dave88sw

3.9 V8 Ignition timing

6 posts in this topic

I didn't know where best to ask this as the engine is more common in a Range Rover but it's actually in my Discovery. I hope it's ok to post it here but mods please feel free to move it if necessary.

I've been searching google all morning and can't find the factory figures for timing a 3.9 V8. Lots of posts asking how to get it close statically to fire up a newly built engine but mine currently runs and i want to adjust it for optimum performance.

I have a timing strobe so can set dynamically, i just need to know the figure to aim for, most people say they set by ear but surely there is a figure quoted somewhere from land rover?

The reason i want to set the timing properly is my engine "surges" it idles perfectly without fluctuating but on the road with a constant throttle position and under 2000 rpm, you can just feel it "kangarooing", so i was thinking to start with a good tune up (replace all consumables, spark plugs/leads/rotor arm etc) and go from there. Has anyone else experienced this?

Thanks in advance

Dave

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This from RPI Engineering's website:

ts also worth noting that the best ignition timing in any given engine, is to achieve the most advance it can tolerate without pinking. ( Audible pre-ignition).
This is achieved by setting your V8 timing to about 4 deg. BTDC (assuming you've been through the distributor check list completely). Then tighten the distributor so that you can (with effort) still turn it by hand. ideally put a tip-ex mark or small scratch on the distributor body and engine block to record this spot.
Next road test the car and simulate high load by quickly shifting into a high gear or if Auto allow to change quickly up to 3rd or 4th Ideally you need to find a small hill or incline, now if you apply full throttle the engine should respond without pinking, find a safe place to pull over, open the bonnet and turn the distributor through a couple of degrees only, anticlockwise, this will add slightly more advance timing and if you do the same test, and repeat it until pinking is noticed you will be very close to your absolute best timing criteria
So now all you need to do is turn the distributor clockwise by the same amount by an amount to counteract the last adjust, retest for the absence of pinking and that the job done, you will have just achieved the best maximum timing position for your car

Having done this an ideal engine would run perfect in all areas and pull as you would expect from all load and rpm areas. you would also expect the final timing position to be somewhere close to 6-8 deg. btdc, (exceptions assumed) However if this is not the case and or your engine developers other strange habits then it is almost certainly pointing to another issue with your engine of which there can be many.

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6 degrees is about right on petrol.

Assume it is on EFI? Is everything sensor-wise in good fettle?

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is that 6 degrees before measured at idle?

Yes it's EFI and otherwise drives perfectly, i've only had it a week but will read the faults at work asap, i'm quite happy to spend some time and money to get it running as well as possible.

thanks for all the replies, i can see the theory behind the rpi method and when i have a free afternoon i will try it, it's just at the moment i'm lucky to get an hour or 2 to tinker so having a figure to set it to with the timing strobe was preferable.

Thanks

Dave

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