I'm running a race motor with 17 front and 38 rear and 18 inch tires and it wouldn't go fast enough for me so I'm trying a 18/38 with 18 tires should go at least 85 to 90mph

 

i put my realators back on now and would i gane any topend wiht a 15 casue i think a 17 would be to much to pull but i think i would have more low end then with hte 15 with the 22 ince realtors right

 

Try larger rear tires. I know that desert racing DS's run 17/38 and 22 inch tires and run about 100 MPH top end with CT pipe, RW CDI and stock engine. with the 18 inch rear you are not getting all the power to the ground.