1912Minerva Posted June 15, 2019 Share Posted June 15, 2019 (edited) Hi All, Just wondering what people thought was a good cylinder compression reading (PSI) for a Model 20. I am getting 55 PSI on 1,2 & 3 and 25 on No.4. Obviously there is a problem with 4. I did a leak down test and it looks like rings are not seating. Any thoughts appreciated. Cheers, Andrew. Edited June 15, 2019 by 1912Minerva (see edit history) Link to comment Share on other sites More sharing options...
Guest Posted June 15, 2019 Share Posted June 15, 2019 Atmospheric pressure time compression ratio gives a good estimate of compression readings. Obviously number 4 needs some attention. Even readings are more important than how high the number is. Link to comment Share on other sites More sharing options...
1912Minerva Posted June 19, 2019 Author Share Posted June 19, 2019 Thanks for your advice Tinindian - appreciated. Regards, Andrew. Link to comment Share on other sites More sharing options...
Morgan Wright Posted June 25, 2019 Share Posted June 25, 2019 I wonder how they figure compression ratio. Atmospheric pressure is 15, but if the pressure in the cylinder is 60 that's not really 4 to 1, because the 60 is a gauge pressure not the real pressure. So, with a 60 gauge pressure, its real pressure of 75, which would be a 5 to 1 ratio. If you use gauge pressures, you are comparing 60 to 0 which is impossible. Gauge pressure of the atmosphere is 0. Link to comment Share on other sites More sharing options...
C Carl Posted June 25, 2019 Share Posted June 25, 2019 Compression ratio is simply swept volume (pi x bore radius squared x stroke), over combustion chamber volume. Compression pressure is another matter. Dr. Spinneyhilll posted the more complex formula some several months ago. It does take into account your observations, but is more involved. Volumetric efficiency (in this case think cam profile/duration rather than gas fluid dynamics), is a factor. Let me see if I can conjure up an appropriate key word to put into the search box in order to bring up the posting. I think I will try "atmospheric". Stand by......... - CC Link to comment Share on other sites More sharing options...
C Carl Posted June 25, 2019 Share Posted June 25, 2019 Yes, that got it. I was trying to bring the topic back from its last contribution (June 3rd, 2018), with a comment regarding volumetric efficiency. There is a statement in the yellow slide show box claiming compression pressure drops with increasing rpm due to lessening intake charge from reduced pressure (partial vacuum) behind the fast moving piston on intake stroke. This is not categorically true. As we know, volumetric efficiency at speed depends on intake and exhaust tuning (sonic effects), along with valve timing and scavenging at overlap. It can and does exceed 100% on some normally aspirated engines at higher rpms. Anyway, page 2 near the top as accessed by "atmospheric" in the search box. I kept getting tripped up, so I had to resort to this cumbersome technique. I am generally patient to a fault, but I am somewhat short fused when being second guessed by the high speed moron (my iPad mini with which I have a love/hate relationship), I am getting tired of diddling with my somewhat arthritic thumbs. A little grouchy, think I'll go do something else for a while. By the way, Morgan, you were a contributor to the referenced posting regarding a 1933 Buick. Compression ratio, compression pressure : two different things. - Carl Link to comment Share on other sites More sharing options...
1910Hupp Posted June 26, 2019 Share Posted June 26, 2019 I'm not sure that the actual figures are important in a Model 20 . Lets face it they don't go very fast and your aren't going to improve that by increasing the CR by planning the the head cause you don't have one . What is significant is difference between the figures . As in Andrew's case they are an indication of something not right on the out of whack pot . Sounds like a valve grind is in order . I always repeat the test with some thick oil down the offending pot to check its not a ring problem . A vacuum gauge is also a useful diagnostic tool but no facility to attach one on the Hupmobile . I find a timing light to be quite useful I use a standard timing light which I run off a 12 Volt battery and use Lead one and the markings on the flywheel and block to see where we are at. Certainly on my car if set up by the book ie slightly retarded after TDC it performs and starts much worse than if i adjust the ignition to about 15 to 20 degrees advanced Link to comment Share on other sites More sharing options...
Hupp36 Posted June 26, 2019 Share Posted June 26, 2019 Well yours may not go very fast but in 1995 on a Hupp tour in Ohio, I followed Ed Kiley with his 1909 Model 20 between 45 and 50 Mph. Now thats hauling A_ _. Link to comment Share on other sites More sharing options...
