ignition timing setting.
Thread Starter
Melting Slicks
Joined: Feb 2001
Posts: 3,330
Likes: 13
From: Europe , Luxembourg
ignition timing setting.
Hi
As I did a panic built up of my 68 big block to get it onto the road about a month ago, I knew that my ignition setting wasn't top.
I set it to 6 BTDC with the vacuum disconnected and it went to 51 BTDC at 3000 RPM, this with the vacuum and the flyways working.
The engine worked well, but today I readjusted all.
When I rebuilt the distributor, the new distributor main shaft came with a rubber bushing installed on the pin that limits flyway travel advance.
As the old one didn't have this, I removed this bushing, hence the 51 BTDC.
So, I reinstalled this bushing, readjusted the idle to 4 BTDC without the vacuum, this giving 17 BTDC with the vacuum connected and 41 BTDC in at 3.000 RPM with the vacuum and flyways maxed.
Is this now acceptable ?
What I find strange is that the vacuum advance stays in from idle up through the 3000 RPM range . Is this correct ? When will it loose the vacuum ? At 5000 or higher RPM. This would reduce the total advance from 41 again, wouldn't it.
My engine is a 427 CI solid lifter square port type with a double pumper HOLLEY and PERTRONIX ignition with ACCEL 50,000 V jellow coil.
Hope I have this explained correctly. Gunther
[Modified by WESCH, 3:10 PM 4/28/2003]
As I did a panic built up of my 68 big block to get it onto the road about a month ago, I knew that my ignition setting wasn't top.
I set it to 6 BTDC with the vacuum disconnected and it went to 51 BTDC at 3000 RPM, this with the vacuum and the flyways working.
The engine worked well, but today I readjusted all.
When I rebuilt the distributor, the new distributor main shaft came with a rubber bushing installed on the pin that limits flyway travel advance.
As the old one didn't have this, I removed this bushing, hence the 51 BTDC.
So, I reinstalled this bushing, readjusted the idle to 4 BTDC without the vacuum, this giving 17 BTDC with the vacuum connected and 41 BTDC in at 3.000 RPM with the vacuum and flyways maxed.
Is this now acceptable ?
What I find strange is that the vacuum advance stays in from idle up through the 3000 RPM range . Is this correct ? When will it loose the vacuum ? At 5000 or higher RPM. This would reduce the total advance from 41 again, wouldn't it.
My engine is a 427 CI solid lifter square port type with a double pumper HOLLEY and PERTRONIX ignition with ACCEL 50,000 V jellow coil.
Hope I have this explained correctly. Gunther
[Modified by WESCH, 3:10 PM 4/28/2003]
Pro
Joined: May 2001
Posts: 596
Likes: 0
From: Yardley PA
Re: ignition timing setting. (WESCH)
Hi Gunther!
In general, vac advance only goes away at WOT and in idle if connected to ported vacuum. Only at WOT you have almost atmospheric pressure. For instructions on how to properly set timing, Read Lars' tech-paper:
http://www.corvettefaq.com/c3/HowToSetTiming.doc
So as a summary: Your scenario is very possible, but total timing seems a little to low.
Good luck!
Prost:cheers:
Stefan
In general, vac advance only goes away at WOT and in idle if connected to ported vacuum. Only at WOT you have almost atmospheric pressure. For instructions on how to properly set timing, Read Lars' tech-paper:
http://www.corvettefaq.com/c3/HowToSetTiming.doc
So as a summary: Your scenario is very possible, but total timing seems a little to low.
Good luck!
Prost:cheers:
Stefan
Le Mans Master
Joined: Sep 2000
Posts: 5,635
Likes: 4
From: Orlando Floriduh
Re: ignition timing setting. (WESCH)
The advance curve sound about right with the bushing installed. The vacuum advance will not advance under LOAD. You may not get it to drop out until the car is driven. It should drop out when vacuum gets below 8"hg. as would happen if you stepped hard an the gas at low speed in 4th gear and then give you advance slowly as the vacuum increases. I can send you the distributor specifications if you want them.
Thread Starter
Melting Slicks
Joined: Feb 2001
Posts: 3,330
Likes: 13
From: Europe , Luxembourg
Re: ignition timing setting. (bluevetteman)
Hi
Thanks so far.
I did read Lars's tech paper, but possibly misunderstood it.
May be, my previous setting was the better one ?
So, I should have about 38 to 41 advance at 3000 RPM with the vacuum advance disconnected, or ?
This would bring the total advance , when the vacuum is connected again , to 51 or 52 degrees, this at 3000 RPM .
