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Piston milling question, My buddy is building a 497 BBF has crank, pistons, Zero deck'd block, and FMS aluminum SCJ heads. The problem is his pistons are 13.5 with his set-up. They have a .095 dome on the piston with valve cut-outs, can the dome be, milled off? The pistons have also been milled on the bottoms to remove excess weight. What is the minimum piston thickness, to safely run 10.5 compression? The application is a jet boat, the bore is (4.40) .080 over. Thanks in advance.
Sleek
ttt
Sleek, depending on the piston, the dome is probably hollow underneath and can't be milled much at all.
Min. thickness should come from mfgr, but I wouldn't go much less than .100 on top. Probably better to get the right pistons.
He milled one piston, it's still just shy of 1/4 in tick on top, probly more like 3/16. The bottom of the pistons were not hollow under the dome?? just had extra material where the valve reliefs were cut in. Just the milling from the bottom is the concern, as not to get too thin. Thanks
Sleek
Piston milling question, My buddy is building a 497 BBF has crank, pistons, Zero deck'd block, and FMS aluminum SCJ heads. The problem is his pistons are 13.5 with his set-up. They have a .095 dome on the piston with valve cut-outs...can the dome be milled off? The pistons have also been milled on the bottoms to remove excess weight. What is the minimum piston thickness, to safely run 10.5 compression? The application is a jet boat, the bore is (4.40) .080 over. Thanks in advance.
SleekHow are you coming up with 497 cubes? .080" over would be 4.44" bore by the way, not 4.40". Please reply with bore, stroke, and piston brand. We particularly need this info in order to calculate compression ratio, but I would like a piston brand and part number if you have it.
I am not aware of anyone making 460 slugs with hollow domes, but I know of a piston manufacturer that is playing with the hollow dome Chevy slugs by running a Ford program on them...for R&D purposes only. So unless I am mistaken, you will have solid dome pistons which you say are giving this engine 13.5:1. I'm guessing you might have a TRW with the peak of the dome already cut down from .400" to .095, or perhaps a custom pleateau-domed piston...custom made by Ross or Venolia or Diamond (much more likley than a TRW, since this motor is a stroker).
If you have a custom forged piston and it is made from 2618 forged aluminum, then you may weigh the piston before machining, whack the dome off, and then re-weigh. Every 2.81 grams of aluminum removed = 1 cc of dome removal. You can use this to recalculate your compression ratio.
With those heads, getting a 460 stroker down to 10.5:1 will require dished pistons. Converting a piston designed for dome into dish may be more re-engineering than might be acceptable. But I wouldn't assume anything until I know what the bore & stroke combo is in this engine...and the piston brand and part number. Get that info and your question may be more accurately answered.
LO
Thanks LakesOnly, I'll get this info straight, or maybe I'll get him to post it up. The deal is he bought a partial engine, the rods were sold off, the were GM based. He has everything but the rods. Your probly right on the bore, I might have heard wrong. Stay tuned... Sleek
You were right on the bore LO, it is 4.44 the pistons are JE, and the stroke is 4.00 and set=up for the chevy rods. The piston PN? unknown. As for the engine Displacement, He was told. it was a 497, but don't know for sure.
Where is the compresion cut-off for pump gas on Ford strokers? Trying to run on 92 octane fuel.
Sleek
You were right on the bore LO, it is 4.44 the pistons are JE, and the stroke is 4.00 and set=up for the chevy rods. The piston PN? unknown. As for the engine Displacement, He was told. it was a 497, but don't know for sure.
Where is the compresion cut-off for pump gas on Ford strokers? Trying to run on 92 octane fuel.
Sleek4.44 bore x 4.00 stroke is a 495 cubic inch motor. Neat package.
Are you sure this package had chevy rods? The reason I ask is because most strokers use an aftermarket rod that utilizes chevy rod journal dimensions, but not an actual chevy rod (exception: the old Lunati 514 stroker kit...NLA). If this motor actually had a chevy 6.535" rod in it, the peculiar thing is that the required piston pin height with your 4" stroke would be that of a production 460 piston...but of course the 460 piston pin diameter woudn't happen with the chevy rod.
So the smoke has not yet cleared and you still need to figure out what you have there. With what little info we have about this engine, it's tricky to speculate but I'd say these are your options:
Since you don't know what the pistons are, at least measure pin height and also confirm crank stroke. This way you can determine the length of rods needed. But if you go this route, those dome-tops cut down to flat-tops will give you about 12.3:1, and that won't work with pump gas.
If you indeed have a 2" stroke (with 2.200" journals) and a 10.300 square-decked block, and need pump gas compression, I'd recommend a 6.800" stroker rod and a set of, say, Probe 24cc dished pistons at 4.44" bore. These shelf pistons are available in a 1.52" compression height, and it would be mandatory to cut the top down to 1.50" (cut them down just .020"). The 4" stroke crank is not a common stroke for shelf parts these days, but lucky for you cutting a shelf piston down just .020" ain't no big deal and certainly wouldn't scare me away from a custom stroker deal, if I were looking at your motor to buy, for example. The 24cc piston dish (less .020") will put you at perhaps 10.6:1 compression ratio (I'm ballparkin' it since we don't know your combo for sure), and that is a good amount of compression to shoot for with pump gas and aluminum heads. Put the dome tops on ebay or sell them to me.
Of course, before you decide or do (or buy) anything, find out what you have in front of you to work with. What's the compression height of those pistons? What's the rod journal diameter of the crank? Stroke? Confirm these things and the rest is just a matter of combining the right parts.
LO
I will answer the simple question regarding piston thickness since the rest of the details are unclear. I would design the piston you speak for a marine application which is more for pleasure than drag race at .210" thick in the deck. Now depending on the variables such as forging material (probably 2618 if these parts are JE) this thickness could change between .180" and .230" for a naturally aspirated boat motor. If the thickness throughout the deck is between 3/16" and 1/4" as you described I wouldn't think twice about running them. If you can get me the JE job number I can tell you exact thicknesses and even do a quick stress analysis.
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