School me on timing.

[handloader90]

I've looked all over Google and I'm not finding the answers I want.

I have a 350 SBC with an Accel HEI Dizzy with a Super Coil I don't know anything about the internals of this engine. Also, it has a 600 CFM Carb.

Now I'm going to set the timing in about two weeks (the truck and I are in different locations for now).

When I hand turn the engine, do I want it the timing line to be lined up on 0 (TDC) or do I want it to be lined up 8*-10* BTDC? This is the main area I'm confused in.

Now let's say I put the line at 10* BTDC, what number am I looking for on the timing light after I fire the engine up for initial timing?

I think I understand the rest of timing after this point.

1)Unhook vac advance, plug vac advance.

2)Get initial timing, which is what I want to make sure I'm doing right

3) adjust dizzy so I get 34*-38* timing, timing should be all in by 3000 RPM

4) tighten dizzy clamp

5) shut off engine, turn it back on and verify same timing.

6) hook vac advance up and be done with it.

Does this seem right or am I missing something.

Also I want to use manifold vacuum for the vac advance. My brake booster will be hooked to manifold vac with a "T" fitting, can I put a fitting in the other port of the "T" and hook vac advance to that? Will that cause braking issues or vac advance issues?

 

[F-ingrob]

whoa whoa when doing static timing you want the pointer to be at 8*ish and when you do your total timing you want it to be around 32* total and the way to do total is when your shinning the light on the timing mark slowly rev the motor until the timing stops advancing this is done with the timing gun set at 32 with vac advance hooked up to the vacuum port on the carb
static timing is done with the timing gun set at 0
34*-38* is a little on the high side this is all done while the motor is running
static is done at idol and operating temp advance should be around 2500rpm
THE VACUUM ADVANCE NEEDS TO BE CONNECTED TO THE CARB ON THE VACUUM PORT
ON A HOLLY CARB ITS ON THE PASS SIDE FRONT ON THE METERING BLOCK

 

[handloader90]

Ok. You've totally lost me. It was recommended to me to use full manifold for the vac advance for a better idle and a cooler engine and from what I do know that is how vac advance was originally setup before all the emissions stuff kicked in and manufacturers started to hook it up to the port on the carb. From what I understand that's why the temp on thermostats went up and why radiator caps are made to hold more pressure.

The next thing is... from what I understand the vac advance is to stay blocked off until your completely done with initial and advanced timing. After you're timings where it needs to be you tighten down the dizzy clamp and hook the vac advance back up and set your idle screw on the carb.

I don't have timing tape on my balancer, but I do have a pretty good dial back timing light. I may have over exaggerated a little on the advanced time, just a tad. I'm hearing it should be 34* - 36*, it could be possibly more, depends on when you test drive if it starts pinging then you back it off 2* and test drive again, no pinging equals good, which could be more advanced than 34*-36*

But your reply didn't really answer my question, at least not to the point where I fully understand.

So I'm hand cranking the engine, the TDC line on my balancer is starting to get close to the the timing tab, what degree BTDC do I stop or do I just line everything up TDC? I've been reading around and see different things... 4* BTDC, 8* BTDC, 10* BTDC and plain ol' TDC. 10* BTDC seems to be the most common thing I've seen.

Now let's say I'm at 10* BTDC and I've got my timing light hooked up and then I fire the engine up, what number am I supposed to see on the screen with the my timing line at 10* BTDC?

Or do I put the line on the balancer at 10* BTDC and set my timing light to 10*?

This is really the only area I'm confused in.

I know how to find TDC, I know how to install the dizzy correctly, I know where the rotor is supposed to be pointing etc. I'm just confused on the very first steps of getting the initial timing, where the line is actually supposed to be and what my readings or adjustments on the timing light should be.

FYI, my engine is pretty much stock. It's rebuilt so it might have been bored out a little and I think there's an aftermarket cam, nothing extreme though.

 

[F-ingrob]

If you want you can call me tomorrow any time after 7am I'm in California
I build engines from stock to full race and race sprint cars so I'm sure I know how to time a motor
My number is
650-444-4523 ne is rob

 

[handloader90]

I never said you didn't know how to time an engine, but what you've told me isn't helping. I'm looking for a specific piece of info that I don't have a full understanding of.