1910Hupp Posted June 27, 2019 Share Posted June 27, 2019 I've had mine up to 40-45 mph so they can get up there -but certainly wasn't fun with the steering and lack of shocks and I could feel I was thrashing it - I found myself asking myself why am I doing this and how would I feel when I blew it up - so I backed off. Mostly the max I get up to is about 30 mph and at that speed I figure that I might get some longevity out of my engine. I drive mine frequently but only short distances so the difference in travelling at 30mph and 45mph is about 2 mins when you get there . I do hear of Model 20's achieving up to 50 mph ( Edgars , Eds and Davids off the top of my head ) and while I'm sure they do achieve this speed I don't think they represent the vast majority of Model 20's . The technical adviser for the Model 20 Bill Cuthbert once told me that in his opinion any Model 20 that gets to 30 mph is a good one and one that gets to 50mph is on a trailer ! LOL Link to comment Share on other sites More sharing options...
trimacar Posted June 27, 2019 Share Posted June 27, 2019 I've had mine over 40, it does get a little busy with the steering being so quick, if you sneezed while doing it you'd be out in the field next to the road..... I think it's a combination of condition and which rear end one has in a 20, either 3.50 or 4.00. My best friend up here used to own a worn out Model 20 (which subsequently was restored to the nth degree and at one point sold for 80K or so). We were driving mine, long after he'd sold his, we came to a hill and he said good luck getting up that one. My car just loped along, slowing some but easily climbing the hill mentioned. I will admit I had a good head start. His comment was similar to "it's a good one". If Ed Kiley's car is the one I'm thinking of, I've seen it on a tour, and it is HIGHLY modified, from light weight flywheel to different transmission, and so forth. Not that there's anything wrong with that, but it's not a true representation of Model 20 performance. The sweet spot on my car seems to be around 35 mph, and out in the open as you sit in the car, that's plenty fast! I have a windshield, but not on the car, and of course mine is a 1910 with no doors. I once drove the car to work and my then secretary walked out, looked at the Hupp, and said "David, it's a shame you can't afford a whole car....." Link to comment Share on other sites More sharing options...
Hupp36 Posted June 27, 2019 Share Posted June 27, 2019 No, Eds was not modified, you are thinking of one of the Hupp club members that put a different engine and a 3 speed transmission in his Model 20. Link to comment Share on other sites More sharing options...
trimacar Posted June 27, 2019 Share Posted June 27, 2019 23 minutes ago, Hupp36 said: No, Eds was not modified, you are thinking of one of the Hupp club members that put a different engine and a 3 speed transmission in his Model 20. Ok thanks for correction. A stock Model 20 would be scary at 50, I'd think. Link to comment Share on other sites More sharing options...
1910Hupp Posted June 28, 2019 Share Posted June 28, 2019 I agree David rear end ratio is crucial . I'm not sure what ratio I have in mine . I suspect it is 1: 3.63 as I believe that my diff internals are Model T and that is the standard T rear end . What I need to do is jack up the rear end and in top gear turn the engine over once and count the rear wheel revolutions . I know that the Model T had an optional 1:3.10 ring gear which increased speed by about 7 mph Not sure a good idea if you want to climb any hills . Link to comment Share on other sites More sharing options...
Hupp36 Posted June 28, 2019 Share Posted June 28, 2019 We did not travel those speeds very long. The road in Ohio we were on was very straight and flat with no turns. Ed had driven his Model 20 many miles and was a very experienced driver. Link to comment Share on other sites More sharing options...
trimacar Posted June 28, 2019 Share Posted June 28, 2019 I know I've been over 40 in my Hupp, my wife was following behind and told me speed. It definitely has to be a flat road, wind at your back doesn't hurt either! I'm running a stock ring and pinion, 3.50 ratio. As to the Model T innards, at one point my spider gears chewed themselves up, and I was devastated since had no idea how I was going to find another set. I started looking at early Model T spider gears and noticed how close they were in size. Ordered a set, and I don't remember specifics, but one minor modification and they slipped right in and worked perfectly. The only other thing scary about that speed in a 20 is the stopping, not so much the brakes, but if one hits the brakes and forgets to hit the clutch. At that speed, the momentum of that big flywheel on the front of the crankshaft can do really bad things. Link to comment Share on other sites More sharing options...
1910Hupp Posted July 3, 2019 Share Posted July 3, 2019 Interestingly I took my car for a run this afternoon despite it being in the middle of winter here . In light of this thread I opened it up and 30 mph was about it . Pondering on this I took particular note of where the throttle arm on the Breeze was at full throttle and it appears that the throttle plate is only about 2/3 open at full throttle . Further inspection revealed that there is about 4 .5 cm of movement of the throttle lever on the carb from closed to fully open throttle plate in the X plane . However fully depressed gas pedal only moves the gas pedal carb linkage open 3cm in the X plane ie with the present set up I'm never going to get fully open throttle plate in the carb. The solution is to make a shorter lever between the throttle plate and the gas pedal linkage Which I will get onto on the weekend . The 40-45 mph I have had previously was with the Holly NH set up -I wonder if the getting the throttle plate right will make a difference -I suspect so ! Link to comment Share on other sites More sharing options...
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