Ported vacuum and manifold are EXACTLY the same above idle. Ported vacuum is ONLY unique when the throttle plates are almost closed at idle (held open by the idle speed adjustment screw). The only other vacuum that is present is "ventura vacuum" which is drawn from a port into the carb throat just below the ventura (where the carb throat gets smaller then enlarges to approximately throttle bore size at the butterflies. Ventura vacuum is what pulls the secondaries open (hollys) when engine speed increases because neither ported or manifold would provide that function during acceleration. Ventura vacuum increases as air flow through the ventura increases which acts on the diaphram of the pull-up cannister to pull secondaries. Ventura vacuum is a consistant (with speed of the air into the carb) source, unlike either of the other two sources. Look at the carb diagrams and read a little. Non Hollys use a slightly different valving arrangement to provide the secondary pull in.

All this rangling is about an extremely small period of time in the operation of the carb, and measured in degrees would only be a few degrees, after which they are the same vacuum. The only difference is that ported vacuum does not provide any vacuum out to whatever, when the butterflies are closed. They can both be easily accommodated by tuning---unless, of course, you cant even tune a 2 hp briggs!

Curb idle speed must be adjusted, but none of the advance features (crank, distributor, or vacuum) need to be screwed with. The extra advance created by manifold vacuum at idle absolutely, positively does nothing but increase (greatly) the engine efficiency at idle speed. It does not "hurt" the engine nor does it affect the total timing curve you have set up for the particular engine.

I can accept whichever method works for you! Whatever you chose, then run with it. As I have said before, I can and have tuned for both.

BTW, I dont know what they called the purpose of ported vacuum back in "02" or in California. In the modern carb, (dating back to the mid to late 60's) it is an emissions consideration that dinasaurfan has also explained.

OOPS!! Gotta go, popcorns ready

 

Please explain how something that existed almost ten years before emissions came on the scene is suddenly an emissions thing in the late 1960s. It was used to improve gas mileage and only that. The dual diaphragm dist. were an emissions thing and using temp switches and vacuum switches to move the timing around were emissions things, but the basic vacuum advance was for improved gas mileage and nothing else. I was alive and working on cars then but hey believe what you want, but you will be wrong.

 

Ported vacuum was NEVER a consideration to increase MPG. It is used at idle only to decrease efficiency which decreased emissions at idle. All the valves, switches etc thrown onto the engines came as an attempt to address some emissions driveability issues. Air injection into the exaust manifolds was emissions as was EGR etc.

You may have been alive back in 02 and working on cars, but that is a scary prospect given that you dont understand emissions or tuning.

You are absolutely correct, I will believe what I want--.

No I will not be wrong-----I am in agreement with credible sources. As I told you earlier (previous pizzin contests) those sources have something you do not----CREDIBILITY!! Credibility is not self imposed.

Whattyathink Bear----reckon we have once again gone about as far as we can with our arguments?

 

Bull, you are telling me that when Ford started using the Holley 1850s on their engine in 1957 and 1958 that the ported vacuum was for emissions? You are insane if you believe that. Hell, they still had road draft tubes on car engines back then, the PCV didn't exist yet. No one had ever heard of or cared a damn about emissions from engines or anything else. Get real. Oh yeah, retarding the timing at idle lowers emissions? In your dreams maybe, but in real like life, no.

 

So cite your sources:

Have any SAE papers you'd like to share with the class?

How about blueprints, engineering notes, job orders, or even interviews with the people responsible for these designs?

So you tell me plenty of cars came from the factory with the only vacuum advance source at the manifold:

Year, make, model please, as many as you can remember.

Inquiring minds would like to research these responses.

 

"that one"---once again you are not capable of any reasonable discussion/disagreement without name calling---you are of no consequence.

Hypoid---reasonable request, will attempt to give main reference I use. You are not correct, I did not say that plenty of cars came from the factory with only manifold vacuum. That I could only factually say if I knew what the state of all factory cars were. I do not know nor did I even hint at such, but I have seen that statement relating to ported vacuum and I am quite sure it was from a bellicose poster (no names).

I have not stated here or on any post, anywhere that I was the ultimate expert, in fact, I try to make that disclaimer all the time. In his last post bear mentions "road draft" tubes---I knew about them also. In fact a short trip to google will get more than you really wanted to know about emissions and subsequent laws. California, in 1963 (read it, its available) enacted a clean air act that addressed that very issue and required the closed crankcase system. Dont take my word, read it. In fact, California was one of the first to exceed projected federal requirements during the start of emissions concerns. Again, anyone interested, read it, it can be googled.

Now for Hypoid's source request (reasonable), I am (in addition to spending many hours trying to improve on the performance and driveability of both vacuums) using the HOLLY CARBURATORS, MANIFOLDS, & FUEL INJECTION book. 4th updated edition (1994) by HPBooks. Co-authored by Mike Urich & Bill Fisher.

I wouldnt know these guys from Adams house cats, but they have enough credibility to get a book/manual published by a major publisher. Until such time as someone provides me proof that they are more credible than these guys and can show they have published anything, I will go with their explanation. This book can be read, page by page, by google books.

Specifically, chapter 7, "ENGINE VARIABLES", pages 111 thru 115. Starting at 111, the 2nd paragraph "SPARK TIMING" and into p. 3 "CONTROLLING ADVANCE". Going to page 112 to paragraphs "DIESELING" and "TIMED SPARK ADVANCE". I'll not try to quote anything here, so I cant be accused of "misquoting" anything. Read it yourself and draw your own conclusions about this subject----I have.

