I saw an article in here earlier today and someone said that the Iron TBI heads had large 74 or 76 cc combustion chambers. It is my understanding and all GM crate engines using 193 High Swirl Heads have them listed as 65.3 cc. I have the 11402193 heads on my 383 and they are in fact 65.3 cc. The chamber resembles a L31 Vortec in as much as the spark plug position and chamber size is similar. Most 94-95 GM trucks run 9.4 CR and a flat or dished piston so wouldn't the chambers have to be smaller than 76 cc.? Maybe the LO5 HD trucks or the L03 may have been larger..  

The swirl-port heads I have seen are also 64-66cc chambers. I saw that reference elsewhere that they is a 76cc chamber version but I think it's a myth. Mortec does state there some 90's 350 crate-motor heads that have large chambers but I don't know how accurate this information is.

Swirl-ports on a 383? I hope it's a tow rig. Did you measure the combustion chamber volume yourself?  

The engine builder did, thats how he came up with 65.3 cc. I don't tow or haul anything and you'd be very surprised how well these 193's work on a heavy truck. You see I don't need to rev past 4800 rpm and the builder and I weighed all the options and for what I wanted, (brutal Low End Power) stop light to stop light, there were no other heads better suited than the 193's for my particular case.

My local Drag Strip is closed for the winter and I just got the 383 in and running a few weeks ago so I don't have any real track numbers yet, but I do have my Accelerometer which I calibrated at the drag-strip last summer with my 350 and I also have TTS DataMaster Quarter Mile calculator as well as Desk Top Drag Strip. and all three of these theoretically have me running 14.50's at 93 mph with 1.98-2.1 60' times, 1/8 mile in the low 9's and 0-100 mph in under 15 seconds. The truck with me weighs in at a bit over 5000 lbs. For an Old Body Style 1995 Extended Cab, Sport Side and a mild 383 with TBI, I think 14.50' are darn quick!