So, only at full WOT, the vacuum advance would be lost and total advance would be reduced to max flyway, hence 41 degrees.
Is this correct ?
So, I need to remove this bushing again , set initial to 4-6 degrees at idle with vacuum disconnected, this brings it to 17 advance with the vacuum connected at idle and somewhere between 2500 to 3000 RPM, it would peg at 51 degrees. Is this the ideal courve ?
Sorry for all this questions, but this timing setting is different from what I thought it would be.
I never realized, that the vacuum advance is working together with the flyway advance and adds up to it till I hit the pedal against the floor.
Thanks Gunther
:seeya
Thanks so far.
I did read Lars's tech paper, but possibly misunderstood it.
May be, my previous setting was the better one ?
So, I should have about 38 to 41 advance at 3000 RPM with the vacuum advance disconnected, or ?
This would bring the total advance , when the vacuum is connected again , to 51 or 52 degrees, this at 3000 RPM .
So, only at full WOT, the vacuum advance would be lost and total advance would be reduced to max flyway, hence 41 degrees.
Is this correct ?
So, I need to remove this bushing again , set initial to 4-6 degrees at idle with vacuum disconnected, this brings it to 17 advance with the vacuum connected at idle and somewhere between 2500 to 3000 RPM, it would peg at 51 degrees. Is this the ideal courve ?
Sorry for all this questions, but this timing setting is different from what I thought it would be.
I never realized, that the vacuum advance is working together with the flyway advance and adds up to it till I hit the pedal against the floor.
Thanks Gunther
:seeya
Pro
Joined: May 2001
Posts: 596
Likes: 0
From: Yardley PA
Re: ignition timing setting. (WESCH)
Well, it's easier to just adjust total MECHANICAL advance. Just unplug the vac-advance. REMOVE the springs that pull in the weights and you get your total mech advance right away at idle. Adjust to 36-38 degrees. I would NOT go over 38 if you do not now more about timing than Lars does or have a knock sensor.
Then of course you reconnect eveything inlcuding springs and voila!
You have your timing :D
Prost!:cheers:
Stefan
Then of course you reconnect eveything inlcuding springs and voila!
You have your timing :D
Prost!:cheers:
Stefan
Thread Starter
Melting Slicks
Joined: Feb 2001
Posts: 3,330
Likes: 13
From: Europe , Luxembourg
Re: ignition timing setting. (Stefan69)
Thanks,
Thats also the way, Lars recommends it. I just misread or misinterpreted it.
I will try this and check all other settings afterwards, just to see what they are.
Oh, an other may be stupid question: I read that most camshaft chains gears have a 4 degree BTDC, a zero and a 4 PTDC setting.
How do I know myne is set to ? What are they normally set to ?
Thanks a lot for all feedback. Gunther
Thats also the way, Lars recommends it. I just misread or misinterpreted it.
I will try this and check all other settings afterwards, just to see what they are.
Oh, an other may be stupid question: I read that most camshaft chains gears have a 4 degree BTDC, a zero and a 4 PTDC setting.
How do I know myne is set to ? What are they normally set to ?
Thanks a lot for all feedback. Gunther
Tech Contributor
Joined: Aug 1999
Posts: 14,376
Likes: 6,375
From: At my Bar drinking and wrenching in Lafayette Colorado
Re: ignition timing setting. (WESCH)
Gunther -
Don't remove the advance stop bushing. Removing the stop bushing will not give you enough intial advance without exceeding the 36-degree max spec. Leave the bushing in place to get as much initial advance as you can while setting the total timing (with vac advance disconnected) to 36-38. 4 degrees initial is not enough - you want to get that initial timing up into the low to mid-teens in order to get a good idle with good throttle response.
With the mechanical timing set to a maximum of 36, you want the vacuum advance to pull in an additional 16 degrees for a total combined maximum timing of 52.
The only way to know if your cam has been advanced or retarded 4 degrees is by knowing your cam spec's and degree'ing the cam. This is not easy to do with the engine in the car - it would actually be easier to pull the front end of the engine apart, remove the timing chain cover, and visually inspect the installation to see if it has been installed "straight up," retarded, or advanced. Most engine builders will install the gears set "straight up," since advancing or retarded a cam 4 degrees is a bit drastic. I usually advance my cams a maximum of 2 degrees using an offset key.
Don't remove the advance stop bushing. Removing the stop bushing will not give you enough intial advance without exceeding the 36-degree max spec. Leave the bushing in place to get as much initial advance as you can while setting the total timing (with vac advance disconnected) to 36-38. 4 degrees initial is not enough - you want to get that initial timing up into the low to mid-teens in order to get a good idle with good throttle response.
