X-heads vs J-heads: what's the difference??

Baxter61 said
Does anyone have any tests showing the 1.88 valve making more power on a 340 than a 2.02 valve head? Not flow bench results, dyno or track results showing less power/slower ET after 2.02s were installed in the head?

Baxter,

One of our Car Club Members had a 1968 340 GTS Dart with Factory Stock 'X-Heads'.

Basically 'stock', with Headers and 3.91 Gears and a few Bolt-Ons.
It ran 13.85's @ 101 MPH.

He did 'swap' on a set of 1972 'J-Heads' with 1.88" Intakes. He lost 2/10's
at the Drag Strip and ran in the 14.00's.

But, the 340 was more responsive at lower RPM's {for Street Driving}
and with improved Gas Mileage.