Crazy Timing Issue!
Thread Starter
Pro
Joined: Sep 2004
Posts: 579
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From: North Texas
Crazy Timing Issue!
I used 3 timing lights to make sure this was right. For best vacuum I have to set initial timing to 30 which is 17" vacuum. Any point below that drops the vacuum to 15" and below. No amount of tweaking the carb will let me get up to 17" without the initial 30 degrees of timing. This is at an idle RPM of 900 with nothing hooked up to vacuum except the gauge.
I know my harmonic balancer mark is accurate because I checked it when I had the heads off.
The vette is running like a turtle until 2800+ RPM. Do I forget about the initial timing and just make sure I only have about 32 degrees by 3000RPM?
Any clue what's going on? Why would I need so much initial advance with vortec heads?
355CID vortec heads/~9.7cr
Voodoo 268/276 (227/233 @ .50)
vortec performer intake
Holley 650dp
HEI
I know my harmonic balancer mark is accurate because I checked it when I had the heads off.
The vette is running like a turtle until 2800+ RPM. Do I forget about the initial timing and just make sure I only have about 32 degrees by 3000RPM?
Any clue what's going on? Why would I need so much initial advance with vortec heads?
355CID vortec heads/~9.7cr
Voodoo 268/276 (227/233 @ .50)
vortec performer intake
Holley 650dp
HEI
Last edited by Nate 76x; May 21, 2005 at 09:55 PM.
Race Director
Joined: Sep 2004
Posts: 11,874
Likes: 263
From: Arlington Va Current ride 04 vert, previous vettes: 69 vert, 77 resto mod
normally you don"t set timing to achieve the highest vacuum....you adjust the carb to achieve the highest vacuum. set the timing as close as you can to get 36* by 2500-3000 rpm and try to get 16*- 18* base timing at idle with the vacuum can disconnected. don't worry about the vacuum when setting timing.
Thread Starter
Pro
Joined: Sep 2004
Posts: 579
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From: North Texas
It seems like if all you do is advance the timing and get an increase in RPM and Vacuum then your engine is becoming more efficient with the advance and that would be a good thing. But 30 deg initial is quite a bit.
I know others that use timing to vacuum to tune but they end up with max at about 18 deg initial.
I guess at this point I'll set initial to ~18 and ~32 max in by 3000RPM.
Any more thoughts?
THX!
I know others that use timing to vacuum to tune but they end up with max at about 18 deg initial.
I guess at this point I'll set initial to ~18 and ~32 max in by 3000RPM.
Any more thoughts?
THX!
Drifting
Joined: Sep 2004
Posts: 1,959
Likes: 1
From: North Bend Ohio
You could set the initial at 16 then hook the vacuum up to manifold to get about 30 degrees at idle. This won't drag the starter down on start up and as soon as you give it some throttle the timing will retard so it won't ping on ya. Once you get up to speed some centrifugal will be working for ya and when ya back off the throttle to cruise the vacuum advance will come back in.
Cool ain't it?
BigBlockk
Later.....
Cool ain't it?
BigBlockk
Later.....
Thread Starter
Pro
Joined: Sep 2004
Posts: 579
Likes: 0
From: North Texas
Originally Posted by BigBlockk
You could set the initial at 16 then hook the vacuum up to manifold to get about 30 degrees at idle. This won't drag the starter down on start up and as soon as you give it some throttle the timing will retard so it won't ping on ya. Once you get up to speed some centrifugal will be working for ya and when ya back off the throttle to cruise the vacuum advance will come back in.
Cool ain't it?
BigBlockk
Later.....
Cool ain't it?
BigBlockk
Later.....
Drifting
Joined: Sep 2004
Posts: 1,959
Likes: 1
From: North Bend Ohio
Originally Posted by Nate 76x
That's the only thing I could think of too. Is there a reason this engine would want so much initial?
(2)If this engine had old heads it would probably want even more advance. The heads you are using have a little more efficient combustion chamber than the original ones.
By the way, did you install the cam strait up or did you retard it. This will have an effect on advance lead.
BigBlockk
Later.....
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Drifting
Joined: Sep 2004
Posts: 1,959
Likes: 1
From: North Bend Ohio
Originally Posted by Nate 76x
I installed it straight up.
Should I advance it 4 degrees?
Should I advance it 4 degrees?
BigBlockk
Later.....