Z

Are there any compressor maps for the Whipples shown somewhere? I couldn't find any on their web site, and only saw a mention of an adiabatic efficiency of 70%-80% in a rough comparison chart they had on there.

Lysholm has some compressor maps for their twinscrew superchargers on their web site at: http://www.opcon.se/subStart.asp?ContentID=15&CatID=87
Select a model there then click on "performance" to display the map for it. The highest adiabatic efficiency shown on any of those is 66%.

Depending on the model, Vortech lists the adiabatic efficiency for their's as ranging from 72%-79%. The compressor maps for those models that they have online show 72%-74%.

The last time that I looked at the compressor maps for the Rotrex superchargers, they didn't look like that good of a match for a later 928 engine. For probably the same reason, the Rotrex based kit that's available for the small block Chevy uses two of them, like the Koenigsegg does.

I got a response from ProCharger in the mail yesterday. Yet again, they completely ignored everything I asked about, and told me about stuff I didn't ask about. All that the letter said was that they didn't currently have a kit for my car. They have no plans for one in the near future. They have my contact information on file. They'll let me know as soon as information is available, if they ever do develop a kit for it.

Jim Nowak

http://www.whipplesuperchargers.com/....asp?PageID=65

Keep in mind that they compared a procharger with a straight impeller design vs a Vortech with a curved impeller desigh. Not really an apples to apples comparison but here ya go:
http://www.superchargersonline.com/i...1sc_report.pdf

Vlocity

OK.....I think the following is pretty unbiased and maybe it will summarize a lot of the previous information and disspell a couple of things that people continue to get wrong. Much of this is a compilation from what I have gathered from SAE material that I reviewed and gathered while enjoying my SC project.

And while I did settle on a path that was right for me for a lot of different reasons, I like them all.....so don't be a hater.

Forced Induction for More Power

Turbos and superchargers both perform the same basic function - they’re pumps that force-feed an engine its fuel air mixture at a greater than atmospheric pressure. But the difference between them lies in how they go about getting the job done.

A supercharger is driven mechanically from the engine’s crankshaft to provide the necessary huff, while a turbocharger utilizes exhaust waste gases to spin an impeller at tremendously high speed and generate the puff. The supercharger looses out to the turbo in some ways because it drains power from the crank, while the turbocharger, driven by waste exhaust gases, gets it power for free. But because the supercharger is driven mechanically with no slippage, it’s already ready to deliver buckets of extra grunt at virtually any revs, from idle upwards, while the turbo is at a disadvantage at slow engine speeds, when the exhaust gases lack the energy to get the impeller really spinning.

A supercharger is connected directly to the crankshaft by a belt, unlike a turbocharger, which is driven by exhaust gases. A supercharger provides improved horsepower and torque, at lower rpm's, by pumping extra air into the engine in direct relationship to crankshaft speed. The positive connection yields instant response, in contrast to turbochargers, which must overcome inertia and spin up to speed as the flow of exhaust gases increases. The supercharger is a way to get around "turbo lag". The lubrication system also differs, in that the supercharger is self-contained whereas the turbocharger requires engine oil.

Because superchargers provide more air and fuel to burn, there’s a huge increase in horsepower and torque, at low and midrange engine speed. The output of a supercharged engine can be easily varied by simply changing the size of pulleys between the engine’s crankshaft and the blower. In my own application I can quick change the pulley and go from about 6.8 PSI with a 2.5 inch diameter blower pulley to 8.5 PSI with a 2.25 inch pulley. (8 rib pulley and belt, there is enough adjustment in my tensioner that one belt fits both) I have very little if any belt slip and my original belt has lasted 2 years, including 15-16 full on DE days at three area tracks.

Whatever charging system you use, whenever building an engine for big power, you must always remember, too many horses and bad tuning can destroy an engine, even if the engine is built up. Therefore, it is most important to increase power and torque for reliably, rather than for peak power.

Heat is not good and compressing air produces heat!

Forced induction compresses air, and as a law of physics the temperature of the air increases as a direct counterpart to its compression. A lot of engineering goes into trying to compensate for this fact in supercharging and turbocharging design.

