gmonsen:
Am I being sardonic? hm, maybe
If you are conserned about turbo lag you may choose a "smaller" turbo with faster spool up, or as you say, staying with the org sequential system also eliminates lag.

So, twin's is the best options? In my opinion, yes. (driveability)
The intention with my own RX7 is to keep the sequential twin's and make the most out of it (I use it as a daily driver)

To me, a supercharged rotary engine is fun and unique, but not my choice of breathing help, but, if anyone have any evidence/proof that a supercharged rotary runs just as good as the turbo version, then why not do it if you want to

 

Interesting. The Rotrex is a centrifugal blower, and as I was mentioning before, needs to spin at seriously high rpm to move a significant amount of air. The ones I've seen use a unique setup that does away with heavy and bulky geartrains to multiply the engine/turbine shaft rpm; it utilizes a planetary roller system with a hydraulic fluid that solidifies under high pressure so that the rollers are both driven and lubricated at the same time. One additional issue with the Rotrex is that a heat exchanger is required to keep the hydraulic fluid cool.

It would be interesting to see what size they used, because even with the planetary roller setup, there is still significant parasitic drag at lower rpm, and the 13b isn't noted for its low-end torque, especially with something like a turbine blocking the intake tract. Of course, if the car is meant as a race car, then it doesn't really matter much.

All things considered, I'd opt for the Whipple screw-type positive displacement blower because of its better low-rpm performance, but that's just my opinion.

 

Off topic, but the best part is the exhaust!!!

 

I think it would be cool to see something like this. Sure it is easier to go single, and there are other tried and proven methods of power, but I like seeing something different every once and a while. Good luck, and keep us updated.

 

I've had the chance to drive a whipplecharged 3 rotor before. I was disappointed with the power but I really loved the sound. You could make more power if you wanted but it really wasn't my ideal setup.

- The gas mileage sucked ***. 4mpg

 

One advantage of a turbocharger is once it reaches full boost it's held steady at that boost level. So it would be producing more midrange power. I'm not as familiar with the newer superchargers but maybe they now have some that reach higher boost levels sooner and then use a clutch to slip once it reaches a targeted boost. It's not a route i would like to take, i love the power delivery of turbo cars. However it is something facincting and i would definately follow along with someone willing to try it. Maybe someone can do a roots style blower with a large single turbo to have something really unique.

 

The supercharger produces varying amounts of boost dependent on the rpm of the engine. Up to it's maximum capacity. The maximum capacity is dependent on the size of the supercharger and the rpm at which it spins. The rpm can be controlled by the size of the pulley used. The max boost is controlled by a boost controller just like a turbo. One of the reasons it hasn't really been explored is because the superchargers in the past were not very efficient. New technology brings new possibilities. Obviously one is not going to make 700hp monster with a supercharger. Most people don't want that anyway.

 

I spoke with one of the persons working on the supercharged FD at Monster Garage in Singapore. He said they are still in the development stages. The car was put together and taken to Tokyo Auto Salon 09 to show. Knightsports is shipping it back to Singapore for testing. The car must have some merit if Knightsports is trying to develop the idea. They are using a large Rotrex supercharger which flows over 900 CFM and is capable of making 600 + HP at max boost. Plus the unit only weighs 13lbs. Not bad. Interesting to watch

 

Negative. The supercharger will always reach higher boost levels sooner because it is driven directly by the engine, not the exhaust energy, so it will always produce more midrange power. That is the main advantage of a SC versus a TC.

The disadvantages are the parasitic drag losses and relative inefficiency at high-rpm boost levels (the main problem with Roots-style fixed displacement petal blowers), which is where turbos have always held an advantage. However, there have been many recent developments to help deal with those disadvantages (the bypass valve for the parasitic drag, and screw-type positive displacement blowers that don't suffer as much inefficiency as the Roots-type petal blowers).

 

Except a supercharger builds boost with rpm up to its max boost. So if its geared to make 15 psi at 8k it will be making much less at 3500 rpm. Compare that to a turbocharger such as a gt35r that will be making 15 psi from 3500 on and you have less midrange power with a supercharger. Thats what i was pointing out.

 

And what about comparing to smaller ball bearing turbos? I'm not supporting either side of the arguement. But please explain how something dependant on rpms to make boost can make more power in the mid rpms when a small or medium size turbo is at full boost by that time? I can understand lag but thats not the same as mid range power, unless your talking about big turbos. Mid range power to me is from about 3000 to 5000. Shrug

 

I thought superchargers had the boost increase with the rpms. I guess i do need to look into them more. So what keeps them from over boosting? Some kind of pop off or clutch system?

EDIT: The centrifical superchargers are the ones that only have full boost at redline correct? They have more of a turbocharger powerband. Is this right? And the positive displacement blowers or screw type make boost more instantly. Am I dreaming? cause I could have sworn the centrifical supercharger on my friends mustang had boost that was gradual with rpm.

 

It actually seems like a pretty good idea. The rotary being so low in the torque department could stand to be woken up down low. And if you could still make 450-500 with the right size supercharger, then why not? Does the high rpm range of the rotary make it a more difficult task for the supercharger to keep up with air supply? IE running out of breath on top?

