Timing question

[6768chevylover]

I read several books and articles on setting timing. they usually say set your timing around 5-12 degrees before tdc. then install the distibutor facing the #1 plug. if I do that would what ever degree I set at(lets say 8 degrees)be considered tdc or 8 degrees?

[LandonL]

If your timing tab was like mine, each tick marks 2 degrees. Theres most likely a "0" on there, and every tick before it is "X" degrees before TDC.

[Captainfab]

It would theoretically be 8 degrees. When the groove in the balancer is lined up with the '0' on the timing tab, that is supposed to be TDC. However due to various possibilities, that may be slightly off. To find the absolute TDC you need to use a piston stop and follow a specific procedure to find the exact TDC. I would suggest reading the FAQ: SBC ignition timing sticky at the top of this section, following that and see how your engine runs. Then let us know if you need further help.

[prostreetC-10]

Initial timing at 5, 6, 7 ish would be if this was 1973 and the Govt wants to de-tune your motor for emissions reasons. Not sure I would go lower than 12* on ANY motor. My Gen 1 BBC's are all set at about 18*

[6768chevylover]

I have it set at 16 degrees,at least what i think is 16 degrees. but was just wondering if i was off on the timing cause of what I started off with at 8 degees for my tdc. everyone says start at tdc and for initial timeing and books say start at setting at 5 or so for initial timing, the engine is gauranteed to start. i just get thrown off with this stuff.

[3r!c84]

So set it higher? Mines at 6deg and it's running ruff. What should I set it at.mild 400sbc lil cam intake 750carb
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[geezer#99]

Originally Posted by 3r!c84

So set it higher? Mines at 6deg and it's running ruff. What should I set it at.mild 400sbc lil cam intake 750carb
Posted via Mobile Device

Experiment!! Try 10 degrees. If it doesn't ping Increase it 2 deegrees more and listen for pinging. And then maybe another 2 degrees.
Not every motor is the same.

[Ticker]

There's no reason to run more than 12-14 degrees initial on a street engine.

Everything you need to know to correctly set timing for maximum power, driveability and fuel economy is found here; it's a little long-winded but it's right

http://67-72chevytrucks.com/vboard/s...d.php?t=290498

When it comes to GEN I SBCs, they're all the same They all want 36 degrees total advance (mechanical + initial) before 3,000 RPM and 10-12 degrees initial.

Tuning by ear will *always* give too much advance.

[prostreetC-10]

Originally Posted by Ticker

There's no reason to run more than 12-14 degrees initial on a street engine.

Everything you need to know to correctly set timing for maximum power, driveability and fuel economy is found here; it's a little long-winded but it's right

http://67-72chevytrucks.com/vboard/s...d.php?t=290498

When it comes to GEN I SBCs, they're all the same They all want 36 degrees total advance (mechanical + initial) before 3,000 RPM and 10-12 degrees initial.

Tuning by ear will *always* give too much advance.

Alright Tick......then why is it that every carb and ignition manufacturer's lit saying to run as much timing as you can "safely"? My entire ignition is MSD, which I value as the best. When I bumped mine up from 14* to 18* I noticed a huge improvement in the very low end driveability with absolutely NO pinging, deto or anything else in the upper R's. I also played with the springs a bit to get the curve my motor seemed to like the best. total is still 36*. Leaning on your experience here Sir!

[69 longhorn]

On a mild street sb(pump fuel), I try to shoot for a 34 total,all in around 3000 rpms. With an HEI dist, this usually relates to 12-14 initial, to get the total on that stock HEI. as a rule they will handle 10-15 degrees vac timing(@ the crankshaft) added to your total figure(you have to experiment with the vac advance). When you bump the compression, shave the decks for "quench", & add a really "rowdy cam....this changes what the engine is asking for on the timing. Many of these "wilder mills" do not run a vac advance, & do run better with more initial timing(provided that the mechanical advance can be adjusted for the proper total). crazyAL

[Ticker]

Originally Posted by prostreetC-10

Alright Tick......then why is it that every carb and ignition manufacturer's lit saying to run as much timing as you can "safely"?

Can you link to the documents that gives that guidance?

I've never seen a GEN I SBC that doesn't provide the best power at 36 degrees total timing by 3,000 RPM. If the engine has configuration issues (large quench, too high CR, etc.) or doesn't have sufficient quality fuel for it's configurtion then it may not accept that much advance...and if so, then the engine is never going to make the power it's capable of.

