14psi on turbo = 14 psi on supercharger?

[LeeRoy]

How can exhaust gas recirculion in an engine on boost achieve more efficiency? I can see how when it has manifold vacuum (lower pumping losses), but not how when on boost .

Although the majority of exhaust gas is pushed into the exhaust, hot exhaust gas expands in the headers and pushes on a closed valve being forced into the turbo - and drives it.

A supercharger is purely parasitic whereas a turbo is only party parasitic so to speak.

[oldcorollas]

ok let me try to find a SC14 and plumb it up as SC-> Turbo -> Intercooler and set it off while at cruise or idle. we'll see how it goes..

turbo -SC-intercooler
although other way may work also... but then you are limited to the amoutn of air the SC can push, so if the turbo can flow more air, then it gets a higher pressure differential, and then surges, while the SC has a pressure DROP across it...

so.. there is no point having the turbo, except to increase the pressure of the air the SC can move.... seems.. backwards...

[Duk]

what is the definition of a Roots SC?
the real roots had 2 lobes per rotor, straight lobes, and no internal compression.
then was "twisted lobe" roots, with 60deg? twist (current eatons).
TVS has 4 lobes with progressive pushing of the air. the only thing stopping it from having internal compression is length.

same as you can make a "twinscrew" shorter and have no compression.
the lysholm design (imo) refers to the type of male/female lobe engagement style...

i don't profess to be an SC guru.. but that guru is wrong .... or maybe all SC's are roots? or maybe none?
anyway, SC12/14 are Roots SC. 2 straight lobes.

it depends what efficiency you are talking about? VE? fuel per kw, fuel per engine cycle etc etc...

Eaton call the TVS a Roots http://www.eaton.com/EatonCom/Produc.../TVS/index.htm.
A twin screw with no internal compression would be dam short.

[oldcorollas]

thats because eaton can't call the TVS a screw.. an why would they? american public know "roots" as a kind of brand name.

TVS is 160deg twist. just short of forming compression. you would just need to make it longer to make and then increase internal compression.

twist of a screw is hard to figure, since the rotora turn at different speeds, and different brands have different number of lobes (lysholm = 5 and 3, ken belle = 6 and 4)

the only functional difference between the TVS and the "screw" is that while BOTH are screwing the air down, the TVS has the intake and exhaust ports, and twist such that the exhaust opens just as the inlet closes, whereas the "twinscrew" has the exhaust open later (due to more twist, or longer length etc).
the twist on a twinscrew can be reduced, and the casing lengthened, to have more output pre rev... and then you could shorten it and make a funny shaped lobe TVS
Lysholm will custom make your "twinscrew with as much length or internal compression as you want, or reduce it to have none... if you have a large enough order. BUT, the main issue is patents (esp US ghey patents)

or, they could increase the twist, or lengthen the rotors of the TVS, and then it becomes a twinscrew? doesn7t make sense if it is a "Roots type"



(edit: top pic is TVS, bottom pic is twinscrew.. for those that can't tell )

[JustenGT8]

ok let me try to find a SC14 and plumb it up as SC-> Turbo -> Intercooler and set it off while at cruise or idle. we'll see how it goes..

Nope.... turbo > SC > IC

No harder to plumb up with an SC14 so go this way.

[JustenGT8]

While I won't argue the efficiencies (or lack there of) of the SC12/14, it's a bit wrong to call all Roots type SC's inefficient. The new Eaton/Magnuson TVS SC can be as high as 75+% efficient. That's centrifugal levels.
The back pressure on the engine caused by the turbine housing and turbine wheel rob the engine of power and potentially (probably) cause more heat and exhaust gas retention in the combustion chambers. The higher combustion chamber temps can obviously cause detonation issues, typically countered with retarded ignition timing (less power) and the exhaust gas contamination also reduces the available volume for fresh air/fuel.

Theoretically , a supercharged engine should tollerate more ignition advance per pound of boost if the air entering the engine is at the same temp as that supplied by a turbo and if the exhaust system starting at the headers/exstractors can flow well enough.

