle more boost than a single centrifugal supercharger can give you. The supercharger might be able to deliver a lot more air flow then the engine uses at this boost level. Then it makes senese to plumb two superchargers in series. The higher boost will force more air into the engine and result in more power.

Using the same supercharger on a huge engine it might not be able to flow enough air to make any boost. In this case it makes sense to add another supercharger in parallel to provide more air and build boost to make more power.

With a properly sized centrifugal supercharger boost is a function of impeller speed. If you have a supercharger that makes 30psi on one engine then bolts it to another engine (same pulleys) and you only get 15 psi, then the supercharger is way too small for the second engine. If it was big enough it would still make 30psi and force a lot more air into the second engine.

On a displacement supercharger, like the roots blower, your statement would be true. The roots blower would force the same amount of air into the engine. The bigger engine has less restriction and you get less boost.

How do you get more air without more boost without modifying the engine?

I agree to that.

To get more air into the engine you need more boost.
Depeding on the limiting facor you should plump them in series or parallel.
In both cases you could increase boost at a lower supercharger rpm.

383backinblack

comparing boost pressure on 2 different systems is meaningless......as in, a dual supercharger system, vs. a single.....because you could have 200psi, but only be flowing 5cfm......thats why boost pressure is irrelevant, its only talked about so much because its a covenient number thats easily measured and monitored........flow/volume isnt as easy......pressure IS meaningless......pressure is not what produces power, airflow is........the increased VOLUME of air, which is INDEPENDANT of pressure, by the equation

PV= NrT, where P pressure, v = volume, and N is the gas constant, T is temperature etc.

im pretty sure i said that......however i disagree with series linked blowers......i've ONLY seen that done with a roots blower, and it was for show.....as it stuck up well above the roofline of the car. like i said before, boost is irrelevant, volume of air is important.......are they related? yes, but they are independant and ONLY related in context of the individual system in question......putting 2 blowers in series, would heat the air well over 300 degrees, you'd need some seriosly efficient cooling to handle that. with a single blower, mine gets the air close to that hot........that heat would well outweight the benefit.

placing 2 centrifugal blowers in series would likely cause a restriction for the first blower as well, creating even more heat........theres no way you will find an engine that you can't get a centrifugal big enough for.......like i said, mine isn't even close to the biggest and it will support over 1300hp

please show me some fact of this actually happening because i haven't seen anyone do it

no, it makes sense to use a larger supercharger. and regardless, we're still talking about volume......it takes a given volume of air to burn a given volume of fuel and make a given amount of power...........if you have the air, you have the power........pressure is not a factor.......as pressure is a measure of restriction in the intake tract not flow.


boost is a function of the impeller speed, impeller design, and the engine thats in front of it......an engine that swallows x amount of air will see xpsi of boost with a given blower, now if you take a bigger engine that swallows 2x amount of air, you will see less boost......REGARDLESS of the size of the blower or what flow its capable of, because there is less restriction.



my statement is true, the engine does NOT care what type of blower it is.....its a compressor, thats it.......its forcing air into the engine the same rules hold true......the only difference between supercharger types is the method they use to compress air, thats it. It has no effect of any kind on how the engine produces boost.......the engine is not concerned in any way with whats in front of the carb/throttle body.


no you dont NEED more boost, you need more air.....boost is a byproduct of airflow into a restriction.......once again.

I've worked with roots blown alcohol big block chevys, and centrifugals.......they're vastly different, but they do the same task

Drac0nic

Lets start here. Boost pressure is not meaningless. I've never seen a Supercharger or a turbocharger flow chart that didn't mention the pressure. To evaluate the efficiency of the blower of turbo accurately you must know the pressure it will be operating at.

Most people don't run gasoline engines to a pressure ratio sufficient to require sequential turbos or superchargers. If they do it's for throttle response reasons usually, however it's not common due to the added complexity and expense.
If you start talking diesel it becomes far more common to run sequential turbochargers or twin-charged setups (turbo/super) due to running significnatly higher pressure ratios with a higher degree of efficiency. Some tractor pullers run HUNDREDS of pounds of boost and 4 or 5 stages, even though it's usually turbos.

Sure it would create some intake tract restriction to have a second blower on the line, however nothing more significant then if the blower were placed on the engine as-is. While I tend to agree, there's a BIG difference between it being viable and it being possible. Where you start to get real benefits is by having a configuration that uses two different types of supercharger like a centrifugal/roots or a turbo/roots that come on in different RPM ranges. This is especially true with turbos that are dependent on exhaust gas volume for spooling.

383backinblack

fairly sure i qualified that statement, on more than several instances throughout that post.....which i also did in the next statement you responded to.

ya, for example the new ford powerstroke......biturbo......takes care of spooling issues quite nicely.

tractor pullers are smart, friendly people......you should get to know some, they're fun to drink with.


im pretty sure they did that on old detroit diesels in buses and what not, waaaay back in the day.

rmmstnr

hmmm, I'm really liking these posts.

but, in responce to putting superchargers in series, this seems like a very inefficient setup depending on how the sizes of the superchargers are staggered, and I doubt it would be of any use when you can go parallel, which is what I was referring to. it is much simpler to get parallel superchargers set up right and I doubt any series setup could match it.

as for the dispute of multiple smaller units v. one bigger, the multiple smaller units win in a cross-reference with less overall rotating mass/inertia, and of course, less generated temperature from the lower turning speed of each unit.

ex1- a bigger unit that is overdriven to flow the same amount of air as multiple smaller units will generate more heat, the hotter charge will be less dense, and will develop less power due to less oxygen per volumetric unit of air.

ex2- a larger unit that is big enough to flow the same amount of air as multiple smaller units but is big enough to do it without being significantly overdriven or overdriven at all will have more rotating mass/inertia that will lower it's efficiency overall, but especially at lower engine speeds. here is a graph of roots blower efficiency at different speeds and boost levels


the rules of scale govern this- area increases with the square of size (area that can be used as sealing points along the rotors), but volume increases with the cube of overall size (volume of metal that comprises the rotors and gears, etc). simply put, the ratio of weight/mass/inertia to output is far superior in a system that utilizes the multiple units (helped by the fact that there are twice or even more sets of rotors/sets of sealing surface). scale can also be applied to centrifugal superchargers and turbos

plus, the bigger design that spins slower will be more subject to air/pressure leakage between the rotors both because of it's larger size, the rotor-to-wall clearance issues with larger units (smaller units are very often made to smaller clearences), and simply because it is spinning so slow, giving air/pressure more time to escape (not much of a problem on smaller units, especially those with the teflon and nitrile sealing strips).

however, both designs can be messed up if not sized or driven correctly, so one good design will obviously outdo a bad one, no matter what data is present above. at equal quality set-ups, both unit groups will be governed by the data stated above, although in many cases practicality will outdo or rule out some of this (why pay for 2 units on a street car? high-end racers will benefit more than a street car from this)

now we come to the boost v. airflow war. starting at the basics, superchargers were initially designed to overcome engine airflow limitations by creating boost, or false atmosphere (bare with me now, the answers are coming). the higher level of air pressure allows air to enter a combustion chamber quicker, and of course lets more in than atmospheric pressure without backflow (naturally aspirated cars can do this as well when taking advantage of Helmholtz resonance, but that's a different topic).

while boost isn't meaningless, airflow is indeed what is trying to be accomplished with superchargers, boost is just the tool. boost creates more airflow due to higher pressure, as you can only flow so much air into a given engine naturally aspirated. more airflow into the engine=more oxygen=more power (when coupled with more fuel).

lastly, more efficiency talk. roots and screw type superchargers have the potential to be very efficient, usually with the more expensive screw design ahead by a fair bit. as a general guide, their golden area is the lower boost and speed area, as shown in thye graph up above (no exact points, just in general). despite that, their good points have been put to used in spots greatly contrasting those regions if the need for their particular benefits was needed enough (high speed drag racing).

centrifugal superchargers and turbos are the opposite due to their design, working well in very high speed areas generating very high boost. I wish I had an efficiency graph to give everybody a general overview of this, but I don't know where one is, and I am a bit too tired to even attempt to make one. hence the uses of the word "general" in my last descriptions.

JoBy

Drac0nic

JoBy

Vortech has compressor maps for centrifugal supercgargers on their site.
http://www.vortechsuperchargers.com/...pressor%20Maps

Example:


A displacemet supercharger and a centrifugal supercharger has very differnt compressor maps.

The blue lines are constant supercharger RPM. Along this blue line I have marked two working points (red circles) in each compressor map.

For the roots blower CFM is contant and boost varies.

For the centrifugal supercharger boost is constant and CFM varies.

D's89IROCZ

Hay joboy . On the S trim compressor map . Isn;t haveing a preasure ratio of 1.6 realllly low. Like at 18 psi ...you take 18 psi + 14.7 /14.7= 2.2 ???? Putting it well into the 65 % efficiency range ? Or am I missing something ?

JoBy

A pressure ratio of 1.6 is 0.6 over atmospheric. 0.6*14.7=8.8 psi boost.

TurboedTPI

383backinblack

i've never seen a roots blower that didnt have teflon seals regardless of size.......unless of course you come from the seriously old school

this is a moot point, on a race car you'll almost exclusively see a much larger single blower, because theres no point in having 2 smaller units for lower RPM efficiency, because the car does not operate there......its a maximum effort design. in fact, i've never seen twin blowers on an all out race car.......you'd just step up to an f2, f3, or f4

resonance is more like a cute little interesting phenomenon that takes place in such a small window, that it doesnt really change anything, its just a neat little quirk thats fun to talk about...........i made this explanation in the post above, although i stressed my opinion on "boost pressure" because its so heavily and erronously relied upon, where volume of air is far more important.

JoBy

You can not compare boost on one engine with boost on another engine that is built differently, that is true.


