Re: Need some clarification on distributor tuning.
[Re: 68CoronetRT]
#1630366
06/08/14 01:17 AM
06/08/14 01:17 AM
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Joined: Jun 2003
Posts: 52,972 Romeo MI
MR_P_BODY
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Master
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Posts: 52,972
Romeo MI
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Start with one thing at a time.. unplug the vac and plug the carb port and see when and how much mech timing you have
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Re: Need some clarification on distributor tuning.
[Re: 68CoronetRT]
#1630368
06/08/14 02:01 AM
06/08/14 02:01 AM
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Joined: Apr 2005
Posts: 12,271 Overpriced Housing Central
RobX4406
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Quote:
My vacuum is nearly zero at idle. It goes to 17 hg when I rev the motor.
Mr_P_Body, I will give that a go tomorrow after work.
You likely have the gauge hooked up to the wrong port.
More initial timing.
The allen wrench only changes the amount of vacuum required to activate the can. Doesn't change the amount
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Re: Need some clarification on distributor tuning.
[Re: RobX4406]
#1630369
06/08/14 02:07 AM
06/08/14 02:07 AM
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Joined: Jun 2003
Posts: 52,972 Romeo MI
MR_P_BODY
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Master
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Romeo MI
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Quote:
Quote:
My vacuum is nearly zero at idle. It goes to 17 hg when I rev the motor.
Mr_P_Body, I will give that a go tomorrow after work.
You likely have the gauge hooked up to the wrong port.
More initial timing.
The allen wrench only changes the amount of vacuum required to activate the can. Doesn't change the amount
Yep he is reading above the blades
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Re: Need some clarification on distributor tuning.
[Re: 68CoronetRT]
#1630371
06/08/14 01:33 PM
06/08/14 01:33 PM
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Joined: Jun 2003
Posts: 52,972 Romeo MI
MR_P_BODY
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Master
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Romeo MI
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I dont know of any but I havent looked... I play with the dist in a few different segments.. first when on the engine I figure out what the engine wants for base timing then what the engine wants for total timing.. then I put the dist on a dist machine(I have access to a old one).. I test it for when the timing starts to come in at(thats adjusted with the springs).. then I test for the total mech advance.. thats adjusted by the slots... the last dist I got has adjustable advance with just a simple screw(I believe its a MP part).. but if you have slots then its weld up the slots to limit the total mech timing.. the vac pot can have too much travel and pull more timing than needed and you can adjust that travel... if you want to slow the vac to the can you can get small in line vac restrictors to slow it down but it just slows it.. the vac advance is more of try it and see thing since your not on a dyno.... but if you think about using a stock dist on a modified engine your increasing the base timing and all of the numbers move up by that amount(difference of the stock base timing to the new modified base timing) so that dist need to be modified
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Re: Need some clarification on distributor tuning.
[Re: MR_P_BODY]
#1630372
06/08/14 05:14 PM
06/08/14 05:14 PM
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Joined: Jan 2003
Posts: 27,421 Balt. Md
383man
Too Many Posts
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Also remember the vacum advance is mostly for part throttle driving when intake vacum is still high. It like ported vacum will drop to about 0 at wide open throttle as the only vacum that wont is venturi vacum which is not a real strong signal but strong enough to work vacum secondary carb diaprhams. Your total mechanical at 36 is not a bad starting point and may be fine for your combo depending at what rpm its all in. My self my dist does not even have a vacum advance as its basically a race dist thats all mechanical advance and I have full mechanical avdance by about 1800 rpm. But the vacum advance is good for a street car as it helps gas milage and helps part throttle power and most cars have 50 to 55 total with all mechanical and vacum advance in. But when you floor it you will only have the mechanical advance because as we said at full throttle you wont have any vacum to work the vacum advance since the throttle plates are wide open there will be no vacum in the intake. It may help you if you know that what they call ported vacum that alot of vacum advances are hooked to are actually intake vacum but the port they hook to is above the throttle plate so it will have no vacum at idle with the throttle plates closed because the port is above the throttle plate. As soon as you step on the gas a bit it uncovers the port and the vacum advance starts working. But it is intake vacum that will drop to 0 when floored. Intake vacum ports are usually refered to that when the vacum port is below the throttle plate or anywhere on the intake as that will be full intake vacum at idle with the throttle plates closed becuase the intake vacum ports are below the throttle plates. Ron
Last edited by 383man; 06/08/14 05:26 PM.
