Base vs Total Timing
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Base vs Total Timing
Adjusting the timing on my 2.8, Duraspark II, no smog, only PCV.
With the vacuum advance hose disconnected and plugged, at ~750rpm, the timing is 10 BTDC. With the advance re-connected the rpm's go up, after re-setting back to ~750rpm, the timing is now 26 BTDC. Is that normal?
I remember reading something about a 'total advance' of 36 but I thought that was at ~3500rpm. But maybe what I have now, 10 and 26, is good? (36)
Just to note, the vacuum advance is currently t'd in with the choke pull down but I can alternatively 't' it into the PCV vacuum port at he carb.
With the vacuum advance hose disconnected and plugged, at ~750rpm, the timing is 10 BTDC. With the advance re-connected the rpm's go up, after re-setting back to ~750rpm, the timing is now 26 BTDC. Is that normal?
I remember reading something about a 'total advance' of 36 but I thought that was at ~3500rpm. But maybe what I have now, 10 and 26, is good? (36)
Just to note, the vacuum advance is currently t'd in with the choke pull down but I can alternatively 't' it into the PCV vacuum port at he carb.
Lead Driver
Joined: Sep 2003
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From: SoCal
It sounds like you've connected your distributor to manifold vacuum. It should go to "ported" vacuum; the source should come from the narrow point of the throttle, so that vacuum is generated only when the throttle is opened.
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Very confusing, ported vs manifold. Your right, it's currently connected to manifold, it was connected to ported but after reading a bunch of posts on the net it seemed manifold would be a better choice. (?)
My 85 2.8 has no smog junk on it other than the PCV valve. It's my understanding ported vacuum was used just for EPA reasons to get the engine warmed up quicker but without that concern better performance can be had by using manifold vacuum. (?)
Post Fiend
Joined: Apr 2002
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From: Waterloo, Iowa
Incorrect. Ported vacuum has been around about as long as carburetors have. It was invented/used so idle would be steady. Other than at idle, there is no difference in the vacuum signal anyway.
It will add lots of advance at idle this will tend to keep engine temps down and can be useful for that. It's a little trickier to use because modern vehicles have power brake boosters, automatic transmissions, AC, etc that also depend on vacuum signals for operation. This causes the idle to fluctuate, without all those gee-gaws on the hoses you see on GM stuff for example.
Just connect to ported and set the total mechanical up right and it will run great
It will add lots of advance at idle this will tend to keep engine temps down and can be useful for that. It's a little trickier to use because modern vehicles have power brake boosters, automatic transmissions, AC, etc that also depend on vacuum signals for operation. This causes the idle to fluctuate, without all those gee-gaws on the hoses you see on GM stuff for example.
Just connect to ported and set the total mechanical up right and it will run great
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Messed around with the timing today.
At operating temp, vacuum advance disconnected and the hose plugged, and ~750rpm, here's what I'm getting...
At Idle. Degrees 10 12 14
At 2600rpm. Degrees. 30 32 34
'Seems' to run fine on all three base degree settings (can't road test it till I get a driveshaft). It's a stock motor, no emissions, should I just stick with the 10 BTDC? Is 30 degrees enough? I thought it should advance with rpm up to 36?
Also, I did a Duraspark II Conversion so the distributor was changed to a Cardone Remanufactured Distributor.
http://www.autozone.com/external-eng...or/700864_0_0/
At operating temp, vacuum advance disconnected and the hose plugged, and ~750rpm, here's what I'm getting...
At Idle. Degrees 10 12 14
At 2600rpm. Degrees. 30 32 34
'Seems' to run fine on all three base degree settings (can't road test it till I get a driveshaft). It's a stock motor, no emissions, should I just stick with the 10 BTDC? Is 30 degrees enough? I thought it should advance with rpm up to 36?
Also, I did a Duraspark II Conversion so the distributor was changed to a Cardone Remanufactured Distributor.
http://www.autozone.com/external-eng...or/700864_0_0/
Post Fiend
Joined: Apr 2002
Posts: 19,311
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From: Waterloo, Iowa
With a conventional (mechanical) distributor you have to make sure it's all done advancing, the stock OEM curve can be real slow. Not sure about V6 but some V8 would not finish till somewhere around 4500 RPM. The light spring does its thing, the heavy spring is a little loose and doesn't do its thing till much later.
That's where the lighter springs come into their own. Again on a V8 it's typical for a mild truck performance curve to see that it is done advancing by say 2800 or 3000 RPM, and no more than a total of 34 or 36, maybe 38 with a low compression engine. Let the initial fall wherever it has to, just make sure 36 - 38 is never exceeded. Most V8 run nice with 12 to 14 or so initial, this is why the mechanical has to be limited usually.
That's where the lighter springs come into their own. Again on a V8 it's typical for a mild truck performance curve to see that it is done advancing by say 2800 or 3000 RPM, and no more than a total of 34 or 36, maybe 38 with a low compression engine. Let the initial fall wherever it has to, just make sure 36 - 38 is never exceeded. Most V8 run nice with 12 to 14 or so initial, this is why the mechanical has to be limited usually.
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Good points Ted, thanks.
I'm not very knowledgeable (obviously
) about this engine and aspects of tuning in general. This 2.8 seems a bit more difficult for a couple reasons. One is I've read on forums the base timing should be 10 BTDC, it's 12 BTDC in my Chiltons and I've talked to 2.8 owners that keep theirs at 14, confusing. The others is my engine is stock but taking off all the smog stuff nullifies much of the Chiltons tuning specs (from what I've been told). Also, my cheap Cardone dizzy doesn't help ( I bought the one recommended for a Duraspark conversion). I don't think the can on it is adjustable, maybe not even the inside of it.
I'm not very knowledgeable (obviously
) about this engine and aspects of tuning in general. This 2.8 seems a bit more difficult for a couple reasons. One is I've read on forums the base timing should be 10 BTDC, it's 12 BTDC in my Chiltons and I've talked to 2.8 owners that keep theirs at 14, confusing. The others is my engine is stock but taking off all the smog stuff nullifies much of the Chiltons tuning specs (from what I've been told). Also, my cheap Cardone dizzy doesn't help ( I bought the one recommended for a Duraspark conversion). I don't think the can on it is adjustable, maybe not even the inside of it.
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