The word "adiabatic" describes a process in which no heat is gained or lost - 100% adiabatic efficiency would be the perfect forced induction device, creating no heat gain whatsoever, probably impossible to achieve ever. And the closest anyone can come yet is around 80% efficiency.

The problem with heat is it defeats the original purpose - the hotter the air, the lower the density possible, and the extra power comes from dense air. Another problem from heat is ignition - the hotter the inlet air, the more tendency the engine will have towards detonation and pre-ignition (knock and ping), which damages the engine, besides diminishing performance. Thats why it's a good idea to monitor a knock sensor which I plan to add to my 85.

The goal of efficient charging is to compress the air and to keep it cool, for maximum power. The cooler the intake charge, the denser the air and the more horsepower produced.

It's important to start with cool air and with a filter of the proper size so that it does not create a drag on the blower....regardless of type. Cool air increases horsepower at the rate of 1% for every 10 degrees. So lose that awful underhood exposed filter. When I was setting up my vehicle, I corresponded wth K & N. Their technical staff advised me that I would need 150 square inches of filter area. That is a honken big filter....but
I ended up with a filter of 162 square inches with a 4 inch base. I am pulling cool air from the fender well and I have enough capacity now, even when the filter is dirty. Would my engine run with a little filter, sure. But guess what happens to your HP and effeciency when there is all of that "drag" on the blower and it has to suck through a straw.

The greater the adiabatic efficiency with which a supercharger compresses air, the less the heat that gets added to the intake manifold. Efficiency is measured by the discharge air temperature at a given pressure. Boost itself is only the measure of pressure the intake air is under, not an indication of the power produced as horsepower.

Which has greatest adiabatic efficiency?

The Roots blower has the lowest adiabatic efficiency of all the forced induction designs (including the turbocharger, which has to start off with hot exhaust gases to deal with) - generally around 50 percent. The roots type is so inefficient because it doesn't compress the air directly, but delivers uncompressed air which wells into the intake manifold, becoming more compressed, but with additional heat gain from the turbulence and reverse flows of air mixing.

Centrifugal superchargers can vary from 60% up to perhaps approaching 80%+ efficiency, as can turbochargers; both are more efficient at higher rpm, which is another way of calling them more inefficient at lower rpm.

The twin-screw supercharger normally delivers lower output temperatures, for adiabatic efficiencies of 70-80%+ across the whole rpm range. I am running a 2.4 liter "Opcom Autorotor Twinscrew Compressor", a lot of the language for these units gets tossed around and grouped the same as it does for the centrifigals and turbos. If I recall Whipple started the seperate Autorotor company and split it from their other Lyshom style blower with a specific eye toward the automotive application some years ago. The numbers I have for my 2.4 being spun to make 8.5 PSI is about 75% adiabatic effeciency. By "going big" I am only spinning my blower at a little over 14,000 RPM to make 8.5 PSI and a little over 13,000 RPM to make 6.8 PSI. When you compare that to 40,000 RPM and up for some of the other types of blowers and turbo chargers it is easy to understand why the heat is lower and the effeciency recovers. It's just not beating the air to death. (as much)

Twin Screw Supercharger - a positive displacement compressor

The twin-screw supercharger is a positive displacement air mover, in that it moves fixed amounts of air per revolution, like the roots type blower. Unlike the roots however, which is only an air delivery system, the twin-screw supercharger is also a compressor. The counter rotating lobes and chambers of the twin-screw are designed for a screw-like tapering effect which runs its intake air into a smaller space for output, thus compressing it. The rotors have very close tolerances yet never touch. Compressed air is delivered into the compression environment of the intake manifold with very little leakage or energy loss.

Because of the increased mechanical efficiencies of these new designs, the output air temperatures of the twin-screw positive displacement supercharger are radically improved from the roots type. The Autorotor produces adiabatic efficiency of 70%-80%+ range across the WHOLE powerband.

As with the roots, since the supercharger is under continual drive, and since it delivers boost practically from idle, overboosting is prevented by the use of an intake bypass system, which allows the engine to breathe normally at cruising or idle: the bypass closes on throttle use, delivering full boost.

Full boost by 2000 rpm

The twin-screw supercharger creates boost the instant the throttle is touched, and generally reaches full boost by 2000 to 2400 rpm. Full boost is then available all the way to redline. A positive displacement compressor is ideal for street performance cars.

