[bklounge]

Has anyone done this? Any dyno plots? My 1m is wondering.

[skinrock]

I'm sure Shiv can provide a more detailed answer, but since the price is the same, I'm not sure why you would want to do that:

http://www.e90post.com/forums/showthread.php?t=708483

The plots are nearly identical, but the 62 has a huge advantage when paired with the 7200 shift point of the MT, resulting in a good +60hp to redline.

[OpenFlash]

No 6mt owner has ever driven a 62mm and said that they wish there was less lag. So no 6mt owner has ever opted for the smaller 52mm turbo. I think a 58mm turbo on a 6mt would be very fun if you we're building an autocross car. Short of that, a 62mm is a better match for anyone who shifts themselves.

[JamesM3M5]

Originally Posted by shiv@vishnu

No 6mt owner has ever driven a 62mm and said that they wish there was less lag. So no 6mt owner has ever opted for the smaller 52mm turbo. I think a 58mm turbo on a 6mt would be very fun if you we're building an autocross car. Short of that, a 62mm is a better match for anyone who shifts themselves.

So you'd still opt for the 62 over the 58 for a dedicated track car - NASA GTS, Time trials, etc? The reason I ask is max HP won't be the goal, and more HP = more heat and more other possible issues. Just spitballing turning a 335i into a dedicated racecar.

[Joshboody]

I'd be curious too... I'm not going past 6500rpms on stock motor. In the future we'll be seeing some comparisons (hopefully) between single and vargas stg3 twins. The twins will likely spool faster, always, but I think the setup will add complications mechanically, install, space, etc. Single is just much simpler.

[OpenFlash]

Originally Posted by Joshboody

I'd be curious too... I'm not going past 6500rpms on stock motor. In the future we'll be seeing some comparisons (hopefully) between single and vargas stg3 twins. The twins will likely spool faster, always, but I think the setup will add complications mechanically, install, space, etc. Single is just much simpler.

Twins capable of making the same power will actually spool up slower than a single.

[Joshboody]

Originally Posted by shiv@vishnu

Twins capable of making the same power will actually spool up slower than a single.

I was thinking about this and concluded that inertia would be the biggest factor. Please explain

[Dave W.]

Just take a look at the dyno chart for twin GT28's on a Supra. Plenty of lag, late spoolup and very ordinary power output. Even the 62mm Single on a 335 spools up quicker and puts out a lot more power.

[Eleventeen]

I'm still on the fence with this. I would assume that using two smaller turbos to flow X amount of air, would present more combined mass and friction to be overcome, than using one larger turbo to flow a comparable amount. I think there are other factors I'm not considering, though (e.g. displacement, RPM range, pressure ratios, fluid dynamics, etc.)

Then you have the twin-scroll turbo. On the surface, it's logical to think a twin-scroll single setup would be the best solution; but I can't find any evidence of a twin-scroll improving spool more than a few hundred RPM over a traditional turbo. A few hundred RPM is nice, but a bit of top-end power is sacraficed. Seems to be the same tradeoff as simply lowering A/R...

[OpenFlash]

Frictional losses are certainly a consequence of using two smaller turbos vs. one larger one. Also remember that hot side efficiency (something that you won't know by reading a compressor map) has much to do with the relative clearance between the wheel and the housing vs the diameter of the wheel. The smaller the wheel/housing, the larger the relative clearance and lower efficiency (which impacts spool-up/response). This alone usually offset the low inertia/mass benefits of two small turbines vs 1 big. Not to mention that there has been many advances in aero and turbine material over the last decade which greatly changed the playing field when it comes to big turbo spool-up. Larger frame turbos spool-up much quicker now then they did just 10 years ago. And make more power to boot.

If you have a V configured motors, twin turbos still make sense since using a single would require excessive long/uneven runners between the two banks. Fortunately with an inline motor, this isn't the case. Packaging two larger-than-stock twins in the n54 is, by any definition, an exercise in compromise. You will need sharper bends for manifold runners, more bends in downpipes and more restrictive intakes plumbing. Each compromise will cost you in terms of both spool-up and power. To offset the power losses, twins will have to be sized larger than what you would expect to use on paper. Which will, in turn, make them less responsive than a properly designed single turbo that isn't subject to any of these mechanical compromises.

If you are sizing twin turbos for the 3.0 N54, it should offer boost response just like if one of those turbos powering a 1.5L motor. I don't know about you guys, but a 2871 on a 1.5L motor is going to be very laggy. They are typically used on 2-2.2L engines.

Attached below is a dyno of a 2871 (with small .64 AR exhaust housing) on a 2.0 Nissan motor. Spool up on a 1.5L motor will be significantly worse.

My 2c,
Shiv

[OpenFlash]

And here is a comparison between a GT28 with 0.86 A/R and a GT2871 with a 0.63 A/R on a slightly more applicable 1.8L VW engine. The GT28 is the one that spools up quicker but makes less power.

[King mode]

Originally Posted by Dave W.

Just take a look at the dyno chart for twin GT28's on a Supra. Plenty of lag, late spoolup and very ordinary power output. Even the 62mm Single on a 335 spools up quicker and puts out a lot more power.

That tune must be way off or something. I have a friend in Denver that makes 420rwhp on his stock turbo supra. I also have a friend making 700+awhp with gt2871's in his b5 s4 (sea level). Keep in mind thats all wheel hp Decent spool too.