All Big Six 351w Cast Piston

Relates to all big sixes

6 Shooter

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Does anyone know off hand which 351w piston would match the stock compression height and compression for the 300? Wondering if anyone has a manufacturer and part #. I do not need forged pistons for my application since I just want stock replacement. Had a 1965 240 fall into my lap for $25 so it makes the use of 351w pistons appealing now.
 

pmuller9

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Does anyone know off hand which 351w piston would match the stock compression height and compression for the 300? Wondering if anyone has a manufacturer and part #. I do not need forged pistons for my application since I just want stock replacement. Had a 1965 240 fall into my lap for $25 so it makes the use of 351w pistons appealing now.
Yes the 1965 to 1968 300 uses the 351W pistons but the 1965 to 1968 240 uses the Ford 289/302 pistons.
Do you need pistons for the 300 or 240 six?
 

6 Shooter

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Rebuilding a 1978 industrial 300 to put into my 1980 Econoline. Need 351w pistons to put on the 240 rods to put into the 300 engine. Looking for cast pistons that match the 8 to 8.5:1 stock compression ratio. No need for forged pistons since this is basically a stock rebuild.
 

pmuller9

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I used some step dish pistons designed for the N351 sportsman engine. They have the correct compression height.
He is looking at using the 240 rods which means the CH needs tp be 1.200" or slightly less.

6 Shooter,
There aren't any dish 351W cast pistons with around a 1.200" CH.
There are Ford 302 KB hypereutectic pistons but they do not have enough dish volume and they cost as much as a custom forged piston.

The least expensive piston with enough dish volume for your engine is the Autotec custom forged piston shown below.
The dish volume shown below is 10cc. You will need a 25cc dish to get an 8.5 compression ratio.

300 piston 2.JPG

Will you be using the stock cam or an aftermarket cam?
 
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BigBlue94

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He is looking at using the 240 rods which means the CH needs tp be 1.200" or slightly less.

There aren't any dish 351W cast pistons with around a 1.200" CH.
The least expensive piston with enough dish volume for your engine is the Autotec custom forged piston shown below.
The dish volume shown below is 10cc. You will need a 25cc dish to get an 8.5 compression ratio.

View attachment 9080

Will you be using the stock cam or an aftermarket cam?

Lol yeah, the 1.77x height would cause some catastrophic results with longer rods! Didnt see that bit.
 

6 Shooter

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Ok. So no cast options with a 25-26cc dish. What about forged options? I imagine the pin height may influence the dish volume, not enough crown depth (thickness) to do it. Going to an aftermarket cam, leaning toward a Crower.
 

pmuller9

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Whats the reason for the 240 rod on the 300 crank?
The only reason is for a 30% reduction in piston and pin weight and it is reserved for those that will be running the engine above 5500 rpm.
It is not recommended for the average build that benefits more from longer piston skirts for better stability in the bore.
 

6 Shooter

New member
Reliability. I’m not a fan of the skirt design on the 300 piston. Decrease the rod angularity, lighter pistons, less stress on the rotating assembly. I know I could run hypos and most likely not have any problems, have run them in hi rpm 4 cylinders before. I have the 240 rods. Had a 1965 240 fall into my lap a couple of months back for $25 Cdn, close to free when you do the currency conversion. I plan on running cross country with this outfit so trying to keep everything as simple as possible and avert any potential let downs.
 

6 Shooter

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That long skirt design does not lend itself to stability. Broken skirts are the evidence. That off balance design lends itself to rocking in the bore. So when it bottoms out on the stroke and it‘s not perpendicular to the bore it catches the bottom on the compression stroke and breaks the skirt, it doesn’t take much. Probably more of a problem on high mile engines but I’ve seen it on engines with just over 50000 miles. Stronger pistons may prevent broken skirts but it doesn’t correct the inherent design flaw.
 

pmuller9

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That long skirt design does not lend itself to stability. Broken skirts are the evidence. That off balance design lends itself to rocking in the bore. So when it bottoms out on the stroke and it‘s not perpendicular to the bore it catches the bottom on the compression stroke and breaks the skirt, it doesn’t take much. Probably more of a problem on high mile engines but I’ve seen it on engines with just over 50000 miles. Stronger pistons may prevent broken skirts but it doesn’t correct the inherent design flaw.
Yes the stock piston skirts do break off into the oil pan but there haven’t been any skirt failures with the Hypereutectic pistons.
Broken 300 piston 2.jpg

The least expensive forged piston option is the custom Autotec piston I posted previously.
I haven't talked to them lately but the dish pistons were $550 for a set of six.
There is room for a 25cc dish especially if you shorten the rod beam balancing tab above the small end.
 
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THE FRENCHTOWN FLYER

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I always thought the weakness of the stock cast pistons was due to the stress risers created by casting in steel expansion control struts, not the design of the skirt per se.

I'd use the later hypereutectic pistons on the stock rod. I use them in a drag engine that sees 5500 RPM regularly.
 

BigBlue94

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I always thought the weakness of the stock cast pistons was due to the stress risers created by casting in steel expansion control struts, not the design of the skirt per se.

I'd use the later hypereutectic pistons on the stock rod. I use them in a drag engine that sees 5500 RPM regularly.

A '74 240 I have has been sitting since '86 with two broken piston tops. It had a 300 head on it too. I would never use a basic cast piston IMHO.

I run my 300 to 5000+ rpms on occasion with hyper pistons.
 

pmuller9

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"6 shooter" has the 240 rods and wants to use them.

Any decisions on pistons?
 
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InlineDave87

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On the note of CH, what is the stock CH? I ran some of the numbers before and the advertised CR for the mid 90s is 8.9:1 but i can only get those numbers if i assume its 0 deck, going off what Pat did on the PN build with his being .032 in the hole at a 1.776 CH wouldnt that mean the stock piston is about .041 in the hole? And if thats the case ive found the SCR to be closer to 8.3:1 give or take. Which with my 31 dish pistons it gives me a SCR of about 7.8:1 which i assume would make the engine really lazy and not good for a hotter cam. Does the piston expand that much to end up 0 decking after its warm? Or did ford fudge the numbers?
 

Frank

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The CH of an non-planed block at 0 deck height would be 1.80": 10" deck - 1/2 stroke (1.99) - rod length (6.21) = 10 - 6.21 - 1.99 = 1.8. I've not come across any piston offering with this number. They all leave the piston under deck in varying amounts. Tallest CH I have seen is 1.778" , .022" under deck. A 1.776 CH is .024" deep, not .032"
 
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