Successful engine builders never, ever rest on their accomplishments, and those engine builders who lead the charge are always looking for ways to improve power, torque, and engine efficiency. Case in point: Bob Book of Book Racing Enterprises, who has been working hand-in-hand with Richard Maskin of Dart Machinery on this amazing LS Next-based engine combination.

We reported on the naturally-aspirated engine back at the end of August. At that time, Book had coaxed nearly 1,160 horsepower from the 400 cubic-inch small-block engine, but felt there was still a bit of room for improvement with more refinement.

“Based on the dyno results and the testing I did with it, we could tell that we had a little bit of room for improvement in the exhaust port. The engine took a really big main jet, and in order to get the tuneup right–the exhaust port was still black–I sent the heads back to Richard and they went up a size in the exhaust valve and made the port linearly larger based on the size of the valve,” explains Book.

Initially they had a plan to address the port deficiency with a new camshaft, but ultimately made the choice to make the cylinder head change, which is where the power gains came from. After making the cylinder head and valve change, Book was able to take out .010-inch of main jet, yet move the same amount of fuel. This shows the efficiency of the exhaust port changes. Previously, the engine made 1,158.90 horsepower and 660.0 lb-ft of torque, and after these most recent changes, cranked out 1,168.9 horsepower and 660.8 lb-ft of torque. The torque number doesn’t change much because they are starting the pulls at 8,500 rpm. For this exercise, the horsepower improvement is most important.

“Dart is really doing better than I had expected and putting way more effort into this–they’ve really done an excellent job. We’re done with it for a little bit because we’re going to put the engine into a car and run it down the track,” says Book.

“But we’re going to continue to work on it over the winter; I still think by the time we’re done rubbing on it we’ll be at 1,175 or 1,180 horsepower. It’s just a nice package.”