Re: Where is 69 Yenko Camaro 124379N663539
<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: novadude</div><div class="ubbcode-body">I would imagine that "stock" is moving far away from stock parts as more and more items become NHRA approved. From what I can tell, the port shape on those Edelbrock castings and GMPP intake look nothing like the OEM L78 parts. Can someone be competitive with the "NHRA approved" stuff using real GM castings from 50 years ago? </div></div>
novadude,
Everyone is entitled to their opinion, however, unless you have x-ray vision or you have a set of Edelbrock heads and Chevrolet intake manifold as described above in front of you for comparison, I don't know how you can make the statement "the port shape on those Edelbrock castings and GMPP intake look nothing like the OEM L78 parts". NHRA makes the rules and if they say that these parts are legal for replacement, then it is up to the individual racer to decide what parts they want to run. Obviously, I did not mention it, but all of the above replacement parts are interchangeable with an original Mark IV block. NHRA mandates the cc's requirements on intake ports, exhaust ports and combustion chambers to maintain the integrity of the stock dimensions, also included are valve dimensions including diameters, stem size and weight of the valve. All of those cc measurements were obtained in the mid to late 1980's off of stock big block L78 parts. The one big difference between the replacement heads and the old iron is the combustion chamber cc's have been changed since both the aluminum 401 Chevrolet Head and the Edelbrock replacement head (Edelbrock did the castings for the aluminum Chevrolet 401 head) are both the open chamber design, rather than the closed chamber design as were the originals back in the 60's and 1970, so that the compression ratio is correct for the year claimed. If the intake runners or exhaust ports are bigger than the NHRA specification and/or the combustion chamber is smaller than the specification and the tech department does a random check or if you get torn down for setting a National Record, and these dimensions are not correct, NHRA will tell you that you cannot race at their events for one year from the time of the infraction. After the year suspension they will also require you to bring the heads to them, they will cc them and then you can re-assemble them to the engine before you can compete at that event. Stock is the most regulated class in NHRA racing and I will agree that a lot of the requirements have been relaxed over the years due to the unavailability of stock parts, but dimensionally, the requirements regarding various weights and dimensions are still in the rule book and are enforced. Are there racers that stretch the rules, of course there are, but in my humble opinion, they are just kidding themselves if they decide to go outside of the spirit of the rules.
To answer your other question, I think the original heads can be very competitive, in fact between the original iron head and the aluminum head, NHRA imposes an increase of 5 horsepower, so you have to weigh more depending on which class you are running if you choose to run the "new" replacement aluminum heads. My original engine had cast iron heads (291 castings) that could have been updated, but I chose to go to the aluminum heads (even though there is the horsepower penalty), but I did it anyway since I am getting old and the iron heads are approximately 40 lbs per head heavier than the aluminum and with two broken wrists, it is getting harder for me to pick them up.
Above statements are my opinion, and as I said you are entitled to your opinion.
Gary Merrick
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