titancronos

Ok, I think we all know the difference between a turbocharger, and a supercharger.

Turbo = run by exhaust gases to force air into combustion chamber

Supercharger = run by engine belts (ie. waterpump, alternator, a/c, etc.) to force air into combustion chamber.

I hear a lot of you guys talking about adding a turbo to your n/a, and so forth. But nobody ever seems to want to add a supercharger. Is there something I'm missing here? A supercharger (to me anyways) seems to be a much simpler addon. you simply mount it in the engine bay, run a belt to it (you could even put in in place of the a/c pump), and have the airflow directed through it.
Perhaps it would not give you as much boost as a turbo would, but it WOULD give boost, and some boost is better than none.

So anyways, this is something that has puzzled me for a while, and I hope someone could enlighten me.
Thanks
Dan

Freaky Monkey007

I think the main reason is the fact that the 7 is more suited for a Turbo with the high exhaust temps, and high revs. A supercharger would work but why spend the same amount of cash on something that will only get you half the boost??

Samps

The supercharger is a good option if you can find someone to fabricate all of the mounting hardware. Superchargers are not cheap, and niether are turbos, the SC has the advantage of running without an intercooler and the added piping, but it also requires power from the motor. Some have SC on thier NA's and are putting down over 200 to the wheels. The other issues are the drive train capabilities and the fuel system. And the SC needs to handle 8k RPMs which is a SC nightmare. To get the SC to safely run in the 7-8k range you must run a large pully which moves its boost pattern higher in the RPM range. For the money, I would go turbo, just because thier is already a turbo model to get parts from. But the SC option is a lot easier.

tesla042

Yeah.. The very fact that a turbo version of our car is what killed any "serious" peformance mods for the n/a's.. I've heard people go "there are turbo kits for civics and neons...why not for the rx7?" Well, because the rx7 came WITH a turbo to begin with!

As much as everyone would love to just be able to slap on a super and go, it's not quite that simple. Just like with a turbo, you will need more fuel. And not more fuel all the time, only when under boost--and boost is something that the n/a CPU knows nothing about. So, while getting the extra air into your engine may not seem that hard, getting the right amount of fuel is another problem indeed..

Another nice thing about a super is when you blow your apex seal, it doesn't smash into a turbine spinning at 110,000 rpm..

-Tesla

bcty

or u could run both SC and Turbo?!!!

Ichiban

we got supercharged 13b in perth and ther some in sydney theres one running 12psi (that blower howl is mad) with a large extend port

very nice sounding engine that is

UniqueTII

I wonder what ever happened to SuperchargedRex...I don't see him on here much these days.

EDIT: He's still around...maybe he'll wander into this thread.

Evil Aviator

Yes, and the rotary engines tend to make thier power at the higher end of the rpm range, anyway. Yes, most superchargers are only capable of half the boost (or less) as turbochargers. Why put a SC on your RX-7? Because it looks and sounds cool!

The reason that you see a lot of SC kits without an intercooler is because it has low boost, and to avoid the added complexity, cost, and space requirement. You can run a turbo at low boost without an intercooler, too. In fact, you can run a turbo without a boost controller, BOV, and wastegate if you like, but you aren't going to get much performance increase that way.

You can get rotary SC kits here:
http://www.atkinsrotary.com/supercha.htm

If you are interested in superchargers, Corky Bell's new book in very good.
http://www.amazon.com/exec/obidos/ASIN/0837601681/

Felix Wankel

Ever heard of a rising rate fuel pressure regulator?

christi

And isnt it harder to Turbo/SC a N/A?

vaughnc

I'm planning a supercharged convertible based on the TII's 13b-t engine.

The main advantages for a supercharger are:

- instant throttle responce
- V8 feel, V4 weight
- low end torque
- smooth/flat power curve
- no "rush" of power at 3500rpms like with a turbo
- all you want is 250 ft-lbs of torque under the hood

Things I still have to research are:
- ECU (assuming haltech will work)
- primary injector sizes (since boost is on at 500rpms)
- if an intercooler is an option

titancronos

damn... that looks NICE...
I'm thinking I gotz to get me one of those babies!!

scathcart

The question is why would you? You can buy a boosted RX-7 for much cheaper, and it'll make more power.

Sure, it can be done, but the question is why? If you wanna be different, do a three rotor.

The NA is still limited to horsepower due to the weak drivetrain. So with a total of $7000 invested, you're putting 220 or so to the wheels.
The higher compression limits higher boost.

You could buy an 87 TII for $3500 and then spend $3500 on fuel, haltech, and intercooler, and be putting making much more horsepower, not to mention much more reliability.

