I'm not trying to gain anything for this switch, Just the sound
I don't really think that i'm going to lose any power either. I hate how people say that it can't be done because i have talked to many people that have done it. I have a 93 engine so I've bought the 95-97 opti spark, the 95-97 timing cover, the gear drive and the electric water pump. I have done a lot of other things to the car so i'm sending my pcm chip to "Pcm For Less" Which they are going to fix the knock sensor for me. I have even talked to Alvin at Pcm For Less and he concered that I will be able to do this. so why is there so many diferent views. I hate typing all this so if you have something to say that you think that i might need to know then you can call me at 859-881-0177.
Thanks
Andy Hawkins

 

No, the PCM cannot [automatically]correct for an incorrect indexing of the opti on the dowel pin. The indexing is crucial and is the only way the PCM can have a "baseline of understanding" (new term I just made up, lol). This is because of the multi-length slots on the shutter wheel that indicate cylinder position. The sensor merely reads the slots to compute cylinder position. If that is mechanically out of phase, then the whole spark timing curve will be off.

 

Then can we agree, er have a "baseline of understanding", Rob, on what I stated in my original post here, followup posts, and what I've been 'harping' on (check archives), from whom knows when? The LTx cam/crank drive assembly suffers from the same accumulation of tolerances and potential errors as any preceding sbc, and requires correction also, as any preceding sbc. Careful, you are probably still in very small company.

This then amounts (further off topic) to: Can we now, also agree, 'degreeing in' an LTx cam, will NOT cause the opti timing to be incorrect, by the amount of cam degree correction, but will actually bring the opti back into time? IOW, If the cam is off, the opti is off. 'Degreeing in' a cam, will not screw up the opti (and injector) timing, but will, in fact, correct, what was off, from GM assembly line, to begin with. Disclaimer:This contends of course, the errors are in the linkage assembly (cam gear dowel, crank gear keyway, crank key, etc., etc.), and not in the cam itself (dowel out of location in camshaft, or lobe grind screwup), which is rare.

Topic got diverted a bit, didn't it? Sorry, for 'off topic', (WL). Hopefully, back to the regularly scheduled topic.

EDIT"No, the PCM cannot [automatically]correct for an incorrect indexing of the opti on the dowel pin."
In that case, I consider http://www.gmhightechperformance.com...htp_optispark/ very misleading, or even inaccurate, in it's content. Paying lip service to gm tech bulletin, is one thing, objective accurate article writing, is quite another. Anybody can COPY 'reports', GM spits out.

 

The tolerance errors that I can see would be the dowel pin machined positioning on the cam (in relation to cam lobes) and the small amount (virtually none) of slack in the opti drive slot that goes over the dowel pin (though the 93-94 have the splined drive that may even be more accurate). Cam twist errors would be no different than with the conventional SBC.

The opti relies on the physical position of the cam dowel for the baseline. IOW, the opti is physically constructed to "know" that the dowel pin is precisely at 9 o'clock for #1 TDC. Any alteration from that precise position will throw the base timing off. So if by degreeing the cam, the pin is no longer at 9 o'clock, then timing will be off by whatever degree the change is.

While you cannot physically change the timing relationship in the opti, you can re-program the computer to advance or retard baseline timing to match whatever advance or retard was done by degreeing the cam.

 

I think by degreeing in, arnie means verfifying the manufacturers specs and setting the cam to them. If by degreeing you mean advancing or retarding cam timing from the manufacturers indended specs then I would agree it has to throw off bas timing.

 

Precisely!

Hmmm, Rob, for a minute, I thot you understood, and agreeed with what I had stated.


"The tolerance errors that.....to cam lobes)"

No, and this was not what I was attempting to convey, with my explaination. As I noted above, that would be a rare cam mfr. mistake, and not something we would/could easily correct. If it is screwed up, send it back.

"Cam twist....with the conventional SBC."

As noted above, I attempted to keep cam twist, out of the equation, to keep this discussion as simple/basic as possible. It is an intangible/variable I'd rather keep out of the discussion here. But to reply; actually the twist in the cam itself, would be similar, but the negative effect on the sbc, with the distributor being in the back, would exist, but the extent of which, would depend on variables (spring pressure, rpm, etc.), in the assembly. However, with the opti being located in the front, where the drive assembly is located, the effect of cam twist, would be nil, or basically nonexistant.

"Any alteration from that precise position will throw the base timing off."

Yes, yes! :tail wagging:

"So if by degreeing the cam, the pin is no longer at 9 o'clock...."

No, not correct! :tail between legs: Degreeing in the cam, would put the cam timing, where oem intended to be. Maybe I didn't explain it well above. Not being at '9 o'clock, is where it would start out, prior to the degreeing process. Degreeing in the cam (and it's drive dowel) reestablishes the correct base timing, in the opti. Or, if the oem assembly, is indeed, 'spot on' correct to begin with, the degreeing process would merely check/verify such, and no correction steps would be taken, or necessary.

 

Well i attribute the poor vacuum, power, and running little hot to the valve timing being all wrong, nothing the ECM has any control over. A tooth off is what, guessing 15 degrees? Without drilling an opti pin WAY off, and leaving the cam timing wherever it should be, im not sure its possible to fullfil what you are asking for proof.

Anyways, i dont have much more to say on this topic, but its been a good read/discussion. I'll still be checking up on it though! You guys have a good new years.

 

I think we might be trying to say the same thing in different ways. (and I may have misunderstood what you were meaning by "degreeing")

Perfection for opti timing (as far as #1 TDC goes) would be the dowel pin at 9 o'clock.

If by degreeing, you mean bringing the dowel pin to 9 o'clock (like it should be), you have made an imperfect situation perfect again.

If by degreeing, you mean advancing/retarding the cam for performance benefits, the dowel pin is no longer at 9 o'clock at #1 TDC, we are back to imperfect and opti timing will be off.

 

I'm confident different people will label/identify it with different terminology, but as for me, I'm comfortable with identifying that procedure (adv./ret. for perf.) as 'dialing in' a cam, done to optimize valve timing for a given performance application or situation. Start with 'nominal/straight up', and 'tweak' it either way, from there. That form of tuning aid, obviously (noted above) does not lend itself well, in an LTx environment.