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Oh, that's only about 50% more than Saab rates the c900 'boxes can take... (310 Nm). Torque spikes are what kills the box, granted, but Saabine peaks at a relatively modest 363,6 Nm at 2,500 rpm (which is all the dyno engineers will give me, given the frail nature of c900 gearboxes as well as to preserve FWD driveability - it's at 1.15-1.2 bar boost whilst the engine itself happily copes with 1.5+ according to them) right now, while having over 320 Nm at her disposal all the way from 2,250 to 5,500 rpm, all with the .48 turbine. A typical 'all boost - no flow' configuration would see like 300 lbs/ft at 3,500 rpm, above which it rapidly tails off. That way, you have all the potential for serial transmission killing but not that much performance to show for it... But slow turbo spool up too much with a bigger turbine and you'll find the car being painfully slow under normal driving conditions despite making gobs of power on the dyno. The ideal scenario would be to have good transitional behaviour (on/off throttle) which favours the smaller turbine, but with a 'soft' ramp up of torque versus rpm. On the turbo I have, the blades of the compressor wheel are 'angled' lsightly different vs. stock to aid high rpm flow at the expense of midrange torque. Inertia lag, however, remains unchanged.
The result in my case is a very wide ans smooth torque band, although the ramp-up from 2,000 to 2,250 is a tad aggressive on the (static) dyno. I might try slightly more aggressive cam timing to soften the blow down low and extend the useable rpm range by a few hundred to gain some top end hp at the same time. OTOH a acceleration dyno run might show things to be slightly different in this respect (ever wondered why many turbo engines are quoted to make peak torque from about 1,800-2,000 rpm, yet on the road it feels like things only really start happening from about 3K rpm?)...
posted by 82.169.6...
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