Heymow - Lawnmower Racing Forum
Engine Help => Kohler Engines => Topic started by: beezerboy on November 21, 2013, 02:47:33 pm
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My research on the long rod conversion is coming up with very mixed results. There is tons of opinion and calculation out there, but is there any dyno proof that the long rod produces more useable power in this type engine, and if so, at what rpm range is it most beneficial. doing the long rod requires a different piston, so what I am primarily interested in is results due only to the rod.... not counting changes in compression ratio. any comparison of different rod with same C/R would be useful. thanks for any insight
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Anytime you can use a long rod it generally should produce a little bit of gain. Now the question is it worth the extra money that a descision you have to make. You asked about dyno results mwsc should be able to give you an answer. I'm in the process of building a cv730 vtwin and I put the long rods in they cost the same. The pistons are what puts you to sleep je is proud of there stuff but that's racing.
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the long rod idea has been around in auto and motorcycling a long time. Smokey Yunick made a living outta doing it. I was a believer until I started reading (many) threads about what it does and doesn't do. Every mod has trade offs, and now I'm curious... just how much (if any) does it add. Apparently Smokey's success was due to the fact that the head designs of the times were pretty poor, and modern high flow heads eliminate most of the advantage long rods had. like I said, theres a lot of talk, opinion, calculation, and seat of the pants testing... I'm looking for some hard data. it is likely that there is no advantage, and possibly a detriment to using long rods on low RPM engines.
thanks though & keep it coming
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Your only hard data will come through personal experimentation.
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in 40 years as a professional aircraft mechanic I have learned that is easier to learn from the mistakes of others than to make them all my self.
surely somebody has some quantitive data, and not just some stories.
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You cannot argue with what works if ya do you wont never get nowhere!!!
Ask 10 different engine builders you will get 12 different answers.
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give zach kerber a call. he has some reasonably priced combos and the replacenet rings are cheap for rebuilds in future. have built 2kohlers with this combo and friend running same combo. run them hard with no problems other than traction
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not trying to be a smarty but I specifically asked for data..... not stories from 12 different builders. data comes from testing.... like on a dyno. it's surprising but there doesn't seem to be much real testing going on that I can find anyway (that people are willing to release). am I looking in the wrong place?
I have already been in touch with Zack. looking for all the data I can lay my hands on
thanks
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Your only hard data will come through personal experimentation.
Dont know how to tell ya any clearer. Its a cheap sport or used to be. And if there is data like that they spent a boat load of money to do it in parts alone was it worth it was anything found out after that amount of time and money it aint gonna be given freely. That kinda knowledge costs money and thats why some are faster than others. SO I refer you back to the above quote which is as good of advice your gonna get. And I am not trying to be smart just factual.
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i have seen dyno sheets from same engine with just long rods vs std rods. was 5-10 hp diferance peak. added power throughout power range.
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ok.... that's getting there, but still anecdotal. I know mwsc has pretty much that same statement in their write up/sales pitch for the rod. only question I have about that would be if the engines had the same compression ratio, and the only difference was the rod. the obvious reason for that question is because the pistons for the long rod are flat tops & change C/R.
there are dozens or long rod/short rod threads.... the nut is most engines lose on the bottom end to gain on the top end. every alteration is a trade off, it would be nice to see some numbers so I can make some informed choices. Also, I'm not running my engine in a tractor, and my installation is a lot harder to remove/install.... I want to do changes that will work to my advantage...
http://www.patmanracing.com/Dyno%20Stuff/KLR%20dyno/KLR%20Dyno%204%20Mk2.jpg
that's the lowly klr, you can find a lot of similar info on any sport bike with a few key strokes.... why all the mystery on the Kohler
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There is no mystery with personal experimentation, and nobody's going to hand you specific details on a platter. We are not mass-marketing motorcycle engines here, we are racing lawnmowers in some form or another, and what information that is out there will be only handed out on a discretionary basis.
In other words, we all pretty much do the math and open our checkbooks.
Best thing to do is attend some races, and get to know some people.
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I guess I should have prefaced this thread like my others....
first.... I'm Alaska.... no tractor racing up here, second, not likely I'll ever get to one of your events to meet people that race (though it's interesting) third, I'm not building a tractor engine... it's for my hovercraft
and get real.... there are several companies producing long rods and as far as I can tell, no one has posted data on what this product will do all by itself.... removing the effects of the compression increase that comes with the required piston change.
I'm 63, I raced motorcycles in the 70's when the long rod was still a new idea and considered a must have in the day.... you just did it. now.... I'm researching this and there is a lot of different opinion, and some of it makes sense. every mod is a trade off.... I don't want to trade my low RPM power..... I want to increase it, and frankly, the long rod looks like it could be the wrong thing to do. I'm looking for peak power at 3000-3300.... whatever that is, yes I know more RPM means more power, but my props limit the engine speed. anyway, if I wanted only to increase C/R.... no problem, I know how to deal with that. btw, I'm a licensed aircraft mechanic (40 years) with a machinist background among other industry experience.
p.s. - "opening the checkbook and doing the math" is no problem.... I also have an airplane.... that will stress your checkbook, even though I'm licensed to do all work on it
right now the math says there is no reason to pursue the long rod for my application. that based on the fact that no one can show me that it does anything positive at my RPMs (or any RPM for that matter). (bearing in mind that I built long rod motors in the early '70s)
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Stick with your stock rods for your RPM range.The very small gain from longer rods won't start to show up until high RPM.
Just my :twocents: