View Poll Results: Twin Screw or Roots
Twin Screw
50
84.75%
Roots
9
15.25%
Voters: 59. You may not vote on this poll
Twin Screw vs. Roots
12-09-2010, 04:05 PM
#11
4th Gear Member
Join Date: Mar 2006
Location:
Posts: 1,547
The bypass lets out the excess pressure not needed anymore when you romp on it and let off the gas quick. You don't want all that pressure in your engine if you let off the gas. The twin screws are designed so the only time they compress air is if they are spun up fast.
12-09-2010, 04:07 PM
#12
1st Gear Member
Thread Starter
Join Date: Nov 2010
Location: MI
Posts: 74
Ehh, I answered my own question with this one: the bypass is located before the internals. But it is not to let out excess boost:
http://www.whipplesuperchargers.com/...sp?ProdID=1233
It's to prevent the SC from making boost at cruising speeds, so your not hurting your fuel economy.
http://www.whipplesuperchargers.com/...sp?ProdID=1233
It's to prevent the SC from making boost at cruising speeds, so your not hurting your fuel economy.
Last edited by 302_GT; 12-09-2010 at 04:10 PM.
12-09-2010, 07:34 PM
#15
Not quite, screw lobes are different from the straight lobes (now colloquially called "Roots"). Think of it just like helical cut gears (just like in your rear diff) versus straight cut gears.
By this comparison, in terms of the classic SAT comparison-match-up, screw lobes are to helical gears as straight lobes are to straight cut gears
By this comparison, in terms of the classic SAT comparison-match-up, screw lobes are to helical gears as straight lobes are to straight cut gears
Last edited by JIM5.0; 12-09-2010 at 07:40 PM.
12-09-2010, 07:56 PM
#16
5th Gear Member
Join Date: Dec 2006
Location: Redding, CA
Posts: 4,552
LOL, I see the votes are pretty well speaking for themselves, and this was the answer I was expecting. But I was hoping for some more reasoning to back it up.
I'm curious to see how many people are familiar with eaton's Gen 6 TVS technology. The previous generation Roots SC's had obvious heat soak issues, but eaton seems to have made some major headway with the Gen 6.
My biggest argument with the twin screw is it's constantly creating boost. Even though it has a bypass so the boost doesn't make it to the engine, the SC still has the added stress of consistantly making boost.
Where the roots has the bypass before the internals, so the SC isn't under anywhere near the same load as a twin screw during cruising speeds. But you still get immediate boost at WOT.
I'm curious to see how many people are familiar with eaton's Gen 6 TVS technology. The previous generation Roots SC's had obvious heat soak issues, but eaton seems to have made some major headway with the Gen 6.
My biggest argument with the twin screw is it's constantly creating boost. Even though it has a bypass so the boost doesn't make it to the engine, the SC still has the added stress of consistantly making boost.
Where the roots has the bypass before the internals, so the SC isn't under anywhere near the same load as a twin screw during cruising speeds. But you still get immediate boost at WOT.
There is a reason why Lysholm blowers are banned in some forms of NHRA racing. Efficency.
that does not mean the Edelbrock and Rousch TVS type blowers aren't bad asz blowers making really good power very efficently. Both of those blowers are great and are good choices for anyone wanting a postivie displacement blower.
12-09-2010, 08:05 PM
#17
5th Gear Member
Join Date: Dec 2006
Location: Redding, CA
Posts: 4,552
Basically you have to go to ZERO vacuum so that the bypass valave actuates and closes. This creates the resistance and then pressure.
It's based more on the load placed on the motor. Not a rapid application of the gas pedal. If you put your car in neutral and rev the motor, the car may make a pound or two of boost at a very high rpm. Put your car in 5th and cruise down the freeway and give moderate throttle input and the car will make tons of boost.
12-09-2010, 08:19 PM
#18
Now there is a name I have not heard in such a long time, the name Lysholm.
Prior to Whipple making screw-lobe blowers, Lysholm I believe was the first to do it, and back when I was a child, people called screw-lobe blowers "Lysholm" blowers instead of "Whipple" blowers.
And even back then, screw-lobe blowers were considered superior to straight lobes (A.K.A. "Roots" blowers) as far as pumping air into the manifold.
Screws have the advantage of creating a constant stream or compressed air going into the manifold where straight cut lobes have always made pulses of compressed air.
Another SAT comparison-match-up: screw compressors are to a jet turbine as straight lobe compressors are to a reciprocating piston engine.
The jet turbine makes continuous torque on the shaft where the reciprocating piston makes pulses of torque. In pistons, you have to wait for a combustion to get positive torque, where while you are in between combustions between cylinders, you get negative torque from internal friction (cranks turning in the journal bearings, conrods turning on the crank, piston rings rubbing on the cylinder walls, etc.) Sure the reciprocating piston is doing positive work from the point of ignition to the point the exhaust valve works, but as soon as the exhaust valve opens, the internal friction starts to do negative work on the engine. And of course, the inertia of the moving parts, especially the flywheel with positive rotating energy, continues to make the crank turn in a positive direction, otherwise, the engine would eventually stop turning.
And speaking of pumping work, even a straight lobe compressor is superior to a reciprocating (piston) compressor, and that is why no superchargers are of a piston design.
Prior to Whipple making screw-lobe blowers, Lysholm I believe was the first to do it, and back when I was a child, people called screw-lobe blowers "Lysholm" blowers instead of "Whipple" blowers.
And even back then, screw-lobe blowers were considered superior to straight lobes (A.K.A. "Roots" blowers) as far as pumping air into the manifold.
Screws have the advantage of creating a constant stream or compressed air going into the manifold where straight cut lobes have always made pulses of compressed air.
Another SAT comparison-match-up: screw compressors are to a jet turbine as straight lobe compressors are to a reciprocating piston engine.
The jet turbine makes continuous torque on the shaft where the reciprocating piston makes pulses of torque. In pistons, you have to wait for a combustion to get positive torque, where while you are in between combustions between cylinders, you get negative torque from internal friction (cranks turning in the journal bearings, conrods turning on the crank, piston rings rubbing on the cylinder walls, etc.) Sure the reciprocating piston is doing positive work from the point of ignition to the point the exhaust valve works, but as soon as the exhaust valve opens, the internal friction starts to do negative work on the engine. And of course, the inertia of the moving parts, especially the flywheel with positive rotating energy, continues to make the crank turn in a positive direction, otherwise, the engine would eventually stop turning.
And speaking of pumping work, even a straight lobe compressor is superior to a reciprocating (piston) compressor, and that is why no superchargers are of a piston design.
12-09-2010, 08:49 PM
#19
2nd Gear Member
Join Date: Jun 2010
Location: iowa
Posts: 187
screws also compress air from one end to the other end along the length of the s/c unit. They also compress air threw the center between the lobes.
Blower spins the opposite direction and moves air around the outside of the lobes.
Blower spins the opposite direction and moves air around the outside of the lobes.
12-09-2010, 08:51 PM
#20
2nd Gear Member
Join Date: Jun 2010
Location: iowa
Posts: 187