Let's talk Camshafts (again)
 

So, Nighthand has installed a LS2 cam and, as far as I know, this is the first documented LS4 cam swap - at least on this forum.

I occasionally come across statements to the effect that other LSx cams won't work in the LS4, Nighthand's swap seems to have disproven that concept.

I've pretty much come to the conclusion that any LS1/2/6 cam ought to fit. The only question is whether or not DOD/AFM can be retained.

So what do we know?
1. Cam journals are on the same centers.
2. Push rod length is the same for LS1/4/6 @7.40".
3. Deck height is the same on the LS1/4/6.
4. LS4 has the LS6 heads (small valve version due to smaller bore).
5. Non-DOD lifters on the LS4 are the same as LS6. (These are the ones that don't collapse)
6. LS4 has more lift on non-DOD lobes than DOD lobes.

This implies that the base circle on the cam lobes is the same between the LS4 and LS1/6 - at least for 4 cylinders that don't deactivate.

Has anyone actually measured the DOD lifters to determine if the distance between the roller and push rod seat is the same as non-DOD lifters?

Alternatively, has anyone found data on the base circle of the DOD lobes?

I have not been able to find data on the base circle of the DOD lobes, but if the same as the others, then I don't see any impediment to putting in a strong LS6 cam (and keeping DOD) that a tuning session can't overcome.

Comments?

:cheers:

So now that I've had a chance to sleep on my prior post, I've come to the conclusion that the base circle on the DOD lobes is irrelevant. If it's larger or smaller than on non-DOD lobes, the difference can be made up by choosing push rods with the appropriate length to retain proper valve train geometry.

:cheers:

yeah good thinking. you thinking about swapping cams? if you do don't forget to post

Not doing much more than thinking about it at this point. Spending my time this year working on another rebuild project.

One thing I do know is that there's no way I'm going to try this with the engine in (or almost in) the engine bay. Having dropped one engine cradle this year (what a PITA that is), I know I'm going to have to improve my lifting equipment in order to pull the GP off its engine cradle. Thats really the only way to go though, it's so much easier to work on an engine when it's on an engine stand.

May not even find time this year to install the valve springs and rockers that are sitting on the shelf.:(

:cheers:

I will take those rockers/springs off your hands :D

Nice try! :devil:

They'll go in eventually, just need to finish another project first.

:cheers:

Should be finishing up my LS4 swap into my 88 Fiero GT in a month or so. I plan on running it stock for about 6 months them pulling it out for a cam and other parts. From reading it looks like to go with a bigger cam then the LS2 you need to swap lifter and do away with the DOD. Will be wathing/reading around to see what will work the best.

Everything else you said seems reasonable. No. 6 needs to be corrected. The higher lift is on the DOD cylinders supposedly to compensate for a little "lost motion" in the DOD lifter/valvetrain. In theory, all 8 cylinders would have the same lift in V8 mode and of course the same power.

Chip

Just a note on terminology. I refer to non-DOD cylinders as the ones that are always active and DOD cylinders as the ones that are deactivated when in 4 cylinder mode. My understanding is that the higher lift is on the cylinders that are always active, which makes sense as those 4 cylinders need to work harder when in V4 mode.

When in V8 mode, we actually have 4 cylinders where the cam does not allow the same breathing capability as the other 4.

The downside of trying to use a cam with all 8 cylinders the same is that there may be more surge when entering or leaving V4 mode because of the slightly higher power and torque delivered by the cylinders that deactivate as compared to a stock cam profile.

:cheers:

I did a bit more research into this. ChipC was correct, the higher lift is on the cylinders that deactivate. It seems that the construction of the DOD lifters leaves a few thou of extra play in them, therefore higher lobe lift is required to get equivalent valve lift compared to the cylinders that do not deactivate.

Crap. That really means a custom grind to get a cam that allows all cylinders to breath equally in V8 mode. Wonder how the L76 cam compares to the LS4?

:cheers: