Quote:
Originally Posted by s0sl0w
Taking care of the fundamentals will only make a f/i'd motor that much better. F/I isn't a replacement for a proper internal work.
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Ok, assume for discussion's sake that the FA20 can stand up to whatever cylinder pressure you throw at it as long as it doesn't experience heavy knock or preignition. That is, durability isn't an issue. And furthermore let's assume your engine is set up appropriately for E85, since it's basically race gas and that's what everyone around here likes.
Well what do you do then for n/a power? Headers are already out there, and we've figure out the appropriate lengths to reduce the torque dip (to my pleasant surprise). Well then what do you do?
So what does that leave you? Higher compression? Once you get much higher than 12.5-13:1, the piston crown gets so high in the combustion chamber that it causes mixture formation issues. Mazda did an in-depth study on it and found 13:1 to be the max for an n/a DI SkyActiv engine.
More lift and duration on the cams? Well let's say you don't have any valve collision issues. That's going to hurt your low and mid range torque. Change the valve timing? You can already do that. You can dial in however much overlap you want, and set relatively early or late closing of each valve. And ITB's? With electronic throttle, you need a way to control them--that won't be cheap.
Look at all the high-end n/a BMW engines from the past 10 years (which were admittedly PFI). They had ITB's, continuously variable valve lift, cam phasers, continously variable intake runner lengths. That stuff can only take you so far.
Quote:
Originally Posted by Calum
Recent work with DI seems to conflict with that. I don't understand it so I'm not even going to attempt to paraphrase it, but from what I've read if you just look for all out flow your gonna have an engine that runs very poorly.
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I've talked about this a lot. High flow ends up hurting the motion of the mixture in the cylinder. GM has recently published a bunch of stuff about the new Corvette DI engine. Guess what they did? They added a swirl characteristic to the old LS7-style heads which required a reduction in flow capability. Without that it had a knock problem.
Right now the main path for n/a mods on these cars is basically full exhaust. You can also do E85--I'm still skeptical of long term reliability with stock fuel system components, but time will tell. There isn't a whole lot further you can go without exponential increase in cost and potential loss of driveability and low-mid range torque.