How much Initial timing do you have?
07-11-2012, 08:14 AM
#1
Drifting
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How much Initial timing do you have?
Thinking if i can perhaps improve my advance curve? I am using the MSD pro billet and from memory thats the 8361 but anyway i am using the large black stop bushing which limits 18 degrees of mechanical advance and im running around 16 degrees of initial. Because i have fastburn heads i try to keep it around 34 degrees total.
My question is that i believe more initial would be great especially with the cam and engine combo i have but how do i achieve this when I am already using the largest stop bushing available ?....I would like to experiment with 18 perhaps 20 of initial or should i just be happy with 16 initial even though i dont think its enough ?
My question is that i believe more initial would be great especially with the cam and engine combo i have but how do i achieve this when I am already using the largest stop bushing available ?....I would like to experiment with 18 perhaps 20 of initial or should i just be happy with 16 initial even though i dont think its enough ?
07-11-2012, 08:42 AM
#2
Melting Slicks
I locked out my MSD Probillet at 36 degrees, but my cam is 254@.050 and idle vacuum was about 8 inches. Pretty roudy idle. Starts fine, no surge, never pings.....
I had tried the 18 degree limiter (black bushing) and it was not enough initial timing for mine either.
I had tried the 18 degree limiter (black bushing) and it was not enough initial timing for mine either.
07-11-2012, 09:18 AM
#3
Race Director
I don't know what cam you guys have but I have a 248/254 @ .050" and mine runs fine with the 18 deg. bushing. I have 34 degs advance and obviously 34-18 = 16 deg initial timing.
I have run at 40 deg advance with no noticeable difference that I could feel, meaning I may have gained or lost a few ponies but startup was just the same at say 22 degs or 16 degs initial, no vacuum advance
I have run at 40 deg advance with no noticeable difference that I could feel, meaning I may have gained or lost a few ponies but startup was just the same at say 22 degs or 16 degs initial, no vacuum advance
07-11-2012, 10:00 AM
#4
Team Owner
If you actually talk to the people that design ignitions they will tell you that about 18 is tops in a well tuned motor with modern chambers.
Higher exhaust dilution, poor fuel atomization, higher octane than required, poor spark, low % of cylinder filling, spark shielding from non indexed plugs............ are all things that can cause it to appear to run better with more than 18 degrees.
So fix what is wrong with your motor before you chase the additional spark lead.
You can easily prove the best advance for a given combo on a dyno. you set the dyno to load the motor to a HP level like 100 at some rpm above idle before any advance starts to come in. then rotate the dizzy changing the timing up and down and watch what happens to the HP read out. On tuned motors I've seen it drop off rapidy over 18 degrees.
I don't care if you believe me. Make some phone calls and do some dyno time
Higher exhaust dilution, poor fuel atomization, higher octane than required, poor spark, low % of cylinder filling, spark shielding from non indexed plugs............ are all things that can cause it to appear to run better with more than 18 degrees.
So fix what is wrong with your motor before you chase the additional spark lead.
You can easily prove the best advance for a given combo on a dyno. you set the dyno to load the motor to a HP level like 100 at some rpm above idle before any advance starts to come in. then rotate the dizzy changing the timing up and down and watch what happens to the HP read out. On tuned motors I've seen it drop off rapidy over 18 degrees.
I don't care if you believe me. Make some phone calls and do some dyno time
07-11-2012, 10:13 AM
#5
Drifting
You can buy bushings that will give you a shorter mechanical advance curve.
Here is one source. - http://www.4secondsflat.com/MSD%20Di...r%20Tuning.htm
I typically give the engine the initial timing that results in the smoothest idle, highest vacuum, & best throttle response.
Then I shorten the mechanical curve to limit the max advance to where I want it.
In my case, I'm running about 28° of initial advance, with another 10° of mechanical.
I'm running an engine that's quite a bit different than yours though. (498 BBC)
Here is one source. - http://www.4secondsflat.com/MSD%20Di...r%20Tuning.htm
I typically give the engine the initial timing that results in the smoothest idle, highest vacuum, & best throttle response.
Then I shorten the mechanical curve to limit the max advance to where I want it.
