Big buck engines will not win races without the rest of the formula, being tires, setup, driver, etc... The engines don't make as much difference as the tires will, as you can only do so much to the engine without cheating. Some of the engine builders who sell these high dollar engines have everything maxed out and will not pass tech after just a few races due to rocker wear, valves seating, etc. I would suggest buying an engine from a reputable dealer for a decent price and use the money saved to buy tires. If you are paying more than 500-600.00 for a stock clone, race ready, you are spending too much. Better to find speed elsewhere and be a better racer, than try to get an extra 1/4 hp for another 400-500 bucks. I have seen a stock engine with a restrictor plate in it, properly set up, with a great driver win in the stock classes that have no restrictor plates. This is how important it is to find speed other than with a big buck engine. It's your money, but you will find more speed with a good set of tires and the proper setup than you will ever find with a high dollar engine that will wear out quicker or become out of spec after a few races or sometimes right out of the box.