Engine guru question?
Race Director
Joined: May 2005
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From: Millington Illinois
St. Jude Donor '08-'09
Burning Brakes
Joined: Aug 2005
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From: Europe, France
Burning Brakes
Joined: Aug 2005
Posts: 1,164
Likes: 1
From: Europe, France
If you are using a dual plane manifold, maybe some cylinders are richer, and others leaner ( higher temperature )...
Check idle mixture first.
Last edited by 73StreetRace; Sep 18, 2009 at 04:19 AM.
Thread Starter
Pro
Joined: Jul 2001
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From: Blairsville Ga
I'm in the process of doing a resto mod frame off, so all i have is the engine sitting on the frame. It will be awhile before seeing the road. THis weekeng i'm going to readjust the valves again. That has to be where my problem is. It's just the exhaust that is getting hot
Burning Brakes
Joined: Aug 2005
Posts: 1,164
Likes: 1
From: Europe, France
I'm in the process of doing a resto mod frame off, so all i have is the engine sitting on the frame. It will be awhile before seeing the road. THis weekeng i'm going to readjust the valves again. That has to be where my problem is. It's just the exhaust that is getting hot
it is still burning when the exhaust valve opens, so it produces a lot of heat in the headers...
Thread Starter
Pro
Joined: Jul 2001
Posts: 704
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From: Blairsville Ga
I believe I've figured out what might be my problem. I'm only getting 1 to 2 pounds of fuel pressure for some reason so the engine is running extremly lean. The car is also not level with the drivers side a little lower then the passenger side. not sure if that matters, but I starting the think the the even bank is not getting fuel and the reason why the odd side is getting so hot is because it is running so lean. I' ll keep everyone posted
Burning Brakes
Joined: Aug 2005
Posts: 1,164
Likes: 1
From: Europe, France
I believe I've figured out what might be my problem. I'm only getting 1 to 2 pounds of fuel pressure for some reason so the engine is running extremly lean. The car is also not level with the drivers side a little lower then the passenger side. not sure if that matters, but I starting the think the the even bank is not getting fuel and the reason why the odd side is getting so hot is because it is running so lean. I' ll keep everyone posted
If you're running lean check spark plug colors and condition to confirm. Some of them should be bone white, with maybe signs of overheating, pre-ignition or detonation.
Have a look at this if you want to see what I mean :
http://www.verrill.com/moto/sellingg...colorchart.htm
Last edited by 73StreetRace; Sep 19, 2009 at 02:04 AM.
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Race Director
Joined: Apr 1999
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From: CORVETTE 77 385 C.I. TEXAS
Originally Posted by shamby
I'm only getting 1 to 2 pounds of fuel pressure for some reason so the engine is running extremly lean. The car is also not level with the drivers side a little lower then the passenger side. not sure if that matters, but I starting the think the the even bank is not getting fuel and the reason why the odd side is getting so hot is because it is running so lean. I' ll keep everyone posted
The first time I changed a fuel pump on a Corvette w/ A/C, looked the situation over & pulled the right front tire & used long extensions. Have posted that tip many times. Esp. w/ A/C.
Burning Brakes
Joined: May 2008
Posts: 860
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From: Stratford Ontario
Was there a new cam and lifters installed? If so you need to go through a 20 min breakin period before allowing the engine to idle.2500 to 3000 rpm. Unless it is a roller cam then you don't need a breakin.During breakin each cylinder will get hot at different times but they will all glow red after a few minutes.Make sure its getting fuel first though.
Burning Brakes
Joined: Jul 2008
Posts: 923
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From: Green Bay Wisconsin
Hello,
Check your Heat Riser Valve operation. It creates higher exhaust back pressure to warm up the engine quickly from a cold start.
So it would be normal that the passenger side of the engine would initially be much hotter during warmup. After engine is at operating temps the engine temperature should equalize from side to side. If it does not and the car begins to overheat at idle then expect a stuck or poorly operating Heat Riser Valve.
Hope this helps.
Douglas in Green Bay
Check your Heat Riser Valve operation. It creates higher exhaust back pressure to warm up the engine quickly from a cold start.
So it would be normal that the passenger side of the engine would initially be much hotter during warmup. After engine is at operating temps the engine temperature should equalize from side to side. If it does not and the car begins to overheat at idle then expect a stuck or poorly operating Heat Riser Valve.
Hope this helps.
Douglas in Green Bay
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Joined: Jul 2001
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Hello,
Check your Heat Riser Valve operation. It creates higher exhaust back pressure to warm up the engine quickly from a cold start.
So it would be normal that the passenger side of the engine would initially be much hotter during warmup. After engine is at operating temps the engine temperature should equalize from side to side. If it does not and the car begins to overheat at idle then expect a stuck or poorly operating Heat Riser Valve.
Check your Heat Riser Valve operation. It creates higher exhaust back pressure to warm up the engine quickly from a cold start.
So it would be normal that the passenger side of the engine would initially be much hotter during warmup. After engine is at operating temps the engine temperature should equalize from side to side. If it does not and the car begins to overheat at idle then expect a stuck or poorly operating Heat Riser Valve.
