Just put a 350 in my 67 special and my intake is very hot in fact it burned the paint off near the carb this was with a 2 barrel then today i put a 4 barrel manifold on and its even hotter burned the paint off right away i have access to a thermal imaging camera and the center of the intake is running 320-380 degrees while the rest of the engine runs around 180 or cooler whats going on ? PS it only seems super hot around the center of the intake the front and rear are around 200 degrees
It is super hot because exhaust gases run through the center. It's a pain because hot intakes are power wasters, but it helps with winter driving and emissions. :3gears:
Sean did i use the wrong gasket then or is there a specific one i can buy. thanks for this info i was going crazy trying to figure this out and you have put the light bulb on the top of my head on. Man i hate to have to pull that intake again
It's not a gasket issue. The heads have holes above the two center exhaust valves that allow exhaust gas to travel up under the carb to warm it up. It helps with cold weather warm up and it also operates the bimetal choke spring. What I would do is plug these hole off. I used 18.05mm freeze plugs with my 70 455. I don't know exactly what size they would be for the 350. All you do is get a drift and pound them in with a hammer. I have almost 10,000 miles on my 455 without any problems from them.
Check your exhaust manifold thermostat valve. If its stuck in a closed position it will cause overheating, poor performance, cracked exhaust manifold, etc. It should only be closed when engine is cold, open when hot. DougB
Page 3 post 5 of this thread shows pics of what Hector did, mine are the same idea. http://www.v8buick.com/showthread.php?t=92424&page=3&highlight=exhaust+passage
OK Sean now i got it i was thinking of covering the entire port with tin and could'nt understand the freeze out plugs now i see what iam covering PS i had the car out today for a 50 mile trip on the expressway and it ran fine overheating is not an issue so i may just leave it this way for a while
Unless you plan to do much winter driving, block the crossovers. Better for performance and even a little gas milage under normal driving conditions. Good winter project.
:beers2: :beers2: :beers2: I would double check the exhaust manifold valve on the drivers side. It was set from the factory to cause "some" of the gases to flow through the intake manifold. It would open when the flow was enough and send the remaining exhaust out the tail pipe. Now 30+ years later the valve is most likely frozen shut or mostly closed. The only way the entire drivers side of the exhaust Or most of the exhaust can get out of the car is to go though the intake manifold and out the right exhaust manifold. "Path of least resistance" I always remove the valve from the manifold as they all will eventually stick.
Could you or someone post a pic of this valve or exactle what it looks like and where? I understand things better with visuals. Thank you.
FLIR picture posted. Not exactly what you were looking for, but interesting viewing. Better pictures to follow. ElectraJim
I have the hot intake prob too (hot is an understatement) and I've been digging around for some freeze plug info so that I can get the ports blocked off. According to Hectors post the plugs were a 20mm, but some have used 3/4" as well. Called Clevite and got pn's for their steel cap style freeze plugs, they gave me: 20 mm (.787) - 219-2180 3/4" (.750) - 219-3038 installed the Mr Gasket 3712 phenolic spacer with heat shield as well to stop the vapor locking problem, we'll see how that goes soon. some hacking to get it to clear the qjet fast idle cam and intake vacuum lines required.
So you yanked the heat riser flapper??? Hmmm once I got ride of my flapper, gutted it. It didnt get so hot anymore, as the exhaust doesnt really want to flow up. Sure it not something else, plugged muffler or such, making the exhaust want to flow up n over?
Should say I used a carb heat shield but not a thick one. MR gasket has one with a metal shim that run down the middle for a heatsink. I had and old one of them and pulled the metal shim out. Then used the metal shim between two regular thin gaskets. I dont like them 1/2 - 1 thick carb spacers.
QFT. I have 455ci Big block olds motor, and we have a custom welder that does work for our shop, and I just had him weld those passages closed instead of the freeze plugs. Very good advice Joe. It gets mighty hot through those passages and I have seen many cracks due to the heat.
WOW this is an old thread. I really didn,t have any problem with the crossover i just didn,t know about it and didn,t understand why my intake was so hot it has not caused a problem. Thanks Gerry
