This is apparently the only guy on the internet that gets it. There isn't a right and a wrong, you just try both. It's so easy, it's switching a vacuum line! Some cars will like ported, some do better with manifold. Try it one way, then switch the vac line. Takes a minute. Nobody is wrong or right on this, just experiment. No big deal. Thanks for the common sense !!!!

I've always used the timed port with my HEI distributor along with a 10degree vacuum can for years before i knew any better. Now im using a progression ignition distributor, its all electronic(no springs/weights), it uses manifold vacuum pluged into its MAP sensor. You can adjust the initial as well as full timing and other parameters on the fly via bluetooth with either a cell phone or tablet from the driver's seat. Good Stuff

In the 50+ years I've been 'playing with engines' that's the first time I've seen the 'spiral' of engine events. You had a real smart shop teacher

Thank you. Great video! Trying to figure out my newly acquired "57 Chevy Bel-Air with a 350.... its getting better!

When I dumped my 3.23 gear in my 455 oldsmobile , and went 4.56 gear 10" converter hot cam , dump the vacuum advanced ran like a beast

At 67 age I'm like a danged kid when I get to playing around with these small-block chevy's with carburetors ! Especially the ole standbye EDELBROCK 600 cfm !HELL! I've made these things do things unheard of by experimentation and playing with timing,vacuum,fuel and such ! Great video brother !!!

Look into the history of advance. Early on, it was manual with a lever - you did it as you drove. Then came vacuum advance and things got easier. Ported vacuum advance was never available until the late 60's and early 70's. So from the 30's to the late 70's it was always manifold vacuum. The biggest reason to use manifold vacuum is to help with with lower engine temps at idle. If you are using manifold vacuum you are not opening the transfer slots on the carb, so more timing with leaner idle. With ported vacuum you have to adjust the idle up with the throttle idle screw, partially opening the transfer slots and running more fuel. The vehicle will idle hotter and your fuel consumption will go down. However this is OK if you have a performance motor with a cam. You have no reliable vacuum from the manifold at idle and your idle has to be higher anyway. The lope from the cam will be amplified by the swinging vacuum signal to the vacuum advance. The other reason to use ported is to avoid the slight dip in timing when you flat foot it off the line with manifold vacuum. For drag racing (even street racing) the initial timing and slightly richer mixture with the transfer slots open is the best way to get reliable "leave" 😁 But not the best overall fuel economy 🙃

You left out what IMO is the biggest reason for deciding between timed and manifold. With a lumpy long duration cam the engine obviously requires a higher idle speed to keep running. Normally this is done by way of the curb idle screw. However, as you screw it in you run the risk of exposing too much of the idle transfer slot in the carb. The result is a flat spot off idle. By adding manifold vacuum advance, torque is increased, raising the idle speed and allowing you to back out the idle speed screw and reestablish the correct relationship between the throttle blades and the transfer slot.

God what a awesome video I have been playing with my 302 for the past couple months I'm on portage vacuum I do have a little bit aggressive cam I've been tuning my carburetor getting good results and playing with my distributor. I'm excited to try manifold vacuum after listening to your demonstration. It is sluggish out of the hole but runs really strong at the high end I just found your channel and now I'm a subscriber keep the videos coming I'm sure I'll learn more from you have a great day

Ii never had that perspective on the time ......and why I need to add a little more time untill I seen your drawing about timing degrees awesome appreciate that ..

I think you give the best videos on carbs especially edelbrock carbs you helped me fix my carburetor problems I was having I used a tune up kit to get it to run better especially after my heads were upgraded and cam tuning thanks for all of the help, you’r awesome. On this subject ported verses vacuum both will work but it depends on what you’re trying to do I mostly use ported but if I want more responsive throttle vacuum works better but normal driving ported but anyway thanks for the help

My 350 crate motor from Jegs prefers ported. I believe it is because my total timing is at 36 degrees which landed my initial timing around 18 degrees. If I plug into manifold vacuum it makes very little difference at idle. The motor is more responsive off the line and overall performance is better when plugged into ported. So try both and go with what your engine likes best.

Thanks, excellent information and easy to follow! I'm trying to get the 351w in my newly acquired 86 F150 4x4 tuned. Someone swapped out the stock 4 barrel for a Holley 4160. When I got it, the plugs said it was running VERY rich, and I finally figured out it was using manifold vacuum. Since I'm going to be mostly street driving, and will be using it as my daily driver (hopefully), I'm more interested in economy vs performance, so this video reinforcing my thinking that timed vacuum (I'm seeing it called ported in the other videos I've watched) is what I want to stick with. I'm now your newest subscriber.

I have a 290 HP 350 motor it runs best with just mechanical timing it gave me a lot of trouble running timed and manifold vacuum plugged both of them off and it runs great.

Great video.. I have locked out distributor, on blown my 383, with msd 6al-2 programmable, can i use vacuum advance?(i want 26 initial and 34 total). Or should i cancel vacuum advance? I want good throat reponse.. thank you.. how do we adjust distributor and crank degrees for the first start?

I run a lock out with a 7al MSD on my Hemi 512in it works great 👍.

I love your technical videos

On my Holley if I'm not using the timed port does it need to be capped? Also on this Brawler there is a hole in the other metering block. What is it for?

Another great video simple and detailed explanation

the issue I found with manifold vacuum on my engine is I need to increase the idle but that increased the engine trying to diesel after the ignition was turned off. perhaps If i was to use an idle up solenoid it may have worked better than just turning up the idle screw. 5.0 B303 1406 Edlebrock Performer 5.0 heads DuraSpark II

I have a 4 speed '69 roadrunner w/stock 383 (bored 30 thousandths with oversized rings and hardened valve seats). I have had it 38 years. I installed a 650 thunder series (1806). An old motor head tuned the carb drawing manifold vacuum, not ported. Played around with sluggish acceleration for years (don't drive it much) and this year had fuel pump failure. When I replaced it it ran better than ever. I would like to retune the carb now that it has correct fuel flow. Instead of reinventing the wheel, and as a general rule, what is the best set up for this car (metering rods, jets and springs)? Should I go back to the factory set up and start there? Timing is about 12 degrees at idle and I run Pertonix electronic ignition. Thanks and great videos!

Note that during the HP wars 1962-1970, I.E. 1967-72 Z/28’s, they never had a timed port on the Holley for a good reason. “Ported vacuum" was strictly an early, pre-converter crude emissions strategy, and nothing more. The vacuum advance still worked at steady-state highway cruise (lean mixture = low emissions), but it was inoperative at idle. Use manifold vacuum if you have a performance engine.😢

Great info. Very helpful. Love your channel. Thank you

this is a really good explanation.

"Ported" is also a way to reduce NOX emissions at idle. Even EFI cars have it: a switch that retards IGN timing, only at idle. On old US cars, I always try full vac first, then go back to ported if I can't get it right. Fords in particular are sensitive to vac advance, factory settings do not work anymore with the available pump gas here in the EU. I usually end up with only 5 degrees of vac advance, and full mech advance as late as 3200 crank rpms.

Thank you Sir . Your awesome , so this would create the rich mix smell at idle with higher comp and 246 @ 50 cam

Finally, all the information I've been looking for. Well explained, thank you! Now, for tuning with a Vacuum gauge, we need to hook to Manifold, correct?

Ok.. how about setting an adjustable vac port distributor ( msd streetfire), when ,why and how ,please.

I have a brand new pertronix vacuum advance distributor and the factory weights allow it to advance 24°. When determining total timing, how would I factor in the vacuum advance? If I set it at 10° base timing and mechanically it will advance another 24°, that would make total timing 34°. How do I know how much the vacuum advance is advancing and should I take that into account? I’m planning on using the timed port on the carburetor. Thanks again for another great and informative video!

