Recurve Kit and Timing
Thread Starter
Drifting
Joined: May 2004
Posts: 1,258
Likes: 0
From: Huntsville Alabama
Recurve Kit and Timing
Ok well I got the mr. gasket recurve kit installed today used the gold springs (HEI) . Set the timing by Lars's Paper. Advance is in by 3000 @ 36 degrees. Timing at idle is 22 degrees. Timing at idle with vaccum advance hooked up 28 degrees. does this sound ok. if not what should i be setting the timing for. I have an adjustable vac. can that im still playing with.
Tech Contributor
Joined: Aug 1999
Posts: 14,380
Likes: 6,391
From: At my Bar drinking and wrenching in Lafayette Colorado
Sounds perfect. The car should have very nice idle quality and crisp throttle response. Take it out and drive it and make sure it fells good with no detonation. If so, you got it. Good job!
Racer
Joined: Apr 2005
Posts: 465
Likes: 1
From: FRANCE (Lyon)
22° seems to be too much
hom much total advance ?
22°@idle (w/o vaccum advance)
28°@idle (w vaccum advance)
So you have 6° of vaccum advance!
and you said 36°@3000 (w/o vaccum advance i think)
so you must have: total advance 42° (it seems too tiny)
vaccum advance at maximum at idle! if not you can have a non stable idle speed!
FORGOT ALL I SAID!
hom much total advance ?
22°@idle (w/o vaccum advance)
28°@idle (w vaccum advance)
So you have 6° of vaccum advance!
and you said 36°@3000 (w/o vaccum advance i think)
so you must have: total advance 42° (it seems too tiny)
vaccum advance at maximum at idle! if not you can have a non stable idle speed!
FORGOT ALL I SAID!
Last edited by jerome1979; Jun 27, 2007 at 05:18 PM. Reason: Lars is always right i will copy it 100000 times! :s
Drifting
Joined: Nov 2003
Posts: 1,634
Likes: 4
From: Northern NJ
St. Jude Donor '04 & '05
I had a brand new adjustable vac can when Lars tuned my car. First thing he did was remove it and replace it w/a fixed version. I believe what he used was an AR-12 but someone please confirm or correct this if necessary. He indicated that no matter where the adjustable unit was set that I wasn't going to get the results we were looking for. FWIW.
Now as far as what those results should be, here's all the info you could ever need about setting timing, advance, etc. It's the first sticky at the top of the C3 Tech/Performance section.
http://forums.corvetteforum.com/show....php?t=1430339
Good Luck!
Now as far as what those results should be, here's all the info you could ever need about setting timing, advance, etc. It's the first sticky at the top of the C3 Tech/Performance section.
http://forums.corvetteforum.com/show....php?t=1430339
Good Luck!
Thread Starter
Drifting
Joined: May 2004
Posts: 1,258
Likes: 0
From: Huntsville Alabama
Yeah i read the sticky about timing and lars's paper. I just wanted to make sure that the timing was in the ball park. I think im going to change the vac. can eventually. I think the one i need will be a AR-12?
Tech Contributor
Joined: Aug 1999
Posts: 14,380
Likes: 6,391
From: At my Bar drinking and wrenching in Lafayette Colorado
When you use the Mr. Gasket gold springs on the HEI, you often get a little centrifugal advance in right at idle speed (about 700-800). This can make the initial timing seem just a tad high, but that's okay as long as idle quality is still good. To see if this is happening, you can leave the timing where it is and install the stock, stiff springs. This will usually pull the centrifugal advance back and show "true" initial timing.
The HEI units usually have about 20 degrees of centrifugal advance in them, so "true" initial timing with 36 total usually ends up at about 16 degrees. I am not aware of any HEI that only has 14 degrees of advance in it, so chances are he's getting a little centrifugal thrown in at idle.
With an adjustable vacuum advance, he could very well only have 6 degrees. This can be okay, but I'd recommend getting rid of the adjustable unit and use a fixed unit with known specs. I like to use part number VC1838 for most performance applications, and part number VC1862 if the engine has poor vacuum at idle (AR12 and AR31 respectively).
The HEI units usually have about 20 degrees of centrifugal advance in them, so "true" initial timing with 36 total usually ends up at about 16 degrees. I am not aware of any HEI that only has 14 degrees of advance in it, so chances are he's getting a little centrifugal thrown in at idle.
With an adjustable vacuum advance, he could very well only have 6 degrees. This can be okay, but I'd recommend getting rid of the adjustable unit and use a fixed unit with known specs. I like to use part number VC1838 for most performance applications, and part number VC1862 if the engine has poor vacuum at idle (AR12 and AR31 respectively).
Thread Starter
Drifting
Joined: May 2004
Posts: 1,258
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From: Huntsville Alabama
Ok just got back from a drive all is good no detination. Im going to ditch the adjustable vac. can i rechecked the timing and its still at 22 at idle. The vac can is doing nothing so its getting changed. Now its time to figure out the off idle hesitation on my 750vs holley that i have posted about before. Got my tuning dvd and my super tuning books and Lars's papers so I should have good luck.