You are to draw your own conclusions about these articles. I am not an expert, but I do have lots of experience and do know, at least some, "chit"
BTW I dont hate anyone who disagrees. Nasty people pizz me off for other reasons.

I hope this shows the facts behind my opinions on this subject---

 

Personally, I think all discussion on the topic of ported vs manifold vacuum should cease immediately and all posts on the subject, deleted. Anyone daring to post a question on this subject should be banished for life from any and all message boards or forums on the Internet. Finally, we all need to recognize that the FE is an archaic beast soon to be replaced with souped up hydrogen fuel cell powerplants that actually improve atmospheric quality and have unlimited fuel economy.

Given that none of this will ever happen, I'll settle for a civil discussion on the topic.

But then the chances of that happening are probably pretty slim too.

Carry on.

 

That is true, you did not make any such statement. Dinofan has made the claim in prior discussions. I apologize for my poor composition.

The question to Dinosaurfan is: What cars came from the factory with manifold only spark advance?

Year, make, model please.

Whenever I get my truck together, I just might make an experiment out of this argument, start my own thread instead of hijacking someone else's.

grump out....

 

Hypoid--

Now theres a great attitude! Try it and see which one works for you. Dosnt matter which method you use, or any "science" that might be involved, if it "dont" work for you it isnt good

If you need any suggestions for either and are interested in what I have discovered, PM me. I can tune for both sources.

 

Sorry for the double---
Hypoid--in defense of dinosaurfan, I did some looking into the 1850 series of the 4160 holly carb. The Holly site shows that the original model was not an emissions legal replacement carb. My suspicion is that they did did not provide a ported (AKA timed) source on the carb, therefore, not emissions compliant. There is somewhat a "symantics" game on these definitions. Some people refer to "ported" vacuum because it is manifold vacuum provided on a "port" on the carb itself, not from the intake. I suppose it would correct to call above the butterfly vacuum as "timed" vacuum. They did manufacture a replacement model that was, and as I recall a slightly different model designation and it was for post 79 emissions compliance. I could not determine if that early model even had a ported source on it. I spent some time working with one of those carbs as a replacement for a quadrajet on a marine 350 engine (yep, I changed the intake as well--no adapters). Back then, marine engines did not use any vacuum advance, so porting was moot. I even added the jet plates so that it would use standard brass jets.

Without emissions compliance, dinosaurfan may have been correct to a degree, that only manifold vacuum was provided, maybe from a vacuum tree on the intake.

 

I will qualify my post with the following statement.

For vehicles that came with ported vacuum advance from the factory, to reverse that and use manifold vacuum when going with a big cam, high compression or other factors, it is usually to mask issues that can be dealt with in other ways. Usually.

Personally, that's exactly what I did. I had a 292/292adv, 230/230@.050" cam, degreed for low-end torque, 11:1 compression, and a WAY too big carb at 750cfm. Using manifold vacuum, with an adjustable vacuum advance can, and recurving the distributor, I was able to get a decent amount of vacuum at idle w/20 degrees of advance, and get rid of the horrible ping the thing had on 93 octane gas, all the while getting some decent low-end torque out of the thing, THAT WAS NOT POSSIBLE with pure mechanical advance. PERIOD.

In retrospect, I should have NEVER gone so over-the-top with a 390 for a highboy.

--

As moderator of this forum, I have probably gone and sprayed gasoline on the fire, but hey, I do want this discussed in a gentlemanly manner, WITHOUT insults. The instant it goes down the toilet, it's closed

 

krewat--

I dont think you threw any gasoline You expressed your opinion without making it personal or aiming at anyone in particular. Nothing wrong with being convinced about something.

I have done a lot of surfin lately on the subject and have discovered threads dating back to 2002 that raise all the same points and issues we have here. Chebby, Pontiac, Mopar are all in on this one as well. I dont think this one is ever going to be definately resolved one way or another. Reason being (to me) is that there are just too many variables and most importantly, personal preference. 230 deg @.050 cams and more, street, strip, compression etc all require unique timing curves and events. I also noticed that there seems to be a lot of "symantics" involved. I always considered "ported" to mean "above the butterflies at idle". Apparently, some people think it means a port, on the carb, that provides manifold vacuum. Go figure!

The only thing that I will stick to in this argument is that more advance at idle (to a point) makes the engine more efficient and run cooler and less emissions compliant at idle. Also a big component of any success is the tuning for whatever you have. It is not a one size fits all. For most of the rest, because of too many good opinions, I am going to acknowledge many different possibilities. Plainly put, NONE OF US WIN A TRIP TO THE SUPERBOWL!

Besides that, given the election and economy, I may not be able to afford the popcorn.

 

benshere, thanks for the tip on google books. It took me a minute to figure out how to get the books options going but that is way cool. Thanks! I'll be reading up over the weekend. This whole mani vs port thing has me ready to try a test on my own shortly after a fine tuning soon to take place when time & $ drop by for a visit LOL
Cheers!

 

Man, I've witnessed this "debate" on like three threads, and it never stops being amusing!!! Clearly, there are justified and concrete points of view held on both sides, and when I first stumbled upon this sight, I was quite vacuum advance type ignorant. So I tried both to see which I liked, since both sides of the debate were quite firm on their respective POVs. Now I did decide which one CLEARLY was the better set up, IMO, and rather than pick sides, I'd invite anyone unsure to take the small investment in time and try both set-ups in order make up your own minds. I personally appreciated this debate as it made me see for myself which side of debate I settled on (and my snappier throttle response and headers not melting thank all of you!!!)

 

WELL PUT!