tjbubb007

im looking for any help for supercharing my 90 GXL. ive been lookin through threads all day and have found a lot of people talk about instaling an sc but no write up on how they did it or what they used. i can find kits for a root type sc which in my opinion suck but nothing on installing a centrifugal type supercharger. fabricating parts is not a problem. links to a write-up on how to do it would be greatly appriciated.

Evil Aviator

Actually, they blow, hehehe. Seriously though, they are ancient pieces of junk, but they do have their place in some low-boost applications. The problem is that nowadays everybody is boost-happy, and a high-boost pulley on a Roots doesn't do anything but tear up the supercharger and detonate the engine.

It is a problem if you don't know what you are doing, which I think is the case.

You are pretty much on your own, but you can do some research with the following media:

Corky Bell's "Supercharged!" book is available from most online retailers.

Also see these links:
http://www.superchargersonline.com/c...at.asp?group=2
http://pbgarrott.tripod.com/Garrott.html
http://www.geocities.com/boatseason/rx7.html

It would be cheaper and easier to sell your car and simply buy a nice TII. A stock or slightly modified TII will probably also have more overall power than a supercharged NA block.

stevie1020

i have the camden SC, i like it. i can out run a slightly modded TII. its hella fun to drive, very responsive. my suggestion get water/meth injection. bigger injectors help with the irradict idle as well. uhhh im hopeing to go with a 12 psi pully soon just to have alittle more fun with it

Roen

iTrader: (2)

Why not go with a twin-screw / lysholm supercharger instead? (Google it.)

tjbubb007

still not as efficient as a CSC

Evil Aviator

... and a CSC is still not as efficient as a turbocharger.

Roen

iTrader: (2)

if you're going CSC, might as well go turbo and gain some efficiency out of it, otherwise, I'll take the full boost earlier of a lysholm vs. the CSC.

jgrts20

superchargers easier to install.

anewconvert

iTrader: (1)

.....


A CSC is essentially a turbo compressor spun via the crank shaft instead of a turbine off the exhaust. They are nearly identical.


Supercharger = great for high overlap engines.

Turbocharger = great for low overlap engines.

What type of engine is a 13b rotary... high overlap.


Reversion is non-existent, or nearly so, in a high overlap engine when the intake is at a higher pressure than the exhaust. Thats not possible with a turbo.


BC

rotarygod

iTrader: (1)

Just to show some basic comparisons between different blower types, here are a few forced inducted RX-8 dynos. Boost is admittedly not the same between all of them. This is merely a comparison of the different boost profiles of different systems. In this case the stock Renesis baseline is 190 rwhp. The failry small Greddy turbo when tuned properly and actually pushed pretty hard (it's not a huge power making turbo) did 275 rwhp. A larger SFR turbo setup (unknown which one) using a T04 (unknown boost level) made 326 rwhp. Finally a centrifugal supercharger from DNA motorsports also made 326 rwhp. It's the average power that makes you fast. Peak power means nothing without knowing the average.

In this case let's say that our powerband in a race is between 6500-8500 rpm. The Greddy turbo makes about 265 average rwhp across this area. The centrifugal supercharger with it's 51 more hp also makes about 265 average rwhp through this powerband. Which one do you think is faster? The Greddy will hold a more steady state of acceleration. The DNA will not accelerate as fast after a shift but quickly catch up right as it has to shift again. Odds are in a race that the finish line will occur somewhere while the DNA is trying to catch up. Only after you reach top gear can the DNA finally walk away on the top end. That's going to be pretty fast though. The SFR turbo makes an average of about 290 rwhp in this rpm range and stock only makes about 180 rwhp or so. Which one is fastest? Out of the 4 choices, 1 of course being stock, it's pretty obvious that the DNA is only a better choice that stock and only if you intend to stay over 4500 rpm. Most of us spend most of our time below this on the street maybe going over it for a moment when accelerating. It's a power robber 95% of the time and nothing to brag about (unless you believe Supra dyno curves are nice) as far as power goes. Notice that the centrifugal makes LESS horsepower than stock below about 4700 rpm. That's half of your rpm range!

