Timing Light Accuracy

[mopowers]

With what fuel,heads, and Q; might I ask?

I've been running 91 oct E15 CA pump gas. Heads are RHS/Indy X prepped by IMM. I'm assuming by 'Q' you mean quench? I'd have to double check, but i believe it's around 0.037"? If I recall, pistons were 0.015" out of the hole and I'm using 521SD gaskets.

I'm picking up another timing light tomorrow btw.

 

[yellow rose]

I've seen 4 different timing lights give 4 different readings. Buy a new, non dial back timing light and if your damper isn't degreed get a timing tape and ONLY use THAT timing light. Let the plugs tell you how much timing you need on THAT timing light. I don't care if it says 20 total or 60 total.

Obviously that's an exaggeration, but I've seen up to 6 degrees difference in lights. Buy a light and use it on your stuff.

 

[RustyRatRod]

Problem is, it's hard to find a decent one now because none of these new POS "cars" needs a timing light.

....and I ain't payin 300 bucks for somethin off a tool truck. YR makes a lotta sense. Just buy one and go by IT.

btw, @yellow rose .....where you been pecker?

 

[yellow rose]

Problem is, it's hard to find a decent one now because none of these new POS "cars" needs a timing light.

....and I ain't payin 300 bucks for somethin off a tool truck. YR makes a lotta sense. Just buy one and go by IT.

btw, @yellow rose .....where you been pecker?

Busy busy busy. I have one more load of laundry to do tonight, and as soon as the dishwasher is done (I suspect about an hour and a half from now) I'll unload that pig and be done for the night. Tomorrow starts all over. My parents aren't doing well and I'm taking care of them for awhile. After two years of taking care of the inlaws I hoped I'd get a break but evidently, 2019 is going to be another year of taking care of family.

 

[RustyRatRod]

Busy busy busy. I have one more load of laundry to do tonight, and as soon as the dishwasher is done (I suspect about an hour and a half from now) I'll unload that pig and be done for the night. Tomorrow starts all over. My parents aren't doing well and I'm taking care of them for awhile. After two years of taking care of the inlaws I hoped I'd get a break but evidently, 2019 is going to be another year of taking care of family.

You have my admiration for that. Will add them to our prayer list.

 

[AJ/FormS]

I've been running 91 oct E15 CA pump gas. Heads are RHS/Indy X prepped by IMM. I'm assuming by 'Q' you mean quench? I'd have to double check, but i believe it's around 0.037"? If I recall, pistons were 0.015" out of the hole and I'm using 521SD gaskets.

I'm picking up another timing light tomorrow btw.

Those are Iron heads, right? Glad you figured out how to make that work. I bet that's a sharp combo.

 

[mopowers]

After using a buddy's Matco timing light this weekend, it gave the same reading as my old Craftsman. Apparently this little 340 just likes a TON of initial ignition timing - I ended up with 30* initial.

Those are Iron heads, right? Glad you figured out how to make that work. I bet that's a sharp combo.

Yes, they're iron heads.

 

[yellow rose]

After using a buddy's Matco timing light this weekend, it gave the same reading as my old Craftsman. Apparently this little 340 just likes a TON of initial ignition timing - I ended up with 30* initial.



Yes, they're iron heads.

If you are using an aftermarket box of a Chrysler module the timing retards with RPM. You can't see it with a timing light, but it happens. As much as 2 degrees per 1000 RPM.

I've never lost sleep over a timing number that seems high to everyone else. Most guys don't test. They only do what others have told them.

If your stuff runs better with 30 degrees initial with your timing light, do it. Unless it's hurting parts.

 

[mopowers]

If you are using an aftermarket box of a Chrysler module the timing retards with RPM. You can't see it with a timing light, but it happens. As much as 2 degrees per 1000 RPM.

I've got a 4-pin GM HEI. Seems to run the same with a couple different ones.

 

[Mike69cuda]

Could be inaccurate timing marks. If the engine has been apart over the years, who knows. If you feel like chasing it some more the next move would probably be to check it with a piston stop & see if TDC is really where you think it is.

 

[mopowers]

Could be inaccurate timing marks. If the engine has been apart over the years, who knows. If you feel like chasing it some more the next move would probably be to check it with a piston stop & see if TDC is really where you think it is.

That was the first thing I checked and the mark is dead nuts.

 

[yellow rose]

I've got a 4-pin GM HEI. Seems to run the same with a couple different ones.

That's OK because the HEI will retard with RPM too. You can't see it with a timing light but you damn sure see it with a good distributor machine. That's why locking out the timing is a bad deal.

 

[mopowers]

That's OK because the HEI will retard with RPM too. You can't see it with a timing light but you damn sure see it with a good distributor machine. That's why locking out the timing is a bad deal.

Are there HEI modules that don't retard with RPM?

Would it worthwhile to screw in as much timing it takes to make it detonate, then pull it back some? Seems like a light becomes pretty useless if the ignition is retarding on it's own at RPM.

 

[yellow rose]

Are there HEI modules that don't retard with RPM?

Would it worthwhile to screw in as much timing it takes to make it detonate, then pull it back some? Seems like a light becomes pretty useless if the ignition is retarding on it's own at RPM.

I'm not up on the HEI as I should be. But, most any electronic device has a slew rate so I'm pretty sure every HEI has retard with RPM like any other. How much you can only learn by testing the entire system with a distributor machine. And then tune accordingly.

 

[KitCarlson]

Perhaps some quantitative information about timing lights and ignition delay would be helpful.
Xenon strobe tube flash delays are typically a few microseconds. A microsecond is a millionth of a second. That delay is fairly small, has little impact setting base timming, and only fractions of a degree even at 6000 RPM. 6000 RPM divided by 60 converts RPM to 100 Hz, then multIply by 4, is 400. The reciprocal of 400 is 0.0025 or 2.5 milliseconds.

The turn off time for an ignition transistor, modern IGBT is also a few to several microseconds. Old style bipolar or darlington transistors may be 10 times slower.

At 6000 RPM, on a V8 ignition events occur at 90 degrees intervals of crank. The time between ignition events is 2 5 milliseconds. As an example, 5 microseconds delay divided by 2.5 milliseconds, times 90, is only 0.18 degree.

Mopar variable reluctance distributors have more significant errors, a few degrees due to runout, slop, and crude powdered metal reluctor, and other mechanical parts and linkages.

 

[Johnny Mac]

Do inductive timing lights ever go bad and give off inaccurate flashes? I've got a vintage Craftsman chrome inductive light that I'm questioning because of how much initial timing my 340 wants. I've verified the TDC mark - it's spot on. Maybe this 340 just an anomaly because it seems to want 30* initial adv.

Without having a second timing light to check it against, I'm curious if these thing ever go bad.

View attachment 1715317628

I have that same one...works well for me, even with digital and cdi ignitions.

 

[Ironracer]

Are there HEI modules that don't retard with RPM?

Would it worthwhile to screw in as much timing it takes to make it detonate, then pull it back some? Seems like a light becomes pretty useless if the ignition is retarding on it's own at RPM.

Old Post, but That's how we did it back in the day. Dial it Up, then drop er a Lil, run her, listen well, then check for kickback at starter. If no Det, good to go!

 

[RustyRatRod]

Old Post, but That's how we did it back in the day. Dial it Up, then drop er a Lil, run her, listen well, then check for kickback at starter. If no Det, good to go!

I still do it like that. Mainly because I'm too lazy to get my timing light out. But it works, there's no denying it. Almost without fail, when I come back and recheck it with a light, it's right where it should be.

 

[67Dart273]

That's OK because the HEI will retard with RPM too. You can't see it with a timing light but you damn sure see it with a good distributor machine. That's why locking out the timing is a bad deal.

Sorry not correct. If a timing light does not move, then neither did the timing. I DO NOT trust "dial up" lights. I've seen at least 3 over the many years, that were not accurate for some reason. I have two very old Craftsman "Roger Penske" lights, one is direct wired, and one is an inductive, both look identical from the mid -70's

If you have some test setup that shows the dist. changing and the timing doesn't then it is changing "in the box"

 

[halifaxhops]

Dial back timing lights I do not trust at all, I have seen way too many off. Timing tape is the way to go. Now the newer DIGITAL lights are spot on but not cheap. And also the old style non dial back lights are 99% of the time right on. No advance feature though.

 

[halifaxhops]

I still do it like that. Mainly because I'm too lazy to get my timing light out. But it works, there's no denying it. Almost without fail, when I come back and recheck it with a light, it's right where it should be.

Same here Rusty works every time.