Any timing experts out there that can explain some some timing paremeters

[conoco]

I was hoping someone on the forum could help explain the different timing parameters and maybe some base numbers I can start with on my new distributor.
I just installed the Progression Distributor and I can now control timing on the fly or make different timing tables for different driving. I know just your standard intial timing and all in, just the basics but could use some help explaining the different values with this new distributor so I am able to get the most out of it. Here is the different tables I need to populated. I would like to have a table for cruising around town and being able to get into the throttle a little bit and also for highway driving. Any help with explaining the different numbers would be awesome. I am trying to research as much as I can but can not get explanations for some of the values and I am kinda lost

So far with just the auto set up my truck is running way smoother, I have not driven it yet, waiting until I get the gear vendors unit installed. Thanks everyone.

[HO455]

In order for us to make informed recommendations we need detailed information on your truck.
Carburetor and intake
Cylinder head type and combustion chamber size
Compression ratio
Camshaft specifications and lifters installed
Transmission
Rear end ratio
Rear tire size
Now if you don't know the answers to all of these some assumptions can be made as long as timing is kept on the conservative side to prevent engine damage.

Here is an article covering the basics.

https://www.onallcylinders.com/2020/...to-make-power/

And if you really want to dive down the rabbit hole.

https://etrr.springeropen.com/articl...544-013-0099-8

[tdangle]

I have this system also. Nice thing is you can save multiple tables and switch on the fly, also edit specific rpm/advance cells on the fly and then save the changes.

I have a SP350/357 GM crate motor that has a mild cam with a very tight LSA at 108. I set idle in park at 850, 15 degrees idle, 32 total at 3000 and aggressive mode. Since I have a 4 speed OD auto trans and with 4.10 gears I'm just at 2000 at 65-70 mph I tuned the vac advance parameters very agressive with 15 total advance starting at 70 full at 50. Now at cruise I'm at about 40 total advance but even light throttle drops it to the mid to high 20 range.

Its a trial and error thing, every engine will be different. Here is a image of my timing table. I'm also open to comments

[conoco]

Originally Posted by HO455

In order for us to make informed recommendations we need detailed information on your truck.
Carburetor and intake
Cylinder head type and combustion chamber size
Compression ratio
Camshaft specifications and lifters installed
Transmission
Rear end ratio
Rear tire size
Now if you don't know the answers to all of these some assumptions can be made as long as timing is kept on the conservative side to prevent engine damage.

Here is an article covering the basics.

https://www.onallcylinders.com/2020/...to-make-power/

And if you really want to dive down the rabbit hole.

https://etrr.springeropen.com/articl...544-013-0099-8

Thank you for the article, I had to quit reading the other day, I was starting to get confused by all the data. Thank you for sharing and I will give it ago today. Here is the info needed, thanks again for your time.

Carb: Edelbrock AVS 2 / 650 cfm/ performer intake/ 2" spacer
Cylinder heads: fuelie heads/ 72 cc chamber/
Valves: 1.94 and 2.02
Lifters: 1.52
Compression: 11:1 ( has domed pistons)
Transmission: TH350 with gear vendors overdrive
Rear end: 4.11
TIRE: 35 inch
I'm not sure on the cam shaft and the compression is just what I got when I looked up my heads, I have not taken the cam out though. I bought my truck the owner rebuilt the engine to a 383 stroker. Sorry I can get some of the other specific details. Thanks again for your help.

[conoco]

Originally Posted by tdangle

I have this system also. Nice thing is you can save multiple tables and switch on the fly, also edit specific rpm/advance cells on the fly and then save the changes.

I have a SP350/357 GM crate motor that has a mild cam with a very tight LSA at 108. I set idle in park at 850, 15 degrees idle, 32 total at 3000 and aggressive mode. Since I have a 4 speed OD auto trans and with 4.10 gears I'm just at 2000 at 65-70 mph I tuned the vac advance parameters very agressive with 15 total advance starting at 70 full at 50. Now at cruise I'm at about 40 total advance but even light throttle drops it to the mid to high 20 range.

Its a trial and error thing, every engine will be different. Here is a image of my timing table. I'm also open to comments

That's great info! I really want to find the sweet spot, I know it will be a ton of trials I just didn't know where to start with some of the other values because ai didn't know what they really meant. I'm trying to read up as much as I can though just wanted some base numbers I could try out and adjust from there, thank you for the screen shot.

How long have you had yours? Really like mine so far but don't have any road time yet, feels like it's built really well. Thanks again.

[tdangle]

Originally Posted by conoco

That's great info! I really want to find the sweet spot, I know it will be a ton of trials I just didn't know where to start with some of the other values because ai didn't know what they really meant. I'm trying to read up as much as I can though just wanted some base numbers I could try out and adjust from there, thank you for the screen shot.

How long have you had yours? Really like mine so far but don't have any road time yet, feels like it's built really well. Thanks again.

I've had mine a year now. The parameters for setting it up are fairly straight forward. The only thing I really played with was when the "vac" advance started and was fully in. My understanding is a light cruise you want 40-50 degrees advance and since my cruise rpm was on the low end, originally i was not seeing much over mid 20's degrees. the full throttle settings are right on. Just set a starting or in park idle advance and total advance and when you want it all in by. What I like is when the idle drops below what I set the idle rpm at, the advance is advanced so kicking on the A/C and/or the load of a torque converter the rpm speed is slightly compensated by being raised slightly.

[tdangle]

Originally Posted by conoco

Thank you for the article, I had to quit reading the other day, I was starting to get confused by all the data. Thank you for sharing and I will give it ago today. Here is the info needed, thanks again for your time.

Carb: Edelbrock AVS 2 / 650 cfm/ performer intake/ 2" spacer
Cylinder heads: fuelie heads/ 72 cc chamber/
Valves: 1.94 and 2.02
Lifters: 1.52
Compression: 11:1 ( has domed pistons)
Transmission: TH350 with gear vendors overdrive
Rear end: 4.11
TIRE: 35 inch
I'm not sure on the cam shaft and the compression is just what I got when I looked up my heads, I have not taken the cam out though. I bought my truck the owner rebuilt the engine to a 383 stroker. Sorry I can get some of the other specific details. Thanks again for your help.

With that much compression, you may want to limit the total advance to 30 to 32 or so and watch listen for detonation on full throttle runs.

[conoco]

Originally Posted by tdangle

With that much compression, you may want to limit the total advance to 30 to 32 or so and watch listen for detonation on full throttle runs.

So I finally got my truck out in the road today and I must say it's like a completely different truck. So much more smooth and responsive. For fun I put in your values for my truck and it was a rocket from 1st to 2nd. It lagged a little going into 3rd but you should have seen my face lol.... I very much look forward to playing with this !! Thanks for the help.

[1970-CST]

You need to get a manifold vacuum number at idle, and off idle so you can set the vacuum advance parameters. At idle, you want around 15-20 degrees of “vacuum advance” for best efficiency. This will lower EGT and engine temps.

11:1 ? You would need a pretty large overlap cam to bleed that down to something manageable on pump gas. Big cams need more idle timing due to intake air being diluted with exhaust gas.

[Rich72C10]

Not sure how I missed this thread, I just got mine installed last weekend (love it).

I am just not sure what to do with the below, so I haven't even tried to touch them.
Max Vacuum Adv
Start Vacuum Adv
Max Vacuum Adv At

After a controlled test drive, using the App's Vacuum gauge to help me keep my foot inline, I got 18.5 MPG on mixed highway/city!

Though before trying to mess with anything the truck started up and idled better than it ever had in the past.

My Engine is more or less stock with a mild cam (really don't know its model/stats). 72 SBC with 993 heads with 76cc chambers, 72 Qjet (tuned for a 68 model by Cliff High Performance), Th350, 3.08 Rear End, and 235/75 R15 tires all around. Cliff says my engine is likely lower compression because of the “builder” 350 pistons & head gaskets. Something about messing up the "quench" and probably down around 7.5-7.7 to 1 or so.

For what it is worth, here is my current settings.

[1970-CST]

Rich72C10 can you change the Kpa unit to Inches of Mercury? Hg”

There is another thread going “Timing” and someone posted an article by the Late John Hinckley. The article is considered the Bible as far as timing and dist. Function.

You need to have more then 8* of vacuum advance. If your engine idles at say 16”Hg, you need to have the vac advance full in at 14” (two inch rule).

