Lets talk compounds with bypasses...

[jgsturbo]

Is there a specific reason why most people are not bypassing the small charger compressor side? IMO if both sides of the small charger can be bypassed the small charger can be smaller without restricting the large charger on the top end.
OR Are we just missing the hardware>? A compressor side bypass can be much smaller than an exhaust side bypass., not to mention lighter- all aluminum instead of SS.

[DirtyMaxx03]

bypass?

[jgsturbo]

Installing a wastegate that is plumbed back into the system between the small and large chargers on a compound setup equals a bypass of the small charger.
That's the typical usage I see.

[Tate]

Because then it would not be compounding the the pressures, would it? That would be more of a sequential style setup, which is great if we are running low PR's. But not at 6:1 or greater.

[jgsturbo]

Correct it is a sequential but my point is most people just end at half a sequential.

[DirtyMaxx03]

Originally Posted by jgsturbo

Installing a wastegate that is plumbed back into the system between the small and large chargers on a compound setup equals a bypass of the small charger.
That's the typical usage I see.

ok i see what your saying. a gate on the charge pipe that will let air through the small charger then (when tuned right) would plumb air past the compressor inlet of the small charger straight into the IC pipe when the compressor inlet became a "restriction"....is that the general idea or am i an idiot...

[Tate]

You will still have power generated on the little turbine. The main thing is to get the pressures up, which the secondary fulfills. My truck was much more powerful with GT37R/GT42R twins than GT42R alone. Driveability was night and day.

[DirtyMaxx03]

Originally Posted by Tate

You will still have power generated on the little turbine. The main thing is to get the pressures up, which the secondary fulfills. My truck was much more powerful with GT37R/GT42R twins than GT42R alone. Driveability was night and day.

your truck felt stronger running a compound setup then one big single? I've heard the opposite from several people. driveability is a no brainer tho

how does the CFM of say a s300 over an s400 setup vs. a single s400 of the same size compare? seems like the large single would move more air

[jgsturbo]

Originally Posted by DirtyMaxx03

ok i see what your saying. a gate on the charge pipe that will let air through the small charger then (when tuned right) would plumb air past the compressor inlet of the small charger straight into the IC pipe when the compressor inlet became a "restriction"....is that the general idea or am i an idiot...

Nope your right on the money. We have something like this on a S400/66mm (IIRC) truck and it makes more power than without.

[JQmile]

Originally Posted by jgsturbo

Nope your right on the money. We have something like this on a S400/66mm (IIRC) truck and it makes more power than without.

The engine will always be way more of a restriction than a small turbo....plus, it's hard to get singles to live at 80-100psi....

That being said, the sequential setup on the BMW 335d is awesome.

[jgsturbo]

Sequential turbos are where OEMs are making big advances in total output vs engine size.
the 335d is one of of those.

[DirtyMaxx03]

i guess if you spent enough time monitering the pressure in the charge pipe vs boost pressure going into the motor you could figure out if a gate would help anything. but like stated above seems the motor is the most restrictive part of any turbo setup. That is what "makes" boost afterall isnt it....

[jgsturbo]

Tuning is also something that is required IMO as well, my ideal setup would be to activate the setup @ a certain RPM AND pressure.

[jgsturbo]

A setup that would work better with bypasses would be if your trying to run a small charger that's say 30-50% the size of the large charger.

[DirtyMaxx03]

to me, between setting it up and fine tuning it, gains would be minimal to the amount of time spent getting it dialed in. a good compound setup shouldnt need/benefit from any sort of gate on the compressor side of the small charger. it should be able to flow freely what the atmospheric charger is feeding it.

[DirtyMaxx03]

Originally Posted by jgsturbo

A setup that would work better with bypasses would be if your trying to run a small charger that's say 30-50% the size of the large charger.

i dont see the need for a charger that small.

[jgsturbo]

There is something to be said about power band, especially in an RPM limited diesel engine.
Power band width is WHY we have VGT turbos, "quick spool" valves, etc. etc.
Bigger you go, single or straight compounds the more low rpm torque you give up.

[DirtyMaxx03]

But when guys are launching at 30+psi the power band is almost instant. Vgt turbos are great for a mild DD application IMO. But for a high hp competition app they are garbage. This whole bypass thing would be great for a street truck. I just can't see any advantages to running one in a higher hp truck

[JQmile]

I think if you're going to do it, something like the Banks blower/turbo setup makes more sense to get true instant boost without having to worry about surging.

[jgsturbo]

Your right , single charging definitely has its limits... but then again nothing says your can't add another charger to this system... everything is scale-able. This technique will give the ability to light larger turbo systems that the engine alone would have a tough time without losing any power from the smaller than normal small charger.