You mean is there a difference if you keep stock jetting?
The answer is YES!
your sled will run like crap.
Flow optimizers change the intake air speed and this affects the stock jetting. Venturi affect is completely different from factory jetting. Just call UFO and get there jetting recommendations if your not good at jetting.
Yes the ufo's do work.Are they worth the time and money to set them up?Only you can answer that.I have used them,but spent many hours tuning.I burnt a piston in the dialing process.But once set up they are a improvement. Your better off putting in a good clutch kit and gear,and don't waste your winter tuning your carbs. I've said it before,these are "not" a bolt on and go product.My .02