In my case, I'm running about 28° of initial advance, with another 10° of mechanical.
I'm running an engine that's quite a bit different than yours though. (498 BBC)
07-11-2012, 01:22 PM
#6
Melting Slicks
I run a th400 with 3000 stall. The problem I had was idling in gear for extended periods. (traffic light). If I kept the trans in gear it would stall eventually. The vacuum advance could not hold any advance because of the 6-8 inches of vacuum (bouncing)
I posted this quite a while ago on a few different sites and the general opinion was that locking out the timing would be the best way to deal with it. The cam I have is an Isky Z-35 flat tappet solid, 254@.050, 108LC, and I am running 1.60 rollers,so lift is .560.
If I had a manual trans,...likely I would not have had any issue.
I posted this quite a while ago on a few different sites and the general opinion was that locking out the timing would be the best way to deal with it. The cam I have is an Isky Z-35 flat tappet solid, 254@.050, 108LC, and I am running 1.60 rollers,so lift is .560.
If I had a manual trans,...likely I would not have had any issue.
07-12-2012, 01:19 PM
#8
Le Mans Master
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Thinking if i can perhaps improve my advance curve? I am using the MSD pro billet and from memory thats the 8361 but anyway i am using the large black stop bushing which limits 18 degrees of mechanical advance and im running around 16 degrees of initial. Because i have fastburn heads i try to keep it around 34 degrees total.
My question is that i believe more initial would be great especially with the cam and engine combo i have but how do i achieve this when I am already using the largest stop bushing available ?....I would like to experiment with 18 perhaps 20 of initial or should i just be happy with 16 initial even though i dont think its enough ?
My question is that i believe more initial would be great especially with the cam and engine combo i have but how do i achieve this when I am already using the largest stop bushing available ?....I would like to experiment with 18 perhaps 20 of initial or should i just be happy with 16 initial even though i dont think its enough ?
http://www.corvette-restoration.com/...c_Adv_Spec.pdf
Keep the shiny side up!
Scott
07-12-2012, 03:40 PM
#9
Melting Slicks
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St. Jude Donor '05-'06,'11,'13-'14,'16,'18,'19
I think it really depends on your set up,
I run a Lunati solid roller with mid 250 duration and a little over .700" lift,
I've tried many different set-ups and it runs its best with the timing locked out at 36*
Neal
I run a Lunati solid roller with mid 250 duration and a little over .700" lift,
I've tried many different set-ups and it runs its best with the timing locked out at 36*
Neal
07-12-2012, 06:54 PM
#10
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St. Jude Donor '05
Wouldnt believe Gkull til I unless Id seen the results myself.
None of those MSD bushings worked worth a damn and didnt time the way they claimed;had me scratching my head forever tried every combo of bushing/spring they had.
Was convinced I needed to lock mine out also...
Someone who knew better got ahold of it and at the end of the day have a lot less intial ( no vac adv) than seems reasonable.
Curve comes in late and slow. Never would have guessed....absolutely night and day difference in the way it runs, starts easy no pinging still responsive. 11.5:1 on pump 91.
Not sure you need all that locked out business but as said everyones setup is a little different.
None of those MSD bushings worked worth a damn and didnt time the way they claimed;had me scratching my head forever tried every combo of bushing/spring they had.
Was convinced I needed to lock mine out also...
Someone who knew better got ahold of it and at the end of the day have a lot less intial ( no vac adv) than seems reasonable.
Curve comes in late and slow. Never would have guessed....absolutely night and day difference in the way it runs, starts easy no pinging still responsive. 11.5:1 on pump 91.
Not sure you need all that locked out business but as said everyones setup is a little different.
Last edited by cv67; 07-12-2012 at 07:02 PM.
07-12-2012, 11:54 PM
#12
15 degrees initial with 36 total on 468/11:1/248-254@0.050/0.600 plus lift. I run vacuum advance and 93 octane on an 8572 MSD distributor.
Last edited by Super6; 07-13-2012 at 05:05 AM. Reason: Spelling.
