The 1947 - Present Chevrolet & GMC Truck Message Board Network







Register or Log In To remove these advertisements.

Go Back   The 1947 - Present Chevrolet & GMC Truck Message Board Network > 47 - Current classic GM Trucks > The 1967 - 1972 Chevrolet & GMC Pickups Message Board

Web 67-72chevytrucks.com


Reply
 
Thread Tools Display Modes
Old 09-22-2016, 03:52 AM   #26
1969c10joe
Registered User
 
Join Date: Sep 2016
Location: lompoc ca
Posts: 228
Re: HEI ignition secrets

i should be able to do this at idle im curious what kind of adjustment can be made .Seen the thread what did i do to my truck today? I FLOORED IT
1969c10joe is offline   Reply With Quote
Old 09-22-2016, 03:56 AM   #27
1969c10joe
Registered User
 
Join Date: Sep 2016
Location: lompoc ca
Posts: 228
Re: HEI ignition secrets

I just cant help it thanks do you mind if i call you richard?
1969c10joe is offline   Reply With Quote
Old 09-22-2016, 10:51 AM   #28
Big Kev-O
Registered User
 
Big Kev-O's Avatar
 
Join Date: Mar 2014
Location: Simi, CA
Posts: 194
Re: HEI ignition secrets

If you would like some good info on timing read the link below. I would never run vacuum advance off the ported connection. The reason GM and Summit state to use ported is for legality/SMOG green tree hugger reasons.



http://www.jalopyjournal.com/forum/t...ot-time.54221/
__________________
Made in America by Americans
Big Kev-O is offline   Reply With Quote
Old 09-22-2016, 11:57 AM   #29
VetteVet
Msgt USAF Ret
 
VetteVet's Avatar
 
Join Date: Jan 2005
Location: Kalamazoo, Michigan
Posts: 7,924
Re: HEI ignition secrets

http://www.superchevy.com/how-to/97438/


This website gives a lot of great information about the subject of this thread. Here is a quoted part of it by me. Everyone should read it



Where should the vacuum canister be routed?
There’s been a lot of debate whether or not the vacuum canister should be plugged into a ported or direct vacuum source. Internet forums are rife with opinions on both sides of the argument. However, there is a right and wrong way. And it’s not an opinion; it’s just a fact.
Plugging your vacuum advance into a direct source will allow it to engage at idle, which is good for a number of reasons. Much like cruise conditions, engines run leaner at idle than they do under load. Again, this means the mixture burns slower and needs an earlier spark to optimize the burn. Ensuring that the mixture has a complete burn before leaving through the exhaust port also helps the engine to run cooler at idle. All carbureted cars were set up with direct vacuum to the distributor before more stringent emissions requirements reared their heads.
Ported vacuum sources are a result of emissions laws and manufacturers doing whatever they could to get big V8 engines to pass smog before the incorporation of the catalytic converter. The idea was that by using little to no spark advance at idle, the exhaust gas would leave the cylinder still-on-fire and help maximize the efficiency of antiquated air injection systems. Engines from this era often ran very, very hot, were prone to warped exhaust valves, cracked cylinder heads and all other manner of issues. Using a ported spark advance will still allow the vacuum advance to do its job at steady cruising, but all of the benefits of idle cooling will be lost.
Here’s a quick experiment you can try on your car. Plug the vacuum advance into a ported vacuum source and check the idle rpm. Now, switch the vacuum advance to a direct source of vacuum and again check the idle rpm? We’ll bet money the RPM increased. Why? Because the additional ignition timing provided by the vacuum canister and full manifold vacuum source allowed the engine to more effectively burn the air/fuel mixture. It therefore produces more power (even at idle) and rpm rises as a result.

Maybe us Old Geezers know what we're talking about.
__________________
VetteVet

metallic green 67 stepside
74 corvette convertible
1965 Harley sportster
1995 Harley wide glide

Growing old is hell, but it beats the alternative.

Last edited by VetteVet; 09-22-2016 at 12:13 PM.
VetteVet is offline   Reply With Quote
Old 09-22-2016, 01:00 PM   #30
RichardJ
Registered User
 
Join Date: Apr 2010
Location: So Cal
Posts: 808
Re: HEI ignition secrets

>>The reason GM and Summit state to use ported is for legality/SMOG green tree hugger reasons.<<

That simply is not a true statement. GM used ported vacuum long before they started with the serious smog systems.
PCV System was the first smog system used on automobiles and it was used to replace road draft tubes.

Early 50s 235 six with Rochester B. The two metal lines to the carb are fuel and vacuum advance line connected to ported vacuum next to mixture screw.



Here is a mid '50s 283 with 2GC and again ported vacuum.



From your link in jalopyjournal.
>>The number one main reason you want full time vacuum is that you need to run a considerable amount of advance at idle.<<

need to run a considerable amount of advance at idle ? What need?

