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Old 09-12-2012, 12:03 AM
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Help me correctly time a 360 magnum plz

I have a 300hp crate 360 magnum engine. I am running a dual plane edelbrock rpm air-gap intake manifold and a 600cfm manual choke edelbrock carburetor. I have a brand new mopar performance distributer that i purchased from Don over at Fbo systems, he curved and phased it for me.
Problem i am having is i cant get this engine to run right with the vaccum advance on manifold vaccum, wich is where don at fbo systems told me to run the vaccum advance off of.
I set my initial timing at 14 degrees and my total timing is at 32 degrees and i had the vaccum advance set to add 10 degrees of timing at 18 inches of vaccum, wich is how much vaccum my engine produces (18hg)
so with it set at 14 initial 32 total and 10 degrees from the vaccum advance on manifold vaccum the engine runs and sounds great, but when the engine is sitting still idling i hear thudding out the exhaust a slight (miss) every once in awhille while its an idle... I was running ngk v-power zfr5f11 plugs and decided to try a 1 step colder spark plug to see if that would help with the extra advance at an idle so i bought 8 brand new autolite 3923 plugs and that didnt seem to help at all, in fact seemed like it made it even worse.
I have tested my spark plug wires, everyone tested out at about 450 ohms of resistanceper foot. I even bought a tool that will tell you if the spark plug is working correctly with the engine running and my plug wires are working.
All of the wiring to my ignition is brand new, i am running a 4 pin Wells ignition module and a Wells 2 prong ballast resistor wich is a 1.0 ohm ballast my coil is a crane cams lx91 e-core style coil. My ignition module is grounded, i have an extra 10 gauage wire grounding my ignition module.
I am at a loss as to why this is happening, i put my vaccum advance back on the ported source and this issue mainly goes away but sometimes it comes back every once in awhile. I even dumped some atf down the carburetor while it was running just incase i had an exhaust valve that was sticking?
Just wondering if any of you guys have some suggestions for me, don at fbo systems told me that the whole problem is my carburetor and that i need a carburetor with a 4 corner idle circuit like a quickfuel ss series or a demon.
I dont have money for a brand new carburetor at the moment and this edelbrock i have is brand new.
I guess the first thing i am going to do is make a piston stop and make double sure that my balancer is reading correcly, thats the first thing i need to do.
I did a compression test on the engine and every cylinder was at 150psi.
I Dont know why my balancer would be reading wrong??? this engine doesnt even have 20 thousand miles on it. But i gess it is possible, i have pulled the distributer a couple different times, and i did have to find top dead center a few times on the compression stroke with my distributer pulled out of the engine. But i think my balancer only has 1 indicator line in i and it matches up with the zero everytime i check my initial timing with my dial back timing light.
But i know i need to first make sure the balancer is reading correctly then go from there. Any other suggestions would be great, this has been very frustrating. A friend of mine told me he thinks my balancer is reading wrong, he said my engine with 14 degrees initial timing plus another 10 degrees from the vaccum advance on manifold vaccum should not be too much timing for my engine, specially since i run 91 octane fuel.

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Old 09-12-2012, 12:17 AM
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If Don set up your distributor it is good and yes he sets them up the good way, for manifold vacuum. It will give you more timing at idle without affectin g hot starts.

Do you require a ballast with that ignition? Did Don say that was correct for the application.

Here is how I do my iginitions since the 80's..A 4 pin gm hei and stock mopar hei distributor with Dons curve kit. All you need and clean. About $80-90 total cost. Wires, kit, coil, module, etc.

Dont pour junkin your engine.

24 is not too much at idle or any other moment.

I have to stop editing, and it is hard to understand what questions to answer with all the information .

