I am trying to get my "shopping list" together for my 406 build. All components will be new, so I am starting with a fresh slate here. My basic plan is to use a Scat 9000 cast crank, 6.0 rods, hypereutectic pistons, Brodix IK200 heads and a XE284 cam. I am shooting for 450hp/tq for my 68, 4-speed, 3.73 car.

I am confused on what piston combination I want. I want to be at about 10.5-1, as this is my first performance engine and I hope that will give me a little cushion incase I don't get my tune exactly right. I do understand that quench and CR go hand in hand when talking about tune.

So my first question....I have searched here and have seen conflicting reasons as to whether to go with a dished piston and 64cc heads, or flat tops and a 70cc head? So is there a difference? Comments??

Another question, How is the advertised CR of a piston figured? at .025 in the hole, or at 0 deck, or with a .040 quench?

Thanks,

Jon

it's best to just ignore the "advertised compression" of a piston most of the time.
Rather, dig a lil deeper and find the real specs, and calculate your engine from there.

Flat tops with 4 eyebrow valve reliefs are -6 to 7 cc's.
D-Dish pistons are around -14
Those are the only ones I know.

If I plug the numbers into the calculator, assuming an 040 gasket and zero deck...

70cc heads and flat tops = 10.8:1
70cc & d-dish = 10.0:1
64cc & flat tops = 10.6:1

Cool Jim, thanks. That makes sense to me. The dished pistons I was looking at were -16cc and I've seen flat tops listed at both -5cc and -7cc. I will use those numbers and a cr calculator from now on.

So what about the chamber size, how do you determine whether to use a 64cc head or a 70+cc head? Does it make a difference? I thought I read somewhere that on a larger cubic inch motor, to use a larger chambered head, which does make some sense. But I have also seen some recomendations to use the 64cc head on the 400. Just looking for suggestions/recommendations, as chamber burn characteristics and such get over my head. :noway:

Thanks.

The difference? I dunno. I think in a "Max effort" situation, you want the smallest chamber possible, and the flattest valve angle possible, with a d-dish piston if you need a lower compression. But that's a max effort scenario.

For your basic street car, it matters not. More important things would be the available parts that fit your budget. In this case, you can go with flat tops, and end up either a lil high or a lil low, or go with the D-dish and hit your target comp pretty close.

If I plug your cam specs into the dcr calc, you get 8.44:1 with a 10.9:1 static comp (70cc heads and flat tops) and 8.26 with 64cc and d-dish. Either would work on pump gas with good fuel and spark control.

64cc. :yes:

Jim