12valvesmoke

This one is really dumb but i dont really know exactly everything about turbos so bare with me... Why dont both turbos in a twin turbo set up use and air filter. i understand why the exhaust goes to the secondary first but why cant air go to both at the same time??

The other i dont think is so dumb... Why doesnt anyone make two VGT's into a twin turbo setup... you could have one big VGT as the primary and one small VGT as the secondary.. seems like it would be pretty significant drop in spool time right there.

Jared

Number47

depends on the turbo setup compond iirc is one turbo feeding another, vs a sequencal(sp?) one is used for low end and the other for top end, ie of the setup is the TT supras with all their elaberate piping, a large VGT will operate better by itself that compound because a VGT on the new 6.7L cummins is basiclly a variable displacement exhaust housing i can change volume is the exhaust housing allowing for faster spooling

Big Blue24

If you look at normal twins used in our trucks for performance, they are like Number47 said, compound turbos. One air filter feeding the big bottom turbo. Pressurized outlet from bottom turbo feeding the top turbo. Top turbo then takes 25 psi intake air from big turbo and steps it up to 50-60 psi and sends it to the after cooler and then on to the engine.

The banks duramax drag truck uses two identical turbo on opposite sides of the block that feed a centrally connected manifold that feeds all 8 cylinders. So in the banks application, both turbos get their own air, they don't share a fresh air intake. They actually run without a filter but that is another topic.

12valvesmoke

ok then why dont any aftermarket companies make high performance VGT's then? BD, ATS (i know they have the multi stage turbo in progress), HTT, Garret all the big names..

Or does someone make one that i dont know about?

turbos10

The confusion lies in the poor terminology for compound turbos; they are not twins, rather different in fact. Twins are just that....two identical turbos feeding a common plenium. The are popular on V8's for easy plumbing, but most 6's get a single unless it is really high RPM/cid where one big one is not enough. I have see twin compound hybreds before. They use two large "twins" as the primary compression stage, and one larger single for the secondary compressor.

Tate

I'd guess cost and complexity would be the biggest hurdles. You'd have to vary the turbing inlet size based on RPM, load, boost, and probably a couple other parameters. Putting it on a 24v would be challenge. Putting it on a 12v would be worse, since there is no sensor outputs.

Mike Holmen

Look at the new ford, it has VGT technology in their series discharge compressor/turbine 'twin' turbo system. Most gasser don't run with the boost pressure that we do. A big single would be laggy and it would difficult to find one that would push 70+psi as easy as 'twins'. Tate I just finished up putting mine new twins together (garrett 3788-2R/BTH-3B), Wow decent spool-up ...Works pretty good in comparision to the HX-40/BTH-3B system that I ran before. You have to hurry up and get your's done.

HOHN

Mike, got any pics of the new twins coming?

How do you define "decent" for spoolup.

Most reports on the GT3788 say it's the best spooling charger anywhere near that airflow size.

jh

Mike Holmen

The initial spool-up is almost HY-35 area, the 5 to 20 psi area is nice and solid boost build. I'll grab some pics later today. I'm using 3in down tube. I have a 3.5in down pipe coming. I'm still playing with the wastegate. Right now its set at 40 psi (stock). The garrett air discharge nozzle interferes with wastegate activator, so its not perfect yet. I have a boost regulator and 7 psi wastegate activator on the bench, just not enough time right now to get this twin set-up perfect. I think my VP is on its last leg as the truck starts to fall on its face around 40psi area. The truck will idle is erratic (runs on three or four cylinders) until stab the throttle again, so the wot passes are kinda weak. I can sweak the tires during acceleration, the 1 to 2 shift, I have put down 5ft of rubber a couple times. There is still sand and some gravel on our roads here, so traction is limited. Its definately better than the HX-40/BTH-3B combo I had before. The most egt's I've seen are 1200 deg's (could be my VP), the 40/3b combo would peg the pyro. I'm pumped

Mike Holmen

Here are the twin pics.