I drive a car with a turbo, and power does come on hard at 3k, but, you know where it hits, you stay above that point, and it's always on. i.e. you use trailbraking, or you use a lower gear to keep in the power range. It just takes a different style of driving. Both definitely have their advantages.

 

What was this post about??

you guys are deviating so much that I can't seem to know what the earlier post was about.

you want to deal with it, just go have a race on a private mountain road
might help you to cool down.... twinscrew you all.. LoL

 

is this right?

"So that's the concept about the twinscrew and throttle position. I can go WOT at 3000rpm and have full boost immediately with the twinscrew. With the eaton, I can go WOT at 3000rpm and full boost is not achieved until I hit my rev limiter. So I can get 17psi boost at 3000rpm instead of having to wait to see 17psi until the rev limiter. Don't get me wrong, you will have boost with the eaton at 3000rpm, just not max boost."

I also heard the autorotors are real screamers. anyone heard one?

regarding Tonyb's comment comparing install time twinscrew vs twincharge: I'm guessing the 'screw will take considerably longer. you have to relocate the alt, r&r the blower and intercooler, drain the coolant, install the new water pump w hose and wiring, install a new belt tensioner, then there is the intake tubing and throttle body fitting, coolant radiator, pump, tank and hoses. I'm guessing around 10-12 hours.

the twincharger involves inserting the turbo manifold turbo and oil lines and fitting the charge air hose to the throttle body, adding larger injectors and the fuel manager. all done without removing the front end. I think they can get a kit in in 6 hours

 

I think this is one of the most accurate things you have stated on this board.

 

It is scary when people selling products can't even grasp this simple concept. If you let your RPM drop that far on the track people will be passing you so fast because it takes awhile to get a 1.6L going

 

Actually, the twin-screw designs are WORSE than the Roots at providing high boost at low RPM. There is a great diagram in Corky Bell's "Supercharged" showing the relative boost curves of the three blower types (Roots, twin-screw, centrifugal). Here are the rankings:

Low RPM boost:
1) Roots
2) twin-screw
3) centrifugal

Thermal efficiency:
1) centrifugal
2) twin-screw
3) Roots

Quietness:
1) Roots
2) centrifugal
3) twin-screw

As you can see, the twin-screw represents a compromise. It doesn't have the low-end boost of the Roots and it doesn't have the thermal efficiency of the centrifugal. But, it should offer better high rpm performance than the Roots without the dead low-end of the centrifugal, with the downsides of high cost and loud noise. Randy may be right, the water/air intercooler could be more needed for creating a tolerable volume and pitch level for the sound of the twin-screw blower, than it is for any performance reason.

Any forced induction vehicle with a throttle can supply varying levels of boost at a particular RPM. I can hold my boost gauge at 6 psi, 8 psi, 10 psi, etc. simply by altering the movement of my right foot.

 

Help me out here people. What I'm hearing about the twinscrew supercharger is that they produce the same boost level across the RPM band. If the supercharger is driven off the same belt that attaches to the crank, how does the twinscrew SC vary it's own internal speed to maintain a constant boost level over the varying RPMs? Maybe the TSSC isn't driven off of the crank?

 

Having driven turbocharged, supercharged, and naturally-aspirated cars at the track (LRP, Pocono, etc), both of the boosted ones required more of a deft touch of the throttle while cornering than did the non-boosted. It's simply a matter of having a range of, let's say, 25 inHg vacuum to 15 psi available with the right foot rather than, let's say, 25 inHg to 5 inHg available. Forced induction can literally double (or more) the amount of air increase into the engine for a given throttle movement. So, it is easier to hold the engine at the torque limit of the tires in a sweeper, for example, with a non-boosted car.

I would think that how well the engine is tuned and set up for the track (including properly sizing components like turbocharger or supercharger) would make a bigger difference in track performance than the source of power for a particular 250 whp, 2800 lb car.

 

The Roots-type blower grabs a specific volume of air (45 cu. in. in our case), moves it using rotors from one side to the other, and dumps it out. The air isn't compressed inside the blower, only once it gets dumped into the manifold. In a twin-screw, the rotors are shaped and geared differently, so that as the air enters the blower, it has a smaller and smaller space to live as the rotors turn. This way, it is already compressed when it dumps out into the manifold. Avoiding the sudden shock of compressing the air instantly at blower exit (as is done in the Roots) results in the twin-screw being gentler with the air, thus better thermal efficiency.

