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Pop-Up Piston
#1
We just pulled the heads to replace the gaskets and found the engine has what my mechanic calls "pop-up" pistons. I thought this engine was a quench head M-code and now find these pistons with open chamber heads.
What engines used these pistons?

mike

[Image: 1_11_11_13_11_50_27.png]
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#2
Take alook at this forum. They discuss them in depth.

http://www.mustangsandmore.com/ubb/Forum...08898.html

It seems the idea behind using the pop up forged is to gain compression since the 351M was extremely limited. Intersting reading about milling and fire notching. Didn't realize you could pick up 20hp. Myself, I decided to go with a 1970 351 block that showed good cylinder thickness. I'm also going to use 1971 closed chamber 62cc 4V heads and forged flat top w/dual relief to increase the compression.

[Image: 2rr7aiv.png]

Just cruising along minding our own business when BAM!!! The LAWS show up.
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#3
well..they wouldnt work if they was closed chamberd heads i dont think....no room for them....the reason they pop up is too make up for the space missing between the head and the piston...if it had closed chamber heads it wouldnt even turn over...it would ding all the valves or ding the spark plugs...or just bottom out and not start or move at all untill the heads were unbolted...would be like sticking a peice of metal in there...pop up pistons are great for boosting compression levels in open chamber heads if you really want to run high octang gas.

[edit] M-codeThe 351C 4V engines produced in 1970 and 1971 used this code. Engines varied in compression ratio; 1970 engines were 11.0:1 compression and produced 300 bhp (224 kW; 304 PS) at 5400 rpm, while 1971 versions had a slightly lower compression ratio of 10.7:1, and a reduced power output of 285 bhp (213 kW; 289 PS) at 5400 rpm. Ford owner's manuals for these engines recommended high octane gasoline (100+ octane in 1970) which was at the high end of the leaded gasoline available at the time. However, with the mid-1970s introduction of unleaded gasoline and lower octane ratings, and subsequent disappearance of the super high octane leaded fuels required to power these high compression engines, motorists were either unaware of potential damage or simply unable to find this kind of fuel any more. As a consequence, many of these otherwise durable engines met with an early demise due to the destructive effects of severe engine knocking caused by using low octane fuel.
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#4
If your engine is a 351C the piston could be a Boss 351 piston or an aftermarket piston. If it is a 351M it is an aftermarket piston. Chuck
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#5
Pop-up or "Dome" pistons can be used in both the open and quench chambered heads; they will just provide a different compression ratio, dependent upon the CC of the heads involved. To the best of my knowledge, the only dome 351C piston from the factory were the ones use in the Boss 351. The others (to include the 1972 HO which was forged like the Boss 351 pistons) utilized flat top pistons with two valve reliefs

This brings me to a point that I think bears repeating. You can have custom pistons made to satisfy your need for almost any compression ratio. You do not have to even go to the quench chambered head. In fact, I would venture to say that from a starting point, the open chamber heads might be better for a "street" car as they have harden seats already.

Mike, I am thinking that your engine might have the old TRW L2348F piston which has a .425" dome. This will give you @11.9 compression with the 63cc head; 11.2 with the 67cc head; and 10.0 with the 76cc head. As an aside, this same piston will give the 58cc head a compression ratio of approximately 12.6.

Perhaps you could post up any casting or part number on one of the pistons?

Hope this helps.

BT


Do the RIGHT thing.
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#6
Speedpro made a piston in the early 80's that was 12:5 to 1 just for the open chamber heads. I used these in an open chamber motor that we milled some of the dome off to drop the ratio to 11:1. That was my favorite Cleveland motor of all time! I wished I still had it! Traded for machine work on a 429. Bad move in my opinion. That's another story!

[Image: 16kuyc0.jpg]
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#7
cobra3073;33268 Wrote:Mike, I am thinking that your engine might have the old TRW L2348F piston which has a .425" dome. This will give you @11.9 compression with the 63cc head; 11.2 with the 67cc head; and 10.0 with the 76cc head. As an aside, this same piston will give the 58cc head a compression ratio of approximately 12.6.

Perhaps you could post up any casting or part number on one of the pistons?

Hope this helps.

BT

Yes, thanks for all the input. These heads have other issues like the head gasket. We bought one for a 351C 4V head and it did not fit, the holes did not line up. The only one that would fit was a gasket made for a Boss. The holes lined up and were the proper size. Another gasket I looked at had the proper holes but the oil channels were smaller on the gasket than in the head. I remember when we changed the valve covers about 4 years ago for a different look (kept the old ones) my mechanic commented that the rockers seemed "large" even for a Cleveland. Another thing was the lack of exhaust manifold gaskets, it was metal to metal. I will get casting numbers and pictures to post later.

mike

[Image: 1_11_11_13_11_50_27.png]
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#8
Post up some pictures or casting numbers.
351 Cleveland and Boss 351 use the same head gasket
there are pop up pistons for open and closed chambered heaads
some gasket oil holes and water holes are different sizes on purpose to restrict or meter flow.
Exhaust manifolds did not use gaskets from factory, just metal to metal contact.
It is best to identify what you have before assembly to avoid any problems,

[Image: mustangnight010.jpg]
1972 Mustang Convertible 351C 4V
1966 Ford Galaxie 7 litre-4speed

Jorge
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