distributer advice
Thread Starter
Intermediate
Joined: Apr 2011
Posts: 26
Likes: 0
From: katonah new york
distributer advice
I set the total timing on my 68 327/300 to 36 total with the vacume pluged ,my inital is now at 17 the car seems to be running very good. my question is with stock springs I am all in at 1700 rpm.Should i try and find heaver springs or different weights to get it all in a little later and what differance would it make.Thanks for all advice
Anthony
Anthony
Pro
Joined: Oct 2006
Posts: 734
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From: Bryan Texas
17 initial sounds a little high... like you're not getting all your mechanical advance in. Sounds like you have a busted spring or something. I shoot for all in at 3k to keep pre-ignition down.
You are only getting 19 degrees mechanical advance, you should be getting about 24. Getting the initial down will help with starting easier too.
You are only getting 19 degrees mechanical advance, you should be getting about 24. Getting the initial down will help with starting easier too.
Le Mans Master
Joined: Jun 2004
Posts: 6,231
Likes: 65
From: Seattle WA
St. Jude Donor '14
Agreed that you should take a look at the mechanical advance travel to require less initial.
The timing sticky has everything you need - but yep, all in around 3K; so you're a bit early.
The timing sticky has everything you need - but yep, all in around 3K; so you're a bit early.
Team Owner
Joined: Jan 2006
Posts: 37,637
Likes: 3,118
From: Crossville TN
If the idle mechanical advance is 17 degrees, and the mech advance increases smoothly from idle to 1700 rpm to a maximum of 36 degrees, then your springs are too weak and/or your weights are too big. You need to get that maximum mech advance point up to 2500-2800 rpm.
Actually, you shouldn't be running that well with that much advance. You should be getting pre-ignition [pinging] with such early advance numbers. Are you certain that your "0" TDC timing mark on the damper really coincides with true TDC for cylinder #1?
Actually, you shouldn't be running that well with that much advance. You should be getting pre-ignition [pinging] with such early advance numbers. Are you certain that your "0" TDC timing mark on the damper really coincides with true TDC for cylinder #1?
Thread Starter
Intermediate
Joined: Apr 2011
Posts: 26
Likes: 0
From: katonah new york
distributer advice
thanks for the help I guess I'll have to look into some different weights because I bought two different spring kits and the stock springs are stiffer and heaver. Could the the weights if they are to big keep the mech advance from turning all the way. Thanks
Anthony
Anthony
Drifting
Joined: Feb 2005
Posts: 1,879
Likes: 38
From: Los Gatos CA
Stock 68 distributers had a lot of mechanical advance built in (the curve was slow). If your distributer is stock, 17* initital sounds pretty high, your total might be approaching 50* at sufficient RPM.
Pro
Joined: Oct 2006
Posts: 734
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From: Bryan Texas
I'd bet you aren't revving the engine enough to get "all in". Rev that sucker up to 3500 or 4k and see how much timing you are getting. I'd set the intial back to 12 or so until you get the dizzy doing right.
Thread Starter
Intermediate
Joined: Apr 2011
Posts: 26
Likes: 0
From: katonah new york
to set the total timing I used the weakest springs that came in the moroso kit and I was all in just a little above idle . I can only assume its the original distrbutor the car was half assed restored before the last owner had it. I seem to fixing every thing a little at a time. Most people (mechanics?)don't have a clue about old corvettes ,total timing ,shims for wheel bearings whats that. I can give it a good rev tomorrow it will be a good excuse to go for a little ride and see if i can make it ping because i don't think it does. thanks
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Drifting
Joined: Feb 2005
Posts: 1,879
Likes: 38
From: Los Gatos CA
If you post the numbers of the distributer I can look up the specs in my Motor's Manual. It is possible the centrifugal advance was modified to reduce advance. Who knows in our 40+ year old cars?
Team Owner
Joined: Jan 2006
Posts: 37,637
Likes: 3,118
From: Crossville TN
You may have some aftermarket weights in the distributor (too heavy); or there may be some wear/slop in the advance mechanism which causes early advance. Certainly, the way to 'extend' the advance curve is to lighten the weights and/or stiffen the springs.
Drifting
Joined: Feb 2005
Posts: 1,879
Likes: 38
From: Los Gatos CA
According to my 1968 Motor's Manual: 68 Corvette 327/300 HP Distributor
ID:1111194
Centrifugal Advance (Distributor): 15* @ 2550 RPM
Vacuum Advance (Distributor): Starts 6" vacuum; 7 1/2 @ 12" vacuum
Double the values for Crankshaft RPM.
Assuming you have the stock distributor, it has not been modified and is working properly, your total advance is 17* initial + (15* times 2) = 47* @ 5100 RPM.
And 15* vacuum advance is probably too high for taday's crappy gas on an iron-headded engine.
Just my 2 cents...
ID:1111194
Centrifugal Advance (Distributor): 15* @ 2550 RPM
Vacuum Advance (Distributor): Starts 6" vacuum; 7 1/2 @ 12" vacuum
Double the values for Crankshaft RPM.
Assuming you have the stock distributor, it has not been modified and is working properly, your total advance is 17* initial + (15* times 2) = 47* @ 5100 RPM.
And 15* vacuum advance is probably too high for taday's crappy gas on an iron-headded engine.
Just my 2 cents...
Melting Slicks
Joined: Aug 2008
Posts: 2,200
Likes: 3
From: Lehigh county Pennsylvania
runs at half crank speed, so any dizzy specs need to be doubled to make sense.
Team Owner
Joined: Jan 2006
Posts: 37,637
Likes: 3,118
From: Crossville TN
But, remember that you only have the ability to measure engine RPM when you are working on your ignition timing. So, all the info is relative to engine RPM. The distributor specs could be relative to engine RPM or distributor RPM, depending on how the manufacturer defines the spec.
Drifting
Joined: Feb 2005
Posts: 1,879
Likes: 38
From: Los Gatos CA
To add to the above posts: The distributor runs off the cam shaft; at the same speed. The cam runs @ 1/2 the crankshaft speed. So you double the values for crankshaft rpm. The amount of centrifugal advance is built into the distributor. The rate of advance (curve) is adjusted with springs and weights. I like timing tapes because they make it easy to plot the curve of the advance at increasing rpm levels. Plotting your existing curve is the 1st thing I would do... Aint timing fun?
Burning Brakes
Joined: Jan 2007
Posts: 1,057
Likes: 4
From: Concord Calif
Yes check to be sure that the dampener has not turned on you. You can bring cylinder one up on compression TDC. To be sure your at Full TDC you would need to pull the valve covers. At TDC firring on cylinder one you will have number six on overlap, meaning both intake and exhaust valves will be open the same amount. Turning the engine by hand one valve will be closing and the other will be opening, stop when both are equally open, that is TDC and your timing mark should show 0. Do as others have said to be sure that your dizzy weights are moving freely. If all looks good great. If the advance numbers you have cause no pinging then run it, the more total advance up to 36/38 you have and the sooner it all comes in after idle speed the better as long as no pinging. But in general your numbers are a bit high assuming a stock camshaft. I run real close to the numbers you claim with no problems at all but my cam is not OEM either.