Evening SN,

Was looking art the BMW Post ( Turbos).

I know that the Legacy had 2, the little one that kicked in early & the Bigger one which took over when things got intersting.

Question, can you do that with your Scoob, as a project, have 2??

If so, how would you go about it??


Regards.


Alan MaC

 

P.S Lewis will know, if you can`t stand the excitement of having to wait for him to appear on your thread then just send him a PM.

 

Actually the Leggy twin turbo doean't work like that, the primary is on its own up to 4k rpm then the secondary joins in, both then work together from 4200 up. Pants system and not worth the effort, look into a twin scroll hybrid.

bob

 

Evening Bob,

Thanks for that.

Regards


Alan MaC

 

Or the Delta S4 Gp B system with a supercharger for low down grunt and a gurt big turbo for mega-power at high revs. Once the turbo was up and running a clutch disengaged the drive to the supercharger so it didn't sap power when it was doing nothing useful. The plumbing for that lot was horrendous.

 

You should go for a twin engined impreza never mind a twin turbo, one in the boot as well driving the rear and the one in the front driving the front wheels. The bhp at the wheels would be

 

Don't think the supercharger on the S4 dis-engaged at a certain point.

 

he lives

 

You could run two, in series is in theory best, but harder to get right, or in parallel.

IF I did it, I would use two Forester (01 on) TF035-14/6, this would give you boost on one from about 1800rpm, then use an external wastegat opening at about 0.7bar to open the up-pipe feed to the second, the two should be able to hold 1.5bar+ from 2200 to 7000rpm, reasonable flexibility and responce, the only issue would be to get slow enough opening of the exhaust feed to turbo2 to stop turbo1 slowing while turbo2 gets upto speed.

I would use a chargcooler, from preferance the Legacy quad cam setup but with higher rated pump and larger rad.

Simon

 

> Don't think the supercharger on the S4 dis-engaged at a certain point.

I've read somewhere about an electro-magnetic clutch to dis-engage the drive to a super charger at high revs. Thought it was the S4 but can't find anything on the web about it and can't recall where I read it now. So you may well be right. Still had horrendous plumbing.

 

Thanks everyone.

I think looking at what's involved, I'll stick with what I've got.

Thanks once again for all input.

Regards


Alan MaC

 

old merc racing cars circa 1920/30,s had twin superchargers one was a precharger for the main one

 

There's also a parallel setup where you run 2 turbos at the same time, same as used in toyota supra twin turbo, and some nissan gt-r's. But as far as im aware it can only be done on a V engine; a turbo for each side with 3 cylinders that spool at the same time means that the same power can be achieved by using 2 smaller turbos with less lagg instead of 1 big turbo with big power and big lagg.

 

It could be done with any engine with an even number of cylinders - so in a scoob, you could run each half of the flat four off a single charger. However, realistically you're only running two "half sized" turbos in parallel, which gives very little advantage for a lot more complexity. There's only a couple of plus points for doing this, firstly you can get the turbo nearer the cylinder head which may enable better gas flows to improve spool, and secondly if you're going for really big power, it's may be cheaper/easier to get hold of e.g. 2 TD05/18G's than a single 700bhp+ turbo. Generally, again not worth the hassle for questionable if any gains.

Also noticable that a lot of the big power Skylines and Supras seem to convert back to a single large turbo for tuning purposes . . .

 

Just the Legacy system, or pants generally, because it seems to have been implemented quite well on a few vehicles now.

 

I'd agree that the system as implemented on e.g. a couple of the beemer's seems to work pretty well. The leggy - every time I've encountered it - just has a distinct "hole" in the torque curve around the point the "changeover point" which makes it really rather irritating to drive. The small turbo might spool a touch earlier than a TD04, but it leaves you with relatively puny torque until the second turbo is fully working - and by that point, a TD05/20G car would have long since spooled up and provide much more torque anyway.

 

Would that be a V engine like the inline6 in a Skyline GTR?

If ruuning twins you have to either have dicrete feeds to each one like the Skyline or most V's such as the supra, or you have wastegates to open each in turn like the legacy...

Many superchargers use an electromagnetic clutch (like on an AC compressor), the Delta S4 was one of them, as was the mk1 MR2 supercharger.

Simon

 

The skyline engine is an INLINE engine has you said yourself, a V-Engine has its cylinders in banks..

Twin Turbos in series with one smaller turbo are mainly for economy the smaller turbo will be a serious restriction on exhaust gasses.. Best to run two smaller turbos in parralel for a quick spool rather than one MASSIVE turbo.

You can run in parrallel on any engine.. the Lotus Carlton used two tiny T25 turbos in parralel on a 3.6 straight six, it was torqqqqqqquey as a ****..

 

Quite. The 300ZX has a V6, the Supra/GTR have straight-six engines. Also, the twin turbo system on the Skyline is indeed parallel, whereas the twin turbo system on the Supra is sequential - that is with two identically sized turbos, one working up until 4000rpm, the other joining the party from that point on.

 

I had a Legacy B4 RSK twin turbo, supposed to be 270 bhp, I reckon it was hiding close to 100 of them somewhere I never found

Smoother response, but you had to work it real hard to make it sing and boy it drank fuel.

 

Yeah i was a bit confused about the whole V, or inline engine stuff. Thought both supra and gt-r used V's. So if such setup can be used on the inline engine, sounds like a good idea unless the plumbing is terribly hard to do.

 

Personally, Legacy B4 setup is just a big mistake, but it works much better with an automatic gearbox, unless you are power hungry. You have good power from 1.5-3.5k revs when the first turbo works on light throttle (the gearbox will shift gears once you reach 3-3.5k rpm on part throttle) - very suitable for city driving and very economical. And then if you want to really get going, just press the pedal, gearbox shifts it down to the right rpm - second turbo kicks in at around 4.5k-5k and you are off.

However, most of the leggy owners will tell you that the 4 speed gearbox was a very poor choice for that job, as its very easy to catch the gearbox at the wrong rpm even when it kicks down a gear. I have an automatic B4 and drove a manual one, the auto is still a much better choice though - with a manual it just becomes a honda civic where you have to constantly shift and keep it in the high rpm if you need to go fast and if you dont like shifting gears too often you constantly get stuck in the VOD zone where there is no boost at all.

 

Agree on the B4 gearbox, I had the auto tiptronic - good through the traffic, although I thought the consumption was poor. I remember trying to keep up with a mate in a 1.9TDi golf and having to thrash it just to keep up on a B road.

That set up isnt great, never ever felt like 270bhp and as you say thats mostly down to the gearing.

 

Having owned a Supra the corrections have been made, it is a straight 6 with two turbos one coming online after the other and then running together.

Many do go for a big single for tuning purposes, you can have the power on earlier but also it is actually more controlable. A lot of Supra accidents occur when Turbo Two comes on boost and shoves masses of power through the rear wheels in one go. A single is generally a bit more progressive.

5t.

 

I think the recent BMW engines are all diesels and maybe use VNT turbos.
They have certain advantages to start with.

Not that I've owned one but I've read that the Legacy setup seems to have a hole in the midrange. Figures I've seen suggested in-gear times were better than an Impreza STi. The STi felt faster but the Legacy was faster.

The Americans (see NASIOC) attempted to get a kit together to run two small turbos. ISTR they retained the stock single plenum and throttle body and ran into problems.

Has to be said, the Americans maybe have a headstart in doing "odd" things to the Impreza as they only recently got a turbo version. Lots of conversion projects on NASIOC including superchargers, chargecoolers and the like.

J.