[quote] [/q At the same time, the custom piston can be dished to lower CR a bit, depending on the head. I'm not sure how that effects quench and detonation. I have not found much discussion about that. uote] 68Bigbird, You are right on your post on 0-deck but you seem to have misted the point that if you use 0-deck to get the proper quench height by cutting the block or by using taller pistons you CAN run 10 to 1 compression on pump gas with no detonation. If you go to all the trouble of 0-decking and then dish the pistons to reduce compression you just lost the power gain you wanted in the first place.
The other part is being careful with the cam you use. Need one with late intake valve opening to help with dynamic compression, Should be around 170 LBs per cylinder.
The cam may be why Vikki will have trouble with 0-deck. (she wants to stay original).
My main point was to address detonation problem of the original design operated on widely available pump gas by setting zero deck and dishing the piston. That way you drive the car where ever you want without concern for finding fuel that won't harm the motor. This idea is supported in the article at:
With the concern of milling the deck on an original motor, I proposed the alternative of moving the pin in the piston (taller piston) so zero deck is still obtained without cutting the deck. The stroke and compression remains the same for either way of setting zero deck. I don't see there is any real difference in outcome for either approach.
You can argue the original motor design ran fine. And it did with fuels commonly available in the day and when the engine was fresh and had good oil control. The point of this discussion in my mind is to return the engine to reliable operation while running it on widely available fuels. If the engine is detonating, the reliability will be poor. We have a few here with engine failure caused by detonation.
Another thing to consider is as the engine wears and had poor oil control, oil consumption will lower the effective octane. That may be why some combinations run okay at 10:1 while someone else building the same recipie has problems. Taking the compression down to 9.2-9.5 gives you more margin than 10:1 for fuel variations, tuning error and wear.
Just as TOHCan says you don't zero deck so you can say you did it, you don't cling to factory CR and all original parts just to say you did it when the sacrafice is not enjoying the car because you can't take it out of range of good fuel.
