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Old 01-18-2013, 12:28 PM   #16 (permalink)
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Manifold vacuum isn't necessarily incorrect. Lots of cars came from the factory that way. It should only make a difference when the engine is idling.
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Old 09-28-2014, 01:10 AM   #17 (permalink)
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Im havn similiar overheating issues after a intake manifold gasket change. Is the 69 351w different? could i have screwed up installing? THanx 4 any help!
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Old 09-28-2014, 11:22 PM   #18 (permalink)
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Interesting article written by a GM engineer from the 1960's I found when researching distributor stuff:

Ported vs. Manifold Vacuum



I found my engine runs much cooler and idles better when the distributor is connected to the full time/non-ported vacuum. Once the throttle comes off of idle and the throttle plate opens, the vacuum produced by either port is the same.
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Old 09-29-2014, 09:50 AM   #19 (permalink)
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So by that article, it seems like ported vacuum is the wrong way to go for everybody. But, would reversing the lines to manifold as opposed to ported really affect the operating temp while off idle? It shouldn't right? I'm not sure you actually fixed your problem... it may have gone away, but I can't wrap my head around what you did actually fixing it.

You said you have a 3 row radiator... how big are your tubes? I run a two row with 1 1/4" tubes and have no issues with cooling between that and a clutch fan.
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Old 09-29-2014, 10:35 AM   #20 (permalink)
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My first guess would have been the timing being too far advanced. Not sure why the vacuum lines would cause an overheating. But if it's fixed then it's fixed. These cars have their own personalities. Gotta find out what suits them and make em happy. Lol
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Old 09-29-2014, 11:45 AM   #21 (permalink)
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Quote:
Originally Posted by ruger View Post
These cars have their own personalities. Gotta find out what suits them and make em happy. Lol
So very true. I enjoy speaking with owners who have much greater carburetor/distributor experience than I do, and find their choice of vacuum port use changes to which works best on the car they are driving that day.

My understanding was that my 351w at idle with no vacuum runs hotter because the combustion is still occurring as the cylinder going down which in turn elevates the temperatures in the engine (thereby creating less emissions). With vacuum at idle, that combustion is taking place sooner (but without pre-detonation) keeping the temps down. The combustion is all finished while the piston is in a higher position in it's down stroke.
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Old 09-29-2014, 01:28 PM   #22 (permalink)
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I guess, in thinking through this trying to figure out the best way to ask the question, I may have figured out some things. Retarding the timing, by moving to the ported, would have lowered your compression therefore your temp. Have you felt any power differences? I assume it would coming off the line, and not really anywhere else in the band right?

I'm genuinely trying to understand this, and learn before I start making changes to my engine ( I have done a bunch, but rather admittedly somewhat blindly). Been getting an itch for a little more seat of my pants oomph.
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Old 09-29-2014, 03:11 PM   #23 (permalink)
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Quote:
Originally Posted by the ponz View Post
So very true. I enjoy speaking with owners who have much greater carburetor/distributor experience than I do, and find their choice of vacuum port use changes to which works best on the car they are driving that day.

My understanding was that my 351w at idle with no vacuum runs hotter because the combustion is still occurring as the cylinder going down which in turn elevates the temperatures in the engine (thereby creating less emissions). With vacuum at idle, that combustion is taking place sooner (but without pre-detonation) keeping the temps down. The combustion is all finished while the piston is in a higher position in it's down stroke.
Ponz: Nice explanation. I couldn't see the vacuum working that way.
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Old 09-30-2014, 09:58 PM   #24 (permalink)
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Quote:
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Ponz: Nice explanation. I couldn't see the vacuum working that way.
I especially enjoy the part where I describe the cylinder as going down. Cylinders don't go down, pistons do. Oh well.

As the ported vs non-ported vacuum article explains, the lower the initial timing, the hotter the engine becomes. With the ignition occurring close to top dead center, the combustion continues long after the piston is travelling back down.

The 351w in my 69 Mach 1 always knocked due to pre-detonation even under moderate acceleration. Conventional wisdom dictated I should retard the initial timing. Before adjusting the timing, it was set to 9*. So I warmed up the car, and proceeded to lower the initial timing one degree until I was at 6* BTC. Pre-detonation was still slightly occurring. And the engine was not idling smoothly at all. I was curious at what setting the engine would idle best, so I turned the distributor cap, advancing the timing until the engine was running oh so smooth. It turned out to be around 15*. Well, I knew that would never work, as the engine would knock itself to death when accelerating. I ended up cleaning the distributor which had a gummy/sticky substance inside and on the fly weights; removed most of the lash from the heavy fly weight spring, and connected the vacuum advance to the full time vacuum, which yielded 13* of timing at idle. Using full time vacuum for spark advance does not affect the rate of advance under acceleration because as soon as the driver mashes on the gas pedal and opens the throttle plate in the carb, the amount of vacuum provided by the ported and non-ported ports in nearly the same. After several hard acceleration runs, (adjusting the play in the fly weight spring), I got the rate of advance adjusted just this side of pre-detonation. The engine idles super smooth, steps out with face tightening acceleration, and runs much cooler. How much cooler? Before the adjustments, the temperature gauge was sitting a little below half way. After the adjustments, it moved a good 3/8 to the left.
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Old 09-30-2014, 11:45 PM   #25 (permalink)
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New thermostat sticking.

Bits of something in the cooling system jamming part of the back of the thermostat.

Vacuum leak opening up making the engine lean way out would do it or the carb just being way lean.

I've never seen timing set so bad it would cause an engine to max out the cooling system. I don't think it would run at all. I guess it might be possible but I have not seen it or encountered it. I used to run my hot rod with 38 to 40 degrees of timing all in all the time and it didn't run hot that way. I had a 70 model 429 Ranchero GT that rattled on pump gas unless I backed the timing down quite a bit and it didn't run hot either. I think it was in love with Ethyl Lead though.
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Last edited by macstang; 09-30-2014 at 11:49 PM.
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Old 10-01-2014, 10:02 AM   #26 (permalink)
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Quote:
Originally Posted by macstang View Post

I've never seen timing set so bad it would cause an engine to max out the cooling system. I don't think it would run at all. I guess it might be possible but I have not seen it or encountered it.
I have. I never would've believed it if it hadn't been my own car. I had a '66 with a stock 302, and it always ran hot. Going down the road, it would cool down and run about halfway on the gauge, but the minute you got stuck in traffic, it would climb. I carried around an IR temp gun, and one day I popped the hood and verified that the motor was really running that hot.

We had tried everything--new radiator, new water pump, cooling system flush, etc. For some unrelated reason, we finally started moving the timing, and with the timing retarded, the engine cooled right down and never ran hot again. You could sit all day in traffic and it would never even offer to heat up.
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Old 10-01-2014, 10:17 AM   #27 (permalink)
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My last 351C ran fairly cool until I installed an MSD dist. Started overheating, belching out coolant. After a little research and playing around with it I brought the timing down just a bit. That's all it took to stop it from overheating. These machines are finicky and some folks remedies are different from others. As long as they run to your standards that's all that matters. I have high standards as I don't enjoy being parked on the shoulder of the road.
One thing that I do know is that the more I am on this site the more I learn. I appreciate all info that I read. It allows me to understand my vintage vehicles a lot more. Thanks to everyone.

Last edited by ruger; 10-01-2014 at 10:27 AM. Reason: additional comments
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