So just a quick one, I know ported vs manifold has been debated until the cows come home, and to be honest, I have read a lot of good arguements for using both. I've recently been down that rabbit hole and still cannot decide. So this weekend I am going to try manifold vacuum. Last weekend while connected to ported, I set the initial timing at 12* bftdc around 700rpm, and was getting 30* at around 2,500 rpm. The problem was after idling a short while the temp started climing on the gauge from the midway 80 mark into 100. Rather than have the thing start boiling I shut the engine off. Its pulling around 19 on the vacuum gauge and is running quite lean. I had backed off the idle set screw to drop the rpms down to 600 . I then re set my timing to 7* initial and was getting around 24/25* at higher rpms. This seemed to help a little with the hot running issue, ( obviously I still have to check other factors such as coolant, thermostat etc) After reading this week that ported was bassically used for controlling emissions, but would cause engines to run hot at idle, and Manifold is better for keeping the engine running cooler, I figured that this weekend I would hook the Vacuum to Manifold and see if that helps with the temp. My question is, when connecting the vacuum advance to Manifold, do I now advance the timing back to 12 at initial, so I am getting 30 at higher rpms? Or is it best to leave it retarded at around 5/6/7 etc also, do I lower the rpms and run the idle mixture screws a little richer? Or does it not make too much difference? I am also going to try replacing one of the silver springs for a gold ( lighter) one in the distributor. Its a 364 Nailhead, with Edelbrock 750 and HEI distributor.
I think……. Set the initial timing, with vacuum advance disconnected, to 10 degrees. Run the rpm’s up to measure centrifugal advance. Let’s say 20-25 degrees. Then connect the manifold vacuum so it tops out at 30-34 degrees. I think that would be the best scenario for you try to get the motor to run cooler at idle. I’m kind of dealing with the same thing only I have no vacuum advance so I have to cheat the initial.
It was running too rich before, now lean? Jet change? Manifold vacuum is what Buick did. Verify that your crankshaft damper timing marks are correct. Nail heads like to run hot. I am assuming the original style timing cover with a 3-blade water pump is being used. Could go to the later style timing cover and use a 5-blade pump. 7 degrees initial may be correct with that year engine. Try what Kevin said.
Not sure what the Nail heads like, but one way to do it is run it up so you have 32-34ish total w/o vacuum hooked up and let the initial land where it may. When you play with ported vs manifold you would use that initial as a base. So yes, when switching, set back to that #. Just make sure that if you find it likes more initial that that will be added to total. If total ends up to much you will have to limit it. Keep in mind most HEI vacuum cans have way more advance. I use/limit to 10-12 total vacuum advance. 2 digit number on can will give you advance in distributor degrees, so x2 for at the crank. You can limit amout of vacuum can advance by welding up slot and filing, but it would be trial and error. Do a quick search for Lars Grimsrud timing papers. Very good explanation and he has part numbers and specs on most factory vacuum cans. Most all available at your FLAPS.
Maybe this will help, https://www.crankshaftcoalition.com/wiki/images/e/e4/Vacuum_Advance_Specs.pdf Total timing doesn't change, you still want 32-34 or what ever the engine likes at wide open throttle. Start with that and get it set. Vacuum will drop off as soon as the throttle is opened ( even just a touch ). Changing between ported or manifold is for idle only, once running down the road it doesn't matter. Adjust the idle speed and mixture accordingly for which ever port you hook to, but don't adjust the timing. Adjust the curve and limit the vacuum if needed.
If timing is correct and it's running hot, and plugs show lean, then backing off timing wont fix it. It sounds exactly like the carb is too lean, which changing timing is a bandaid, and doesn't address the need to richen the jets up. You could end up burning a hole in a piston if you don't get the air/fuel mixture right.
Yeah it was running rich and I w as having trouble trying to get the idle mixture screws to do anything..i went 1 stage lean by changing rods and jets, and that seems to have improved things quite a bit. I was able to properly set the idle mixture screws and ease off the rpm screw to slow idle down. I still need to pull plugs again and see what they look like. But they were very light grey after the jet change, rather than black with soot.
