Can anyone provide a photo of an original piston from a closed chamber, high compression Pantera Cleveland?
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I thought they were just flat tops, with a small ring around the circumference - but I’m interested in seeing a picture as well!
Looks like no one can provide one Rocky.
I might have kept them when I have mine engine rebuild, will check tomorrow and advise
I was interested in seeing if they were the same ones used in the Boss 351.
The B351 pistions are pop-ups. Those are advertised as 11.3:1 but will measure out as about 10.7:1. That is way too much static compression for current pump gas in the US.
9.7:1 actual static compression is about the limit for 93. In some places SUNOCO is advertising that their premium is 94, but not here in NY.
Interestingly enough, I had this issue when we suddenly lost SUNOCO 260 leaded in the pumps around 1976 or 77. I swapped out the high compression heads for the open chamber heads and the engine still was too high for the new unleaded Premium gas.
At one point the detonation was so bad that the engine would misfire and just shut off.
I even tried water injection but it did nothing but bog the engine when "launching" the car.
All the water vapor did was displace the fuel vapor and replace it with water vapor so additionally it was taking power out of the engine.
The '70 high compression pistons are flat tops.
Thanks Rocky and Doug. The pistons are different: cast vs forged and flat top vs domed. Doug, what was the VIN of the vehicle with the high compression you struggled with? Do you know if the heads were the '70 DOAE or '71 D1AE? How did they lower the compression between the two closed chamber heads? Were the pistons different, or was there a head or head gasket change?
The engine was not in a Pantera. It was in a Mustang. D1AE Ford Service Boss heads as delivered, uncut.
I believe that the actual CR was 10.7 withe the pop ups and closed chambers and 10.3 with the open chamber heads.
Part of the issue was the domed pistons, These were TRW's +.030 with fire slots.
Those pistons are actually very well designed but they were intended to use the old 106 leaded fuel. They don't particularly like the unleaded fuel including the Sunoco unleaded racing gas.
It was no better then 93 pump premium.
That is all just ancient history.
They don't work as well with the open chamber heads either. The fire slot is for flame travel and the chamber shape change effects that. Don't bother with them.
The current flat tops with closed chamber heads are really close to a problem with Premium pump gas now. That set up would be better with closed chamber aluminum heads where you limit the total advance to about 32° instead of 36°. The dished are actually more practical with the close chambers for a street car with iron heads.
There are more ways to make power then compression ratio. In fact many aftermarket camshafts will bleed off compression through the exhaust valve intentionally.
If you match your components correctly, you can easily make 650 to 700 hp in a 5.7 Cleveland with a 9.5:1 cr.
When I put the borescope in my cylinders my pistons looked like they are domed…
4V heads..
VIN # please. Do you know if it is the original engine and if the pistons were ever replaced?
Never mind. I see you identified it as 4679. Is it original and untouched?
@judgepaul posted:Never mind. I see you identified it as 4679. Is it original and untouched?
Don’t know… it doesn’t have the # engraved on the engine boss…