Dudemaaanownsanrx7

iTrader: (23)

How much boost are you running with the SC? Very interesting setup.

I agree with RotaryRocket88, you should really find a way to check your afr's and tune them. At least check them somehow.. If you're overly rich you're leaving a lot of power on the table, and if you're overly lean your asking for a blown engine. Just adding a fuel pressure regulator (one you're not even sure of the ratio increase at that) is not a safe way to add a major power adder like a supercharger. Shoot on my FD just switching from a t61 to a t70 required my whole boost map to be retuned. Fortunately the water injection will give you some increased safety margin, and it's major benefit is inside the engine more so then reducing AITs.

I'm not really familiar with the older rx7's and the fuel injector setup on them, but it doesn't take much to start maxing out stock injectors. Also on the FD's the wiring to the fuel pump sucks, rewiring it gives 2 extra volts, if the older cars are similar a fuel pump rewire could give you more output from your pump.

RotaryRocket88

iTrader: (7)

9s are the trailing plugs. And they're going to be colder plugs than than the stock leading BUR7EQs.

I think the 5,800 rpm number was referring to engine speed rather than blower speed. If the pulley was too small originally, the blower would spin too fast at high engine rpm.

remtec76

that's a nice kit, where can I get one?,ive been for something like that.

rotarygod

iTrader: (1)

You can't buy those anymore. Any you do find will have to be used. There were some design issues with the original kit. The sc pulley was too small causing the blower to overspeed. The solution of course is to use a larger sc pulley which also reduces boost. That kit also has no bov. Easily remedied. I'd personally use one that is from Vortec and then plumb it back into the intake side of the sc. They have a unit which is not only a bov but also a bypass valve depending on load level.

Those kits did not have any kind of engine management. They only had the rising rate fpr. It came preset and the owner was instructed to back off 5* of timing on the cas. Of course this also hurts power everywhere at every load as well. The hope was the the rich mixture and the slightly lowered timing would result in no detonation yet still have a performance benefit. It had it but admittedly not nearly what would be considered optimal. There is power being left on the table without ecu tuning. Those kits typically dyno'd 210-215 or so. Not that bad for no tuning, no intercooler, and only about 7 psi or so. Then you had the issues below.

You had the blowers themselves. Those were very old designs. The compressors were very inefficient by today's standards with their straight blades. A good 10-15% lower in effiency than modern units. Their drive systems were also inefficient. It takes alot of effort to spin those old things. They were not belt or gear driven. They were friction drives. Imagine ball bearings compacted together so tightly that the force or friction between them moved the others when one spun. That's basically how those work. More or less. So now we have a less volumetrically efficient and more mechanically parasitic blower design. Still pretty decent numbers considering all the things going against it. Compare that to a TII at the same boost! I'd love to see a more modern centrifugal such as a Vortec which is less parasitic and with a higher VE combined with proper ecu tuning. I'll bet it could be pretty nice.

It's no wonder so many rotary people hate superchargers. They've only ever seen 2 designs. The old Paxton units suffing the issues I just described and the Camden roots blowers which are the oldest most antiquated and least efficient of all blowers, even roots style. Throw a good sc on a rotary and I'll bet many people would change their views of superchargers a little bit. There will always be the debate over turbos vs supers of course but at the end of the day the only real answer to the argument is "it depends". Everything has it's place, including superchargers.

remtec76

well it would be nice if they made a kit like that,but like you said more efficient,thanks for the info.

mike_merryguy

iTrader: (8)

you can buy a kit from someone maybe with a blown unit, and get a new blower, a guy in San Marcos CA still deals with these on a daily basis, he loves them, sells mustang kits for like 1800 he said, sure if someone was to remake the bracket it would be pretty cost efficient, the prices on the used kits are higher than a new one would probably be just cause they paid so much for it.. the pulley situation sucks, they were designed for low RPM piston engines, you red line a lot lower so the pulley can be smaller bringing the boost levels higher, sucks but that is the way it is.

