DOD Delete Theory

GM has all their cams' specs, including the cams with Cylinder Confusion.

I won't know for certain until I do it but when a dod engine is in 8 cylinder mode I don't see how the lobe specs can differ without causing a cylinder imbalance; that is why I think the only difference is the smaller base circle to account for the extra lifter length.

If that length is corrected with a longer pushrod it should run exactly as when stock in 8 cylinder mode. I do know that the roller on the bottom of a dod lifter is identical to the rollers on the non dod lifters and the plunger travel is also listed as the same (but I haven't verified that yet)

Maybe you can measure the lengths of the two different length push rods and post the measurments here. Maybe note that the spring visable on the upper end of the dod lifter"s function is to keep the rocker arm, push rod and lifter internal plunger correctly positioned during the dod activation period.

Donal said:

Maybe you can measure the lengths of the two different length push rods and post the measurments here. Maybe note that the spring visable on the upper end of the dod lifter"s function is to keep the rocker arm, push rod and lifter internal plunger correctly positioned during the dod activation period.

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I ordered everything but the pushrods from Summit today, when I figure out what length to order the 8 new pushrods I will post it as well as the results of this experiment

I don’t see this working. These are hydraulic lifters, not solid, and you’re trying to move length from the solid side to the “collapsible” side.

Donal said:

Maybe you can measure the lengths of the two different length push rods and post the measurments here. Maybe note that the spring visable on the upper end of the dod lifter"s function is to keep the rocker arm, push rod and lifter internal plunger correctly positioned during the dod activation period.

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That spring is to allow the lifter body to move up and down with the cam lobe but the valves stay closed. The pushrod, rocker, and valve do not move in V4 mode.

91RS said:

I don’t see this working. These are hydraulic lifters, not solid, and you’re trying to move length from the solid side to the “collapsible” side.

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This makes no sense, the length required is what is necessary to preload the hydraulic lifter to between 50 & 65 percent of its plunger travel to establish normal operation of the valves; which area in that straight line or which component has which individual length is irrelevant as long as the lifter plunger is within spec when the lifter roller is on the respective lobes base circle.

I don’t see it working. I would risk the amount of pain in the ass it is to get heads off of a V8 S/T truck. If it worked, this would be a million dollar idea and everyone would offer a kit to do it.

91RS said:

That spring is to allow the lifter body to move up and down with the cam lobe but the valves stay closed. The pushrod, rocker, and valve do not move in V4 mode.

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That is exactly what I stated, thanks for agreeing.

91RS said:

I don’t see it working. I would risk the amount of pain in the ass it is to get heads off of a V8 S/T truck. If it worked, this would be a million dollar idea and everyone would offer a kit to do it.

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They do offer a kit to do it, most DOD delete kits don't include a cam, just the option to add the cam you want; most kits also specify to verify the pushrod length needed after the heads are back on and order the appropriate lenth, don't just assume the stock pushrods will be right. People skip that step but many complain later about noisy lifters as a result.

There is no money to be made with this idea that is not already being made, just an opportunity to save some money and work for those whose cam is not damaged and are not looking for an improvement in performance.

If it works that is, the parts came today so I will see if I have time this weekend to get the heads off and eyes on the cam; if it looks good I will calculate the pushrod length and get them ordered next week.