School me on what affect initial timing has... - Hot Rod Forum : Hotrodders Bulletin Board
Hotrodders.com -- Hot Rod Forum



Register FAQ Search Today's Posts Unanswered Posts Auto Escrow Insurance Auto Loans
Hot Rod Forum : Hotrodders Bulletin Board > Tech Help> Hotrodding Basics
User Name
Password
lost password?   |   register now

Reply
 
LinkBack Thread Tools
  #1 (permalink)  
Old 09-13-2013, 02:59 PM
Motochris's Avatar
Registered User
 
Last photo:
Join Date: Jul 2007
Location: Ridgecrest CA
Posts: 101
Wiki Edits: 0

Thanks: 0
Thanked 4 Times in 2 Posts
School me on what affect initial timing has...

What does varying initial timing do for you?
Let's say your magic "all in" number for your engine is 36*.... you could get that with 2* initial timing and 34* mechanical..... or go 20* initial and 16* mechanical....or anything in between. The end result would be the 36* you wanted...
So what is it the initial timing is doing for you that you would want to change it? I understand too much initial and you can have hard starting.. but beyond that, what difference does initial timing make in performance/milage/idle...whatever?

    Advertisement
Reply With Quote Quick reply to this message
Sponsored Links
Advertisement
 
  #2 (permalink)  
Old 09-13-2013, 03:56 PM
Silver Surfer's Avatar
More machine than man
 

Last journal entry: bwaahhaahahaaahhaa
Last photo:
Join Date: Jul 2005
Location: Kansas City, MO
Age: 36
Posts: 806
Wiki Edits: 0

Thanks: 91
Thanked 60 Times in 50 Posts
Your initial timing needs to be set where the engine wants it. Your total timing needs to be set where your engine wants it. You do not want to link the two values like you are doing.

Not enough timing at idle (retarded) will lower the RPM's. To compensate, people will adjust the carb to idle the engine higher. This (1) will lower the engine vacuum (2) cause the engine to diesel (run on) when shut off.

Low performance engines (low performance cams) need only a small amount of initial timing. Somewhere in the 4-8 range.
High performance engines (long duration cams) need more initial timing. Somewhere in the 12-26 range.
Some high performance setups want locked out timing. Say, for example, 36 of initial timing, and NO mechanical or vacuum advance (engine always will run on 36).

If you find your engine wants 20 initial, and that means with full mechanical advance you have 40, you will need to modify your distributor to limit the total mechanical advance (to remove 4). You do NOT want to retard the initial down to 16.

This might help
http://www.crankshaftcoalition.com/w...EI_distributor
Reply With Quote Quick reply to this message
  #3 (permalink)  
Old 09-13-2013, 06:20 PM
Motochris's Avatar
Registered User
 
Last photo:
Join Date: Jul 2007
Location: Ridgecrest CA
Posts: 101
Wiki Edits: 0

Thanks: 0
Thanked 4 Times in 2 Posts
Quote:
Originally Posted by Silver Surfer View Post
Your initial timing needs to be set where the engine wants it. Your total timing needs to be set where your engine wants it. You do not want to link the two values like you are doing.

Not enough timing at idle (retarded) will lower the RPM's. To compensate, people will adjust the carb to idle the engine higher. This (1) will lower the engine vacuum (2) cause the engine to diesel (run on) when shut off.

Low performance engines (low performance cams) need only a small amount of initial timing. Somewhere in the 4-8 range.
High performance engines (long duration cams) need more initial timing. Somewhere in the 12-26 range.
Some high performance setups want locked out timing. Say, for example, 36 of initial timing, and NO mechanical or vacuum advance (engine always will run on 36).

If you find your engine wants 20 initial, and that means with full mechanical advance you have 40, you will need to modify your distributor to limit the total mechanical advance (to remove 4). You do NOT want to retard the initial down to 16.

This might help
http://www.crankshaftcoalition.com/w...EI_distributor
You are saying not to link them... but they ARE linked if you are figuring total advance. It's the combo of the initial and mechanical that is giving you your total.
Like I said... if your engine likes 36* of total... you could come up with that in a number of ways.