While we are at it...another myth is that the 5 speed cars don't handle the positive displacement well. I am running a close ratio 5 speed with a 2.75 LSD in my 3075 pound "street" car. Would I turn a 16 year old loose in it...probably not, but it is very driveable and I have had no drivetrain failures even with the sticky track only 315s on the back.


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Selecting an Intercooling System

Be aware that Temperature reduction AFTER the supercharger will not make any more horspeower as some "experts" would have you believe. It's impossible. Look at it this way. My supercharger discharges 2.4 liter or 144 cubic inches of air in one revolution. Lets trap all of the air into a container. The oxygen in the container will always weigh the same no matter how much it is cooled. The air can not suddenly acquire more molecules. The cooler air will however allow you to run more igntion advance and or more boost for a given octane level.

Both air/air and water/air systems have their own benefits and disadvantages. Air/air systems are generally lighter than water/air, especially when the mass of the water (1kg a litre!) is taken into account. An air/air system is less complex and if something does go wrong (the intercooler develops a leak for example), the engine behaviour will normally change noticeably. This is not the case with water/air, where if a water hose springs a leak or the pump ceases to work it will not be immediately obvious. However, an air/air intercooler uses much longer ducting and it can be very difficult to package a bulky air/air core at the front of the car - and get the ducts to it! Finally, an air/air intercooler is normally cheaper than a water/air system.

A water/air intercooler is very suitable where the engine bay is tight. Getting a couple of flexible water hoses to a front radiator is easy and the heat exchanger core can be made quite compact. A water/air system is very suitable for a road car, with the thermal mass of the water meaning that temperature spikes are absorbed with ease. However, note that if driven hard and then parked, the water within the system will normally become quite warm through underbonnet heat soak. This results in high intake air temperatures after the car is re-started as the hot water takes some time to cool down.

Type of Intercooling Advantages Disadvantages
Air/Air
Efficient at constant high speed
Cheap
Cores readily available
Bigger is better
Longer induction air path
Packaging of large intercoolers difficult
Large pipes to and from intercooler required
ambient air as the cooling medium, less efficient when in traffic: heat soak

Water/Air
Short induction air path
Easy to package
No heat soak
Excellent for short power bursts
Consistant efficiency for every day driving: stop and go
Heavier
More complex
More expensive
Heat exchangers harder to source


Technically, a water/air intercooler has some distinct cooling advantages on road cars. Water has a much higher specific heat value than air. The 'specific heat value' figure shows how much energy a substance can absorb for each degree temp it rises by. A substance good at absorbing energy has a high specific heat value, while one that gets hot quickly has a low specific heat. Something with a high specific heat value can obviously absorb (and then later get rid of) lots of energy - good for cooling down the air.

Air has a specific heat value of 1.01 (at a constant pressure), while the figure for water is 4.18. In other words, for each increase in temp by one degree, the same mass of water can absorb some four times more energy than air. Or, there can be vastly less flow of water than air to get the same job done. Incidentally, note that pure water is best - its specific heat value is actually degraded by 6 per cent when 23 per cent anti-freeze is added! Other commonly-available fluids don't even come close to water's specific heat value.


The high specific heat value of water has a real advantage in its heat sinking affect. An air/water heat exchanger designed so that it has a reasonable volume of water within it can absorb a great deal of heat during a boost spike. Even before the water pump has a chance to transfer in cool water, the heat exchanger has absorbed considerable heat from the intake airstream. It's this characteristic that makes a water/air intercooling system as efficient in normal urban driving with the pump stopped as it is with it running! To explain, the water in the heat exchanger absorbs the heat from the boosted air, feeding it back into the airstream once the car is off boost and the intake air is cooler. I am not suggesting that you don't worry about fitting a water pump, but it is a reminder that in normal driving the intercooler works in a quite different way to how it needs to perform during sustained full throttle. However, the downside of this is once the water in the system has got hot (for example, after you've been driving and then parked for a while), it takes some time for the water to cool down once you again drive off.

Which is better an air-to-air intercooler or a water-to-air intercooler?

