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New Motor Start up- Exhaust Too Hot ??

F14JetJock

Member
Joined
Nov 24, 2004
Messages
24
Location
SoCal
Corvette
1969 Burgundy Convertable
The Geek and I just fired off my new crate motor (chevy 350/330 hp). After some fits and starts (loose starter motor post, then a balky Holly carb and a number of start attempts), We got the motor fired up, set the idle at 2000 rpm and set the advance at 12 degrees. The engine was running great. After 5 min, we noticed the exhaust manifolds and pipes were cherry red. I shut the motor off and used a laser temp gun to take some readings.
The outer exhaust sections on both manifold sides (1/7, 2/8) were all about 575 to 600 degrees, which I thought was about right. The center bank (4/6) on the right went up to 1,100 degrees. The center bank (3/5) on the left side was 850 to 900 degrees. As I said, I shut the motor down before it could get any hotter ( water temp at the water neck was 180-190 degrees).
I would expect the center banks on each side to be somewhat hotter than the outer banks, but not this much hotter. I’d like to get some airflow over the manifolds but I haven’t run the engine long enough to break the cam in yet.
Has anyone had this problem with hot center banks while the outer banks are OK?? And what was the solution?
Thanks in advance !! BTW does anyone know what the normal temp should be, at the various exhaust ports?? Thanks.....
 

fine69

Well-known member
Joined
Dec 12, 2004
Messages
975
Location
Maryland / D.C.
Corvette
'69 Convertible Vette; '72 Z28 Camaro Rally Sport
The Geek and I just fired off my new crate motor (chevy 350/330 hp). After some fits and starts (loose starter motor post, then a balky Holly carb and a number of start attempts), We got the motor fired up, set the idle at 2000 rpm and set the advance at 12 degrees. The engine was running great. After 5 min, we noticed the exhaust manifolds and pipes were cherry red. I shut the motor off and used a laser temp gun to take some readings.
The outer exhaust sections on both manifold sides (1/7, 2/8) were all about 575 to 600 degrees, which I thought was about right. The center bank (4/6) on the right went up to 1,100 degrees. The center bank (3/5) on the left side was 850 to 900 degrees. As I said, I shut the motor down before it could get any hotter ( water temp at the water neck was 180-190 degrees).
I would expect the center banks on each side to be somewhat hotter than the outer banks, but not this much hotter. I’d like to get some airflow over the manifolds but I haven’t run the engine long enough to break the cam in yet.
Has anyone had this problem with hot center banks while the outer banks are OK?? And what was the solution?
Thanks in advance !! BTW does anyone know what the normal temp should be, at the various exhaust ports?? Thanks.....


This may sound elementary, but after turning getting the motor running, did you add more coolant to compensate for the amount used for the water jackets in the block?

I neglected to do that and got similar results as you experienced when did my initial start. I needed to add another gallon.

Just a suggestion...

Ralph :beer
 

RUSS O'BLENES

Active member
Joined
Aug 23, 2006
Messages
29
Location
LYNN MASS.
Corvette
1970 BRONZE COUPE/WHITE 69 CONV
The Geek and I just fired off my new crate motor (chevy 350/330 hp). After some fits and starts (loose starter motor post, then a balky Holly carb and a number of start attempts), We got the motor fired up, set the idle at 2000 rpm and set the advance at 12 degrees. The engine was running great. After 5 min, we noticed the exhaust manifolds and pipes were cherry red. I shut the motor off and used a laser temp gun to take some readings.
The outer exhaust sections on both manifold sides (1/7, 2/8) were all about 575 to 600 degrees, which I thought was about right. The center bank (4/6) on the right went up to 1,100 degrees. The center bank (3/5) on the left side was 850 to 900 degrees. As I said, I shut the motor down before it could get any hotter ( water temp at the water neck was 180-190 degrees).
I would expect the center banks on each side to be somewhat hotter than the outer banks, but not this much hotter. I’d like to get some airflow over the manifolds but I haven’t run the engine long enough to break the cam in yet.
Has anyone had this problem with hot center banks while the outer banks are OK?? And what was the solution?
Thanks in advance !! BTW does anyone know what the normal temp should be, at the various exhaust ports?? Thanks.....
WHEN THE MANIFOLDS GET CHERRY RED LIKE THAT ON BREAK-IN, IT GENERALLY MEANS THAT THE TIMING IS RETARDED. IF YOU SET THE TIMING AT 12 DEGREES AT 2000 RPM IT IS TO RETARDED. THE TIMING SHOULD BE SET AT 36 DEGREES AT 2500 RPM WITH THE VACUUM ADVANCE DISCONNECTED(IF YOU HAVE ONE). THE CENTER EXHAUST PORTS ARE GENERALLY HOTTER BECAUSE THEY ARE RIGHT NEXT TO EACH OTHER. WHEN YOU FIND A CRACKED VALVE SEAT IT IS GENERALLY ONE OF THE CENTER EXHAUSTS. HAPPY MOTORING. RUSS
 

F14JetJock

Member
Joined
Nov 24, 2004
Messages
24
Location
SoCal
Corvette
1969 Burgundy Convertable
Russ, You were right on the mark. I set the timing as you indicated and it worked like a charm. Thanks again !!!
 

fine69

Well-known member
Joined
Dec 12, 2004
Messages
975
Location
Maryland / D.C.
Corvette
'69 Convertible Vette; '72 Z28 Camaro Rally Sport
WHEN THE MANIFOLDS GET CHERRY RED LIKE THAT ON BREAK-IN, IT GENERALLY MEANS THAT THE TIMING IS RETARDED. IF YOU SET THE TIMING AT 12 DEGREES AT 2000 RPM IT IS TO RETARDED. THE TIMING SHOULD BE SET AT 36 DEGREES AT 2500 RPM WITH THE VACUUM ADVANCE DISCONNECTED(IF YOU HAVE ONE). THE CENTER EXHAUST PORTS ARE GENERALLY HOTTER BECAUSE THEY ARE RIGHT NEXT TO EACH OTHER. WHEN YOU FIND A CRACKED VALVE SEAT IT IS GENERALLY ONE OF THE CENTER EXHAUSTS. HAPPY MOTORING. RUSS


Ah... that makes more sense! :duh
 

F14JetJock

Member
Joined
Nov 24, 2004
Messages
24
Location
SoCal
Corvette
1969 Burgundy Convertable
Ah... that makes more sense! :duh
That's OK. I burped the coolant system (pulled a manifold water plug and topped off the water), just in case.... However, in this instance, changing the timing was the answer. Thanks for the input.
 
Joined
Jan 1, 2002
Messages
7,246
Location
Washington, Michigan
Corvette
'67 Marina Blue Convertible
This is a very common question/problem, and almost always has the same cause - retarded timing at "first-fire". Anxiety about this event generally results in not taking the time to static-time the engine first to the correct advance setting, making sure the centrifugal advance system is working properly, and forgetting to verify the vacuum advance unit's operation and to connect it. Setting up the timing parameters first, before firing the engine, avoids all the problems.

:beer
 

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