Sorry to hear about this George.
The engine sounded good, like it was about 50-Cubic Inches Larger than a 388..lol
What RPM's were you shifting at?
What times and mph did you get?
I noticed that the pistons were flat tops with gas ports.
What was the 'Quench Gap'?
I ask this because of the burn pattern I see on the piston
you show at 4.05 minutes into the video.
I see what appears to be a lot of 'Squish Velocity'.
Squish velocity is the speed at which air is displaced from between
the piston and head surface as the piston approaches TDC.
It is the result of three factors: clearance, area and piston speed.
Also, what type of fuel?
How did they set the deck height and quench gap?
Rod length, piston pin location, deck the block, etc.
See, you post a video and we play 64-Questions..
You said your going to build another 388 cid.
Nice engine combo. . . .
You said your going use a better con rod, an I-Beam.
You said your moving up to an LS7 Head.
Good decision as you can generally get more air / cfm through
the cylinder head by convergence lift, on up to 0.600" valve lift.
With the above in mind; if you desire too, use the 2.204" valve and
bore the engine to 4.155". Have the combustion chamber fitted for
the 4.155" bore and shaped / contoured to get as much air into
the cylinder by convergence lift as you can. Convergence lift for
a 2.204" intake valve will be 0.551" of 'Valve Lift'.
-note- make sure you have the block checked for core shift
before boring it to 4.155".
Just for the record. . .
The earlier blocks were crap in this department,
but the new blocks are good. The blocks they are making today
can be bored to 4.185" and are good for 1,500 fwHP.
Or consider a Dart block instead. . .
If you do this correctly you can get about 385 cfm to 395 cfm
through the head by 0.551", to 0.600" valve lift.
Don't put a camshaft in it with over 0.665" valve lift.
The heads simply go turbulent by about 0.635" lift on
a 'Running Engine. And that is with a good head!
Lesser heads won't flow past about 0.585" of valve lift.
That's one of the reasons so many camshaft grinders don't
grind cams with much more valve lift.
0.665" gross lift, less all valve train flex and geometric
losses, will most likely generate a 'Net' valve lift of
about 0.635". Effective cam lift would be 0.87 multiplied
by 0.665". That would be 0.579" of valve lift. That will
put you right about where you need to be with valve
lift versus cylinder head flow as I have specified above.
Without using something like one of those Comp Cams
that opens and shuts the valve like a 'Hammer', get
as much 'Area' under the curve as you can.
If it's okay with your engine builder, I can put you in
touch with someone who can do that for you.
Faster 'Flank' and opening rate and, more area under the curve
without acting like a hammer.
Be careful with that 12.0:1 static compression ratio.
Make sure the intake valve closing point is 'Dead On'
and the fuel is specified correctly. Also, make sure
the 'Quench Gap' is sufficient.
I might 'Reconsider' moving up to that high of a static Cr.
Just might not be worth it. . . .
If you want to contact me again to discuss this engine,
as we did the previous one, just let me know.
You build expensive engines and I myself would like
to see the next one last my friend.
Take care George!