How much base timing is too much?

[Paul G]

This little motor just keep responding to more base timing. I just added more base timing and it responded very well to it, again.

The total timing is kept at 34°, all in by 2500 RPM, that's what it seems to like the best with no detonation. With the adjustable dizzy I have I can change the curve easily.

The dampers timing mark is so far off the chart at idle I am using a scribed mark I made on the damper to calculate the base timing.

I measured the timing marks on the housing, 10° is 10/16" per my extremely well calibrated measuring tape  . So I figured 2 3/8" on the damper is going to be 38°. I got that this way, (2 3/8" is 38/16", 1° per 1/16" = 38°). I scribed a mark that distance, 2 3/8", away from the factory mark on the damper. Using my scribed mark, at idle right now, it is right on the 7 1/2° ATDC mark on the housing, that puts the base timing at about 30 1/2°, (38° - 7 1/2° = 30 1/2°).

I know, all the math is horrible, and I am probably doing something wrong. 

I have read that if the base timing is too far advanced the starter will buck. I tried to find that point, the dizzy has to be advanced a ridiculous amount to get the starter to buck. Where it is right now it starts at the turn of the key. Even if slightly flooded, it still will not buck, just cranks a few times and fires up. Went for a drive, throttle response is quicker than before this timing adjustment, tires break loose a little easier than before the adjustment.     

I don't know the cam specs, or the compression ratio. I do know it is stock stroke 360. RPM air gap intake, Holley 670 carb jetted up 2 sizes primary and secondary, long tube headers, a little port work to the heads that I have seen, MSD ignition. 

So where am I going wrong here? I don't want to blow this motor up before the next one is ready.

[BSB67]

If you don't have any detonation, and it starts okay, you're fine.

Are you using your vacuum advance?

[Paul G]

If you don't have any detonation, and it starts okay, you're fine.

Are you using your vacuum advance?

No vacuum advance. It doesn't like it.

[fy469rtse]

Paul , look up summit or jegs , you can get a stick on timing tape,
takes the guess work out of it ,

[red79]

Or an old school advance timing light, unless you have a multi-spark ignition box 

[mhinders]

My low compression (below 8:1) and low vacuum 383 was equipped with a half-hot cam and needed 24 degrees base timing to run at all.
The dizzy was limited to 12 degrees and no vacuum advance. The engine was a pain to run, I estimate power output to about 50% of the factory output.

With a crappy A/F mixture (due to the low vacuum) the combustion is very slow and a lot of pre-timing is needed.

[Paul G]

This is a good read.

http://www.badasscars.com/index.cfm/page/ptype=product/product_id=76/prd76.htm

Makes me feel a little more secure. I question the cam that is that motor. Must have a long overlap and low compression.

[Dino]

I'm running mine at 24 base with advance hooked to full manifold vacuum.  My car needs lots of spark to run decent.  Can't wait to get this cam out because it's a pain to tune.   

[myk]

Yeah I've got 18* base timing as well; seems radical but it works...

[Paul G]

Paul , look up summit or jegs , you can get a stick on timing tape,
takes the guess work out of it ,

I have tried the tape before. It works very well for a couple of weeks, then it comes off. I never thought to use the tape and scribe across the lines in to the damper at certain points. Then the lines would be permanent. An idea??

Or an old school advance timing light, unless you have a multi-spark ignition box  

Yep. MSD box. Advance lights wont work, I have tried that.
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The base timing was at 12° BTDC when I got the car a few years ago. Ran ok but just wasn't right. It had a big Holley 750 dumping loads of fuel in to the motor. 8 MPG city 9 or 10 highway. Something wasnt right.

I have been stepping up the base timing and it keeps liking it. With the base now at 30° BTDC it is practically locked out. That is only about 4° of mechanical advance. It's all in by 2000 RPM. Puzzling?

A little history, I swapped out the 727 for an A518 a couple years back. Before I installed the overdrive trans the base timing was about 12° or so, full advance all in by 1500 RPM, I dont remember what the total was back then. Worked fine like that with the 3.91 gears that are in the car. I assume the 3.91 gears had the RPM high enough and engine load managed so the full advance at 1500 RPM was ok with that set up, no detonation I could hear. The more I think about, full advance at 1500 RPM? What does the base timing really matter? Just off idle full advance is already in. Idling at 850, the motor doesnt pull till around 1200, full advance is right around the corner at 1500. Hmmm,  

After the overdrive trans install it would ping at cruise when below 2000 RPM. I used 1 heavier spring in the dizzy to hold full advance to 2000 RPM, the base timing was still around 12°. Worked better liked that with the A518 trans. That gets me to where I am today, base at 30°, total at 34°. It seems to run even better?  

I just dont see how this motor likes so much base timing with a total of 34° to 36°? I have read that low compression motors with poorly chosen cams need lots of timing. Lots of base timing and total up to 38°, this motor likes lots of base with total around 34°.

I wonder what a simple cam change would do for this motor? I hate to do to much to it anymore. I am planning a big block build over the next couple of years. A "lowly 440" following Bob's recipe, or a 500" build if the machinist here in Phoenix tells me the crank is no good in the core I have a handle on.

Sorry for the long read, again. It helps to put ones thoughts down in words. Sorting out the details sometimes helps to put things in perspective.

[c00nhunterjoe]

I wouldnt worry about it. Alot of our race/street car engines are locked out at 40° and they are big cammed, big compression engines. They start fine. Just because you have alot of base timing does NOT mean you have the wrong cam.