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Discussion Starter · #1 ·
Would you be able to warm up your car for a few min and take a reading on all your header tubes for me? Can you post what you found?

Thanks
 

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Discussion Starter · #3 ·
Marc,

Why?
I just want to see if some others are like mine.

My temps at idle.

278 (8) 268 (7)
370 (6) 250 (5)
238 (4) 230 (3)
200 (2) 198 (1)

My temps at 2500 rpm for 30sec.

#2 = 320 #1 = 318
#4 = 375 #3 = 377
#6 = 650 #5 = 390
#8 = 399 #7 = 410
 

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I don't have a reading for you, but I did find your data interesting. Here is the measurement delta following the pattern you first posted (which matches the cylinder layout):

#8=121 #7=142
#6=280 #5=140
#4=137 #3=127
#2=120 #1=120

IR temp readings can be affected by lots of things. First off, they'll reflect from a surface similarly to the way light does. As a result, a shiney spot will read lower than a dull rusty or corroded spot. A flat surface will radiate more evenly and read higher than a curved surface.

I might recommend you view your data in centi-degrees. This will help reduce some of the variance. For example, the deltas in centi-degrees would be:

#8=1.2 #7=1.4
#6=2.8 #5=1.4
#4=1.4 #3=1.3
#2=1.2 #1=1.2

There is definately something different about that #6 cylinder. Is the header tube where you're taking your measurment configured considerably different to account for the reading difference?
 

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The numbers are fairly low so I'm guessing coated headers. Copmparison to others' numbers is not real relevant, measuring style and such will give variances, the most important thing is the differences in cylinders you find. 6,8 and 5,7 are typicaly hot on chevys, esp 6,8 from distribution issues, and the center two will often read hot, since they are siamesed.
Your numbers look good, except for 6, thats too much difference, I would say idle air adjustment if only at idle, but it's there up in the rpms as bad or worse, looks like you need to do some carb tuning maybe.
What motor, what intake, what carb? Are there any off idle stumbles, or other odd drivabilty issues?
 

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Holy freakin smokes, I missed those threads, lots of reading.
I don't know what to tell you, you've done everything almost, the one thing that keeps popping up in my mind is a bad valvespring, either broken or just dead, the only way it would show up is running funny (does the miss get worse at higher rpm?) or testing the spring, compression and leakdown wouldn't show it.
Obviously you have the cylinder pinpointed, you are just going to have to start taking things apart and looking close at everything. I would try checking your valvesprings first, you can do that with everything assembled still.
Good luck, it's going to be interesting to see the result.
 

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68 SS Convertible, 383 EFI w/TPIS Mini Ram II, TKO 600, Aluminum flywheel, 3.31 12 bolt posi
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If a weak spring could cause this, I'd switch springs with a different cylinder and see what happens.
 

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Discussion Starter · #9 ·
If a weak spring could cause this, I'd switch springs with a different cylinder and see what happens.
Thanks, I'll replace my heads before I change a spring on these POS's. Can anyone take some temps for me?
 

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Discussion Starter · #11 ·

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Discussion Starter · #12 ·
Can anyone else check it out?
 

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Geeez, I'm thinking 'leaking intake gasket'. Do the oil-test on the top. A leak on the underside is harder to diagnose. Good luck!
 

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Can you swap you head around that will help :
1: will tell if there is a issue with #6 piston
2: will help to see if there is a sealing issue around #6 intake
3: if the hot tube goes to the other side it is in the head
 

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Discussion Starter · #15 ·
Can you swap you head around that will help :
1: will tell if there is a issue with #6 piston
2: will help to see if there is a sealing issue around #6 intake
3: if the hot tube goes to the other side it is in the head

Sure hold on a min....give me a sec and I'll let you know! Just kidding...I'm sure that would be a good/best test, but dude thats alot of work. I just got a leak down tester today from a friend. I know my compression is good, spark and fuel. If the Leak down test comes out OK maybe I'll pull the passanger head and have it checked out for cracks ,spring pressure ect... To pull the drivers I need to raise the engine to move the headers so I can get to the head bolts. It's a PITA because of the power steering box.

I'm wondering what other engine temps are.
 

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I know I said I'd post mine on another site but the weather held me up. I'll check my notes tonight. The temps will be what I recorded on my 355 at the time after a 30 minutes cruise. with uncoated headers. Temps were taken 1" from the flange.
 

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Discussion Starter · #17 ·
I know I said I'd post mine on another site but the weather held me up. I'll check my notes tonight. The temps will be what I recorded on my 355 at the time after a 30 minutes cruise. with uncoated headers. Temps were taken 1" from the flange.

Thanks, let me know. I took these temps after 10min of running and 30sec at 2500rpm.
 

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Marc, I just ran mine from Buford - 88 MCSS with a 71 307/AFB/360*(single plane) manifold 20" of vacuum at 1500 rpm for 5 minutes:

1 590* 2 590*
3 575* 4 620*
5 590* 6 660*
7 580* 8 650*

Hope this helps out,
 

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Discussion Starter · #19 · (Edited)
Marc, I just ran mine from Buford - 88 MCSS with a 71 307/AFB/360*(single plane) manifold 20" of vacuum at 1500 rpm for 5 minutes:

1 590* 2 590*
3 575* 4 620*
5 590* 6 660*
7 580* 8 650*

Hope this helps out,
Thank you very much. I just finished replacing my intake manifold gasket AGAIN... The one that was on there was part # Fel-1206 1.28" x 2.21"The intake ports on the manifold are 1.16" x 1.92". Edlebrock reccomends a gasket EDL-7201 with this manifold that measures 1.28" x 2.09". I put on a FPP-1205 on there that measures 1.28" x 2.09" So who knows. We'll see what happens tommorrow.
 
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