Quote:
Originally Posted by WingsofWar
Ill be shooting for 250whp for my n/a build. which is going to be horribly challenging to gain that extra 100whp while retaining good reliable performance. The engine needs to comfortably make 250whp rather than straining at 250whp, so moving the powerband up on the RPM scale might be necessary to achieve that.
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Oh dear, that's going to be hard. Do cheat with E85 to get you that extra 10% :P Moving the power peak from 7k to 8k with longer duration cams and a different intake manifold (full exhaust and the rest of the jazz too) can net perhaps 8/7*165?lb-ft/150lb-ft * 200hp=251.4hp, at the crank, with very little room to play with after 8k, and a rather peaky powerband before that. From the exhaust numbers and stuff we're seeing, I think 170lb-ft shouldn't be too hard to hit. But now you are looking to find that last 10-15% "drivetrain loss", that's going to be tough on pump gas! (let's admit it, 9000rpm with a 1.5 rod stroke ratio isn't so good for the cylinder bore or bearings) E85 should get you there though, if you can direct inject all of it. When done right the charge cooling effect on pre-combustion pressures alone should be worth 3% more power, or something like that (I did some calculation a long time ago).
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MattR, I think Crower or someone did post a picture of the EJ rods next to the FA rods, and after I asked what the rod lengths were they did post it. I just remember it was 130+/-1 mm.
Quote:
Originally Posted by Bonburner
how do you plan on getting 9k rpm AND 34 mpg?
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Actually, this should be much easier than you think, given that we're willing to accept slight compromises in cam design. I believe one of the biggest reasons for the poor low end performance of big cams is that the big amount of overlap introduces large amounts of exhaust gas into the charge, completely ruining combustion efficiency. They say direct injection helps to increase the tolerance for internal EGR, but when you're idling and the vacuum is high, any overlap is going to mean a lot of exhaust sucked back in.
Larger cams however will lose volumetric efficiency at low rpm cruising conditions, which will decrease pumping losses and allow a cooler charge which further increases efficiency.
If you see some Toyota diagrams for VVT operation, you'll notice the range of cam movement allows the stock cam to be retarded to the point where it opens several degrees after TDC. So a performance cam that doesn't go too crazy on overlap can likely maintain near stock combustion quality characteristics at low loads. I mean this for both intake and exhaust. We lose a little bit of scavenging like this, but maintain driveability and increase fuel economy.