 

[F-ingrob]

Ok no biggie call me tomorrow and I'll do my best to help you out

 

[dremu]

When I hand turn the engine, do I want it the timing line to be lined up on 0 (TDC) or do I want it to be lined up 8*-10* BTDC? This is the main area I'm confused in.

Base timing varies by motor year and type and individual characteristics, but is in the region of 8-12*. I'd start with 10* and then fine-tune once you've got the hang of reading the light.

With an old-school, non-adjustable light, you look for the white stripe by, say, 10* on the timing tab and say "That's 10* BTDC." Which is great until you want to read farther than the tab goes, then you need a timing tape or a fancy light.

With your fancy light, you don't just read it like, say, a voltmeter. You press the up and down buttons to set an offset (more on this in a minute) and when the white stripe is by 0* on the timing tab, then you read the display on the light. Make sense?

Anyway, for base timing you set the offset to, say, 10*, then look for the white stripe by 0*. To get the 10* base, you rotate the dizzy until the white stripe is right at 0* when the light is set to 10*.

And yeah, you unplug the vacuum advance canister and put a golf tee in the line for base and mechanical advances, at least at first.

Now, when you go to measure the mechanical advance, this is where the fancy light comes in. Now you set the offset to 20-something and blip the throttle, and see where the white stripe lines up with 0*. Your light should have a tach on it, so you can see 28* at 3000RPM, or whatever.

If you want to change the mechanical advance you get the "distributor advance curve" kit that has the weights and springs and you can switch them around until you get the desired advance.

Once that's dialled in then you hook back up the vacuum canister. These can also be adjustable, either inside the vacuum fitting with a tiny allen wrench, or at the end inside the dizzy.

The whole process is actually more like setting base timing first, then mechanical, then vacuum to get total, but each time you're reading with the light and it's the same, so you'll get used to it real quick.

Once it's all hooked up, you don't want more than the 32-34-36-ish or your motor will ping and be angry with you. Then it will start shedding parts in ways very unfriendly to your wallet. Again, it's motor-specific and even once you set it all, you go for a drive and see how she runs under load, which is different than in the driveway. It's a very iterative process of "lather, rinse, repeat."

The question of where to connect the vacuum advance will stir an ugly pot of accusation and anger. It's a religious thing. There are people who absolutely demand it must be connected to manifold vacuum, or the world will swirl into a black hole and the universe will cease to exist. There are also people who demand that it must be driven by ported vacuum or else fire and brimstone will ravage the earth and your truck.

Note that "manifold vacuum" doesn't necessarily mean you connect it to the manifold, just that it's below the throttle plates on the carb.

Me, I'm a manifold vacuum man, so I run the vac advance hose to one of the lower ports on my carb. Were I of the other faith, I'd run it to an upper port on the carb. You could even try each for yourself and see which makes the truck run happier. I believe in freedom of religion for vacuum source.

There should be a plethora of ports on your carb, and while I don't know Holleys (I'm a Quadrajet man, again, a religious thing) I imagine you can determine where the dividing line is and pick an appropriate port. On the Q-jets the brake booster goes to a fitting on the back of the carb, and the vacuum advance to one of the many on the front, so I don't see the need for a tee fitting.

Or post pix and a Holley person here can point at the ports and tell you which is which.

Hope that helps; if not, welcome to post questions.

-- A

 

[Blazer79]

This:

So I'm hand cranking the engine, the TDC line on my balancer is starting to get close to the the timing tab, what degree BTDC do I stop or do I just line everything up TDC? I've been reading around and see different things... 4* BTDC, 8* BTDC, 10* BTDC and plain ol' TDC. 10* BTDC seems to be the most common thing I've seen.

Is only needed when you first start the engine to get it in the ball park and make the engine capable of running. While you do that, you try to make the distributor to point at #1 spark plug. It's no big difference if it's 4, 8 or 10*. Just get it running.

Now let's say I'm at 10* BTDC and I've got my timing light hooked up and then I fire the engine up, what number am I supposed to see on the screen with the my timing line at 10* BTDC?