>>Running the engine at idle without the extra advance provided by the vacuum advance system will have the engine running hot in almost all cases.<<

I guess lack of air flow through the radiator at idle has nothing to do if whether an engine heats up or not at idle?

>>engine needs quite a bit of advance at idle since the fuel/air mixture is lean and it takes longer to burn the mix at a low engine rpm<<

If I was worried(?) about a lean mixture taking longer to burn at idle, I'd just turn the mixture screws out a little.

He goes on to mention that manifold vacuum provides Vacuum Retard, but only in reference to engine cranking conditions. He needs to take a closer look at cranking rpm, low vacuum during cranking and the simple fact that ported vacuum would provide 0"Hg and 0* advance while cranking.
__________________
'67 GMC, 3/4 ton, 292, 4 spd
RichardJ is offline   Reply With Quote
Old 09-22-2016, 01:11 PM   #31
RichardJ
Registered User
 
Join Date: Apr 2010
Location: So Cal
Posts: 808
Re: HEI ignition secrets

>>All carbureted cars were set up with direct vacuum to the distributor before more stringent emissions requirements reared their heads.<<

Again the bologna about vacuum source before emission systems.

In the '70s, manifold and ported vacuum were often both used on the same engine and routed through various temperature and electrical controlled devises to determine the best timing to make the engine run like crap.

Mixture and burn time at idle sounds more like an emissions issue.
I guess 50s and 60s engines were never allowed to idle for very long if the had ported vacuum.
__________________
'67 GMC, 3/4 ton, 292, 4 spd
RichardJ is offline   Reply With Quote
Old 09-22-2016, 01:51 PM   #32
1969c10joe
Registered User
 
Join Date: Sep 2016
Location: lompoc ca
Posts: 228
Re: HEI ignition secrets

Thankyou i didnt mean to start a debate about manifold vs ported vacuum kind of like tastes great less filling. I understand the difference. got to go and make some money ill be back
1969c10joe is offline   Reply With Quote
Old 09-22-2016, 02:00 PM   #33
geezer#99
Registered User
 
geezer#99's Avatar
 
Join Date: Aug 2009
Location: Bowser
Posts: 9,190
Re: HEI ignition secrets

Quote:
Originally Posted by RichardJ View Post
>>All carbureted cars were set up with direct vacuum to the distributor before more stringent emissions requirements reared their heads.<<

Again the bologna about vacuum source before emission systems.

In the '70s, manifold and ported vacuum were often both used on the same engine and routed through various temperature and electrical controlled devises to determine the best timing to make the engine run like crap.

Mixture and burn time at idle sounds more like an emissions issue.
I guess 50s and 60s engines were never allowed to idle for very long if the had ported vacuum.
What makes you think that just because the vac ports on both the 235 and 283 are up near the top of the carb above the throttle plate that they have to be a ported vac source.
They are manifold vacuum!
geezer#99 is online now   Reply With Quote
Old 09-22-2016, 02:05 PM   #34
davepl
Registered User
 
davepl's Avatar
 
Join Date: Aug 2006
Location: Redmond, WA
Posts: 5,572
Re: HEI ignition secrets

My understanding of the matter is that the vacuum advance was moved to ported in order to retard timing and increase heat at idle; this serves to ensure a more complete burn and also assists cars with A.I.R. pumps, as a hot charge makes it easier to finish burning "unburned hydrocarbons" in the exhaust.

I've long been an advocate of setting it up the way the factory did, but the question is whether or not there's a downside to running manifold vacuum on a car designed to be set up ported. I don't have an AIR pump.

Is the mechanical advance curve from an early 60s (manifold) different from that in the early 70s (ported)?
__________________
1970 GMC Sierra Grande Custom Camper - Built, not Bought
1969 Pontiac 2+2 427/390 4-speed Coupe
1969 Pontiac 2+2 427/390 4-speed Convertible
davepl is offline   Reply With Quote
Old 09-22-2016, 03:23 PM   #35
1969c10joe
Registered User
 
Join Date: Sep 2016
Location: lompoc ca
Posts: 228
Re: HEI ignition secrets

1I wont be adjusting weights or springs anytime soon2My immediate goal is to fine tune adjustable vac advance 3ive tried both ways it is connected to manifold at the moment starts right up idles vac gauge needle looks glued in place. but that could change cuz im always learning. badass engines has an excellent explanation of ignition timing very concise most of you guys already know that stuff
1969c10joe is offline   Reply With Quote
Old 09-22-2016, 03:32 PM   #36
1969c10joe
Registered User
 
Join Date: Sep 2016
Location: lompoc ca
Posts: 228
Re: HEI ignition secrets

so i will find out when my my adjustable vac starts to kick in i will watch my vac gauge when driving ill add up the advance numbers and report back to you i will test and record manifold and ported results wish i could drop everything and do.it.now
1969c10joe is offline   Reply With Quote
Old 09-22-2016, 06:43 PM   #37
1969c10joe
Registered User
 
Join Date: Sep 2016
Location: lompoc ca
Posts: 228
Re: HEI ignition secrets

thankyou Mr Geezer for your input due to the fire and ash in the air my eyes are burning(unless that kid turner is idling nearby) i have to postpone my test.
1969c10joe is offline   Reply With Quote
Old 09-22-2016, 06:51 PM   #38
1969c10joe
Registered User
 
Join Date: Sep 2016
Location: lompoc ca
Posts: 228
Re: HEI ignition secrets

I believe my test will be thorough and accurate and should be very interesting to all members maybe even surprising to some I will test and record results from manifold and ported vacuum.judging from the interest i better do a good job
1969c10joe is offline   Reply With Quote
Old 09-22-2016, 06:56 PM   #39
1969c10joe
Registered User
 
Join Date: Sep 2016
Location: lompoc ca
Posts: 228
Re: HEI ignition secrets

Mr. Geezer back where i was raised addressing a man with Mr is a sign of respect. Thankyou for your valuable experience and input
1969c10joe is offline   Reply With Quote
Old 09-23-2016, 08:17 PM   #40
1969c10joe
Registered User
 
Join Date: Sep 2016
Location: lompoc ca
Posts: 228
Re: HEI ignition secrets

and to vette vet thankyou for taking the time to post
1969c10joe is offline   Reply With Quote
Old 11-10-2016, 12:34 PM   #41
Mike_The_Grad
Registered User
 
Mike_The_Grad's Avatar
 
Join Date: Oct 2013
Location: Santa Paula, CA
Posts: 224
Re: HEI ignition secrets

Any chance that you were able to resolve your issue?
__________________
1972 C/10 LWB
Instagram: Mike_The_Grad
Mike_The_Grad is offline   Reply With Quote
Old 11-10-2016, 01:30 PM   #42
demian5
Registered User
 
demian5's Avatar
 
Join Date: Aug 2016
Location: Lake Forest, CA
Posts: 1,068
Re: HEI ignition secrets

Quote:
Originally Posted by 1969c10joe View Post
I have a goodwrench 350 with accel distributor and adjustable vacuum advance edelbrock 1405.I would like your ideas on custom ignition curve right now im running conservative 12 static 20 distributor 16 vac my starter doesnt like 13. Ihave almost 20 in. hg people doubt me when i say that.This my daily driver work truck

Lock out (disconnect) the vacuum advance and time it to 38 degrees total advance at about 2500 rpm (or more, just watch for when it stops advancing), then adjust down or up from there.
__________________
"Work hard, use your vacation days."
1970 C15 GMC Long Bed
1986 C20 Scottsdale (grandpa truck)
1964 Impala SS
1959 Austin Healey 100-6 BN6
C10s of OC
demian5 is offline   Reply With Quote
Old 02-10-2018, 10:08 AM   #43
crabman
Registered User
 
crabman's Avatar
 
Join Date: Nov 2017
Location: Blairsville, GA
Posts: 14
Re: HEI ignition secrets

I would like to share my experience with timing my 69 C10 396 TH400 bone stock with HEI and QJet. I read several threads and Googled the topic and did some experimenting of my own. My truck was set at 10* initial and 32* total with 20* of vacuum advice thru ported vacuum. The truck ran fine no complaints. I decided to change to manifold vacuum for the vacuum advance and immediately the truck idled smoother. I drive the truck and it was better down low and transitioning to midrange. I brought it back and bumped my initial timing to 12* for a total of 34* timing and left the vacuum advance at 20* and manifold vacuum. After all of that i had to reset the idle speed to 750RPM and the QJet was rich so I adjusted the mixture screws until I got it to idle at 750 RPM and smooth. The timing with the vacuum advance hooked up and idling at 750 is 32*. The truck is much smoother low and mid range and it starts super quick. I am a believer in MANIFOLD vacuum for vacuum advance after this experiment. After driving like this for a while I will try more initial timing and see what it does but for now it is a nice improvement.

Edit: All my timing is in by 2800 RPM
__________________
1969 CST/10 396

Last edited by crabman; 02-10-2018 at 10:15 AM. Reason: forgot to add something
crabman is offline   Reply With Quote
Old 02-12-2018, 11:05 PM   #44
mike16
Registered User
 
Join Date: Dec 2009
Location: bisbee, arizona
Posts: 1,228
Re: HEI ignition secrets

I always used the vacuum advance from a 75 corvette
mike16 is offline   Reply With Quote
Reply

Bookmarks

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Forum Jump


All times are GMT -4. The time now is 04:58 PM.


Powered by vBulletin® Version 3.8.7
Copyright ©2000 - 2018, vBulletin Solutions, Inc.
Copyright 1997-2013 67-72chevytrucks.com