I can make you huge list of reasons if you wnat, but the main reason is you can build a faster boosted rex for much less $$.

titancronos

that is very very true, I CAN buy a faster/stronger TII for less $$, but it would not be MY car. I am totally in love w/little Renee (my 91 n/a), but it would be nice to give her some OOPH again...
ah, who am I kidding, I'll love ANY rx-7 I get my hands on...

scathcart

I offered to make kits a while back, and no one was interested. If there's interest, I can do it.

BUT... a TII can be made faster for less cash. Only way this makes sense is if you have gobs of mods to the suspension, interior, and body.

vaughnc

Like I said my project is a TII convertible - supercharged. I CRAVE MAXIMUM streetability. That means a soft (but strong) clutch, low end/low rpm torque, instant throttle responce, and large engine feel.

Can't get that with a turbo.

Plus I already have a TII for craaazy power

titancronos

How much were you planning on charging for your kits? What would the kit include?

FPrep2ndGenRX7

vaughnc - I've thought about working on a S/C setup for my car also. If it seems doable I might consider selling the intake pieces needed and letting the customer provide the S/C and stand alone EMS. Since money is always a concern I was going to use the Eaton M62 or M90 blower. Those are readily available on Thunderbird SC and Many Gm products and can be bought on ebay. The problem with that blower is the location of the intake on the blower. Its on the back of the blower which poins it at the firewall and that complicates the requirements of the upper part of the intake not to mention the injectors need to be mounted after the blower meaning the lower part of the intake might be to big to work in an FC chassis. I've done some drawings and measuring and its close on clearances but it can be done. Maybe next year will present enough time and money for me to work on it more.

vaughnc

Yeah if you look at the pics above they mounting kit and piping adapters were purchased with the paxton/nelson kit I believe.

There's an underdrive pully on the supercharger to prevent the 8000rpm readline from overspinning the supercharger as well.

RETed

There's a lot of BS being posted in this thread...

SC Pros -
*Easier to install versus turbo (not counting Turbo II's)
*No mods to exhaust necessary (to a point)
*Slightly better low end torque
*Control of boost by pulley size

SC Cons -
*Control of boost by pulley size
*Higher intake temps versus turbo
*Not easily intercooled (I did not say it was impossible)
*(Possible) lubrication issues of SC
*Top-end power inferior to a turbo

The long-standing myth that SC's have tremendous low-end torque advantage is BS with today's turbo technology.&nbsp Those who tout this haven't been in a GT-series ball-bearing turbo'd engine or a VNT turbo powered one.&nbsp The word "lag" doesn't even come into play.&nbsp Compare dyno graphs, and there is still a slight advantage to the SC, but under real-world driving conditions, I'd bet you'd almost never see it.

Add a stand-alone EMS into the whole mess and with proper tuning, I'd bet you can barely feel the difference.&nbsp I'd challange any SC's NA FC out there with my car right now down the 1/4-mile.&nbsp Sure, you'll beat me out of the hole and probably beat me to the 60' line, but my stock turbo will beat you on the top 1/2 of the track.&nbsp My car barely makes 250hp at the wheels, so the power levels should be pretty close with most SC'd NA dyno numbers I've seen.&nbsp Remember, this is with a stock turbo.

If I swap out to some GT-series ball-bearing turbo, this race wouldn't even be close.&nbsp You want real-world driving?&nbsp 1/4-mile simulates almost anything you see on the street...&nbsp You're not going to try and argue 60-150mph races, are you?


-Ted

Evil Aviator

You also forgot the "instant boost" BS. Oops, did I let the SC internal clearance leakage issue out of the bag?

Didn't we already determine that the SC defies all laws of physics and compresses the air without heating it?

RETed

Oh yeah, you're right - just like the $5k 20B conversion - duh, how could I have forgotten!



-Ted

vaughnc

Well now that you've pooped all over our conversation

Seriously we all know turbos will yield more hp & torque. That's not the point here.

Your right I would like to see some dyno graphs here. I'll e-mail superchargedrex and see if he'll post his dyno graph & experiences.

titancronos

That would be very cool! I'm not really looking to add huge amounts of boost, just enough to revitalize my old (and favorite) car.
by the way... what seems more efficient? to leave the air intake where it is, or to get a turbo II hood, and have the intake where the hood scoop is??
Just a thought.

vaughnc

Here's a quote from Superchargedrex's page that physics me up

"The increase in low end torque is great, and the mid-range power is a rush. Throttle response is also improved, its much crisper now. When the six-ports open up, you can actually feel a rush of power. Got some jerk tailgating you? No problem. Drop it down a gear, floor it, and you... are... GONE!!!"

The hood is mostly for looks unless you have a intercooler under there.

You'd do better having www.mariahmotorsports.com stamp your headlight cover to let more air into intake. Better yet build your own or buy their cold airbox.