The head of the Vauxhall VXR team for the BTCC said it best when asked if he thought Diesel engines were the future, he said they might be but shouldn't be because Motorsport is about the excitement, and the noise. Fans dont come to the track to watch a bunch of quiet cars potter about, they like to hear the engines.
IMO there's maybe too much attention toward the fans and not not enough toward racing for the sake of racing. In the beginning years of motorsport spectators were the by-product of racing and the racing for the most part was unrestricted.
Today's racing wouldn't survive without fans and sponsors because those involved have simply gotten too greedy for the green. It isn't as much about the racing any more, but about a big paycheck. To draw that check you need to have a large fan base, sponsors, and video rights to sell for big $$$.
There was a Cummins Diesel raced at Indy twice that I know of. Once in 1931 with a Model A Duesenberg fitted with an 85hp, 361ci four-cylinder diesel. It qualified last, ran the whole race without pitting, and finished 13th. And again in 1952 Cummins was back with the inline turbocharged Cummins 6.6L Kurtis Kraft Special, which won the pole position with a speed of 138.010 mph and was 4 mph faster than Ferrari's V-12.
Indy also had the STP Special turbine cars, which came very close to winning.
Now we have the Audi diesel in ALMS and I love it. I don't care about noise and to me excitement is a pass for the lead while going into a difficult corner.
As for turbos I remember the Can-Am series where in 1973 the Porsche 917 had a 5.4L 1500 powerplant. Porsche only went to Can-Am after the FIA banned the 240 mph supercars from the period. Unfortunately they were killed off by rules restrictions.
just my 2