There could be a bunch of reasons why your engine appears to "like" more initial advance...but without more information on the advance curve (which is really the key to power - not initial) and the vacuum can and where it's connected it's impossible to say. But I guarantee that a change in the curve and/or vacuum can would let you run less initial and have equal or better throttle response.

Hey, if you're happy - it's all good I'm just noting my experience that on the chassis dyno the guidance I'm offering is dead-on consistent every time.

[Ticker]

Originally Posted by 69 longhorn

With an HEI dist, this usually relates to 12-14 initial, to get the total on that stock HEI.

Or, you just buy a spring kit and put the timing exactly where you want it

Originally Posted by 69 longhorn

as a rule they will handle 10-15 degrees vac timing(@ the crankshaft) added to your total figure(you have to experiment with the vac advance).

A vacum advance can add far more than 10-15 degrees under load - at lower RPM, you may see as much as 45-50 degrees total advance

Originally Posted by 69 longhorn

When you bump the compression, shave the decks for "quench", & add a really "rowdy cam....this changes what the engine is asking for on the timing. Many of these "wilder mills" do not run a vac advance, & do run better with more initial timing(provided that the mechanical advance can be adjusted for the proper total). crazyAL

It really doesn't - although anything without vacuum advance really isn't a street engine Racing engines are a whole different deal...

[3r!c84]

ok so whats the correct way to set timming? run it up to what rpm. unhook the vac advaced. plug the hole? exc...exc...

[Ticker]

I'm a bit worried this thread is going to turn into a , so I'm going to unsub, leaving a thought behind.

The GEN I SBC isn't a new engine, and most of what's known about building and tuning them is pretty stable and has been for quite a while. Specific to timing, the best curve and stats for a street engine has also been around for a long time and been validated time and time again. Achiving those curve and stats takes some investment of time, but it's *always* worth it.

'nuff said, have fun

[69 longhorn]

Originally Posted by 3r!c84

ok so whats the correct way to set timming? run it up to what rpm. unhook the vac advaced. plug the hole? exc...exc...

I hate to make an ass/u/me, but assuming you are running an HEI dist. Go pick up a Crane adjustable advance can/springs. If you follow the instructions to the letter , you should be able to set up a pretty good curve. Nothing is set in stone....your eng will no doubt time a little different than mine, so you need to play a bit. The guidelines that I gave will get you into the ballpark, & you adjust from there. I agree with ticker, it is the total & the curve that sets the power (not the initial). The reason I stated 12/14 initial, is THAT is what it takes to get a 34 total on a stock HEI The stock HEI does not lend itself(easily) for adjustment of the mechanical timing(not without welding & filing the slots). 1 thing I do not agree with Ticker on, is the 36 total ,on the run of the mill street motor....if its decked & the quench is right on, go for that 36-38 degree mark, but MOST street engines do not have the quench set properly. And yes, no vac advance is a race motor deal(big cams do not provide enough vacumn to work the advance can).....but we still see these motors on the street! In the case of the dual quad/tunnel ram BB, that is really a race motor. Just trying to clearup the BS on differing opinions, so you can go about you project & have fun. crazyAl

[prostreetC-10]

Tick.....I meant to say "as much INITIAL timing". This is straight out of the MSD dizzy instructions:

Tip s on S electi ng an A dvance C urve
• Use as much initial advance as possible without encountering excessive starter load.
• Start the centrifugal advance just above the idle rpm.
• The starting point of the centrifugal advance curve is controlled by the installed length and
tension of the spring.
• How quickly the centrifugal advance (slope) comes in is controlled by the spring stiffness. The
stiffer the spring, the slower the advance curve.
• The amount of advance is controlled by the advance bushing. The bigger the bushing, the
smaller the amount of advance.


What I did was set my initial at 18* and then select the proper advance lockout bushing so I'm still only hitting around 36* total. Once that was selected, I started testing difference spring combinations to get the correct speed and style of the curve for my application.

I am sorry that you will not be able to comment anymore Tick. In addition to you unsubscribing to this thread, I have had you banned from replying to any threads that will possibly make it look like you know more than I do.

For everyone else....I'm giving Tick a hard time because he is a walking hot rod Britannica

[69 longhorn]

Prostreet, are you running a vac advance can on that tunnel rammed BB?

[prostreetC-10]

No and I made a mistake. I am going to the MSD 8361 small cap vac dizzy this spring when I do my carb change. I should have stayed away from the mechanical but didn't. I have it running really good but it will be even better with the vac can. The 450's don't have a vac port in the base but the other carbs will.