Not sure what kind of timing light you have, but as mentioned, the timing light is not actually reading timing FROM your engine. If adjustable, then you'll be reading the setting the timing light is in. By setting, I mean how many degrees the timing light is delaying the flash of the light so you can arithmetically add the numbers of your screen and the number you see lined up on the balancer with the timing pointer to get the timing the engine it actually is in. It might read RPMs from the engine, but this is only for your reference. For base timing, put this setting in zero, so it actually flashes exactly when the spark plug is sparking.

So with the engine warmed up and idling, you disconnect and plug the vacuum hose that comes from the carb. Now you measure base timing by looking at the balancer number that is lined up with the pointer when the timing light flashes. This is the one that should be 8-12* as mentioned. Not the one when you turn the engine by hand.

Hope this helps.

 

[handloader90]

Base timing varies by motor year and type and individual characteristics, but is in the region of 8-12*. I'd start with 10* and then fine-tune once you've got the hang of reading the light.

With an old-school, non-adjustable light, you look for the white stripe by, say, 10* on the timing tab and say "That's 10* BTDC." Which is great until you want to read farther than the tab goes, then you need a timing tape or a fancy light.

With your fancy light, you don't just read it like, say, a voltmeter. You press the up and down buttons to set an offset (more on this in a minute) and when the white stripe is by 0* on the timing tab, then you read the display on the light. Make sense?

Anyway, for base timing you set the offset to, say, 10*, then look for the white stripe by 0*. To get the 10* base, you rotate the dizzy until the white stripe is right at 0* when the light is set to 10*.

And yeah, you unplug the vacuum advance canister and put a golf tee in the line for base and mechanical advances, at least at first.

Now, when you go to measure the mechanical advance, this is where the fancy light comes in. Now you set the offset to 20-something and blip the throttle, and see where the white stripe lines up with 0*. Your light should have a tach on it, so you can see 28* at 3000RPM, or whatever.

If you want to change the mechanical advance you get the "distributor advance curve" kit that has the weights and springs and you can switch them around until you get the desired advance.

Once that's dialled in then you hook back up the vacuum canister. These can also be adjustable, either inside the vacuum fitting with a tiny allen wrench, or at the end inside the dizzy.

The whole process is actually more like setting base timing first, then mechanical, then vacuum to get total, but each time you're reading with the light and it's the same, so you'll get used to it real quick.

Once it's all hooked up, you don't want more than the 32-34-36-ish or your motor will ping and be angry with you. Then it will start shedding parts in ways very unfriendly to your wallet. Again, it's motor-specific and even once you set it all, you go for a drive and see how she runs under load, which is different than in the driveway. It's a very iterative process of "lather, rinse, repeat."

The question of where to connect the vacuum advance will stir an ugly pot of accusation and anger. It's a religious thing. There are people who absolutely demand it must be connected to manifold vacuum, or the world will swirl into a black hole and the universe will cease to exist. There are also people who demand that it must be driven by ported vacuum or else fire and brimstone will ravage the earth and your truck.

Note that "manifold vacuum" doesn't necessarily mean you connect it to the manifold, just that it's below the throttle plates on the carb.

Me, I'm a manifold vacuum man, so I run the vac advance hose to one of the lower ports on my carb. Were I of the other faith, I'd run it to an upper port on the carb. You could even try each for yourself and see which makes the truck run happier. I believe in freedom of religion for vacuum source.

There should be a plethora of ports on your carb, and while I don't know Holleys (I'm a Quadrajet man, again, a religious thing) I imagine you can determine where the dividing line is and pick an appropriate port. On the Q-jets the brake booster goes to a fitting on the back of the carb, and the vacuum advance to one of the many on the front, so I don't see the need for a tee fitting.

Or post pix and a Holley person here can point at the ports and tell you which is which.

Hope that helps; if not, welcome to post questions.

-- A

Thanks for the clarification. My carb is an Edelbrock 1406, 4 barrel, 600 CFM, electric choke. I'm not exactly why Holley got brought into this.

I was speaking of actually hooking the vac advance to a port in the manifold. I have a Vac port about one inch behind my carb (Intake: Edelbrock Performer RPM) and was going to hook it up the blocked off port on my "T" fitting, my brake booster is hooked up to the other port on the "T"" fitting.

Also, when exactly in this process does the vac advance get hooked back up, from what I understand when you hook the vac advance back up and shine the timing light on it you will get a high reading.

Ok, so initially when I hand turn the engine and get the balancer at 10* BTDC, that is just for the purpose of getting the engine to run.

