[DGthe3]

Originally Posted by syr74

My guess is that they were telling the truth when they said it doesn't fit, and if we see a V8-powered Genesis coupe it wont be in this generation.



I think the 500+hp estimate is doable, but touching on your emissions comment if it could be produced in an emissions-satisfying trim at that power level my money says it would suck gas like nobodies business. Look at how much petrol the LS7 sucks down compared to it's lesser brethren even with 7.0L of displacement. A production trim, 6.3L version of the same basic engine that produces as much power probably wouldn't even manage a rated 20mpg highway in a Camaro.

Also worth mentioning, Direct Injection almost certainly isn't going to bring as much to the table with the pushrod V8 as a lot of folks are hoping because one of direct injections most troublesome shortcomings was overcome in part by using one of the inherent advantages of a DOHC design. Put simply naturally aspirated, DI engines still technically suffer from fairly serious drive-ability issues under certain fairly specific conditions, you just never encounter that problem because you never see those conditions while driving. The really abridged version is that you end up with some fuel/air mixture issues that cause problems with the combustion process and, the next thing you know, you're mega bucks, DI V8 is 100hp down on power and running like a 9N Ford tractor.

The reason you don't see this in the DI DOHC engines being produced right now is because they have literally programed the engine system to run around the problem. You're driving down the road, approaching a scenario where engine load, rpm, etc, etc are all going to merge perfectly to create the above mentioned problem and presto-chango the camshafts swap profiles, the timing changes, and the problem never occurs and all the while you never notice that anything happened to prevent it.

One of the problems with the implementation of DI on pushrod engines thus far is that you simply can't fix this problem in that same way because there just isn't enough room on the one camshaft a pushrod engine uses to employ the same level of variability two intake and two exhaust camshafts can provide for obvious reasons. And since that is exactly how virtually every other company on earth fixes this problem that creates a problem. My guess is that all the buzz about a cutting edge combustion chamber has something to do with this, but I will be curious to see how well it actually works at solving these issues.

Throw in the fact that DI by itself is really only a 5 percent or so improvement on a DOHC motor on a good day and I think this is an area where what the average GM enthusiast wants this to mean and what GM is actually using it for are two different things. My guess? The advantage GM is looking for with DI is the ability to run higher compression in a smaller, pushrod V8 so they can downsize the engines in the search for better fuel economy without losing very much in the way of power production.

You're going to have to go into a bit more detail for me. On the surface, I don't see any inherent conflict between DI and OHV engines. The air doesn't care about the valves that let it into or out of a cylinder. It will get cooled either way by the vapourization of the high pressure fuel. Plus, the engines will feature VVT and while it won't allow the same degree of control as what can be achieved with DOHC's, it should still be sufficient. So I don't see where the problem lies.