To advance or retard timing?

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Looking for some insight on whether or not advancing or retarding the timing on my 5.9L Magnum in my Jeep Grand Cherokee would be beneficial at 280,000 miles.

I would like some more low end grunt, but I'm unsure if doing anything other than keeping things stock at this point is worth it.

Advice??
 
Detonation would not be good for a head gasket of that mileage, or for the rings and bearings either. The stock timing got it to 280k, leave it be, unless you just want to see what happens.

If you could recurve it like the old days, so you have more advance curve and less total timing, that would be okay. But just turning the distributor more advanced will probably give you more total timing, not what you need.
 
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Isn't your timing controlled by the ECM? On something like an old V8 with a cam driven distributer and a timing chain, a worn out timing chain will retard the ignition timing slowly over time if it's not reset. If you have the original timing chain in your engine, I'd replace it if you are capable.
 
Originally Posted By: skyactiv
Isn't your timing controlled by the ECM? On something like an old V8 with a cam driven distributer and a timing chain, a worn out timing chain will retard the ignition timing slowly over time if it's not reset. If you have the original timing chain in your engine, I'd replace it if you are capable.


Yep I've done them a few times. Just curious about whether it's worth the extra bucks to get an adjustable chain, or just stick to a regular chain.

Maybe a double roller with a tensioner. Hmmm.
 
If your interest is mostly bogging around off road, there are replacement cams specifically cut for low rpm torque.
 
Easy enough to experiment and doing so costs next to nothing. Try it and report back with your findings.

My 10:1 SBC is happy w/ ~36° beyond 2600 consuming 91. Shortened its curve to allow 18° initial.
Good tip-in and solid mid-range.
smile.gif
 
Originally Posted By: splinter
Easy enough to experiment and doing so costs next to nothing. Try it and report back with your findings.

My 10:1 SBC is happy w/ ~36° beyond 2600 consuming 91. Shortened its curve to allow 18° initial.
Good tip-in and solid mid-range.
smile.gif




That jargon is above my pay grade lol

Not really sure what you mean by shortening the curve. Did you rotate the distributor? I'm just looking to install the timing chain and crank gear either +4 or -4, or simply keeping it 0 and install it stock.
 
Originally Posted By: Dumc87
Looking for some insight on whether or not advancing or retarding the timing on my 5.9L Magnum in my Jeep Grand Cherokee would be beneficial at 280,000 miles.

I would like some more low end grunt, but I'm unsure if doing anything other than keeping things stock at this point is worth it.

Advice??


You can't easily change the ignition timing on a Magnum, its crank-triggered with the advance curve set by the PCM and not adjustable without a custom PCM program. Yes, you can still spin the distributor in the block, but all that does is change the rotor-to-cap phasing, and there's only one correct spot.

If you're talking total camshaft timing, a Magnum of that age could certainly benefit from a new set of timing gears, a chain, and tensioner (if applicable- most later year Magnums have a tensioner shoe, earlier ones don't and I don't know the crossover year). As the chain wears, the average cam phasing relative to the crank retards and retarding the cam timing does indeed somewhat sacrifice low-end torque... so bringing everything back to spec should provide a slight improvement in low-end. You *could* get a 3-keyway adjustable timing set, or just use offset bushings, and advance the timing a skosh more than stock, but I really wouldn't go very far- no more than 2-3 degrees or you'll probably start making it lay over on the high end.
 
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Originally Posted By: Dumc87
Originally Posted By: splinter
Easy enough to experiment and doing so costs next to nothing. Try it and report back with your findings.

My 10:1 SBC is happy w/ ~36° beyond 2600 consuming 91. Shortened its curve to allow 18° initial.
Good tip-in and solid mid-range.
smile.gif




That jargon is above my pay grade lol

Not really sure what you mean by shortening the curve. Did you rotate the distributor? I'm just looking to install the timing chain and crank gear either +4 or -4, or simply keeping it 0 and install it stock.


The above jargon isn't applicable to a crank-triggered ignition engine. He's talking JUST about spark timing. "Shortening the curve" means limiting the amount of mechanical advance that the distributor will apply with increasing RPM. It is usually performed when you want *more* spark advance right off idle, but you want to keep the *same* advance you already have at high RPM. For example, the older Mopar LA smallblock (273/318/340/360) engines prior to the Magnum liked about 38 degrees total advance (not counting vacuum advance) at 2500-3000 RPM (with a mild performance cam, more like 36 with a stock cam), but from the factory for emission reasons the idle advance was set to between TDC and +12 TDC depending on year. This meant that the mechanical advance curve was "long," because it had to take the engine all the way from 0 to 38 degrees as RPM increased. For more performance-oriented applications, its often good to shorten the curve so that you can keep ~38 degrees at 2500-3000 RPM, but start out with as much as 18-20 degrees at idle. That gives a car a lot more punchright off the line, and with a looser torque convertor, the right cam overlap, etc. it won't have a detonation problem. It will have high NOx emissions, though.
 
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