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Tractor Pulling Discussion Forum

less weight=more or less power?

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Marty in Mi.

12-19-2004 18:46:41




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If you have a 4 cyl. engine and you run a piston that is 130 grams lighter and a rod that is 500 grams lighter, and everything else remains the same, will you lose or gain horsepower? Will your torque go up or down? Marty




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Paul Winter

12-22-2004 17:57:17




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 Re: less weight=more or less power? in reply to Marty in Mi., 12-19-2004 18:46:41  
half of con rod as well as piston rings and pin is reciprocating weight half of conrod is rotating. ruducing reciprocating weight will greatly reduce internal stresses but will have no affect on power out put as reciprocating weight starts and stops twice every crank rotation. increasing rotating mass may increase momentem like heavier flywheel but at constant rpm on dyno will not show increase in power output. a lot has been written on rod stroke ratio's, Smoky Yunik said it best put the longest rod as is feasable. but--- there a lot of street stokers that have a short rod , alot of early pro stocks had rod stroke ratios way out of wack and many big div.4 tractors have rod stoke ratios as low as 1.3 to 1 a long rod will be easier on cylinder walls as well as increasing dwell on tdc.increasing dwell will increase pressure exerted on crank.(power)a shorter rod will get piston off tdc. faster increasing vacume signal. with some cam timing mods a short rod( especially with extreme stroke)will do very well . bottom line have fun Paul

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clarence barenie

12-21-2004 06:24:55




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 Re: less weight=more or less power? in reply to Marty in Mi., 12-19-2004 18:46:41  
Marty:
second post
FARMAL M
IF you built an m with a 6.25 stroke, stock rods,
10didided by 6.25 ratio 1.60. more piston speed
identical (m) 6.25 with a longer conn rod 11", their would be plenty of pin heigth to move it up , ratio would go up closer to stock 1.76, i would bet a bunch of money that torque at low end would be greately improved !
would love to build to in the same to prove a point ! smaller cubes may act as a bigger motor on small engine build-ups !
i've seen several build ups where the wrist pin was rite at or as close to the deck !
it's just more expensive to build it that way

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Marty in Mi.

12-21-2004 14:49:39




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 Re: less weight=more or less power? in reply to clarence barenie, 12-21-2004 06:24:55  
Clarence, my freind did it this way for one reason-he is cheap! He got the custom chevy pistons for free(they are used) and used the wrist pin end of an older set of custom "H" rods that he bought off the internet about 6 or 7 years ago. The "H" rods have the same .927 wrist pin that the pistons have, so he cut a little over 6" off them and had them tig welded to the bottom end of the "M" rod. The result was much less weight. He has less than $500 into this set-up. He did this mainly because of an article that I showed him from Hot Rod a few years back that was titled,I believe,"Less is More",that talked about the hp. and torque increases that can result from less reciprocating mass on a big block chevy. He is retired, divorced, and a gearhead who loves to tinker, so the time involved to do this little project did'nt matter much to him. I'm not really up on what a stock bore/stroke "M" should put out, but I think this one makes more torque than the majority of them, and in his mind it is still "diamensionally" stock, so he feels that if he beats up on some of the strokers, he really has something to brag about. Now you know the "Rest of the Story". Marty

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Clarence Barenie

12-22-2004 05:14:16




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 Re: less weight=more or less power? in reply to Marty in Mi., 12-21-2004 14:49:39  
the rest of the story is a darn good one !!!
i think in this test case you have uncovered some logic, that only proven could be believed.
lighter components will make torque. you dropped piston weight in half. and a longer rod,(bigger lever) creates more torque! i think he will be amazed at the difference on the track. I'm assembling a m@w type stroker in an m rite now, there is nothing on earth i can enjoy more, than when an individual wants to pull and beat bigger motors with smaller cubed ones !!! that is the exact same theory as i have ! a win is a win when the playing field is fair !

good luck on the build up and happy pulling !
thank-you

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Goldie

12-20-2004 22:27:36




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 Re: less weight=more or less power? in reply to Marty in Mi., 12-19-2004 18:46:41  

Another thing to consider is the rod lenght. A longer rod will gain more power.



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Marty in Mi.

12-20-2004 19:36:08




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 Re: less weight=more or less power? in reply to Marty in Mi., 12-19-2004 18:46:41  
The reason I asked this question was based on an experience I had a few weeks ago. An old freind of mine who believes that tractors that pull farm stock classes should be dimensionally stock, went through and bought custom rods and pistons for his Super M. The only dimensions that changed were the rod length(about 1 inch longer) and the compression distance(about 1 inch shorter. The cyl. compression stayed almost the same, within 4 psi. from the old set-up. On my dyno, this tractor went from 52 hp. to 60 hp. at 540 rpm. Where it made the most improvement was down to 400 pto. rpm., where it registered just over 70 hp. (Did not convert it with my M&W calculator,but that should still be over 60 hp.). When you brought it down that low before it would only register about 56 hp. I guess I already knew my answer before I posted this title, but I just wanted to do a little brain-pickin'. Bottom line:Less weight=more hp and torque. Marty

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clarence barenie

12-21-2004 06:11:44




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 Re: less weight=more or less power? in reply to Marty in Mi., 12-20-2004 19:36:08  
Marty:
I just had the machine shop send me info on conn rod length. 350 g.m. motors had more torque with
longer con -rod ratio ! they went from about a 165 ratio to 172 stock m has a ratio of 10(rod length) divided by stroke (5.25) or 1.9047 ratio.
ADDING 1" to the ratio changed it to 2.09-1, which would keep the piston at a stall at tdc longer ! i'm absolutely not understanding, the true importance of this rod length , and why !
a g-moline has almost exactly the same (stock) ratio as a farmall (m) their has to be a proven theory in this ratio (torgue) YOUR friend went to a lot of work !! I'm sure it wasn't just a brain storm !

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buickanddeere

12-21-2004 04:37:19




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 Re: less weight=more or less power? in reply to Marty in Mi., 12-20-2004 19:36:08  
Tough call. The longer rods do reduce side thrust loads/drag from piston to cylinder wall friction. I have to wonder however if the new pistons had less impeded/smoother flame travel across the top? And/or the rings sealed better when the engine was up to temp and rated rpms compared to the stockers? I'm glad to see that some people actually do under stand HP is torque x rpm/5252. So many people load the engine down from pto rpms to where ever peak torque is read. However they still run the HP formula with the 540 rpm number? And then come up with some amazing HP numbers. She was making about 52HP when lugged down to 400pto rpm.

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buickanddeere

12-20-2004 15:40:23




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 Re: less weight=more or less power? in reply to Marty in Mi., 12-19-2004 18:46:41  
HP is the same. If the rotating equipment is as strong or stronger than stock but weighs less. Then more rpms can be turned to increase airflow per minute providing the induction system isn't maxed out. A lighter bottom end accelerates faster which is vital in sprint cars etc. However tractor pulling in nearly stock classes is another matter.



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ChadS

12-20-2004 18:42:30




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 Re: less weight=more or less power? in reply to buickanddeere, 12-20-2004 15:40:23  
It would help alot in throttle response time,, that I agree 100%. I think of a 2 cyl JD and how heavy the pistons, the rods, and the crank are, and how much torque they make in low rpms. Ive never been one to love to rev up an antique, unless it was balanced properly to run the higher rpms. Im one for 540 and below rpms on dynos,, In tractor pulling, you need gobs of torque, and look how heavy those cranks rods, and flywheels are in these engines! Built to lug the dickens out of them, all day long. Pulling engines are not much different, you hit a tough spot in a field, or on the track,, the tractor is gonna lug down, maybe even stall it. What could help keep the engine rotating under these circumstances? heavier, lighter flywheels? lite, or heavy rods, cast, or lite aluminum pistons,, Compression??? Always belived,, that heavy internal parts, and high compression compliment each other, to build torque,, hp comes natually,, on lite engines,, you make hp,, and can rev them higher, but ask any one who runs an oliver that has lite rods in them,, big hp when they are 2500+rpms,, drop em in a hard lug, below 2000, and they will fall on thier nose, or they will stopthem before they do any damage. (Not picking on Olivers guys!!!!! Please dont read me wrong! but, Ive seen one too many 15 mph olivers die at the end!) Also seen em shoot rods out the pans when they did put a lug on it.. thats a high rpm lite weight engines charateristics, racing,, not pulling,, Now the Olivers have gotten better in div 2 and 3, they dont seem to be reving them up so high inthese classes, and can lug them, but, betcha they are not very lite inside the engines,, I can stick my foot out, and say that each part weight, all the same, would help in not shaking so bad at higher rpms,, it relives stress from the crank a bit,, in an engine that should constanlty change rpms on the track, guess I wouldnt know which I would want, would it make that much difference when the lug is put on it? ChadS

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Earl S.

