I have been thinking about muscle car engines. More specifically muscle car engines that were only installed in a muscle car, were there was no regular or low performance version of them. If you look at the 454 Chevy, the 440 Mopar or most other muscle car engines, there was also a version of the same engine that was used in regular cars and trucks.
While thinking about it, I realized that you could look at another engine in the same family as another version, and in that case, every engine would be disqualified. Since I wanted a number greater than zero on my list, I decided that one of the criteria would be if that displacement engine was only offered as a high performance version, then it would qualify.
So the list of engines I was able to come up with that fit that list would be the 302 Chevy, the 340 Mopar and the 427 Ford. As you can see, they are not completely unique. The 302 Chevy is a obviously a small block Chevy etc. But I am not aware of any application of any of the three that was not a high performance engine. For other uses, Ford had the 428, Mopar had the 318 and 360 and Chevy had many variations of the small block. The Ford 428 was the same engine family as the 427 (which was actually a 425, but 427 sounded better to the marketing guys since it was 7 liters, and the limit for displacement in many racing classes). The 427 was more expensive to manufacture since it had a larger bore. The bore size was about the max of what they could do with the casting technology of the time and the block design. Since it was pushing the limits, it required more care and more precise machining. So Ford created the 428, with a smaller bore and a longer stroke to get about the same displacement but with lower manufacturing costs.
The 302 Chevy owes it’s existence to Trans Am racing, which had a limit of 5.0 liters (305 cubic inches). It was created by putting the crankshaft of the 283 into the 327. This created an over square (where the bore is larger than the stroke) engine that met the displacement requirements of Trans Am racing. It was only used in 1967-1969 Camaros, specifically the Z/28 model.
I am not aware of any particular reason how 340 Mopar came to that displacement, but it did work well. It was more widely available than the 302, and probably the 427 Ford also. It was most often found in Darts, Dusters and other compacts, but in the later years of the muscle car era, it was also found in mid-sized cars such as Road Runners.
Since there were only three engines that met my original criteria, I thought I would add a second class that would be engines that used the same displacement/bore and stroke of other engines, but the block was different.
This increased the list to include the Boss 429, the Boss 302, the 426 Hemi and the ZL1 427 Chevy. The ZL1 is obviously a different unique from other 427s since it has an aluminum block and heads. That meant that the big block weighed about the same as the run of the mill small block.
The Boss 429 had a reinforced block to deal with the stresses of NASCAR racing, and since the block didn’t interchange with the regular 429, at least not in exact function, I added it to my list also. The 426 Hemi was the same. Both had unique heads from the regular engines, and reinforced blocks that were different from the regular high volume production engines.
The Boss 302 was a combination of the Ford Windsor block and the Cleveland heads. This resulted in a high revving engine destined for Trans Am racing, the same as the 302 Chevy.
So out of all the muscle car engines that I know of, I am only aware of the 7 listed here that were only offered in high performance trim. Not a surprise when you consider the cost of developing and producing an engine, even in the 60’s. It was easier and far less expensive to just put a better set of heads, a hotter camshaft and a different intake manifold on an existing engine than to create a dedicated muscle car engine. Not surprisingly, all the engines on the list except the 340 were aimed specifically at racing. ford and Chrysler were especially big believers in the win on Sunday, sell on Monday mentality. GM had a ban on factory backed racing, but still managed to get a couple of special engines out.