An example of what small block cubic inches can do, and ....

[femtnmax]

...what good cylinder head flow is worth.
The article is in the winter 2006 engine masters; done on an ALUMINUM block chevy LS1, 346 cubes, built by the chief cylinder head designer for Air Flow Research for his 2000 Corvette.
The 346 bore and stroke is 3.905 X 3.622, almost a combo of a mopar 318 bore and 360 stroke.  The engine used AFR's smaller cylinder head with 205cc intake runner.  AFR believes in high port velocities.  They said you'll never go back to big runner cross section lazy port flow once you feel the difference.  Note that port SHAPE is very important.
Cam was hyd roller 224/228 duration at 0.05 lift. Valve lift was 0.581/0.588 using 1.7 rocker ratio.  Most valve lift for the least duration is the way to go.
They then added a 4 inch stroker crank to up the engine size to 383 CID, and used the same heads and cam to produce the following dyno results:

   Cubes   Torque at 3000 rpm   TQ at 5000 rpm   Peak HP at rpm   Compression ratio
    346          410                       475                550 at 6500             11.3:1
    383          450                       525                550 at 6000             10.9:1

The engine had no accessories, used an electric H20 pump.
So the cubes increased 10% (346 to 383), and the torque increased a consistant 10% everywhere throughout the range from 3000-6500 rpm.
So small blocks can be made to run.  and yes, we need an aluminum block for the small block mopar.

[Ck[FIN]]

Good numbers. Though you can get same horsepower from cast iron block too. Its heavier but still 550hp is definitely enough power for street car?

[71chally416]

The problem is those heads cost $2,300. They  flow 298cfm (according to AFR) and you can easily get 300cfm from a stock 5.7 Hemi truck head with 20 minutes of work in each port (270 stock) So compared to stock GM heads they're great, but compared to the new Hemi they aren't. The reason for using aluminum blocks is it's way easier to machine than high nickel cast iron. Ask any machinist.    

[HP2]

So small blocks can be made to run.  and yes, we need an aluminum block for the small block mopar.

They already exist. A8 aluminum race block part numbers P5153378 for 9.015 deck, P5007905AB for 9.1 deck, and P5007909AB for 9.435 deck.

[72hemi]

The problem with those aluminum blocks is you can't use direct LA series bolt on parts like timing cover. Plus the price on those blocks is a bit high.

[femtnmax]

Great responses.  Thought I might piss people off with chevy info.  I just wanted everyone to think airflow, cams, and weight to improve performance.

[72hemi]

You have to admire what Chevrolet has done with the LS platform. The Z06 Corvette (both the C5 and C6) get 30 mpg on the hwy while throwing down either 405 or 505 hp (depending on generation) and the car is insanely reliable and streetable. I believe the Z06 comes in around 3200 lbs.

[HP2]

The problem with those aluminum blocks is you can't use direct LA series bolt on parts like timing cover. Plus the price on those blocks is a bit high.

Given the valve train geometry issue with LA blocks, I can't see why they would have ever wanted to reproduce it in aluminum anyway. Yes they are spendy, but they aren't destined for your average cruiser anyway.

The reason for using aluminum blocks is it's way easier to machine than high nickel cast iron.    

They also can be repaired after you window them. Iron just gets thrown away. Factor in the cylinder sleeves and their usable service life is greatly extended over an iron block.

[71chally416]

I agree with the valvetrain issue. The bad geometry dates back to the 1st gen Hemi. They never changed the angle when they tooled for the Wedge in the 60's.

Trust me, you don't have to tell me about repairing aluminum blocks. I just sold a KB that had a few windows over the years. Cast Al blocks are really outdated today in racing. All the fast Hemis use billet blocks.

I always here this 30mpg figure for Vettes but it doesn't jibe with the info on GM's website (26 for a 6 speed) That's one MPG better than a 5.7L 6 speed 4,200 lb 2009 Challenger (25)

[72hemi]

I have several friends who have both C5 and C6 Z06 vettes and the C5's are getting between 30 and 35 mpg on the hwy while the C6's are getting between 28 and 30.

[quagmire]

Those cars definitely knock down 30+ MPG driven easily, I have several friends with LS powered vehicles.  They all get better economy than my car with a 2.5 V-6!  I know several people with Hemi powered Chargers and Challengers, and they say they are pigs on gas.  I think it has more to do with the heavy barges they put these engines in rather than the engine itself.  ALL fuel economy ratings are much more conservative nowadays to keep people from complaining about not getting the rated MPG when their driving styles lowered it.  They changed the testing a year or two back.  That's why they are rated much lower but people can get way above that rating with easier driving.  My car's new rating is 3MPG less than it was two years ago, and I routinely get several above the old rating. 

[71chally416]

All new cars are rated by the same method.

[quagmire]

Yeah they are, but that method has changed in the last two years which is why they are rated lower now. 

[71chally416]

The numbers I quoted are both 2009 figures taken from the websites today. It obviously has to be consistent company to company to have any meaning. I suppose you could better it by 7MPG but I think I'd have to see actual proof of that instead of just taking somebodys word for it. Like be there at the fillup, be in the car till the tank was emptied and do the math myself. I don't know how you could ever determine actual Highway MPG anyway because you'll never use a whole tank of gas without stopping and starting. If that's just what flashes on the MPG display on the dashboard, then it's the same thing I saw in my Father in Law's old HT4100 powered Cadillac Fleetwood. At least for milliseconds when he let off the gas going down hills with a tailwind. 

[72hemi]

My friends have actually calculated the fuel economy of their cars during long trips they have taken their cars on. I trust their math. You can be as skeptical as you want, but these numbers are legit.