DemonicPupil

I'm planning on supercharging my N/A in the same fashion ZBrown tried to do his. I have a few questions, and please hold off on the just swap a TII in, as I'd prefer some torque and HP throughout the power band, not just at the top.

My plan:

Run directly into the throttle body where the current intake goes in. Use a BOV to keep the motor from getting too much boost. I plan to run around 6-8psi. I assume that the N/A's richness will cover my fuel for now. Create a custom bracket for the supercharger. I'm looking at the Eaton m90's that have the oval backside intake and the blower coming off the top through a tube. I think this will eliminate the need for an adapter plate on the bottom of most supercharges and eliminate losses like that big fat flat plate that Zbrown had on his. Despite all the controversy over this, I look forward to the project and plan to document it fully so that others can follow (if I don't blow something up)

My Questions:

What problems am I likely going to run into?
Idle problems or vacuum lines that need to moved away from the blower and routed into the area of the intake that the blower is pulling from?
If my fuel system is running lean or too close for comfort, will higher octane take care of my problems?
What kind of power increase can I expect from 6-8 psi of boost?
Would it be a good idea to start premixing and running the OMP to keep good seals for the boost?
Anything else anyone would like to add other than criticizing?

Aaron Cake

iTrader: (1)

zbrown's setup is horrid. Absolutely horrid.

TII's don't act like that at all, and turbo 6-port engines don't even come close. Full boost anytime you want it...

That's the wrong way to do it. Using a positive displacement supercharger before the throttle body is a great way to make sure that BOV absolutely wails at anything but WOT. You need to place the throttle body before the compressor. I I should also mention that using a BOV as a boost control device confuses the hell out of the stock fuel injection, since the AFM indicates that a lot more air is entering the engine then the throttle plates are allowing. Very rich...


Nope. You're going to want 4 x 550CC injectors, with an S-AFC to tune them.

Aside from the normal fabbing problems, I pretty much covered it above.

If you copy zbrown's setup, then probably serious idle issues.

With the larger injectors, S-AFC and better gas, you'll be fine.

Nope.

DemonicPupil

I don't want Zbrowns exact setup, I'd really rather come up with a better way of doing it, while still staying cheap, so thanks for the reply. Again, I assume (dangerous, yes?) that there is no way to put the throttle body before the compressor using my stock throttle body. and what would make a better boost controller than a BOV?

http://cgi.ebay.com/ebaymotors/ws/eB...977113735&rd=1

I get the funny feeling that something like that isn't what I want? or is it? I'm new to the boost scene and tread lightly. I'd prefer to stick with manual things and stay away from digital add-ons.

Jager

iTrader: (10)

If you're trying to tread lightly, there are a few options. First for if you just want boost, go for http://www.1300cc.com. They have a bolt on turbo kit (after you find some parts).

Also boost can get complicated. Check out Aaron's site (if you haven't already). Alot of people have done the same set up on their cars with success and with ease.

SonicRaT

iTrader: (6)

You can rather easily move the TB around (using the stock TB), it's the intakes that eventually pose problems due to lack of locations/room, but it all depends on the charger. You'll be hard pressed to find one that's efficient for a rotary and puts out any decent ammount of power.

DemonicPupil

Been reluctant to post what kind of charger I'm looking at for fear of suddenly having a problem getting it for a decent price, however...

http://cgi.ebay.com/ebaymotors/ws/eB...MEWA%3AIT&rd=1

I planned on using this setup, I found one with the intercooler and air box and everything. Figured with a little adapting, I could get the entire system to fit in the car. Now I'm just looking at the complications. I figured that if the compressor went on the other side of the TB, then it would constantly be giving boost even with the throttle plates shut. Is there something else on the other side of those plates that restricts air flow? or would I constantly have boost, even at idle? then, having boost at idle, good thing or bad thing.

As far as a turbo kit, that thing is 1450 before I add in the costs of a turbo, exhaust manifold, etc. etc. etc. I am definitely looking for the cheaper route, otherwise I would have gone ahead and ordered a bolt-on kit and left it at that.

"If you don't have the money, you shouldn't have an RX-7", I've seen it in other threads. There's no reason I should have to shell out thousands of dollars for some horsepower gains, just because everyone else can. I don't like throwing money at things, I like throwing some ingenuity at things... So in order to avoid the flames about funds, better to end it before it starts...

RotaryEvolution

iTrader: (30)

ask snub disphenoid why he is getting rid of his charger, i don't know why for sure but i can speculate....

and the fact that turbos are cheap and easy to find and a lot less hassle and gamble.

why do we push to just go turbo? because we are trying to save YOU the headache.


sure you can make a charger work but i hope you know what you are getting into and do it right.

