All Big Six 351w Cast Piston

Relates to all big sixes

InlineDave87

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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"
So then did Pat get it wrong? Cause that would end up putting his SCR at 10.2:1. Again i would like to re-iterate that i am a novice engine builder still working on my first build. And to go along with the 351 piston topic, check out these ones i found (im sure they have been mentioned before but i just came across them). Looks like they would come up with a 9.7:1 SCR, that is with the promaxx head i have.
 

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Frank

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Yeah Dave, I have not done a lot of gasoline engines either, and none in 20 years. Big diesels already had the ideal cams, pistons, etc, so I didn't calculate this stuff. I try to get my numbers right before I post. IF Pat had .024" deck and pistons with a 4 cc valve relief area (I think he said 4 or 5), 76cc ported Promaxx head, .039 gasket = 9.89 @ 5 cc- 9.98@ 4 cc SCR.
https://uempistons.com/p-27-compression-ratio-calculator.html
This is the calculator I use. It's also where to find all the Silvo-lite pistons. Interestingly, The factory D dish we keep calling 25cc they post as 26.1cc dish. Their D dish have 2 CH, 1.776 and 1.767. (The felpro 1024 gasket is .039 thick, bore of 4.180 )
 
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pmuller9

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Yeah Dave, I have not done a lot of gasoline engines either, and none in 20 years. Big diesels already had the ideal cams, pistons, etc, so I didn't calculate this stuff. I try to get my numbers right before I post. IF Pat had .024" deck and pistons with a 4 cc valve relief area (I think he said 4 or 5), 76cc ported Promaxx head, .039 gasket = 9.89 @ 5 cc- 9.98@ 4 cc SCR.
https://uempistons.com/p-27-compression-ratio-calculator.html
This is the calculator I use. It's also where to find all the Silvo-lite pistons. Interestingly, The factory D dish we keep calling 25cc they post as 26.1cc dish. Their D dish have 2 CH, 1.776 and 1.767. (The felpro 1024 gasket is .039 thick, bore of 4.180 )
The DSS 5000 series pistons used in the build have 5cc valve pockets and a 1.775 pin height and are 4.050" diameter.
The Promax head in the video has a 73cc chamber.
You can clearly see that the block deck was not machined. Often times the factory deck height can be a few thousandths taller than the 10.00" spec.
The stock connecting rods are 6.2097" and become shorter after they are resized.
It could be that the compression ratio was 9.95.
 

CNC-Dude

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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.
That statement simply is not true! The longer the skirt design, the less the piston can rock. The broken skirts are not evidence of that, but as FTF suggests is stress risers caused by the metal inserts cast into the pistons. The Ford 302 is also notorious for this. Really short skirt designs like the piston required to be used in the 240 rod swap will rock very badly, and compression heights that short have other issues when used in street driven engines. Even though it has a support rail for the oil ring, the ring stack often ends up being undesirable for street engines, but acceptable for racing applications.
 

InlineDave87

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🙋🏽‍♂️ I got another question for the group… ive been looking on and off the last couple of days for bushings so i could see about what it would take ($$) to change over to a 351 piston… where would be a source for these bushings
 

bubba22349

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Many of the earlier Ford engines used that .912 connecting rod small end pin size and some also used a pin bushing. Here in the below link is one sorce for bushings that might work it's for the old 239, 256, 272, 292, 312, Ford & Mercury Y Block V8 engines of the 1950's and 1960's. A good connecting rod rebuilder can use the bushing install to get the rods so that they all match in lenght they also somtimes use a custom made bushing too. https://egge.com/part/mah-1606-223-3608/
Best of luck
 

wallen7

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Many of the earlier Ford engines used that .912 connecting rod small end pin size and some also used a pin bushing. Here in the below link is one sorce for bushings that might work it's for the old 272, 292, 312, Y Block V8 engines of the 1950's and 1960's. A good connecting rod rebuilder can use the bushing install to get the rods so that they match in lenght they also somtimes use a custom made bushing too. https://egge.com/part/mah-1606-223-3608/
Best of luck
That's the bushing we used and honed to .927 Chevy sized pins
 

