once the supercharger is under the hood then well be able to keep up

 

question, are any sites showing there rx-8 super chargers in production? or any sites with Specs? Boost Solutions etc..?? have nothing listed

 

Fuel economy under heavy throttle use will be significantly worse, fuel econonmy udner light load, i.e. normal driving and cruising without driving fast you will see a slight mpg loss, 1-4 gallons. Because boosted cars make a lot more heat, A/F rations have to be a lot more rich so being under boost you lose even more fuel.

 

i spoke to SSR-Engineering the other day and they said that they are going to work on their turbo kit and finished that first and that plans for a S/C are far down the road for them. possibly a year

 

There is no reason to have any worse fuel mileage on a stock motor in an off boost situation unless you have poor tuning or too large of an injector. The problem is no one who goes with forced induction drives this way!

Bltiz is working on a screw setup for the RX8 similar to what they have done on the Celica. Rotarygod already summed it up, but I see no reason to go with a roots over a screw except in a low boost situation where there is a cost factor and little power gain is expected. Does a whipple even cost more than an eaton?

 

I don't know for sure, but I suspect yes... a Whipple is slightly more expensive than Eaton. According to literature and application, Eaton seems to be a decent performer as well. Remember an Eaton is more like a hybrid between roots and screw-type.

 

Ssr says there turbo will be ready in November, is this the soonest well get some boost, anyone one know if anything else is coming out earlier??

 

Dude... plenty has been discussed already... Greddy, Blitz, SSR, another turbo under development, other S/C kits under development, NOS... Do a search.

 

A Roots type supercharger (Eaton) is not at all similar to screw type (aka Lysholm) superchargers made by Whipple, Opcon, etc. Even a Roots supercharger with twisted lobes is totally unlike a Lysholm. A Roots supercharger uses external compression versus the internal compression of a Lysholm. Thermodynamically this is a huge difference.

 

I'm no mechanical engineer, but...

" To make the Roots type more efficient, Eaton has modified the impellers by adding a twist to them and moving the intake port to the end. This makes them more efficient and quieter. This is called a "Modified Roots" type supercharger. This is the type used in the TRD Supercharger kit. The biggest difference between the modified roots type and the Lysholm supercharger is that the modified roots type has two impellers that are same, where the Lysholm uses two dissimilar ones, a male and a female rotor." - http://www.gadgetonline.com/Super.ht...arger%20works:

"The Eaton supercharger is essentially a Roots blower pump, with one substantial design wrinkle; each rotor has been twisted 60 degrees to form a helix. The two counter rotating rotors have three lobes, which intermesh during operation. These twisted rotors, along with specially designed inlet and outlet port geometry, help to reduce pressure variations resulting in a smooth discharge of air and a low level of noise during operation. This arrangement also improves efficiency over traditional Roots superchargers. With helical rotors and an axial inlet the Eaton supercharger can be spun to up to 14,000 rpm, thereby reducing package size. " - http://www.automotive.eaton.com/prod...rchargers.html

"The original designs used straight lobes running the length of each rotor, with air induction coming from a whole at the top of the unit. They also had loose internal tolerances that hurt performance and efficiency, as well as creating excess heat from friction. Some of these old designs had typical thermal efficiencies below 60% (called adiabatic efficienc,: the ability of an air pump to come as close to ideal in terms of pumping performance as possible), putting them at the bottom of the scale in terms of supercharger efficiency. More modern designs first added a third lobe to each rotor, then twisted them axially for greater efficiency and less noise. Advances have also been made in how air flows through the housing, with modern designs pulling air in from the rear of the unit, and pumping it through carefully designed outlets for increased performance. Internal tolerances have also been improved greatly, and better lubrication/sealing of the units has become commonplace. Eaton Corp. has nearly perfected the originally inefficient design, to the point that it’s thermal efficiency is the best in the business, and nearly on par with other designs... LYSHOLM COMPRESSORS...Also called screw compressors, these offer all the advantages of roots type blowers and then some. This design’s pros and cons are very similar to Roots s/c’s, with one major difference; efficiency. Typically these compressors have peak adiabatic efficiency at or above centrifugal designs.
Externally these look nearly identical to the current Eaton design, but internally they do have some differences. The main difference between roots and lysholm compressors is in how the two rotors interract in the supercharger housing; being that the roots rotors really don’t. Lysholm compressors have the familiar two rotor, twisted lobe design, but each usually has 4 lobes instead of 2 or 3, and each rotor’s lobes have their own specific shape. One rotor will have thin blade style lobes with a fat ridge on top, while the other will have fat teardrop shaped lobes with a sharp edge. As the two rotors spin, the lobes interlock to form nearly airtight sections within the supercharger housing. This interlocking and sealing action is where the design gets it’s advantages over roots blowers, being better thermal efficiency and much improved high pressure boost performance..." - http://www.automotiveforums.com/t425.html

