Quote:
Originally Posted by IMOA
I think you're underestimating how hard it is to get a flat torque curve! The engine has variable valve timing but lift is fixed and intake length is fixed, you're going to end up with a hole somewhere as you just don't have the adjustability in the intake to maximise VE everywhere. It's a sportscar so it needs to work up top but it is intended as a road car so it needs bottom end to cope with DD. That leaves the lower/midrange which you don't really need for either duties as the one which is the least important. It's not a matter of choosing to leave a hole, it's a matter of not being able to fit the more expensive intake/cam technologies in the price target and then selecting the other items (intake length, cam lift and duration etc) so that they are their most efficient where it matters and least efficient where it doesn't.
You also have to remember that direct injection only gives better torque, not worse. As it's able to deliver the fuel charge very close to the plug the flamefront propogates through the fuel charge quicker minimising the risk of detonation, this lets you run more timing to maximise torque. A number of tuners have remarked that the tune is very aggressive through this area in the maps which re-inforce that the issue is intake harmonics, not tune. The fact that no-one has been able to tune this out even though they have contol over when the port injectors are used also tells you that the problem is harmonics, not tune.
Everything in an engine is about compromise and to me it screams that they've compromised on cost by not using variable lift or variable length intakes (also a reliability issue for that one) which will result in losing VE somewhere which they've placed at the least important spot in the rev range. To minimise this they've gone aggressive in the tune however you can only make up for a lack of air so much in the tune so we're still left with a hole.
|
Are you are suggesting the port injection was turned off in that rpm range so that purely direct injection could maximise the torque to compensate for a lack of air? That it's nothing to do with an emission target?