Frank

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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.
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.
These observations apply much, much more to V engines, especially small blocks where everything is jammed together in the crankcase and pulling in different directions. 1) Long skirts are the only design that give the longest life. All heavy duty diesels have long skirts, and the best have full-trunk pistons, round on the bottom, some with an oil ring down low. The warranty on a new truck engine for internal rotating parts is 1,000,000 miles. 2) "rocking in the bores" applies to all piston machines, and is mostly a function of rod/stroke ratio, but is exacerbated ("to make more violent, bitter or severe") in V configuration mostly, and all other engine configurations that are not inline, six cylinder. The inline six is the only engine configuration that is balanced, by natural physics. "that off balance design" does not apply to any L6 with matched internal components. The 300 has a rod/stroke ratio of 1.56 which is in no way extreme. 3) Reliability: Heavier pistons go with heavier crankshafts. In racing, the piston and rod mass is cut to a minimum, but engines built for hard-load durability, the mass of the rod and piston is matched to the crank. There is more stress on the rotating assembly with mis-matched light-weight rods and/or pistons, due to harmonics from a loss of balance. The lighter parts will rev up higher, and deliver more horsepower- but they will not live as long as balanced, heavy parts operating at the correct speed.
And all of the above objections evaporate completely in any engine if the average piston speed never exceeds 28 mph (2500 feet/minute.) Diesels last by being well balanced, yes. But their long life is mostly due to the fact that they live their whole lives with a pistons speed between 1300 and 1900 FPM, and never exceed 2300 fpm. Any engine's rpm range is determined by piston stroke. Higher rotating mass lowers the rpm, but is a secondary governing factor.
Any engine will live well beyond the averages if it is operated at a piston speed of aprox.17 mph, 1485 fpm. This is also where they deliver maximum torque (in stock trim), and balance. Examples: Electromotive Diesel (train engine), 745 rpm. Average simi-truck diesel, 1500 rpm. Ford 300, 2200 rpm. Ford 240, 2800 rpm. Average small block V8, 3000 rpm. Lawn mower, 3400 rpm. Sthil blower, 6100 rpm. All these engines can rev higher. But if they run here, they last forever. If they never exceed 2500 fpm, they will not have piston skirt issues- ever. Ford 300 @ 2500 fpm av piston speed= 3775 rpm. I promise you, you will never have a piston skirt issue with a properly maintained 300 kept under 4000 rpm.
An amazing longevity example- A 7740 cu in V12 2 cycle diesel (12V-645 GM Electromotive) in an 800 ton ferry boat: we cracked the valve covers and set valves and replaced injectors for the first time at 52,200 hours. that equates to 1.5 million miles @ 30 mph. At maximum governor speed the pistons move 1490 fpm.
Use stock rods and hypereutectic pistons in your 300. You will not be disappointed.
 

THE FRENCHTOWN FLYER

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... Reliability: Heavier pistons go with heavier crankshafts. In racing, the piston and rod mass is cut to a minimum, but engines built for hard-load durability, the mass of the rod and piston is matched to the crank. There is more stress on the rotating assembly with mis-matched light-weight rods and/or pistons, due to harmonics from a loss of balance. The lighter parts will rev up higher, and deliver more horsepower- but they will not live as long as balanced, heavy parts operating at the correct speed...
Truedat.
A forged 300 crankshaft weighs about 83 lbs. Those guys that run drags nationally and are getting between 600 - 700 HP out of them NA lighten the cranks up under 50 lbs. They get revved to 9K plus. They have to replace them, well, occasionally, and replace bearings even more frequently.
My forged cranks are knife edged and have the journals turned. That is the extent of their lightening. However, they last many seasons of use. I keep it under 7000 RPM.
 

Firepower354

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Several of the Ford Industrial/tractor engines used them as well as Y-blocks. I'd thought of using a set to run 351W Lightning 18cc hypers with the shallow ring grooves.

259409189_10226634177897480_8166941431629804316_n.jpg
 

InlineDave87

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Found another set of pistons that im not sure has been discussed before… looks like 1.816 CH and with a thick enough gasket i would guess there should be enough room to clear the cylinder head… these are cast 352 pistons, wonder if there is a set of hypers available for them… my scr calculator says compression could be 10.6:1 so maybe a dished set could yeild a very good compression ratio and maybe a more ideal quench?
 

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pmuller9

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Found another set of pistons that im not sure has been discussed before… looks like 1.816 CH and with a thick enough gasket i would guess there should be enough room to clear the cylinder head… these are cast 352 pistons, wonder if there is a set of hypers available for them… my scr calculator says compression could be 10.6:1 so maybe a dished set could yeild a very good compression ratio and maybe a more ideal quench?
The 352 pistons have been used before but required machining to get a low enough compression ratio for street use.
There are no hyper pistons for the 352 V8.

 

Dipstik86

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Truedat.
A forged 300 crankshaft weighs about 83 lbs. Those guys that run drags nationally and are getting between 600 - 700 HP out of them NA lighten the cranks up under 50 lbs. They get revved to 9K plus. They have to replace them, well, occasionally, and replace bearings even more frequently.
My forged cranks are knife edged and have the journals turned. That is the extent of their lightening. However, they last many seasons of use. I keep it under 7000 RPM.
Do u do your own knife edging?
 

THE FRENCHTOWN FLYER

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The gent who prepares my cranks does all the grinding, balancing, and knife edging.

There's not a lot of rocket science to it as far as I can tell. I've seen the counterweights shaped like a boat prow, and I've seen others ground to a wedge to deflect oil away from the rod path.
Of course after knife edging comes final balancing.
 
There's not a lot of rocket science to it as far as I can tell. I've seen the counterweights shaped like a boat prow,
If you're talking about a bulbous bow that seems like cargo culting.

Bulbous bows are optimized for specific speed ranges in a specific fluid (we can just think of the crankcase environment as a highly aerated fluid) and it takes a bunch of fancy math to make them work right (that math is probably just an add-on package for your CAD software these days) but it suffices to say that nobody is using that kind of design effectively without a whole bunch of hours in front of the computer.
 

CNC-Dude

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Arse_sideways, there is a photo in Leo's book that has a crank I lightened in one of our many 292 inline 6 drag engines. I was able to lighten those cranks between 10-12 pounds, including knife-edging, taking about a 1/2" of diameter off the counterweights and removing material from the front and rear sides of the rod cheeks. I'll see if I can snag a photo to post....
 
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CNC-Dude

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The newer version of Leo's book that I have changed the picture from the original one. This pic only shows the lightening done to the rod checks. But I turned the counterweights down a little over 1/2" and all the counterweights were knife edged on both the leading and trailing edges. Then all the remaining factory drill balance holes were welded up and the balancing began.
20211130_174703.jpg
 
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