lucky_golf

Probably being a bit dumb, but what is the twin scroll turbo on jap import cars all about?

Cheers

john banks

New manifold design into a "double snail" turbine housing to use pulse as well as pressure turbocharging. This helps spool up.

lucky_golf

cheers john

submannz

A duct leading the exhaust gas to the turbine was split into two passages, all the way to the turbo there is an actuator that opens at low revs to allow both pipes to feed the turbo all the pressure causing the turbo to spool up earlier.
This system reduces the amount of exhaust sucked back into the cylinders at full load, reducing knock and can allow a higher compresssion ratio. Because knock is reduced, there’s no need to enrich the mixture at high load, all of this provides more torque and can provide much better fuel consumption.

john banks

Does the Subaru system actually have the actuator?

MorayMackenzie

I believe this system uses two seperate manifold and uppipe systems attached to two equally sized turbine scrolls such that each scroll is fed by the two cylinders at opposite ends of the 4 stroke cycle.

This practically eliminates exhaust gas reversion issues and feeds an even stream of pulses to each scroll, which will ultimately mean the turbo is receiving pretty evenly spaced descrete pulses, which is good. The reduction in exhaust gas reversion will make for better fuel air mix, which is also a good thing. Thus the twin scroll system will improve engine efficiency and turbo efficiency at the expense of a bit more hardware.

The Toyota 3S-GTE engine (MR2 turbo etc) uses this style of twin scrol turbo (also ceramic) on a straight four engine, and that engine has incredible throttle response, almost like a big Normally Aspirated engine.

I don't think the subaru twin scrol in the sti 8 type ra spec c uses the twin non symetric scroll and valve system. The car certainly drives a lot more like the 3S-GTE than a sequential scroll system. The 8 ra spec c turbo response is just silly.

[Edited by MorayMackenzie - 4/30/2003 11:58:06 AM]

AJbaseBloke

Just wait for the Legacy then - max torque at 2400rpm

Twin scroll, but lower spec than the STi of course (did someone say titanium?).

And Moray has it bang on - lots of pulses, well timed, less turbulence in the system = goooood The ball bearing turbo on the spec C is luverly

It may not be perfect, but it sure is nice!!

Mcbrun555

This system sounds fantastic from what I have read but the sacrifice of razor sharp throttle response is the loss of the flat four "warble".

Is it really worth it losing such a fantastic characteristic of the car?

Mcbrun555

AJbaseBloke

Some of the rumble may be gone, but the sound is now a drier, sportier tone IMHO. Once on song it is pretty hard to miss the flat four growl/howl though

Nothing a decent exhaust can't fix though...

submannz

Actually you are right the Subaru one doesn't seem to use the actuators, sorry to be misleading.

RT

I seem to remember reading here before that one of the mappers (JohnBanks?) said that he'd seen a standard car / standard ECU det badly on an aftermarket "equal length" header.

My prime consideration (aside from cost) against installing the latest Spec-C's twin scroll setup would be - if it causes det or worse, transcient det or lift-off det, how are we to correct it?