Thank you for the video bud! 💯👌🏻

Thanks from jamaica 🇯🇲

Manifold vacuum if you're tuning for an efficient motor and not an emission band-aid. Runs cooler, less gas, more vacuum, less throttle angle, the motor tells you what it wants. GM engineers knew it and put in a work around temp switch to change back to manifold from ported to keep from overheating. This is an old video so I hope you've seen the error of your ways lol.

Tried both ways on my 283. What made the most difference was the initial timing. Ported or full vac didn't seem to make much difference..

AWESOME post 😎

You mean 2 step or rev limiter can only run on locked distributer..??

Timed vacuum predates EPA. Most early Pontiacs used timed vacuum. It tends to give a smoother idle and the power comes in as you tip on and the vacuum advance kicks in. It makes the engine seem eager.

Thanks finally making sence to me

Question: when adjusting the carb idle mixture with a vacuum gauge I connect the gauge to the manifold VACUM yes?

Actually, simply, vacuum advance is used to advance the timing at part throttle cruising. Part throttle is a lean mixture and that lean mixture requires more time to burn. Ignition timing is done with the vacuum advance disconnected, set total timing then reconnect the vacuum. Vacuum advance has nothing to do with total timing, it's just a way to get more advance at part throttle.

I am a noobie to this and I need to ask... I Have a '86 Bronco with a 351W and a C6 AT I'm currently working to restore .I intend to use an AVS2 1906 Edelbrock carburetor on it since the original Holley 4180-C was missing. Should I use the carb timed port , connecting a vacuum hose to distributor for street drive? Which vacuum hoses should I hook up to the carburetor and which ones I need to plug for street use? It also has the "hat" style air cleaner; do I need to keep it or use an "open air cleaner? Thanks!.

"Mild 700+ horse...." 😂 Seriously, though: U spoke about compression. What is the best way to test? I'll number what I think: 1) warmed up engine? 2) pull out all plugs 3) fix throttle plates fully open? 4) crank 4 or five times- needle seems to stop advancing? Mild cam(not RV ☺) Please advise. Thank you.

My truck ran the best using timed vacuum a lighter front spring on the dist and about 2_4 more initial timing it took off like a rocket 🚀 although the exaust was 50 percent louder and it ran hotter I didn't like that part of it although I could get a great AFR on my wideband , idle cruise WOT . Manifold vacuum I had to buy a adjustable vacuum advance to use manifold vacuum.

68 mustang, Ford rebuilt 351w, Mild cam, Holley 600 can, MSD distributor, MSD 6AL. Runs fine in town and cruise speed, after running 30 - 40 minutes on interstate at 70-75 mph, then floor it, it stalls and sounds like misfire. I let off the throttle and she limps back but only if I lower speed to 40-50. What’s gives?

WHAT ABOUT COMPRESSION AND FUEL OCTANE

Hi thanks for info whats ur set up? whats ur initial ? I have 350 chevy stock. I have mine 36 total manifold vacuum. Runs good but when hooked to timed port it runs bad.

Just got my DUI Chevy street / strip distributor. Have a Brawler 670 and a Comp Cam 224/230 @ .050. and 110 lobe separation. New engine not broken in or started yet. Would appreciate your opinion on what's best for initial break in, timed or manifold vacuum.

What happens to timing when you are running a long rod , long dwell piston engine such as a 351m?

Just curious do gear drives send vibrations through the distributor?

Well, if you want your street driven carbureted engine to run cooler and more efficiently (especially with a bigger cam), you use full manifold vacuum. Using manifold vacuum will give you a smoother idle and use less fuel when idling because with the low fuel/air volume in the cylinders with the earlier spark advance makes the engine more efficient. The idle speed will then increase using manifold vacuum and adjusting the idle speed down will reduce the fuel consumption and result in a smoother engine that also generates less heat so it will run cooler when at idle in traffic. My 1979 Pontiac Trans Am 400/4-Speed with a big cam and high CR 1970 heads runs at least 10-15 degrees cooler and gets 2-3 more MPG with the vacuum advance connected to a full manifold source.

Hi there , I have a stock Camaro 78 with 350cu engine with 4 speed manual what you recommend? As I searched I found factory connected to full vacuum.