LOL the age old argument from those stuck in the past.....pick the worst turbo design and the best SC design and compare Funnily enough the turbo still always won hands down

A properly sized and designed turbo system has none of those issues but this is not the thread to rehash this old and done to death debate

[oldcorollas]

only problem with turbo is lag and mushy response... ans an SC twincharge can fix that

[JustenGT8]

Come for a drive in any of my turbo cars Stu....mushy response is the biggest myth of all. As crisp as any single TB car you can find

Lag is an overused term used to describe a variety of turbo responses....in reality no different to an n/a engine being asked to perform outside a suitable torque band.

Low rpm boost production is the forte of the positive displacement SC though no doubt. Very keen to develop the MkII UZ twincharge setup...it won't be on the GT8 though.

Back to thread.

[oldcorollas]

totally agree
stock turbos aren't usually set up for crisp response.. and NA lag is something rarely mentioned

[4DaDrift]

Edited post.

[X kyle X]

hey OCs didnt toyota produce a N/A engine with a heap of lag???


oh wait i got Lag mixed up with TVIS, sorry..


hahah

[oldcorollas]

usually toyotas cams are too conservative (recently) so there is no NA lag down low..

compared to something like a 4AG with 288 cams...
i've had both turbo and cam lag, and i would prefer SC (until i own one maybe)

[feral4mr2]

ans an SC twincharge can fix that

indeed.

*subribed to thread.*
eager to see what you can come up with CHB. i have run a TC system in my aw11 turbo-TB-s/c-i/c-inlet and i was rather impressed with it. tis some hardware problems that have dulled the TC project for a while (though i got a great ~year out of it).

[TERRA Operative]

For a SC only system, you'll need a crank to SC pulley ratio of 1:0.96 to get 14 psi. That's running just inside the absolute edge of the SC14's capabilities.

The temp from the SC will be around 136deg and you'll need an intercooler with an endtank area of 117cm2 (23cm high for a 2" core) and at least 30cm long (make it as long as possible to keep intercooler efficiency above 85%). This will drop boost temp to 45deg with a pressure drop of about 5% across the intercooler due to temp drop (disregarding flow restriction in the intercooler).

Estimated power is 131Kw or so.

[big_zop]

For a SC only system, you'll need a crank to SC pulley ratio of 1:0.96 to get 14 psi. That's running just inside the absolute edge of the SC14's capabilities.

The temp from the SC will be around 136deg and you'll need an intercooler with an endtank area of 117cm2 (23cm high for a 2" core) and at least 30cm long (make it as long as possible to keep intercooler efficiency above 85%). This will drop boost temp to 45deg with a pressure drop of about 5% across the intercooler due to temp drop (disregarding flow restriction in the intercooler).

Estimated power is 131Kw or so.

That it some great work there except that i have a query about the power figure you quoted. Is that the estimated GAIN over the original power (ie: stock boost of the SC14) or the total power that the engine will generate. I suspect its the former but it isnt quite clear.

I do hope its the former as i would seriously consider sticking an IC on my car and upping the boost for that sort of gain. When you say you need a pulley ratio of 1:0.96, can you show me what dimensions you have used to worked this out (im not too familiar with the stock dimensions).

As for the TC system. The ones that i have seen work (apart from JustenGT8s one) are in a S15 from Bee-R and a personally developed 13B here in Aus.

The S15 uses a TD06 and a TX12 (SC12 equiv - thanks TERRA for your other thread). Its conventional in its approach that the turbo system is standard (turbo > IC) with the throttle body fronting the SC which is mounted on the inlet manifold - there are no valves or switches involved. Its says that it has 1bar from the moment you open the throttle but doesnt say what the turbo runs and goes on to suggest that they are going to upsize the compressor as the system is working well.

The 13BZT uses a 550hp T04 and a SC14. This is much more complex and i believe is executed quite well. It is set up that the SC blows through the turbo then the IC and to the inlet manifold. It is designed to run soley on the SC when <4500 rpm with its own intake and is spun twice the speed of the engine and said to generate 0.82bar pressure at any rpm. The turbo has a intake valve that closes while the SC is on. When the engine gets >4500rpm, the turbo intake valve opens and they run combined till 5000rpm when the SC clutch is switched off, where the turbo is said to be generating 1bar. Then its the turbo past there. It is only generating 258rwkW but he loves the response more than anything else.