Morgan Wright Posted January 5, 2018 Share Posted January 5, 2018 (edited) Do you have 7/8 inch spark plugs? Thank Ford restorers for the adapter: https://parts.modelastore.com/show_Product.asp?ID=12635 Only $6.50. According to http://www.carnut.com/specs/gen/buick20.html the compression ratio for all Buicks from 1904 to 1929 was 4.5 to 1. Atmospheric pressure in pounds at sea level is 14.2 on a rainy day and 15.2 when it's sunny, times 4.5 gives a compression of 64 rainy/69 sunny. Adjusted for altitude: Sea level..........64/69 1000 m............58/62 2000 m............51/55 3000 m............45/48 above 3000 use an airplane engine Edited January 6, 2018 by Morgan Wright chart I used was meters not feet. duh (see edit history) 1 Link to comment Share on other sites More sharing options...
C Carl Posted January 6, 2018 Share Posted January 6, 2018 Thank you for the adapter source , Morgan. As to calculating compression pressure , it is considerably more complicated. Please use the search box in "Technical" under "GENERAL DISCUSSION" , and enter "Spark knock in a 32 Packard ??". Therin a more sophisticated understanding evolved , and by post #8 , the highly esteemed Dr. Spinneyhill , a beloved multi thousand posting PhD researcher , (somehow I seem to think he may have 2 PhDs , but I am not a good enough researcher to confirm this) , dead nails it and quotes reference. Again , thank you for the info. I enjoy your contributions very much , and particularly apreciate the data you share with us. I almost always learn something from you. Now , something else I am curious about and , thanks to you , will never forget is the uniformity of the compression ratios all the way through 1929 ! Do you have a reference which continues on another couple or three decades ? - Carl Link to comment Share on other sites More sharing options...
Morgan Wright Posted January 6, 2018 Author Share Posted January 6, 2018 http://www.carnut.com/specs/gen/buick20.htmlhttp://www.carnut.com/specs/gen/buick30.htmlhttp://www.carnut.com/specs/gen/buick40.htmlhttp://www.carnut.com/specs/gen/buick50.htmlhttp://www.carnut.com/specs/gen/buick60.html Link to comment Share on other sites More sharing options...
C Carl Posted January 6, 2018 Share Posted January 6, 2018 Oh also , as long as I am up , your posting reminded me of a little factoid from my flight engineers training 50 years ago : HALF ATMOSPHERE occurs at 18,000'. This is the elevation at which 1/2 of the sum total of all gas in the atmosphere is below you. The other 1/2 ? Stretches up several dozen miles , (with a few rogue gas molecules wandering further afield) , ever less dense. At some point , it does not really exert pressure , although it is EXPRESSED as a very small fraction of barometric pressure. It is then merely an expression of density. Aerodynamic control , of course , is impossible without any air pressure whatsoever. Is there some drag on low earth orbiting satellites ? Yes , accumulated collisions with the occasional gas molecule add up over extremely long periods of time. Newtonian physics applies. ALWAYS SLOW YOUR ANCIENT CARS DOWN WHEN DRIVING INTO A HEADWIND !!!! Your engine's continued good health will be assured ! - Carl 1 Link to comment Share on other sites More sharing options...
Morgan Wright Posted January 6, 2018 Author Share Posted January 6, 2018 So I guess the nominal compression ratio they give to cars is not really the compression ratio. Link to comment Share on other sites More sharing options...
Morgan Wright Posted January 6, 2018 Author Share Posted January 6, 2018 I forgot to account for gauge pressure. If atmospheric pressure is 14.7 and the gauge says 0, then 4.5 atmospheres would really be 66 but the gauge will say 51. But I guess it doesn't matter because it turns out nominal compression ratio is not compression ratio. Never mind. Link to comment Share on other sites More sharing options...
