snub disphenoid

Air-air intercoolers aren't good, air-water intercoolers that sit directly below the blower seem to work somewhat well. Water/alcohol injection may work, as well.

rotarygod

iTrader: (1)

We'll just ignore those apparently biased parties in this thread. Experience with supercharging doesn't count if it wasn't supercharged correctly in the first place. That's not useful experience. Edison went through over 700+ combinations of failed atttempts to make a successful lightbulb before he got it right. Just think if he'd have given up after the first try! That 1st try didn't make him an expert on it. It made him an expert on the fact that that particular way of doing it didn't work. The difference with supercharging is that there is plenty of information available on how to do it and how not to. The rotary community as a whole is typically pretty ignorant as to how to do it properly and the only supercharging kits we have for the rotary use the single oldest and antiquated supercharger design out there and what is there can be improved on. No wonder the rotary community hates them! Needless to say there will always be those that think turbocharging is always the best option and there will be those that will see supercharging as an alternative that is right for them. Why these parties can't keep their own opinions to themselves is beyond me. There is a place for every system.

I love remarks like "what if you want more power?". Yeah, what about it? You change pullies if you haven't maxed out the units ability and if you have, you change to a larger blower. What if you want more power from a turbo? You raise the boost and if you maxed out the turbo and want more power you get a different turbo. What's the point?

How about this one? "Do you have any power goals?" This is classic. What if I said my power goal was 220 rwhp? Can I hit it with an M90? Sure I can. Can I hit it with a turbo? Sure I can. I could hit it with a stock T-II turbo. What if my power goal is 400 rwhp? Can I hit it with an M90? Nope. Can I hit it with a stock T-II turbo? Nope. As with anything else out there you design according to your goals. What if I just want a nice little bump in power and don't care to dyno race anyone on the internet? Can I do this with either turbocharging or supercharging? Sure. Why not? I think it is safe to say that anyone considering supercharging on a rotary isn't looking for 400 hp and those that are had better be ready to spend alot of money. Most are just looking to make their car a little faster and more fun and like the option of supercharging. Let's face it, your own car doesn't have to meet anyone else's approval.


"How can you intercool it?" The same way you can intercool a turbocharger. What's so hard about that? You can use an air/air and an air/water intercooler with a roots blower too. Obviously you can't if you didn't leave room to pipe it in but that would be a design error and not an intercooler problem. The Thunderbirds that used these M90's originally were air/air intercooled. Admittedly their systems were a poor excuse but they too could be upgraded. There was no greater an issue with the long piping distance after the throttlebody than there is with the long intercooler piping with a tyical front mount intercooler. Look around the internet for cars that have front mounts with roots blowers. You'll find a few. Yes most use air/water but this is also the smallest system that has the least piping. Take your pick but even a roots is very good to intercool. Since air heats up in the manifold with these blowers, you'd come out very far ahead to find a way to intercool it just like a turbo.

How about this. "You can't make it work normally with a stock ecu." Actually if you want to get technical, you can't make an n/a ecu work properly with a turbo either. The stock ecu's on the RX-7 even the T-II's is pathetic at best. It's afm is terribly restrictive and you never see them used on 400+ hp RX-7's anyways. That kind of did away with the power goals statement as well. Anyone with huge power goals wouldn't use the stock ecu anyways. Can the stock ecu be made to work with both turbochargers and superchargers? Yes. They will never be optimal but can be made to run just fine. For a supercharged system, run the vaccum line from the map sensor to in front of the blower between it and the throttlebody. It will never sense pressure this way. Now just run a rising rate fpr. This simple setup while not perfect will do very well with a positive displacement supercharger at holding the a/f decent. Yes, it works.

I like this one. "Superchargers rob power while turbos use free exhaust energy". While I do agree that a properly sized turbo is less of a parasitic drag on an engine than a supercharger is, turbos by no means do not hurt power. Some of them such as the T-II turbo rob tons of power to make it. People like them. This is apparently a worthwhile tradeoff for a turbo so why isn't it worthwhile for a supercharger? Would you run your n/a engine with a small 1" exhaust pipe restricting the exhaust? Of course not, that would kill power. While that was an extreme example, that's what a turbo does. It too robs power to make it. How much of a power difference would an n/a engine make with a single 1" tailpipe vs a complete free flowing system such as a true dual or a good header? Tons! Yes larger turbos restrict the exhaust side less but they also spool slower. There is always a tradeoff with any setup. Smaller superchargers rob less power and make less boost, larger superchargers rob more power and make more boost. No surprises here. Personally if I wanted 400+ hp out of a rotary, I would turbo it. Wait, I have done that!

The whole point of this isn't to change anyones mind about what they do or do not like. It is to keep those people who are still open minded that there is actually more than 1 viable option in the world that will give your rotary more power. The perfect engine for supercharging is also not the perfect engine for turbocharging which isn't the perfect engine for naturally aspirated use. Think about that one for a while!

