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phil400
Cochise

Canada
456 Posts

Posted - 25 Jul 2010 :  7:24:57 PM  Show Profile  Reply with Quote
Hi,just wondering how many of you guys run ported and how many run direct manifold?
is one better than the other?
thanks

78T/A 4-SPEED Marty blue 400/milled 6x-4's/268H,comp roller tip rockers/ performer Q-jet/RA manifolds 2.25" exhaust with x-pipe/ mine since '99 3rd & final owner as long as I'm alive
"sometimes I do what I want to do,rest of the time I do what I have to"

Mark S.
Cochise

USA
432 Posts

Posted - 25 Jul 2010 :  7:29:55 PM  Show Profile  Reply with Quote
Direct manifold.

In general, here's a quick & dirty explanation:

Manifold vacuum drops as RPM increases (throttle plates open), distributor weights take over and advance to total (whatever is set).

Ported vacuum is venturi vacuum. This will be low or zero at idle, and increase with RPM.

Now, during cruise, throttle plates are pretty much closed and manifold vacuum will be present but should not be as high as at idle. If it is, you've got other issues.

Rule of Thumb: Ported vacuum comes from above the throttle plates, manifold vacuum comes from below the throttle plates...

PSP Member since 1996

Never enough cubes...

"The difference between genius and stupidity is that genius has its limits." - Albert Einstein


Edited by - Mark S. on 25 Jul 2010 7:43:02 PM
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bnorris_74
Crazy Horse

USA
1442 Posts

Posted - 25 Jul 2010 :  7:51:20 PM  Show Profile  Reply with Quote
Ported.

I feel my car idled better in the transition from the transmission being in park and then dropped into gear. I figure some vacuum signal to the advance was being lost when the idle dropped when placed in gear with manifold vacuum. With ported there is no advance at idle.

Edited by - bnorris_74 on 25 Jul 2010 8:40:46 PM
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Bill Boyle
Horse Feathers (Charter Member)

USA
4793 Posts

Posted - 26 Jul 2010 :  07:03:32 AM  Show Profile  Visit Bill Boyle's Homepage  Reply with Quote
Ported.

"Dedicated to keeping the classic Pontiac engine alive."

----
400 bored +.030, forged TRW pistons, ported 62 heads, Hedman headers, 2.5 SS dual exhaust X Pypes, Comp 276AH10 cam, Scorpion 1.65 RR, 850 Q-jet, stock intake & tuned HEI; original owner.
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Phil
The Great White Buffalo

USA
7214 Posts

Posted - 26 Jul 2010 :  10:30:09 PM  Show Profile  Reply with Quote
I ran direct for decades until about 8 years ago when I did alot of experimenting. I found that I had alot more control of the timing across the board with ported and the car runs better (street) overall, including starting and idling.

Bowties are for Pee-wee Herman. "Chevy": even the name sounds cheap, but not as cheap as your Pontiac will be with an LS transplant.
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Taman
Red Bird

USA
844 Posts

Posted - 27 Jul 2010 :  1:32:39 PM  Show Profile  Reply with Quote
If you run direct vacuum then you will have full vacuum advance at idle. Vacuum advance should be a timed or ported signal.

Everything Under The Sun Is Intune
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phil400
Cochise

Canada
456 Posts

Posted - 27 Jul 2010 :  11:19:00 PM  Show Profile  Reply with Quote
Ok so it isn't just me, I was running direct(car was like that since I bought it)but recently switch back to ported,I too find it runs better.

I googled the topic and found many run direct,I guess it's whatever you prefer.

78T/A 4-SPEED Marty blue 400/milled 6x-4's/268H,comp roller tip rockers/ performer Q-jet/RA manifolds 2.25" exhaust with x-pipe/ mine since '99 3rd & final owner as long as I'm alive
"sometimes I do what I want to do,rest of the time I do what I have to"

Edited by - phil400 on 27 Jul 2010 11:19:56 PM
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clintww
Cochise

USA
582 Posts

Posted - 27 Jul 2010 :  11:32:25 PM  Show Profile  Reply with Quote
I remember HPP doing an article on this a few years ago. From what I remember it all depended on your complete setup as to which worked best. For what it is worth I have hooked my 400 to ported and find it idles better also. I think the article outlined an exact testing procedure to find your best performance
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Mark S.
Cochise

USA
432 Posts

Posted - 28 Jul 2010 :  07:06:46 AM  Show Profile  Reply with Quote
FWIW, most if not all ported vacuum advance systems came about because of emission control systems (C.C.S., T.C.S and C.E.C to name a few) and their associated temperature switches that only allowed vacuum advance in high gear or at certain operating temps. Generally, full vac advance at idle usually helps with cooling and fuel economy.

Now on my "interim" engine, I run manifold vac to a adjustable canister on an HEI distributor with 12 deg initial and 32 deg total at 3200 RPM.
Cam is an old HC02, heads are ported 4X-7's, Perf RPM intake with a 780 CFM 3310 vac. sec. carb and long tube headers to 3" exhaust.
Throttle response is excellent and I have zero driveability issues with manifold vacuum on my set-up. Haven't tried running ported with this combo... might have to do a little experimenting!

PSP Member since 1996

Never enough cubes...

"The difference between genius and stupidity is that genius has its limits." - Albert Einstein

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Vanmor
Cochise

USA
573 Posts

Posted - 13 Sep 2012 :  07:44:45 AM  Show Profile  Visit Vanmor's Homepage  Reply with Quote
I just read this article written by an automotive engineer. It's text seems to agree with Mark S.

http://www.corvetteactioncenter.com/forums/c3-technical-performance/60830-ported-vs-manifold-source-vacuum-advance.html

or

http://www.camaros.org/pdf/timing101.pdf

"A man has got to know his limitations." Dirty Harry

Edited by - Vanmor on 13 Sep 2012 08:18:34 AM
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Blued and Painted
Chief PONTIAC

USA
3404 Posts

Posted - 13 Sep 2012 :  10:09:44 AM  Show Profile  Reply with Quote
I like manifold vac for all around drivabality. Less throtle angle at idle and cooler combustion temps. Then i would switch to ported at the drag strip an ran a more consistant time and slightly lower ET. Then switch back and drive home. Stock 455+6x-8 w/logs and 2 inch duals.


Bull Nose Formula/ 461/ Q-Jet/
TH400/ 3.08 8.5 / R44TS.
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Blued and Painted
Chief PONTIAC

USA
3404 Posts

Posted - 13 Sep 2012 :  10:39:44 AM  Show Profile  Reply with Quote
Someone here posted an artical where manifold and ported vac were plotted on a graph through out the load and rpm range. Outcome, they were the same except at idle.


Bull Nose Formula/ 461/ Q-Jet/
TH400/ 3.08 8.5 / R44TS.
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phil400
Cochise

Canada
456 Posts

Posted - 14 Sep 2012 :  8:07:28 PM  Show Profile  Reply with Quote
After running ported for 2 summers,this year I switched back to full manifold vacum,and the car does idle better with less throttle angle,and cooler when stuck in major traffic.

When I think about it now,my original post that the car ran better on ported was false I think,after switching back to full vacuum,I see no diffrence in how it drives on the street.

I did alot of reading on the topic and pretty much what I Found is the engine will tell you what it wants one is not "better" than the other,it's what suits your combo.




78T/A 4-SPEED Marty blue 400/milled 6x-4's/268H,comp roller tip rockers/ performer Q-jet/RA manifolds 2.25" exhaust with x-pipe/ mine since '99 3rd & final owner as long as I'm alive
"sometimes I do what I want to do,rest of the time I do what I have to"
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phil400
Cochise

Canada
456 Posts

Posted - 15 Sep 2012 :  09:24:18 AM  Show Profile  Reply with Quote
Although on my dad's vette with the stock cam it's on ported and runs fine.

78T/A 4-SPEED Marty blue 400/milled 6x-4's/268H,comp roller tip rockers/ performer Q-jet/RA manifolds 2.25" exhaust with x-pipe/ mine since '99 3rd & final owner as long as I'm alive
"sometimes I do what I want to do,rest of the time I do what I have to"
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beertracker
Cochise

350 Posts

Posted - 17 Sep 2012 :  7:22:33 PM  Show Profile  Reply with Quote
Very informative thread. This seems like a good place to add my vacuum advance questions. I am not trying to hijack threads.

I wanted to ask a few questions about vacuum advance. I have initial timing at 14 deg and centrifugal advance is limited at 16 deg (3000 rpm) for a total of 30 deg. When vacuum advance comes in will it pull the advance higher than 30? Or put another way is vac. adv. additive on top of centrifugal plus initial? Or is vac. adv. just added to initial advance?

How do I know if I have too much vacuum advance? How do I limit vacuum advance? I read about adding a tab to the vacuum canister to limit diaphram travel. Not sure how to do this? I have also seen adjustable vacuum cans at Summit. That's all for now.
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cortcomp
Coyote

USA
5335 Posts

Posted - 17 Sep 2012 :  8:17:50 PM  Show Profile  Visit cortcomp's Homepage  Reply with Quote
It can add on top, i've seen with timing light like 50+ degrees revving in the driveway. but again, under load in the car, and throttle angle, etc will change things.
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Blued and Painted
Chief PONTIAC

USA
3404 Posts

Posted - 18 Sep 2012 :  10:31:00 AM  Show Profile  Reply with Quote
I think Your OK unless you here some clatter at light throtle take off or light acceleration at cruising speed. Witch vac source are you using?


