I have a real problem with my 454 build up, I currently have a standard bore 396 in a 70 chevelle with head casting number 3872702 which is a 65 model closed chamber head with 96.4 cc chamber, I want to use them on my fresh 454 with a TRW .100 dome piston. Summit, the place where I bought the parts says it will work with no clearance problems, but will not allow me to return the pistons for exchange if by chance it does not! So I called TRW and they said its a possibility for it to work and I should just playdough the heads and check clearance. Local engine builder (good reputation and does mostly drag engines) says he has done it before and made it work by opening up combustion chambers slightly for piston dome relief, BUT if largeer valves have already been installed it will not work even with flat tops. If I can make this work he said I would have exact 10 to 1 comp ratio. Has any of you ever tried this combo of open chamber piston and closed chamber head? If i switch to a 781 head will it flow as well as my 702 casting? Will this great loss of compression hurt my 292 550 comp cam I already have for engine? Sorry so long winded but wanted you to have as many facts as possible and all help greatly appreciated

Sammy,
According to my TRW catalog, there is no 454 piston with a .100 dome. There is one with a .095 dome that is designed for an open chamber head. Which piston number are you looking at ? The .095 dome one will be will be almost 11 to 1 compression ratio depending on the deck hgt of your motor (I figured it with .015 deck). I do not think the piston will work with the closed chamber heads but I do not have one here to be sure. If you want to stay with the heads you have, you will have to go with a flat top and you will end up with around 9 to 1 . This is assuming you want to stay with the TRW pistons. There are many others out there with different domes etc that may work.

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Bill Koustenis
Advanced Automotive Machine
Waldorf Md

Sammy, anytime domed pistons are used piston to head clearance should be checked. A very easy way to be sure of your clearance is to mock up your motor with 1 piston (no rings) and roll the motor over without the head gasket with the head just sitting on the dowels. Listen closely for any hitting of the piston on the head. Dye the piston and head to determine if the tight spot. Many times it is easier to clearance the dome slightly than the head. Piston is aluminum, softer, you might be near the gasket sealing surface on head etc. In my experience on a combination like this it is usually just a small amount off either surface that would have to be removed. Doing with this without the gasket is assuming you are using a gasket at least .038 thick. This is the standard Fel Pro BB gasket thickness and just happens to be just the right amount of clearance you need between your piston and head. Valve size won't effect pist. vs head clearance. Remember to check all pistons if one hits. The 781 is open chamber and the 702 is closed. The 781 is much better especially with a little modification. 9.2:1 compression on the street is a very versitable combination, however with a 292 cam and a 4:10 or lower gear you can get away with a little more maybe 10:1 or so depending on the weight of the car. With the 781 I think you will have around 9:2 and 10:2 with the domed piston. I hope this helps. Rick

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