This is a hard one to follow. I would suggest the OP take a step back and spend some time learning and understand the basics of timing. This bling shotgun approach (while fun to watch) will not get you very far. Everything starts with the basics.
So very stuck...
- Thread starter R3N0
- Start date
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You're doing OK, fix the issue w/o worrying about vacuum advance first, then You can address adding it later. There are different "cans" that add different maximum amounts of timing, and then there is the spring tension adjustments, but none of that matters with Your right foot planted in the floorboards.
One thing that is lost is the that the fast-burn heads require less timing, & most J-X-U headed SBs end up with 33-34° total as best. Don't get obsessed trying to achieve a fictitious "ideal" total, & "best power" isn't always safe either, unless You've cc'd & matched all the chambers within 1-2cc's. I've seen 1 chamber cast shallow on a run of heads, in the case I often cite, 906's were run with the cyl.#3/#6 position chambers a good 5-6 cc shallow of the rest. Power timing will put six cylinders at their best, and two into detonation, because the 6 will mask the 2. Pulled heads on these & found the telltale pitting on the pistons 3&6, "running fine", so it's not worth pushing the max limit of timing....especially on a heavy ride.
P.S. I skipped a page, but be sure engine temp is normal & fuel isn't going a little lean on You.
Ironracer
Gearhead
Sounds like flex plate or a bad 'Verter
R3N0
Well-Known Member
Okay, so after some research and a bit of reducating myself on timing, I believe i have found my truck happy spot. Currently it seems to run best at 22* initial and 36* all in. Did some research on my distributor to find out I can adjust it without a recurve kit. Lossen a couple of screws and I can adjust how much all in I'm getting. Right now its 14* mechanical. Completely disconnected the vacuum advance as it's not really needed. At 22* initial im idling at 750 rpm and am pulling a steady 15hg of vacuum. Any higher on the initial and my vacuum starts getting erratic. Did a couple of pulls on our local hill and he gets right up and stays on it all the way up with no ping, or detonation detected. Now that my timing is set, I'm going to start fine tuning the carb. I may even turn up my line pressure 1 more turn to see if I get better response from the transmission... not that its bad... just feel like it can handle a bit more.
Dartswinger70
Well-Known Member
OP, you mentioned rattling, and you've tweaked timing, have you considered an imbalance? does the rattling happen at a certain RPM? does it rattle while sitting still or rolling down the road ,does it rattle during both?
R3N0
Well-Known Member
No the rattling went away, I believe it was caused by the advance. Too much on the all in, if I remember correctly it was somewhere around 42*. Once I realized that my distributor had a recurve plate installed, I simply limited my mechanical advance to 14* and moved my initial to 22*. That gave the motor the what it wanted and my distributor what it needed.
Dartswinger70
Well-Known Member
Oh good.It's good that you figured it out.
Ironracer
Gearhead
Love a Happy ending!
TT5.9mag
Two atmospheres are better than one
@R3N0 it sounds like you have a much better understanding of what’s going on now. And I’m glad you’re on the way to figuring it out. Once you get the basic tune in the distributor and the carb happy, because it’s a street car, you’ll want to add the vacuum advance back in. There is a drivability and mileage gain when you add the cruise timing back in.
R3N0
Well-Known Member
I've thought of that, but at this point I feel that pushing an 8,500 lbs truck down the road isnt really gonna see much gain with the can. I could be wrong though... wouldn't be my first time
512Stroker
We are all here because we are not all there.
If you care at all about fuel economy you will want your vacuum advance working properly.
You do know that most are adjustable.
Everything I've read whether ported or manifold VA, it's used(or should be) except on all out drag cars.
TT5.9mag
Two atmospheres are better than one
It will help, but like everything else it needs to be adjusted/tuned to the situation. An 8500lb truck will not need the same amount or curve from the VA can as a 2800lb duster.I've thought of that, but at this point I feel that pushing an 8,500 lbs truck down the road isnt really gonna see much gain with the can. I could be wrong though... wouldn't be my first time
R3N0
Well-Known Member
Yes I understand that it is adjustable, I believe the one I have runs from 6* to 15*, but even at 6* and putting the distributor back to 16* I'm still back at 22* with the can. Anything higher than 22* and my vacuum signal gets super erratic. So I have to ask, can the vacuum stay consistent with the can pushing my inital higher? Running the truck at 28* sounds like a bad idea. Am I wrong on this track of thinking?