Spinneyhill Posted January 6, 2018 Share Posted January 6, 2018 10 minutes ago, Morgan Wright said: So I guess the nominal compression ratio they give to cars is not really the compression ratio. It is exactly the compression ratio, which is defined as the ratio of the capacity of the combustion chamber at its maximum volume to that at its minimum volume. The compression pressure is related to the compression ratio as well as the volumetric efficiency of the engine. The engine has to "suck" in the fuel-air mixture, on which there is a bit of drag (friction) on the way in, so the combustion chamber at maximum capacity (piston at BDC) is not completely filled with mixture at atmospheric pressure. Clearly you can increase volumetric efficiency a lot, e.g. port and polish the inlet passages (reduce the drag on the incoming mixture) or put on a blower to overcome the drag. VE on some of today's blown engines is greater than one. Ask the www, it is all there for you to read about if you can be bothered. 1 Link to comment Share on other sites More sharing options...
Morgan Wright Posted January 6, 2018 Author Share Posted January 6, 2018 When they redid the head on my 263 engine they milled about 1mm of metal off the head to make it flat. The compression after I had it running a few months and the rings were all seated properly was quite a bit more than when the engine was new. The way they raised the compression on that engine for use with a Dynaflow was simply to use a thinner head gasket. Same thing. Link to comment Share on other sites More sharing options...
C Carl Posted January 6, 2018 Share Posted January 6, 2018 (edited) It is the compression RATIO , which is a simple expression of mechanical comparison between swept volume , and combustion chamber volume. Compression PRESSURE is dependent on several factors , including cam profile/valve timing. This translates to volumetric efficiency. Volumetric efficiency at various operating rpm could exceed 100% in some cars eg. Jaguar , by the late 40s , and Chrysler Hemis , particularly with their tuned intake , did it very well in the 50s. Normally aspirated O.H.C. racing engines (Duesenberg , Bugatti , etc.) almost certainly achieved over 100% by the late(?) '20s.I am sure that modern normally aspirated computer designed/controlled , variable valve timing ,engines have volumetric efficiencies well over 100% over a fairly broad rpm range. Supercharged engines by definition have VERY high volumetric efficiency. But take a look at a supercharger camshaft. Different set of bumps. So cranking compression pressure , all other things being equal , will be lower , as will a high speed engine with a long duration camshaft. This gives high volumetric efficiency , and better scavenging at speed. By the way : Dr. Diagnosis , an analyst who infrequently (thankfully) , makes a contribution(?) here , says I suffer from mild compression obsession , complicated by an almost pathological octane fixation. I am grateful to you for supplying the comprehensive compression data as an Rx for my affliction. Quite interesting to see how immediate pre war compression ratios then fell , and did not recover until 1950. I am convinced that the ease by which one can raise compression ratios on ancient low compression OHV engines by piston design and manufacture should be taken advantage of at rebuild time , or , for that matter , right now. Just depends what else you need to do with your time and money. Stutz guys who either do , or by continued tending their cars do NOT have sufficient money , take them up to 7 , or 7.5:1. I would think Biick could go to a bit more. I see other guys have joined in. I hope my arthritis provoking tapping will not have been in vain , now being merely redundant ! Here you are : Edited January 13, 2018 by C Carl Changed "be" to "by" , per Dr. Diagnosis (see edit history) 2 1 Link to comment Share on other sites More sharing options...
Morgan Wright Posted January 6, 2018 Author Share Posted January 6, 2018 That sounds like the volume ratio. But if you define the compression ratio as the volume ratio, then yeah. If you define the compression ratio as a bird with two webbed feet that wobbles, then the compression ratio is a duck. Link to comment Share on other sites More sharing options...
C Carl Posted January 6, 2018 Share Posted January 6, 2018 That is an interesting , but totally correct way of putting it ! And speaking of putting : that put a great huge smile on my old face ! Again , thanks ! - Carl Link to comment Share on other sites More sharing options...
Morgan Wright Posted January 6, 2018 Author Share Posted January 6, 2018 I balk at trying to increase the compression of 100 year old engines with new pistons, etc. These old babitt bearings, you know. Like giving a 90 year old man a new heart. Just put them back the way they are supposed to be. Link to comment Share on other sites More sharing options...