With the mechanical timing set to a maximum of 36, you want the vacuum advance to pull in an additional 16 degrees for a total combined maximum timing of 52.
The only way to know if your cam has been advanced or retarded 4 degrees is by knowing your cam spec's and degree'ing the cam. This is not easy to do with the engine in the car - it would actually be easier to pull the front end of the engine apart, remove the timing chain cover, and visually inspect the installation to see if it has been installed "straight up," retarded, or advanced. Most engine builders will install the gears set "straight up," since advancing or retarded a cam 4 degrees is a bit drastic. I usually advance my cams a maximum of 2 degrees using an offset key.
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Thread Starter
Melting Slicks
Joined: Feb 2001
Posts: 3,330
Likes: 13
From: Europe , Luxembourg
Re: ignition timing setting. (lars)
Hi
Thanks a lot.
I readjusted all.
Now 37-38 at 3000 RPM , vacuum diconnected.
10-11 initial, vacuum disconnected.
22-23 idle, vacuum connected
51 total at 3000 RPM.
This with the stop bushing installed.
It's the best I could get it to. Is this now OK ?
Looks like if I need to replace the timing chain due to 1-2 degrees of fluctuations when at steady power. OK during spool up. Only shows when keeping steady RPM.
As the distributor has been overhauled and should not have any more play, it must be the chain. :mad
Well, this is for next winter.
Now I need some good weather to try this ignition setting out.
It's pissing down with rain , but tomorrow, the 1st might be OK.
Thanks again for all help.
Oh yes, something else I found out after following Lars's advise to remark the 36-38 degree on the damper after measuring it's circumference is, that the existing pointer marks where in 2 degree increments. I thought they where in 1 degree increments. So, actually I had 8 initial and thought I only had 4. I did confirm this 2 degree increments with a adjustable timing light.
Gunther
[Modified by WESCH, 7:18 PM 4/30/2003]
Thanks a lot.
I readjusted all.
Now 37-38 at 3000 RPM , vacuum diconnected.
10-11 initial, vacuum disconnected.
22-23 idle, vacuum connected
51 total at 3000 RPM.
This with the stop bushing installed.
It's the best I could get it to. Is this now OK ?
Looks like if I need to replace the timing chain due to 1-2 degrees of fluctuations when at steady power. OK during spool up. Only shows when keeping steady RPM.
As the distributor has been overhauled and should not have any more play, it must be the chain. :mad
Well, this is for next winter.
Now I need some good weather to try this ignition setting out.
It's pissing down with rain , but tomorrow, the 1st might be OK.
Thanks again for all help.
Oh yes, something else I found out after following Lars's advise to remark the 36-38 degree on the damper after measuring it's circumference is, that the existing pointer marks where in 2 degree increments. I thought they where in 1 degree increments. So, actually I had 8 initial and thought I only had 4. I did confirm this 2 degree increments with a adjustable timing light.
Gunther
[Modified by WESCH, 7:18 PM 4/30/2003]
Pro
Joined: May 2001
Posts: 596
Likes: 0
From: Yardley PA
Re: ignition timing setting. (WESCH)
Is this now OK ?
Looks like if I need to replace the timing chain due to 1-2 degrees of fluctuations when at steady power. OK during spool up. Only shows when keeping steady RPM.
As the distributor has been overhauled and should not have any more play, it must be the chain. :mad
As the distributor has been overhauled and should not have any more play, it must be the chain. :mad
Stefan
Tech Contributor
Joined: Aug 1999
Posts: 14,376
Likes: 6,375
From: At my Bar drinking and wrenching in Lafayette Colorado
Re: ignition timing setting. (WESCH)
Gunther -
Your numbers look great! Leave it just like that.
One thing you can do to eliminate a bit of timing fluctuation is to tighten up the hole that attaches the breaker plate to the vacuum advance control unit rod: There is usually a bit of slop in the hole that the vacuum advance rod goes through in the sheet metal breaker plate. This slop allows the plate to rattle back and forth a bit, making the timing fluctuate. Remove the distributor, pull out the shaft, remove the snapring that holds the plate in place, and then place the plate on a hard surface. Whack the raised hole for the vacuum rod with a hammer. This will crimp the hole and make it fit snug on the rod. This will then eliminate all of the play and wobble in the plate, and it will tighten up your timing by several degrees.
Your numbers look great! Leave it just like that.