My questions are,
1-what is it that determines what your motor likes for the initial timing?
2-what effect does changing the initial up/down have?

example- If I'm currently at 11* initial and 25* mechanical for a total of 36*..... what would going up or down 5 degrees on the initial change (and compensating for the total by adjusting the mechanical accordingly so I still end up at 36*) ?
When I'm all in... The performance is what it is...doesn't matter how I got there. I'm wondering what changes are made in performance/etc. by the initial timing changes.

Last edited by Motochris; 09-13-2013 at 06:34 PM.
Reply With Quote Quick reply to this message
  #4 (permalink)  
Old 09-13-2013, 06:55 PM
Proud LOSER
 
Last photo:
Join Date: Mar 2008
Location: Ottawa
Posts: 1,799
Wiki Edits: 0

Thanks: 54
Thanked 249 Times in 216 Posts
Quote:
Originally Posted by Motochris View Post
You are saying not to link them... but they ARE linked if you are figuring total advance. It's the combo of the initial and mechanical that is giving you your total.
Like I said... if your engine likes 36* of total... you could come up with that in a number of ways.

My questions are,
1-what is it that determines what your motor likes for the initial timing?
2-what effect does changing the initial up/down have?

example- If I'm currently at 11* initial and 25* mechanical for a total of 36*..... what would going up or down 5 degrees on the initial change (and compensating for the total by adjusting the mechanical accordingly so I still end up at 36*) ?
When I'm all in... The performance is what it is...doesn't matter how I got there. I'm wondering what changes are made in performance/etc. by the initial timing changes.
So you set your initial at 6*
Then you have 30* advance
You now have your 36* total.
To get your long duration cam to idle at only 6* you compensate by what?
By simply turning up the idle on the carb right?
The problem there is now your transfer slot exposure is wrong. You no longer run of the idle circuit but now off the main circuit. Now its pig rich, now its lazy, now its smelly.
Now it suffers from run on.
Half the people you hear claiming 750 is to much Carb for a 350 are simply missing the tune. Having a tiny Carb masks this somewhat. I can make a 283 run fantastic with a 750 on it. Snappy, clean and pulls hard. Its going to take a combination of initial timing and vacuum advance from a manifold source to get the idle comfortable where I can get the transfer slot exposure right. You may see 36* at idle with vacuum and that's perfect, it will idle clean, response will be crisp and as throttle input drops vaccum your mechanical is coming in and your still giving it all the timing it wants.
Your not driving around at 3000rpm all the time, so your initial matters.
If you have a big cam, a 4000 stall and the motor leaves the line/light at 3000+ rpm then you can simply lock you timing at 36*(or what produces the best MPH) and call it good. Street cars need to accelerate away from lights, need to merge in traffic, and be able o accelerate away strongly.
Reply With Quote Quick reply to this message
  #5 (permalink)  
Old 09-13-2013, 07:04 PM
Motochris's Avatar
Registered User
 
Last photo:
Join Date: Jul 2007
Location: Ridgecrest CA
Posts: 101
Wiki Edits: 0

Thanks: 0
Thanked 4 Times in 2 Posts
Quote:
Originally Posted by bygddy View Post
So you set your initial at 6*
Then you have 30* advance
You now have your 36* total.
To get your long duration cam to idle at only 6* you compensate by what?
By simply turning up the idle on the carb right?
The problem there is now your transfer slot exposure is wrong. You no longer run of the idle circuit but now off the main circuit. Now its pig rich, now its lazy, now its smelly.
Now it suffers from run on.
Half the people you hear claiming 750 is to much Carb for a 350 are simply missing the tune. Having a tiny Carb masks this somewhat. I can make a 283 run fantastic with a 750 on it. Snappy, clean and pulls hard. Its going to take a combination of initial timing and vacuum advance from a manifold source to get the idle comfortable where I can get the transfer slot exposure right. You may see 36* at idle with vacuum and that's perfect, it will idle clean, response will be crisp and as throttle input drops vaccum your mechanical is coming in and your still giving it all the timing it wants.
Your not driving around at 3000rpm all the time, so your initial matters.
If you have a big cam, a 4000 stall and the motor leaves the line/light at 3000+ rpm then you can simply lock you timing at 36*(or what produces the best MPH) and call it good. Street cars need to accelerate away from lights, need to merge in traffic, and be able o accelerate away strongly.
Makes sense...
At what point do you STOP advancing the initial...when it becomes hard to start?
Beyond idle... are you tuning the initial for driveability THEN going back and re-adjusting the mechanical to get your desired "all in" number?
Reply With Quote Quick reply to this message
  #6 (permalink)  
Old 09-13-2013, 07:21 PM
bubbahotep's Avatar
Registered User
 
