Short answer - Yes

Long answer - it depends on the accuracy of your elimination method. If you could eliminate a short(ish) priced horse every race 100% of them time then you would of course profit. The key in anything like this is about how accurate you are and that can be hard to measure.

Lets assume you get it right 80% of the time and take 100 examples of your 4 horse race...

* 80 times you would be able to make an 82% book...$18 profit per $100 staked = + 1440
* 20 times you would lose the $100 staked = -2000

So in that example you're down $560. And that is with what may be considered a fairly high accuracy level. The hard part is that every race is different - different number of runners, different horses, different odds so you will neve get an exact measurement of your accuracy at any given odds level.