Its certainly leaner than it was, but only by one stage according to the Edelbrock Calibration chart. I could back the idle mixtures out a bit more, but maybe some of the problem is that it needs a 600 cfm carb instead of 750.?
The problem with setting total timing and letting the initial fall where it may, on a street driven car anyway, is the potential for detonation on acceleration, especially under a load. The old school way to set the timing was to set the initial and then take a drive to a local hill and accelerate up the hill. If the engine knocks back the timing down 2 degrees and try it again, and repeat as necessary until there is no knocking. If it doesn't knock when you accelerate up the hill bump the timing up 2 degrees and try it again. If it knock back it back down to where it was; if it still doesn't knock advance it another 2 degrees. Repeat until it starts to knock then back it back down to the last setting with no knocking. BTW, advanced timing doesn't make the engine run hot, it's retarded timing that causes an engine to run hot. Re idle air screw adjustments, set the idle speed where you want it then adjust the air mixture screws to achieve highest idle speed, or highest vacuum reading, then adjust them In just until the engine idle speed drops ~20 rpms (lean roll) for smooth idle and crisp transition from idle to acceleration. Don't be afraid to redo the adjustments on both sides multiple times to get the best, smoothest idle. "I could back the idle mixtures out a bit more, but maybe some of the problem is that it needs a 600 cfm carb instead of 750.?" This won't affect the idle quality, only throttle response and top end power. Too small carb will restrict power on the top end; too large of a carb will affect quality of throttle response. Neither one will cause an overheating condition.
On all but full race manifold is best. It backs the timing off under initial load and it advances as the engine vacuum and RPM increase. Where to set all of it, usually what was originally engineered and upgrade from there based on mods and use. Blues has a good way of finding what it likes posted above. It's fun too.
I noticed above you stated you "adjusted" your idle with the mixture screws......DON'T DO THAT ! Curb idle is for adjusting idle speed. Mixture screws (in&out) adjust the highest vacuum reading and gives 'crispness' when giving the engine fuel. Plug your vacuum advance when setting timing.... (I LEAVE mine plugged!) Get the MOST timing in it WITHOUT the engine knocking/rattling going up a slight grade in top gear. Max advance gives a cooler running engine and the best mileage & power. Isn't that what we want ?!! 6sally6
Ported and manifold vacuum are identical at every throttle position and load, EXCEPT at idle. At idle, I see manifold vacuum providing these benefits: 1. Increases engine rpm, due to additional advance. 2. This allows adjusting idle speed slower, closing the throttle blades some, which 3. Makes the idle mixture screws more sensitive to adjustment. 4. Finally, when the above adjustments are made, coolant temperature at idle is lowered due to leaner idle mixture. It's hard to imagine causing lean mixture damage at idle, when there is no load on the engine. I hope this helps.
Seems like its still running rich, ( see the photo of one of the plugs), but its now running at normal opperating temp. Sat an idled for 40 mins and stayed at normal. In fact after switching to Manifold vacuum, it was running about 15 degrees even cooler. I am now thinking that switching to the edelbrock 1406 (600 cfm) is probably the only way I'm going to get it running at optimal performance with the best fuel mixture.
Thats a big help, thank you. I set the idle to 750 rpm, and set the idle mixture screws to get a smooth tickover, it was easily hitting 20 on the vacuum gauge, but I might lower tickover further maybe to 600, and then adjust the idle mixture screws accordingly. Although not sure that will stop my plugs going black.
