1969 Smokey Yunick Camaro

[markjohnson]

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: jannes_z-28</div><div class="ubbcode-body">The Hemi heads have the intake and exhaust runners in line, and the valves meets in the semisphere opposing each other. That way you get a straight line for the gases to flow. The shape of the combustion chamber requires a very heavy piston to get any compression and makes high RPMs difficult to reach.

What Chevy did with the Mark IV head was a great compromise where they could reach good flow and also directing the flow in to the cylinder in a better way that the Mopar HEMI head could do. This design was then applied to the special heads for the Small Block. One other design with similar technique were the Ford 351 Cleveland that you could say were a small block engine with a Chevy BB head.

With the good flow from the runners and the shape of the combustion chamber they could run lighter pistons in these engines.

Look at the Pro Stock era pre 500 cu in, the 351 Cleveland had great success with Glidden, Dyno Don and Gapp&amp;Roush. The Chevy guys were good too with de-stroked BB's getting pretty much the same kind of engine combo that the Ford guys had.
Using a 348 crank (with offset grinded taps) in a Mark IV block you could get down to around 330 cu in with a 4.25&quot; bore, which were bigger than the Ford guys could do with the Cleveland block.
These Chevy engines could rev over 10.000 and making a lot of power. Back then the Mopar Hemis were to big and heavy and didn't have much chance... ProStock rules then had a weight/cu in ratio with different factors for different engines. The Cleveland had a higher rate than the Mopars.

Jan</div></div>

I'm a fan of the Big Block Chevy but NO WAY does it do better than the Chrysler Hemi when it comes to the ports dumping into the cylinders! The Hemi has the air/fuel charge dumping straight into the center of the cylinder while pretty much most people know that the BBC has four &quot;good&quot; ports and four &quot;bad&quot; ports. The bad ports actually turn the air/fuel charge into the cylinder wall and many people actually consider the BBC to be almost two different engines in one package and even run a different range of spark plug into these four bad cylinders. Hemis are also interesting in that there is no &quot;quench&quot; part of the combustion chamber while an early closed-chamber Rat motor cylinder head has two &quot;quench&quot; spots and while the later open-chamber head sacrificed one of these quench portions of the chamber to be more like a true Hemi. As far as early-'70's Pro Stock racing, the Hemi was just dominant and it was NHRA that just factored them out of competiveness with the stroke of a pen by adding weight time and time again until the Fords and Chevys started winning. I'm a GM man, but what NHRA did to Chrysler was really a dirty thing to do.