I was looking at the NHRA Stock Car Engine Blueprint specs (http://nhra.com/tech_specs/engine/index.html#chevy) for 1962 and noticed something interesting. The speced deck clearence for the 340 and 360 hp 327 is .002", the speced gasket is .018". This makes the quench .020". Am I reading this right? Maybe a typo and the Deck Cl should be .020"? The other 327's and the 283 have .014" Deck CL and .018" gaskets for .032" Q. If this is correct, I guess we have all been setting our quench distances way too wide.


</font><blockquote>code:</font><hr /><pre style="font-size:x-small; font-family: monospace;"> Deck Piston Type
H.P. Disp. Cl Dish/Dome Ht/Vol Valves Cam Lift Springs Gasket Head Casting


340 327 .002 Dome .122&quot; 5.3cc 1945/1505 393/399 Outer w/Damp .018 461,462,041,492,291
360 327 .002 Dome .122&quot; 5.3cc 1945/1505 393/399 Outer w/Damp .018 461,462,041,492,291</pre>[/QUOTE]I'm very surprised to see this tight of a quench distance on any engine, much less a factory engine.

If you use the 041 or 492 casting, it's nowhere near as important, because there's a "quench" area built into the chamber casting, looks sort of like a little ramp over on the spark plug side. I know 461s don't have that; can't recall whether 462 or 291 have it.

Pat,
I believe those are the minimum accepted specs per NHRA.
I have run .025 to 7500+ in short stroke 350's without problems & a 482 at .031 to 8500+ where the pistons were just touching the heads (hey, it keeps the rods from stretching :D ) but don't recommend it as every piston, rod & crank throw needs to be correct. .020 would probably work with tight piston clearances & in an engine that is inspected on a regular basis but not real practical long term in anything but maybe a small bore long piston deal of some sort.

The -461 and the older real early, shrouded, sparkplug's in a trough, 265 and 283 heads are the only stock heads that have a true flat quench on the sparkplug side..

I think the "Turbo" head's chamber was made like the old -461 but the sparkplug was raised??

pdq67

Mike, you're probably right, a minimum. I can't imagine GM warranting an engine with that tight of a quench.

Of course, the spark plug side isn't the only place that quench occurs. The other side of the chamber over the piston is quench area.

265 and 283 heads are the only stock heads that have a true flat quench on the sparkplug side That is wrong.

292 casting: http://cgi.ebay.com/ebaymotors/ws/eBayISAPI.dll?ViewItem&category=33617&item=7922978117&rd=1

186 casting: http://cgi.ebay.com/ebaymotors/ws/eBayISAPI.dll?ViewItem&category=33617&item=7922890826&rd=1

These are 041s. They have it. http://cgi.ebay.com/ebaymotors/ws/eBayISAPI.dll?ViewItem&category=33617&item=7922411805&rd=1

Here's some 291 heads; they don't have it. http://cgi.ebay.com/ebaymotors/ws/eBayISAPI.dll?ViewItem&category=33617&item=7922764762&rd=1

Here are 461s; they don't either. http://cgi.ebay.com/ebaymotors/ws/eBayISAPI.dll?ViewItem&category=33617&item=7922414421&rd=1

How about more 041s. http://cgi.ebay.com/ebaymotors/ws/eBayISAPI.dll?ViewItem&category=33617&item=7922076406&rd=1

ebay is an excellent source for pictures of stuff. If you really want to see what something looks like, just go there and look for it. Obviously with heads, it helps if they include a pic of the casting # itself.