DemonicPupil

Exactly why I posted here.. I want it to work, work well, and be a permanent setup that isn't going to be problematic.

speed_monkey

Try pm'ing Rotarygod he got a supercharger, I think he has it all figured out as to how its going on. He also ported it or something to make it more effecient.

hondahater

iTrader: (2)

those cheap manual boost controllers suck! I've got one now and it was a waste of 10 bucks!

DemonicPupil

Willing to spend more than 10 bucks =P Anyone know of any decent ones that are manual?

DemonicPupil

Then I still don't understand why the compressor is going in after the throttle plates? If I let off the gas, isn't the charger going to continue pushing boost if the plates are closed but the compressor is blowing into the intake?

hondahater

iTrader: (2)

oh this is for a supercharger sorry, I just saw the link to the cheap *** mbc and had to say something about it, lol.

slpin

iTrader: (9)

the compressor is going to keep blowing

thats why you have a valve that bleeds the pressure

also, you do NOT use a manual boost controller to control the boost on a supercharger....

there is nothing wrong with a supercharger setup...

it is obvious that no one in this thread knows how a supercharger works....

DemonicPupil

slpin.. I understand that boost can be controlled with the correct pulley. More RPM from the motor, more boost from the SC. That's easy to understand and take care of. You seem to know all, so tell me and the rest of us...

Blower, before or after throttle body/plates?
If after plates, then your telling me/us that the motor will always be under X boost, even at idle?
If above is correct, then I know absolutely nothing about motors, because last I checked, you step on throttle, throttle plates open, more air and fuel go into motor, thus increase in RPM and etc. Can the motor idle normally under boost? I thought it couldn't...

rotarygod

iTrader: (1)

I have an M90 supercharger and although I haven't installed it on my car, I have had it in place to see the best way to make it work. It isn't hard at all.

You absolutely have to place the throttlebody before the blower. A roots type of supercharger is a positive displacement supercharger. It displaces the same amount of air per engine revolution (theoretically) regardless of rpm. At lower rpm's however it does suffer from a little leakage between the blower rotors though. Since the blower is always moving air towards the motor, this air will just back up once it hits the throttle plate. When this air backs up, it puts alot of stress on the supercharger and you are also trying to compress the air before the throttle plate. This heats the air up. If you recirculate this air, it will be warmer air going back through the cycle all over again. Obviously it can only get so hot this way. Your bypass valve would have to be absolutely huge to work properly and even then isn't working properly.

The easy (and proper) way to do it is to move the throttlebody to in front of the blower. First of all you don't need any form of a bov this way. Will you make boost at idle? Nope. Not even without a bypass valve. Why? If you are restricting the airflow to the blower, where is it getting air to blow towards the engine? It can only move what can come in. Basically you are just spinning it in a vacuum. That is far more efficient than spinning it in a pressurized environment such as before a throttlebody. At part throttle, it is still only moving a regulated amount of air. If you were to place the blower before the throttlebody, it is always trying to move an unregulated amount of air towards a restriction. Your bypass valve would be open 99% of the time. This is a huge waste and is robbing power from your engine more than the correct way of doing it at any location other than full throttle.

You are correct when you say that the throttle plates open and send more air and fuel into the motor. When you step on the throttle and allow more air to get to the blower (with the blower after the throttlebody), it can pass this air along. Until you step on the gas, the blower is essentially doing nothing since hardly any air can get to it. With your blower in front of the throttlebody you are just letting the blower work full time since it always has an air supply. No a motor can't idle under boost so why would you want to send high pressure air to it? With the throttlebody after the blower this is what you are doing. I know you want to use a bypass valve but it would have to be larger than the inlet of the blower to prevent this from happeneing. By restricting the blower inlet with a throttlebody, you are telling it when it can make boost.

Zbrown was a prime example of how a little knowledge can be dangerous. He knew that a supercharger could increase power but he didn't know how to properly execute it's installation. He decided to take the easy way out and just fit it into the engine bay and plumb it in. It isn't this easy. Here's the easiest way to do it "properly" assuming of course you are content with low boost and no intercooler. You also need to have some fabrication skills and be able to weld.

Use the S4 stock lower and middle intake manifold. Make a small plenum adapter that replaces the dynamic chamber. Install your blower onto this. Custom fab up an inlet that turns towards the passenger side of the vehicle and place your throttlebody there. If you hold the blower in place you can easily see how this would be accomplished. You can retain the stock fuel rails this way and the stock throttle cable. You will have to relocate the alternator elsewhere and obviously fab up a pulley system. You could purchase a full pulley set from Atkins Rotary that they use on their Camden kits and then retrofit them but this will set you back about $400. Get creative.