A good start would be (assuming 16” idle vacuum)
20* advance at 14”
18* advance at 13”
16* advance at 12”
14* advance at 11”
12* advance at 10”
10* advance at 9”
8* advance at 8”
6* advance at 7”
4* advance at 6”
2* advance at 5”
1* advance at 4”

This is very important, and highly misunderstood. Burned headers, heat soaked starters, overheating engines, vapor lock, poor fuel economy, sluggish part throttle response are all the symptoms of not having an active vacuum advance and not having it set right.

It appears you have the advance backwards, you want it to start at 4”-6” (the sooner the better as the engine will allow) and max out at 14”

Kpa to Hg
13.5 Kpa = 4” Hg This will be the START VACUUM ADVANCE
54 Kpa = 16” Hg. THIS WILL BE THE MAX VACUUM ADVANCE

A cam spec and manifold vacuum reading at idle will tell a lot about your valve timing and what your engine timing should be.

[Rich72C10]

no, it doesn't have an option to change from KPa to Hg. Though I am not sure which bit would get "20*" at 14 degrees initial. Which I do happen to have a solid 16hg at idle.

[1970-CST]

Originally Posted by Rich72C10

no, it doesn't have an option to change from KPa to Hg. Though I am not sure which bit would get "20*" at 14 degrees initial. Which I do happen to have a solid 16hg at idle.

Here is a Kpa/Hg converter
https://www.convertunits.com/from/kPa/to/in+Hg


If you have solid 16” at idle, you want full vacuum advance at 14”, which equals 47.4 Kpa. And the start at 4” or 13.5 Kpa.

I would set the following

MAX VACUUM ADVANCE = 20*
START VACUUM ADVANCE = 13.5 Kpa
MAX VACUUM ADVANCE AT = 47.4 Kpa.

This is telling the computer to do this: Start adding vacuum advance at 4” and add up to 20* of spark advance, all in by 14” Hg to respect the 2 inch rule. If it knocks or pings, back the 20* down 2* at a time until it doesn’t.

[Rich72C10]

well, can only use whole numbers in the app and for "Start Vacuum Advance at" can't be less than 20 (must be a value between 20 and 101).

so that is a bust to try out.

Though I didn't put in the values backwards - that is what the app started with. I haven't messed those Advanced timing values at all.

[1970-CST]

Originally Posted by Rich72C10

well, can only use whole numbers in the app and for "Start Vacuum Advance at" can't be less than 20 (must be a value between 20 and 101).

so that is a bust to try out.

Though I didn't put in the values backwards - that is what the app started with. I haven't messed those Advanced timing values at all.

That’s an emissions type vac adv schedule. Not optimum at all. Just use whole numbers and use the 20 Kpa as the lowest setting which is around 6” Hg. And the rest as described in the above post.

Vacuum advance is only a factor for idle, low load cruising, and trailing throttle. It is meant to decrease its spark advance as engine vacuum drops, not increase.

When you mash the gas pedal down, vacuum goes to near zero, and all the vac adv should go away, incrementally by 4-6” Hg or the engine would ping and knock. Inversely, as the engine gains RPM (gas pedal still mashed) manifold vacuum will begin to rise, and vac adv slowly added back in.

90% of our driving is part throttle cruising, where we want the vac adv for engine efficiency, fuel economy, etc.

[Rich72C10]

I have looked at a few screen captures (other users that have posted) and videos on YouTube - the three settings we are talking about are pretty much the same as my screen shot. Nothing really talks about changing these values at all.

Heck, the last thing I want to do is blow a rod out the side of my engine ha!

[1970-CST]

Originally Posted by Rich72C10

I have looked at a few screen captures (other users that have posted) and videos on YouTube - the three settings we are talking about are pretty much the same as my screen shot. Nothing really talks about changing these values at all.

Heck, the last thing I want to do is blow a rod out the side of my engine ha!

That won’t happen. This appears to be an emissions compliant vac adv setup which was meant to overheat the EGT to burn hydrocarbons, prior to catalytic converters.

I would change it.

Here is John Hinckley article. http://www.camaros.org/pdf/timing101.pdf

The short of it is GM used the vac adv schedule as described in my post, then changed to a degraded / less optimum “ported system” to comply with the emissions standards in the late 60’s.

