which pistons can (should) be used

[blueovalz]

Do any of our Ford guys know the differences between pistons for the different 302 SBFs? I believe I have some mid '80s flat tops in my late '60s 302, and it seemed the top of the piston is flush with the deck (which I like), whereas the normal piston for this engine was about .050 shy of the deck at TDC. To make a long question short, which is the best year piston to use (J302 heads).

[Guest Anonymous]

Don't the Keith Black, Speed Pro, etc. hypereutectics have better deck heights than the Ford or rebuilder pistons? I have read that this is the case. But, I will admit that I haven't tried this myself.

 

Any aftermarket hyper pistons would be cheaper than going to your local Ford parts guy (at least where I live!).

 

You could always deck the block, I suppose. That might mean remachining your manifold, depending on how much was removed from the decks.

 

What kind of cr are you shooting for?

 

GrinZ

[blueovalz]

All I really want is a plain old forged flat-top, but some from TRW have them split depending on years. The valve reliefs are different in the photos, etc. But compression ratio is still going to be about 10:1 with these heads (supposedly they are the same size as the early 289 heads (58cc???). I wonder about the hypers. Whats the story on this material. I've read very little about these pistons (cheaper than forged, but more expensive than cast).

[Guest Anonymous]

The hypereutectics are made of a higher strength aluminum alloy than regular cast pistons and are durable enough for just about any naturally aspirated engine application. You'd need to be doing something with very high cr or be turning a zillion revs to cause one to fail. And, they can be run with tight cylinder bore clearance than forgings.

 

They are not the best choice for nitrous or blower duty. If that's the game plan, go forged.

 

GrinZ

[BLKMGK]

What GrinZ said is about right. Fine for NA apps but do NOT run NOS withthem or a blower. They're harder and more brittle and if you experience knock you will have problems that you will NOT enjoy. Check the piston weights on the pistons you're looking at - the TRWs are reportedly heavy so be careful.

 

As for picking a piston from an OEM perspective - the 87-mid92 (think that was the ending year, Ford lied about the switchover so don't believe them) pistons in the HO apps were forged. They used low tension oil rings though so make sure you could use something else. These may also be a bit heavy and the valve cuts might not match your application. They hold up better than the OEM hyper pistons in blower and NOS use (ahem).

[blueovalz]

Thanks for the input. By the way, these "hyper" pistons. Are they in reality a cast piston that has had some forging done on it during its manufacture?

[BLKMGK]

Okay - someone double check me but I think this is how th ethree processes are done:

 

1) Cast - Pour into mold, let cool, tool.

2) Hyper - Pour into mold, strike the mold, cool, tool.

3) Forged - Cold blank is struck with great force to produce the desired shape, cool, tool.

 

Look at Probe forged pistons. I believe you'll find them to be good quality. This is what many of the Ford guys here run if memory serves.

[Dp351zcar]

the hypereutectic pistons have a higher silicon content. They are cast and not forged. That is about all I think I know them.

 

[ October 05, 2001: Message edited by: Dp351zcar ]

[Guest Anonymous]

Yup, hyper's are cast pistons. It's just that what they are cast from is superior to regular cast pistons.

 

GrinZ

[BLKMGK]

Some info -> http://www.parttrackers.com/library/1/8/12/

 

I'm not seeing anything on KB's site about them being cast or forged in some manner but I'm thinking that they ARE indeed just cast with a different material. Hrm, I think I may like them less What process pours molten metal into a mold and strikes it? Is THAT how forging is done? Oy, going to have to speak to a friend of mine who's big into turbos, is an engineer, and shoudl now for sure. Heh, we were looking into what it would take to make a smelt not long ago

 

Hrm, an interesting link. Scroll down to the comments on KB Hyper pistons - same experiences I've heard about! -> http://asa1000.com/Sucks.htm

 

[ October 07, 2001: Message edited by: BLKMGK ]

[Guest Anonymous]

I'm no engineer, but I slept at a Holiday Express last night!

 

Basically, forgings are castings that are formed under pressure. A billet of cast material is worked under pressure until certain mechanical properties are obtained.

 

This can be from rolling, pounding with really big hammers (as in many tons), or anything which upsets the material enough to work harden the metal and align it's grain structure in a consistent direction.

 

That's what makes a cast plug into a forged piston. It is literally pounded into shape in a die until the grain structure of the material is aligned to give favorable mechanical properties (like making it stronger).

 

The word hypereutectic has to do with the reactions of the alloy to heating in it's liquid stage. High silicon alloy aluminum is all most of us need to understand.

 

Whew! I just hurt my brain. Slide-rulers can correct any nuances that I forgot.

 

GrinZ

[Guest tom sixbey]

i know that for certain year models, ford actually used TRW forged pistons in some of the 302's. i couldnt tell you the year models, but i read it in a 5.0 magazine the other day. - it must have been during the "good" years 5.0's - (88-92?)

 

in 1986 and possibly some other years (if i remember correctly) the pistons were cast flat tops, and would build great compression on a late motel head swap. i had a friend with such a motor, and it was tearing up 94 cobra motors all day long with nothing but the head swap - however the fact that they were cast pistons eliminated the possibility of using forced induction...

 

my memory on the subject is very sketchy, so correct me if i'm wrong on any of this...

[74_5.0L_Z]

I know for certain that the 1987 - 1989 5.0 engine came with TRW forged pistons. They are four valve relief with a small dish. They were rated at 9.2 to 1 compression when used with 60 cc combustion chamber heads. I have these pistons in my 1989 5.0.

[Kevin Shasteen]

Ok, this is the skinny on Hypereutectic pistons per David Vizard's book "Vol 1/How To Build HP"...cant believe I actually found this book as it was the first Hi.Perf. book I bought & has a copywrite date of 1990(!) Wow, almost 12 years already gone since then-where'ld the time go?

 

Anyway: Hyper-Eutectic pistons were pioneered in England & as of 1990 were being mfg'd both in England & America. They're called Hyper-Eutectic because of their mfg'ing process.

 

Hyper: Material that is cast at a higher temperature (than normal piston casting temp's)....and,

 

Eutectic: means melting point

 

So, in other words-they are cast at a higher melting point. Their hardness is due to the material used & the higher heat treatment process which results in a piston that is cast yet contracts/retracts similar to a forged piston.

 

The minimal expansion rate of the Hyper-Eutectic pistons allows for a tighter piston skirt clearance which means a tigher piston fit in the cylinder. Vizard claims the tolerance of .0022-.0030inch Piston/Cylinder clearances.

 

The tighter piston fit also translates into less piston slap & on a Hi.Perf. engine also means a quieter engine on the street (less muffling) due to lesser blow-by.

 

Vizard claims (at the time of this book/1990) his experiences were such that a Hyper-Eutectic piston can be used in engines where the HP/Cubic Inch ratio DOES NOT exceed 1.1hp/cu.in. He also says that Hyper pistons work great on all 4cyl's under 100 cu.in's upto 1.5hp/cu.in's.

 

I believe the time Vizard wrote this book KB Pistons Mfg was just beginning to come on strong. I do believe that KB is the leader in Hyper-Eutectic pistons.

 

Kevin,

(Yea,Still an Inliner)