Manifold vs Ported Vacuum Advance: Quick Testing Update
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- Опубліковано 18 жов 2024
- Just a quick update on my testing for the manifold vs ported vacuum advance debate.
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David Vizard already settled this debate: FULL MANIFOLD VACUUM!
He did! But I'm going to show all the numbers that prove it!
Awesome! Cant wait to see how well the truck plows snow! 😀
I'll try to film some!
Great mission. Excited and looking forward to your summery
Thanks!
Shes a beauty👍 thank you for keeping it on the road
Thanks!
The 1976 Jeep Technical Service manual discusses a Spark Coolant Temperature Override (CTO) switch (a temperature actuated vacuum valve) that connects manifold vacuum to the distributor cooler than 160F and ported vacuum above that temperature.
Not sure how that fits into the analysis you are taking on.
Excellent discussions. Thanks for driving the explanation forward. 4:43
My 78 F250 had a similar system on it when it was stock. I think it was pretty common during the 70s. Thanks for watching!
That’s ok, I already know what the answer is. Manifold advance.
I mean, we all know that's the answer. Just gotta prove the ported guys wrong. ;)
Im over the rain.. good video .
Good time to go get some deer!
I would assume Manifold Vacuum would be better overall, since it is more constant so to speak and not relying on the plate of the carb to move. Plus one would think you would want all the vacuum at a lower rpm/light throttle as you transition to higher rpm wot when the mechanical timing kicks in and vacuum drops. It seems to make more sense because if race cars and drag cars dont use any va and so only rely on mechanical then your base total timing without VA is all you need at WOT and should be the most efficient. Obviously race cars and drag cars are not cruising through towns and cities at stop lights and trying to obey speed laws, watch out for slowing down traffic, etc etc, hence the need for vehicles to use Manifold Vacuum. It would then make sense, that the ported vacuum would be used as some early day emissions crap as I have heard because it functions almost the same way but only really activates in the middle of light throttle and not also at idle. Still it makes no sense to even bother using ported because its basically just a slightly delayed version of manifold vacuum, seems like just a less accurate version of manifold vacuum after i really look at it.
As you already stated during your dual gauge test, there's no difference in vacuum to the advance once you open the throttle.
So ported would always be better since no adjustments are needed when you connect the hose after setting base timing and idle mixture.
Well, the debate has to do with different tuning methodologies. Some people tune to manifold vacuum, some to ported, and others don't use vacuum advance at all!
Even though both ported and manifold vacuum signals are the as the throttle is opened, the question is do you want advance when your throttle is shut?
There are also debates on what your initial timing should be set at. Some guys set their initial timing to 15-20 BTDC, others set it between 6-12 BTDC.
@@thejunkyardnecromancer Heavy load and racing applications don't use it due to operating where there is no part throttle vacuum situations like heavy trucks, boats and racing.
Base timing would be more engine specific and not a general one size fits all.
Higher timing at idle increases HC counts so can affect smog testing where applicable.
Timing is a combination of base + mechanical and then vacuum where applicable for light throttle driving.
Normally a larger cam likes more idle timing so you could use the manifold vacuum to apply more at idle.
It will be interesting what you find for your specific application.
There is a major difference at Idle and just off idle (where the engine spends a significant portion of its life). All the space between a closed throttle blade and the ported vacuum hole in the carburetor needs manifold advance.
@@BillUSN1 this is all true! I'm working too n find a general rule of thumb
What is the specs on the Engine? and what cam specs
It's a 300ci inline six. Single barrel Carter yf carb, and bone stock cam (as far as I know).
That motor is def gonna want manifold vacuum. I don't think anybody would run ported vacuum on a stock engine@@thejunkyardnecromancer
Update?
The full length testing video will hopefully be out by the end of the month!
My stock rebuilt 331 Cadillac motor runs best on ported, tried manifold, just didnt like it. My cammed 351 Cleveland runs best on manifold and not as well on ported, go figure 🙂