I personally have a Turboxs BOV, the BOV isn't really needed, I guess when you shift or if you are using engine to slow speed, when I slow from about 45 in 2nd the thing screams like crazy, it really isn't needed though, you would just have a boost build up and when you hit the gas you would probably just get more of a rush but at idle it produces 0 boost anyway, I have 18 vac at idle and typical acceleration I only get to about 0 boost, until I am over about 3.5 to 4 K is when it builds, so on a normal drive it just sounds cool, and has a little better throttle response
You are right about the engine management, the FPR is supposed to keep things in line, but with no FPG, hell I don't even know if its working, I didn't read about the timing, better double check that to make sure I am not gonna blow something LOL, I however am injecting water at about 1PSI, yea I know low, but I have only seen about 5PSI according to my boost gage, that I am sure will help a little, thinking about just running washer fluid so that it will act as more fuel basically, see how this next tank of gas sounds, I heard a little knock yesterday and backed off right away, don't want that apex popping!!!


You are right about the old design, there is an impeller upgrade, the fins are not straight in them, they produced a little more boost than normal of course too, I also don't like the drive system, not that great, you are right the pulley is on the main shaft, which has a CAM in it to drive the oil pump, that pump only provides fluid to the two bearings in the front, then the shaft attach's to a brass thing-a-ma-bob, it has 5 spots in it for the bearings to sit in, that is all sandwiched between two races, in the center of the 5 ball bearings is the output shaft that attach's to the impeller, which of course creates the boost, very weird how that works, the red line of this system sucks as well, 3800 RPM, a better design I am sure could yield more boost, They still make the Paxton blowers like I said, they sell for about 1800 new..

I don't think so many hate the supercharger just the price tag on it, a turbo is a lot cheaper cause all you need is a ecu, map, afm, and whatever else, all which can be had from a parts car fairly cheap, the s/c on the other hand is all custom work, so of course its going to cost A LOT more, for instance if I can't get the knock under control I am going to be forced to find a stand along, probably go with haltech if the new system has been fixed to allow timing retard under boost, haven't looked into that lately, now I may not have to do anything, forgot I had mostly 87 fuel in it when I got in the pedal, was only able to get a few gal of 91 in when I finished the kit, I did top it off today with another 9 gal of 91 so hopefully that helps things out as well... The only real problem with other types of blowers is the input and outputs, the only one that I have seen that can be put where it is is this one, a lot of the other ones push the air out of the side, the guy at Paradise Wheels said that even this blower has to have a custom back plate put on for the RX7, there is nothing easy about supercharging these beasts LOL

And like I said before there is a guy selling one in the 2nd gen section, just search for PAXTON

mike_merryguy

iTrader: (8)

got screwed by the seller, you can read about it in his for sale thread, I had to rebuild this thing for almost a grand on top of the 2250 he charged me for it..

https://www.rx7club.com/2nd-generation-rx-7-1986-1992-parts-194/fs-paxton-super-charger-kit-800695/

SonicRaT

iTrader: (6)

As already mentioned, the killing factor is cost. I think i've only met/known about two other people who've had as much experience supercharging 2nd gens as I have. I've put just about every setup there is through it's paces. Comparably, the Paxton kit with the compressor upgrade kicks the absolute **** out of the camden kit with any amount of money thrown into it. The largest issue with most blowers is finding one that's a nice size/fit for the FC bay and also one that flows within it's peak efficiency range. The majority of the modern Vortech's would surge without a bypass valve. That was the route I went a while back with my GTUs. You can indeed get some fairly decent numbers (I never got anything spectacular), but the noise/issues with the bypass and overall complexity was really a turn off. Twin-screws are definitely my favorite path on a rotary, they're just ungodly expensive.

There's a boatload of threads from a while back with the various dyno comparisons (I think it was pianoprodigy that made the spreadsheet?) It has one of my whipple cars, his Paxton setup, and some of the camden/other setups graphed out. If you've got the money to spend but not much fabrication skill/time to make your own setup, the Paxton kits are a very nice find.

Injectors/pump/SAFC are definitely the minimum i'd suggest even with the Paxton, they do seem to work alright on the stock equipment but from everything I've seen it was pretty strained.

