I went by the no.s on this thread . I was allready running the bigger valve size in my cnc,d heads .I didnt want to go backwards. The lift on my cam is 621,if im not mistaken Ill check the springs are a triple spring from comp.

Thanks. Let us know the comp spring number when you can.

Any pictures available of the Dart heads in full dress including rockers?

Dart just sent me their head flow numbers.

DART 8.1L GEN7 Iron Eagle BBC Flow

Valve 2.190" 1.880"
Lift 320cc Int 128cc Exh
.200 159 131
.300 221 178
.400 271 211
.500 312 237
.600 345 255

4.500 bore

Note: Flow numbers can vary up to 5% in
production castings.

how can the boar be that large 4.280 is 30 over.

That's what fixture they obviously tested them on and going down to a 4.250-4.280 will most likely make a reduction in flow numbers . This is exactly why one must be carefully read the fine print and check things out closely when looking at testing and numbers. Dart should go back and run the same test on a 4.250 bore and state whetther they are using a pipe on the exhaust or not? I think Tyler may have flowed them but I am not sure what bore size he used on his tests if he did them.
Still not sure why any Merc 496 owner would want to put heavy (100lbs heavier), lower compression ratio possible ,moderately expensive iron heads on an already fresh water cooled Merc 496 when they could put on aluminum heads., but them I am obviously biased and self serving with that comment!

Good Catch Crayolacrazy!

Best Regards,
Ray @ Raylar

Thanks Ray a little salt in my wound.Im getting a nother set do you want me to ship them to you ,you can test them.

Update on the intake on mine.
Pics first

and the raylar

So dynoed it with the raylar and mine withe same parts
stock tb with port job 78mm
stock exhaust manifolds for the rear mount turbo
stock 85mm maf
aftermarket cold air intake for a 5.3
3 inch y pipe into a 4 inch collector then reduced to 3 inch single into turbo to a 5 inch down pipe
single 3 inch to increase velocity to 85mm tv8101 turbo outback
raylar made 390 to the wheels and i want to say 480 torque
my intake made 330 and torque unk probably less due to the shorter runners if you go back and look at pics you can see how short i made them.
zz502 camshaft
h beam rods
mahle forged pistons

The good news
took off 78mm tb and put on 102mm tb and hooked up turbo to my intake
7 lbs of boost 680rwhp
Thats almost 800 flywheel hp
I asked him to give me a dyno sheet with all my sessions superimposed
You should see the drop in midrange NA without the headers on it

Here is the dyno with stock intake and headers and a single 4 inch system stock tb and maf

Oh in all these test the heads are cnc ported by tom at champion.
he did 85 sets of heads for the GM marine engines and he used the same cnc job on these heads.
stock intake size but 11/32nds stems and 1.88 exh valves sense the stock ones are kinda small





I also fell into a set of raylar heads and a forged short block with je pistons and a raylar crank that i will be building for 30 pounds of boost and a bigger cam
cam specs
244/244 @ .050 .650/.650 hydraulic roller
I am going to upgrade the head bolts to 1/2 inch if not bigger and convert the intake bolts to 1/4 inch since finding really long m6 bolts is next to impossible. I actually tig welded 4 bolts to make the length i needed to hold the fuel rails on since i used 4 intake bolts to work double duty.
If you google, 496 into 04 silverado, you can read more about it usually is the first link to come up

Also thanks to raylar for helping me out with some details a few weeks ago when i called. I have another question since i am in afghanistan. What are the cam specs for the 106 cam?

SPC Coss
US Army
currently deployed

Send them to Jim Valako to test.

Hey Ed. Are those factory castings or Darts?

Im hear to tell you darts heads dont flow as good as the cncd heads from Tyler Crocket Im running the same valves in booth and the darts make half pound of boost higher then gm head . I thought they wouldnt need any port work .If any one orders a set make sure you order the bolts stock bolts dont work .