Re: [Chrysler300] Thermodynamics of a Ram

From: "Flathead Engineering" <flatheadeng@xxxxxxxxxxx>

Date: Fri, 9 Nov 2012 16:33:49 -0700

My understanding of the ram effect based on fluid dynamics is the when a traveling wave of pressure meets a boundry condition, closed valve, the velocity goes to zero and the pressure doubles. The velocity of the traveling wave and the frequency depend on the geometry of the passage and the RPM of the engine. The Chrysler ram is long thus tuned to a lower frequency to complement the large displacement of the engine which turns a relatively low RPM compared with a race engine. Understanding this you can see why the wrong camshaft will destroy the ram effect and make for a poor performing engine. I imagine Chrysler spent a large sum to optimise the cam profile and I doubt if some race engine builder can improve on it. More than likely they will not understand the principles and put in an inappropriate cam that works great on a dual plane manifold but is totaly wrong for the ram effect. ----- Original Message ----- From: Rich Barber To: 'Michael Moore' ; mgoodknight@xxxxxxxx Cc: Chrysler300@xxxxxxxxxxxxxxx Sent: Friday, November 09, 2012 3:15 PM Subject: [Chrysler300] Thermodynamics of a Ram Warning: There will be a quiz at the end of this mini-lecture. If you're not interested in engine performance and the ram induction effect, tune out now. If the cam allowed some valve opening before TDC on the compression stroke, the effective compression could be lower. That would be a real power robber, methinks. Simply speaking, a 4-stroke cycle engine acts as an air compressor while being spun by the starter. The compression pressure is measured as the peak pressure in the cylinder over a small number of strokes-as PSIG (Pounds per square inch-gauge). The Shrader valve in the peak pressure indicator acts as a check valve to hold the peak pressure on the gauge until released. Ideally, the peak pressure can be estimated by the cylinder's compression ratio. The laws of physics mandate use of absolute units when dealing with the gas laws, therefore we must use pressures expressed in PSIA (pounds per square inch-absolute). PSIA=PSIG plus atmospheric pressure. Differential pressures are expressed as PSI. Examples: Sea Level Atmospheric Peak Peak Elevation Pressure Compression Pressure Pressure Feet PSIA Ratio :1 PSIA PSIG Engine & Location 16 14.69 9.6 141.02 126 (My ram K engine at Newark, CA) 16 14.69 8.5 124.87 110 (My C-300 hemi at Newark, CA) 5,280 11.68 9.6 112.13 100 (My ram K engine on the first step of State Capitol Building in Denver) 16 17.69 9.6 169.82 155 (My ram K engine at Newark with a 3 psi boost from ram induction) So the ideal peak pressure depends on elevation and cylinder compression ratio. Using the same pressure measuring device and techniques in an engine at operating temperature and at similar cranking speeds should provide valid cylinder-to-cylinder comparisons. Lower peak pressure indicates air leakage-either/or past the rings, valves, gaskets, pig iron. Adjusting the valves on a solid-tappet engine before the test makes sense-although having them buried below 30" long ram induction intake manifolds makes that a challenging job. BTW, the ram effect is designed to increase the apparent atmospheric pressure at the intake valve while it is open. The only reference I found indicated the ram effect could amount to as much as 3 psi at resonant speed. As our engines are limited by the amount of air they can inhale (free air capacity), a 3 psi boost at the inlet could theoretically increase the engine's power by 20% at sea level. Chrysler only claimed 8.3% (390 HP vs. 360 for a non-ram K). This suggests a 1.2 psi ram effect. Anyone heard or measured anything different? C-300K'ly Rich Barber Brentwood, CA (Elevation at my home here in the Bay Area is about 120') Ps: Quiz: What is the theoretical peak compression pressure of a cylinder of a C-300 hemi engine parked outside the state capitol building at Denver? (Just before the park police tow the car and arrest the mechanic) Answer: Scroll down to under Marshall's signature. rb From: Michael Moore [mailto:mmoore8425@xxxxxxx] Sent: Friday, November 09, 2012 5:01 AM To: mgoodknight@xxxxxxxx Cc: c300@xxxxxxx; Chrysler300@xxxxxxxxxxxxxxx Subject: Re: [Chrysler300] Compression pressure , 300H Marshall, I have been gradually getting my 300H, which I have owned since 1964, back into a more drivable condition. Some of the major problems which kept me from driving it much (brakes, steering) are resolved, but the engine issues, while better, are still with me. In general, it has suffered from a lack of power dating back to the engine rebuild I had done many years ago. The rebuilder, a highly respected race engine builder, misunderstood California (where I was moving to) requirements. He also knew high test was going away. Among the mods he made was to lower the compression with a custom Barnes cam, rejet the carbs with richer needles and install a smog valve. The car had power, but ran so rich your eyes burned. The carbs were rebuilt and rejetted to stock needles and it began to run better. I know it still does not run as strongly though as it did even in the 90's. I obtained a correct 300H camshaft from a member and have a new set of lifters. My plan is to replace the camshaft with the stock 300H camshaft. Recently though, I have been wondering if the rebuilder may have installed lower compression pistons. If so, now would be the time to replace the pistons also. I also don't fully appreciate how the custom camshaft lowered the compression ratio other than he adjusted the overlap. Thanks, Mike Moore Morgan Hill, California 300H On Nov 9, 2012, at 3:44 AM, mgoodknight@xxxxxxxx wrote: Thanks for your research Rich, That's a good write-up on compression testing. One might conclude from that reading that too much emphasis is often put on the results of compression testing and that proper (valid) compression testing is not often accomplished. Much can be learned about the condition of an engine from studying the results of a valid test, but inaccurate diagnostics are more commonly the main outcome. My recommendation is to avoid such a test unless you have strong evidence of a problem that can be easily identified by a test. If the engine runs well and performs properly, don't do the testing. You might see results that will cause you undue worries. Marshall Goodknight, engine failure analyst (Answer: 88 psig-for about a 20% loss in potential power. The C-300 becomes a C-240) Please note: message attached From: "Rich Barber" <c300@xxxxxxx> To: "'Michael Moore'" <mmoore8425@xxxxxxx>, "'300'" <Chrysler300@xxxxxxxxxxxxxxx> Subject: RE: [Chrysler300] Compression pressure , 300H Date: Thu, 8 Nov 2012 22:47:28 -0800 __________________________________________________________ 7 foods KILL fat Surprising foods that boost your metabolism http://thirdpartyoffers.juno.com/TGL3131/509cecd8c55056cd87e56st01duc From: "Rich Barber" <c300@xxxxxxx> Subject: RE: [Chrysler300] Compression pressure , 300H Date: November 8, 2012 10:47:28 PM PST To: "'Michael Moore'" <mmoore8425@xxxxxxx>, "'300'" <Chrysler300@xxxxxxxxxxxxxxx> Individual compression pressures on a long non-operated, 85,000 mile, cold, ram K block ranged from 100 psi to 140 psi. I found this interesting text on analyzing compression pressures. According to the 75% criterion, the engine failed, although a properly operated and warmed up engine with properly adjusted solid tappets would have probably tightened the range and marginally passed. C300K'ly, Rich Barber COMPRESSION TESTING Note: although this is written primarily for 4cycle gas engine testing, 2cycle gas and diesel follow pretty much the same sequence of procedures. Also, many diesel engine companies do not publish specific compression readings so the values, in the chart, at the end of this section will be too low for use with a diesel, you'll have to do the calculation. 1. Be sure the crankcase is at the proper level and the battery is properly charged. Operate the engine for a minimum of 30 minutes at 1200 rpm, make sure that the choke has opened, and the engine is at normal operating temperature. Putting a load on the engine for at least 10 minutes, can increase the accuracy of your test. Turn the ignition switch off; then remove all the spark plugs (injectors on the diesel). If the engine has closed cooling, (green anti-freeze) relieve pressure in the cooling system. (carefully) 2. Set the throttle plates and choke plate in the wide open position. On 4 cycle gas engines: Try not to pump raw fuel into the intake with the accelerator pump. 3. Install compression gauge in No. 1 cylinder. 