Quadrajet Problem Solving > Diagnose a Quadrajet carburetor problem
17059216 new issues vs old issues
Cliff Ruggles:
186 castings from 1969-1970 are about at good as it gets for a factory iron head.
I don't buy them these days simply because by the time you completely rebuild them and convert to screw in studs, guide plates, hardened exhaust seats, etc, you can purchase a complete set of World Products SR heads (for example) for about the same money.
The 186 castings are pretty much duplicates of the older 291/461/462 castings that had the "double hump" on each end and no accessory bolt holes, but the 186's have the flat machined pads and the bolt holes.
I wouldn't stick my nose up at a set of them, they are actually pretty valuable to restorers, but take into consideration the cost involved with getting them rebuilt and up to par for this new fuel.
Also consider that the ports are apprx 165/65cc and the SR heads are 170cc, and they come with 2.02/1.60 valves, so have improved flow potential plus all the additional benefits mentioned. Going from memory they are available in several versions, 67cc combustion chambers, 76cc chambers and even a smaller offering for 305 Chevy engines.........Cliff
77cruiser:
With the 882 heads you probably don't have any where near 9.5-1 C/R unless the block has been decked or you have a .015 shim head gasket.
Cliff Ruggles:
Good point Jim.
Very few of these engines are anywhere near as high in compression as the owner/builder thinks they are.
Quench distance is a very important part of engine building, and folks don't put enough compression in these engines anyhow.
SBC engines absolutely LOVE very tight quench. I shoot for around .030-.035" for my engines. The tighter quench improves combustion efficiency, it will run cooler, take less timing/fuel to be happy, and less octane at any given compression ratio.
Higher compression also improves idle quality and low speed manners with any given cam choice.....Cliff
blazer74:
Flat tops can be quite a bit in the hole depending on brand and deck height, ask me how I know.
I run 64cc Vortecs with flat tops. lucky to be around 8.7 or so doing the math.
von:
I have #3973487 heads on my 350. How are they at performance potential? I know the combustion chambers are large for the lower '71 compression ratios.
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