FWIW: I used to own a 400+ rwhp turbo 2nd gen a few years back so don't think I am biased against turbos or vice versa. I'm not. I just have an open mind for alternative power goals and uses and intolerance for misinformation, poor advice, and biased opinions. If you want a supercharger, the turbo people will not convince you otherwise and if you don't like superchargers we can't convince you otherwise either. Why everyone cares what the other person does is beyond me.

SonicRaT

iTrader: (6)

The m90 isn't a good fit for the rotary. Yes, you can get 220rwhp (why the hell would you waste your time for that?). The things are HORRIBLY inefficient. You will ABSOLUTELY require an intercooler. I dumped about $3500 into my M90 setup, and the most I could ever squeeze out of it was 270 to the wheels before the thing would just spew out nothing but heat. If your goal is a shitty cheap setup, well then the M90 is for you. You'll have excessively high intake temps, very low power output, and more fabricating than 90% of you think. (sitting the m90 on the middle intake manifold hits the roof, just for your info).

Now, if you REALLY want a decent supercharger setup, find a properly sized centrifugal or go with a twin-screw where you're not limited by a shitty adiabatic efficiency range.

Why do people dislike them and complain so much about them? Because it's usually wasted money, almost all scenarios you can build a very similar power curve for less using a turbo (and don't argue the whole low-end thing, with some turbos the torque from 2k up is the same as the previous 'supercharger' dyno's provided here).

rotarygod

iTrader: (1)

I agree that the M90 isn't a perfect fit for a rotary (then again that's goal dependent too) but 270 rwhp isn't too bad. That's just about the limit for the stock T-II turbo before it too does nothing but spew heat. That's also the turbo setup that so many seem to recommend going to for "cheap". "Just do a T-II swap". That's all people ever say anymore. Around here you can't even find a T-II yet alone a good engine setup out of one.

I would definitely like to see a properly sized twin screw supercharger used on a rotary. That could be really cool. Centrifugals are worthless IMO. I just don't like their powerband.

Off topic: Sonic: I heard you were in Houston now. Are you coming out to the club meet on Tuesday?

DemonicPupil

At the moment power goal wise... I'd be happy to reach anything higher than stock. I was disgusted by getting toasted by this lil bitz in a 5.0 stang that had it completely riced out (sorry rice on American muscle is so wrong) anyways, my N/A was holding strong, but it just needed some more horse power. I'd love to be able to grab a hold of his tailpipes and hang in for the ride if that's the best I can do. I also am very dissapointed with my top end speed, right now it's topping out at around 120. A little more push would do wonders.

I also plan to add Nitrous when I upgrade the fuel system at a later time. 50 extra horses on the end of what the SC gives me will make me more than happy. I'm looking to do the SC setup for less than 1,000. Less than 500 would be wonderful. IF I throw in an IC and it costs me a crapload more, I can deal with that. When/If I decide the SC isn't enough for my needs, at least I'll have the IC for whatever choice I make after the "shitty" cheap setup that gives me some much needed HP.

The 7 looks far too hot and handles far too well to be slower than just about anything else out there. I'm a college student and don't have the cash to just start throwing it at my car.

rotarygod, thank you for the advice and information to get this mess straightened out and giving us all a better understanding of the best way to go about a project like this. Clearing up some common misconceptions and pointint me in the right direction. Thanks for supporting those of us that are willing to go whichever way we choose.

I have no problem with turbo setups, however in my mind they are far more complicated than an SC setup, especially when it comes to needing exhaust manifolds etc.

270 HP is at least what, 100+ more than I currently have in my N/A?? 33% more HP, sounds like a good fit to me.

Jager

iTrader: (10)

Cheap, reliabile, and fast. Keep in mind you can only have two. Topping out at 120? You should probably check some **** out, both my 7's I've had up to 135mph.

Have fun.

SonicRaT

iTrader: (6)

270 comes at WAY more than you can afford. Think ported intake plenums, ported charger, raised outlet, air/water intercooler/etc.

Ok, to be realistic here...

Your average pulley setup with an FD alt is around $200-250, or around $100-150 without the alt, depending on how you 'plan' to rig this up. (This is for 6rib btw). 8rib the price increases because you either need a custom waterpump pulley made, or you need to stick the nose out so far that you run on a crank and idler/tensioner alone.

Idler runs about $40, tensioners are about $50+, so now lets say we're at around $100 for that.... you then need brackets to hold all of this. Weld them yourself for a cost of around what, $25?

Total so far: $375.....
Average cost of a charger: $200
Fuel pump: $100
Fuel injectors: $120 for some 720's and $50 for some 550's
S-AFC to even control it: $150-300
Clutch since the stock n/a one gives out at around 200rwhp: $300

Now comes some custom fab work. First you need some brackets to even hold the charger, and like I said, you'll hit the roof in most locations. Now... figure that since you probably cram it into the passanger side area to solve this issue instead of using better intakes, you now need a custom intake plenum, (which is almost gauranteed to flow worse than the original),. You then need to change your TPS wiring, get a new throttle cable to go to the relocated throttle body. Now, you need an intercooler because guess what, you have less than 52% adiabatic efficiency, you're going to make so much damn hot air running without one is just stupid. So... now figure in a cheap front mount and pipng (say what, $300 at the VERY least?), which someone then has to weld a bypass into, and also adds lag and isn't as effective as an air to water. Generally in materials alone the custom work runs you damn near $200, throw in the intercooler and piping, and you're at damn near $500 alone (at the VERY least assuming you do almost all of it yourself).

