need experts on the BBC 427 racing combos

Sorry for the long post. I am looking for real world experience or knowledge for 427 BBC combos that work. I recently purchased a 69 camaro bachhalved drag car with 29.5 x 11.5 slick and glide with brake and 8" 4500 stall converter. No issues with spinning.I will give the specs and info. I put the car on a chassis dyno 2 weeks ago and got the fuel curve and ignition dialed in. The car made a peak 450 hp at 6500 and 400 tq at 5800. The car weighs 2950 with me in it and is running 10.80's. I would expect more from the combo though.

427 mark iv 4 bolt
3.76 steel crank
6.135 h beam rods
aries pistons
solid roller 269/277 @.050 698/700 lift 108 lobe
roller rockers with girdle
merlin iron rect 320 cc heads 2.30/1.88 valves 119 chamber
2" hooker comp open headers
weiand 2" single plane intake
850 holley double pumper
dual snorkle ram air intake inlets replace headlights
msd dist, wires, coil and 6a plus box

I cannot verify the cam, pistons and compression ratio since I did not build the engine but I was told it was 12.5 to 1. Cranking compression is 175 psi without loosening the valvetrain or opening the carb plates. My issue is that I would expect well over 500hp with this combo and that compression at the wheels. My suspicion is it is closer to 10.5 to 1.

Let me know if I am in left field or if you see issues with the combo.  

What displacement are the piston domes? If you do not know, what is the part#? What is the compressed thickness of the head gasket's ? Has it been bored out, and if so, how much? With that info, you can compute swept volume and find an actual static comp. ratio. True cranking compression needs to have throttle plates open. 175psi. sounds high for that camshaft.  

Unfortunately I do not know anything on the pistons other than they are supposedly aries pistons. Head gasket thickness is another unknown. The bore is supposed to be .030 but again I cannot verify the information without tearing it down. I did not have the throttle blades open when I did the test. Am I mistaken in thinking that with the components and if the compression is 12.5 - 1 that this motor should be making around 625hp and 550 tq at the flywheel?  

If in fact it is 12.5:1 and everything was set up correctly, you should be making at least 525- 550 HP and around 500 ft lbs torque. Without knowing the things that really count, it will all be a mystery. And yes, the throttle blades must be fully open for a compression test.  JW.  

I forgot to say, if it was in the 10:1 range, that camshaft is way big and would kill torque and consequently kill HP.  JW.  

I am assuming you are talking about hp and tq at the wheels. Because the motor is according to the info from the chassis dyno would be putting out around 530 hp and 500 tq at the flywheel currently. I agree that if the compression is around 10-1 that would be why the numbers seem low to me. I guess the bottom line is I won't know until I tear it down to spec everything. I just want to make sure I am thinking correctly before I spend the time and effort to tear it down. Thanks for all the info  

merlin 320's dont really flow that well to begin with.in addition to the possibility of having 10-1 compression and that cam makes the scenerio even worse.i'd be opening up that engine to take a looksie.  

Just an update on this post. I finished the season running consistent 10.30's at 130 after further tuning with exhaust extensions, timeing and jetting. Pulled the engine at the end of the season to find out exactly what I had. Turns out the compression was 9.2-1 with a .060 quench. I swapped out the pistons to get a true 12.5-1 compression ratio with a .040 quench. I am guessing that the additional 3 points of compression should help the cam out and produce an additional 75+ horse. We will see if it breaks into the 9's now.  

Did you do any "profiling" on those domes?

That becomes increasingly important as the dome gets higher. Hopefully though since you maximized quench you didn't have to use a large enough dome to get yourself into trouble.

You will probably have to throw in some more timing depending on what fuel you will be running now.  

The pistons are Ross 51cc domed pistons. The dome is .700 tall. So it is a pretty big dome. The piston is .020 in the hole with a .020 shim gasket. The valve clearance is tight at .060 on the intake and .050 on the exhaust. I did have to swap plugs because the pistons were closing the gaps on the projected spark plugs. I went to recessed plugs to fix that. I am running VP fuels 110 in it currently and will try 112 later after I have dialed her in to see if there is any difference. Currently I have backed the timeing down to 35 degrees to start and the jetting is 81 all the way around which is what it had before the upgrades.  

Holy dome volume batman!

I would've been scared to death to put those in out of the box? Did you?

What kind of chamber are these going into again?  

The heads a open chamber Merlin iron heads with 119 cc volume and 2.3/1.88 valves. I did install them the way they came after checking the valve clearance with clay. I am a little nervous with the clearances being so tight, but it is in the car and running and hopefully nothing stretches too much when hot at WOT.