![]() |
|
![]() |
#1 |
Senior Member
![]() Join Date: May 2002
Location: mt juliet, tennessee, usa
Posts: 237
|
The Vacuum Deal
Greetings All:
I'm running a 69 C10 Pickup with a 350CID engine that uses a 600cfm Holley 4 barrel. I'm posting a link to a pic of the engine below: http://mywebpages.comcast.net/wxgeek/holley_600cfm.jpg Ok, here's the question. When I disconnect the vacuum advance line from the distributor I see NO change in the timing mark for number one cylinder. The line is connected per Holleys instructions to the Vacuum Advance Port. The port below is the full manifold vacuum port that the modulator for the transmission (TH350) is connected to. So whats the deal...Is the vacuum advance can bad or what? Engine timing at idle with the vacuum advance line disconnected is around 11 deg BTDC. Jim M. Mt Juliet TN |
![]() |
![]() |
![]() |
#2 |
Resident Young Old Dude !
Join Date: Jul 2001
Location: Nevada
Posts: 1,948
|
You are either hooked up to the wrong vucuum port or, the diaphragm in the advance canister is bad.
|
![]() |
![]() |
![]() |
#3 |
Senior Member
Join Date: Dec 2001
Location: Redding,CA...USA
Posts: 4,736
|
Hi..your hooked up on ported vacuum right? This port has no vacuum at idle, it builds vacuum as the throttle is opened..I use the ported vacuum for my th350 and the full vacuum (the lower port) on the vacuum advance
__________________
It's called "drag racing" if they called it "tic..tic..WHAM!..BANG! F*&K!!!", they'd have to keep the magazines under the counter with the other men's publications click the clicky to join the site.... http://67-72chevytrucks.com/vboard/payments.php 67 lwb..first hotrod in 25 years..540 best ET is 9.45 @ 141.44 Anderson,CA |
![]() |
![]() |
![]() |
#4 |
Registered User
Join Date: May 2000
Location: Storm Lake, Ia
Posts: 1,449
|
I am not a motor head but I don't understand why you would want full vacuum at idle. Is'nt the whole idea of vacuum advance to increase timing at higher speeds (ie higher vacuum)?
If you hook it up to full vacuum port isn't that the same as just advancing the timing to that point initially and skipping vacuum advance unit?Like I said I am no motor head but was just wondering about this
__________________
|
![]() |
![]() |
![]() |
#5 |
Senior Member
Join Date: Dec 2001
Location: Redding,CA...USA
Posts: 4,736
|
not quite..if you have your initial at 10 deg. then add full manifold vacuum limited to 10-12 degrees this gives you 20-22 degrees at idle...where your motor likes it...then when you accelerate the vacuum drops off and the mechanical picks up..giving you 20-22 degreees of mechanical advance plus the initial of 10..giving you a total of 32 at 3000 rpm..now if you use ported vacuum..you will have 10 deg initial plus 20 degrees of vacuum plus 20 degrees of mechanical thats 50 degrees at 3000 rpm..can you say detonation??? GM used ported vacuum with real stiff springs on the mechanical for emissions...they would have 2-4 deg. of initial with the vacuum doing all the work until 5000 rpm...you will find more performance with non proted vacuum....
Jim
__________________
It's called "drag racing" if they called it "tic..tic..WHAM!..BANG! F*&K!!!", they'd have to keep the magazines under the counter with the other men's publications click the clicky to join the site.... http://67-72chevytrucks.com/vboard/payments.php 67 lwb..first hotrod in 25 years..540 best ET is 9.45 @ 141.44 Anderson,CA |
![]() |
![]() |
![]() |
#6 |
Senior Member
Join Date: Jun 2001
Location: Shelbyville, KY
Posts: 3,269
|
Assuming you set your initial vacuum at let's say 10 degrees advanced with the vac advance disconnected. Now if you have the original stock ignition, you would hook up to the full manifold vacuum and you should see the timing change for more advance. That would be correct ~~~~~~~. IF you have HEI ignition, you should hook up to the ported vacuum which would not produce any advance at idle as discussed above.
I would try the ---hook up to manifold vacuum with a timiing light--- to check the advance can on the distributor. If you do not get timing change = bad advance mechanism. Now a lot of what has been said depends on things being original like springs on the timing weights in the distributor. So, sometimes our recommendations will need tweeking to allow for 30+ years of some butthead modifications. Huck |
![]() |
![]() |
![]() |
#7 |
Fabricate till you "puke"
Join Date: Jun 2002
Location: Ill
Posts: 9,403
|
If you are running a stock or very mild cam , the vac can will probably do better hooked to ported vacumn. for the guys running hotter cams, fat carbs ,ect......i feel you will do better with the vac advancehooked to full manifold source at the carb. To set up this way, you will need to do some recurving & go to an adjustable can(I run a Crane can). I run 14 initial, 34 total(with the can unhooked & plugged). The can is set to give 8 degrees, & hooked to manifold source. This brings timing @ idle to the 22 degrees (with can hooked), that Big jim was talking about, & totals @ 42degrees with can hooked & no load. I am running very close to 10 to 1 on compression, so it was nessissary to trim the vac timing back a little from that 10-12 degree figure. To answer the original Q, if you hook the vac can to manifold vac......& the timing doesnt change, the can is bad. good luck.......crazy AL
![]()
__________________
69 longhorn,4" chop,3/5 drop, 1/2 ton suspension/disc brakes,1 1/2" body drop,steel tilt clip, 5.3/Edelbrock rpm intake/600 carb, Hooker streetrod shorties,2 1/2" exhaust/ H pipe/50's Flows , 6 spd Richmond trans,12 bolt/ 3.40 gears.... |
![]() |
![]() |
![]() |
#8 |
Senior Member
![]() Join Date: May 2002
Location: mt juliet, tennessee, usa
Posts: 237
|
Update on timing/vacuum deal. Got a good vacuum
meter. Hooked to manifold port on engine reads 15 in at idle and goes up to 22 inches at 3000 rpm. Hooked to port vacuum above the butterflys and reads about 1 in at idle and goes to around 22 inches at 3000 rpm. Disconnected vacuum advance line from carb and connected it to my hand operated vacuum pump. Applied about 10 in of vacuum and while watching timing light on timing tab the spark advanced to about 18 deg BTDC. So I would have to assume that the vacuum can is working. Thanks to Huck and others for cluing me in on the HEI systems not have any advance at idle. All the engines I had fooled with always had a few degrees of advance at idle because they always tell you to disconnect the vacuum advance line before checking the ignition timing. this is the first engine that I've had that had an HEI distributor. Bye the bye...I'm posting a link to a pic of my distributor. It a little out of focus, but its a Delco-Remy. It has some markings on the cap but none of them are model numbers/serial numbers. Is anybody familiar with this distributor? Know what model number it is? Link is: Pic of my distributor |
![]() |
![]() |
![]() |
#9 |
Senior Member
Join Date: Dec 2001
Location: Redding,CA...USA
Posts: 4,736
|
Im glad it worked out for you...but...the statement that HEIs do not have vacuum at idle is erronous...It depends on the setup..I have a HEI hooked to manifold vacuum, and it works great..it depends if you want performance or not, as crazylonghorn stated, if you have realitivly stock set up..the ported vacuum will work fine..but as soon as you step up to a performance build, you'll want to try the manifold vacuum
Jim
__________________
It's called "drag racing" if they called it "tic..tic..WHAM!..BANG! F*&K!!!", they'd have to keep the magazines under the counter with the other men's publications click the clicky to join the site.... http://67-72chevytrucks.com/vboard/payments.php 67 lwb..first hotrod in 25 years..540 best ET is 9.45 @ 141.44 Anderson,CA |
![]() |
![]() |
![]() |
#10 |
440 american Horses
Join Date: Mar 2001
Location: Anoka, MN USA
Posts: 470
|
Your distributor looks like just a stock setup. Might wanna look into an adjustable vacuum advance can so you can tweak the timeing a little.
__________________
Seth Petro 1969 Chev Short Step 425hp 350, TH400, big tires, fast truck 1979 Pontiac Trans Am 1991 Saturn SL1 - gas mileage! (and free) 1977 Buick LeSabre - for sale May America bless God, and may God bless America ![]() |
![]() |
![]() |
![]() |
#11 |
Thats the Hillbilly way
Join Date: Jul 2001
Location: Torrance,Ca
Posts: 5,980
|
[QUOTE][i]...I'm posting a link to a pic of my
distributor. It a little out of focus, but its a Delco-Remy. It has some markings on the cap but none of them are model numbers/serial numbers. Is anybody familiar with this distributor? Know what model number it is? The #'s should be stamped on the side of the Distributor if you can post them someone will tell you what model it came from . Good luck
__________________
BILL Torrance Calif 90504 Member DUF Club Member Old Farts Club 72 3/4ton Custom Camper BB402/400 trans Dynomax Cerama-coat headers , Hei distributor ,Edelbrock 1411 air,ps,pb,leafsprings ,98 chevy 60/40 seat,S10 shoulder belts tilt,3.54 Dana 60 rear. 16" Eagle wheels with LT265/75 16 tires,Gaylord Lid,H4 headlights with 100W relay conversion. " If I knew I was going to live this long I would have taken better care of myself " Marriage changes passion...suddenly you're in bed with a relative. A GUY'S PRAYER.... Lord, I pray for a nympho with huge boobs who owns a liquor store and likes to fish and hunt and has a Harley .Amen , |
![]() |
![]() |
![]() |
Bookmarks |
|
|