Now... you've got it all bolted up and running and you can only run 8psi before the charger starts exceeding itself and pushing hotter air out than is actually doing a benefit, which leaves you at what, 215rwhp for a grand total of roughly $2k. If you REALLY like wasting money, then go ahead.

SonicRaT

iTrader: (6)

I'll be in Houston in about a week, I seriously doubt I'll be joining a club or going to many meets simply because I'm not a very good people person. I tend to get a bit on the offensive side when I see people throw around the idea of 'do whatever I can to go fast without understanding or even thinking about it'.

As for the 270hp thing... This was after doing almost EVERY mod possible to the charger and car, as I said, it cost WELL over what your average TII runs.

I have built a twin screw rotary before with very good results, had around 350hp, very nice car! The problem with centrifugals is sizing them for the rotary, they have their place and benefit (small size, easy to install, etc), but they're so hard to find sized to benefit a rotary.

gingenhagen

exhaust manifold? I've never heard of needing such a thing. For 270 HP on a stock turbo, you'll need in general a new exhaust, new intake, more fuel (pump, injectors, computer), and a boost controller. Correct me if I'm wrong.

SonicRaT

iTrader: (6)

He's saying to fit a turbo on an n/a block.

staticguitar313

iTrader: (2)

This dead horse has been beat, even i prodded at supercharging. The only real advantage to it is uniqueness. Uniqueness wont gain you speed.

rotarygod

iTrader: (1)

I wouldn't expect to just bolt on an M90 and get that much power. Understand that Sonic did just about everything he could to get every last little bit of power out of it. Don't consider him typical. Just look at it as about the overall max potential out of that unit. Realistically I'd expect closer to 215-220 or so but even that is more power than you have now.

Don't underestimate the amount of work needed or the amount of money needed to make it work properly as well. While I am by no means against supercharging a rotary, I do not feel that it can be done very well without spending a little money. Zbrown did it for about $300 but he also got the worse of the M90 superchargers and fabbed everything up himself. He also messed up in just about every single aspect of the design. Sometimes that's how you have to learn though and I at least give him props for the attempt. There were 2 different M90's on the Thunderbirds. The later ones were only available for 2 years and are about twice the price of the older ones. Typically $300 or more vs $150. They are also more efficient which is obviously very important. Do a search on the web for the differences between Thunderbird superchargers to see what I mean.

If you want to supercharge it, go for it. Others have and like it and still others have and hate it. One way to find out. Just don't assume this is a cheap easy thing to do with good results. Don't take shortcuts. They never work. Just remember the number one question when it comes to custom work. Why is there never enough time and money to do it right the first time but always enough time and money to do it again?

rotarygod

iTrader: (1)

I'm not sure if that was a shot against me or not but who cares what others think or do? There are always people with different opinions but that never stops us from having a good time and from seeing some cool cars. I still think you should come on out. You'd have fun. I can already think of one guy in the club who is very talented at rigging up the biggest pile of running parts (if you can call it that) you've ever seen. I don't agree with his methods but he is at least entertaining and good for a laugh.

snub disphenoid

What's more complicated, custom fabricating a setup to run an M90 on an RX-7, or putting on direct-fit parts that you don't have to fabricate?

Doing a supercharger setup on the super-cheap doesn't really get you anywhere, as we found out with Zbrown, and if you want to spend a ton of money to have a maximum of 270hp, feel free to do so. If you need to use your car often, custom fabricating a supercharger kit probably wouldn't be a good idea. Just stop thinking "supercharger, supercharger, supercharger" and think rationally about your goals, your abilities, your materials, and your resources before you step into a project like this. I wish I could have back when I had a chance to, but I chose to ignore people who had real experience with this.

SonicRaT

iTrader: (6)

Not against you at all, was simply stating that usually the groups have those select few who have very little knowledge/respect of the car, and just do whatever there is to make it just stupid fast and then ramble on like it's the best thing in the world, they usually get me going pretty quickly, lol. But I'll see what it's like once or twice and see if I end up killing anyone or not, hehe.

rotarygod

iTrader: (1)

I didn't think so. My car isn't rigged up though. I'm a firm believer in standlones and doing everything only once. There really isn't anyone in the club who is like what you are concerned about. Alot of the owners are RX-8 people. We've got RX-7's that come out. There is one guy who compiles random parts to make his car run and he is proud of it but he is just good for entertainment valvue. There is another who trys things randomly but he is also very open to suggestion and criticism. I've actually never had any problems with anyone at meets. 5 or 6 years ago everyone fought with each other and was proud of their rigging job. I think the club has progressed away from that and is now more centered on hanging out with other fellow owners. The stupid fast cars in the club are actually very nicely done stupid fast cars. You probably won't end up killing anyone. At least not for the first few meets!