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| Joe's advance curve spread sheet https://slantsix.org/forum/viewtopic.php?t=55740 |
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| Author: | DadTruck [ Mon Jul 07, 2014 6:51 pm ] |
| Post subject: | Joe's advance curve spread sheet |
https://onedrive.live.com/view.aspx?res ... xcel&wdo=2 for the vacuum number that go into the column at D7 certainly these are the values from the carbs ported vacuum fitting,, do I need to obtain these at the various RPM's while the vehicle is powering down the road,? I know on the 83 D150, at a given RPM,,the engine load (vehicle moving in gear vs stationary in neutral) really influences manifold vacuum values,, thinking that ported vacuum is also influenced by throttle plate position,, correct? thanks |
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| Author: | wjajr [ Tue Jul 08, 2014 5:03 am ] |
| Post subject: | |
That first page listing of vacuum readings is a bit confusing as it is three groups of data in three individual recordings for lack of better pre coffee remarks… A better way to list that data would be to use three columns; static, mechanical and vacuum advance all on one chart at various rpm while trying to capture exact rpm at which mechanical and vacuum advance kicks in. Yes, plot that shows zero†at 1, zero†at 2, two†at 3, etc. is reading from ported vacuum controlled by throttle opening. To take a look at “Curve Graphâ€, click on second tab or sheet at lower left of sheet. [quote]do I need to obtain these at the various RPM's while the vehicle is powering down the road,?[/quote] Probably not, but what you could do is connect your vacuum gage to a long length of vacuum hose and place gage on dash and drive the truck around for a few days observing how the gage reacts. At some point you will get a good feel of what normal vacuum levels your engine makes during day to day driving. Armed with that general info you can make changes to mechanical and vacuum advance curves as needed. A truck will show lower vacuum reading for two reasons, one it is heavier than a car, and being a brick it pushes a lot of air both conditions the engine sees as additional load over what one would see when performing the same exercise with a car. Your truck may like total timing to be into the mid-forties, and not mid-fifties, and mechanical added in a bit slower. Truck guys chime in here as I’m not fluent in truck for the details. [quote]thinking that ported vacuum is also influenced by throttle plate position[/quote] Yes it is totally controlled by throttle position because it sees only air movement above throttle plates. Slow or low velocity air produces low vacuum as when throttle is suddenly opened wide and remains at that way such as when pulling up a hill, but when throttle closes down but not full closed air moves much faster past the little hole causing an increase in vacuum to the vacuum advance. |
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| Author: | Aggressive Ted [ Wed Jul 09, 2014 12:20 pm ] |
| Post subject: | |
Quote: certainly these are the values from the carbs ported vacuum fitting,,
Yes! These are generally taken during acceleration up to cruising speed.do I need to obtain these at the various RPM's while the vehicle is powering down the road,? Document what you see on the vacuum gauge. I use my vacuum gauge to drive by for best mileage. It is amazing the difference it makes especially going over the mountain passes. There is a rpm range where you are in the pocket (peak torque) and can get the highest vacuum numbers and get some really good mileage. Here are the instructions: http://www.slantsix.org/forum/viewtopic.php?t=41705 |
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