Yeah, don sells demon and quick fuel so he will go for the sale to correct your issue. That engine would be better off with a 600 afb. You sound new to carbs and that is the easiest one. What you have is fine, dont go buying stuff.
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Old 09-12-2012, 02:48 AM
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i was just trying to be as detailed as i could about whats going on and what i have... I know the number 1 thing i needto do is make sure my balancer is reading correctly. Since i have had the distributer out of this engine a couple times and have had to find top dead center on the compression stroke i guess it's possible my balancer got lost in the midst of all that and is reading wrong.
Cause if it is reading correctly, wich there is a good chance it is, then i dont know what in the world is causing the miss while its idling with the vaccum advance hooked up to manifold vaccum. Distributer is new brand new wires are good ignition wiring is good. I didnt buy any ignition module from don, just the distributer that he curved and phased. I'm running the stock mopar electronic ignition basically except i have a little hotter then stock coil and a little lower ohm rating ballast to feed the coil more.
Don suggested a new carburetor because he says the noise i am hearing from my exhaust is my engine telling me it wants more fuel, so i turned out the idle air mixture screws to richen it up and it does help, but when i do that i am not longer getting the highest vaccum reading at an idle, wich is how i was told to tune the idle air mixture screws on an edelbrock carburetor, with a vaccum gauage and set them to the highest vaccum reading.
Don told me the edelbrock carburetors are extremely limited on the idle circuit and they suck to try and dial inn perfectly, he said i would benefit tremandously with a carburetor that has a 4 corner idle circuit. I am not familiar with any carburetors except for the edelbrocks, theey are the only carbs i have ever owned, i can take apart and tune an edelbrock all day long, i'm sure i could easily learn how to tune a demon or a holley or a quickfuel if i bought one and started playing with it because thats how i taught myself to work on the edelbrocks.
Rigt now i am running .092 jets in the primary side and .092 jets in the secondary side of my edelbrock with the 7047 metering rods and the silver step up springs, i have my accelerator pump linkage in the middle hole. And i hve my idle air mixture scrwes tuned for the highest vaccum reading, i have also triple checked my floats and they are good. I guess i could try going a step up on the primary jets and see if that helps the car while at an idle but i thought i have read the primarry jets in the edelbrocks have no affect on the idle circuit... I will have to double check, i have 2 books on edelbrock carbs.
I'm going to make a piston stop and make sure my balancer is reading correctly, thats what i need to do first, if it is reading correctly then it will be interesting trying to figure out whats causing this miss with the vaccum advance on manifold vaccum.
I'm running the ngk v-power zfr5f11 plugs right now, (stock heat range) and i'm running 91 octane fuel and i'm also 4000 feet above sea level. But i will try and get a piston stop made asap and i'll let you know if my balancer was reading right or not and go from there.
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Old 09-12-2012, 09:14 AM
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You did not give any specifics. That is important. Like, what carb cfm, what is this noise, at rpm, how bad does it shake, if you pull a boot does it keep running, stuff like that. A miss could be hundred possibilities you need to investigate.

The 360/300 is a nice mild road engine. A baseline edelbrock 600 would be perfect, you would not need to cange jets and rods to get a god ride. The airdoor would compensate for hard throttle.

The jets and rods have no effect on idle. Edelbrocks idle feed is more than sufficient for the engine.

Is this the original harness, and do you have 12volts at the distributor / coil, if you took power from the coil + wire that has 9-10volts? How did you delete the mopar ignition box? run jumper wires from the battery to the coil + and - see if that cures it.

Did you see my picture, that is all the ignition equipment you need.

My oppinion, a 4 corner is not going to anything to fix this, that makes no sense. Don, will baseline a carb for you so that will be crossed off the list of possiblilities.
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Old 09-12-2012, 09:40 AM
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Put the timing at 24 mechanical at same idle, vacuum hose off and plugged. Is the problem the same? What tests have you done? Why the carb changes?

The balancer is keyed to the crank. That is not going to variate unless the outer balancer ring failed and the balancer needs replacement.

