compression ratio question
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Category: Other Topics
Forum Name: Pulling Forum
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URL: https://www.allischalmers.com/forum/forum_posts.asp?TID=74949
Printed Date: 26 Jun 2024 at 1:57am
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Topic: compression ratio question
Posted By: Alex09(WI)
Subject: compression ratio question
Date Posted: 11 Aug 2013 at 12:15am
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I am attempting to build an engine with 4 1/8" flat top WD pistons (not M&W) and a WD45 crankshaft. What is the compression ratio that this arrangement will produce? Thanks ------------- www.awtractor.com A&W TRACTOR 920-598-1287 KEEPING ALLIS-CHALMERS IN THE FIELDS THROUGH THE 21ST CENTURY |
Replies:
Posted By: CTuckerNWIL
Date Posted: 11 Aug 2013 at 6:25am
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http://www.rbracing-rsr.com/compstaticcalc.html" rel="nofollow - http://www.rbracing-rsr.com/compstaticcalc.html ------------- http://www.ae-ta.com" rel="nofollow - http://www.ae-ta.com Lena 1935 WC12xxx, Willie 1951 CA6xx Dad bought new, 1954WD45 PS, 1960 D17 NF |
Posted By: DrAllis
Date Posted: 11 Aug 2013 at 6:44am
| It will depend upon which piston you are actually using....compression heights will vary somewhat from one vendor to another. |
Posted By: patrickmull
Date Posted: 11 Aug 2013 at 7:19am
| my first pulling tractor a 37 wc was set up like this it had a mag i hand cranked it |
Posted By: cotncrzy
Date Posted: 11 Aug 2013 at 8:01am
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I set my first engine up like that, we figured it 9.5:1 or so. Had 140 psi cranking compression. Way up from 100, where it was. ------------- C, WD45,WD puller, 185, 200, 7060 Red Belly, 7060 Black Belly,8010, and a R52 Gleaner, AND PROUD OF THEM! |
Posted By: DrAllis
Date Posted: 11 Aug 2013 at 8:08am
| A model One-Seventy gas has 8.0 to 1 compression and will crank at 170 to 180 psi with electric start. |
Posted By: cotncrzy
Date Posted: 11 Aug 2013 at 8:17am
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We wasn't sure of the math Dr Allis, I have spoke with others after the engine was assembeled that agreed we were close to that. So, I stand corrected on the ratio, we were still useing the old hand crank to turn the engine though, might of made some difference. ------------- C, WD45,WD puller, 185, 200, 7060 Red Belly, 7060 Black Belly,8010, and a R52 Gleaner, AND PROUD OF THEM! |
Posted By: wi50
Date Posted: 11 Aug 2013 at 8:46am
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It will depend on your pistons original compression ratio, but putting that taller piston on a longer stroked 4.5" crankshaft will boost it a fair bit. It's easy to figure out if you work the numbers backwards.
I just ran some round numbers for comparison, the higher the original compression ratio, of course the higher the ratio will be when swapped to the longer stroke, but it grows exponentialy because of the added swept volume and the lesser compressed volume. Just for example if you originally had a 6.5 to 1 compression ratio with the 4" stroke crankshaft by simply swapping that piston to a 4.5" stroke crankshaft you have a 10.5 to 1 compression ratio. If it had a 7 to 1 compression ratio the swap will yeild a 12 to 1 compression ratio. If you have an 8 to 1 compression ratio originally, the swap will yeild about 15 to 1 comperssion ratio.
------------- "see what happens when you have no practical experience doing something...... you end up playing with calculators and looking stupid on the internet" |
Posted By: DrAllis
Date Posted: 11 Aug 2013 at 9:35am
| If you hand crank to test, it will show weaker than it really is. If you have the throttle at an idle, it will show weaker than it really is. Open the throttle wide open and put a chain on it and pull it with another tractor to get a good compression test. |
Posted By: mike a
Date Posted: 11 Aug 2013 at 11:14pm
| i put wd dished in my e-gleaner engine,cranks 175 psi. |
Posted By: cotncrzy
Date Posted: 12 Aug 2013 at 5:03am
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I will say this, the first build wouldn't run on regular gas. Well it would run but knocked and had to choke it out, the ignition wouldn't kill it. ------------- C, WD45,WD puller, 185, 200, 7060 Red Belly, 7060 Black Belly,8010, and a R52 Gleaner, AND PROUD OF THEM! |
Posted By: Alex09(WI)
Date Posted: 12 Aug 2013 at 4:48pm
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I measured the compression height of the piston and as far as I can tell it is 2.465" from the center of the wrist pin to the top of the piston.
------------- www.awtractor.com A&W TRACTOR 920-598-1287 KEEPING ALLIS-CHALMERS IN THE FIELDS THROUGH THE 21ST CENTURY |
Posted By: Hudsonator
Date Posted: 12 Aug 2013 at 9:43pm
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Its been so long ago, I cannot remember the compression height of the pistons in my own "first build". But, they were TISCO WD 4.125" diameter pistons for 4000' altitude. They were originally bought around 1969-70. At the time I obtained the pistons/sleeves (1985), the guy stlll had the original tag on the box - so I'm positive of what they were.
They had "power crater" type tops that were fairly deep, with a much narrower flat-band at the edge than Allis Power Crater pistons. The only measurement I can remember is that the piston edge was 1/32" from the deck.
When fresh, it made 280 psi on the compression gauge -being pulled vigorously in 4th gear with the throttle wide open. It would only run/crank on 110LL aviation fuel without complaint. It was a hand cranked, mag fired tractor built to scoot within the rules circa 1986. Here's a picture of it in its heyday - 1990.
http://s661.photobucket.com/user/Hudsonator/media/Allis%20Stuff/Spinout.jpg.html" rel="nofollow">
 Cheapest fun I ever had - for 17 years. ------------- There isn't much a WC can't do. WD's just do it better. |
Posted By: blue924.9
Date Posted: 13 Aug 2013 at 3:26pm
| nice I like the look, everything tractor background, everything |