Not shown is a dyno curve of a Pettit twin screw supercharger that did about 270 rwhp peak. The curve was actually pretty nice. It almost followed the Greddy turbo curve except that it was lower in power all across the board. I do know for a fact though that it was running less boost than the Greddy so all in all, the twin screw would have been quite quick. The centrifugal is not a good choice for a small high revving engine with little low end power. On a V8 that redlines at 5500 it may work just fine. On a Viper that has tons of low end power, it may work just fine. As a general rule, the smaller the engine or the higher the redline, the less desirable a centrifugal becomes.

I don't like the whole this is more efficient than that argument. It's highly subjective as a small turbo is more efficient than a larger turbo within a certain range and vice versa. The same is true for superchargers or even comparing them to each other. A better argument would deal with which one will make more power over the usable rpm range. It's probably not a centrifugal.

rotarygod

iTrader: (1)

I highly disagree with this. In fact just reverse it. A turbo works much better with high overlap than a supercharger does. You actually want less with a supercharger.

In a supercharged system, the intake side is always under higher pressure than the exhaust side. During overlap this means that you will just blow some of the intake charge out the exhaust port. You are bleeding off boost. To overcome this, you need to run more boost, which heats up the air more and wastes more out the exhaust.

A turbocharger almost always has higher exhaust pressure than intake pressure although in a properly designed system you can get them nearly equal to each other. Due to this you will never blow your intake charge out the exhaust. Yes you will have some carryback dilution from the exhaust into the intake but that's OK to a point. Even an n/a running at 100% VE still has 10% of it's intake carried back from the exhaust. The less backpressure you have, the less carryback you have. At higher rpms, the exhaust gasses want to keep moving towards the turbo just as they would in an n/a. This helps reduce this dilution. You will never get that with a supercharger.

On a high overlap engine, you will make more power with a turbo than a supercharger. This is why turbos work with bridge and peripheral port engines. It's not to say that this is the best setup. That's the subject of heavy debate. However a supercharger and a high overlap engine are a bad idea. When you build an engine for boost, the device making the boost much be known. You don't build engines the same for turbos as you do superchargers. You also don't build them the same for n/a applications vs nitrous or any of the forced induction types. They all have different requirements. A common mistake is to assume that if a porting style works good for one application, it must work good for all of the others. This isn't true.

Rx7TyreBurna

iTrader: (1)

I am considering a SC. But, I need to research more about the types. Also, can the 6-port system and VDI be utilized?

The CF SC looks interesting, but how does it compare to the twin screw ones? It looks like the CF would be easier to "bolt on". I was thinking it would be fun to run a CF SC and have a small IC.

If I end up doing it, I will take lots of pictures and do a "write-up" on it. But I got to pay for the rest of my college first. Damn electrical engineering degrees are expensive.

For now I am going to stick to N/A power.... LoL.. i know those two don't go well together. N/A and power... haha. Anywho..

TehMonkay

iTrader: (-1)

Take off your AC and PS and do a serpentine conversion, then mount a SC in place of the PS and AC. Fairly simple.

I want to try and to a twinsharger system like this the the SC off of a toyota MR2.

Evil Aviator

Given the same compressor, they are identical with respect to adiabatic efficiency, but the supercharger has less mechanical efficiency due to the drive power consumption. Also, the supercharger will only make max boost near engine redline, while the turbocharger is able to make max boost earlier in the engine rpm range. If maximum efficiency is the prime goal, a turbocharger wins every time.

I realize that the book answer is that it is easier to install a supercharger than a turbocharger, but in actuality that is not the case with the RX-7. If you think about it, how many successful supercharger installations have you seen on this forum? Now compare that number with the number of aftermarket turbo systems on this forum. If it were really practical to install a supercharger on an RX-7, you would see more of them.

I agree, but the original poster seems to be focused on efficiency rather than performance.

Yes, everything else being equal, a centrifugal supercharger will have the least torque over the usable rpm range when compared to a Lysholm supercharger or turbocharger. A centrifugal supercharger finally shines right about when a Roots starts to run out of steam, so that battle would be a bit closer, although I would bet my money on an Eaton barely winning the battle of average torque.