Some other mistakes that Zbrown made that really hurt him in power are the terrible inlet and outlet pipes. A blowers efficiency is hugely impacted by how well the inlets and outlets flow. They are much mroe sensitive to these than any other form of forced induction. Zbrown had a small 2" inlet from the afm. Admittedly you are going to lose alot of efficiency through the afm but the point is to keep the intake velocity high while still keeping it flowing as much as possible. The outlet needs to be done very well. Zbrown had just a small plate with a pipe attached to it that sent air the the throttlebody. This absolutely killed his efficiency but no one knew it. This small outlet that he made had the same effect as putting the throttleplate after the blower which he also did. It restricted the outlet causing the blower to have larger pumping losses. This also heats up the air worse. Have that blower outlet dump straight into a plenum that goes straight down into the intake runners for best results. The best setup yet would be to just bolt the blower to the top of a Racing Beat Holley manifold. There are also mods you can do the the blower case that will make it far more efficient but I won't get into that here as you have to know exactly how to time the inlet and outlets of the blower cases and then also know what shape to make them. You don't just hit them with a grinder.

First and foremost, get the blower fabrication done and get it running "properly". Then worry about that later.

DemonicPupil

That was a perfect explination and understood easily as well. In my mind, throttle plates before the blower, wasn't throttle plates blocking the blower from grabbing air. I thought it blower blowing into the intake and the throttle plates.. I don't know what I was thinking, but it wasn't how you explained it. Now it all makes better sense.

Lucky for me I have another 7 that isn't even close to being in shape to run so I can work on fitting a supercharger to it's intake and making it ready to bolt on to my other vehicle. Thanks RG for the explination.

RotaDrift

that was that greatest explaination of how superchargers work and actually how to install

I bow down to your knowledge...

DemonicPupil

Sure works better than 2 posts about how little everyone knows

Theoretically, what if (for less intake modifications) the blower was run before the throttle body, but plates were put before the intake of the blower that are connected to the throttle body? Thus when the throttle plates are opened, so are the intake plates before the blower. Maybe a little less efficient, but not as bad on the blower. Theoretically this could work right? So that the only modifications done to the system are at the intake?

speed_monkey

Yo rotarygod I was waiting for you to chime in. lol

rotarygod

iTrader: (1)

Why make it more complicated than it has to be? If you still want a similar setup to Zbrown's setup, do it like he did but with much better inlets and outlets and just move the throttlebody to before the blower. You'll only have to replace the throttle cable with a longer one this way. Positive displacement superchargers do not like long intake runners so you'll lose some efficiency this way but it will work fine. I could write a book explaining that last sentence but I won't.

DemonicPupil

I was just trying to eliminate the hassle if I decided I didn't want it on there or I found that it was making my car run like horse ****, I could just pull it off and toss my old plumbing back on. Wasn't trying to make it even more complicated, just trying to eliminate any hassles of reverting back to stock. Thanks again RG... just trying to look at all my options.

rotarygod

iTrader: (1)

If you install it like I described, all you'd have to do to put it back to stock is remove the blower and the small plenum and bolt the stock dynamic chamber back on. You could get it all back to stock very quickly.

DemonicPupil

I take it this means that intercoolers aren't good for PD SC's?

snub disphenoid

Why would you supercharge your RX-7? The rotary engine has such an incredible abundance of exhaust gas energy. You don't have exhaust valves in the way. Do you not have any sort of power goals? What happens if you want more than 200hp?

Yes, superchargers can work on RX7s. They don't work terribly well, but with enough money, you could probably make a decent setup that worked somewhat normally, but it sure as hell wouldn't be done with a stock ECU. My car has been supercharged for 6 months and it still hasn't made it to a single racing event this year. You talk about low-end power, well I don't have much (although the road/race exhaust has a little something to do with that). A BNR hybrid turbo is on full boost by 3500rpm, and it's not like your car is going to be gutless below that anyways. On top of all that, the M90 is poorly sized to the rotary engine (it's sorta like slapping on a T25 onto a TII).

The bottom line is - if you want a car that drives like it's stock, has good power response and a healthy top end, AND you want to do it cheaply, go turbo. Don't argue, because you can't. There is no way that you can justify supercharging an RX-7 over turbocharging it unless you want to be "unique", in which case you can spend a few grand, still be slow, and feel special. You can look up my old threads where I thought like you, and six months later, with nearly nothing to show for my efforts, I think my opinion has changed a bit.