One thing you can do to eliminate a bit of timing fluctuation is to tighten up the hole that attaches the breaker plate to the vacuum advance control unit rod: There is usually a bit of slop in the hole that the vacuum advance rod goes through in the sheet metal breaker plate. This slop allows the plate to rattle back and forth a bit, making the timing fluctuate. Remove the distributor, pull out the shaft, remove the snapring that holds the plate in place, and then place the plate on a hard surface. Whack the raised hole for the vacuum rod with a hammer. This will crimp the hole and make it fit snug on the rod. This will then eliminate all of the play and wobble in the plate, and it will tighten up your timing by several degrees.
Thread Starter
Melting Slicks
Joined: Feb 2001
Posts: 3,330
Likes: 13
From: Europe , Luxembourg
Re: ignition timing setting. (lars)
Hello
OK, I will check this hole for play.
The fluctuations are at 3000 RPM and above, so with the flyways bottomed and at 3000 RPM also with the vacuum bottomed.
Accellerating at any speed to 3000 RPM gives steady increasing timing.
Don't know if I explained this correct the first time.
Could this still be the vacuum advance ?
Thanks Gunther :seeya
OK, I will check this hole for play.
The fluctuations are at 3000 RPM and above, so with the flyways bottomed and at 3000 RPM also with the vacuum bottomed.
Accellerating at any speed to 3000 RPM gives steady increasing timing.
Don't know if I explained this correct the first time.
Could this still be the vacuum advance ?
Thanks Gunther :seeya
Melting Slicks
Joined: Feb 2003
Posts: 2,330
Likes: 6
From: Long Island NY
Re: ignition timing setting. (WESCH)
You keep asking if you set the timing right. You haven't said how the car feels...does it put you in the back of the seat... ;) , that's the BEST test! LOL
[Modified by mvftw, 10:19 PM 5/1/2003]
[Modified by mvftw, 10:19 PM 5/1/2003]
Tech Contributor
Joined: Aug 1999
Posts: 14,376
Likes: 6,375
From: At my Bar drinking and wrenching in Lafayette Colorado
Re: ignition timing setting. (WESCH)
Gunther -
If there is a little slop in the breaker plate hole, it doesn't matter if the vacuum advance is fully pulled in or not - the plate can rattle around at elevated rpm. You can test it by simply pulling off your distributor cap and rotor so you can get your fingers onto the plate: wiggle the plate back and forth and see if it has any play against the vacuum advance rod. Any play will cause a timing scatter of twice that number of degrees. So if it wiggles, you'd be best off to pop it out, give it a good hammer smack, and get it tight.
If there is a little slop in the breaker plate hole, it doesn't matter if the vacuum advance is fully pulled in or not - the plate can rattle around at elevated rpm. You can test it by simply pulling off your distributor cap and rotor so you can get your fingers onto the plate: wiggle the plate back and forth and see if it has any play against the vacuum advance rod. Any play will cause a timing scatter of twice that number of degrees. So if it wiggles, you'd be best off to pop it out, give it a good hammer smack, and get it tight.
Thread Starter
Melting Slicks
Joined: Feb 2001
Posts: 3,330
Likes: 13
From: Europe , Luxembourg
Re: ignition timing setting. (lars)
Thanks Lars.
I test drove it today. Wow, it is different now.
B4, when slamming the pedal to the floor, the first reaction was a bogging . I thought this was normal for the double pumper HOLLEY as it injects lots of fuel with the simple action of the pedal. But now it's not doing this anymore. No bogging, instant reaction and endless power. :yesnod:
Also, B4, when starting the car up ( cold ), I had to rev it at 2000 RPM or drive it for a while B4 it kept idling without shutting down. ( carb has no choke ). Now, it starts up nicely and idles right away at 750 RPM without any need to step or pump the gaspedal.
I'm positively impressed and a bit pissed off about the books's specs of 4 degrees initial.
Hi mvftw ,
Problem was , this big block always but me into the back of the seat and since I don't know any other big block Vette owner in my area, I just couldn't compare. :cry
Gunther
:thumbs:
I test drove it today. Wow, it is different now.
B4, when slamming the pedal to the floor, the first reaction was a bogging . I thought this was normal for the double pumper HOLLEY as it injects lots of fuel with the simple action of the pedal. But now it's not doing this anymore. No bogging, instant reaction and endless power. :yesnod:
Also, B4, when starting the car up ( cold ), I had to rev it at 2000 RPM or drive it for a while B4 it kept idling without shutting down. ( carb has no choke ). Now, it starts up nicely and idles right away at 750 RPM without any need to step or pump the gaspedal.
I'm positively impressed and a bit pissed off about the books's specs of 4 degrees initial.
Hi mvftw ,
Problem was , this big block always but me into the back of the seat and since I don't know any other big block Vette owner in my area, I just couldn't compare. :cry
Gunther
:thumbs:
