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I only use a valley pan IF I'm using the exhaust crossover passage. If the intake manifold or cylinder heads don't have the exhaust crossover passage, then I don't use one. Just my experience and never had a problem. As a matter of fact, some intake manifold manufacturers (such as the Weiand Stealth) actually instruct you NOT to use a valley pan intake gasket.
If your intake manifold and cylinder heads have the exhaust crossover passage AND you're using it, (meaning it's not blocked off) then I'd recommend using a valley pan type of gasket. Remember, Ford used either a valley pan or a small square shaped heat shield (secured with three push rivets) under the factory cast iron intake manifold, in order to prevent oil from baking underneath the manifold (around the exhaust crossover area).
IF you're using an aftermarket aluminum intake manifold AND blocking off the exhaust crossover passage, then a valley pan gasket is not necessary (because there isn't any additional source of heat). If you think that you'll reduce the temperature of the intake manifold, by using a valley pan, your wrong. A valley pan is not an insulator that completely seals off the bottom of the manifold from engine heat, it's only an oil barrier for the exhaust crossover passage. In order to prove my point, David Vizard once did dyno testing on several intake manifolds and his comments on the Edelbrock Air Gap manifold may surprise you. This is an excerpt from David Vizard, after dyno testing several intake manifolds including the Edelbrock Air Gap:
"Exactly what is the Air Gap's air gap worth? Temperature testing with an infrared heat gun revealed much. First, the heat soak from a hot engine will, in about 10 minutes, bring the runners of the Air Gap manifold up to that of a non-air gap one. Under full-power conditions, the runners of either type of manifold drop and stabilize after about 15-20 seconds at full throttle, but the Air Gap manifold drops (depending on ambient conditions) about 20 degrees more at 2,500 rpm and about 15 more at 5,500 rpm. The net worth of this in output is about 6 lbs.-ft. at 2,500 rpm and about 4 lbs.-ft. at 5,500. Nevertheless, there is an overriding concern here. If the carb being used has inadequate fuel atomization, the cooler runners can actually detract from output, so be sure to use a carb that does a good job on mixture preparation."
Now this was on an Air Gap manifold, which in fact DOES have the intake runners completely sealed off from hot engine oil, and it STILL reached the operating temperature of a non Air Gap manifold.
While we're on the subject of intake gaskets (and since some of you won't use the valley pan now), lets just quickly cover conventional intake gaskets. The Fel-Pro 1230/1231 intake gasket is NOT intended for a street application. It is designed with a soft rubber-fiber base (resistant to gasoline & alcohol) AND without a steel core reinforcement so race builders can trim material for a custom port opening. The 1230/1231 is only supposed to be used on a race engine that gets disassembled (for inspection or rebuild) on a regular basis. It was NOT designed to withstand long term daily street usage. This is from my in-depth research on this subject and from speaking to a Fel-Pro technician. People who have used these gaskets successfully on the street, don't put many miles on the vehicle. While there may be a few who contest this, there are many more who will substantiate the 1230/1231 failure streetwise. The Fel-Pro MS901101 (Dove port) & Victor Reinz NitroSeal 95074SG (CJ/SCJ port) intake gaskets are the proper choice for a daily street driven engine that will stay assembled for a long period of time. (Fel-Pro doesn't make a CJ/SCJ 'street longevity' intake gasket set.)
The 1230/1231 intake gaskets also aren't meant for an exhaust crossover passage. They are race only gaskets for aftermarket heads and manifolds without the exhaust crossover passage. If you insist on using these gaskets with an exhaust crossover passage, then you'll need to either cut the opening in the gasket or block it off with a thin piece of stainless steel sheet metal (fitted between the gasket and head). It will burn through, if you don't cut out the opening or block it off with any effective method you choose.
Blocking off the exhaust crossover passage:
The hardware store sells small square pieces (about 4"x4") of sheetmetal (by their ducting material) for less than $2. I used a small thin piece of stainless steel sheet metal to block off the exhaust crossover passage. (It doesn't need to be stainless steel, I just had it.) The important thing to remember is to place the sheet metal between the cylinder head and intake gasket. I coat the cylinder head side of the sheet metal, with a 1/4" thick layer of high temp silicone and push it into position (so the silicone creates a 1/4" barrier inside the heat crossover passage), then wipe off the excess around the outside edge. I recently disassembled my 466 (soon to be a 508") with about 100,000 miles and the sheet metal block off was still right in place (on the cylinder head).
Sorry for the long post, however, I've done alot of research and discussed this, at length, with Fel-Pro technicians.
If your intake manifold and cylinder heads have the exhaust crossover passage AND you're using it, (meaning it's not blocked off) then I'd recommend using a valley pan type of gasket. Remember, Ford used either a valley pan or a small square shaped heat shield (secured with three push rivets) under the factory cast iron intake manifold, in order to prevent oil from baking underneath the manifold (around the exhaust crossover area).
IF you're using an aftermarket aluminum intake manifold AND blocking off the exhaust crossover passage, then a valley pan gasket is not necessary (because there isn't any additional source of heat). If you think that you'll reduce the temperature of the intake manifold, by using a valley pan, your wrong. A valley pan is not an insulator that completely seals off the bottom of the manifold from engine heat, it's only an oil barrier for the exhaust crossover passage. In order to prove my point, David Vizard once did dyno testing on several intake manifolds and his comments on the Edelbrock Air Gap manifold may surprise you. This is an excerpt from David Vizard, after dyno testing several intake manifolds including the Edelbrock Air Gap:
"Exactly what is the Air Gap's air gap worth? Temperature testing with an infrared heat gun revealed much. First, the heat soak from a hot engine will, in about 10 minutes, bring the runners of the Air Gap manifold up to that of a non-air gap one. Under full-power conditions, the runners of either type of manifold drop and stabilize after about 15-20 seconds at full throttle, but the Air Gap manifold drops (depending on ambient conditions) about 20 degrees more at 2,500 rpm and about 15 more at 5,500 rpm. The net worth of this in output is about 6 lbs.-ft. at 2,500 rpm and about 4 lbs.-ft. at 5,500. Nevertheless, there is an overriding concern here. If the carb being used has inadequate fuel atomization, the cooler runners can actually detract from output, so be sure to use a carb that does a good job on mixture preparation."
Now this was on an Air Gap manifold, which in fact DOES have the intake runners completely sealed off from hot engine oil, and it STILL reached the operating temperature of a non Air Gap manifold.
While we're on the subject of intake gaskets (and since some of you won't use the valley pan now), lets just quickly cover conventional intake gaskets. The Fel-Pro 1230/1231 intake gasket is NOT intended for a street application. It is designed with a soft rubber-fiber base (resistant to gasoline & alcohol) AND without a steel core reinforcement so race builders can trim material for a custom port opening. The 1230/1231 is only supposed to be used on a race engine that gets disassembled (for inspection or rebuild) on a regular basis. It was NOT designed to withstand long term daily street usage. This is from my in-depth research on this subject and from speaking to a Fel-Pro technician. People who have used these gaskets successfully on the street, don't put many miles on the vehicle. While there may be a few who contest this, there are many more who will substantiate the 1230/1231 failure streetwise. The Fel-Pro MS901101 (Dove port) & Victor Reinz NitroSeal 95074SG (CJ/SCJ port) intake gaskets are the proper choice for a daily street driven engine that will stay assembled for a long period of time. (Fel-Pro doesn't make a CJ/SCJ 'street longevity' intake gasket set.)
The 1230/1231 intake gaskets also aren't meant for an exhaust crossover passage. They are race only gaskets for aftermarket heads and manifolds without the exhaust crossover passage. If you insist on using these gaskets with an exhaust crossover passage, then you'll need to either cut the opening in the gasket or block it off with a thin piece of stainless steel sheet metal (fitted between the gasket and head). It will burn through, if you don't cut out the opening or block it off with any effective method you choose.
Blocking off the exhaust crossover passage:
The hardware store sells small square pieces (about 4"x4") of sheetmetal (by their ducting material) for less than $2. I used a small thin piece of stainless steel sheet metal to block off the exhaust crossover passage. (It doesn't need to be stainless steel, I just had it.) The important thing to remember is to place the sheet metal between the cylinder head and intake gasket. I coat the cylinder head side of the sheet metal, with a 1/4" thick layer of high temp silicone and push it into position (so the silicone creates a 1/4" barrier inside the heat crossover passage), then wipe off the excess around the outside edge. I recently disassembled my 466 (soon to be a 508") with about 100,000 miles and the sheet metal block off was still right in place (on the cylinder head).
Sorry for the long post, however, I've done alot of research and discussed this, at length, with Fel-Pro technicians.