The heat riser valve does not create back pressure with the goal of warming the engine faster. It diverts exhaust flow from the passenger side through a passage in the intake manifold under the carburator to join the exhaust flow on the drivers side. This heat warms the intake faster than it otherwise would, allowing the choke to come off sooner. It can also help avoid carb icing when the engine is still cold and the intake temp drops below the dew point.
Further, the passenger side exhaust manifold operates at the same temp as the drivers side as the heat riser valve is downstream of the manifold. This means that only the passenger side exhaust pipe and muffler will remain 'cold' during initial operation after start as most of the engine flow is directed throught the driver's side. This effect is very visible on dual exhaust cars on cold mornings.
A stuck valve will not cause an engine to overheat at idle or while driving but may induce some carb percolation issues in borderline cases.
Thread Starter
Pro
Joined: Jul 2001
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From: Blairsville Ga
Thanks for all the post and suggestion, but I have not have time to work on the car this weekend. Sick 8 month old no fun. I need to check my valves, my timing (maybe to advanced) and my fuel pressure. I hope to be back in the garage first of the week to get this resolved. I'd say it's something simple that I'm missing.
Scott
Scott
Burning Brakes
Joined: Jul 2008
Posts: 923
Likes: 37
From: Green Bay Wisconsin
This explanation is not correct, besides the fact that the OP has headers.....
The heat riser valve does not create back pressure with the goal of warming the engine faster. It diverts exhaust flow from the passenger side through a passage in the intake manifold under the carburator to join the exhaust flow on the drivers side.
The valve is allowed to open slowly as the engine warms with a bi-metal spring. That action creates back pressure that allows the warm exhaust flow to be diverted to quickly warm the intake. The majority of people on here are bright enough that detailed explanations are not necessary, thanks for your additional input.
This heat warms the intake faster than it otherwise would, allowing the choke to come off sooner. It can also help avoid carb icing when the engine is still cold and the intake temp drops below the dew point.
Your right again, I think the majority already undertand this.
Further, the passenger side exhaust manifold operates at the same temp as the drivers side as the heat riser valve is downstream of the manifold. This means that only the passenger side exhaust pipe and muffler will remain 'cold' during initial operation after start as most of the engine flow is directed throught the driver's side. This effect is very visible on dual exhaust cars on cold mornings.
This is where your incorrect, with the increased backpressure the passenger side exhaust manifold will warm up to operating temperature quicker than the drivers side. "Watched this action many times with my infrared thermometer." Once the engine is completely warmed the bimetal spring will have opened the heat riser valve entirely, if the heat riser is stuck or doesn't open all the way the exhaust manifold and head will run hotter.
A stuck valve will not cause an engine to overheat at idle or while driving but may induce some carb percolation issues in borderline cases.[/QUOTE]
Maybe not on a cool day if the cooling system can carry all the excess heat away, but on a warm/hot day the cooling system will be overwhelmed and the car will run hot at an idle.
It's important to do your homework on here and don't guess. These are good people on here and they rely on good information to get their cars running right.
If your heat riser has been removed then none of the above really matters until you run into one that is not functioning correctly.
Hope that helps,
Douglas in Green Bay
The heat riser valve does not create back pressure with the goal of warming the engine faster. It diverts exhaust flow from the passenger side through a passage in the intake manifold under the carburator to join the exhaust flow on the drivers side.
The valve is allowed to open slowly as the engine warms with a bi-metal spring. That action creates back pressure that allows the warm exhaust flow to be diverted to quickly warm the intake. The majority of people on here are bright enough that detailed explanations are not necessary, thanks for your additional input.
This heat warms the intake faster than it otherwise would, allowing the choke to come off sooner. It can also help avoid carb icing when the engine is still cold and the intake temp drops below the dew point.
Your right again, I think the majority already undertand this.
Further, the passenger side exhaust manifold operates at the same temp as the drivers side as the heat riser valve is downstream of the manifold. This means that only the passenger side exhaust pipe and muffler will remain 'cold' during initial operation after start as most of the engine flow is directed throught the driver's side. This effect is very visible on dual exhaust cars on cold mornings.
This is where your incorrect, with the increased backpressure the passenger side exhaust manifold will warm up to operating temperature quicker than the drivers side. "Watched this action many times with my infrared thermometer." Once the engine is completely warmed the bimetal spring will have opened the heat riser valve entirely, if the heat riser is stuck or doesn't open all the way the exhaust manifold and head will run hotter.
A stuck valve will not cause an engine to overheat at idle or while driving but may induce some carb percolation issues in borderline cases.
[/QUOTE]Maybe not on a cool day if the cooling system can carry all the excess heat away, but on a warm/hot day the cooling system will be overwhelmed and the car will run hot at an idle.
It's important to do your homework on here and don't guess. These are good people on here and they rely on good information to get their cars running right.
If your heat riser has been removed then none of the above really matters until you run into one that is not functioning correctly.
Hope that helps,
Douglas in Green Bay
Race Director
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As I said, 'The heat riser valve does not create back pressure with the goal of warming the engine faster' meaning that the act of passing the exhaust through the intake warms the intake. I did not say that there was no additional back pressure created. No doubt there is, due to the restricted and convoluted path.
I'd like to see an example of a car that overheats at idle due to a stuck heat riser. If true, then cars that have suffered blocked converters would also overheat. At worst, they experience low power/poor acceleration.