4. Install an auxiliary starter switch in the starting circuit. Ground the coil wire on gas engines. Next, using the auxiliary starter switch, crank the engine (with the ignition switch off) at least five compression strokes and record the highest reading. Count the approximate number of compression strokes required to obtain the highest reading. 5. Repeat the test on each cylinder as was required to obtain the highest reading on the No. 1 cylinder. If the readings degrade from front to rear, re-check the battery and possibly re-run the test starting at cylinder #1. In this way you can have a set of two tests to compare an average. TEST CONCLUSION 2 Cycle Engines: Your test results need to be within 15 psi range to be considered an engine worth using. For example; a 3 cylinder with readings of 130, 135, and 120 would be considered a good engine. Some might argue that there should be no more than 5psi difference between high and low cylinders. But, obviously, the closer the readings are to each other, the better. 4 Cycle Engines: The indicated compression pressures are considered normal if the lowest reading cylinder is within 75% of the highest. Refer to the following example and chart. Seventy-five percent of 140, the highest cylinder reading is 105. Therefore, cylinder No. 7 being less than 75% of cylinder No. 3 indicates an improperly seated valve or worn or broken piston rings. If one, or more, cylinders read low, squirt approximately one (1) tablespoon of engine oil on top of the pistons in the low reading cylinders. Repeat compression pressure check on these cylinders. 1. If compression improves considerably, the piston rings are at fault. 2. If compression does not improve, valves are sticking or seating poorly. 3. If two adjacent cylinders indicate low compression pressures and squirting oil on the pistons does not increase the compression, the cause may be a cylinder head gasket leak between the cylinders. Engine oil and/or coolant in the cylinders could result from this problem. Note: An engine compression test is easy to do but, your results need to be tempered with the knowledge of testing conditions that reduce the accuracy of your test. As the battery gets weaker, starter gets hotter, and the engine cools down, your results from any one cylinder will change. It is important to do the test a quickly as possible, with as little cranking as needed to complete the test. Circumstances arise where a more accurate leak down test should be utilized before you start tearing the engine down. Readings that are at the extremes of the chart, (meaning over-all very high or very low readings), may indicate conditions inside the cylinders that a compression test won't depict properly. You can do the math yourself but, the following quick reference chart should be used when checking cylinder compression pressures. ( to avoid mathematical errors) The chart (below) has been calculated so that the lowest reading number is 75% of the highest reading. Special note: Although the "actual" compression readings are not all that important, keep in mind that very few engines will run with a compression under 100 psi. However, there are some engines that will test with readings in the 90 psi range on a regular basis. If you're not sure if you have one of these engines, contact your servicing dealer before you get excited. Although 75% range is tolerable for an older motor, keep in mind that most modern engines are designed at much closer tolerances. Also, on a V8 engine, if 7 cylinders test at 150psi and only one tests at 113psi, this is not a good sign... -----Original Message----- From: Chrysler300@xxxxxxxxxxxxxxx <mailto:Chrysler300%40yahoogroups.com> [mailto:Chrysler300@xxxxxxxxxxxxxxx <mailto:Chrysler300%40yahoogroups.com> ] On Behalf Of Michael Moore Sent: Thursday, November 08, 2012 11:13 AM To: 300 Subject: Re: [Chrysler300] Compression pressure , 300H Sorry, that would be engine compression. Mike Moore On Nov 8, 2012, at 11:00 AM, Michael Moore wrote: Does anyone have available the pressure I should read for a stock 300H when cranking (with all plugs out) ? 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