Have you done a video on phasing your rotor?

I'm not a mechanic, but my mechanic for my 1970 C10 with a small block set me up with a manifold vacuum, there's a vacuum line on the distributor that's is plugged off--- is it difficult to just set up the distributor of timed advanced? Can I do it in my driveway? The truck is automatic with a mild cam--- thanks for your time in advance 😀

I've been revisiting this debate as i need to decide on things while my 70 nova is undergoing restoration. Motor is 355, 9.7 compression, sr torquer heads 170cc runners, 202/196 valve, 480/230@50 110 lsa cam, tunnel ram with dual avs2 500's, 3.73 gears with muncie wide ratio 4 speed. I'm thinking of running 16° initial, 37° total, and 16° manifold vacuum advance. I have heard tunnel rams like lots of timing, and would love to hear your thoughts of if I'm in the ballpark.

Good stuff. Vacuum advance is load determined. Mechanical is load related. On the highway, light load equals max advance, on the strip up it for a quarter of a mile, mechanical advance or lockout.

Problem I have is with manifold vacuum I can't get my idle as low as I want it and if I decrease the timing it doesn't work as well higher rpm!

After a 1/4 mile run is it helpful to have timed vacuum so that as much timing is taken out for instant cooling with retard vs manifold vacuum. Been playing around with it last few months.

Good explanation, but the bottom line is try both and let your engine tell you which one it likes!

Very interesting, thanks much! Was wondering if you have a video on how to set the initial and total timing with good visual/ verbal methods. I have that same Edelbrock carb on an Edelbrock performer intake Manifold running on a possible stock 350 Chevy engine (don't know anything about the engine) as it's a different motor from another vehicle when purchased. Will subscribe & like to your channel if you can help me here! Thx much.

10:18 why it makes richer..???

What is epa side??

16:55 "hopefully not a gear drive" Lol that made me laugh. Just yesterday i ordered a chain driven timing set to replace my gear drive the previous owners installed on my 1984 k10 with a 400sbc. That thing is ridiculously loud, it's annoying. Why do you not like them? Same reason or?

What is the difference between Manifold Vac and Ported Vac? Thanks much!!

If you use ported vacuum on a gm you are messing up. The advance is centrifugal, you can't have both under acceleration.

Please point to whats manifold and whats port and how to hook up the gauge. Very confusing.

Was wondering why you said "hopefully not a gear drive" ?

Ported and manifold vacuum are the same - except at idle. Connecting to manifold vacuum is better because the engine needs more timing at idle which ported cannot supply. The engine will idle cooler.

Unfortunately there is no legitimate use case for ported vacuum. if this were the case before a emitions controls carburators would have had pointed manfull vacuum. Also your late model fuel injected engines would apply this and have very low timing at idle but they do not, they are 20 to 30° just like your carborated engine with manifold vacuum.

I do have a question. We have a blueprint 350 crate . Dyno says 405hp ( sold as a 373 hp at summit. )$ 2799.00 if you want to see exact specs . Anyway can’t get off the line good with a 650 cfm AVS carb . Had to go down to the 500 cfm . Do you think the 650 is a loss cause or maybe play with another torque converter.

Why not buy a gear drive ???

My car seems to idle better with manifold.

700 hp is mild??

Just a mild 700hp big block lol

Theory is fine, but evidence is better. Just watched a video with a very simple, clear demonstration of why to always use manifold vacuum. All he did was show what happens on a vacuum guage with each port. Manifold vacuum gives you advance at idle to compensate for the lean mix. As you get into the throttle, that advance goes away. Your mechanical advance should be curved to come in pretty quickly off idle as the vacuum drops off. The two advances don't add together, they cover different needs. Think of vacuum advance as the idle circuit of the ignition system and mechanical advance as the main jets. Using ported vacuum leaves you with zero advance at idle and then both advances kicking in when you hit the pedal. That makes no sense.

the video would have been a lot better without your hand waving around for 23 minutes, with all due respect it is very distracting and detracts from the presentation :/

Reduce your video in half.