Ah hmm, OK, where to start.
All things being equal, stroke, equals torque, especially at lower rpm's.
fran...k.;121866 said:
Exactly what a good cylinder still on the origional bore and not tampered on with dremmel tools or their air powered equivelant die grinder probably should be approximately equal to the cost of a piston to re bore it to, a new one. However I think most are sold on ebay in such a manner the buyer has to low ball it as more often than not they will get something less than what I described in the first sentence. Perhaps $50 in reality but don't ask me to sell one this year.
Oh man, huh, OK, I think I'm interpreting this correctly. 50 bucks lol. Not what do we wish they cost, which in my case would be ohh, 5 bucks lol. But what is the fair market value tending to bring on used ones. Maybe I'm already fairly equipped to answer my own question, since I watch ebay with such consistency. I paid $125 for the good standard bore 500 cylinder and head. See plenty of numb nuts put them on there for 2 and 300 bucks, in much worse shape. Have noted one slightly rougher looking bore 500 cylinder alone go for 35 bucks a while back, and have been kicking myself for not grabbing that one every since. Got my NOS Mahle standard bore piston, ring, wrist pin, and circlips kit for 120 shipped. While I wish they were cheaper, I'd say a fair average price, from what I've seen watching just ebay (my only barometer), is probably right around what I paid. As always, with so many popping up way over priced, just because they are "500" cylinders, you do have to be quick to assess ones down in the 150 and below price range. Still kicking myself over that 35 dollar one. Think it needed an overbore from standard, but have seen NOS overbore pistons on occasion.......
Anybody else have any observations on cylinder pricing???? Perhaps from markets other than ebay?
fran...k.;121866 said:
As to your raising the compression on your 500. If you deck the cylinder meaning cut some off the bottom and then mount the head on a plate on a lathe and sculpt the squish you desire you could end up with gains in torque on the low end of the revolution per minute range. I have a 360 this has been done to. It is quite enjoyable to ride, the steel kick starter has been lengthened. Generally on two strokes going too high on the compression leads to pumping losses and no real gains if you are after high rpm power and higher total horsepower. Some of the 400 heads at least one off of a water cooled dual shocker have higher compression than a 430 head when put on a 430, some seem to be the same as a 430 head just not stamped 430. I have tried the higher compression head on the 430 head and it didn't seem to make any gains, the 500 head makes it fun to ride harder to stall and easier to start, Probably not as good out in the open areas of the rocky mountains or west near the grand canyon or such or even a local gravel pit but certainly pounding through rock gardens it works good.
Fran
Great info Fran. The compression increase debate on 2 strokes I have seen in other forums, and is often filled with those completely against the concept as having any place in the 2 stroke world. I was just curious what the concensous in here might be.
Back in '94 I grabbed a basket case '85 Red CR250, and dug out all my old MX mags and pulled every privateer punch I could find on what was done when new, to run with the factory bikes. However, not knowing any better, and it being such an automatic gain mod on V8's, I had the head milled. Don't recall the specs, but between myself and the machinist we tried a what we thought was a small safe amount, that should show something, if it was going to. I wish I would have done it separately, because the bike wound up being an absolute hotrod of a 250. Was a bit tough to start, and needed high octane gas, but neither were an issue for me at the time. Despite my porting mods, it was still a low rpm animal, but did carry over into a stronger midrange powerband. The bike would easily run down 92 & 93 250's I'd often practice with. I mean like obvious big hp advantage, on short straits. Everytime I had the bike out, I seemed to have fathers that were timing their sons coming right over to me when I'd be taking a break, and asking me all about the bike, because they couldn't believe how easily it seemed to be out horsepowering the newer bikes. Always would get the "what year is this thing, wow it looks like new, and what the heck did I do to the motor". I could never help but think that the raised compression played some part in the power advantage.
I need to delve into it further, perhaps in the karting arena as well, or snowmobile, etc. I know it's a guaranteed big power increaser on V8's, and great there especially if taking a low compression mill, with room to spare before race gas comes into the picture. No other changes, and it yields big smiles. The 2 strokes are just such a different animal I come to realize, I really want a better understanding of modding them this time around.
Oh, and yes, forsure there are gains to be had if all things are equal and you can start nocking grams out of the reciprocating assembly on a V8. Hence a 347 stroked sbf, often running a touch stronger than say a stock bottom end 351w. The stroked 302 has much shorter rods, and much much shorter compression height (mass) on the pistons. Equaling free revs as it were. Though the shorter rod to stroke ratio has it's cons as well, being much increased frictionional piston/cylinder sidewall loading and thus dramatically increased wear rates.
So I can see how some 430's could be real hotrods motor wise, with the same port area, and lighter reciprocating assembly. Less leverage always equals less torque though. Always a trade-off somewhere.