Last photo:
Join Date: Aug 2008
Location: NYC
Age: 42
Posts: 487
Wiki Edits: 0

Thanks: 1
Thanked 1 Time in 1 Post
Initial , or idle timing if you want to call it that, will correct a rough idle on a choppy cam. If you have too much idle timing you might get a situation where the car continues to run even after the key if off (pre-ignition). That horrible sputter you hear as the motor tries to die

They are linked. If you wrongly rotate the dizzy to give a higher initial timing you'll also have a higher total, so that's bad. If you go higher initial you'd need less advance with weights

My 383 stroker is at 28' idle timing, 10' advance. 38' total. I ran 28' idle to increase my rpm at idle to about 1100rpm. If I use less idle the car is choppy at a stop. At 28' I have my carb idle screw almost fully released, its barely doing much other than tweaking my idle.

To answer your question I guess a "correct" initial timing is part of the overall idle tune. It won't affect the WOT performance really so long as the total
Timing advances properly. An incorrect idle timing might give a sluggish acceleration depending on the motor.
Reply With Quote Quick reply to this message
  #7 (permalink)  
Old 09-13-2013, 07:36 PM
Member
 
Last photo:
Join Date: Dec 2004
Location: San Antonio, Texas
Age: 50
Posts: 4,021
Wiki Edits: 0

Thanks: 0
Thanked 23 Times in 23 Posts
low timing at idle is a type of emissions device.

read this.

http://www.corvette-restoration.com/.../Timing101.pdf
Reply With Quote Quick reply to this message
  #8 (permalink)  
Old 09-13-2013, 07:36 PM
Proud LOSER
 
Last photo:
Join Date: Mar 2008
Location: Ottawa
Posts: 1,799
Wiki Edits: 0

Thanks: 54
Thanked 249 Times in 216 Posts
Quote:
Originally Posted by Motochris View Post
Makes sense...
At what point do you STOP advancing the initial...when it becomes hard to start?
Beyond idle... are you tuning the initial for driveability THEN going back and re-adjusting the mechanical to get your desired "all in" number?
I'm trying to achieve the most comfortable stable idle, while maintaining proper transfer slot exposure and highest vacuum.
I would set up my total from a common used number, ie:36* total or 34* if using vortec heads, then let MPH and detonation tell the tale and adjust from there.
If it pings its too much, adjust for the highest MPH
As for hard to start, don't let that stop you, there are expensive or inexpensive solutions to that.
On my pro-filler headed 355 Trans Am, it had initial at 8* and total at 36* (weird HEI curve)
I changed that to 18* initial and 36* total, the difference was huge from just that . Cleaner idle, more stable, and far snapier....it came alive much faster and was all around more drveable.
Reply With Quote Quick reply to this message
  #9 (permalink)  
Old 09-14-2013, 11:29 AM
Motochris's Avatar
Registered User
 
Last photo:
Join Date: Jul 2007
Location: Ridgecrest CA
Posts: 101
Wiki Edits: 0

Thanks: 0
Thanked 4 Times in 2 Posts
I'll play with mine some more to see what differences I can tell.
I'm at 11* initial, 36 total on a Vortec headed 383. (Cam--.495/.503 lift, 218/224 duration @ .050 and 112 degree lobe seperation to help control idle quality...it's a heavy car with power brakes, steering, AC, etc. so idle vacuum is important) I want to try less total timing, but just bringing back the initial to 8 seems to make the car lazier.
The 11*/36* actually works well, idles surprisingly smooth. Most guys are saying leave it alone. I just want to play with it for my own learning.
I can step back my mechanical to 18* or 21* with bushings. I'll most likely try the 18* first...which will let me set my initial at around 16 for a total of 34* and see where I am.

