Engine Cylinder #8 header glowing red after rebuild?

BigPapiVin

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Sep 17, 2021
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Hey all!

I'm new here, and I'm sure its been spoke about but I have a 84 fox with a carbureted 87 5.0. I'm a little new to cars and just rebuilt the engine. Stock bottom end with TFS2 cam and gt40p heads. Upon the first start up, we let it run for a minute or so and noticed that the cylinder number 8 header started to glow red and burnt up my spark plug. I'm assuming the timings off as my step father told me the balancer line wasn't matching the TDC which was odd. Is this a problem with the head exhaust valve being stuck open? Or most likely a timing issue?

Thanks in advance!
 
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manicmechanic007

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Sep 26, 2017
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Find TDC
You can use a long bolt with spark plug thread 14mm- 1.25
Screw the bolt in about 20 threads
Use the damper bolt to turn the engine over slowly until it stops
Make a mark
Reverse direction and turn the engine over backwards (ccw) until it stops
Make another mark
Divide the distance and that is your TDC
If you do that using #1 plug you will be looking at the actual timing marks and can easily see if the dampner has slipped
 

manicmechanic007

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Sep 26, 2017
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Cherry red is okay
Want to see them all cherry red
Possible intake leak near cyl 8
Fix the plug wire check the timing
Sounds like you have a bit of a hotrod
They run plenty hot
Not real concerned about a header that gets cherry red
When you out and around your first camaro
They will all be cherry red
 

manicmechanic007

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Sep 26, 2017
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The carbureted ones flow more air with a 600 holley than the fuelie motors
I would be more worried about lean
The outside 4 cylinders are leaner than the inside 4 with a carb setup
That is okay and normal
Also is normal for one cylinder to lean misfire first
That cylinder is usually 4 or 8 on a sbf
imho the 84 was the fastest one until well into the 2000's because of the carbureted 5.0 HO
I used to align cop car mustangs at the dealer the 84's would do 85mph in second gear. The fuelie 1985 models would only do 72mph in second gear
When you hit the rev limit the factory processor has in mind... All bets are off...
The Holley however keeps revving higher and higher until the ignition cant keep up
 

Noobz347

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The carbureted ones flow more air with a 600 holley than the fuelie motors
I would be more worried about lean
The outside 4 cylinders are leaner than the inside 4 with a carb setup
That is okay and normal
Also is normal for one cylinder to lean misfire first
That cylinder is usually 4 or 8 on a sbf
imho the 84 was the fastest one until well into the 2000's because of the carbureted 5.0 HO
I used to align cop car mustangs at the dealer the 84's would do 85mph in second gear. The fuelie 1985 models would only do 72mph in second gear
When you hit the rev limit the factory processor has in mind... All bets are off...
The Holley however keeps revving higher and higher until the ignition cant keep up


This is good conversation but I don't know that it makes perfect sense...

84 Mustangs while being carbed, have a different set of heads, a different cam, intake, pistons, and so on. About the only thing they had in common was the block and crank. :)


"fuelie" or fuel-injected models didn't start until 1986 and top speed in second gear is a product of gearing and not induction. A fuel-injected Mustang cutout doesn't come around until 6250 rpm. It stopped making power before that.
 
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General karthief

wonder how much it would cost to ship you a pair
Mod Dude
Aug 25, 2016
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polk county florida
Hey all!

I'm new here, and I'm sure its been spoke about but I have a 84 fox with a carbureted 87 5.0. I'm a little new to cars and just rebuilt the engine. Stock bottom end with TFS2 cam and gt40p heads. Upon the first start up, we let it run for a minute or so and noticed that the cylinder number 8 header started to glow red and burnt up my spark plug. I'm assuming the timings off as my step father told me the balancer line wasn't matching the TDC which was odd. Is this a problem with the head exhaust valve being stuck open? Or most likely a timing issue?

Thanks in advance!
Ok, this reads sooooo familiar. Let me look around and find it :runaway:
 

manicmechanic007

Active Member
Sep 26, 2017
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This is good conversation but I don't know that it makes perfect sense...

84 Mustangs while being carbed, have a different set of heads, a different cam, intake, pistons, and so on. About the only thing they had in common was the block and crank. :)


"fuelie" or fuel-injected models didn't start until 1986 and top speed in second gear is a product of gearing and not induction. A fuel-injected Mustang cutout doesn't come around until 6250 rpm. It stopped making power before that.
The ssp cop cars all had the same gears 3.08 X code and 5 speeds I think the fuelies were out in mid year 85 but no matter
 

General karthief

wonder how much it would cost to ship you a pair
Mod Dude
Aug 25, 2016
20,645
7,073
203
polk county florida
Here's one, there are others.
Now let me get you pointed in a direction.
Since it is a new rebuild, I would check compression, pull all the plugs, squirt a little clean oil into the cylinders, guard against cylinder wash.
Note the compression on each one pay'n attention to #8, there should be very little difference.
A glowing red header tube is not good.
 

manicmechanic007

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Sep 26, 2017
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The fuelie is what I would want
The carb'd ones were hell to start hot
The under carb heat plate made it almost impossible to adjust the fuel mixture
Cool cars though and I have a 750 vacuum secondary on mine
Steel alky needles in the holley That helps keep the holley blues away
 
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