So, in the end you picked the 'right' blower of the two kits available and it's nice to see they're still floating around.

MazdaMike02

iTrader: (4)

Seems quite expensive, If it were cheaper Id consider giving it a try. I used to have a 93 T-bird Supercoupe it was fun.

FC-Dan

Does anyone think that a traction drive supercharger would be possible? I'm sure it could be done with the right amount of money. I've heard many good things about traction drives, and I'd think it would be awesome on a second gen. http://www.mazdatrix.com/8forcedinduction.htm <----- Something like that would be amazing for a second gen, without the whole $8,000 price tag.

myersprostatus

iTrader: (2)

i wanna hear it, make a vid

rotarymandan

iTrader: (15)

Video please!

mike_merryguy

iTrader: (8)

be back in cali the 22nd, i'll make a vid i promise... lol

walken

iTrader: (6)

IMO upgraded pump, 550cc, and Full T2 electronics are a must. you have no timing control and the engine wont know how much fuel to add or even how much boost you are running. even after all that it still isn't mapped for the SC, just a good template so you'll need a AFC or similar and some wideband time. seriously just a heads up. go through all the SC threads and see how they ended badly and what engine management they chose.

mike_merryguy

iTrader: (8)

So I have switched from running water to washer fluid with good results, still no dyno but I can feel a decent improvement.
I also finally installed my Banzi Racing Poly motor mounts, not the best product in the world, the directions were not very clear if I should keep the original pucks or not, I couldn't get the ds mount out of the top cup, I dont even know if it should come out or not anyway So I didn't use the top cups, I did use the bottom ones though..
The quality of them isn't that great, as I was tightening one down the nut stripped out in it.. there is a bolt that threads through a disc with a nut on it to compress the mount for installation, not that big of a deal I just used the main nut to compress it, they are not kidding when they say increased vibration, I hope they break in well..

I have a guy that wants to look at the car this week, hope he buys it. I hate to see it go but can't afford to keep two 7's, well I could but my wife would kill me LOL

still no vid, sorry I will make one, I just don't have a camera man, If this guy doesn't buy it this week it will go to 7stock and I am sure I can get a video of it there...

mike_merryguy

iTrader: (8)

sold pending payment and pickup

some young guy in san diego, his first car, just hope he doesn't destroy it...

tulok

so no video then?

dennis blackstone

dyno dyno dyno dyno

SirCygnus

iTrader: (1)

i wanna see someone build a kit for the new supechargers.

mike_merryguy

iTrader: (8)

well the car was sold today, I didn't get what I wanted, but I expected that, the guy that got it is young but seems pretty responsible, both his parents and his brothers came up for the exchange and they are an awesome family, hope you enjoy the car man!

I did get a quick video of the car, just start up and a little boost in the car and popped the hood and got a couple revs in, wanted to do a drive by but my battery was dead on the camera and its a 15mph zone in my neighborhood (my wife volunteered to record), I'll post that up soon, I have to convert the file to the right format and I'll put it on you tube..

ifryrice

Nobody in their right mind is going to put together a decent RX7 supercharger kit. It's silly to imagine someone buying a kit that's valued more than the car itself would be. Roots blowers are just crap. The camden unit proves this in every possible way. Biggest waste of money someone can throw at the car. Centrifugal are alright, but require a bypass to get the blower in a decent range for the FC which introduces a LOT of noise. They're probably the only 'kit' that would be worth it (still pricey...). That's why the Paxton's are still so sought after, they actually WORK (albeit it if only for relatively smaller numbers). Twin-screw is where the numbers are and nobody wants to pay to go that route so just throw a proper sized turbo on and be on the way or find a paxton kit.

For those demanding dynos, just search. There's at least 20 threads with all kinds of supercharger dynos/info.

