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By 56 big window - 16 Years Ago
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The 272 in my truck is completely stock and totally rebuilt . It runs great , but i noticed that the center runners on each side of the intake manifold get extremely hot . hot enough to turn the bright yellow paint brown! , and only in that area on each side of the carburetor ( 2 bbl). Engine temp fluctuates up to 180 at the radiator and never goes above . is this normal for y blocks ? Frank
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By lowrider - 16 Years Ago
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Yes thats normal. The center runner of the intake manifold is an exhaust crossover passage. Its purpose is to transfer heat to the carb for cold weather operation. If you don't plan on operating your truck in cold weather there are intake gaskets available with that port almost completely blocked off. Or you can you can take a thin piece of metal and make a block off plate for each side. Should cure the paint burn-off.
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By 56 big window - 16 Years Ago
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Thanks Dan !
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By 57f100 - 16 Years Ago
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on my 57 f100 272 some one made the 2bbl into a manual choke so that little heat riser on the intake is no good they took the cross over pipe and made it into a dual exhaust
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By Rods - 16 Years Ago
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I don't mean to hijack this question but I am having the same issue on my 312. Front of intake is 160-180 degrees, middle is 220-245 degrees and the read of intake is 170-190.
My mechanic said this is not good for the car and could damage the motor. I found an article that shows how to drill additional water holes in the heads and block but do not want to get into that if this temp is OK.
Can anyone tell me if I should be concerned about this heat? I think this is part of the whole 312's running hot.
Thanks
Rod
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By charliemccraney - 16 Years Ago
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That sounds about right. The middle of the manifold is where the hot exhaust gasses flow. It shouldn't damage anything. Many stock engines from many manufacturers use a similar feature. You can install gaskets which will block or restrict that passage.
Assuming that your engine was up to operating temp, 160 - 180 at the front of the intake is not running hot. In my book, that's running slightly on the cool side.
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By GREENBIRD56 - 16 Years Ago
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On a T-bird with stock exhaust manifolds - the heat riser valve on the RH bank (at the outlet of the RH manifold) needs to be checked out. When it gets stuck the crossover becomes a main exhaust passage - which is OK for a rapid warm-up - but not so good for driving. Even if it partially opens, too much heat flows under the carb. I took the valve out of mine (replaced it with a spacer) - and put the truck type intake gaskets on there with the reduced crosover openings. It gives the RH exhaust system something to do. For guys that are trying to keep the complete stock appearance (with a T-bird) there are gutted valves available - that look like a new one on the outside. Just takes money.........
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By crenwelge - 16 Years Ago
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I think a lot depends on the purpose of the car. If you want originality, they came from the factory with a heat riser. Also if you live in cold country and want an automatic choke, it needs to work. My y-blocks are fair weather drivers and I have no heat riser. In the Texas heat, I like to get as much heat out the tail pipe as possible rather than near the carb. Y-blocks in my opinion are not near as cold natured as inliners.
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By 63 Red Stake Bed - 16 Years Ago
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I have always noticed the same on both of my y blocks. I did however notice it more over the last few years... Interestingly enough last weekend when pulled the heads for the head upgrade I noticed that the head gasket on the driver's side was installed with the "FRONT" text to the back... OOPS! That could be an issue. I have Best gasket's going in so I shouldn't experience too much heat either way.. It's like the mesure twice & cut once thing... Look twice, & install once.. Something like that. Is that's what they say in the south..?
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By John Mummert - 16 Years Ago
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I believe that stuck heat riser valves caused a lot of the cracked heads I see. The first place that 57 and later Y-Block heads crack is the exhaust seat for the port that leads to the crossover passage. In fact, if 57-later head isn't cracked there it probably isn't cracked anywhere. The heat riser valves need to be either kept in good working order or gutted. Most new carbs have electric chokes and few owners drive in extremely cold weather. Heck, most Holleys don't even need a choke around here. Check your distributor advance and timing also, retarded timing will cause excessive exhaust heat.
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By Rods - 16 Years Ago
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AZ28 (9/26/2009)
On a T-bird with stock exhaust manifolds - the heat riser valve on the RH bank (at the outlet of the RH manifold) needs to be checked out. When it gets stuck the crossover becomes a main exhaust passage - which is OK for a rapid warm-up - but not so good for driving. Even if it partially opens, too much heat flows under the carb.
