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Timing Mech vs Vac advance Good Read

Questions, answers, tips and tech on drivetrain issues.

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406Regal

Post by 406Regal » Tue Jun 20, 2006 2:03 am

kybowbender wrote:I just purchased a new holley 650 double pumper and the instructions say to hook the vacuum advance on the ported vacuum port up above the idle mixture screw. After reading this I'm kind of confused. A reputable company like holley don't know where you are suppose to hook the vacuum advance?


If your Gonna use the Vacuum advance this is where you need to hook it up,
It's called Ported Vacuum,
The Port Holley is referring about Makes Little to any Vacuum at Idle,As RPM's Increase so does the Vacuum at this Port 8)

kybowbender

Post by kybowbender » Tue Jun 20, 2006 6:38 pm

What I was saying is that holley instructions conflict with the post that starts this thread. I have tried it both ways and I have to say that manifold vacuum seems to give better thottle response and a smoother idle at lower rpms. Right now I am at 15 degrees base and 36 degrees at 3200 rpm with vacuum advance disabled. When I hook up the vacuum advance my timing is at 32 degrees at 1000 rpm. Idle mixture screws at 2 turns out.

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LS6 Tommy
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Post by LS6 Tommy » Tue Jun 20, 2006 6:59 pm

kybowbender wrote:What I was saying is that holley instructions conflict with the post that starts this thread. I have tried it both ways and I have to say that manifold vacuum seems to give better thottle response and a smoother idle at lower rpms. Right now I am at 15 degrees base and 36 degrees at 3200 rpm with vacuum advance disabled. When I hook up the vacuum advance my timing is at 32 degrees at 1000 rpm. Idle mixture screws at 2 turns out.



Do you have a stock emissions distributor? If so, that's why your advance comes in too soon on manifold vacuum.

Tommy
20k mile '80 Malibu, currently undergoing long term (aka no money) factory style install LS6 454, Cowl Induction, Legend LGT 700 5 speed. Full Global West suspension, 17" N90 wheels, 12" front/11" rear disc brakes, 9" 3.70 Auburn Pro posi.

"The older I get, the faster I was"

kybowbender

Post by kybowbender » Tue Jun 20, 2006 7:06 pm

I have a gm performance HEI destributor that I ordered from summit. I thought that the vacuum advance was suppose to be in at idle and drop out as the throttle opens.

406Regal

Post by 406Regal » Thu Jun 22, 2006 11:11 pm

[quote="kybowbender"]I have a gm performance HEI destributor that I ordered from summit. I thought that the vacuum advance was suppose to be in at idle and drop out as the throttle opens.[/quote]

If you run Vacuum advance there is Not suppose to be any Vacuum to the Vacuum Port of Distributor until engine is under Part throttle that is the reason Holley recommends This Port.

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Jeff.Mc.KC
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Post by Jeff.Mc.KC » Thu Aug 31, 2006 12:02 pm

So just how high does your timing get going through the lights letting off and you have Full Mech. Static and Vac adavance all at once ?????

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Post by MALIBU7902 » Thu Feb 22, 2007 8:55 pm

kybowbender wrote:What I was saying is that holley instructions conflict with the post that starts this thread. I have tried it both ways and I have to say that manifold vacuum seems to give better thottle response and a smoother idle at lower rpms. Right now I am at 15 degrees base and 36 degrees at 3200 rpm with vacuum advance disabled. When I hook up the vacuum advance my timing is at 32 degrees at 1000 rpm. Idle mixture screws at 2 turns out.


You are right these people didnt read the post right or all the way.
Great info by the way.
I am dealing with this right now setting up my brothers ford truck.
New dist. and I couldnt figure out why after setting the timing with no advance it would be fine then plugging it back in timing was at 30 at idle but now I know thats what its supposed to be with vac. advance.
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Post by Dom87SS » Tue Mar 13, 2007 7:00 am

please BAN Edsterder8
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Post by 78_Elky » Thu Jun 21, 2007 12:26 am

this is really interesting, I am in the LONG process of tuning my car and trying to dial in the timing. This article really cleared up what to do about the port, and now I am kind of thinking I need a new vacuum advance can, as my car rarely sees over 14" of Hg. Maybe that is why my engine surges at idle? If I am on the right track let me know. Thanks.
-Josh
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Post by malibuguy » Wed Sep 26, 2007 8:57 am