 

Here's a link to a gallery with 8 pictures of the Monster Garage supercharged FD:

http://www.madwhips.com/monster-gara...rcharged-rx-7/

 

For street applications, it seems the supercharger concept is very well suited. Obviously, in drag racing cars that live in the top of the power band, I still think a turbo is the most viable solution. But when looking at a project developed specifically for the street, the low end power bump that a supercharger can provide would really punch up the powerband below 3500 RPMs, where many of us on the street drive at or below when cruising.

I would really like to see the dyno charts on a supercharged rotary. Anyone have some? Looking at the dyno sheets for single turbo rotaries, virtually all of them are making less than even the stock twins at or below about 3000-3500 RPMs. This is where I would want to improve power the most, from 0-4000 RPMs, on the street.

 

Wouldn't this make your gas mileage worse on the street. Would be nice to drive but I wouldn't want to pay the fill ups

thewird

 

Probably, more power = more gas. Are you really worried about gas mileage in your RX7, though? That's what Priuses are for! Edit: Prii?

 

Thinking more about it, another advantage of a supercharger would be exhaust flow. The unique qualities of the rotary that allow so much flow could possibly be accentuated by a supercharger in lieu of a turbocharger. Since the supercharger does not use exhaust gases to spool, the exhaust would be completely free flowing from the header on back... Theoretically, this would reduce EBP and CCP significantly, two of the major drawbacks of the rotary. Theoretically....

 

gmonsen, more air = more fuel. With a supercharger you'd get boost really quick and you'd also have the parasitic loss from turning the turbocharger all the time. Just seems that way but dont quote me on it lol

I enjoy cruising in my FD as much as the prius owner. If its properly leaned out, its not that bad, it only gets bad when you boooooooost.

thewird

 

This sounds very interesting. I've wanted to go single for a while now but couldn't really let myself do it because of no spool till 3.5k+ RPM.
Gordon I've talked to camden, to Chris and this other dude...forget his name but it looks like they'll make the kit but we'll have to fab it up so that it'll fit. I didn't ask for a 20B because I am interested in doing it in my 13B-REW but I'm pretty sure that you'll have to fab something up yourself as well.
And so for someone who said that it wasn't for drag, camden used their supercharger kit on his Cosmo (13B-RE) and won, don't know the details though.
If I go with this I'll either use lindsey racing's intercooler pipes or go with none.
Oh, and they did say that the ECU they recommend to use with their supercharger is the Electromotive. Don't ask me why.



~Shar

 

There are different types of superchargers. You have centrifugal units that are basically like a turbo but driven off the engine mainshaft instead of exhaust energy (such as the Rotrex). Then you have fixed displacement blowers like the Roots vane-type and the Whipple screw (or sometimes referred to as "twin scroll") type.
The centrifugal SC uses a vane setup that forces airflow into the engine by compounding the airflow's momentum as it passes through the vanes. Thus, it has to spin at extremely high rpm in order to build boost.
The fixed displacement blowers are like the name suggests: they force a fixed volume of air with every revolution. They're not depending on airflow momentum to build pressure, they forcibly ram in chunks of air. Thus they only have to spin at a fraction of the speed of the centrifugal unit to build boost. Yes, they are dependent on rpm, but at a far lower scale than any turbo or centrifugal blower.
The disadvantage to fixed displacement blowers is that they are notoriously inefficient at higher rpms, in other words, the constant compounding of compressed chunks of air creates a ton of heat. This is why turbos/centrifugal blowers are used for high rpm applications, because they don't create near the intake heat.
The Whipple/twin-scroll type is said to avoid this problem because it gradually compresses the charge before it forces it into the intake, whereas the Roots-type interlocking vanes basically continuously "smash and stuff".

 

For sure Gordon I knew you knew about fabbing it yourself, can't wait to see your setup. I know I won't be able to do it since school is really killing my time and if the FD is down I have no other car since it's my daily.


~Shar

 

Thank you Kento that was a very helpful post. I knew I wasn't imagining progressive boost on my friends mustang. That explains why.

 

It's alright, learn something new everyday. I think my friends was either a vortec or a paxton, I know it was the centrifugal type though. I just didn't know the positive displacement SC's built boost differently, just thought it was a different design of essentially the same thing. I can tell you his bloated mustang still lost to me haha.

I was looking at some other blowers and found a website that has the 6-71 and 8-71's for around $1500 or less. Seems like mounting this with a custom LIM and UIM on the top could be done fairly inexpensively for someone fabricatically (new word) inclined. If I had another RX7 I think I would devote it to experimental projects like these. Wait.... 2 money pits? I would probably have to live in one. eek

 

You guys might find this interesting. This guy developed a two speed supercharger system for the Rotrex that basically turns it into a positive displacement supercharger. Might be the best option for the FD. I have been trying to get a hold of someone to find out if they are available. They make a kit for the H3. The one on the Lexus is custom. Video sounds good.


http://www.engine-expo.com/forum_200...risbayliss.pdf

http://www.antonov-clubsite.nl/00000...803/index.html