bellracing2 Posted March 18, 2011 Report Share Posted March 18, 2011 what are the performance gains from either a big bore (68+mm) vs. 4-7 mm stroke crank vs. stock crank long rod setup . note all the above would be with stock cylinders , and stock port timing . what would be the best way to go with a stock motor to achieve the most torque with 100% stock cylinders ? Quote Link to comment Share on other sites More sharing options...
SuprSlow50 Posted March 18, 2011 Report Share Posted March 18, 2011 Why not port the cylinders instead?? Quote Link to comment Share on other sites More sharing options...
Pasi S. Posted March 18, 2011 Report Share Posted March 18, 2011 I´m not an expert here, but I think you can´t go to a bore -size as big as 68mm (or bigger)- without having a set of new sleeves ->big bore sleeves. After that I think that you don´t have stock port timigs. Also I think (not 100% sure) that having a stock stroke (54) long rod crank will not make your torque any bigger. 4mill crank is a "drop in" mod, but I´m 100% sure that you should port the cylinders for the longer stroke. It is not a must thing to do, but that way it will give you a much more torque and overall power. 7mill crank will make that power even bigger, but you need to mess with you cases before you can drop that crank in. My choice would be a 4mill crank and porting. (sorry my bad english) -Pasi S. Quote Link to comment Share on other sites More sharing options...
Burt Reynolds Posted March 19, 2011 Report Share Posted March 19, 2011 Coolhead with racegas domes/+4timing/pro circuit or fmf gnarly pipes/good quality reeds like boyesen,i would say vforce but i wouldnt put down 2-300 for reeds. I personaly would also run a 33-35mm single carb,but lots of people disagree on that. Quote Link to comment Share on other sites More sharing options...
jbooker82 Posted March 19, 2011 Report Share Posted March 19, 2011 Stroker crank will gain more toruqe. It moves the conecting rod journal out. This gives the conecting rod more leverage to turn the crank. Just like using a longer handled ratchet or cheater pipe. Quote Link to comment Share on other sites More sharing options...
gotta_goatsfast Posted March 19, 2011 Report Share Posted March 19, 2011 I'm curious as to why you want to leave the cylinder ports completely stock? There are minimal gains going up in displacement through a bore without adjusting the airflow to match it. The 58mm stroke isn't going to be very exciting when the ports are designed for a 54mm stroke. A 115mm rod will provide minimal if noticable-at-all gains over a 110mm rod, but is smart to do for reliability and stability in the engine. The banshee is almost limitless, so don't limit yourself here. A good woods/MX port job on stock cylinders with a stock crank and stock bore will be a more exciting ride and make more power everywhere than all three of the previous mentioned mods combined (on stock port timings of course). A great budget power build is to purchase a 58mm crank with 115mm rods and have the stock cylinders ported to match this. You can damn near pull a stump out with it... okay maybe that's a little over the top haha. Quote Link to comment Share on other sites More sharing options...
bansheesandrider Posted March 19, 2011 Report Share Posted March 19, 2011 Your port timing NEEDS to match your stroke- so if you go with a 4mil stroker, you will need to get it ported to match. A long rod crnk will not make any more power over a stock rod crank, assuming they are both the same stroke. It will make the motor more reliable. To get to a 68mm bore, you will have to install big bore sleeves in the stock cylinders and they will reduce the size of the transfer ports so much it won't have any power. Depending on what is done now, I would put on a set of pipes, a better filter(pods or 2 into 1), bump the compression(coolhead or cut and chamber the stock head), bump the timing(modify the stock plate or Chariot timing plate), and jet it accordingly. When you are due for a top end, you will need to decide if you can afford to port and/or install a stroker crank. If you can afford to buy a crank and new domes for the cool head in addition to getting it bored AND ported then you would be set up with a 4mil. If you can't get the crank and domes, then just get it ported and you will still like it. BUT, if you port for stock stroke, you may not be able to port those cylinders for a 4mil later, so you would have to buy different cylinders and have them portrd for the 4mil later. If you cut and chamber the stock head and port the stock cylinders, it will still LOOK stock to the casual observer. Quote Link to comment Share on other sites More sharing options...
jbooker82 Posted March 19, 2011 Report Share Posted March 19, 2011 To get to a 68mm bore, you will have to install big bore sleeves in the stock cylinders and they will reduce the size of the transfer ports so much it won't have any power. Is this by experiance or just 2nd hand? I have ran big bore cylinders before and not all big bore cylinders choak the transfers. I had a pair of stock cylinders that were 4mill drag ported resleeved with big bore sleeves. The sleeves were 66mm-68mm bore. There are others that do go larger. To say that big bore cylinders will not make power is totally wrong. Yes porting does make more a more noticable difference. Big bores do make a difference but they cost a lot to get done. You cant just keep on porteing your cylinders to get more power out of them. Especially if your looking to buid a stout midrange machine. It has to be the right type of power not just the most. Here is a pic of the transfer ports of my big bore cylinders I ran. How do you figure the transfers are choaked down if there is still aluminum against sleeve? Just to show they are big bore sleeves. Quote Link to comment Share on other sites More sharing options...
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