By connecting your distributor vacuum line to manifold vacuum you pull vacuum at idle which advances your timing. At idle, you are at a very lean condition. By advancing one's timing at idle, this provides adequate time to burn the fuel during this lean condition (lean condition = more time need to burn fuel). The benefits of using manifold vacuum are cooler running temperatures and better mpgs. I am over simplyfying this confusing concept, but one can read a better detailed description in the following site which does a pretty good job of explaining this (post #19 from C9):
I am not going to get into a pissing contest over this issue. This is a suggestion which the OP can try or not. If fordman doesn't want to try my suggest that is ok.
I'm a bit miffed at the closing statement you left at the end of your post here. "I'm not going to get into a pissing contest here" Why the hell was that statement called for?? You think me or any others are in here to pick fights? That statement wan't called for... Here's a SHOCKER for you....
I took 2-3 HOURS and read each and every post on that HAMB thread as well as a couple other links within that thread. Information is golden, and unlike your asumption of me, I'm a bit more open minded, willing to learn new things every day. I see the points, and wouldn't mind revisiting this theory on a couple other rigs I own. I even copied and pasted the large and informative posts to a word document so i can later re-review it. Defintely a good read and worth experimentation.
Here's my issue.
1. In the past, every time I've tried to use manifold vacuum for the dizzy, on a FORD, the damn thing diesels like a locomotive... TOO MUCH ADVANCE, Pre-ignition, even witht e RPM backed down. That would be WHY manufacturers installed anti-dieseling valves/switches on carbs back in the 70s. To cut off the air/fuel supply... only way to stop the dieseling. I understand their reasoning too... keep things hot to burn cleaner for emissions purposes. I get that.
2. The whole time I'm reading these posts they keep saying that "advancing the timing at idle causes the engine to run cooler" That may be BUT- it contradicts what you propose in #2. To me it doesn't sound right as Pre-Ignition = Detonation which leads to buildup of excess heat. This could be just realitive to engine load... but have seen issues 1st hand in non-load situations.
3. You missed another point that was made. It was brought to attention that some of the 70s distributors (especially ford) didn't have enough mechanical advance to make up for the lack of the ported vacum if one were to hook up to manifold vacum. In other words, the distributors mechanical advance was designed to run along with the ported vacuum advance. (two advances combined) You loose that ported advance when you switch to manifold vacuum therefore you'd have to add more mechanical advance to achieve the 'all in' advance number you needed at higher rpms (under acceleration) or atleast until you started to pull your foot out of it and the manifold vacuum caught back up again.
Bottom line is, reguarding this subject, just as they stated in their articles, every car is different and this may not work for everyone or their application. I found it EXTREMELY informative and definately will be doing some future expiramentation on a couple of my rigs to see if they do net better results. I see the theory and it makes sense, but it needs to be put to practice to see if it actually works. I'll be trying that soon.
Thank you for sharing that article and I again ENCOURAGE everyone to read it. Very good info.
Hey guys I've got good news! I went ahead and changed my tstat again!!! And my truck will run at about 220-230 and stop there! So it doesn't continue to get hotter and hotter anymore. But now I need to figure out how to get her to run a little cooler cause that's too hot. What should a 302 run at in about 115 degree weather? Anyone know? At night time I run about 205.
like Wayne said, maybe there is a problem with the gauge/sender setup. You shouldn't see 20 degrees difference day vs night.. On my green truck, even tho the sender was supplied by the gauge seller, the gauge was off 25 degrees and I had to add a resistor inline to recalibrate it. the laser temp gauge helped me find and do that change..
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