Common24 Posted October 14, 2013 Report Share Posted October 14, 2013 I am currently building a 4 mil with super cub top end 72 bore. I have been looking for a set of cases to have sent out ported and milled to fit the super cub bore. I had a guy from here in Kentucky give me a good deal on a set K&T trenched ported and epoxied 12 mil cases. He told me that they have already been bored for the 72 mil and ported for what I need. I have talked to several guys that say that the bottom end will hold a bigger volume with the trenched cases and it will hurt the compression and be a noticeable difference. I run 200ft dirt drags here in Kentucky. Will the 4 mil in 12 mil cases cause power lose because of the case volume? Any info would be appreciated Quote Link to comment Share on other sites More sharing options...
registered user Posted October 19, 2013 Report Share Posted October 19, 2013 do you have a rough idea what the primary compression would be with the trenched cases and your 4mil crank ? im thinkin the extra volume will help you Quote Link to comment Share on other sites More sharing options...
n2otoofast4u Posted October 19, 2013 Report Share Posted October 19, 2013 do you have a rough idea what the primary compression would be with the trenched cases and your 4mil crank ? im thinkin the extra volume will help you Huh? Quote Link to comment Share on other sites More sharing options...
registered user Posted October 19, 2013 Report Share Posted October 19, 2013 huh LOL . maybe skeeter can explain (not likely) this crankcase stuff to ya Quote Link to comment Share on other sites More sharing options...
J-Madd Posted October 19, 2013 Report Share Posted October 19, 2013 A long thread on Planet Sand and the consensus was the less crankcase volume the better. Quote Link to comment Share on other sites More sharing options...
sheerider11 Posted October 20, 2013 Report Share Posted October 20, 2013 I feel like it would just blow the charge all over and not force it up the transfers. Quote Link to comment Share on other sites More sharing options...
dozer Posted October 20, 2013 Report Share Posted October 20, 2013 i wouldnt run it, especially not in a drag situation where every few hp count. when the psiton comes down it has to fill the extra crankcase volume before it forces the charge up the transfers which is goin to slow the air/fuel charge down. in 200ft id think youll need all the power you can get. Quote Link to comment Share on other sites More sharing options...
registered user Posted October 20, 2013 Report Share Posted October 20, 2013 A long thread on Planet Sand and the consensus was the less crankcase volume the better. i havent seen that exact thread but ill bet most of the responses were from parts changers. theyre not even sure how to install clutch plates much less comment on anything else. thats why i asked if he knew approxiamtly what his primary compression will be. even then it would be hard to say better or worse just from seeing a number. testing before and after would be the only way to know for sure. but i would bet the little bit of extra volume wouldnt do much either way and if anything it might help, unless his volume already is grossly too large. but i doubt thats the situation throw it on a dyno and see what happens. epoxy the trench and run it again. wont be no more guessing Quote Link to comment Share on other sites More sharing options...
sprinklerman Posted October 20, 2013 Report Share Posted October 20, 2013 i havent seen that exact thread but ill bet most of the responses were from parts changers. theyre not even sure how to install clutch plates much less comment on anything else. Yea, you'd be wrong there,,, go read the thread,,some very knowledgeable people posted in there..definitely not "parts changers" . Although there were SOME less knowledgeable people in the convo. http://www.planetsand.com/forums/ubbthreads.php/topics/451/1 Quote Link to comment Share on other sites More sharing options...
registered user Posted October 20, 2013 Report Share Posted October 20, 2013 thats quit a lengthy thread. skimmed through a couple pages but got other things to do so ill try and check it out fully in the next few days. what little i did read seemed to be nothing more than theory and speculation which doesnt amount to jackshit without testing to confirm a theory one way or the other. god bless jennings, graham bell and blair but alot of what they wrote has proven to be inaccurate Quote Link to comment Share on other sites More sharing options...
sprinklerman Posted October 20, 2013 Report Share Posted October 20, 2013 True...to a point. Except for the fact that a lot of the speculation come s from some of the most respected names in the industry. (Cp for one) I'd definitely give his theories and speculations a little more credit than "jackshit". Sent from my SCH-R970 using Tapatalk Quote Link to comment Share on other sites More sharing options...
Surfrjag Posted October 20, 2013 Report Share Posted October 20, 2013 call me crazy but I would think in a short race it would be more about your setup than getting the last 2-3 hp out of the motor Quote Link to comment Share on other sites More sharing options...
dozer Posted October 20, 2013 Report Share Posted October 20, 2013 (edited) call me crazy but I would think in a short race it would be more about your setup than getting the last 2-3 hp out of the motor no doubt, setup is going to be crucial along with riding skills. its all got to work together. Edited October 20, 2013 by dozer Quote Link to comment Share on other sites More sharing options...
trickedcarbine Posted October 20, 2013 Report Share Posted October 20, 2013 If the top case really is what you need, epoxy the trench and be done with it. But it would be appreciated if you run it first then epoxy it and run it again and let us know the results. Quote Link to comment Share on other sites More sharing options...
registered user Posted October 20, 2013 Report Share Posted October 20, 2013 for sure theres some sharp folks on these forums. im not disputing that. but the fore most experts on 2strokes dont reside in the usa . whether its albert einstin or a hobo under the bridge, a theory is just a theory regardless whos mouth it comes from. educated guess you could say. we can guess all day long. you need a test to confirm or deny your theory, other wise its just a guess. small case volumes were done in the '70s because they didnt know any better alot of people dont realize it takes quit a significant amount of added or removal of area to eqaul a substantial change in primary compression. although i havent seen the trenched cases that are in question, im sure the added volume is miniscule in comparison to the overall volume. there for i dont believe the trenched cases will have much affect on power, not by seat of the pants anyways. but if you were to go so far as to dyno it with/without the trench i still think you would see some kind of power increase, albeit probly very small. this is some useless info from one of my engines. alittle over 500cc. to change from 1.6:1 to 1.4:1 (2 tenths)would require addition 450cc (15.2oz) . you would think there must be a point where the volume becomes too large. but has anybody found that point ? i cant answer that question Quote Link to comment Share on other sites More sharing options...
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