CTCV Posted August 9 Share Posted August 9 I tried to post a very short video of my engine running as I turn the idle down. Unfortunately I could not get it to post. Tell us your year make and engine and the lowest RPM it can run. Why ? I don’t know. I thought mine ran pretty darn slow. Just wanted to compare. T Link to comment Share on other sites More sharing options...
Pfeil Posted August 9 Share Posted August 9 (edited) I can run my 1954 18" Cooper Clipper 1hp. Briggs & Stratton L/M down to about 100rpm. It was also the fastest on the block back in the 50's and early 60's when all us kids raced their lawn mowers. Today, I take it easy with it and it still gets the job done. FYI never been into the crankcase, but did one valve job in the mid 70's. I recall the service manual for my dad's 50 Pontiac Chieftain Deluxe straight eight with 4 speed HydraMatic says something like 375rpm in drive. I'll have to dig that manual up. ---Dug it up yes, 375rpm drive. I guess they didn't care about generator output! Edited August 9 by Pfeil (see edit history) 2 Link to comment Share on other sites More sharing options...
32buick67 Posted August 9 Share Posted August 9 Interesting topic Tony... 31-35 Buick 8s are spec'd at 340rpm full retard, and about 420rpm full advance per original octane range. Using modern 87-91 octane (non-ethanol), and with about 10deg additional timing, my engine is running about 500-600 rpm full adv at idle. I use a shaft-driven tach to measure rpm. I have tuned a few 8s on modern fuel and found the same - about 10deg more adv than factory specs, and the idle jumps about 200rpm above original spec to get a fuller burn. I haven't tried kero or diesel to drop the octane to check impact with idle rpm. I have tuned my engine down to 340s rpm, and its kinda fun to be able to hear the cylinders fire, but it wasn't running as a tuned system, so up the rpm came to ensure good burning, power and mpg. Most folks say that if you can just about count the fan blade rotating on a smooth engine, then its a good idle. Mario 2 Link to comment Share on other sites More sharing options...
CTCV Posted August 9 Author Share Posted August 9 Granted I am not using the stock updraft and my dwell / tach may or may not be reading correctly. But just for kicks I shot a video of my fan and belt spinning. The belt has a yellow label on it. I shot 30 seconds of video then counted the times the label went by. Assuming both crank and fan pulleys are the same size I doubled the 30 second count. I got a bit over 60 RPM. Can that be right? Link to comment Share on other sites More sharing options...
32buick67 Posted August 9 Share Posted August 9 The starter cranks at approx 120rpm, which is 2x your presumed rpm, so I recommend using a meter or mechanical tach to check rpm - its highly unlikely you are getting less than 60rpm at idle, that would be 1rps. If the car is running well, pulling hills and feeling strong at solid power, its unlikely you are under 500rpm at idle. If you have 300-400rpm at idle, I doubt the car is tuned and sorted for great-running and best mpg while also using modern higher octane fuels. If you are counting yellow label passes, that is different than revolutions of a pulley - did you calculate the linear inches of the belt and do the math on pulley circumference vs belt length? How is the car running - solid, smooth accel from a stop, climbs hills easily, lots of pedal remaining? If no, then you need to keep tuning. Link to comment Share on other sites More sharing options...
CTCV Posted August 9 Author Share Posted August 9 51 minutes ago, Pfeil said: Chieftain Deluxe straight eight with 4 speed HydraMatic says something like 375rpm in drive. I'll have to dig that manual up. I guess that was per the manual. I was just curious how low different engines can idle without stalling. Link to comment Share on other sites More sharing options...
CTCV Posted August 9 Author Share Posted August 9 7 minutes ago, 32buick67 said: How is the car running - solid, smooth accel from a stop, climbs hills easily, lots of pedal remaining? Car runs strong, no hesitation, starts immediately. More pedal than I have the guts to use. Apparently there is an RPM app for the cell phone. You just point the camera at a rotating object. I better double check. T Link to comment Share on other sites More sharing options...
CTCV Posted August 9 Author Share Posted August 9 25 minutes ago, 32buick67 said: If you are counting yellow label passes, that is different than revolutions of a pulley - did you calculate the linear inches of the belt and do the math on pulley circumference vs belt length? Absolutely right Mario, my brain must have been out to lunch. Im not sure what made me use the label. I knew there had to be something wrong. T Link to comment Share on other sites More sharing options...
Grimy Posted August 9 Share Posted August 9 1918 Pierce-Arrow 48-B-5 (dual valve), 6 cyl, 4.5 x 5.5 B&S, 525 cid, 190 rpm at full retard (per manual), 2,500 rpm redline. Normal idle about 250 rpm. 9 Link to comment Share on other sites More sharing options...
95Cardinal Posted August 9 Share Posted August 9 (edited) My 1910 Buick (255 cubic inch, 4 cylinder, OHV) will idle at 260 rpm with fully retarded timing. It's fun to demonstrate it at events. With the exposed valve train moving so slowly, it attracts a lot of attention. Edited August 9 by 95Cardinal (see edit history) 7 Link to comment Share on other sites More sharing options...
TAKerry Posted August 9 Share Posted August 9 I have witnessed a couple of low idle motorcycle contest's but never one with cars! I would imagine some of the old hit n miss motors would take the top prize though. 1 Link to comment Share on other sites More sharing options...
46 woodie Posted August 9 Share Posted August 9 If you have a good running and well tuned Model A Ford, you can retard the spark all the way and literally count the revolutions of the fan. Link to comment Share on other sites More sharing options...
CTCV Posted August 9 Author Share Posted August 9 10 hours ago, Grimy said: 525 cid, 190 rpm at full retard (per manual) Grimy, that is amazing. Using my dwell/ tach ,which I originally thought incorrect , I now believe correct. Did some math per Mario’s information and verified my meter. But 190 RPM? Couldn’t get that low with mine. Tony Link to comment Share on other sites More sharing options...
Grimy Posted August 9 Share Posted August 9 Very low idle rpm suggests, to me, minimal--if any--cam overlap. 1937-48 Cad V8s idle is 375 rpm, remembered from owning a 1939 for 40 years. On the other hand, my Pierce L-head straight 8s (1930, 1934, 1936) all need about 650 rpm which is surprisingly (sometimes frustratingly) high to me, and I use the dial back feature on my Sun machine's timing light because the mechanical advance weights begin to move at 600 rpm. Link to comment Share on other sites More sharing options...
zdillinger Posted August 9 Share Posted August 9 My T doesn't have a tach so I have no actual data, but I can run it slow enough to actually hear each individual cylinder fire with a pause between them. I suppose I could count/time the explosions and figure out the actual RPM. Link to comment Share on other sites More sharing options...
Gary_Ash Posted August 9 Share Posted August 9 Gee, I can't get my engine to idle under 800-1000 rpm. Must have something to do with having four carbs and no vacuum advance on the distributor. But it does run well with my foot in it! 1 4 Link to comment Share on other sites More sharing options...
BillinMd Posted August 9 Share Posted August 9 17 minutes ago, Gary_Ash said: Gee, I can't get my engine to idle under 800-1000 rpm. Must have something to do with having four carbs and no vacuum advance on the distributor. But it does run well with my foot in it! What is top rpm? Link to comment Share on other sites More sharing options...
Marty Roth Posted August 9 Share Posted August 9 I played with this idea several years back using my big old combination Tach / Dwell / etc trying to see just how slow they would go- 1914 Buick 4-cylinder B-37 190 rpm 1930 Packard 733 8-cylinder 320 ci +/- 200 rpm 1937 Buick Roadmaster 320 ci +/- 195 rpm I also once got my 4-cylinder 1927 Chevy to idle so slowly that I could count the fan blade rotation, but didn't have the inclination to measure at the time 1 Link to comment Share on other sites More sharing options...
Gary_Ash Posted August 9 Share Posted August 9 Top rpm is in the 4000-4400 rpm range, about 121 mph in 3rd gear with 3.31 rear and 7.00-18 tires - but I've never had it that fast. Rod and head bolts from ARP, rods shot peened, everything balanced. The engine was the late Jerry Kurtz's last completed project. 2 Link to comment Share on other sites More sharing options...
John Kelso Posted August 9 Share Posted August 9 My Stanley idles at 0 RPM 2 7 Link to comment Share on other sites More sharing options...
Tonz Posted August 9 Share Posted August 9 When an apprentice hot metal printer we had a strip caster machine called a Elrod. I would draw the molten printers metal thru a mould and the skill was getting the correct cooling point, draw length and draw speed. The stroke speed could be varied from nil to 200 strokes per minute, so we were very clued in on what low speed rpms were. So I think my 26 Chrysler 50 idles about 400rpm which makes the cam, valves, distributor and points about 200 rpm which is something I can relate to. On another point ... a warning!... On the big Harleys they recommend no idling under 1000rpm as it loads up the big end bearing and will cause damage, so modern Harley's don't do the "potato potato" idle. I wouldn't really worry about trying to make any motor work a too low a rev, better get to the "happy" spot and stay there. 1 Link to comment Share on other sites More sharing options...
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