Bull Nose Formula/ 461/ Q-Jet/
TH400/ 3.08 8.5 / R44TS.
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beertracker
Cochise

350 Posts

Posted - 18 Sep 2012 :  10:55:09 PM  Show Profile  Reply with Quote
Planning on using ported vacuum. I will listen for some clatter at light throtle take off or light acceleration at cruising speed. I checked Jim Hand's book specifically the ignition chapter and it answered my questions. He mentions generally most Pontiacs like 10-18 deg initial, 20-25 deg mechanical and also 14 deg vacuum advance. His 473 ci with 10:1 CR likes 11 deg initial, 19 deg mechanical and 14 deg vacuum advance equal to 44 deg total.

thanks,
bt
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larryneworleans
Tribal Scout

1 Posts

Posted - 16 Nov 2012 :  3:01:52 PM  Show Profile  Reply with Quote
I have just changed to direct vacuum on my 69 fb(rebuilt 350, rebuilt 2 barrel rochester carburetor, 62 heads. 180 deg thermostat)
I had been using the Thermal Vacuum Switch(TVS).
I have 12 deg. initial timing.
Had to lower the idle throttle speed a little (about a half turn of the idle stop screw)and
of course cap off the DA port on the TVS.
So far it runs cooler and I have much more seat of the pants acceleration.
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BearGFR
Bear

USA
580 Posts

Posted - 17 Nov 2012 :  2:19:43 PM  Show Profile  Visit BearGFR's Homepage  Reply with Quote
My opinion is.... try both and use whichever your car seems to like better.

Bear
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phil400
Cochise

Canada
456 Posts

Posted - 17 Nov 2012 :  6:44:54 PM  Show Profile  Reply with Quote
"My opinion is...try both and use whichever your car seems to like better"

X2

78T/A 4-SPEED Marty blue 400/milled 6x-4's/268H,comp roller tip rockers/ performer Q-jet/RA manifolds 2.25" exhaust with x-pipe/ mine since '99 3rd & final owner as long as I'm alive
"sometimes I do what I want to do,rest of the time I do what I have to"
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Total Jackass
Tribal Scout

0 Posts

Posted - 14 Jan 2014 :  04:34:11 AM  Show Profile  Reply with Quote
Q. How does a moulded fruit-flavoured dessert answer the phone?
http://www.vintbridals.com/prom--evening-dresses.html

I'm a first class jerk and don't you forget it!
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Phil
The Great White Buffalo

USA
7214 Posts

Posted - 14 Jan 2014 :  6:31:55 PM  Show Profile  Reply with Quote
TTT

Bowties are for Pee-wee Herman. "Chevy": even the name sounds cheap, but not as cheap as your Pontiac will be with an LS transplant.
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bluebird
Cochise

USA
292 Posts

Posted - 19 Sep 2015 :  9:19:38 PM  Show Profile  Reply with Quote
I've read a lot on this subject also and it makes sense that they would run manifold to improve mileage on the highway and at idle, not an additional advance to acceleration, but with my vacuum advance disconnected my car likes 10 degrees initial advance, anymore and the starter fights the flywheel, if this is where my car finds its sweet spot why would I then alter it by 15 more degrees at idle running a total of 25 degrees at idle? But it runs with the vacuum on manifold at idle. There is no way it can start with 25 degrees initial advance, so it must be a dynamic occurance. On the flip side why would they design vacuum advance to come completely in at a certain vacuum and by so many degrees if they weren't talking about manifold? I've ran both ways and I find a slight improvement on acceleration on ported, but am I chancing detonation, since it can be inaudible? I do get better gas mileage on long trips with manifold, but better city response on ported. I think I will be running manifold at the ever so slight expense of quicker acceleration. Also if there is a problem with anything vacuum related such as a bad diaphragm it will show at idle instantly. Just my two cents.

"Experience is the best teacher, unfortunately, it's the costliest!"
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Bill Boyle
Horse Feathers (Charter Member)

USA
4793 Posts

Posted - 22 Sep 2015 :  08:38:45 AM  Show Profile  Visit Bill Boyle's Homepage  Reply with Quote

Pitts64 wrote: "No vacuum advance, full time 34 degrees, 100% street..."

Why?

"Dedicated to keeping the classic Pontiac engine alive."

----
400 bored +.030, forged TRW pistons, ported 62 heads, Hedman headers, 2.5 SS dual exhaust X Pypes, Comp 276AH10 cam, Scorpion 1.65 RR, 850 Q-jet, stock intake & tuned HEI; original owner.
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Blued and Painted
Chief PONTIAC

USA
3404 Posts

Posted - 22 Sep 2015 :  12:33:24 PM  Show Profile  Reply with Quote
Agree with Mr Bill. Your leaving low and mid range response and power on the table with locked or semi locked timing.

There is an advantage Bracket Racing where the engine stays in the mid and upper rpm range and Dead Nuts Consistent Elapsed Time is a must to be competitive.


Bull Nose Formula/ 461/ Q-Jet/
TH400/ 3.08 8.5 / R44TS.
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Bentwings
Tribal Scout

USA
28 Posts

Posted - 22 Sep 2015 :  10:35:59 PM  Show Profile  Reply with Quote
I found this on another board. It's pretty interesting. Just a hint, it throws freezing cold water on ported vacuum. Read it, weep, and get some new vac line. Haha

The Echlin part number has been discontinued. There is a replacement but I just lost it. I'll try and dig it up again. It comes from Rock Auto.

http://www.corvetteactioncenter.com/forums/c3-technical-and-performance/60830-ported-vs-manifold-source-vacuum-advance.html

Edited by - Bentwings on 22 Sep 2015 10:41:03 PM
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