The best way to get more performance out of a Honda Accord is to trade it in on a better car. That will cost you a lot of money and unless your 1991 LX is a high mileage car with an unusual amount of wear, you are better off keeping the 1991 Accord in tip top shape until it reaches 200K miles. Save your money for the day when you can't get a price that exceeds the anticipated repair or rebuild prices.