What causes torque to drop off so far?

wren57 · 07-05-2016, 09:02 PM

Been looking for a turbo setup with a nice flat torque curve but it seems our N54s choke and torque falls fast towards redline on every setup. Why is that?

Antetokounmpo · 07-05-2016, 09:16 PM

Small turbos simply can't produce enough volume of air to make big power high in the rpm band.

wren57 · 07-05-2016, 09:20 PM

Quote:

Originally Posted by Heel Toe

Small turbos simply can't produce enough volume of air to make big power high in the rpm band.

Problem occurs even with big singles.

Antetokounmpo · 07-05-2016, 09:33 PM

Quote:

Originally Posted by wren57

Quote:

Originally Posted by Heel Toe

Small turbos simply can't produce enough volume of air to make big power high in the rpm band.

Problem occurs even with big singles.

To a MUCH lesser extent. They are usually still building at 7k, whereas stock turbos build until 5.2k or so.

AYEDEE · 07-05-2016, 09:44 PM

Velocity

jtswole · 07-06-2016, 06:30 AM

Small exhaust housings. That's why you use a big AR on the exhaust side.

Velocity26 · 07-06-2016, 08:33 AM

Every engine (head) is designed for a specific RPM range. As you reach the limits of the range, the torque will drop off. If the engine is still increasing torque at redline, someone did not design the ports properly. They could have gone with smaller ports/valves and increased the performance within the design range.

You can see where some single turbo (maybe even GC twins) can maintain a much flatter torque curve near redline, that is usually done by progressively increasing the boost at RPM where the torque would otherwise be dropping quickly. This extra boost offsets the loss of efficiency of the head and creates more torque/HP. They also feature an improved exhaust manifold that can flow more than the stock manifold, on the main restrictions of our system.

07-05-2016, 09:02 PM	#1
wren57 Roll Tide 591 Rep 2,345 Posts Drives: 335i Join Date: Jul 2010 Location: St Louis iTrader: (10)	What causes torque to drop off so far? Been looking for a turbo setup with a nice flat torque curve but it seems our N54s choke and torque falls fast towards redline on every setup. Why is that?
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07-05-2016, 09:16 PM	#2
Antetokounmpo Brigadier General 1552 Rep 3,475 Posts Drives: E90 6MT FBO; '18 F150 Platinum Join Date: Jul 2013 Location: WI iTrader: (3) Garage List 2018 Ford F-150 Pla ... [0.00] 2008 BMW 335xi [0.00]	Small turbos simply can't produce enough volume of air to make big power high in the rpm band. __________________ 2008 335xi 6MT \| VRSF Catless DP \| VRSF 7" FMIC \| VRSF CP \| TIAL BOV \| DCI \| MHD 2+ BC Racing BR \| Stoptech 600 \| Firehawk Indy 500 255 Square \| Atric Altimax 225 Sq. 2018 F-150 Platinum 701A \| FX4 \| 3.5 EcoBeast
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07-05-2016, 09:44 PM	#5
AYEDEE Captain 56 Rep 936 Posts Drives: 3 Series BMW Join Date: Oct 2013 Location: NSW iTrader: (0)	Velocity
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07-06-2016, 06:30 AM	#6
jtswole First Lieutenant 42 Rep 380 Posts Drives: 335i Join Date: Mar 2014 Location: FL iTrader: (1)	Small exhaust housings. That's why you use a big AR on the exhaust side. __________________ Cam only...
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07-06-2016, 08:33 AM	#7
Velocity26 Resident old fart 146 Rep 575 Posts Drives: 2010 335i M-Sport Join Date: Oct 2011 Location: Florida iTrader: (4)	Every engine (head) is designed for a specific RPM range. As you reach the limits of the range, the torque will drop off. If the engine is still increasing torque at redline, someone did not design the ports properly. They could have gone with smaller ports/valves and increased the performance within the design range. You can see where some single turbo (maybe even GC twins) can maintain a much flatter torque curve near redline, that is usually done by progressively increasing the boost at RPM where the torque would otherwise be dropping quickly. This extra boost offsets the loss of efficiency of the head and creates more torque/HP. They also feature an improved exhaust manifold that can flow more than the stock manifold, on the main restrictions of our system.
	Appreciate 0 Quote