07-13-2012, 01:19 AM
#13
Team Owner
I started working as a pit crew person on sprint cars on the the the early 80's on ignorant alki injected motors with locked out mag ignitions. 60's designed hilborn 8 stack mechanical injection. Once money really got into the sport........ It just took off. Us free thinkers and dyno engine shops left the bubbas behind in the dirt.
Real race cars in the 80's had multi coils like the modern LS engines. Crank triggers and distributerless ignitions appeared in the 90's
When somebody tells me they have some super high advance and or locked out..... I wonder if that is the best they can do?
1/2 a brain is all it would take...... to come up with something better.
I set my Vette advance curve with dial switches. A modern car you can't even put a timing light on it. A program sets it
Real race cars in the 80's had multi coils like the modern LS engines. Crank triggers and distributerless ignitions appeared in the 90's
When somebody tells me they have some super high advance and or locked out..... I wonder if that is the best they can do?
1/2 a brain is all it would take...... to come up with something better.
I set my Vette advance curve with dial switches. A modern car you can't even put a timing light on it. A program sets it
07-13-2012, 04:07 PM
#14
Melting Slicks
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St. Jude Donor '05-'06,'11,'13-'14,'16,'18,'19
Well I don't have the extensive resume that gkull has and I guess using 1/2 a brain has done me good till now.
I seem to remember Alan has his timing locked out at 36* or so and is running in the mid to upper 10's and doing pretty good on the street with AC and all. He has also spent some time on his buddies dyno to get his setup running as it does.
No disrespect to gkull but its hard to make a blanket statement to cover all combo's that are out there, the poster asked who was running what and for the most part that's whats been posted.
In no way ment to insult you gkull and don't appreciate your post at all either.
You no doubt have allot of experience around cars and shops and your input here is usually helpful.
Maybe I'm taking your post the wrong way,
Neal
.I seem to remember Alan has his timing locked out at 36* or so and is running in the mid to upper 10's and doing pretty good on the street with AC and all. He has also spent some time on his buddies dyno to get his setup running as it does.
No disrespect to gkull but its hard to make a blanket statement to cover all combo's that are out there, the poster asked who was running what and for the most part that's whats been posted.
In no way ment to insult you gkull and don't appreciate your post at all either.
You no doubt have allot of experience around cars and shops and your input here is usually helpful.
Maybe I'm taking your post the wrong way,
Neal
07-13-2012, 05:46 PM
#15
Team Owner
If you really want to get technical. super high rpm race motors actually retard the timing starting at about 7000 rpm. atomization is so high that flame travel is nearly instant.
If you actually talk to the people that design ignitions they will tell you that about 18 is tops in a well tuned motor with modern chambers.
Higher exhaust dilution, poor fuel atomization, higher octane than required, poor spark, low % of cylinder filling, spark shielding from non indexed plugs............ are all things that can cause it to appear to run better with more than 18 degrees.
So fix what is wrong with your motor before you chase the additional spark lead.
07-13-2012, 10:33 PM
#17
Le Mans Master
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Keep the shiny side up!
Scott
07-13-2012, 10:58 PM
#18
Le Mans Master
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Well I don't have the extensive resume that gkull has and I guess using 1/2 a brain has done me good till now.
I seem to remember Alan has his timing locked out at 36* or so and is running in the mid to upper 10's and doing pretty good on the street with AC and all. He has also spent some time on his buddies dyno to get his setup running as it does.
No disrespect to gkull but its hard to make a blanket statement to cover all combo's that are out there, the poster asked who was running what and for the most part that's whats been posted.
In no way ment to insult you gkull and don't appreciate your post at all either.
You no doubt have allot of experience around cars and shops and your input here is usually helpful.
Maybe I'm taking your post the wrong way,
Neal
.I seem to remember Alan has his timing locked out at 36* or so and is running in the mid to upper 10's and doing pretty good on the street with AC and all. He has also spent some time on his buddies dyno to get his setup running as it does.
No disrespect to gkull but its hard to make a blanket statement to cover all combo's that are out there, the poster asked who was running what and for the most part that's whats been posted.
In no way ment to insult you gkull and don't appreciate your post at all either.
You no doubt have allot of experience around cars and shops and your input here is usually helpful.
Maybe I'm taking your post the wrong way,
Neal
Keep the shiny side up!
Scott