i printed this out last night, & applied it to my DD

it always suffers from detonation upon medium to high engine loads/ throttle tip in, but it goes away upon full throttle

i had the timing set at 4* initial, with the factory, dual vacuum set up...it has 2 lines coming from the carb, one from P.V. & one M.V. (ported vacuum & manifold vacuum), the M.V. goes to a little valve/junction, that has 2 lines going to a temp senser on the Tstat housing, then it goes back towards the distributor, but right before the dizzy, the M.V. line & the P.V. line go into a little can-like junction, then from that, a short single line to the vacuum advance can on the dizzy

my only guess with that system, is that when the engine is cold, it uses the ported vacuum set up, until its warm up, & i think its also there help cat light off since the timing is much less...i think this explains why it runs like ANUS when cold, off idle stumbles, sputters, it barely gets out of the driveway & neighborhood

with the engine warm, it had vacuum at the dizzy at idle...so i think i'm correct on how that system works

well, anyways, i kicked the timing up to around 10* (can't really read the tab) initial, & i bypassed the dual vacuum set up, so its striaght M.V. to the dizzy, BTW the dizzy only has about 15* of rpm advance, & with the vacuum hooked up,at idle its somewhere over 20* (about .75-1.0" past the end of the tab, haha) & the car runs much much better, definetly more midrange torque & top end power, the car almost doesn't suck anymore, BUT it pings more often @ lighter-mid engine loads...but not as loudly, so i think i took a step in the right direction, as the pinging is less intense...& it was much easier to drive this morning cold

also, when the EGR flows, doesn't it reduce the burn time of the air fuel mixture right? i don't think my EGR is working, i removed it & clean the ports & tested it by directions of a Haynes manual, & it does not flow anything, the EGR flows during cruise/light engine loads, am i correct? so maybe the defective EGR is now causing my detonation now, as i got much more timing, but the pinging went down a little

i think i'm going to get a new EGR anyways today...give me something to do

please correct me if i got anything wrong

-greg
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Post by 200KSS » Fri Oct 19, 2007 9:45 am

Echlin #VC-1810 advance can

My local NAPA has been trying to get one of these for the past month, even special ordered one. The p/n shows up in their system, but the order always comes back as a discontinued part, not available. Has anyone bought one recently? If so where and how? Thanks.
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Post by WhiteTrash79MC » Fri Oct 19, 2007 5:52 pm

200KSS wrote:Echlin #VC-1810 advance can

My local NAPA has been trying to get one of these for the past month, even special ordered one. The p/n shows up in their system, but the order always comes back as a discontinued part, not available. Has anyone bought one recently? If so where and how? Thanks.
I ran into the same problem when I tried to get one... :x
79 Monte Carlo Landau-- 327 with 200k / 3 spd Saginaw / 7.5 Auburn Posi and 3.73's Iceman Xmem, Torque Tech 3 inch exhaust. Spohn upper control arms. 18x8 wheels with 245/45R18

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Post by NEW2MALIBU » Sun Dec 23, 2007 12:39 pm

I got a great deal on some parts. MSD pro billet dist, hvc coil, and digital 6 plus box. I was under the impression that msd dealt with this problem for a street car.
Below 3,300 rpm the Digital-6 Plus produces a series of sparks that glows in the cylinder for up to 20° of crankshaft rotation. This incredible heat ensures combustion to produce great power, quick throttle response, smooth idle and quick starts.

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LS6 Tommy
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Post by LS6 Tommy » Mon Dec 24, 2007 8:37 am

MALIBU7902 wrote:
kybowbender wrote: Right now I am at 15 degrees base and 36 degrees at 3200 rpm with vacuum advance disabled. When I hook up the vacuum advance my timing is at 32 degrees at 1000 rpm.

I am dealing with this right now setting up my brothers ford truck.
New dist. and I couldnt figure out why after setting the timing with no advance it would be fine then plugging it back in timing was at 30 at idle but now I know thats what its supposed to be with vac. advance.
My guess is you're both using unported vacuum on emissions calibrated distributors that need to be on ported vacuum sources.

Tommy
20k mile '80 Malibu, currently undergoing long term (aka no money) factory style install LS6 454, Cowl Induction, Legend LGT 700 5 speed. Full Global West suspension, 17" N90 wheels, 12" front/11" rear disc brakes, 9" 3.70 Auburn Pro posi.

"The older I get, the faster I was"

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