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Re: Need some clarification on distributor tuning.
[Re: 383man]
#1630373
06/08/14 07:18 PM
06/08/14 07:18 PM
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Joined: Mar 2007
Posts: 3,298 West Coast, USA
jbc426
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There is a lot of misconception about how all this works, because of you either view it from a performance perspective or from an emissions perspective.
For performance, the vacuum advance MUST be hooked to a port below the throttle blades for it to work correctly. If the port you are hooking it to is at or near "0" until you rev the motor; you have it hooked above the throttle blades and its on the wrong port.
You want it hooked to a port that has full vacuum at idle and subsequently cruising speed. When the throttle is opened, the manifold vacuum will instantly drop towards or all the way to zero depending on how far you stomp on it.
At that split second, all the added timing from your vacuum advance that was maxed out at idle and/or at cruising speed drops to no added timing via the vacuum advance pod. It saves the motor from detonation as you roll-it-on harder than a mild acceleration, floor it, go up a hill at heavy throttle under load in too low a gear, or just punch it.
At that point, only your mechanical advance, along with your initial timing is dictating your total advance.
It's easy when you think of it this way.
Also, what ever your cruise rpm is on the highway, ideally (if you don't have too much compression) all your mechanical advance should be all in (READ: use the correct advance springs to allow full advance by your normal cruise RPM) When you are at light cruising speed of the freeway or just idling in the driveway all your vacuum advance will be in for maximum fuel mileage and dramatically increased off-throttle responsiveness. Typically, your timing will be up around 50 to 52 degrees total with the vacuum advance hooked up and around 32 to 36 total when it is not. There are a lot of variables at play that dictate those final optimal timing choices like fuel quality, compression (both static and dynamic, altitude, combustion chamber and piston design etc, etc.
Last edited by jbc426; 06/08/14 07:20 PM.
1970 Plymouth 'Cuda #'s 440-6(block in storage)currently 493" 6 pack, Shaker, 5 speed Passon, 4.10's 1968 Plymouth Barracuda Convertible 408 Magnum EFI with 4 speed automatic overdrive, 3800 stall lock-up converter and 4.30's (closest thing to an automatic 5 speed going)
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Re: Need some clarification on distributor tuning.
[Re: jbc426]
#1630374
06/08/14 11:13 PM
06/08/14 11:13 PM
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Joined: Jan 2003
Posts: 27,421 Balt. Md
383man
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You want it hooked to a port that has full vacuum at idle and subsequently cruising speed. When the throttle is opened, the manifold vacuum will instantly drop towards or all the way to zero depending on how far you stomp on it.
This can be misleading to some. If you just step on the throttle 1/4 to almost half way down you will still have a strong intake vacum signal when cruising. If you go past half throttle to maybe 3/4 then yes the intake vacum is dropping off and of course will drop to about 0 when at wide open throttle. I have seen it alot over the years when testing eng vacum for clogged exh systems and so on. And I dont mean it to be smart its just I see alot of people think as soon as you step on the gas a bit your vacum is dropping to zero which when you go right to almost 1/2 throttle the vacum drops a tad and then will stabilize at about the same vacum as intake vacum is at idle if you stay at that throttle posistion cruising along. Dont matter if its ported or intake as they are both intake vacum anyway just one is above the throttle blade and one is below. When cruising you usually wont loose the vacum advance until you go past half throttle or more when the vacum drops. Ron
Last edited by 383man; 06/08/14 11:15 PM.
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Re: Need some clarification on distributor tuning.
[Re: 68CoronetRT]
#1630376
06/09/14 02:04 AM
06/09/14 02:04 AM
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Joined: Jun 2003
Posts: 52,972 Romeo MI
MR_P_BODY
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Master
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Posts: 52,972
Romeo MI
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Quote:
Okay, so I'll plug the upper vacuum port on the carb and run the vacuum advance on the lower one.
Hooking the vacuum gauge to this port will definitely help me in fine tuning the idle mixture screws as I couldn't get any change at all on the upper port - but I understand now why that is so.
I'll also find the rpm where the mechanical is all in and the amount of mechanical advance.
If I am understanding y'all correctly, it is the initial and mechanical timing combined that should be about 36 degrees?
Might take me a couple of days to get this done since my schedule is packed with necessary work related things.
Thanks for taking the time to educate me.
Correct on base and the mech timing together for about 36
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Re: Need some clarification on distributor tuning.
[Re: RobX4406]
#1630378
06/09/14 12:56 PM
06/09/14 12:56 PM
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Joined: Mar 2007
Posts: 3,298 West Coast, USA
jbc426
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I copied the boat guys who run blowers, and use a switch to kill the 12v circuit to the ignition while I begin to crank the engine. Once its spinning good after a second or so, I flip the 12v ignition switch and she lights every time. Most of the time, I only have to do this when its really hot out, but it's a lot cheaper than a timing start retard. I run 22 initial 36 total, all in by 2000 rpm. No vacuum advance. I only have 7 to 8 inches of vacuum at idle as it is. Plus no one makes and adjustable one that's decent.
Although, I did here that the Firecore vacuum advance distributors are being blueprinted and the range of initial timing adjustment available are being improved by the man at Four Seconds Flat. If I could get 21 initial and 36 total with an added vacuum advance that brings me up in the 45 to 50 total advance at cruise 2200 rpm, I'd be interested.
Eventually, I may just drop the nearly $400 on the newer PC programmable MSD unit and lock out my distributor, but that still leaves me with no vacuum advance for increased fuel efficiency in 5th gear.
1970 Plymouth 'Cuda #'s 440-6(block in storage)currently 493" 6 pack, Shaker, 5 speed Passon, 4.10's 1968 Plymouth Barracuda Convertible 408 Magnum EFI with 4 speed automatic overdrive, 3800 stall lock-up converter and 4.30's (closest thing to an automatic 5 speed going)
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Re: Need some clarification on distributor tuning.
[Re: jbc426]
#1630379
06/09/14 01:17 PM
06/09/14 01:17 PM
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Joined: Apr 2005
Posts: 12,271 Overpriced Housing Central
RobX4406
I Live Here
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I Live Here
Joined: Apr 2005
Posts: 12,271
Overpriced Housing Central
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Quote:
I copied the boat guys who run blowers, and use a switch to kill the 12v circuit to the ignition while I begin to crank the engine. Once its spinning good after a second or so, I flip the 12v ignition switch and she lights every time. Most of the time, I only have to do this when its really hot out, but it's a lot cheaper than a timing start retard.
Popular method when run a magneto.
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Re: Need some clarification on distributor tuning.
[Re: Cab_Burge]
#1630381
06/11/14 06:18 PM
06/11/14 06:18 PM
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Joined: Jul 2003
Posts: 12,132 Cleveland
sunroofgtx
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FBO is not a dealer, but you can call and get some specific spring advance rates. Also, Ron Wilson or Bob George will be happy to discuss exacts to your needs. Thanks.
Join the quickest team in motorsports. Team FireCore. CustomWiresets.com
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Re: Need some clarification on distributor tuning.
[Re: sunroofgtx]
#1630382
06/12/14 01:31 AM
06/12/14 01:31 AM
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Joined: Jul 2003
Posts: 5,188 upstate western ny
sogtx
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Quote:
FBO is not a dealer, but you can call and get some specific spring advance rates. Also, Ron Wilson or Bob George will be happy to discuss exacts to your needs. Thanks.
fbO
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Re: Need some clarification on distributor tuning.
[Re: Cab_Burge]
#1630383
06/12/14 12:27 PM
06/12/14 12:27 PM
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Joined: Apr 2006
Posts: 3,675 Akron, Ohio U.S.A.
roadhazard
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Quote:
Most of the stock Mopar distributors I have worked on have the amount of advance stamped into the bottom of the advance plate, most of mine say 13, look at yours and go from there
And let's just make clear that number 13 you are throwing out there is "distributor degrees". That number needs to be multiplied x2 for "crankshaft degrees". So in fact the distributor your working on has a total of 26* mechanical advance built in.
As for vacuum advance. The allen wrench adjustment ONLY tailors the "rate" at which the additional advance comes in. It does nothing for the total amount it moves the advance plate in the distributor.
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