TT5.9mag
Two atmospheres are better than one
Do some research on how to set up a vacuum can to ported vacuum if you want to use it on top of your current tune up. If you run it to manifold vacuum it will pull in timing at idle and you WILL need to recurve the distributor from where it is now.
R3N0
Well-Known Member
I see, I will do some more research, thank for the heads up on that.
I dont know much with timing, but also keep in mind the VA can is adjustable but to my knowledge the "adjustable" part is as to "when" the advance comes in, NOT how much. Now that being said you can modify the arm/slot on the VA to limit it. Hope that makes sense??
R3N0
Well-Known Member
Yes
R3N0
Well-Known Member
Okay, so first off I want to start this by saying I'm not asking to start an argument about which is better "ported" or "manifold". So let's not do that seen to many.
My question: when ported does the motor only use the amount of advance needed? As in when the motor is pulling say 1800 rpm does it only use the amount of advance needed at that point or does it try to use all advance regardless?
So if I turn my can all the way up as the advance comes in will it only pull the advance it needs or will I get the max 15*(on the can) the moment vacuum starts pulling?
My truck really likes the ported side, but I have kept it at its minimum of 8* to be safe and not get pinging. But that means at cruise I'm getting almost 30* should I attempt to push it till it pings and then back off a couple of * on the can?
My question: when ported does the motor only use the amount of advance needed? As in when the motor is pulling say 1800 rpm does it only use the amount of advance needed at that point or does it try to use all advance regardless?
So if I turn my can all the way up as the advance comes in will it only pull the advance it needs or will I get the max 15*(on the can) the moment vacuum starts pulling?
My truck really likes the ported side, but I have kept it at its minimum of 8* to be safe and not get pinging. But that means at cruise I'm getting almost 30* should I attempt to push it till it pings and then back off a couple of * on the can?
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R3N0
Well-Known Member
I know I can control when the timing comes completely in by putting a slightly heavier spring in. I wondering if by doing this I can slow the timing from just coming in all at once so the timing hits more of a curve... if that makes sense.
The spring does NOT just control when the vacuum adv starts coming in, it controls how much advance the can adds per the engine vacuum applied. If You're cruising at a steady speed & the ported vac is 13" on a slight grade, increasing the spring load adj. will reduce how far the can arm moves, and the °adv will reduce as well.
DON'T get all mixed up with the total timing You've already established, leave that alone, the total with vacuum is independent and needs dialed in as such. It will be a variable total at all part-throttle operation above the basic total You've set. What works best will depend on carb calibration, operating temps, burn characteristics ....too many to "guestimate". Trial & error aka test & tune are the only path to nailing it. Have fun!
DON'T get all mixed up with the total timing You've already established, leave that alone, the total with vacuum is independent and needs dialed in as such. It will be a variable total at all part-throttle operation above the basic total You've set. What works best will depend on carb calibration, operating temps, burn characteristics ....too many to "guestimate". Trial & error aka test & tune are the only path to nailing it. Have fun!
It doesn't come in "all at once" at all, it varies as the manifold depression goes up & down, the can arms are notched to control the maximum the can will add to the basic total You've set...the spring tension adjuster is the control of the "curve".
R3N0
Well-Known Member
My initial and total timing are set. What I'm asking is when ported does the carb act like a computer, basically only allowing as much timing needed at on time. Since the vacuum only comes in after acceleration, does this change affect how much timing is pulled? So if you open the can wide open but put a stiffer spring in, your initial timing should curve with the amount of vacuum being applied by the position of the throttle plates. Am I saying this correctly?
R3N0
Well-Known Member
This is what I thought, so a stiffer spring should act as the curve creator forcing the timing to not advance all at once. Allowing a person to set initial timing, then once accelerating more timing comes on as the motor advances in rpms and the throttle blades open up more, allowing more vacuum on the can therefore pulling more timing in that " curve". I can see it in my head... just cant seem to put it on paper as it were.
TT5.9mag
Two atmospheres are better than one
Vacuum isn’t an all in one time deal. It’s constantly variable with load and throttle opening. So the can will add timing based on that. But it will be “all in” at a certain vacuum number.
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