Carb vacuum port ID
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One use is for the distributor vacuum advance. There is always debate on which type of vacuum for the vacuum advance is "best". The simple truth of the matter is there are reasons for either to be used, depending on the situation. While ported vacuum for the vacuum advance is often thought to be for "emissions" applications, in certain cases there are sound reasons for a performance engine to use ported vacuum. | One use is for the distributor vacuum advance. There is always debate on which type of vacuum for the vacuum advance is "best". The simple truth of the matter is there are reasons for either to be used, depending on the situation. While ported vacuum for the vacuum advance is often thought to be for "emissions" applications, in certain cases there are sound reasons for a performance engine to use ported vacuum. | ||
| − | + | A brief Crankcase Coalition article on vacuum advance can be found [http://www.crankshaftcoalition.com/wiki/Hot_rodding_the_HEI_distributor#Vacuum_advance '''here''']. A thread at Hotrodders.com on ported vs. manifold vacuum for the vacuum advance is [http://www.hotrodders.com/forum/port-full-time-vacuum-23169.html?highlight=vacuum+throttle+manifold '''here'''] | |
===Manifold vacuum=== | ===Manifold vacuum=== | ||
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====PCV vacuum ports==== | ====PCV vacuum ports==== | ||
| − | The PCV is often connected to the large front vacuum port in the carb throttle body. Its position there allows the crankcase vapors that are pulled from the engine by the PCV system to be shared equally between both primary throttle bores. The primary side is used instead off the secondary because the primary side is almost always flowing a good quantity of air so the vapors will be well mixed before entering the combustion chambers to be burned. | + | [[File:Egr vac qjet.jpg|thumb|400px|left|EGR port on Q-jet from a Pontiac]] |
| + | The PCV is often connected to the large front vacuum port in the carb throttle body. Its position there allows the crankcase vapors that are pulled from the engine by the PCV system to be shared equally between both primary throttle bores. The primary side is used instead off the secondary because the primary side is almost always flowing a good quantity of air so the vapors will be well mixed before entering the combustion chambers to be burned. | ||
| + | <br style="clear:both"/> | ||
====Power brake booster vacuum port==== | ====Power brake booster vacuum port==== | ||
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Many Holley 4150/4160 carbs will have a ported vacuum port on the side of the metering block. The other vacuum ports will usually be manifold vacuum. | Many Holley 4150/4160 carbs will have a ported vacuum port on the side of the metering block. The other vacuum ports will usually be manifold vacuum. | ||
| + | ==Engine diagnosis using a vacuum gauge== | ||
| + | *'''[[Vacuum gauge engine diagnosis]]''' | ||
| + | *'''[[Finding vacuum leaks]]''' | ||
| + | *[http://www.classictruckshop.com/clubs/earlyburbs/projects/vac/uum.htm Vacuum gauge chart] | ||
| + | *[http://www.secondchancegarage.com/public/186.cfm How to Use and Interpret a Vacuum Gauge] | ||
| + | *[http://www.gregsengine.com/using-a-vacuum-gauge.html Engine Testing with a Vacuum Gauge] | ||
| − | + | ==Table of diagnostic vacuum readings== | |
| − | + | ||
| − | + | bgcolor="white"> | |
| − | + | <td colspan="3"> </td> | |
| + | </tr> | ||
| + | <tr bgcolor="#CCCCFF"> | ||
| + | <th width="26%">ENGINE RPM</th> | ||
| + | <th width="28%">GAUGE READING</th> | ||
| + | <th width="46%">ENGINE CONDITION</th> | ||
| + | </tr> | ||
| + | <tr bgcolor="white"> | ||
| + | <td width="26%">Smooth and steady idle<br> (800 to 1200 RPM)</td> | ||
| + | <td width="28%">Between 17 to 21 inches</td> | ||
| + | <td width="46%">Engine is in good condition, but perform next test to be sure.</td> | ||
| + | </tr><tr bgcolor="lightgrey"> | ||
| + | <td width="26%">Open and close throttle quickly</td> | ||
| + | <td width="28%">Jumps from 2 to about 25 inches</td> | ||
| + | <td width="46%">Engine is in good condition.</td> | ||
| + | </tr><tr bgcolor="white"> | ||
| + | <td width="26%">Smooth and steady idle</td> | ||
| + | <td width="28%">Steady, but lower than normal reading</td> | ||
| + | <td width="46%">Worn rings, but perform next test to be sure.</td> | ||
| + | </tr><tr bgcolor="lightgrey"> | ||
| + | <td width="26%">Open and close throttle quickly</td> | ||
| + | <td width="28%">Jumps from 0 to 22 inches</td> | ||
| + | <td width="46%">Confirms worn rings.</td> | ||
| + | </tr><tr bgcolor="white"> | ||
| + | <td width="26%">Steady idle</td> | ||
| + | <td width="28%">Intermittent dropping back 3 to 5 inches and returns to normal</td> | ||
| + | <td width="46%">Sticky valves. If injection of penetrating oil into intake manifold temporarily stops pointer from dropping back, it's certain the valves are sticking.</td> | ||
| + | </tr><tr bgcolor="lightgrey"> | ||
| + | <td width="26%">Steady 3000 RPM</td> | ||
| + | <td width="28%">Pointer fluctuates rapidly, increasing engine speed causes more pointer swing</td> | ||
| + | <td width="46%">Weak valve springs.</td> | ||
| + | </tr><tr bgcolor="white"> | ||
| + | <td width="26%">Steady idle</td> | ||
| + | <td width="28%">Fast fluctuation between 14 to 19 inches</td> | ||
| + | <td width="46%">Worn intake valve stem guides. Excessive pointer vibration at all speeds indicates a leaky head gasket.</td> | ||
| + | </tr><tr bgcolor="lightgrey"> | ||
| + | <td width="26%">Steady idle</td> | ||
| + | <td width="28%">Constant drop</td> | ||
| + | <td width="46%">Burnt valve or insufficient tappet clearance holding valve partly open or a spark plug occasionally misfiring.</td> | ||
| + | </tr><tr bgcolor="white"> | ||
| + | <td width="26%">Steady idle</td> | ||
| + | <td width="28%">Steady 8 to 14 inches</td> | ||
| + | <td width="46%">Incorrect valve timing. It must also be remembered that vacuum leaks and/or poor compression can result in a low vacuum reading.</td> | ||
| + | </tr><tr bgcolor="lightgrey"> | ||
| + | <td width="26%">Steady idle</td> | ||
| + | <td width="28%">Steady 14 to 16 inches</td> | ||
| + | <td width="46%">Incorrect ignition timing.</td> | ||
| + | </tr><tr bgcolor="white"> | ||
| + | <td width="26%">Steady idle</td> | ||
| + | <td width="28%">Drifting from 14 to 16 inches</td> | ||
| + | <td width="46%">Plug gaps too close or points not adjusted correctly. Damaged plug or | ||
| + | coil wire</td> | ||
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