It really depends on the application. In order for an intercooler to effectively cool the air that passes through it, the intercooler itself must be cooled by some external means. Most intercoolers are cooled just like your engine's radiator - air flows over the outside of the intercooler's fins, which in turn cool the air inside the intercooler - hence the name air-to-air Intercooler. Some intercoolers, however, are cooled by water instead of air, in which case they are generally called aftercoolers, or water-to-air intercoolers. The benefit to an aftercooler is that air passing through it can be cooled more than in a traditional air/air intercooler if very cold water and ice are used to cool the intercooler - in fact, some aftercoolers chill the air to below ambient air temperatures even after it has been compressed by the turbocharger/supercharger.

The reason aftercoolers are more effective in cooling the air charge is because water is a much better conductor of heat than air - in fact water conducts 4 times as much heat (energy per pound) as air! The obvious drawback is that with time, the water will heat up to the temperature of the air passing through it, and its ability to cool incoming air goes away. Some aftercoolers, however, use a small radiator to cool the water that runs through the system, making them ideal for street use as well as racing. The water is constantly pump whilst the ignition is on and is cooled as it travels through the water ratiator. The cool water travels into the charge cooler and cools the boost by absorbing heat energy. The hot water exits the cooler and back to the water radiator via the reservoir. This method of cooling is regarded as more efficient as the cooling action of the water is more consistent than air to air intercooling. The water can in some instances drop to temperatures lower than ambient (see below) and therefore cools the boost with greater efficiency. However charge cooler systems require the installation of more components with a slightly increased cost. Charge cooling is commonly used for high compression engines where efficiency and temperature consistency are key requirements. For drag racing applications aftercoolers packed with ice work very well because they only need to work for around ten seconds or so before you shut down and head to the victory podium. For milder racing and street applications air/air intercoolers or aftercoolers with radiators are more practical as their ability to cool incoming air is not reduced with time.

Extreme Performance

For drag racing, autocross or performance street applications the Liquid/Air system can provide sizeable competitive advantages. Through the use of chilled coolant, you can reach intercooler efficiencies well in excess of 100%.
I have actually used dry ice at autocross events.

I hope this sheds a little light, although I expect the banter and bench racing to continue with or without any comments from me. LOL.

Happy New Year....

Ken

hacker-pschorr

I would like to see some intake air temps to back this up. I’ve seen back to back comparisons of oil fed vs the sealed belt driven supercharges on domestic cars (low boost) with no intercoolers. The difference of intake air temps was almost immeasurable; they were close enough to be considered under a margin of sensor error.

Not to mention 220 degree oil temps is inaccurate since a well designed system will feed oil after the oil cooler to the supercharger.

Let’s assume the 220 degree figure was accurate – then turbos would be off the carts since the impeller on the hot side is seeing upwards of 1,000 degrees. There have been non-intercooler factory turbo cars produced (early 930’s for one, some SAAB’s etc…). Yes these were low boost (under 8psi).
So if 220 degrees on the hot side of a supercharger were actually affecting the intake air temp – how could 1,000 degrees on the hot side of a turbo work at all?

Regardless of how the boost is delivered, compressing air heats it up. There is no way around this.
I’ll go out on a limb here and say we’ve been there for a few years now.

Carl Fausett

Jim Nowak - that was a nice link to the article you posted.

Note that they are comparing a radial-vane impeller (not optimised for either CW or CCW rotations) to one with curved vanes optimised for one direction. Not quite a fair comparison, but the article is good none-the-less.

Not all curved-vane impeller designs are the same: we found that the Powerdyne impeller was fairly unaggressive because of the manufacturing process they chose. To save money, they chose to cast the impeller. But, if the vanes were properly curved to optimize output, the impeller would not release from the casting mold.

My solution was to mill it with a 5-axis mill, and we received a design patent for our impeller. The new impeller is lighter than the cast impeller, stronger, and produces 20% more CFM at the same RPM's than the stock Powerdyne impeller.

Our solution produces a better impeller, but at higher per-unit costs than a cast impeller.

Carl Fausett

On a turbo, the turbo spool is often separated from the compressor side by an axle and some distance. They do not share the same cabinet. This is to reduce the heat transfer from the exhaust side into the make-up air side.

ew928

Neato. 5-axis mill.
So I'm guessing the drill bit is accurate enough so that the impeller does not need to be balanced after milling. That's cool.

Carl Fausett

It is very accurate, but does not eliminate the need for balancing.

Each individual impeller is spin balanced before they ship. This impeller is designed to operate at 60,000 rpm, and although the industry standard for over-speed testing is 10%, we paid extra to have them 20% over-speed tested. The impeller has gone repeatedly to 72,000 rpm without damage.

Accept for racers, the most the impeller will see is about 48,000 rpm, so we have quite a safety margin.

Vilhuer

Very impressive Carl.

Jim Nowak

I stopped reading after this paragraph.

Jim Nowak

Carl, that's so sweet. I applaud your commitment to excellence.

hacker-pschorr

The point I was trying to make is the oil spraying onto the drive system is not heating up the intake charge. It's that simple (at least not a significant amount). If the 180-200 degree oil was affecting the intake charge temp by such a drastic amount, than the 800-1,000 degree temps measured on the hot side of a turbo would have the same affect.

Efficiency of the compressor (turbo or supercharger) is one thing. Making a blanket statement saying you do not need an IC for a non-oil fed supercharger is false. No matter how you compress the air, it is going to heat up, this is a fact.

Check out this simple formula for calculating charge temp for a turbo:
http://www.stealth316.com/2-turbotemp.htm

Even with a very low input temp (lets say 50 degrees) and a compressor efficiency of 90% (not likely) your intake air temp is 125 degrees @ 8 psi. Sorry, on a 50 degree day, this is unacceptable, so an IC would be needed.

Input a more realistic input temperature of 100 degrees your output temp skyrockets to 182 degrees. Run that for very long it's detonation time.

Now drop the compressor efficiency down to a more realistic 90%(still on the high side for most compressors) you now have an intake air temp of 190+ degrees (still at 8psi). Ceramic coating the impeller is not going to drop those temps down anything close to ambient like a well designed intercooler will do.

This is why when I started my supercharger project I designed the intercooler first since there was no way on earth I would add compressed air at any level to my car without one. Was it 100% necessary at 6psi? Probably not, but much more boost I want the charge temp cooled down regardless of compressor efficiency.


Yes I know that calculation table is for a turbo - same theory still applies.

largecar379

Mmm....

Vlocity got it all wrong----cooler intake charges do make more HP as it makes the air more "dense". The more air you can fit into a particular volume area, the more fuel you can throw in with it, and then you'll have more power.

Hacker-

I made reference to checking intake temps on both intercooled and non-intercooled to get real data to back up whether or not a cooler is needed. Same question you are asking.....sort of.

In all my readings here and elsewhere, no one has come up with those numbers. Even the "ricers" don't have that data......

It' s not hard to do. Just plumb a pyrometer lead into the intake tubing (after the blower) of non-cooled intake charge, take it to the track (or street, or dyno) and record the temps for various conditions---idle, cruise, under hard acceleration, psi #'s for each, etc.....

Same test goes for intercooled (air) and aftercooled (water).

Once we have this data presented, there should be no argument, either for or against after/inter cooling.......well, maybe that's wishful thinking.


I was totally ignored on this point, but that discussion centered on which was better (air coolers or water coolers). What an argument that produced......too many engineers for me to keep up with.

I'm gone back to removing the rub strips off my Euro.....at least they won't argue with me too much......

--Russ

ShawnSmith

> Look at it this way. My supercharger discharges 2.4 liter or 144 cubic inches of air in one revolution.

Depending on the temperature of the intake charge, the amount of oxygen you can stuff into 144 cubic inches of space will vary. You can fit MORE cold dense air into the same volume of space, which is why intercooling works no matter where you do it. PV=nRT. Or more usefully, n = PV/RT. At a given pressure and volume, you can fit more cold air in a given volume than you can hotter air.

The flow rate of your supercharger does not limit how much air you can pack into the cylinder (assuming your impeller is sufficiently large) - all that matters is the pressure and the temperature for a given cylinder volume.

pmotts

Russ,

On both of my twin screwed motors (GT's) I have needed to run my ic pump to eliminate detonation under even moderate acceleration.
People had talked about not needing an ic unless you were driving hard but I didn't find that to be the case. I think I have 2 things working against me here, 1 is it's a GT and 2 no cold air intake. 2 is being taken care of
Jim