I took the valve out of mine (replaced it with a spacer) - and put the truck type intake gaskets on there with the reduced crosover openings. It gives the RH exhaust system something to do. For guys that are trying to keep the complete stock appearance (with a T-bird) there are gutted valves available - that look like a new one on the outside. Just takes money.........
Steve,
I am a bit of a novice, as you know. I am not sure what this heat riser valve looks like. Can you provide any pictures of this modification you did?
Appreciate it.
Rod
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By Barry L - 16 Years Ago
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Here's a pic of the valve on the end of the exhaust manifold, the bimetal spring and counterweight open the valve after exhaust heats it enough.The problem occurs when the "flapper" seizes in the closed position,forcing all the exhaust from this manifold back through the intake passage (under the carb.)to the opposite side ex. manifold.....really heats the intake manifold Barry L
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By GREENBIRD56 - 16 Years Ago
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The photo tells the story - a stuck valve is a big RH exhaust obstruction. Its under your heater - down by the starter. I got the "replacement" from NPD - its the basic iron block shown - with no valve / spring / pivot / etc. Just a spacer with an open hole to fit on the longer studs, fill the gap and refit the original exhaust pipe. To fit one, you will need a pair of new gaskets, the spacer and two brass 7/16 fine thread nuts. Try soaking the old nuts with penetrant a few days before you wrench on it. Use a long extension and a six point socket. Take care and use some patience. A broken or stripped stud is a pure pain.
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By DANIEL TINDER - 16 Years Ago
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Inexperienced mechanics often install these valves upside-down. They will fit that way, but won't work as well since gravity acts against the design function, and speeds failure. It also doesn't help that they were mistakenly drawn upside-down when the exploded parts diagrams were originally done.
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By Rods - 16 Years Ago
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Thank you for the picture. That will help>
So based on everything I have reading, we have a consensus that the 245 degree temp is not a serious problem. I am not going to hurt the motor, heads etc... correct?
I will have mechanic check the riser valve tomorrow to make sure it is open. If it is and we are still getting the 245 at the center, I am probably OK other than it affecting the thermostat gauge which I have spoke about before.
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By oldcarmark - 16 Years Ago
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You can check it yourself.With the car cold(so you dont burn your hand)reach down and operate the valve by hand.The thermostic spring closes it and relaxs as it heats up allowing the counterweight to open the valve.You just want to be sure its not seized and you can do that yourself.
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By Rods - 16 Years Ago
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Just wanted everyone to know, I everyone's comments up to my mechanic, and sure enough the valve was frozen cloed and probably had been for a long time. Took the butterfly out, reassembled and the temp instantly dropped to where they let it idle outside for a good 15-20 minutes and never got above the 3/4 mark on the gauge. Drove down the road and back a few times and it dropped even more. He said still hot in the middle port but I told him that is just a quark of the 312's. Thank you again. Off to my next issue 
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By charliemccraney - 16 Years Ago
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I put the infra red thermometer on my manifold when warmed up. 220 at the thermostat housing, 205 at the exhaust crossover, 170 at the rear runner. That's with no heat riser valve and restricted gaskets.
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By ejstith - 16 Years Ago
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I took my heat riser out and I'm fixin' to slide a piece of metal over the center port. Did that back in the day. Maybe it will help my vapor lockin' .... which has been an ongoing problem ever since I've had my ride. I did put a rubber gas line on it (fuel pump to carb) and I hope that fixes it.
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By DANIEL TINDER - 16 Years Ago
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Met a guy recently with a 55 Bird who had installed a nifty chrome plated variable flow/shutoff valve in his fuel line between filter bowl & carb. Though contrary to what I would expect, he claimed reducing the flow/pressure from mechanical pump cured his vapor lock problem. Shutting it off when parked acts as sort of a theft deterrent, and also keeps float bowl/fuel line from draining through typically leaky pump check valve.
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By andyifferts58 - 16 Years Ago
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Can anyone tell me where I can find a heat riser valve for a 58 fairlane with the 292. I looked at macs it only has one listed for a 332 and 352. NPD has them listed for a 55-57 tbird. prt noT-9A427-1. The one from NPD looks the same just making sure it is.
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