This is not one tooth off on the distributor gear is it, You state that you drove thousands of miles when did this start.
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Old 09-12-2012, 03:19 PM
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Quote:
Originally Posted by pjc360 View Post
I have a 300hp crate 360 magnum engine. I am running a dual plane edelbrock rpm air-gap intake manifold and a 600cfm manual choke edelbrock carburetor. I have a brand new mopar performance distributer that i purchased from Don over at Fbo systems, he curved and phased it for me.
Problem i am having is i cant get this engine to run right with the vaccum advance on manifold vaccum, wich is where don at fbo systems told me to run the vaccum advance off of.
I set my initial timing at 14 degrees and my total timing is at 32 degrees and i had the vaccum advance set to add 10 degrees of timing at 18 inches of vaccum, wich is how much vaccum my engine produces (18hg)
so with it set at 14 initial 32 total and 10 degrees from the vaccum advance on manifold vaccum the engine runs and sounds great, but when the engine is sitting still idling i hear thudding out the exhaust a slight (miss) every once in awhille while its an idle... I was running ngk v-power zfr5f11 plugs and decided to try a 1 step colder spark plug to see if that would help with the extra advance at an idle so i bought 8 brand new autolite 3923 plugs and that didnt seem to help at all, in fact seemed like it made it even worse.
I have tested my spark plug wires, everyone tested out at about 450 ohms of resistanceper foot. I even bought a tool that will tell you if the spark plug is working correctly with the engine running and my plug wires are working.
All of the wiring to my ignition is brand new, i am running a 4 pin Wells ignition module and a Wells 2 prong ballast resistor wich is a 1.0 ohm ballast my coil is a crane cams lx91 e-core style coil. My ignition module is grounded, i have an extra 10 gauage wire grounding my ignition module.
I am at a loss as to why this is happening, i put my vaccum advance back on the ported source and this issue mainly goes away but sometimes it comes back every once in awhile. I even dumped some atf down the carburetor while it was running just incase i had an exhaust valve that was sticking?
Just wondering if any of you guys have some suggestions for me, don at fbo systems told me that the whole problem is my carburetor and that i need a carburetor with a 4 corner idle circuit like a quickfuel ss series or a demon.
I dont have money for a brand new carburetor at the moment and this edelbrock i have is brand new.
I guess the first thing i am going to do is make a piston stop and make double sure that my balancer is reading correcly, thats the first thing i need to do.
I did a compression test on the engine and every cylinder was at 150psi.
I Dont know why my balancer would be reading wrong??? this engine doesnt even have 20 thousand miles on it. But i gess it is possible, i have pulled the distributer a couple different times, and i did have to find top dead center a few times on the compression stroke with my distributer pulled out of the engine. But i think my balancer only has 1 indicator line in i and it matches up with the zero everytime i check my initial timing with my dial back timing light.
But i know i need to first make sure the balancer is reading correctly then go from there. Any other suggestions would be great, this has been very frustrating. A friend of mine told me he thinks my balancer is reading wrong, he said my engine with 14 degrees initial timing plus another 10 degrees from the vaccum advance on manifold vaccum should not be too much timing for my engine, specially since i run 91 octane fuel.
Colder plugs are the wrong direction. Miss fires at idle are pretty common and are related on the surface to fuel distribution coming from the intake and or inconsistent ignition. Digging deeper, the idle miss is related to engine operating temperature, intake temperature, the shapes of the combustion chamber both those of the piston and chamber and the amount of space between the piston crown and the squish/quench deck of the head.

The problem is putting a burnable mixture in front of the spark plug that the plug can set on fire in the allocated time. Obviously the first thing is whether the spark is there. Cold plugs especially in a cold engine foul by developing a conductive layer of unburnt fuel and carbon on the insulator, so the spark energy is as likely to bleed down the insulator as it is to jump the electrode gap. A hotter heat range plug, a higher engine operating temp, and a multi-strike high energy ignition are helpful as is more spark advance at idle which has to come out someplace else. Also and this seems counter intuitive, is that too much advance will cause the miss, this is a case of putting in the spark before there is enough mixture density setting in front of the plug to carry the fire through the mixture. When the mixture density is low (this being a measure of fuel and air molecules trapped in a given space) there is considerable distance between molecules early in the compression cycle and always at closed throttle idle. So the fire if it catches at all will burn slowly compared to more open throttle positions and higher RPMs, the fire even if once caught in this situation can go out as it is unable to jump to the next set of consumable molecules. The point is a lot of things can and do go wrong sometimes in unexpected ways. By the way, I donít use resistance wires on anything; the closest I come is spiral wound wires. The electronics of modern ignitions are already creating a square wave profile so a resistance that takes off the lower voltage as it ramps up in a sine wave as in the good old days just isnít necessary.

A four corner idle circuit may, or not, pick up the issues by providing a more balanced fuel mixture between the front and rear cylinders, if indeed that is a problem. A lot of mayhem occurs within intake manifolds especially those that do not have exhaust heat under the plenum. In those cases mixture homogenization is dependent upon high RPMs to provide a sufficiently violent flow within the manifold to bust up fuel globules and mix them with air instead of forcing fuel vaporization with heat. For an engine without this feature it can be expected for it to miss at idle because there isn't enough agitation within the intake to break up large globules of fuel and these just will not burn. Combined with the low molecular mixture density this really gets to a problem at idle. Running the engine at a higher operating temperature can help some but the air gap manifold is a big part of this problem and getting it to heat up to any extent is difficult as it's not intended to get warm. Here-in lies a fundamental problem; while power goes up as the induction temperature goes down, this is a situation that is dependent upon mixture velocity and turbulence to bust up liquid fuel and globules travelling on the manifold walls. For a street engine, this is a situation that is not frequently encountered so it causes operating problems. The Magnum engine's heads like those of the Vortec at GM and the GT40's at Ford were designed for operation with fuel injection which breaks up the fuel with high pressure spray from the injectors, an advantage that carburetors and throttle body injection systems don't enjoy. You may be able to overcome this problem by richening the idle mixture or choking longer, but this will tend to foul the spark plugs and wash upper cylinder lubrication from the walls, pistons and rings. Getting rid of the air gap would help as it would allow you to run a warmer mixture which would fire better due to vaporizing the fuel before it gets to the cylinder.

Bogie
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