It looks to me like Eaton IS very similar to a Lysholm. The design differing essential in rotor design, with the Lysholm being the more efficient of the two.

Your explanation of internal and external compression, doesn't seem to fit with what everyone else has to say. They say that the Lysholm is more efficient, particularly at high boost/pressure levels because the rotor design seals better than a roots or eaton supercharger does. The air that gets lost because of the weaker sealing is what gives the roots supercharger it's low efficiency. Doesn't sound like external or internal compression to me.

http://www.magnacharger.com/

http://www.newdimensions.com/super_20.html

http://www.whipplesuperchargers.com/....asp?PageID=68
(notice that Eaton isn't mentioned... could it be because their advantage isn't so clear and strong then... hmmm)

http://www.procharger.com/tech.shtml
http://www.procharger.com/intercooled.shtml

 

Just to throw a kink in this whole confusion, Eaton is now making twin screw superchargers. Who do you think makes the Ford GT unit?

Here is an end diagram of a roots style Eaton supercharger. The roots can have 2 or 3 lobes. This one has 3. The traditional roots blowers also have straight rotors. The Eaton has a twist in theirs over the length of 30 degrees. Their race units have a twist of 60 degrees. Air comes in and is sent around the outside edge of the housing to the other side. This is a little different than the twin screw. The tolerances in this picture are highly exagerrated.

 

Here is a diagram of a twin screw unit. You can see the immediate difference between the rotor shapes of the roots vs the twin screw. The tolerances are much tighter on the twin screw. Air also does travel around the outside edge of the case but it moves differently. The air also moves forward along the length of the case simultaneously as it moves down and around. During it's path, the available area for the air to travel through gets smaller. This causes the air to get compressed. The roots and the twin screw are similar in that they are both positive displacement units that use rotors and are around the same size. The principle of how air moves through them is completely different though.

 

rotarygod, sorry but... The moddified-roots Eaton S/C doesn't flow air exactly as you described. The description you gave was for a traditional roots S/C. In the Eaton moddified-roots S/C, the intake has been moved to the rear and the outlet has been designed to reduce pressure variations. This has the effect of increasing the efficiency of the S/C over tradition roots.

 

Did a Search, Only thing found still is ssr's turbo, does anyone have a link to any other sites??

 

Let me try and put it in different terms. A Lysholm compressor takes a fixed volume of air into an enclosed area and then shrinks the enclosed area. Kinda like bringing the ceiling down in an enclosed room. All of the compression in a Lysholm is accomplished between the rotors in a cavity that progressively shriks in volume. This is accomplished because the number of lobes is different by one from one rotor to the other with a corresponding change in pitch.

A Roots basically grabs a bunch of air from one room and throws it into another room. The new air smacks into the old air and their pressure increases. This is not as efficient because there are efficiency losses due to the acceleration.

When the lobes of a Roots are twisted the only thing that happens is the pressure pulses are smoothed out. This helps some with efficiency and noise.

 

Makes perfect sense. Thanks!

 

Sorry but... it does work the same. The entrance is only different. Air gets sucked in from the back but gets thrown around the outside of the case. If air came in from the top it would still get thrown around the outside edge of the case. The diagram doesn't show intake locations because they are irrelevant as far as the way the air flow is concerned. Either way air still starts at the top of the case (either by getting sucked into the top from the back or directly on top) and then gets moved around the outside and out the bottom. Twin screw superchargers can also come in both configurations and Whipple has both options available. They didn't move the intake location for efficiency reasons. They did it for packaging reasons.

 

Damn RotaryGod, every time i think I know what I'm talking about you kick me in the nuts. I'm banning myself from the tech forums.

 

No **** newtlicious.