Once the engine is running, I set my timing gun at 10*?

 

[Blue85]

Mechanical advance: gives timing based on engine speed - primarily for performance
Vacuum advance: gives timing based on engine load - primarily for economy

You will not actually run at the "base timing" number unless you use ported vacuum or you sometimes lug the engine at low RPM and WOT. You're setting all 3 so that the combination makes it run right over all the conditions.

Even if you were to run ported vacuum to the advance can, it's still good to connect it to full manifold vacuum as part of your timing adjustments to measure how much the full advance of the can is. There is usually a way to adjust it or limit it.

 

[Blue85]

Ok, so initially when I hand turn the engine and get the balancer at 10* BTDC, that is just for the purpose of getting the engine to run.

Once the engine is running, I set my timing gun at 10*?

For the base timing you have two options:
1) Leave the gun at 0 and set timing by looking at the timing tab. You'll want the timing mark to hit 10BTDC on the tab.
2) Set the gun to 10 and adjust until the timing mark is hitting TDC on the tab.

 

[dremu]

Thanks for the clarification. My carb is an Edelbrock 1406, 4 barrel, 600 CFM, electric choke. I'm not exactly why Holley got brought into this.

I was speaking of actually hooking the vac advance to a port in the manifold. I have a Vac port about one inch behind my carb (Intake: Edelbrock Performer RPM) and was going to hook it up the blocked off port on my "T" fitting, my brake booster is hooked up to the other port on the "T"" fitting.

Also, when exactly in this process does the vac advance get hooked back up, from what I understand when you hook the vac advance back up and shine the timing light on it you will get a high reading.

Ok, so initially when I hand turn the engine and get the balancer at 10* BTDC, that is just for the purpose of getting the engine to run.

Once the engine is running, I set my timing gun at 10*?

I musta misread on the Holley, sorry. Same drill applies, though, you can use one of the ports on the front:

I suspect the bottom right of the "timed and full vacuum ports" at the bottom is manifold vacuum.

If you just wanna set the base timing and be done:

1. Disconnect the vacuum
2. Set your light at zero and leave it there
3. Adjust the dizzy
4. Reconnect the vacuum
5. Go test drive

I understood that you were wanting to do the whole tuning process, which might have come from the same place I saw "Holley", which is to say I made it up

As for the light, lemme try another way of describing it. Blue85 said it too. The timing light display and what you read on the timing tab add up to the total timing. You could set the light to 6* and look for 4* on the tab to make 10*, you could set the light to 10* and look for 0* on the tab, same end result.

As long as you're just doing the base timing which is less than the 14-16 your tab can read, I'd say zero the light and just read the tab so you don't confuse yourself.

Oh, and you realllly should have a Hayne's or Chilton's manual, which would run through this and might be more helpful than my description.

Make more sense?

-- A

 

[mendoman]

Not sure if this is helpful, but the base timing is what will get your total where you want it. There are three factors that contribute to timing. Base timing (set by rotating distributor), mechanical advance (determined by weights in distributor), and vacuum advance (determined by the vacuum canister). Mechanical advance (from the weights in distributor) and vacuum advance have fixed ranges - they will only advance to a max amount point. When you rotate the distributor (to get your total up to where you want it), you are adjusting your base timing.

As mentioned, you just need your initial base timing set within a range that it will start. I set my timing mark at about 10 (before TDC ignition) and then do my best to get the rotor directly on plug 1. Unplug the vacuum advance and start the engine. Let it warm up. Check the timing at idle once it is warm. If it is actually where you set it (10 in my case), you can move on to finding out how much the mechanical advance (weights in distributor) add to the base. Slowly accelerate until the timing mark stops moving and note the RPM. If you started with 10 (base timing) and your mechanical advance has a max of 22, you should be maxing out at 32. (I have a timing tape, but I imagine with your dial back light, you offset it to 32 and look for the tab to indicate 0 on the dampner at the RPM you noted a moment ago).

If you want more advance, you adjust the distributor. If you add 2 - 4 degrees, your base timing will increase by that amount. In my case, I started with base timing at 10. After checking the total advance, I was at 32. I adjusted my distributor until my total went up to 34. I rechecked my base timing at idle and it had come up to 12.