12-22-2004 11:29:07




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 Re: less weight=more or less power? in reply to ChadS, 12-20-2004 18:42:30  
Think about rod length compared to the stroke.The taller block engines will have longer rods . I know a guy that is using 1 1/2" deck plate on the longer stroke 88 .A lot longer cyl. & rods.It works.Here in Illinois (ITPA) we have a 5/16 limit or total gasket and plate .455. Due to the Moline plated blocks. Earl



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stan beaver

12-20-2004 19:52:11




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 Re: less weight=more or less power? in reply to ChadS, 12-20-2004 18:42:30  
been pullin for 20 yrs. love all antique tractors,I pull div. 2 in upstate n.y.,12 pulls a yr. we are allowed 10% over stock RPM , for 2500-2750-3000-3500 4000 lb. they tack us at every pull, stock rear rim up to 10 inch wide, stock tire size no larger then 12.4, a 20 in drawbar height, stock looking drbr, 99 octane or less, tested with sniffer, second gear , 3 MPH,,lazer on transfer, 20% over stock bore, tested with air tuber. I just happen to be pullin an 1949 Oliver 66 , always in 1st-2nd-3rd, and got the trophies to prove it. your theory of less weight,more HP means nothing, sounds like the talk of some one with a paper azz, no logic at all, throw it out the door. and remember as far as modifying is concerned you can do much more to 4 and 6 then you can to 2.

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ChadS

12-20-2004 18:34:17




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 Re: less weight=more or less power? in reply to buickanddeere, 12-20-2004 15:40:23  
It would help alot in throttle response time,, that I agree 100%. I think of a 2 cyl JD and how heavy the pistons, the rods, and the crank are, and how much torque they make in low rpms. Ive never been one to love to rev up an antique, unless it was balanced properly to run the higher rpms. Im one for 540 and below rpms on dynos,, In tractor pulling, you need gobs of torque, and look how heavy those cranks rods, and flywheels are in these engines! Built to lug the dickens out of them, all day long. Pulling engines are not much different, you hit a tough spot in a field, or on the track,, the tractor is gonna lug down, maybe even stall it. What could help keep the engine rotating under these circumstances? heavier, lighter flywheels? lite, or heavy rods, cast, or lite aluminum pistons,, Compression??? Always belived,, that heavy internal parts, and high compression compliment each other, to build torque,, hp comes natually,, on lite engines,, you make hp,, and can rev them higher, but ask any one who runs an oliver that has lite rods in them,, big hp when they are 2500+rpms,, drop em in a hard lug, below 2000, and they will fall on thier nose, or they will stopthem before they do any damage. (Not picking on Olivers guys!!!!! Please dont read me wrong! but, Ive seen one too many 15 mph olivers die at the end!) Also seen em shoot rods out the pans when they did put a lug on it.. thats a high rpm lite weight engines charateristics, racing,, not pulling,, How can the book be written on the differences between the 2 motorsports? I may never know, JMHO, ChadS

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nc jd guy

12-20-2004 18:31:24




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 Re: less weight=more or less power? in reply to buickanddeere, 12-20-2004 15:40:23  
BuickandDeere MAY be right, and INHO he normally is, but this is the FIRST time I haven't believed him...

Which is harder to push, a 5000 pound tractor or a 3000 pound tractor? It takes power out of the system to accelerate that piston. No, I don't mean going from 1000 RPM's to 3000 RPM's as in the sprint car example. I mean making the piston change directions from forward to backward.

