Timing Issue...
Thread Starter
Cruising
Joined: Jan 2009
Posts: 13
Likes: 0
Timing Issue...
I have an aftermarket motor in my car, I didnt install it. I am going to check the timing and Im not sure it i should just go with what the manual says on the timing or should there be something else I should go by because this is not the stock motor??? It is a 350.
Last edited by kclarry; Feb 16, 2009 at 12:51 PM. Reason: posting in tech
Race Director
Joined: Jun 2000
Posts: 10,046
Likes: 675
From: FL
Do want to set timing to stock or for performance? They ware not the same. I don;t ste my timing at idle since I never drive at idle.
Here is a link to a good paper on timimg:
http://www.lbfun.com/warehouse/tech_...t%20Timing.pdf
Shoot for 36 degrees of mechanical advance, all in by 2500 rpm and another 16 of vacuum.
Here is a link to a good paper on timimg:
http://www.lbfun.com/warehouse/tech_...t%20Timing.pdf
Shoot for 36 degrees of mechanical advance, all in by 2500 rpm and another 16 of vacuum.
Thread Starter
Cruising
Joined: Jan 2009
Posts: 13
Likes: 0
I will look for the block number, I have looked at it before and the numbers did not match any for a corvette.
I was looking for performance instead of stock...
I just checked the timing and it was around 10 degrees at idle.
I was looking for performance instead of stock...
I just checked the timing and it was around 10 degrees at idle.
Race Director
Joined: Jun 2000
Posts: 10,046
Likes: 675
From: FL
Read Lars' paper that I linked to above. You don't drive at idle so why set your advance at idle. I have about 16 degrees at idle and 36 all in by 2500. Runs great.
Safety Car
Joined: Nov 2007
Posts: 3,570
Likes: 0
From: bottom of the sea
as usual i feel inclined to chime in on this issue. information given on this forum concerning timing is mostly incorrect. respected members have been given idol status and therefore their information is being taken as gospel. you should never acheive 50+ deg. of TOTAL TIMING. your total timing should be 34-36 deg. total timing. this INCLUDES mech. AND vac. advance. you may check any other source of information ather than this forum and you will find i am correct.
Corvette Stories
The Best of Corvette for Corvette Enthusiasts
Top 10 Most Expensive Corvettes Ever Sold on Bring A Trailer
Brett Foote
10 Things Every Corvette Owner Needs (2026 Edition)
Michael S. Palmer
8 Most "Only Corvette Owners Understand" Quirks and Problems
Pouria Savadkouei
10 Reasons the C6 Z06 is Still A Performance Benchmark After 20 Years
Joe Kucinski
How Much Horsepower Every Corvette Engine "LOST" in 1972
Joe Kucinski
Top 10 DOs and DON'Ts for Protecting Your Convertible Top!
Michael S. Palmer
Top 10 Most Explosive Corvettes Ever Made: Power-to-Weight Ratio Ranked!
Joe Kucinski
150 hp to 1,250 hp: Every Corvette Generation Compared by the Specs That Matter
Joe Kucinski
8 Coolest Corvette Pace Cars (and Replicas) of All Time
Verdad Gallardo
Race Director
Joined: Jun 2000
Posts: 10,046
Likes: 675
From: FL
as usual i feel inclined to chime in on this issue. information given on this forum concerning timing is mostly incorrect. respected members have been given idol status and therefore their information is being taken as gospel. you should never acheive 50+ deg. of TOTAL TIMING. your total timing should be 34-36 deg. total timing. this INCLUDES mech. AND vac. advance. you may check any other source of information ather than this forum and you will find i am correct.
With all due respect, I have to disagree.
Total timing = initial timing + centrifugal (mechanical) advance. Vacuum advance does not factor into total timing since it is only in effect when vacuum is high and load is low.
Under WOT, vacuum goes to zero and so does vacuum advance and you have your 36 degrees of total timing. You only get the 52 degrees of timing under light load when the engine can tolerate more advance.
I stand by my recommendations above. I have used those setting for over 5 years with no problems. I have a ZZ4 clone that pulls hard to 6000 rpm, gets 20 mpg and has no issues with detonation and pinging.
For the OP, read this thread for more info:
http://forums.corvetteforum.com/c3-t...long-post.html
Another source of information:
http://rockridgefarm.com/vettdoc/Timing_101.pdf
The amount of advance added by the distributor, combined with initial static timing, is "total timing" (i.e., the 34-36 degrees at high rpm that most SBC's like). Vacuum advance has absolutely nothing to do with total timing or performance, as when the throttle is opened, manifold vacuum drops essentially to zero, and the vacuum advance drops out entirely; it has no part in the "total timing" equation.
