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By 312YBlock - 3 Years Ago
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I had three things I wanted to overcome with no clue of a relationship, one was excessive heat, second, I couldn’t get it to idle at 500 rpm and third engine run on.
My laser thermometer maxes out at 700 Fahrenheit, after letting it cool for a few minutes the left manifold would read 70 to 80 degrees hotter than the right. That was puzzling, I thought the narrower diameter of the stock 55 manifold would be the hottest. I bought two new manifolds, I was told the flanges would be true but the center two were higher on both. I had them trued and then off to coating. The only installation problem was the 9/16 forward number 7 cylinder bolt would not fit due to the casting. The fix was a 3/8 12 point manifold bolt.
A note: I installed them exactly as Ted Eaton suggested and thank you Ted. I gave coated flanges a light sanding where needed due to coating buildup etc with 220 grit sandpaper, put a VERY thin coating of Permatex Orange high temp RPG on the flanges and installed them without gaskets. I tightened the bolts finger tight, then snugged up with my 3/8 ratchet, then tightened them up working from the center out. Torque specs are 23 to 28’ lbs, I checked my hand tightening with a torque wrench and read 20 to 22, I left it there.
Now for the test. No leaks, or noticeable change in engine operating temp. Now I mentioned earlier that I couldn’t get the curb idle to where I wanted it at 500, 575 to 600 was the lowest. During my test drive the idle dropped to 200 barely running. I had to turn the idle adjustment screw almost 3 turns in to raise it. Ceramic coated manifolds are advertised as reducing back pressure, well amen that’s what happened. Back pressure contains unburned fuel, that’s why the idle refused to go down. The manifold temp now reads 597 right 602 left, time for happy dance 🕺, but there’s more. I mentioned engine run on; the cylinders were choking on carbon buildup which we know can contribute to run on. I have been using SeaFoam religiously for at least a couple of years, one oz per gallon in Sunoco 93. The SeaFoam got rid of the carbon but I still had occasional run on so I got used to turning off the engine with help from the clutch. I thought 💠if back pressure could affect the idle it could affect run on. Now I do not know if I will never experience run on again so I can’t say for certain but I have not experienced any run on since I installed the new manifolds 🚗.
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By DryLakesRacer - 3 Years Ago
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It would have been interesting to see the temps of the “as cast” larger manifolds and whether your problems would been solved. My car was purchased with the larger 57-up on the left and a 56 on the right. The right temp was always slightly higher. 6 months ago I replace the right with a larger 57-up and the temp dropped to the same as the left. Neither are professionally coated, both have been brushed with Eastwood exhaust manifold paint. I fought cooling problems for the first 5 years I owned my car. All have been remedied by help from folks here. Great that something this easy fixed your problems.
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By 312YBlock - 3 Years Ago
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Ceramic coating adds claim a 33% reduction in heat, that would put my pre coating temperature at approximately 900 degrees, also reduced back pressure resulting in a 3% hp increase. The temperature of the radiator return hose was 158 after a 30+ mile drive.
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By Hoosier Hurricane - 3 Years Ago
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One of the primary causes of run-on is high idle speed. You reduced your idle speed in this process, so maybe that stopped the run-on.
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By 312YBlock - 3 Years Ago
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Good point.
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By paul2748 - 3 Years Ago
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What kind of coating and who did it?
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By 312YBlock - 3 Years Ago
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Hi Paul, it’s a satin black ceramic, the only other choice is silver both can handle up to 1,800 degrees.
Mac Powder Coating
https://macpowdercoating.com/
59 Harden Dr, Lagrangeville, NY 12540 (914) 755-7811
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By 312YBlock - 3 Years Ago
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More good news, I was out cruising yesterday, temperature 78 degrees in OD doing about 55 @ approx 1,400 rpm. I run a 170 degree bigmouth thermostat. The temperature gauge read a hair to the right of center, with my old un-coated manifolds the gauge would have stayed at or near the 170 degree mark.
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