Question About Twins

[R.O.R-2.0]

Once this setup is up and running I'll post my impressions.  I think it will work out quite nicely.

its gonna work good no question, but it might get a bit restrictive in the upper RPM range.. you may have to run an external wastegate after the small turbo, and possibly after both turbos if the drive pressure gets too excessive..

[410]

I plan on checking exhaust manifold pressure and between the turbos as well.  I don't plan on running over 3500 rpm under load so I think I've made good choices in turbos.  I am also considering an external wastegate which can go where the egr port is.  I have a k14 and a gt2260 on hand just in case I want to change out one of the turbos.  Hopefully things go pretty quick after x-mas so we can get running soon!

[RabbitJockey]

I don't know enough About it to say what turbos will work best together buying know k24 would make a better small turbo than big. And the sizing of both is really important the small turbo can still be a restriction

yea, ive always thought that a K24 would be a poor choice for a large turbo in a compound setup.. they just are NOT big enough.

and dont they flow a similar amount of air as a VNT?

Yeah I've never seen a k24 compressor map but the Garrett flows about the same as a v t 15 technically the k24 would flow more than a t3 because it's a 38 trim And the t3 is 35 but the k24 is more restrictive on the exhaust side so it kind of negates the benefit of the larger compressor inlet on the k24. Doesn't the corrado guy have a similar setup to this on an aaz?  When andy2 was trying to build a compound I think he had said for a small turbo he found the vw t3 was too big but a k24/k14 hybrid was just right k24 exhaust side with k14 compressor. But he's obviously moved on to totally different things now since he has two absolutely huge turbos on his compound

[8v-of-fury]

Wait.. this thread isn't about the beloved mammography? The study of the mammary gland?

Compound Turbo For The Win

[RabbitJockey]

It's about bending rods with insane boost levels

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How about a dual scroll T3 AR of 78 and using a devided adapter with a flapper. Wouldn't that work? Thats what I plan to do for the next setup but in the Scirocco.

[RabbitJockey]

Which t3? There's 35, 40, 45, 50, 55, 60, super 60 and also the weird grand national wheel. The 45-55 trim wheels are the ones I think would work. 60s won't work and that gn wheel looks somewhat decent. But yeah I think that'd work good it'd be like a little .39 ar when closed and huge .78 open

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This is the turbo I was thinking of running. With the flapper valve. Divided T3 w/Vband .78AR.
http://www.atpturbo.com/mm5/merchant.mvc?Screen=PROD&Store_Code=tp&Product_Code=GRT-TBO-020&Category_Code=GRT

[RabbitJockey]

The flappers a good idea but gt3071r won't work it's too big that turbos good for over 400whp on 1.8ts vegeta gti on vortex has one on his 20v mki gli. I think any of the big vents they use on tdis would work well or gt2259 or gt2056 if it doesn't surge. This threads way off topic haha. If ur going to do the flapper tho u might as well do a vnt flappers easier tho

[R.O.R-2.0]

The flappers a good idea but gt3071r won't work it's too big that turbos good for over 400whp on 1.8ts vegeta gti on vortex has one on his 20v mki gli. I think any of the big vents they use on tdis would work well or gt2259 or gt2056 if it doesn't surge. This threads way off topic haha. If ur going to do the flapper tho u might as well do a vnt flappers easier tho

and not to mention, ball bearing turbos are no good for diesels. the journal bearings are where its at, the shaft is floating in oil, not contacting anything metal.

ball bearing turbos spool great on gassers, and work fine, because of the gassers inherently lower turbine speeds..

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ROR...what the h3ll are you talking about  . Ball bearing turbos are not good for diesels, ha ha.
What, what, what?

[RabbitJockey]

Yeah I thought ball bearings were better in every way faster spool up longer lasting and use less oil

[R.O.R-2.0]

yea guys, ive read that a few different places.. about the ball bearing turbos being a less than perfect match for a diesel because of the turbine speeds on a diesel being soo much greater than on a gasser..

ball bearings have mechanical contact 100% of the time. those balls have been known to fly out of their cages after a while..

journal bearings never have any sort of metal on metal contact..

why do you think they run journal bearing turbos on all the super hotrod tractor pullers, and all that sort of thing?

a ball bearing turbo would EXPLODE at those kinda RPMS..

i KNOW ive read this from more than a few people, and they werent a couple idiots off the vortex either..

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Well I'm no expert on BIG tracktor pulling, but the likly reason they run journal bearings is they don't have an oil restrickor so they can cool the bearings and housings better than with ball bearings?

Sure, journal bearings flow more oil but they are a friction bearing, just like crank and rod bearings.

Ball bearings also make contact with friction but are unloaded, non-friction.

The reason for ball bearings is for longer life under normal(lol) use. The byproduct is faster spooling.

My 2 cents

[Toby]

I don't know enough About it to say what turbos will work best together buying know k24 would make a better small turbo than big. And the sizing of both is really important the small turbo can still be a restriction

I think you guys are missing the boat here. All of the exhaust has to go through the little turbo so if it is a restriction with a single turbo, its a way bigger restriction on a compound set up like the one pictured.

It is my understanding that to make it work for a drivable car, (as opposed to a race car) you need at least one wastegate and some fancy valving to pull this off. Porsche used a system where a small turbo with a big wastegate was the primary. As the wastegate began to open it pre-spooled the big turbo and never let exhaust manifold pressure get high. The secondary turbo had its own air intake with a flapper valve downwind to seal the intake while big turbo wasn't making (much) boost. As the little turbo moved to the limit of its efficiency the big turbo took over the majority of the load. Quick spooling with huge flow.

A big turbo feeding a little one is still faced with the flow limitations of the little one (+/-). I would think that you will need a turbo with an internal wastegate as the primary, dumping the wastegate output back into the exhaust inlet of the big unit so you limit the exhaust manifold pressure. I suspect that big feeds little is going to heat the air a bunch. This might be fine for tractor pulls that lasts 10 seconds, but pulling the Grapevine or Snoqualmie Pass might reduce a lot of expensive stuff to a pool of glowing metal. I think Porsche used inter and after cooling on the 930 rally cars, but is been 30 years since I read the engineering paper on it.

Since ROR is always taking about huge amounts of boost and quick spooling with a VNT, what would you gain with the compound setup that a VNT and a huge intercooler would not give you?