[Rich72C10]

Well, the app won't let you do any of these settings.

1. First the app said I couldn't have more than 50 total timing. So I played RPM/Vacuum Max numbers to get 50 total.
2. Then the apps reported "Start Vacuum Advance At Must be Greater than Max Vacuum Advance At".

So the app isn't having any of these settings.

[zosoppp]

I think some of the confusion is in how progression measures the vacuum pressures. The KPa readings are absolute pressure readings, total barometric pressure (std atmosphere is 101.325 KPa or 29.92" Hg) minus the manifold vacuum.

So in the example screenshot provided, the vacuum advance goes from idle at 20 KPa absolute or about 6" Hg absolute or about 24" Hg Vacuum. Similarly the 80KPa absolute should be about 24" Hg absolute or 6"Hg vacuum.

Here's a review with a small explanation that might prove helpful:

https://board.moparts.org/ubbthreads...al-review.html

[Rickysnickers]

Lots of good info here, thank you. I really had no idea how vacuum advance really worked, and still really don't. I read two of the Hinckley articles and since my engine makes about 10" of vacuum at idle, I am going to try adding 12 degrees of vacuum advance. My engine has always seemed rather sluggish and I wonder if it was because the vacuum advance was low. I run an Edelbrock Pro Flo 4 system too.

[1970-CST]

Originally Posted by zosoppp

I think some of the confusion is in how progression measures the vacuum pressures. The KPa readings are absolute pressure readings, total barometric pressure (std atmosphere is 101.325 KPa or 29.92" Hg) minus the manifold vacuum.

So in the example screenshot provided, the vacuum advance goes from idle at 20 KPa absolute or about 6" Hg absolute or about 24" Hg Vacuum. Similarly the 80KPa absolute should be about 24" Hg absolute or 6"Hg vacuum.

Here's a review with a small explanation that might prove helpful:

https://board.moparts.org/ubbthreads...al-review.html

That makes total sense. There is a MAP sensor in the loop. Thanks for posting.

[Rich72C10]

gee, glad we got that sorted out! I suppose I could have said "its a MAP sensor" does that make a difference?

[1970-CST]

Originally Posted by Rickysnickers

Lots of good info here, thank you. I really had no idea how vacuum advance really worked, and still really don't. I read two of the Hinckley articles and since my engine makes about 10" of vacuum at idle, I am going to try adding 12 degrees of vacuum advance. My engine has always seemed rather sluggish and I wonder if it was because the vacuum advance was low. I run an Edelbrock Pro Flo 4 system too.

10” of manifold vacuum is pretty low. The 30-30 cam in my vintage vette made 10” and it needed A LOT of timing.

For discussion purposes, that engine (327/365hp 30-30 cam) idles at 1200 RPM, and setting base timing is near impossible, as the mechanical fly weights begin to add centrifugal advance around 700 rpm, lower then engine idles. So setting 10* initial timing was deceiving, as some of that was mechanical. In this case, I unhook the vacuum adv hose, and rev the engine until no more advance is added by the fly weights, in this case that was 2450 RPM. So at 2500 RPM I would move the dist. to set 38* advance.

If I set it at idle, I was leaving 6* of timing on the table, as the fly weights were contributing to the timing at idle. So setting 10* on the tab, was actually 4* base timing. When optimizing for performance, 6* is a HUGE amount.

What is your Idle RPM?

Timing is everything, and all the tuning and widgets to make HP are worthless unless you can optimize the timing map for your particular setup.

One needs to remember that “ported” vac adv, and low initial timing was a bandaid to get the engine across the emissions finish line. It was FAR from optimum.

[tdangle]

If you look at the timing map I posed above, you'll see 100 Kpa is 0 inches of vac and it goes inversely. The top few rows are pretty much full throttle and the bottom is high vacuum at deceleration. So at start at 80 is fairly low vac and 20 is very high vac. Its confusing I know.

[1970-CST]

Originally Posted by tdangle

If you look at the timing map I posed above, you'll see 100 Kpa is 0 inches of vac and it goes inversely. The top few rows are pretty much full throttle and the bottom is high vacuum at deceleration. So at start at 80 is fairly low vac and 20 is very high vac. Its confusing I know.

Gotcha. Reread your post. Are you running a fast burn type head?