I know what the timing is supposed to be on my motors (stock) but I have found out that they are not built even close to factory specs. Does this effect where I need to set the ignition timing? if so how do I go about doing it, other than just by ear?

total advance @ 3000 rpm's

Total advance? might be an ignorant question, but what is that?

Motor is a 300 Merc Tempest sbc, I think that comp is 9:1 not sure right now, but I do have it written down somewhere. Heads are the old Chevy angle plug style, someone once referenced them as "bowtie" heads carb is an edelbrock either 600 or 750 cfm, once again not sure (there are no markings on it to indicate cfm) I need to call Edelbrock to find out for sure. Ignition is TB-4 merc, manifolds are both stock Merc.

The motors are not overly moddified, but there are a lot of different parts on it that do not match stock specs.

What TB IV ignition module do you have? V-8 modules can give from 20-24* advance and total advance can come in anywhere between 3000 and 4200 rpms.
You NEED to know how much advance the module gives before you can set the timing at idle rpm.

Like Griff has said,
there are different TBIV modules,
from the ones I have seen, they are marked,
like, for example V8-24, this module has
24* of advance built into it, so if you were to
set your initial timing at 8*, you would have a total
of 32*

jt.

so let me get this straight.

for example I have a v8-24, so I need to set my timing on the pointer at 8 to 10 degrees with the engine running between 3k to 42oo rpms?

NO NO NO!!!!!!!

If you have the V8-24 module, you have 24* of advance. To get a total of 34* you need to set the timing to 10* at IDLE or less than 1000rpms. Full advance for the V8 -24 comes in at 3750rpms. To check total advance or set it that way, you would need to have the engine at 3750 rpms. You should then be at 34*.

To simplify, the 24 of V8-24 means the module will add timing in a linear fashion up to 3000 or so rpm from your base. Base of 10 + 24 is 34 total. There is a chart that shows the curve that the module will add. Just set your timing at 8 or 10 and then check at 3750 or above.

so let me get this straight.

for example if I have a v8-24 Then I set my timing on the pointer to 8 degrees while at 3k rpms to give me a total advance of 32?