If I was smart, and I have never been acused of that, I probably should just agree with B&D and advise everyone to install the heaviest pistons and rods they can find and then fill them with cast iron to make them even heavier. Lord knows, I need all the help I can get. LOL

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ChadS

12-20-2004 08:26:51




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 Re: less weight=more or less power? in reply to Marty in Mi., 12-19-2004 18:46:41  
Morning! Been thinking about this for a long time now. I would belive you would pick up HP when you lighten the parts up,, but you do lose torque in the lug down at the end of the pull. the HP is not enough of a change, to keep it rotating. Im gonna stick my foot in my mouth again and say,, if you want torque, and HP at the same time by tricks, go heavier with the parts and add compression!! That is the only way I know of to really help a tractor engine (and not a car engine) rotating down the track. The added compression create more energy to turn the masses easier, any time you increase compression, the engines work load is relived due to more power and torque, mainly torque,,, Ive had the best of both worlds,, I had a heavy rodded engine,, and a lite rodded engine. the lite rodded engine is bigger in cu in,, and is stronger at 540, but does not have the torque that the stock rodded engine did. it has rpm to back it up,, compression was high, but still too much lug on the lite engine. the heavy engine assembly is slightly weaker in HP, but when lugging it below 540, it blows the big HP engine away in the torque curve on the dyno, by 15 hp. So the heavy rodded engine lugged alot better than the lite high rpm engine. and did the work better at the lower rpms too. I know,, I know,, its not popular beliefs,, but I know someone who has done this in a tractor engine, (ih 966) and I have yet, to ever see it power out, it lays down and hooks upthe tires and darts forward, never drops below 3000 rpm, from 3500 rpm max. Its not a HP engine,, its a torque engine this time round... JMHO, ChadS

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A.P.

12-20-2004 23:07:03




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 Re: less weight=more or less power? in reply to ChadS, 12-20-2004 08:26:51  
I think you are dealing with problems and advantages due to the connecting rod ratio. The connecting rod ratio is the center to center length of the connecting rod divided by the stroke. The larger (better) ratio allows better angularity of the rod to the crank. A small ratio adds a lot of side loading in the cylinder bore and on the crank. An engine with a poor rod ratio number will generally have less bottom end than and engine of the same cubic inches with a better ratio. A lot of the big stroker engines have very poor rod ratio.

Chads, just a thought, wouldn"t you be better off with a heavier flywheel than a heavier rod/piston by your theory? At least it would not be starting and stopping a couple of thousand times per minute.

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nc jd guy

12-19-2004 18:53:17




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 Re: less weight=more or less power? in reply to Marty in Mi., 12-19-2004 18:46:41  
The less you can make the "reciprocating mass" (pistons, con rods, pins) the more power it will produce. The heavier the recip mass, the more energy it takes to make it change direction. Keep in mind that the pistons actually have to come to a complete stop and then change directions at each 180 of the crankshaft. Spend a few extra minutes and balance everything before you put it back together.

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Buzzman72

12-21-2004 04:54:42




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 Re: less weight=more or less power? in reply to nc jd guy, 12-19-2004 18:53:17  
The heavier-flywheel theory is what I believe in, due to my high-school physics class...I just haven't had the $$$ to try it out yet on my old Farmall H. When I do, y'all will be the first to know.



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nc jd guy

12-21-2004 08:04:33




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 Re: less weight=more or less power? in reply to Buzzman72, 12-21-2004 04:54:42  
You can test that heavy flywheel theory for 1 hook fee. Put your tractor in 2nd gear. Get down the track where it is lugging pretty good and hit the kill switch. She doesn't go very far does it? Flywheel were used to balance the engine and to overcome instantaneous loads, not continuing loads (takes power to turn the flywheel) -- Take a shear press for example. never heard of anyone putting a flywheel on their bicycle though (besides the bad gyroscopic effects, it would just make it harder to pull.

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770

12-20-2004 15:36:09




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 Re: less weight=more or less power? in reply to nc jd guy, 12-19-2004 18:53:17  
people are usually very pleasently surprised when they go through the trouble of balancing the engine .



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Marty in Mi.

12-19-2004 19:09:29




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 Re: less weight=more or less power? in reply to nc jd guy, 12-19-2004 18:53:17  
What percentage of the rod length is considered rotating and what percentage is considered reciprocating?



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nc jd guy

12-19-2004 19:13:59




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 Re: less weight=more or less power? in reply to Marty in Mi., 12-19-2004 19:09:29  
It's been a while, but I seem to remember about a 1/3, 2/3 split. 1/3 from the big end. There may be a more exact number, but 1/3 usually puts you just a little past the big end starting down the shaft.

I am not a big fan of rotating mass either if that is where you were headed. That should be minimized as well.



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