Bloo Posted January 6, 2018 Share Posted January 6, 2018 There is mechanical compression ratio, and there is dynamic compression ratio. Mechanical compression ratio can be calculated, at least if one chooses to ignore the leaks. Dynamic compression ratio varies with RPM. Neither are available on a compression gauge. The pressure you get on a compression gauge varies with temperature, barometric pressure, altitude, valve timing, valve overlap, valve lift, lobe center angle, cranking speed, port efficiency at cranking speed, whether the throttle was open or closed, how many "pumps" were used in the test, size (cc) of the individual combustion chambers, and cylinder leakage, mainly through the rings in a healthy engine. Compression gauges are looking for evenness, 20% or less is typical if nothing is really wrong. All cylinders extremely low would also be a red flag. One cylinder down at 25 or 30 pounds is almost always a burned exhaust valve, but any big leak in the combustion chamber, like a holed piston or a blown head gasket can also do this. A leakdown tester along with your eyes and ears will tell you which it is. You can sort of check rings by putting oil in each cylinder and seeing if the compression gauge pressure comes up a lot. If it does, the rings are leaking. Who knows how much? Probably too much. Be sure to squirt the same amount of oil in every time so you don't skew the readings by changing the volume. If only one cylinder comes way up in an engine where the others don't come up much, you probably found a broken ring or piston. That cylinder will need boring. Trying to figure out what the actual number of PSI should be is like asking "How high is up?". Some manuals give a number. It is a guideline. If the number is 210psi, and you have 73psi, then I guess that would be a red flag. Maybe the valve timing has jumped. If it was 170psi and even between cylinders, I wouldn't give it a second thought. Link to comment Share on other sites More sharing options...
Spinneyhill Posted January 6, 2018 Share Posted January 6, 2018 Carl has mentioned the valve timing. That is another way to increase the VE. For example, the inlet valve may remain open after BDC and the mixture can continue flowing into the cylinder, because it has momentum. Also, the piston doesn't move upward much for a few degrees after BDC. That is one of the things they must have been implying when they talked about valve timing in the article referenced above by Carl. The things mentioned by Bloo would be others. Of course, the valve timing (opening and closing and thus the duration) required for power and efficiency are different. This is one reason we have variable valve timing today. At flat, constant speed cruising we need efficiency but when we climb a hill or accelerate we need power. And of course with electronic computer driven ignition the spark timing changes too. 1 Link to comment Share on other sites More sharing options...
Spinneyhill Posted January 6, 2018 Share Posted January 6, 2018 The below, from MoToR's Manual, shows you the difference referred to by Bloo, dynamic and mechanical compression. The compression pressures are significantly higher at 1000 RPM than at Cranking speed. You can also work from the formula to calculate the volume efficiencies - you will see VE is greater at the higher speed. Link to comment Share on other sites More sharing options...
Morgan Wright Posted January 6, 2018 Author Share Posted January 6, 2018 Testing compression at cranking speed is to see if the mechanical parts are functioning properly. Like the gravestone of Lester Moore says.......no less no more. Link to comment Share on other sites More sharing options...
