Mopar Or No Car
I race on a quarter-mile flat asphalt oval track. I drive a '73 Duster with a 360 block and 340 heads and intake. It has a three-speed stick. Track rules allow us to run a 4412 Holley, stock intake, stock exhaust manifold, and up to a .490-lift cam. My 360 has a .474-lift Comp cam and 9.2:1 compression ratio. I also have a 340 with X heads, a stock intake manifold, a .484-lift Mopar cam, and a 10.8:1 compression ratio. Which motor will enable me to develop the most power on this type of track? (Which motor would better enable me to stuff the Chevys?) If it is a toss-up, please give me the pluses and the minuses of both motors. I look forward to reading your answer in the most awesome go-fast-turn-left magazine there is.
It's Mopar or no car for my wife and me!
Name and Address Withheld
Taking a look at the two engines, it would appear on the surface that the short answer to your question is that the 340 would be the better of the two. I say this because of two factors. First is the compression ratio of the 340, which is 10:8:1, versus the compression ratio of the 360, which is 9.2:1. The second factor is the heads. The X heads of the 340 are designed for improved flow characteristics over stock versions, and I think it's safe to say that X-head configuration is superior.
Having said that, let me expand a little more. I am assuming that the 340 has the right cam for what you are trying to do. Unfortunately, I am not provided with the specifications of the cam, so I cannot advise on that issue. But all things being equal, and if the cam is right for the motor, then I would say the 340 with the X heads and the compression ratio of 10:8:1 would be the first choice.
By the way, if you wanted to change cams in the 340, there are some choices we have that offer you a broader rpm range to run in. With the kind of compression ratio the you have in the 340, we can select a little larger duration cam, which would give you a broader power range. By doing that, it should help you get around the track better on a flat track and in higher-rpm environments.
Now, let's talk a little about the 360 engine. This motor is not bad as a second choice, but there is a scenario I can think of that might make it your first choice. It may be used as a first choice if you are running at a track that has a poor surface and you do not need as much torque as you get from the 340. In that situation, the 360 might serve you better.
I hope all of this has helped you, and whichever engine you wind up using, stay safe and have fun.