From the FWIW dept, plugs will always give an initial rich or sooty look when doing low RPM/idle adjustment. Carbs are a compromise. Excess at certain levels is needed for cleaner conditions in use. How sooty depends on how far the engine is modified. You need choke to start, so they blacken at 1st. They clean up under more loaded use. I figured my jetting just like I'd do on a my 2 stroke hot rod sleds. Make a "full pull" and shut it off near the end of the run. Pull a plug, I was looking for a nice tan color, like coffee with a little cream. More critical, I was interested in the heat signature on the ground strap of the plug. I wanted little to no trace of heat in the bend, all heat was desired at the base of the electrode near the threads. I did my racer the same way. I cut the power and coasted into the return road. Pulled a plug and replaced it with an extra, start it back up and drove to the pits. Dammit that plug was hot, but once back I had seen just a little darker than I wanted, more like hot chocolate on the insulator but the heat signature on the strap was near perfect, or I coulda gone leaner. Instead I felt safe to go ahead and hit the nitrous on the next pass. Sadly I destroyed the engine but it wasn't my tuning. When I bought the system he gave me a plate modded to deliver twice what I wanted by mistake. So instead of adding a theoretical 250hp to what I had I gave it close to 400 (!). Broke #4 rod into 3 pieces, took out the whole cyl wall from 9 o'clock to 3 o'clock, and from deck to base. Plugs were nice n clean... All that above may have little to do with what you're doing, but tuning by drive is actually fun. Unless you spray it too hard.
If you want to clean the plugs, drive at 60 mph for an hour or two. Then look at the plugs. Plug color at continuous idle does not reveal useful info. Glad to hear that coolant temperature is now better controlled at idle.
BITD.....(early 60's)... Buddy of mine drag raced a big Galaxy 427/4 speed. I've seen him get up early-early on Sat morning(no traffic) and do a plug test on the race car. His place was a little over a mile down the road from me. He would install the new plugs....push the car out to the highway... fire it and immediately do a full throttle...pinned to-the-floor...full RIP through the gears. (never lifting! ) and cut clean the ignition and coast up to my house. We pulled the hood and he would pull and read every plug! Talk about music on a Sat. morning!! He said that was the ONLY way to get a true reading. No idling.....no low speed stuff...period. Now this was back when we ran REAL Hi-Test 100 octane GASOLINE. Using American made Autolite/Champion spark plugs...no Chinesium knock-off slave labor plugs..and watered down gas-o-hol... "Reading plugs" today with the stuff we burn today ain't really telling you nuth'in ! IMHO Analizers are the only accurate way to get an engine really dialed in. Again....run the Maximum amount of total timing the engine will safely stand ('may' need to limit the total timing to 38-45 to prevent damage). Also...todays fuel STINKS!.... Even if you do get the jetting perfect... your cloths are gonna smell like stink'in gas because all the good stuff stopped when they took all the lead out in the 70's. 6sally6
Have you thought about installing (even temporarily) an O2 sensor so you could see when and where the mixture is rich ? Maybe buy 1 sparkplug thats hotter and install it for a short drive and see how it looks.
Thanks for all the usefull info guys. I had no idea about not getting a great indication from plugs by checking them after it has only been idling I'll give them a clean and take it out for a drive and re check them.
I think your plan to swap to the 600cffm carb is a good one. Unless your nailhead is a high performance build engine the 750 is too much air, and will always be too much for the 364.
A fuel air ratio gauge is the only way to nail down what your carburetor is doing. Although reading plugs used to be the only way to guess at what is going on inside the cylinders, It nevertheless is still a guess. A fuel air ratio gauge can tell you what's going on at all phases of RPM and loading. I used to "guess" too, back in the '80s.
That may be the best advice I've seen lately in this thread. He hopefully should still have a few dollars left after all his other experiments. Also glad to see him paying attention to the vacuum gauge.
Yes, think its running less ruch now.. after installing a 1" carb spacer and setting the choke to the leaner setting, I warmed it up this werkend and drove down the road for a bit, came back and checked the plugs, and although it wasnt a long run, the plugs are starting to turn a coffee colour now
Yeah, its not, apart from being rebored out to 0.40 , everything is stock. So yeah, 600 cfm carb I think is more sensible. I will swap it when funds allow.
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