NV02

iTrader: (3)

I thought I would throw in some observations I've made concerning an '88 vert I purchased with the Nelson/Paxton SC kit already installed. First, I bought the car in the Bay Area with known power issues. On the way home, the poor thing barely made it up the mountain (I live at 7000 ft). Once I got it there, I gave it a good tune up and discovered that the trailing plug on the rear rotor wasn't getting spark. The plug wire was bad and upon removing the plug found that it had never fired! The other three plugs were pretty worked over. All new plugs/wires/fluids, aux port actuator cleaning, and a shot of injector cleaner really got things moving again.

Most of the cars I have owned have been turbo charged, starting with my '87 TII bought in '88. I've also owned a TRD SC'ed 4Runner up here at altitude. Once you get over the initial turbo lag, a turbo charger seems to work pretty much the same as at sea level. The supercharger, on the other hand, seems to suffer the same fate as NA cars at altitude although not as bad. The '88 SC vert that I bought came with a dyno sheet that maxed out around 175 HP. Was that with the bad plug wire? I dunno. I've tried to give the rotary a carbon cleansing every time I take it out, but quite honestly, the performance has been less than thrilling. And does this thing get hot! Talk about a heat sink. I switched to all water coolant trying to keep it from overheating crawling up the mountains. Now it can make it up hills without looking at the temp gauge instead of the speedo.

One thing with this SC is that the power curve is really shifted down. Power comes on right away, but as mentioned earlier, the ride is pretty much over by 5500 RPM. Quite a contrast from my '87 TII. Of course the 16 years between owning my TII and the vert may have affected my memory.

Having said all that, I just recently drove it back to the Bay Area. It was like a whole new car. That thick, cool, sludge that passes for air at sea level really brought the SC to life. Now I wasn't about to hunt down Corvettes or anything, but the throttle response was instant and would actually push you back in the seat a little. The heavy vert actually felt like a sports car. I can definitely see the benefits of the SC at lower altitude (and with a good tune-up).

The moral of this story: for the right price and right altitude, the SC makes for a decent power adder. I personally have TII parts ready for a rebuild and swap into the vert.

ifryrice

It's interesting your observations with the power band. The Paxton kit band while a bit flatter and more predictable suffers a bit from being a centrifugal unit in the low-end, and should come to life later in the band. Do you know if it's an early unit? If I recall they changed the blower around a bit and had a unit that flowed quite a bit better. In any event some kind of fuel/ignition controller really helps to bring them alive. And for a supercharger, the Paxton kits are as good as it gets for bolt on superchargers.

NV02

iTrader: (3)

It looks like the kit was purchased in '98. I'm not sure if that is early or not. It was put on a remaned engine and has run for almost 60,000 miles. I was told the SC was rebuilt at some time, but couldn't find the receipt to prove it. Still looks to be a pretty solid unit although I can't vouch for the PO's driving habits.

Perhaps I've just become accustomed to high altitude turbo lag, but low-end power feels reasonable. Probably a good stand-alone ECU and better header would give it some umph, but I'm going to focus on the TII swap from here on out. At least I have some kind of FI until then.

rotarygod

iTrader: (1)

It makes sense that a supercharged engine would behave much like an n/a at higher altitudes. It isn't going to get as much boost as there is no way to compensate for lack of ambient air pressure. A turbo references manifold boost pressure and will just keep the wastegate closed a little longer to make up for it.

Even a centrifugal will give a power gain on the low end although not a ton. Let's say that at 3K rpm, a centrifugal sc was only giving 2 psi of boost. That's not much. However the engine wouldn't have been breathing ambient pressure without the sc. Very rarely does an engine hit 100% VE on it's own. Let's say that at 3K rpm, the engine was only at 60% VE without a sc. That's not unreasonable. That's only 60% of the engines breating potential or from an effective standpoint the same as having an engine breathing only 8.82 psi of air (ambient at sea level theoretically being 14.7 psi). However that mere 2 psi of boost is over ambient. Now our engine is breathing 17.7 psi which is nearly a 50% increase. You'll feel that. I greatly simplified this so for all those nitpickers out there get over it. It's an example.

It's true that other devices that make boost earlier and make more of it will make more power there. However don't be fooled by only looking at the boost and assuming low boost must mean no gain. A gauge could actually read no boost but there could still be a gain. Think about that one for a while!