C Carl Posted January 6, 2018 Share Posted January 6, 2018 (edited) Common misconception in the automobile universe. Bearing load on the COMPRESSION STROKE is irrelevant. High compression ratio , multi-stage positive displacement air compressor bearing loads are considerably less than the bearing loads generated during the POWER STROKE of an internal combustion engine. THAT is what propels the vehicle. By raising the compression ratio , you are simply restoring the explosion timing to the same point in terms of degrees of crankshaft rotation that the engine was designed for. What happens during combustion in a gasoline engine , is that after ignition , you have a somewhat linear flame front propagation rate , steadily increasing pressure on itself and the yet unburned charge , into an increasing volume. At a certain point of revolution , the entire remaining charge explodes , (compression ignition a la diesel - see : Cetane). Variables determine that point of revolution. High altitude , hence , as you earlier calculated , reduces compression pressure , thus delaying that point of maximum power. You ideally want this to happen very close to , but somewhat before , the point at which the crank pin is at 90 degrees off the thrust line of the powering cylinder. This will be at maximum piston speed , and maximum rate of volume expansion. If this happens too soon , in a sense , the engine will be trying to compress an explosion , by not providing anywhere for the expansion to expand in to - knock. Now modern high octane gasoline delays the point at which compression ignition happens. That is what knock resistance in a high compression engine is all about. 90 , 100 years ago , 40 something octane gasoline danced in perfect step with the 4.5:1 compression engines it then powered. By raising the compression ratio , you are merely putting the original power back in the power stroke. This enables proper efficiency on modern high octane fuel by restoring the point of crankshaft revolution when compression ignition of the as yet unburned , highly compressed charge takes place. The BTUs of the gasoline remains the same regardless of octane. You are just allowing your engine to achieve design power. Your exhaust valves will thank you , too. The bearing loads WILL go up , but will simply return to design spec. Now if your bearings are less than optimal , or if you suspect they are , maintain low manifold pressure , low BMEP. Hmmmmm............ I have just read this explanation. I have never yet read such a simple , concise (to ME) explanation of what goes on regarding this subject. But I don't know how this would be received by someone who does not bear the burden of the malady I suffer from according to Dr. Diagnosis above. It makes an enormous amount of sense to ME , but , dear reader , I beg your critique. I have been studying , thinking about , and living these concerns for a while now , therefore my explanation here may need some refining. Please help me to improve this where needed. Thank you ! - Carl P.S. I would be very interested if in someone's library , you have test setup descriptions , and test data from early engine development. Dynamometer , and manometer data from 100 years or so ago. Hey ! I think I will use AACA library credit ! Edited January 6, 2018 by C Carl Add refinement and P.S. (see edit history) 2 Link to comment Share on other sites More sharing options...
Morgan Wright Posted January 6, 2018 Author Share Posted January 6, 2018 If I were designing a race car at Le Mans to do what my great^4 uncle Wilbur did there in 1908, but with spoilers in the rear to prevent it, I would worry about all this. But I'm merely trying to get an old Buick to do what it hasn't done in 80 years.........start. 2 Link to comment Share on other sites More sharing options...
KongaMan Posted January 6, 2018 Share Posted January 6, 2018 Getting it to start is one thing. Keeping it running -- and in one piece -- might be an altogether different challenge. 1 Link to comment Share on other sites More sharing options...
Morgan Wright Posted January 6, 2018 Author Share Posted January 6, 2018 Good point. Keeping it on the ground at Le Mans WILL be a challenge.......it has no spoiler. Link to comment Share on other sites More sharing options...
Ben Bruce aka First Born Posted January 6, 2018 Share Posted January 6, 2018 LOVE this thread! Ben 1 Link to comment Share on other sites More sharing options...
Brian_Heil Posted January 6, 2018 Share Posted January 6, 2018 13 hours ago, C Carl said: P.S. I would be very interested if in someone's library , you have test setup descriptions , and test data from early engine development. Dynamometer , and manometer data from 100 years or so ago. Hey ! I think I will use AACA library credit ! There is such a book with 20 different standard test set-ups. Let me look if I still have mine. It's all SAE now but back in the day this was the Bible at all GM Dyno Labs, Buick or otherwise. 3 Link to comment Share on other sites More sharing options...
Brian_Heil Posted January 9, 2018 Share Posted January 9, 2018 A fellow BCA Member I hired in with has his, talked with him today. I will copy parts and post. Stay tuned. Mine is still 'hiding'. Link to comment Share on other sites More sharing options...
Brian_Heil Posted January 12, 2018 Share Posted January 12, 2018 Here you go Carl. My copy when I find it is the 1975 issue. You need to find a first edition. 1 Link to comment Share on other sites More sharing options...