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Advanced
Joined: May 2004
Posts: 59
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From: JONESBOROUGH TN
Lars,The MR G kit 929 I have it seems that the gold springs are stiffer than the black and silver.The balck are thin and less coils and the silver are easier to stretch than the gold.Does it make sens to use the gold stiff springs because I am using stock weights?
Thread Starter
Drifting
Joined: May 2004
Posts: 1,258
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From: Huntsville Alabama
yahoo got my adjustable vac. can set finally.
heres the timing specs at idle in park idle is at 750 RPM
Initial 22 degrees @ 750 in park
centrifigal 36 degrees all in by 3000
With advance hooked up @ 750 in park 34 degrees.
Vaccum in gear is @ 12in Hg and steady.
Throttle response is great and so is the idle. The car does not run rich any more. The hesitation in the carb is no where near as bad as it was. Its now just a 2 second hesitation and from what i have read and understand it needs a larger squirter. I have a #35 so I will have to see if that will help. Thanks for all the help.
heres the timing specs at idle in park idle is at 750 RPM
Initial 22 degrees @ 750 in park
centrifigal 36 degrees all in by 3000
With advance hooked up @ 750 in park 34 degrees.
Vaccum in gear is @ 12in Hg and steady.
Throttle response is great and so is the idle. The car does not run rich any more. The hesitation in the carb is no where near as bad as it was. Its now just a 2 second hesitation and from what i have read and understand it needs a larger squirter. I have a #35 so I will have to see if that will help. Thanks for all the help.
Safety Car
Joined: Oct 2000
Posts: 3,593
Likes: 103
From: Southern Indiana
yahoo got my adjustable vac. can set finally.
heres the timing specs at idle in park idle is at 750 RPM
Initial 22 degrees @ 750 in park
centrifigal 36 degrees all in by 3000
With advance hooked up @ 750 in park 34 degrees.
Vaccum in gear is @ 12in Hg and steady.
Throttle response is great and so is the idle. The car does not run rich any more. The hesitation in the carb is no where near as bad as it was. Its now just a 2 second hesitation and from what i have read and understand it needs a larger squirter. I have a #35 so I will have to see if that will help. Thanks for all the help.
heres the timing specs at idle in park idle is at 750 RPM
Initial 22 degrees @ 750 in park
centrifigal 36 degrees all in by 3000
With advance hooked up @ 750 in park 34 degrees.
Vaccum in gear is @ 12in Hg and steady.
Throttle response is great and so is the idle. The car does not run rich any more. The hesitation in the carb is no where near as bad as it was. Its now just a 2 second hesitation and from what i have read and understand it needs a larger squirter. I have a #35 so I will have to see if that will help. Thanks for all the help.
I just installed a cam and have mine set at 12 idle and 36 @2500, how can this be so different with this?
Thread Starter
Drifting
Joined: May 2004
Posts: 1,258
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From: Huntsville Alabama
heres the link to lars's papaer that i used to set the timing http://www.lbfun.com/Corvette/Tech/v...t%20Timing.pdf
Tech Contributor
Joined: Aug 1999
Posts: 14,380
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From: At my Bar drinking and wrenching in Lafayette Colorado
Tech Contributor
Joined: Aug 1999
Posts: 14,380
Likes: 6,391
From: At my Bar drinking and wrenching in Lafayette Colorado
There is no vacuum at WOT. Vacuum is not related to rpm - it's related to engine load. Peak vacuum occurs under no-load or light-load conditions, regardless of rpm. Vacuum is typically highest at idle in neutral, but good vacuum can also be seen at light-load cruise.
The point of the vacuum canister is not to increase timing with rpm - that is the purpose of the centrifugal advance. Purpose of the vacuum canister is to detect engine load condition and advance timing when load is light.
The point of the vacuum canister is not to increase timing with rpm - that is the purpose of the centrifugal advance. Purpose of the vacuum canister is to detect engine load condition and advance timing when load is light.
Advanced
Joined: Mar 2007
Posts: 91
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From: London, UK
Ok well I got the mr. gasket recurve kit installed today used the gold springs (HEI) . Set the timing by Lars's Paper. Advance is in by 3000 @ 36 degrees. Timing at idle is 22 degrees. Timing at idle with vaccum advance hooked up 28 degrees. does this sound ok. if not what should i be setting the timing for. I have an adjustable vac. can that im still playing with.
Racer
Joined: Nov 2004
Posts: 432
Likes: 0
From: Granbury TX
I also have mine timed to 36 deg at 2500 rpm and have initial timing of 22 deg. I could never work out how to maintain 36 degrees at that rpm but lower the initial timing. Starts fine though. Are you sure you have your vacuum on the right port of the carb? You shouldn't pull any vacuum advance at idle, just when you hit the throttle. I have a metered port on my holley that pulls vacuum advance in once you accelerate.
Safety Car
Joined: Oct 2000
Posts: 3,593
Likes: 103
From: Southern Indiana
because everytime someone ask how to time an engine you get 10 different answers.
Some people like vacuum at idle(wrong) and some people like vacuum when you are giving it gas(right), and some like me just unhook the canister and forget about it and let the weights and springs do the job!