At this point you can plug in your vacuum advance - I went with full manifold vacuum (lower port on front of edelbrock) based on my research. Vacuum will not add to your max total when at WOT, but it will increase the max at partial throttle (don't freak out if total is 40-50 at partial throttle). What it does is add to your advance at low and partial throttle and slowly fades out as mechanical kicks in. You can verify this by checking timing at idle with vacuum advance plugged in. You will see that your timing is more advanced than the base setting. As you accelerate (and manifold vacuum drops), vacuum advance will slowly come down, but mechanical will increase at the same time. At partial throttle, you may be up over 40, but this will decrease as you accelerate. At WOT, vacuum advance will have fallen away and your total will be determined by Base + Mechanical.

The final step is a test drive. If your engine is happy, you should have a smooth idle, crisp throttle response from idle, and no pinging. If pinging is at WOT, you need to decrease base setting. If its during partial throttle and you have an adjustable vacuum can, you can dial the vacuum can down.

 

[handloader90]

Big thanks to all you guys for your input. I think I understand now.

The timing light I have is an Innova 5568. It's supposed to be a pretty good gun with a lot of good reviews.

I have one more question for now... I have an extra lead on my timing light specifically for RPM. I have an Accel HEI dizzy with Accel Supercoil. I have a Sunpro Tach hooked up and mounted to my steering column. Where do I attach this lead so I can get the RPM Readout? The manual only speaks of hooking up to a wire in the coil (but mine is internal). Do I attach it to my tach wire thats hooked up to the bottom side of the dizzy?

I have a Haynes manual and a Chilton manual courtesy of the P.O., but they got packed up by the movers... my fault for leaving them out. So I'm not able to reference them at this time.

I'll be retuning my carb at the same time I do the timing. I'll be tuning from Colorado Elevation to about 500 ft. elevation and I know how to work carbs and have the correct jets and metering rods ready to go in once I make it down there.

 

[dremu]

Hey, I know that light! (I have one too )

The green alligator clamp is for reading the dwell angle. I've never dinked with it, but you'd connect it to the signal wire to your tach, i.e. the one going from the dizzy to the tach. (Which prolly says something cryptic like "TACH" on it )

The tach works just reading the #1 cylinder, i.e. hooked up normally. Oh, do watch for the arrow on the clamp-on sensor as I've found mine is picky about which side points at the plug (there's a thing says "PLUG ==>" on it, again, self-evident once you look for it.)

-- A

 

[handloader90]

Thanks for that info. I hooked the tach up about two months ago so I'm pretty familiar with the wiring. What exactly is the dwell? Will it be useful when timing or just leave it alone?

How do you like the light, is it all its cracked up to be... accurate and all? Simple to understand (function wise) and easy to operate?

 

[dremu]

Thanks for that info. I hooked the tach up about two months ago so I'm pretty familiar with the wiring. What exactly is the dwell? Will it be useful when timing or just leave it alone?

I've never dinked with it. I seem to recall it was a big deal with points ignitions but with the "modern" HEI, I think it's all handled by them newfangled transistors. You can Google it if you wanna go cross-eyed.

How do you like the light, is it all its cracked up to be... accurate and all? Simple to understand (function wise) and easy to operate?

Well, I've dialled in two trucks with it, pleased so far. It's more accurate than my old cheapo, but in the end you tweak the timing by hand and ear anyway, so the light is ... a guide, not an absolute, IMO.

-- A

 

[blazer74]

Don't worry about dwell with HEI, when using points dwell is a related to point gap.
HEI does all that for you.

I'm at 10 initial, 24 mechanical, 14 vacuum (10+24=34)+14 vac total 48
My mechanical starts at 1100
Carbed and just under 9:1

 

[ryoken]

I have that light.. I cut the dwell wire off short so it's not in the way and made it a bullet connection cuz I use it so rarely.. and that's with me on occasion still seeing points in the boats.. I get annoyed with customers with points dizzy's.. "dude, if your not gonna drop new dizzy's in, at least convert them with some cheap Pertronix conversion kits"

 

[chulisohombre]

Yep dwell is for points distributors. Mid 70s or so and earlier non hei distributors had it. On edelbrock carb use the bottom right vaccuum port for the advance. Do not use the same port for your brake booster. The rest everyone has sais Is good.