So rotarygod, they only efficiency changes effected by Eaton's changes to the roots design are from the twist added to the rotors? Intaking air from the rear or even front instead of the top of the rotors wouldn't have any effecton stablizing the air pressure inside? As you said the rotors are just tossing in coming air against the sides and out the bottom. Also looking at the direction of rotation of the rotors, you'd think that the relocation of the intake would have some beneficial effect (looking at your diagram the rotors would also push air back against the intake charge it seems... whereas the opposite direction would have avoided this problem). In the of the sites them mentioned the rotor design difference between roots/Eaton and lysholm... the two dis-similar ones of Lysholm creating a tighter seal which would allow it to handle greater pressure and with less losses than the roots/Eaton.

I ask all this because other than the twist to the rotors you seem to be saying that nothing else about the Eaton design improves efficiency and so it's only marginally better than a traditional roots blower. Am I misinterpreting you?

 

I think we have hope. Occasionally he is wrong, like about trucks. Like for example I believe the engine that is in the Ford GT is a Ford truck engine.

 

Actually Rotarian_SC, you are right and wrong. The 5.4L DOHC V8 in the Ford GT is related to the truck engine... but then so is the 4.6 SOHC in the Mustang GT and the 4.6 DOHC in the Cobra. They are Ford's "modular" engines. They are all essentially the same in design... just swapped the SOHC heads for DOHC, or change the bore. That's all. So it is the same in that sense... however, you are wrong in that the Ford GT uses an all aluminum (heads and block) engine, not cast iron like the trucks. Also the trucks are SOHC, not DOHC IF I remember correctly. And the tucks don't have the nifty supercharger we're discussing.... unless you're the F-150 Lightening...

 

Nah, Eaton has other improvements to the Roots blower. The outlet shape triangular (at least the last one I had was) versus the usual rectangular. According to Eaton this shape has improved efficiency.

People keep saying the shape of the Roots versus the Lysholm rotors affords differences in clearances. I don't see why the shape would affect this. All of the Lysholms I am familiar with use machined rotors cut by a Weingartner or Linsinger mill which creates accurate shapes but they are quite expensive. Whereas the Roots uses extruded rotors which are not as accurate but are much lower cost. Is there something I am missing here?

 

How was I wrong about trucks? The statement that was made was how twin screw superchargers are best suited for trucks (not engines from trucks installed in cars). That is false. You mention the possibility of a truck engine being used in a car. This would place the supercharger in a car not a truck. If a truck engine is used in a car, it is no longer a truck engine. It is a car engine. If I install a rotary in a truck, it becomes a truck engine. The GT engine is not just an engine out of one of their trucks. It may share a few of the same components, but that doesn't make it the same engine. If I had a kidney transplant and had one of my dad's kidneys, I wouldn't be my dad.

Eaton improved the efficiency of the older roots blowers by twisting the rotors and adding a 3rd lobe. This also had the benefit of quieting it down. Yes they did make some shape changes to the inlet and outlets that changed their efficiency but this doesn't mean that the blower still doesn't function the same way. Air still enters from the same general side of the blower case which is the top, travels around the outside edge, and exits the bottom. The principle has not changed. The Eaton blowers can actually be ported and improved upon even more. There are other things that have been done to make them more efficient. There is an aftermarket company that has installed light carbon fiber rotors with tighter tolerances. This makes less parasitic drag and doesn't heat up the air as much which in turn allows higher pressures to be run. The principle of how it works is still the same but the efficiency is increased. This is no different than what Eaton did with the original roots blower.

 

Damn Japan8, that was harsh. I wasn't that far off, Car magazines make the mistake of using the words "screw type", "Lysholm" and "Eaton" in the same sentence. These all fall under "screw type" as opposed to centrifugal type. I'm learning here too and I thought that taking a jab at myself might get a laugh out of someone. This "well one is twisted but the intake is at the front" stuff is great but we all have our specialties. I work in the aircraft field. You wanna discuss turbofan vs turbojet vs ramjet vs scramjet vs pulse jet, I'll go all day long but I'll never say "no **** Japan8" sorry I got my intake locations mixed up. All nit-picking aside, it all boils down to the difference between a positive displacemant blower and a centrifugal blower. The differences between whipple, eaton, Lysholm, Roots and twin screw are fairly minor. The differences between those and centrifugal types are great.

 

Actually newtlicious, I meant that to mean "Oh boy did he do me up... looks like I was mistaken..."