Wastegated vs. VNT for forced induction power

[TimpanogosSlim]

There are VNT turbos that are much much larger than a VNT-15. The GTB1756VK I'm using is quite a bit larger plus it is good to a bit over 30PSI. Definitely can't say that of a VNT-15 or even a regular VNT-17. Plenty of folks over on TDIclub running GTB2260vks which are significantly bigger yet again.

There is nothing inherent in VNT technology that makes them run out of steam at 3K RPM. If your turbo runs out down low and you want more then you need a larger turbo, regardless of technology.

Sent from my HTC One XL using Tapatalk

I dream of doing something like that, long term, but don't have the budget for it, and don't want the '84 coupe to sit idle.

Short term i am considering just hot piping the k03 to the intake and using a manual boost controller to push it just as hard as i can.

With EGT and possibly IAT sensors.

[745 turbogreasel]

There is nothing inherent in VNT technology that makes them run out of steam at 3K RPM.

So true, the DSM  guys barely even spool an HE351VE by 3000

[theman53]

Those engines came with either the K03 or the GT15, which are about the same turbo size wise. If that stock turbo off either the 1z or AHU doesn't spool fast enough there is a huge problem with it. That is the only thing that turbo is good for is spool. I wouldn't put it on my lawn mower as it is too small. The newer designed holset I really like. Mine has a ported shroud so the surge isn't near as bad as what a big turbo on a small engine should be. Also, it has a ton smoother power than an instaboost type turbo. Not that it doesn't spool fast as I start making boost almost instantly *13-1400rpm* but I don't have 5lbs until probably 1800-2000rpm. But from there it keeps making boost.
I would think with the higher elevation and less oxygen in the air you would want more boost as there is more air in more boost. At the same time, the power comes from the fuel, so if you are having issues with no power add fuel...to do that without high EGT you need boost to cool it. Again, it comes down to what you want out of your car.

[fatmobile]

I've heard the VNTs provide less backpressure.
 On my Rabbit at full throttle the vanes are completely open and pushing 15-20psi.
 Having the vanes open provides less back pressure than an open wastegate.

[745 turbogreasel]

I've heard the VNTs provide less backpressure.

I think that is pretty much BS, as turbos of both flavors come in 1000s of trims and sizes.
Also a bit irrelevant as different applications will call for hugely different pressures and pressure ratios.
In my car, I'd be worried about 60 LBs drive pressure, but that's completely stock on a late commonrail rig that runs like 4x my factory boost.

[RabbitJockey]

at peak power i would say vnt probably has less back pressure, but any other time they're going to have more, especially during spool up.

[vanbcguy]

All depends on how big the wastegate is. A large external wastegate can outflow a VNT.

Sent from my HTC One XL using Tapatalk

[745 turbogreasel]

You can run a large external gate with either one.

[RabbitJockey]

there is a point with a vnt where if you have large enough compressor the faster spool up isn't really going to help because the compressor is either too inefficient at low rpms or the compressor will surge.

[TimpanogosSlim]

There's a point with a traditional turbocharger where the compressor is too inefficient at low rpms as well.

[fatmobile]

delete

[RabbitJockey]

There's a point with a traditional turbocharger where the compressor is too inefficient at low rpms as well.

yeah but i was making the point that vnts do spool faster, but there is a point from a performance perspective where it is still advantageous but not as much as when you are comparing 2 daily driver cars where performance below 3k rpms is most important, its not like having a large vnt means you can expect to have full boost at 1500rpms and carry it to red line, because even if you had full boost at 1500 rpms its not going perform the way a vnt 15 would at the same rpm

[745 turbogreasel]

so why do all the diesel Lemans  cars use VNTs?

[TimpanogosSlim]

There's a point with a traditional turbocharger where the compressor is too inefficient at low rpms as well.

yeah but i was making the point that vnts do spool faster, but there is a point from a performance perspective where it is still advantageous but not as much as when you are comparing 2 daily driver cars where performance below 3k rpms is most important, its not like having a large vnt means you can expect to have full boost at 1500rpms and carry it to red line, because even if you had full boost at 1500 rpms its not going perform the way a vnt 15 would at the same rpm

Sure, but I'm not talking about pulling a turbo off of a sprinter or bigger.

just maybe a vnt17 off of an ALH rebuilt with a VNT22 compressor wheel.

[RabbitJockey]

so why do all the diesel Lemans  cars use VNTs?

cause they're better?  i think i've said that through out the whole thread