If you keep everything constant (use the same engine and the same temperature of the air entering the engine) then volume of air is a function of boost. You can not get more air flow without raising boost.

Now, what happens if you use the same blower setup on different engines?

With a roots blower the blower size and rpm will give you an airflow. Forcing that air into different engines will result in the same power but the boost will be different. An engine that breaths well will show less boost.

Centrifugal superchargers work differently. That is my point. At a given supercharger rpm you get the same boost. How much air flow (and power) you get depends on the engine behind it. An engine that breaths well will have more air flow and more power.

383backinblack

thats not true at all.......in a centrifugal blower, the amount of pressure might be constant per given RPM INSIDE THE COMPRESSOR HOUSING, not in the engine......the only place there is pressure inside the housing is at the discharge........the amount of air flowed by the blower is regular, and is not related to outside factors, because the blower is dirrectly driven by the engine.....the blower is ALWAYS making 2000cfm of flow at 64,000 rpm (7500rpm engine speed), the question isn't wether or not this flow is being made by the blower,

the question is whether or not the engine can swallow ALL of the air, which unless its making 1,300hp, its not......so therefore the restriction is greater in the intake tract, so that 2000cfm exiting the blower discharge backs up into a greater pressure than on an engine that will swallow all the air

JoBy

Wrong!

Learn how to read a compressor map!



Look for example at the red line labeled 35.000 rpm. That is the impeller speed in the supercharger.
Then look at the scale at the bottom. At 35.000 rpm this supercharger has an operating range of 300 CFM to 1000 CFM.

Then look at the scale at the left. That is pressure ratio. At 35.000 rpm the pressure ratio is between 1.5 (=7.3 psi) and 1.63 (=9.2 psi).

As I said, At a fixed speed ( 35.000 rpm ) a centrifugal supercharger can vary flow a lot (300 CFM to 1000 CFM ) but the boost is almost contant ( 7.3 psi to 9.2 psi ).

You can also notice the upward slope from 300 CFM to 600 CFM. During that part both boost and flow will raise when the supercharger is spinning at 35.000 rpm. Ulike a roots blower you can get more boost by making the engine breathe better.

383backinblack

see, thats not the entire story......the flow will vary, according to alot of things.....but certain things need to be held constant in order to get any useful information out of it......if you change the density of the air available to the blower, or drastically change the size of the tubing below the size which would allow for unrestricted discharge.......then you can affect flow, by placing a restriction on the blower on either end.

also, its important to note that this entire argument is based on thermodynamics......where everything is dependant on everything else.

when that blower is spinning at 64,000 rpm, as long as there is an adequate supply of air to draw and the throttle is open, it will push the same volume of air........compressor maps are for a controlled environment, they very meaningful when the compressor is attached to a working system, other than to compare them with other compressors.

the difference with a turbo, is the lack of a mechanical connection allows the variable flow to be dictated by the load(restriction) on the compressor, where as on a blower it will spin at that speed regardless of the load on it....changing the load will only change the amount of power it takes to turn the compressor as its relegated to turning at a fixed speed with the engine.

however, like i said already......its totally dependant on the entire system.......at part throttle you're 100% right, but centrifugal blowers are bypassed at anything other than WOT..........so the properly sized blower and intake system will flow its maximum at WOT, which is what counts.......because speaking in terms of gradients is just convoluted and long winded. I don't care what the blower does with varying loads/restrictions because thats not the condition under which it supplies boost

JoBy

It is a differance between a displacement supercharger and a centrifugal supercharger.

What you are saying is true for a displacement supercharger, not for a centrifugal supercharger.

On a displacement supercharger, adding a restriction after the supercharger will raise boost as the supercharger continues to force the same amount of air thru the system.

On a centrifugal supercharger, adding a restriction after the supercharger will reduse the air flow. Boost will be about the same.

Of cource, as long as the supercharger is bolted to the same engine the restriction will be the same.

And why would the compressor map not be valid in a real world?

383backinblack

i said, its only valid when you're comparing it to another compressor.......you can extrapolate useful information from it when assuming an application though. But like most things in thermodynamics theres alot more to the story.

thats not true though.......the blower will build boost if theres a restriction, up to the point where it backs up on itself........thats how they actually rate the maximum pressure output of my blower, when it is blown into a closed, fixed volume......in the case of my blower, about 32psi.......because its not a displacement blower, it can do so without a problem.......mainly limited by RPM restriction

so that holds true at maximum output, because the blower can no longer create higher pressure

JoBy

Yes, you get max pressure at max rpm, but not while blowing into a sealed box. That would be way left of the surge line. By allowing enough air flow to be on the right side of the surge line you would get a bit higher pressure.

Also, if you let it blow into open air you will not get any pressure. That goes without saying.

The compressor map shows the intended working range of the supercharger. While you stay inside the intended working range then pressure ratio is primarily a function of impeller speed. Air flow is primarily a function of the restriction after the supercharger.

383backinblack

i just got up, and i think im still drunk......so i'll get back to you later on lol