Gary Lewis Posted December 3, 2019 Share Posted December 3, 2019 Dave...sorry to hijack here, but I have a related question maybe you and others can help with? I've been thinking about vacuum advance. I have mine connected to the ported vacuum barb on my Holley carb, and I have confirmed that there is no vacuum present at idle. However, by barely moving the throttle off idle, I will quickly get full vacuum. But, I don't want full vacuum applied to my vacuum advance immediately off idle, correct? Is that vacuum only present because there's no load on the engine, and I'm just revving it? Just trying to wrap my brain around that. I would assume that I wouldn't want full vacuum advance just off idle...but maybe the vacuum behaves differently when driving with a load on it? Cory - Jim is right. Effectively the only difference between ported and manifold vacuum is that you don't have vacuum at idle. Other than that there's essentially no difference. The reason I like ported vacuum is that it gives a stable idle. This is especially needed with an automatic. With manifold vacuum when you start the engine and let it idle in neutral there is high vacuum so a lot of advance, which creates a high RPM. Then you drop it in gear and the RPM drops, which drops the vacuum, which drops the advance, which reduces the RPM, which drops the vacuum, which.... But with your truck there's no big reason to go with ported over manifold vacuum since you have the manual transmission. Link to comment Share on other sites More sharing options...
Rembrant Posted December 3, 2019 Share Posted December 3, 2019 I've never seen anything but manifold vacuum on a DSII engine. Check some of the many vacuum routing diagrams online. Always red going to the thermal vacuum switch, then through that restrictor. Except when the switch detects overheating. OK, gotcha. I was looking at my vacuum diagram on the truck, and it just shows a line straight from the carb to the vacuum advance. I don't remember what port it was on...the original 2bbl is long gone, but it was just a plastic line with short sections of rubber at each end. That was the factory piece at least. I'll carry on then. I was just thinking of some things to do to get this set up when I get my distributor back. Out of curiosity, what are these Ford "Check valves" for? https://www.summitracing.com/parts/smp-dcv1 I can't understand how that would work if it actually IS a check valve. I DO like the idea of a restrictor in the vacuum advance line. That would address my concerns perfectly. Link to comment Share on other sites More sharing options...
Rembrant Posted December 3, 2019 Share Posted December 3, 2019 Out of curiosity, what are these Ford "Check valves" for? https://www.summitracing.com/parts/smp-dcv1 I can't understand how that would work if it actually IS a check valve. Never mind...I see it's actually a vacuum delay valve. Delay in one direction, full flow in the other. Link to comment Share on other sites More sharing options...
Rembrant Posted December 3, 2019 Share Posted December 3, 2019 Out of curiosity, what are these Ford "Check valves" for? https://www.summitracing.com/parts/smp-dcv1 I can't understand how that would work if it actually IS a check valve. Never mind...I see it's actually a vacuum delay valve. Delay in one direction, full flow in the other. Dave, Sorry for the HIJACK! Carry on folks, I'm good! Link to comment Share on other sites More sharing options...
1986F150Six Posted December 3, 2019 Share Posted December 3, 2019 I DO like the idea of a restrictor in the vacuum advance line. That would address my concerns perfectly. Here you are, Cory. I have used one like this, before. https://www.amazon.com/Dorman-Help-47311-Restrictor-X-0185/dp/B000CO7APW Link to comment Share on other sites More sharing options...
FuzzFace2 Posted December 4, 2019 Author Share Posted December 4, 2019 Dave, Sorry for the HIJACK! Carry on folks, I'm good! When I got home from work I was surprised to see a box from Blue Top so if I don't have to work this weekend you know what I will be doing. Dave ---- Link to comment Share on other sites More sharing options...
Gary Lewis Posted December 5, 2019 Share Posted December 5, 2019 When I got home from work I was surprised to see a box from Blue Top so if I don't have to work this weekend you know what I will be doing. Dave ---- Hope you get to install it, and get to update us on the results. Link to comment Share on other sites More sharing options...
Rembrant Posted December 5, 2019 Share Posted December 5, 2019 When I got home from work I was surprised to see a box from Blue Top so if I don't have to work this weekend you know what I will be doing. Dave ---- I think an upgraded steering box is one of the most (or THEE most) valuable upgrades you can buy and install on these trucks. Congrats Dave. I'd swapped those boxes so many times now I'm sure I could do it all by feel. Keep us posted. PS: If you still have the old C2 steering pump, be careful when you fill/burp it or you will end up with oil all over the floor like I did...lol. Link to comment Share on other sites More sharing options...
Rembrant Posted December 5, 2019 Share Posted December 5, 2019 Cory - Jim is right. Effectively the only difference between ported and manifold vacuum is that you don't have vacuum at idle. Other than that there's essentially no difference. The reason I like ported vacuum is that it gives a stable idle. This is especially needed with an automatic. With manifold vacuum when you start the engine and let it idle in neutral there is high vacuum so a lot of advance, which creates a high RPM. Then you drop it in gear and the RPM drops, which drops the vacuum, which drops the advance, which reduces the RPM, which drops the vacuum, which.... But with your truck there's no big reason to go with ported over manifold vacuum since you have the manual transmission. I was talking to Scott at Parkland last night. He has my new distributor all dialed in and will be shipping it out today. I can't wait to get it. I asked him my vacuum questions, and he said to absolutely use ported vacuum, and absolutely no to any kind of delay or restriction on the vacuum advance. Depending on the weather, I may not have much opportunity to test this thing other than running it in my garage. Stupid winter! Link to comment Share on other sites More sharing options...
Gary Lewis Posted December 5, 2019 Share Posted December 5, 2019 Cory - Jim is right. Effectively the only difference between ported and manifold vacuum is that you don't have vacuum at idle. Other than that there's essentially no difference. The reason I like ported vacuum is that it gives a stable idle. This is especially needed with an automatic. With manifold vacuum when you start the engine and let it idle in neutral there is high vacuum so a lot of advance, which creates a high RPM. Then you drop it in gear and the RPM drops, which drops the vacuum, which drops the advance, which reduces the RPM, which drops the vacuum, which.... But with your truck there's no big reason to go with ported over manifold vacuum since you have the manual transmission. I was talking to Scott at Parkland last night. He has my new distributor all dialed in and will be shipping it out today. I can't wait to get it. I asked him my vacuum questions, and he said to absolutely use ported vacuum, and absolutely no to any kind of delay or restriction on the vacuum advance. Depending on the weather, I may not have much opportunity to test this thing other than running it in my garage. Stupid winter! Yes, the C2 pump will burb fluid everywhere. Glad Scotty is shipping your dizzy out today. Maybe you can catch a break in the weather and test the truck out soon. Link to comment Share on other sites More sharing options...
Recommended Posts