250cc versus 500cc

[rmihalek]

I was wondering if there was any difference in chain speed comparing a 250cc bike saw versus 500cc bike saw? I would think that the 40 or 50hp a 250cc engine can produce would be enough to run very aggressive rackers and that maybe the only place a 500cc bike saw would beat a 250cc bike saw is in really big wood.

If both saws are running 13 tooth .404 sprockets and spinning them at 13,000 rpm in 20 inch wood, it would be a dead heat. But then the 500cc saw vibrates like hell (so I've read) so maybe the operater would have an easier time handling the saw and end up beating the 500cc saw. Comments?

 

[ehp]

Get BD to ask Dennis for you cause he has built both, but what are you cutting in size, is it cold start 3 cuts or 1 cut, and lower your rpm's alot cause they donot turn that rpm. the 250's that Gaston built are running for gears , Donald is using a 19 tooth .404 and Moral is using a 17 tooth .404, Moral's saw is ported and has a higher rpm pipe on it. as far as rotax's they are running a 12 or 13 tooth 1/2 inch gear, the ones i have switched over are using 18 tooth .404, .037 rackers on this setup, the 500 is faster in the wood

 

[rmihalek]

I was intrigued by Stihlman036 (Chris) racing with a Marcel 3120 and beating a couple Rotaxes and a 250 bike saw. It got me wondering how much horsepower is enough and when the law of diminishing returns would kick in. Like you said Ed, I guess it's a matter of the terms of the competition among other things. A "one-cut" race maybe a 500cc saw would always win, but then there may be some conditions of wood and number of cuts where a 250cc saw (or a stroked 3120) could win over a bigger saw.

How many saws to the TimberSports guys bring with them to an event? I got the feeling that Jamie (Arden Cogar Jr.) had only one saw. Maybe the other guys had a few clubs to choose from at each event or maybe they just have extra sprockets and bars to choose from.

 

[ehp]

Guys now are getting good enough with the bikes saws that it is hard to beat them in any wood, even 8 by 8 but if the bike saw works well and it has an operator , in 10 by 10 it is game over for any chainsaw that is why we have classes at shows,

 

[Chopwood]

I've got three racing saws- a Rotax, an Ed Heard 3120 stroker and a Chauncey Varney reed box 3120. There are many factors determining what saw to run, The three biggest being wood size, rules and the amount of money on the line. Especially with the stroker, I don't pull it out of the truck unless I have (or need) to because I can't run one of the others.

 

[rmihalek]

Hi Chopwood,

Your response was kind of what I had a feeling about. Even though the biggest saw I've ever run was a stock 090, I can imagine that, in the Open Class, there would be times when a bike saw would be too much and a better handling 3120 would be the quickest. Maybe something like dead start, 3 cuts in soft 12 inch diameter pine?

What's the Chauncey Varney reed box 3120 all about? I've never read anything on here about that type of saw.

 

[Chopwood]

Chauncey Varney built 3120 modified saws for a few years in the early 90's I believe. The cylinder is completely custom. He cast an aluminum "shell" and head that bolted onto a stock case. The shell uses a cast iron sleeve that the ports are cut into, allowing massive port dimensions. The best part about them is that there is a reed valve box cast into the intake side of the cylinder. Much like a dirt bike or snowmobile engine. As far as I know, there aren't many left out there (maybe 15-20), but the ones that are left are in high demand because of the potential that they have. I would buy another sight unseen if it came up for sale, simply for the fact of dependability, ease of rebuid and the fact they run on gas- none of the "funny stuff".

 

[WoodTick007]

EHP Stroker 3120

Hi Ed,

How many cc's is the 3120 when your done stroking one?

Thanks

Greg

 

[ehp]

they are 131 cc but am building this winter 2 new 139.5 cc for the 140 cc class , one for me and one for NBLogger , I want to run them for a season to see how they hold together before I start selling them, I have 6 of the 131 cc strokers to build this winter,

 

[lucky]

cool stuff

Having never seen a reed box, I have a question. What holds the reeds closed when the piston comes down? Springs?
Thanks, John.

 

[Crofter]

Their own spring tension plus base compression. They open inward away from their seat.

Frank

 

[rmihalek]

I wonder what the advantage of a reed valve is compared to a "piston-ported" induction system?

 

[Crofter]

You can get some effectively wild high rpm port timing without compromising idle. For cold start saws, you cant live with something that is not a reliable starter.

 

[rmihalek]

I'm still wondering if a 250cc saw can pull the same gear as a 500cc saw, with all other conditions being equal. Can they both spin a 13 tooth, .404 at Xrpm (8500, 9000 whatever) with the same chain in 20 inch doug fir, for example?

I'm not sure why I'm concerned about this. Maybe I've been watching too much top fuel and thinking too much about whether 9000hp buys you a quicker time in the 1/4 mile compared to 8000hp or does it just mean you're more likely to smoke the tires?

 

[Chopwood]

in my experience, the more power the more sprocket, that kind of throws the whole argument out about the 250 vs the 500. The question is- what can you hang on to? My answer is that a 250 is easier to hang on to in smaller wood than a 500 and vise-versa

 

[canguy21]

sawguy

You guys are nuts. I tried a modified 090 on alky that was wild. I'd need muscles in my s%&t to hang onto a 500cc bike motor strapped to a saw bar

 

[ccicora]

the problem is you still half to keep it light enough to pick up in a hurry. I not saying it can't be done just nobody has come forward with an answer yet. Just give it sometime you know somebody will try and make it work.

 

[Busy Beaver]

I'd just love to see a alcohol burning 500cc Jawa 4stroker Speedway bike motor made into a Hotsaw, wouldn't you guys? BB

 

[bwalker]

or how bout a KTM 525 based hot saw? Talk about torque. Wonder what size sprocket and chain you would run on a beast like that?

 

[MacDaddy]

2 years ago one of my friends told me he would like to do that maybe someday P.S have you ever ran a hot saw you might want to start out on something smaller first