View Poll Results: Cylinder 7 fails first because the.....
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Why does number 7 fail first (tech only)
05-16-2008, 05:05 AM
#1
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Why does number 7 fail first (tech only)
Well, I'm sure most of us have a dead gm piston sitting in their garage. Chances are, it is number 7. One question, one word,
WHY?
Is it caused by the intake? Fuel railes? Coolant supply? Firing order? Something else? What is your theory and why do you think is is the cause?
WHY?
Is it caused by the intake? Fuel railes? Coolant supply? Firing order? Something else? What is your theory and why do you think is is the cause?
Last edited by Wilde Racing; 05-16-2008 at 05:58 AM.
05-16-2008, 05:48 AM
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A few good links about the topic ** there are thousands of threads that talk about this topic, if you find a good one PLEASE post it**
Talks about the "intake theory"
Another Intake thread
A old Intake thread (with other theroys)
"Best intake for FI" thread
Coolant tube Theory thread
Talks about the "intake theory"
Another Intake thread
A old Intake thread (with other theroys)
"Best intake for FI" thread
Coolant tube Theory thread
Last edited by Wilde Racing; 05-16-2008 at 06:36 AM.
05-16-2008, 05:55 AM
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Pulled from the "coolant thread"
We ran the tubes in the Motorola cup cars because if we put the back plug types in the #7 cylinder would have problems. It seemed to me with the testing we did that air pockets formed in the back of the head from the coolant boiling causing the engine to detonate on the back cylinders. Normally #7 would eat the piston or break the rod and #8 would show signs of trouble. These are just guesses on my part based on what the parts looked like broken!
One thing I did in the late 90's was put thermocouples on the 4 corners of the heads with the water still flowing. Then we put 10 02 sensors in, one in each port and one in the collector of each bank. I then parked the engine at 6500rpm/full load for 15 minutes at a time with the intake on normal and reversed to record coolant temp and afr. Nothing showed up that clued us in on why the 7 cylinder was fragile. The engine was a stock stroke forged piston Motorola cup legal LS.
Around 2000 or 2001 Unocal started sponsorship of the Nascar stuff and the Motorola cup could no longer use 94 Sunoco as the fuel on Union tracks, this forced them into 100 octane and the number 7 problems went away so we stopped looking for why....
Kurt
One thing I did in the late 90's was put thermocouples on the 4 corners of the heads with the water still flowing. Then we put 10 02 sensors in, one in each port and one in the collector of each bank. I then parked the engine at 6500rpm/full load for 15 minutes at a time with the intake on normal and reversed to record coolant temp and afr. Nothing showed up that clued us in on why the 7 cylinder was fragile. The engine was a stock stroke forged piston Motorola cup legal LS.
Around 2000 or 2001 Unocal started sponsorship of the Nascar stuff and the Motorola cup could no longer use 94 Sunoco as the fuel on Union tracks, this forced them into 100 octane and the number 7 problems went away so we stopped looking for why....
Kurt
05-16-2008, 06:22 AM
#5
I didn't vote in the poll. It would be a guess. Something else I found while researching awhile back.
"A book was published recently by a GM engineer named Will Handzell (Manager of GM Performance Parts no less) titled How To Build High-Performance Chevy LS1/LS6 V8's (ISBN 1-884089-84-4) who mentions (on page 49) detonation problems sometimes being encountered on cylinder #7 with Generation 3 LS1 engines. The remedy or "tip" was to fit a cylinder head coolant vent-tube from the earlier build engines.
(From start of LS1 production in 1997 until the end of year 2000 the engines were fitted with these tubes and it was routed to both the front and rear of each cylinder head. Whereas from 2001-on it was reduced to just a cross-over pipe between the front of each cylinder head only).
This example did encounter exactly this problem. All the other seven cylinders and pistons were perfect upon inspection by the only competent workshop known to the owner in the country. It was discovered that part of the #7 piston crown had broken off and whilst caught inside the cylinder had become trapped between the piston and the cylinder wall before disappearing out of the exhaust pipe. This caused the steel cylinder-liner (only 0.100" thick) to "bulge" out against the block cylinder wall enough to fracture it. Effectively rendering the engine block scrap."
"A book was published recently by a GM engineer named Will Handzell (Manager of GM Performance Parts no less) titled How To Build High-Performance Chevy LS1/LS6 V8's (ISBN 1-884089-84-4) who mentions (on page 49) detonation problems sometimes being encountered on cylinder #7 with Generation 3 LS1 engines. The remedy or "tip" was to fit a cylinder head coolant vent-tube from the earlier build engines.
(From start of LS1 production in 1997 until the end of year 2000 the engines were fitted with these tubes and it was routed to both the front and rear of each cylinder head. Whereas from 2001-on it was reduced to just a cross-over pipe between the front of each cylinder head only).
This example did encounter exactly this problem. All the other seven cylinders and pistons were perfect upon inspection by the only competent workshop known to the owner in the country. It was discovered that part of the #7 piston crown had broken off and whilst caught inside the cylinder had become trapped between the piston and the cylinder wall before disappearing out of the exhaust pipe. This caused the steel cylinder-liner (only 0.100" thick) to "bulge" out against the block cylinder wall enough to fracture it. Effectively rendering the engine block scrap."
05-16-2008, 06:35 AM
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My 00 5.3 had the early cross tube still killed number 7.... and 5. I should say, detonation was the cause, but the fact is, number seven still failed first.
05-16-2008, 07:44 AM
#7
Thats just it. Nobody knows definitively and without some very sophisticated test equipment, money and time the debate will continue.
IMO it is uneven airflow and intakes. Solely based upon what setups fail. You see failures primarily in forced induction engines that utilize GM style intake manifolds. Truck manifolds being the worst. Generally #7 at higher airflow tends to recieve more air and contaminants (oil) from the pcv system causing it to go lean.
IMO it is uneven airflow and intakes. Solely based upon what setups fail. You see failures primarily in forced induction engines that utilize GM style intake manifolds. Truck manifolds being the worst. Generally #7 at higher airflow tends to recieve more air and contaminants (oil) from the pcv system causing it to go lean.
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05-16-2008, 08:34 AM
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From reading my plugs using the stock manifold I found #7 to be white all the way around the insulator and all the rest have a small light tan spot where the insulator was closest to the intake valve. This would indicate to me a lean cylinder on #7 however after reading my plugs after the Radix install(different manifold and new plugs) #7 plug insulator is still white while the rest have identical light tan spots as with stock manifold. This points me in the direction of an issue with cooling and higher cyl. temps. in #7.
This is just my observation and I thought I would share what I found with others and let you draw your own conclusions.
This is just my observation and I thought I would share what I found with others and let you draw your own conclusions.
05-16-2008, 08:37 AM
#9
I wanted to vote for 2 items combined but I can't 
It has always been with Chevrolet motors for as long as I can remember and also talking to my father that cylinder number 7 is usually the first to go in an engine. One problem with the small block Chevy, and now I believe the LS*, is that with both heads flowing into a single port, then into a hose back to the rad, each head does not flow at the same time. This was something Smokey Yunick investigated. What happens is that as the coolant heats up and begins to flow, one side(head) will heat up faster ie. hotter, with more pressure. This greater pressure makes only the hotter side flow because of the greater pressure. Then, as the hotter side flows, it cools down enough, aqs the non flowing side heats up. There is then a transition of flow. In the end what happens is an alternating flow, resulting in an inefficient system, and hotter heads, and less compression.
It has always been with Chevrolet motors for as long as I can remember and also talking to my father that cylinder number 7 is usually the first to go in an engine. One problem with the small block Chevy, and now I believe the LS*, is that with both heads flowing into a single port, then into a hose back to the rad, each head does not flow at the same time. This was something Smokey Yunick investigated. What happens is that as the coolant heats up and begins to flow, one side(head) will heat up faster ie. hotter, with more pressure. This greater pressure makes only the hotter side flow because of the greater pressure. Then, as the hotter side flows, it cools down enough, aqs the non flowing side heats up. There is then a transition of flow. In the end what happens is an alternating flow, resulting in an inefficient system, and hotter heads, and less compression.
05-16-2008, 10:26 AM
#10
When I get my engine back I am going to put a second thermocouple in the engine block where the block heater goes back by number 7 so I can monitor coolant temps back there and compare them to coolant temps where the stock sensor goes. I will post up what I find. I am also switching to an early LS1 style coolant crossover, as well as a carb style intake manifold and flow-through fuel rails.