C Carl Posted January 13, 2018 Share Posted January 13, 2018 Thank you very much for taking the time , Brian ! I immediately ordered the 1933 edition. There is an automotive engineer , Alex Voss , who actually has a brick and mortar automotive bookstore here in the far-flung wilds of Seattle. Naturally he is also on line at books4cars.com. He has been able to come up with some wonderful obscure books for me. It is becoming more difficult to browse used bookstores which no longer exist these days. Part of me died when I was making my rounds of Southern California several years back , and found that Cliff's Books on Colorado Ave. , near Cal Tech in Pasadena , was no more. At any rate , Alex and I have initiated a discussion around this subject. We must achieve a breakthrough squaring the NEED for extremely low octane gasoline for use in extremely high elevation regions of the world , with knock resistance , and the elevated EGT of an engine running too high octane gasoline. My simple , incomplete , not quite correct (as I already realize) , theory above , is the product of trying to do this by thought. Sadly , I am not an engineer , but like those of us who share my disadvantageous handicap , we are curious amateur engineers. Simple , elegant test set ups by scientists from Galileo and Ole Romer , through the physicists like Michelson , Millikan/Fletcher , and on to Lawrence and Fermi , are accessible to a great degree by the mechanical minds of us gear heads. That is the kind of early test bed and data I need to finally be able to write what I am trying to understand , and about which there is much confusion. Thanks again Brian , and again I need any criticism of what I have written above. To a great degree I am "thinking out loud" , and already see the need for correction. However , I do think it is counter productive to "fill 'er up" with 92 octane in order to crest Trail Ridge Road in Colorado , or pull the grades leading up to White Pass in California. - Carl Link to comment Share on other sites More sharing options...
Morgan Wright Posted January 13, 2018 Author Share Posted January 13, 2018 This is awesome! I started this thread to discuss testing the compression, at cranking speed, which is around 10 RPM, of an old Buick, to check whether the rings and valves are working properly. Look how far we have advanced! Link to comment Share on other sites More sharing options...
Grimy Posted January 13, 2018 Share Posted January 13, 2018 I'll let you guys calculate how many angels dance on the head of a pin, and I'll be happy with getting somewhere in the 60-70psi range on my 4.5-4.6 ratio engines. As for the ratios at 1,000 rpm, I'll be dipped if I'll start the engine the number of times of my cylinder count to do a compression test. While you are mucking around with that, I'll have finished synchronizing dual points, have set the timing and idle adjustment, and have had at least one celebratory beer. 1 Link to comment Share on other sites More sharing options...
Spinneyhill Posted January 13, 2018 Share Posted January 13, 2018 6 hours ago, Grimy said: As for the ratios at 1,000 rpm, I'll be dipped if I'll start the engine the number of times of my cylinder count to do a compression test. Indeed. I wondered what MoToR was thinking there! Unless it came from Buick? Link to comment Share on other sites More sharing options...
Morgan Wright Posted January 13, 2018 Author Share Posted January 13, 2018 7 hours ago, C Carl said: ........ in order to crest Trail Ridge Road in Colorado , or pull the grades leading up to White Pass in California. - Carl At those altitudes you need a turbo. Link to comment Share on other sites More sharing options...
Morgan Wright Posted January 14, 2018 Author Share Posted January 14, 2018 The first time I drove across Colorado I didn't know why the car had no power. (I was 19 and didn't know anything.) I was driving a 1973 Checker with a Chevy 350 in it. Top speed was 40 MPH and the VW bugs were passing me up the hills. To this day you still see lots of VW Bugs in Colorado. It's not because of the hippies, it's because VW bugs operate very well at high altitude. Link to comment Share on other sites More sharing options...
Recommended Posts
Create an account or sign in to comment
You need to be a member in order to leave a comment
Create an account
Sign up for a new account in our community. It's easy!
Register a new accountSign in
Already have an account? Sign in here.
Sign In Now