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1971 351C-2V Piston type
#1
I have a 1971 Mach 1 with a 351C 2V I recently removed the heads to replace an improperly installed head gasket. Being that I am this far into it I was considering a cam change.
Looking at the pistons I can see that the lower end has had some work on it. The pistons are .030 over, and are a dished type piston.

Is a dished type piston correct for a 1971 351C 2V?

From what I have found, the 1971 351C 2V is rated at 9:1 compression. Is this ratio with the dished type piston that is in my car? Or, is this compression ratio with a flat top piston?

Thanks
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#2
I believe 9.5:1 Compression Ration (CR) is pretty standard for flat-tops with the 2V heads. I installed a set of .060" Keith Black Hypereutectic flat-top pistons in mine, and at TDC, they are flush with the deck with the standard valve depressions. The dished pistons would lower your CR by offering more volume to the combustion chamber, in the way of less piston taking up the area.

The old pistons I pulled out were most likely the stock pistons, and I didn't really notice any 'dishing' - they seemed like flat-tops as well... but they might've had a lower-than-deck-height profile, and still had the 9.0:1 CR.

If you want the recipe for my engine, click the 'Visit My Garage" button below my signature. The engine is running like a beast, supposedly is putting out somewhere around 400hp, and everything seems to be working really well together.

It ain't cheap, though. You can't just go in with a cam change and not expect to have a lot of other things that need to be improved upon along with it. The more cam you put into it, the more you'll need to improve the rest of the valve-train, along with induction and exhaust to take advantage of the increased capacity to move air & fuel through the engine. Depending on what kind of power you're looking for, you might visit CompCams and look through some of their offerings and maybe use their CamQuest utility - to get an idea of what the cam specs and numbers all mean and what they can do for your car. Then pick the manufacturer you prefer and look at similar products.

Hope this helps.

Eric

[Image: mach1sig2.gif]
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#3
Sometime just before 73 model yr, dish pistons were the normal for 2v and 4v. Sad times for performance
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#4
'71 2Vs should have flat top pistons with 9.0:1 compression. A PO may have replaced/swapped engines with one that is 8.0:1.



“If you can't explain it simply, you don't understand it well enough.”
--Albert Einstein
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#5
there is often a part number on the top of the pistons . if you there is you can post that and we may be able to determine the piston volume . you can then measure how far below the block surface the pistons are at tdc . also post the numbers on your heads and with all this info we can give you a fairly accurate idea of what your static compression is.
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#6
I made up a spreadsheet for calculating CR (primarily for stroker builds). As with any calculation, garbage in = garbage out. That being said, for flat top pistons assuming a 4cc valve relief I get the following max/min CR values for open chamber heads:

4.03 bore, 9.206 deck, 1.67 comp ht, & 77cc heads: 9.05
4.03 bore, 9.215 deck, 1.65 comp ht, & 80cc heads: 8.32

Notes: Volume of piston dish will have a major impact on CR. Knowing specific deck, and compression height is also necessary to get an CR accurate number.
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#7
Here's another spreadsheet you can play with. If you run your numbers in it please let me know if it matches yours.
http://www.7173mustangs.com/thread-engin...lculations



“If you can't explain it simply, you don't understand it well enough.”
--Albert Einstein
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#8
Hi Don, I don't see an attachment.
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#9
Yeah, I messed up, it should be there now.



“If you can't explain it simply, you don't understand it well enough.”
--Albert Einstein
  Reply
#10
Don C;284262 Wrote:'71 2Vs should have flat top pistons with 9.0:1 compression. A PO may have replaced/swapped engines with one that is 8.0:1.


Don,
That is what I believed to be type of piston and cr. thanks
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