The twin-screw really is a marvel of manufacturing, it would be very easy to build one and have it destroy itself instantly.

 

YEA FRIGGIN GOD! The point gentlemen, we are gentlemen until we hit the track right? - is a linear power supply!!! The more power the better! Non-linear power spikes, never.

 

The twinscrew should be relatively easy as far as the install goes. The alternator doesn't need to be relocated. You have to remove the front end, which takes about 15 minutes, then remove and install components. I'm guessing 4-5 hours. I used to do the pulley install in this way, and it was down to 2.5 hours. With the additional work of replacing the water pump, running the oil lines, and programming the ECU, maybe add a couple hours.

I have heard one, and with the water-air, it isn't much louder at all. With an air-air, it woul be louder than the Roots. With the front mount, it would sound like a fire truck! I'll be sure to post videos with the different set ups.

Hope that helps!
Randy

 

Great question. It has to do with design differences. Because the twin screw is actually compressing air as it moves the volume, you can create boost where the Roots isn't. You are accomplishing this through rotor design. It is still driven by the crank.

Hope that helps!
Randy

 

Sorry to everyone for the multiple posts - it was the easiest way to quote and organize responses to all. I tried to figure out a way to put them together after I was finished, but then it leaves the deleted post anyway.



Andy,

Thanks for your input - Corky Bell's book is definitely a must read

Randy

 

Can you explain this in more detail. How does running two separate water paths differ from running a single water path?

 

Randy I dont mind the multiple posts.... hell my favourites are the ones after you been drinking. I hope you have more drinking plans for this evening, coz this sheet izz gut.

 

By having two different paths, each of those paths is exposed to the core (where the thermal transfer is happening) for a shorter period than if the mass was one big unit.

It is then easier to keep the temp down, since the peak temps are not as high.

Hope that helps!
Randy

 

I'm going to be working now, so if there isn't a response quick enough - I'm building a car!


Randy

 

That makes no sense at all. Let's say you have 1 gallon of water at 100F and I pass it through a heat exchanger that is 50F at the rate of 1 gallon per minute. Now, let's say I have two systems, each of which have 1/2 gallon of water at 100F and I pass each of them through their own 50F heat exchanger at 1/2 gallon per minute. The amount of heat transfer is exactly the same.

The only difference I can see is the small amount of heat radiated from the hoses since you have more hose surface area.

 

OK, so the twinscrew supercharger (TSSC) pre-compresses the air prior to arrival in the manifold, whereas the roots supercharger (RSC) just forces more air volumn thru which by nature get's compressed in the manifold. So going back to the design of the RCS, it's just an air pump, moving air from one side to the other. So as it's speed increases, so does the amount of air passed. The higher the speed, the more air is passed and all is still being stuffed into the same amount of space hence the higher boost pressure at higher RPMs. Right? So with the TSSC, the air is precompressed to a certain pressure. So at 2k RPM it pressures to (making up a number here, so don't get on me if it's not right ) 18psi. Also at 7k RPM the TSSC is also making 18psi. But isn't more air being moved at the higher RPM with the TSSC. Since the manifold isn't changing it's air volumn, would there be more boost at the higher RPM since more air is being moved?

 

The speed you are going down a straight is directly related to the speed you exited the turn prior to the straight. Horsepower isn't the only determining factor for the speed you reach on the race track.

 

In both the Roots and in the twin-screw designs, boost increases as RPM increases, the curves are simply shaped differently.

 

Your theorhetical situation is wrong, and that may be what is hampering the idea for you. The water temp is lower than the intake charge - and you want to keep it that way.

Randy

 

This goes against what was said earlier in this thread. The marketing hype said: Andy what you said makes more sense... boost is still directly proportional to RPM, even with the TSSC, which just happens to have more of it at better thermal efficiency.

 

Just so it is clear - that wasn't my marketing hype...

Because of the rotor design, you do have more density than the Roots has.

Hope that helps!
Randy

 

but you are selling it right?