What is this hole for???

MDN · #1 (**permalink**) 08-20-2007, 09:38 PM

Hello all,
Can someone please tell me what the hole in center of this 289 head is? I am putting on Webers, and this hole will be blocked (the new gasket will block the hole). Before I do this, I would like to know what purpose is serves (It's not coolant).
Thanks,
Mike
http://clubcobra.com/forums/attachme...1&d=1187667221
cobra (Custom).jpg

fsstnotch · #2 (**permalink**) 08-20-2007, 09:48 PM

coolant I'd guess

Excaliber · #3 (**permalink**) 08-20-2007, 09:49 PM

"Heat Riser", typical on most 'street' type heads. It warms up the intake using exhaust gas cross over through the intake. In some cases coolant may be substituted for exhaust flow, not sure which on a 289. Keeps the carb from freezing up in winter and helps atomize the raw fuel suspended in the air/fuel mixture passing through the head to the combustion chambers, among other things. From a pure performance standpoint it 'upsets' the exhaust flow and 'warms up' the air/fuel charge. COLD air is denser, contains more oxygen thus more potential power. That could be offset by not enough 'heat' to get good atomization of the fuel suspended in the air. Running it promotes better gas mileage at a loss of horse power. There is ALWAYS a 'trade off' when designing an engine. Max power? Drivability? Best mpg? You can't have it all...

High Performance heads/intake will often block this hole using intake gaskets or the hole may not even exist. Like my OEM Ford High Riser heads, no provision for heating the intake at all. Most Edlebrock heads delete the cross over.

Jac Mac · #4 (**permalink**) 08-20-2007, 09:52 PM

Exhaust heat crossover for manifolds of std road cars, not required with your webers. Just put some sealant around that area & bolt em on.

Jac Mac

fsstnotch · #5 (**permalink**) 08-20-2007, 09:53 PM

^^ that makes so much more sense!

Excaliber · #6 (**permalink**) 08-20-2007, 09:56 PM

I had an early Dodge slant six in Michigan, years ago, that would freeze the carb in winter because my 'heat riser' from the exhaust manifold wasn't working. In THAT case, I had to fix it and it was a welcome addition.

MDN · #7 (**permalink**) 08-20-2007, 10:45 PM

Thanks everyone for the quick reply. That makes perfect sense, I now know why there is soot in the hole.
Mike

Rick Parker · #8 (**permalink**) 08-21-2007, 12:22 AM

Be certain that the intake set you will be using has an insert to cover that small area that is impervious to heat. Some gaskets are intended for heads without the opening and consequently are made of regular material instead of a gasket with and insert for the cutout. Felpro 1250 High performance gasket works well for 289 heads. Port sizes etc.