1969 Smokey Yunick Camaro

Hi... just because someone (or a website or two) claims they are "hemi heads", I wouldn't be too quick to believe it. I suspect if you saw the combustion chambers on those so-called "hemi" heads you'd change your mind pretty quickly...L-O-L.

Keep in mind that: A hemi generally needs a central plug location. A hemi needs a large bulky rocker arm assembly. The valve cover would have to be very (very) wide to allow for the valve arrangement on a hemi small block head. On the other hand, Chevy pretty much had a background in Canted Valve or "Semi Hemi" heads in the rat motor family at the time. The canted valve design does not mandate a central plug location nor does it mandate a convoluted rocker arm arrangement that would require a comprehensive cylinder block revision. And a canted valve setup could use a valve cover that was, for all intents and purposes shaped like a little rat motor piece. Following right along, a canted valve 90-degree V6 and then a canted valve small block head was released by GMPP years later that with revised ports looked suspiciously close to the head on the Yunick engine. I suspect if you do some additional research you'll find that this was a canted valve small block cylinder head that Yunick, Jenkins and others were playing with at the time. In fact, I think you'll discover that Jenkins even messed with them in his Vega/Monza era.

And I too discussed these heads with Smokey at length (anyone who knew him in later years will tell you he was pretty free with information).


Wayne

[Carleen]

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Hotrodsled</div><div class="ubbcode-body">Hi... just because someone (or a website or two) claims they are &quot;hemi heads&quot;, I wouldn't be too quick to believe it. I suspect if you saw the combustion chambers on those so-called &quot;hemi&quot; heads you'd change your mind pretty quickly...L-O-L.

Keep in mind that: A hemi generally needs a central plug location. A hemi needs a large bulky rocker arm assembly. The valve cover would have to be very (very) wide to allow for the valve arrangement on a hemi small block head. On the other hand, Chevy pretty much had a background in Canted Valve or &quot;Semi Hemi&quot; heads in the rat motor family at the time. The canted valve design does not mandate a central plug location nor does it mandate a convoluted rocker arm arrangement that would require a comprehensive cylinder block revision. And a canted valve setup could use a valve cover that was, for all intents and purposes shaped like a little rat motor piece. Following right along, a canted valve 90-degree V6 and then a canted valve small block head was released by GMPP years later that with revised ports looked suspiciously close to the head on the Yunick engine. I suspect if you do some additional research you'll find that this was a canted valve small block cylinder head that Yunick, Jenkins and others were playing with at the time. In fact, I think you'll discover that Jenkins even messed with them in his Vega/Monza era.

And I too discussed these heads with Smokey at length (anyone who knew him in later years will tell you he was pretty free with information).


Wayne </div></div>





http://en.wikipedia.org/wiki/Hemi

Forgot something...

I agree...Smokey also told me the heads were actually down on power. If you look at one of the old Jenkins small block Chevy books, there's a picture of the Grump fiddling with what looks like a 351 Cleveland tunnel ram on a small block. Back then it wasn't easy or practical to fab an intake (sheetmetal). I suspect he was trying to figure out how to adapt the intake to a set of these heads.

Wayne

[olredalert]

----Im pretty sure that silver car sat in Al Maynards collection for some time before making it to R.J. If not, theres a twin out there somewhere right down to the engine and options......Bill S

You do not have a &quot;hemi&quot;, but you can believe whatever you wish. I'm sure others will chime in sooner or later. I'm done. Have fun.

Wayne

[iluv69s]

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Hotrodsled</div><div class="ubbcode-body">You do not have a &quot;hemi&quot;, but you can believe whatever you wish. I'm sure others will chime in sooner or later. I'm done. Have fun.

Wayne </div></div>

Hey Wayne..no hard feelings...I dont really care if they are a 'hemi' head or not...just seems a lot more like a hemi than a porcupine...haha...

..and Paul..Thanks for the pic...now that is a hemi head for sure !!!

[PxTx]

I've debated these issues in the past. Hemi was and has become such a buzz word these days that is does get misapplied.

Even the modern &quot;Hemi&quot; advertized in trucks and such has what I call a &quot;roof-top&quot; combustion chamber. From my perspective, if you can take something round, like a ball and a combustion chamber follows the shape, that is what I consider a Hemi.



It also seems the valve arrangement should be opposed, rather than side by side to be considered a Hemi.

Don't get me wrong, I'm a big fan of these &quot;porcupine heads&quot; and was just speaking with Charley about the Yellow one he owned in the 1990's. That car made a huge impression on me then and is one of the reasons I am such a fan of multile carburetion.

I eagerly look forward to your build.

[427TJ]

Magazines in the '60s called the Mark IV big-block the &quot;semi-hemi&quot; for its canted valve design. Looks like the Z/28's &quot;hemi&quot; heads are merely semi-hemi similar to the BBC?

[jannes_z-28]

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

[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.