Thanks for the info
Reply With Quote Quick reply to this message
  #10 (permalink)  
Old 09-14-2013, 01:46 PM
Greg T's Avatar
www.krusinklassics.net
 
Last photo:
Join Date: Jul 2007
Location: Escanaba, MI.
Age: 60
Posts: 1,149
Wiki Edits: 0

Thanks: 20
Thanked 41 Times in 32 Posts
Quote:
Originally Posted by Motochris View Post
I'll play with mine some more to see what differences I can tell.
I'm at 11* initial, 36 total on a Vortec headed 383. (Cam--.495/.503 lift, 218/224 duration @ .050 and 112 degree lobe seperation to help control idle quality...it's a heavy car with power brakes, steering, AC, etc. so idle vacuum is important) I want to try less total timing, but just bringing back the initial to 8 seems to make the car lazier.
The 11*/36* actually works well, idles surprisingly smooth. Most guys are saying leave it alone. I just want to play with it for my own learning.
I can step back my mechanical to 18* or 21* with bushings. I'll most likely try the 18* first...which will let me set my initial at around 16 for a total of 34* and see where I am.

Thanks for the info
With a fairly mild cam such as yours you may not notice a lot of difference from the 11* you're at. You WILL notice a bit of difference in your idle quality and you'll have to set your idle speed back a bit if you bump up to about 16* or so. The milder the cam the less initial you'll actually need. That's not to say you shouldn't advance it. I'm an advocate of as much initial as the combo will take. I have a hydro roller with 234* x 238* @.050" and I'm running 21* PLUS 10 manifold vac at idle. I'm all in at 36* at 3100 rpm on my 388. The motor responds superbly and cruises smooth as silk. Idles perfectly at 850 rpm.
Reply With Quote Quick reply to this message
  #11 (permalink)  
Old 09-14-2013, 05:23 PM
Motochris's Avatar
Registered User
 
Last photo:
Join Date: Jul 2007
Location: Ridgecrest CA
Posts: 101
Wiki Edits: 0

Thanks: 0
Thanked 4 Times in 2 Posts
Quote:
Originally Posted by Greg T View Post
With a fairly mild cam such as yours you may not notice a lot of difference from the 11* you're at. You WILL notice a bit of difference in your idle quality and you'll have to set your idle speed back a bit if you bump up to about 16* or so. The milder the cam the less initial you'll actually need. That's not to say you shouldn't advance it. I'm an advocate of as much initial as the combo will take. I have a hydro roller with 234* x 238* @.050" and I'm running 21* PLUS 10 manifold vac at idle. I'm all in at 36* at 3100 rpm on my 388. The motor responds superbly and cruises smooth as silk. Idles perfectly at 850 rpm.
Yea... I would have like to gone with more cam, but didn't want to have issues with my brakes and overall drivability. It's a '59 Chevy wagon... heavy beast and almost daily driven.
Just ordered a tuning kit for the distributor as I don't have the parts that came with it. We'll see what happens in a week or two.
Reply With Quote Quick reply to this message
  #12 (permalink)  
Old 09-14-2013, 07:34 PM
cobalt327's Avatar
WFO
 
Last wiki edit: Intake manifold
Last journal entry: 1980 Malibu Wagon
Last photo:
Join Date: Mar 2009
Location: Atlanta
Age: 59
Posts: 5,037
Wiki Edits: 1616

Thanks: 128
Thanked 597 Times in 546 Posts
Quote:
Originally Posted by Motochris View Post
What does varying initial timing do for you?
Let's say your magic "all in" number for your engine is 36*.... you could get that with 2* initial timing and 34* mechanical..... or go 20* initial and 16* mechanical....or anything in between. The end result would be the 36* you wanted...
So what is it the initial timing is doing for you that you would want to change it? I understand too much initial and you can have hard starting.. but beyond that, what difference does initial timing make in performance/milage/idle...whatever?
More initial timing is needed when a performance cam is used because the tendency for the air/fuel mixture to be diluted at idle and low rpm with exhaust byproducts due to the natural EGR effect the performance cam causes.

The more cam, the more initial is needed. The extra initial timing is needed to light off the diluted f/a charge because it takes longer to initiate the burn and for the burn to be completed.
Reply With Quote Quick reply to this message
  #13 (permalink)  
Old 09-16-2013, 10:06 AM
Motochris's Avatar
Registered User
 
Last photo:
Join Date: Jul 2007
Location: Ridgecrest CA
Posts: 101
Wiki Edits: 0

Thanks: 0
Thanked 4 Times in 2 Posts
Quote:
Originally Posted by cobalt327 View Post
More initial timing is needed when a performance cam is used because the tendency for the air/fuel mixture to be diluted at idle and low rpm with exhaust byproducts due to the natural EGR effect the performance cam causes.

The more cam, the more initial is needed. The extra initial timing is needed to light off the diluted f/a charge because it takes longer to initiate the burn and for the burn to be completed.
Solid answer..thanks much.
Reply With Quote Quick reply to this message
  #14 (permalink)  
Old 09-19-2013, 08:48 AM
Registered User
 
Last photo:
Join Date: May 2008
Location: ohio
Posts: 1,420
Wiki Edits: 0

Thanks: 28
Thanked 41 Times in 38 Posts
I will throw my two cents in here since your cam is almost the same as mine. I am running a 350 with the one piece seal 880 vortec block and my roller cam is a voodoo 219/227 @50 515/530 lift. I originally ran mine somewhat close to yours around 12/14 initial with 12 from vacuum advance and it ran fine that way but I got a stubborn backfire if I hit the throttle two quickly and I tried different combos with vacuum advance being on ported and full manifold along with initial timing added together. Long story short I tried more initial and its around 20 degrees give or take a few and it still runs the same and just as strong but I no longer get the back fire through the carb so sometimes just a little more is all you need. My cam just needed a little more initial timing to get the magic sweet spot it liked the most. I now have to modify my mechanical to limit its advance to around 15 degrees.
Reply With Quote Quick reply to this message

Recent Hotrodding Basics posts with photos

Quick Reply
Message:
Options

Register Now

In order to be able to post messages on the Hot Rod Forum : Hotrodders Bulletin Board forums, you must first register.
Please enter your desired user name (usually not your first and last name), your email address and other required details in the form below.
User Name:
If you do not want to register, fill this field only and the name will be used as user name for your post.
Password
Please enter a password for your user account. Note that passwords are case-sensitive.
Password:
Confirm Password:
Email Address
Please enter a valid email address for yourself.
Email Address:

Log-in

Human Verification

In order to verify that you are a human and not a spam bot, please enter the answer into the following box below based on the instructions contained in the graphic.




Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)
 
Thread Tools

Posting Rules
You may post new threads
You may post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are On
Pingbacks are On
Refbacks are On


Similar Threads
Thread Thread Starter Forum Replies Last Post
Initial timing ggevaert Engine 32 03-09-2013 10:00 AM
Does PCV hookup affect timing? david-b Hotrodding Basics 2 05-07-2012 10:30 AM
Initial timing PatM Electrical 8 04-14-2010 09:36 AM
Ignition Timing Affect Vacuum lanceks1 Engine 7 01-11-2008 02:10 PM
idel speed affect timing?? smlblcks10 Engine 3 04-14-2004 05:15 PM


All times are GMT -6. The time now is 11:42 AM.


Powered by vBulletin® Version 3.8.7
Copyright ©2000 - 2014, vBulletin Solutions, Inc.
Search Engine Optimization by vBSEO 3.6.0 PL2
Copyright Hotrodders.com 1999 - 2012. All Rights Reserved.