I looked at the Astrodome's dimensions over the years, using the data at Ballparks.com. In 1965, the first year of the Astrodome, the fences were, left to right 340-375-406-375-340. For some reason, they lengthened the power alleys by 15 feet, so the dimensions from 1966-1971 were 340-390-406-390.
From 1972-1976 they shortened all the dimensions to 330-378-400-378-330. Then from 1977-1984 they went back to the same dimensions as 1966-1971. Then in 1985 they shortened again to the dimensions from 1972-1976, where they stayed until 1992 when they were reduced a little to 325-375-400-375-325.
In sum, from 1966-1971 and from 1977-1984, the dimensions were longer: 340-390-406-390-340. From 1972-1976 and from 1985-1992, the dimensions were shorter: 330-378-400-378-330 (with a slight reduction in 1992).
Ignoring the first year of the park (1965) and the first year of the new dimensions (1966), the above data provides 13 years of play with the dimensions twelve feet longer in the power alleys (the "Long Years") and 13 years of play with shorter power alleys (the "Short Years"). The 378/390 switch isn't a perfect match for the 380/395 distinction that Castilla and Guillen were complaining about, but it's probably close enough. One of the reasons the Astrodome is a a great example -- apart from the similar power alley dimensions -- is that weather is a non-factor.
Here is how the Houston team hit at home and on the road during the seasons with longer and shorter power alleys. First let's look at how they did on the road during those years (season averages):
Road
Seasons AB H 2b 3b HR
Long Years 2751 688 113 18 53
Short Years 2793 697 111 17 60
The road numbers are remarkably similar for all the years from 1967-1992, so we need not be too concerned about whether the quality or style of the various Houston teams in those 26 years are skewing the home data we are about to see. Because the road numbers are essentially neutral, they will not be of further use below. But in general, it was much much harder for the Astros to hit homers in the Astrodome compared to road parks, and much easier for the Astros to hit triples -- and to some degree doubles -- in the Astrodome compared to road parks, regardless of the Astrodome's dimensions.
Now the home data for the Astros (season averages):
Home
Seasons AB H 2b 3b HR
Long Years 2586 655 114 32 29
Short Years 2684 678 120 21 44
It's a little difficult to tell the effect of the dimension changes by looking at the raw data, articularly since the batting averages are .253 for both the Long Years and Short Years, which might lead to the conclusion that the longer dimensions did not affect hitting. So let's look at some rates.
Home
Seasons H/2b H/3b H/HR TB/H
Long Years 5.73 20.68 22.96 1.40
Short Years 5.63 32.53 15.28 1.44
Now the differences become more obvious:
Doubles: During the Long Years, one out of every 5.73 hits was a double and in the Short Years one out of every 5.63 hits was a double. So, the dimension changes did not appreciably affect doubles.
Triples: During the Long Years, one out of every 20.68 hits was a triple and in the Short Years one out of every 32.53 hits was a triple. So, lengthening the dimensions increased triples by 57%.
Home Runs: During the Long Years, one out of every 22.96 hits was a home run and in the Short Years one out of every 15.28 hits was a home run. So, lengthening the dimensions decreased home runs by 33%.
Total Bases: During the Long Years, the Astros got 1.40 total bases per hit and in the Short Years got 1.44 total bases per hit. So, the dimension changes only slightly changed total bases per hit.
Putting it all together, lengthening the power alleys (and to some extent the foul lines and center field) shifts home runs to triples.
Looking at Jose Guillen's numbers at home in RFK, he has no triples and one home run. Kind of hard to say some of his would-be homers have been reduced to mere triples when he has no triples. As I mentioned in an earlier post, using a park home run adjustment analysis, RFK suppresses home runs by about half. So based on the park analysis and the Astrodome study, at most Guillen might be able to claim he should have one additional home run at RFK. (The other complainer, Vinny Castilla, has 6 homers at home, and one triple, so he may have a claim for another 3 homers. What is odd is that Castilla has only one homer on the road in approximately the same number of at-bats).
Side note on the Houston teams:
Over baseball history, singles have been worth approximately .46 runs, doubles .80, triples 1.02 and homers 1.4. Applying those to the Long and Short Year average seasons, you get approximately 385 runs for the Long Year seasons and 406 runs for the Short Year seasons, or about a 22 run per year disadvantage with the longer dimensions. That means on the hitting side, they should have been about 2 wins worse during the Long Years, all other things being equal.
Generally clubs build their teams to suit the stadium, so during the Long Years, so it is possible the Astros may have had a little less power and more speed, and in the Short Years may have had more home run hitters. However, the road data for the Long Years and Short Years is nearly identical, indicating on balance that the Houston teams in the Long Years and Short Years were equally capable in terms of power.
Houston did not have a significant number of power hitters in the Long Years. The Toy Cannon and Doug Rader were true power hitters, and combined for 5 seasons of 20+ home runs during the Long Years. The Astros also had Bob Watson, Dickie Thon, Joe Morgan and Cesar Cedeno during the Long Years, who had 9 seasons of 20+ home runs in their careers, but only two for Houston during the Long Years. Watson and Thon, strangely, had their only 20+ homer seasons during the Long Years -- and might be stretching the limits of any power hitter definition. In all, there were only 7 player seasons of 20+ home runs in the thirteen Long Years.
In the thirteen Short Years, there were 19 player seasons with 20+ home runs. The power on those clubs was Wynn (again - 2 seasons), Rader (again - 2 seasons), Cedeno (3 seasons), Lee May (3 seasons) and Glenn Davis (6 seasons). They also got 20+ seasons from Cliff Johnson, Kevin Bass and Franklin Stubbs.
It appears, then, that the Astros were at least trying to incorporate a little more power during the Short Years.
-----
*All park data is from Retrosheet.
