Quote:
Originally Posted by bradleyland
A sequential turbo setup is not a cure-all for the throttle response issues of a high-boost, small-displacement gasoline engine. You keep going back to diesels, but a diesel engine responds very well to turbo charging for reasons that I've already explained (and you seem to ignore).
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Right pedal response quality is one of the big issues with diesel engines because of the HUGE amount of air you have to force-feed to the cylinders in order to assure the most complete mixture between the air and the injected fuel when max. compression takes place, as it is the compression which will eventually lead to the explosion inside the cylinders (there's no spark to ignite the mixture). That's also the reason why you can't revv a diesel engine as high as a petrol engine, you start to run short on time to feed the cylinders the necessary amount of air to assure the proper mixture with the increasingly amount of fuel you demand as you try to climb up through the rev-counter. In a petrol engine, air and fuel are mixed for the entire compression stroke, ensuring complete mixing even at higher engine speeds whereas in a diesel engine fuel is injected just before the power stroke after all the air within the cylinder has been compressed and, as a result, the fuel cannot burn completely unless it has a sufficient amount of oxygen.
Therefore, a very high-boost is necessary from the turbocharging system in a diesel engine which means BIG turbochargers, which, in turn, means HIGH turbo lag.
To overcome this, BMW went as far as using not two but three turbochargers - two small, low inertia and a bigger one - that work in sequence or simultaneously, depending on the engine rpm, forming a three stage arrangement that you can find in the M35d models such as the M535d. This car costs as much as an M3. And, I can assure you that the right pedal response of the M535d is on pair with my 1M's and that it revs eagerly right to the redline.
So, if we recall that the use of sequential twin-turbochargers was first introduced on petrol cars for the very same throttle response quality reasons and it was then adopted by diesel engines for which the issue is in fact critical, it's very easy to understand why such solution makes every possible sense for an high-boost turbocharged inline-4.
This is the last time I'll try to explain to you why BMW's bigger, heavier, higher COG and less fuel-efficient turbocharged inline-6s are a marketing thing.
I'll leave your far too many personal remarks unanswered, past, present and future, for reasons I'm sure you can understand... I really don't care!
Quote:
Originally Posted by bradleyland
I agree that sticking with the I6 involves trade-offs. In a role where you only care about maximum performance in a track environment, the high-boost I4 makes a lot of sense. You're minimizing weight and maximizing power where it counts. On a race track, you don't care about throttle response below 3,000 RPM.
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Except that the AMG inline-4 engine's max torque, which is as high as 332 lb-ft ( just like my 1M without the overboost function), starts as soon as 2250 rpm and with most modern turbocharged inline-4s max. torque is readily available from only 1900 rpm.
So, it's a non issue really!
Quote:
Originally Posted by bradleyland
The M235i isn't that pure of a car though. It's balanced more toward a car that you can live with day-to-day. The CLA 45 AMG is a full-blown AMG car.
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And yet the CLA AMG offers the same, if not better with its 4 doors, day-to-day practicality.