yamaha04 Posted January 19, 2008 Report Share Posted January 19, 2008 i kick over 145psi in both cyilenders wiht 21cc domes. i run pump gas 93. if i switch to 20cc what kinda power should i be looking forward to. by the way i already have to domes it just amatter of spending the money on the race fuel. as said in another post in canada we pay around 110$ to 120 a liter for 93 pump thats like 4.50$ a gallon. is there going to be that big of a defference in power that im going to want to keep them in? is it worth the money in fuel? my mods are T5'S, coolhead, ported reed cages with boyseen power reeds, adjustibale timeing plate +4, pro flow kit with good foam filter. Quote Link to comment Share on other sites More sharing options...
sheerider1026 Posted January 19, 2008 Report Share Posted January 19, 2008 (edited) rule of thumb, for every cc you take away from the domes adds 10psi of compression.. so you should be at about 155 psi with the 20's.. i run 19cc and +5 timing, t5 pipes and it runs great on 93. a lot of people argue that it is dangerous, but i have ran my banshees with this setup for over 6 years, never a melt down, blown gasket, or anything bad. Edited January 19, 2008 by sheerider1026 Quote Link to comment Share on other sites More sharing options...
yamaha04 Posted January 20, 2008 Author Report Share Posted January 20, 2008 19 cc what kinda compression are you kicking over? Quote Link to comment Share on other sites More sharing options...
sheerider1026 Posted January 20, 2008 Report Share Posted January 20, 2008 19 cc what kinda compression are you kicking over? well at the moment it is low, i need to get it bored soon, it still runs good just low on psi.. usually its around 155-165 range Quote Link to comment Share on other sites More sharing options...
yamaha04 Posted January 20, 2008 Author Report Share Posted January 20, 2008 (edited) what was it when you put it together? you must be way abve sea level to have that low of compression on 19cc Edited January 20, 2008 by yamaha04 Quote Link to comment Share on other sites More sharing options...
TurboBanshee420 Posted January 20, 2008 Report Share Posted January 20, 2008 I don't think it's worth the fuel. usually there is a very small gain from changing (raising) your compression. It simply moves your power curve further down the rpm range. you will be making more power sooner but lack on topend. i never understood why you guys go so high on the comp. That's not what a banshee motor is for. Just for an extra pony at 4k? These motors are all topend and that's it. I can understand if your entire build is based on a race fuel engine. Then you might as well go high comp., but not for drags. I guess it's all up to the guy riding it. But high comp motors are usually only put into trails bikes, or bikes with a powervalve. My gasgas 300 has wicked high comp. like 170-180psi. but that will drop way down after the exhaust valve opens. to somewhere around 120psi. also.... never spray a high comp engine with NO2. It makes for a bad day to say the least. thoughts? I know you wanna... Quote Link to comment Share on other sites More sharing options...
91banshee Posted January 20, 2008 Report Share Posted January 20, 2008 i run a stock head shaved 135psi run on pump gas , the power is not from compression but from air and fuel , porting makes power , i wouldnt waste time switching domes to high compression and then have to pay to run race gas . Quote Link to comment Share on other sites More sharing options...
sheerider1026 Posted January 20, 2008 Report Share Posted January 20, 2008 what was it when you put it together? you must be way abve sea level to have that low of compression on 19cc 500 ft above.. it seems happy with 93 Quote Link to comment Share on other sites More sharing options...
csrmel Posted January 20, 2008 Report Share Posted January 20, 2008 on a really nice tight new factory motor it will run 150psi with 22cc domes. so if you are running 145 with 21cc domes then chances are youre motor is a bit worn. you probably losing 15 to 20psi through the rings. instead of spenging $70 on domes, spend the money on a set of rings and a top end gasket kit. you will probbaly gain more power that way compared to new domes. and you get to keep running cheap pump gas. plus its good to open the top end once in a while to check things out. Quote Link to comment Share on other sites More sharing options...
yamaha04 Posted January 20, 2008 Author Report Share Posted January 20, 2008 i was kicking 145 psi on a fresh tight motor with 21cc domes so F.A.S.T racing bored my cyilender to big witch would explain the piston slap after 3 hours on the motor. Quote Link to comment Share on other sites More sharing options...
sheerider1026 Posted January 20, 2008 Report Share Posted January 20, 2008 dam, i would not be happy about that then. i like it when you get a builder that sets the clearance tight on the piston and cylinder, Quote Link to comment Share on other sites More sharing options...
csrmel Posted January 20, 2008 Report Share Posted January 20, 2008 i have bought a few things from fast racing. jeff seems like the kind of guy who would make things right if there was a problem. why dont you call him up and explain the situation. he would probably fix you up. by chance, this motor wasnt ported was it? that would explain the loss of compression. when i said 150psi with 22 cc domes that was for a 100% stock motor on the stock bore and no porting. if you had the motor bored it will change the compression because the ports get changed slightly. if you had it ported then it will also change the compression. just call jeff. Quote Link to comment Share on other sites More sharing options...
yamaha04 Posted January 20, 2008 Author Report Share Posted January 20, 2008 (edited) 100% stock motor this was last year right before i went to the dunes just got all my parts back after him haveing them for 6 months so at 5 months i asked him to forget about the porting and just bore them and send me my shit back because it was getting down to crack time and i needed my motor for this trip so i got it back put it together and did acouple heat cycles ran it rich and took it to the dunes. 3 hours in i hear some piston slap so i called him for the dunes he said it was probably my flywheel not being tight enough and slaping back and forth on the crank so i checked it. it was tight my key was perfect. so i tore the head off and i see that i can move my piston back and forth in the bore enough the make a nasty sound called him again he said the piston is supose to move in the bore and not be really tight so whatever i put it back together took it to a builder in silver lake he said it was piston slap and it wasnt bad enough yet to tear it down but it would get worse. so i ride it for acouple months and tear it down to find my cylinders still have the hone marks in them and my pistons look mint so my guess is the bore was to big. by the way i know alot of people like jeff and all im not trying to bash just trying to get some anwers Edited January 20, 2008 by yamaha04 Quote Link to comment Share on other sites More sharing options...
csrmel Posted January 20, 2008 Report Share Posted January 20, 2008 nobody thinks youre bashing jeff. i dont hold any preference to any builder because they are ALL in the buisness of making money. you have to take what everyone says and does with a grain of salt. that is why i dont get the people here to advertise in their sigs for builders and aftermarket suppliers. unless they are getting paid to put it in their sig, whats the point. Quote Link to comment Share on other sites More sharing options...
yamaha04 Posted January 20, 2008 Author Report Share Posted January 20, 2008 lol i know what you mean. thank i though everyone would be all over me for saying that lol still coupld happen lol. oh well Quote Link to comment Share on other sites More sharing options...
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