Last edited by SteveG75; Feb 17, 2009 at 07:58 PM.
Safety Car
Joined: Nov 2007
Posts: 3,570
Likes: 0
From: bottom of the sea
Reb,
With all due respect, I have to disagree.
Total timing = initial timing + centrifugal (mechanical) advance. Vacuum advance does not factor into total timing since it is only in effect when vacuum is high and load is low.
Under WOT, vacuum goes to zero and so does vacuum advance and you have your 36 degrees of total timing. You only get the 52 degrees of timing under light load when the engine can tolerate more advance.
I stand by my recommendations above. I have used those setting for over 5 years with no problems. I have a ZZ4 clone that pulls hard to 6000 rpm, gets 20 mpg and has no issues with detonation and pinging.
For the OP, read this thread for more info:
http://forums.corvetteforum.com/c3-t...long-post.html
Another source of information:
http://rockridgefarm.com/vettdoc/Timing_101.pdf
I will trust the judgment of two former GM engineers over random internet folks.
With all due respect, I have to disagree.
Total timing = initial timing + centrifugal (mechanical) advance. Vacuum advance does not factor into total timing since it is only in effect when vacuum is high and load is low.
Under WOT, vacuum goes to zero and so does vacuum advance and you have your 36 degrees of total timing. You only get the 52 degrees of timing under light load when the engine can tolerate more advance.
I stand by my recommendations above. I have used those setting for over 5 years with no problems. I have a ZZ4 clone that pulls hard to 6000 rpm, gets 20 mpg and has no issues with detonation and pinging.
For the OP, read this thread for more info:
http://forums.corvetteforum.com/c3-t...long-post.html
Another source of information:
http://rockridgefarm.com/vettdoc/Timing_101.pdf
I will trust the judgment of two former GM engineers over random internet folks.
and the engineer argument is lame, they didnt invent mech. or vac advance. this was created long ago. ive got engineers at my job who cant tie their own shoes
Le Mans Master
Joined: Dec 2007
Posts: 6,422
Likes: 591
From: McHenry Illinois
Race Director
Joined: Jun 2000
Posts: 10,046
Likes: 675
From: FL
sorry, ive been around engines and cars since i helped change reverse thread lug nuts on a dodge when i was 5. my 383 spins over 7000 rpms with no pinging and pulls like a raped ape. it did an 11 sec. 1/4. go get a dail back timing light and get back to me. i have built and helped build many an engine and repaired even more. my family has raced circle tracks for years and have been around many an engine/car builder and race shops. this forum is the only place ive even heard of 50 degress of anything. your own quote proves what im saying. forum members are ADDING vac. advance to what they think is their total advance, and this is how their coming up with advance #'s over 50. your own quote says NOT to factor this in. get a dail back timing light and use it to measure your advance at different rpms and DAIL IT BACK. this is how you measure and add your timing total. respectivly
and the engineer argument is lame, they didnt invent mech. or vac advance. this was created long ago. ive got engineers at my job who cant tie their own shoes
and the engineer argument is lame, they didnt invent mech. or vac advance. this was created long ago. ive got engineers at my job who cant tie their own shoes
I set my timing as follows:
1. Disconnect and plug vacuum advance.
2. Set total timing (initial + centrifugal advance) at 36 degrees at 2500 rpm. My curve is set to that all centrigugal advance is in by 2500 rpm.
3. Initial advance is then about 18 degrees or so.
4. Reconnect vacuum advance to manifold vacuum (not ported).
5. Drive and enjoy.
You initially said that total advance includes mechanical and vacuum advance and now you say that my quote not to add vacuum advance is what you meant.
Questions, on your 383:
What is your initial advance?
What is your centrifugal advance curve? What rpm is it all in by?
Are you using vacuum advance?
If so, how many degrees of advance does the vacuum can add and at what vacuum setting?
Ported or manifold vacuum?
Just read the info here as well:
http://forums.corvetteforum.com/c3-t...ng-post-7.html
Very entertaining.
In that thread, you said:
heck, my msd dist. has all electronic advance and it wont let you get any more than 34 deg. total timing.
Note: The total amount of any timing change that can be achieved is 34° (25° for the electronic advance with vacuum an additional 9°). This includes the electronic advance as well as the vacuum advance.
Note, they say total timing change is 34 degrees NOT total timing. So, if you run 12 degrees initial timing, you could have up to 46 degrees total timing by your own measure.
Just because MSD limits you to 9 degrees of vacuum advance, doesn't mean that you cannot run more.
Last edited by SteveG75; Feb 17, 2009 at 09:10 PM.
