20° Base Timing???
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20° Base Timing???
G'day. My F150 is a 1990 model with the 5.8. Stock except for long tube headers an aftermarket cam.
I feel my truck is pretty sluggish, which was echoed by the guy who recently rebuilt my C6. He reckons the 5.0s he's done had more pep.
So I was mucking around with my timing, to squeeze a bit more out. It was already set at 12BTDC. I pushed it all the way up to 20°, without any pinging at all. This was done with SPOUT out, to set base timing.
My questions are, if my truck was pinging, would this be obvious?
The PO put in an aftermarket cam but doesn't know brand or specs. Could a different cam mean I could, and should, increase base timing by this much?
If no to the above, why on earth can I advance it that far with no problems?!?!
I feel my truck is pretty sluggish, which was echoed by the guy who recently rebuilt my C6. He reckons the 5.0s he's done had more pep.
So I was mucking around with my timing, to squeeze a bit more out. It was already set at 12BTDC. I pushed it all the way up to 20°, without any pinging at all. This was done with SPOUT out, to set base timing.
My questions are, if my truck was pinging, would this be obvious?
The PO put in an aftermarket cam but doesn't know brand or specs. Could a different cam mean I could, and should, increase base timing by this much?
If no to the above, why on earth can I advance it that far with no problems?!?!
Cargo Master
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The reason it can tolerate that much additional timing is because the camshaft has a later intake valve closing and this lowers the cylinder pressures at low speeds. This will also tend to increase cylinder pressures at higher speeds vs the stock cam but by the that happens the speed is high enough that the engine is less inclined to have problems with detonation. BUT what might actually happen is at high speed you'll end up with more timing than the engine requires to run its best. This is why in performance/racing applications the distributor is built to have an advance curve that's much shorter or even locked out.
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The reason it can tolerate that much additional timing is because the camshaft has a later intake valve closing and this lowers the cylinder pressures at low speeds. This will also tend to increase cylinder pressures at higher speeds vs the stock cam but by the that happens the speed is high enough that the engine is less inclined to have problems with detonation. BUT what might actually happen is at high speed you'll end up with more timing than the engine requires to run its best. This is why in performance/racing applications the distributor is built to have an advance curve that's much shorter or even locked out.
Would you suggest then, that I increase the base timing that high? Should I set the timing using vacuum, or just listen for pinging?
Cargo Master
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The computer controls the timing based on RPM, manifold vacuum etc and those parameters are probably pretty optimum for the stock cam and the VE curve that goes along with it. Now that curve is different and that makes the engine's timing requirements different. Without reprogramming the computer I don't know how you could really optimize the timing.
The optimum timing isn't as much as you can run without detonation. There will be a certain amount of advance that runs the the best, adding more than that will reduce power and not necessarily cause irregular combustion.
The optimum timing isn't as much as you can run without detonation. There will be a certain amount of advance that runs the the best, adding more than that will reduce power and not necessarily cause irregular combustion.
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Ah. I suppose then, that to find optimal timing it would require a dyno to collate all the data and make the best calculation. Maybe a little bit beyond my humble ability (and equipment) level! Thanks for your knowledge mate, definitely given me something to mull over. Perhaps in my case, would be best and safest to stay a touch above stock.
Cargo Master
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A dyno would be best but you could also run it at the drag strip on a test and tune day and see what runs best. Who knows but it might be worthwhile to double check the timing marks and make sure that they are correct.
One time I had a customer's 432 inch big block Chrysler engine on my dyno. It had Edelbrock heads and made 500 horsepower. When we first started on it we baselined it with about 32 degrees of total timing and then went from there. Just adding a few degrees was worth something like 15 horsepower and every time we added more timing the power and torque went up. We got up to 42 degrees and it still got better and I told him that in the past when I ran those heads they only needed about 34 or 35 degrees. So we checked the timing pointer and it was off by 10 degrees! When we thought we were running 42 we were only running 32. His engine was based on a 383 and somehow he had a 426 Hemi timing cover which oddly has a timing pointer that's different by 10 degrees, it happens.
One time I had a customer's 432 inch big block Chrysler engine on my dyno. It had Edelbrock heads and made 500 horsepower. When we first started on it we baselined it with about 32 degrees of total timing and then went from there. Just adding a few degrees was worth something like 15 horsepower and every time we added more timing the power and torque went up. We got up to 42 degrees and it still got better and I told him that in the past when I ran those heads they only needed about 34 or 35 degrees. So we checked the timing pointer and it was off by 10 degrees! When we thought we were running 42 we were only running 32. His engine was based on a 383 and somehow he had a 426 Hemi timing cover which oddly has a timing pointer that's different by 10 degrees, it happens.
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might be worthwhile to double check the timing marks and make sure that they are correct.
So we checked the timing pointer and it was off by 10 degrees! When we thought we were running 42 we were only running 32. His engine was based on a 383 and somehow he had a 426 Hemi timing cover which oddly has a timing pointer that's different by 10 degrees, it happens.
So we checked the timing pointer and it was off by 10 degrees! When we thought we were running 42 we were only running 32. His engine was based on a 383 and somehow he had a 426 Hemi timing cover which oddly has a timing pointer that's different by 10 degrees, it happens.
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Another thing that could be making things worse is the axle gearing, what is the axle code on the drivers door pillar decal? One of the thing you will see recommended for performance cams is lower(numerically higher) axle gearing, this along with a high stall converter counteracts the loss of low rpm torque created by the cam.
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All these gas engines in these trucks run out of air around 45-4700 RPM, and if yours has E6, and not E7 heads, yours will run out even sooner, 90 F150 5.8L had around 205-210hp, you sure it has a cam? running out that quick?
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Yeah definitely E6. And as for the cam, I'm only going off what the PO told me. The idle doesn't sound overly lumpy or anything so it would only be a mild grind. It used to be dual fuel and run on LPG (propane) also. I've read you could get cams specifically for that, so I'm wondering if that's what's in it?
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Yesterday I re-stabbed my dizzy according to the Ford factory shop manual. Including the part about aligning the vane on the shutter with the Hall effect sensor. Set the timing at 14°, and I'll leave it at that. I'm not building a race car after all!! The motor runs real nice, no misfires or stumbles, starts well. I'm going just enjoy it for what it is, then get it rebuilt in another 50,000 kms or so.
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Yeah definitely E6. And as for the cam, I'm only going off what the PO told me. The idle doesn't sound overly lumpy or anything so it would only be a mild grind. It used to be dual fuel and run on LPG (propane) also. I've read you could get cams specifically for that, so I'm wondering if that's what's in it?
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Anytime the engine is run on a gaseous fuel, propane or natural gas the camshaft requirements change. The VE is reduced which also reduces the dynamic compression ratio so with that in mind the cam is ground with less duration and on a tighter lobe separation. Sometimes in an engine like this it could be something like 195 @ .050 on 106 or so.
Back in the 90s in Australia there was a big push from the government for cars to be converted to LPG. there was huge discounts for installation/conversion, as well as for the actual fuel itself. So a lot of cars from that era were converted. Unfortunately now the government has long ago ceased that program, it's quite difficult to even find a service station that stocks lpg.