Re: [Chrysler300] Thermodynamics of a Ram
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Re: [Chrysler300] Thermodynamics of a Ram
- From: Michael Moore <mmoore8425@xxxxxxx>
- Date: Sat, 10 Nov 2012 07:14:58 -0800
Thanks Carl,
As a matter of interest, the reason I asked the question initially was to get an idea as to whether my rebuilder 20 years ago, concerned about emissions control and loss of premium gasoline, as he prepared my 300H for a move to California, had installed low compression pistons.
He had made other mods supporting that goal. I was just looking for a general idea of what compression readings stock (driver) 300H's ought to be so I could compare mine and make a judgement about pistons.
Thanks again, Mike
On Nov 10, 2012, at 6:54 AM, Carlton Schroeder wrote:
Hello,
This subject appears to be another example of a question being more
complicated than it might first seem. Just on the matter of an engines
compression ratio I thought (and still do) it is just a volume ratio of the
sum of the cylinder volume the piston moves through + the combustion chamber
volume divided by the combustion chamber volume. With odd shaped combustion
chambers, valve tops, the spark plug, head gaskets, and non-flat piston tops
the exact volume calculations would be complicated. I guess though if you
really wanted to determine a precise CR you could use oil and fill the
volumes (piston at the bottom and piston at the top) and determine the CR
from that data. The valves would have to be closed and to be really precise
you would have to account for that little additional volume in the spark
plug core.
For another method if the piston was at the bottom and you could make a
pressure and temperature reading then and could also measure the pressure
and temperature in the combustion chamber at the end of the compression
stroke then from gas laws you should be able to calculate the CR.
I hope this understanding is consistent with the rest of the posts I've been
reading.
Carlton Schroeder
Eagle River, WI
-----Original Message-----
From: Chrysler300@xxxxxxxxxxxxxxx [mailto:Chrysler300@xxxxxxxxxxxxxxx] On
Behalf Of RICK AND DEBBIE CLAPHAM
Sent: Saturday, November 10, 2012 7:33 AM
To: larry@xxxxxxxxxx; tfm@xxxxxxxxxxxx; mmoore8425@xxxxxxx;
flatheadeng@xxxxxxxxxxx; Rich Barber; mgoodknight@xxxxxxxx
Cc: chrysler300@xxxxxxxxxxxxxxx
Subject: RE: [Chrysler300] Thermodynamics of a Ram
Larry, I have been where you are at many times self-inflicted and with
customer's choice. A camshaft change will cure the problem. Actually
Hemispherical combustion chambers can withstand higher dynamic compression
ratios. The chart / tool you have posted will help. I also know finding a
392 cam is now difficult. Rick
To: rixpac@xxxxxxx; tfm@xxxxxxxxxxxx; mmoore8425@xxxxxxx;
flatheadeng@xxxxxxxxxxx; c300@xxxxxxx; mgoodknight@xxxxxxxx
CC: chrysler300@xxxxxxxxxxxxxxx
From: larry@xxxxxxxxxx
Date: Fri, 9 Nov 2012 21:55:26 -0600
Subject: RE: [Chrysler300] Thermodynamics of a Ram
Sorry This has nothing to do about the ram effect but I thought I would
chime in anyway
The way I understand it is that the 10 to 1 compression is the static
compression ratio which is what you would get when the piston travels from
the bottom of the stroke to the top of the stroke with the valves being
closed at all times
And to get the real compression ratio or dynamic compression ratio all the
figures as far as stroke, bore, head gasket thickness ect. Would be the same
for both Accept putting in the degrees ABDC that you have the intake valve
close
Below is a link that will give you both ratios if you have all the numbers
to put in
http://kb-silvolite.com/calc.php?action=comp
300D 392
I used this when I had my engine rebuilt & had the cam designed so we would
come up with a cam that should be good for the crappy gas we have out here
in CA especially in the Bay Area
I ended up with a static of 9.1 & a dynamic of 7.6 which supposedly it
perfect for 91 octane
I think this works for most engines except hemis from the fifties
After doing all this it still pings under load even by controlling the total
spark advance to 24 degrees
The only thing that makes it happy is 96 octane at the race track which
costs about $7.00 a gallon
If anyone has had this issue of pinging with a 392 and has any solutions I
would like to hear about it
Thank you
Larry Jabin
-----Original Message-----
From: Chrysler300@xxxxxxxxxxxxxxx [mailto:Chrysler300@xxxxxxxxxxxxxxx] On
Behalf Of RICK AND DEBBIE CLAPHAM
Sent: Friday, November 09, 2012 7:05 PM
To: tfm@xxxxxxxxxxxx; mmoore8425@xxxxxxx; flatheadeng@xxxxxxxxxxx; Rich
Barber; mgoodknight@xxxxxxxx
Cc: chrysler300@xxxxxxxxxxxxxxx
Subject: RE: [Chrysler300] Thermodynamics of a Ram
These explanations are quite adequate on the RAM EFFECT. The camshaft design
explanation still has me confused. The short ram is basically a 361 camshaft
with 4 degree retard. I read my fathers papers on cam design and realize
Chrysler had the best labs of any manufactures of the auto industry. They
did know what the wanted and they built it. The bad news is the compression
has not been effectively used until direct injection. I know we think we
have 10 to 1 compression ratio engines we just do not. The valves open and
close at specific timing and if you figure it out we really never use the
rated compression ratio, Less than half the rated. Here in Colorado we can
drive to the top of Pikes Peak on regular gasoline. Being your effective
compression ratio is effected by altitude. at 5000 foot above sea level you
lost 20% of the sea level atmosphere. Actually lowering the efective
compression ratio.
CC: Chrysler300@xxxxxxxxxxxxxxx
To: mmoore8425@xxxxxxx; flatheadeng@xxxxxxxxxxx; c300@xxxxxxx;
mgoodknight@xxxxxxxx
From: tfm@xxxxxxxxxxxx
Date: Fri, 9 Nov 2012 20:20:05 -0500
Subject: Re: [Chrysler300] Thermodynamics of a Ram
Here's a link to our web site where you'll find the operational theory
behind cross ram induction. Cam timing is *critical* to getting the most
optimal performance from this setup.....
http://www.chrysler300club.com/uniq/allaboutrams/ramtheory.htm
TFM
Thomas F. Miller
tfm@xxxxxxxxxxxx
'57 300C
'70 440+6 'Cuda
>>> "Flathead Engineering" <flatheadeng@xxxxxxxxxxx> 11/9/2012 6:33 PM
>>>>>>
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
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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) ?
Thanks, Mike Moore
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