i asked same ? while back, no one answered. so i went out to find my own, and found that stock ecu can only handle up to 310cc injectors. with 450cc injectors/stock ecu, car will not hold an idle, it will stall. but if you are not in that situation (hondata or something like that), the injecters will have a very tight fit using stock injector seals but they will fit. some company, i don't remember which makes seal that have a larger I.D. than stock that will work well with the larger mitsu injectors. hope that helps and good luck.