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I think it's way too short.
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TRW used to and still might have available, both a dome and a flat top forged piston for the 250 with a compression height in the 1.675" range. It is possible that with the 6" H-beam rods that are available for the 250 today,that the LS piston shown could be made to work with a little block decking to adjust the deck height. That price listed seems pretty high. The engine builder price from Ross on a set of flat tops with a custom compression height is around $450 for a similar piston, if you like that brand, that way you could use the stock rod and not have to buy an aftermarket rod + the LS style pistons unless you wanted too. That way you could save the extra $$$$ and put it toward a nice street roller or something....
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CNC-Dude
we do not get engine builder price here.
If you can get some JE pistons (6) for $450 I am sure you could sell a lot of them here.
Or if you can get Ross pistons for these guys w/292's they would buy those also.
It seems the normal price I see is about $100 per piston.
That is why you see prople asking what rods can work w/a 292,because they do not want to spend the $$$ for the pistons.
MBHD
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I have mentioned before about the 292's in another thread, but no one responded. The problem with the 292's is that a flat top is the same price as the 250's at $450, but in a 292 it will give too much compression for a street engine. To get a dish piston in a 292 to give street type compression, unfortunately falls into the same price category as a dome piston...about $600 bucks. I don't have an engine builder account with any of them, but they will sell to anyone with a purchase of (5)sets, the engine builder price. The piston sets have to all be the same type,ie. dome, flat top or dish, but can be different bore sizes and compression heights and ring spacings if they are required, meaning they all (5)sets don't have to be the same in that regard....
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CNC Dude, " It is possible that with the 6" H-beam rods that are available for the 250 today,that the LS piston shown could be made to work with a little block decking to adjust the deck height",,
So w/a 6" rod,,it should work,correct?
Thanks.
It is not that hard to sink the valves & open the chambers to get a lower compression ratio.
Maybe in order to use a 292 flat top piston???
IIRC,my big chamber 250 cyl head was 72 cc's. I had sunk the valves, opened & unshroud the chambers to 82-84 range, cc's
I have SBC 307 TRW forged flat top pistons w/4 valve reliefs.
With a milled small chamber head I ran 12 to 1 compression,it had 220 cranking compression,then switched to the 82 cc head & had about 8.5 to 1 & used a Paxton super charger.
It was a good torquey engine w/12 to 1 compression & three DCOE 48 MM Webers. Fun to drive!
Ross forged 250 pistons are $450 for a set of 6 w/rings & pins?
If so, great price!!
MBHD
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This is not a chamber where I would sink valves to add volume.
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This is not a chamber where I would sink valves to add volume. Just curious,why??? Would you install a 2.15" intake valve? I did not sink the valves that much,most of the volume was from opening up the chambers,which unshrouds the valves & in turn flows better. Worked fine for me.It also flowed good. At the time I did this,, I did not want to buy pistons & go through my engine all over again. Just an option since it seems you cannot run flat top pistons in a 292 w/decent compression for the street. There are tuliped shaped valves (adds volume) & flat,, straight suface valves.
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This is not a chamber where I would sink valves to add volume. Just curious,why??? Would you install a 2.15" intake valve? Thats how you get the big flow #'s out of the "lump" heads we did....330 CFM+, I think I remembered you asking Twisted6 a while back what he thought was being done wrong or different with the #'s you were seeing with the bolt-in "lumps" in comparison, thats the difference, plus a lot bigger port. Needing to feed a 10,000+ RPM, super high compression race engine requires a little more extreme measures that an average street/strip engine....You wouldn't believe how much valve lift we were running if I told you either....
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CNC Dude, " It is possible that with the 6" H-beam rods that are available for the 250 today,that the LS piston shown could be made to work with a little block decking to adjust the deck height",,
So w/a 6" rod,,it should work,correct?
Thanks.
Ross forged 250 pistons are $450 for a set of 6 w/rings & pins?
If so, great price!!
MBHD Hey MDHD, just doing the math, you end up with about -.060 deck clearance(with the LS piston shown and a 6" rod), another post last week, a guy was asking if .040 was too much to deck off a 250, so if you feel that is safe(I think it would be), then that would be a pretty neat rotating assembly for not a lot of money. I also forgot about the Ross pistons including the rings with them to, so that is a pretty sweet deal considering....The H-beam rods are about $350 bucks if I am remembering correctly. Surely it wouldn't be hard to find (5)guys wanting to jump in and get some Ross' pistons to meet the engine builder price requirement.....or 292's or GMC's and 235's for that matter.
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Trying this again (what's with this, 'not recognised host' anyway???) Just out of curiosity, as I have never tried to order a set, but don't several piston manufacturers sell pistons with 'blank' crowns (ie unfinished). IIRC where I have read this it leaves the crown taller and with no valve reliefs. That would leave fly cutting the piston to final compression height and puting a chamfer on the edge of the crown. Or am I missing something? For that matter, if the crown is thick enough, you could carve a 'reverse dome' into it(I mean a dish the shape of the chamber in the head, it leaves the quench pads intact). I know alot of people won't understand why I ask, as this sounds like 'custom machine work' at the local machine shop (read as a big pile 'o $$$$) but I remember the air cooled VW crowd used to have tools you could do all of these things to a piston, and they were used in a common drill press (even said that's what they were for in the 'destructions'  ). Point being, we are working with similar materials (piston aluminum, forgings & castings) if you were going to try to do this kind of work, for the street, for yourself (I would expect a race team or proffesional shop to need faster production, as the tools looked like they would require a fair amount of setup for each operation) wouldn't it be worth it to look into tools like that? IIRC it didn't seem very expensive at the time (for the tools), maybe the price has gone up disproportionately? Maybe they are no longer available? Dunno, the people I knew with the catalogs with this stuff in it have moved away. 
My, what a steep learning curve. Erik II#5155
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CNC dude,
I understand why install a 2.15" valve. In my experience for a sreet engine that size valve is not too practicle,but for racing, yes.
A 2.15" valve is the physical limit for our size bores.
You also open up the chambers so much ,& mill the cyl head so much,sometimes they just fell apart. Fine for racing,for the street???
Not saying anything is wrong what you guys did, but most all the stuff that Cotton did seemed to be just for all out racing & not for a street engine..
You can use some info for a street engine,& not go so extreeme.
"Would you install a 2.15" intake valve?" Sure for racing,, w/an engine that you know will come apart shortly.
[/quote] Thats how you get the big flow #'s out of the "lump" heads we did....330 CFM+, I think I remembered you asking Twisted6 a while back what he thought was being done wrong or different with the #'s you were seeing with the bolt-in "lumps" in comparison, thats the difference, plus a lot bigger port. Needing to feed a 10,000+ RPM, super high compression race engine requires a little more extreme measures that an average street/strip engine....You wouldn't believe how much valve lift we were running if I told you either.... [/quote]
I am sure over 1"
MBHD
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Trying this again (what's with this, 'not recognised host' anyway???) Just out of curiosity, as I have never tried to order a set, but don't several piston manufacturers sell pistons with 'blank' crowns (ie unfinished). IIRC where I have read this it leaves the crown taller and with no valve reliefs. That would leave fly cutting the piston to final compression height and puting a chamfer on the edge of the crown. Or am I missing something? For that matter, if the crown is thick enough, you could carve a 'reverse dome' into it(I mean a dish the shape of the chamber in the head, it leaves the quench pads intact). I know alot of people won't understand why I ask, as this sounds like 'custom machine work' at the local machine shop (read as a big pile 'o $$$$) but I remember the air cooled VW crowd used to have tools you could do all of these things to a piston, and they were used in a common drill press (even said that's what they were for in the 'destructions' ). Point being, we are working with similar materials (piston aluminum, forgings & castings) if you were going to try to do this kind of work, for the street, for yourself (I would expect a race team or proffesional shop to need faster production, as the tools looked like they would require a fair amount of setup for each operation) wouldn't it be worth it to look into tools like that? IIRC it didn't seem very expensive at the time (for the tools), maybe the price has gone up disproportionately? Maybe they are no longer available? Dunno, the people I knew with the catalogs with this stuff in it have moved away.
MBHD
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There's no fixed rule as to when and why, but in general if you don't have .500" of 90° drop from the SSR to the lowest seat cut removing any of it (relocating the seat deeper, even if the new seat cuts are identical) reduces flow - even if the SSR is untouched. If the SSR is affected, much worse.
Whether the local pressure, bulk flow, make this very important or relatively not I can't say but the default opinion on sinking valves is "unless you know it's safe - don't".
Based on the cutaways of the 250 and 292 heads I've seen, there's nowhere near the desired .500".
Unshrouding the head in the chamber is (in general) good, but it's not the same effect, and should be done in any case. The exhaust valve, on the other hand, is frequently unshrouded either too much or in the wrong place (also adds chamber volume).
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Would you install a 2.15" intake valve?
If the bowl can be opened to the usual 85%, yes. Improves low lift-flow. Frequently taking off more metal also allows more radius in the turn (depends on the casting).
I agree - the math (adding .3 to the rod compensates for .3 less CD), and a 250 could probably stand being slowed up around TDC a bit.
I have a feeling that the valve reliefs on the LS don't match the 250 in size, placement or angle (you may luck out, and they're too big so no work needed, although minor compression drop).
I don't see any reason why a cup couldn't be added to an existing solid dome as long as the critical point (typically determined by the span of the dome over the pin bosses, position of valve cuts, blown or N/A, etc.) isn't below .210" or so.
The floor of the cup should be "flat" (90° to the stem axis) under the valves, but not a big deal. The sides can be done with a die grinder if you're careful.
Set up the piston in a mill vice, and the math is easy. Just mark out the area to be cut, typically 3/16" minimum away from the edge to prevent overheating, and matching the quench ledge, Now transfer to graph paper and guess the area. Area × depth = volume.
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Looking at some photos of 250 chambers - some of the intakes look really big, but no dims given.
If the chamber is already bore size (3.875" + O/S etc.) the valves are probably past the point of diminishing returns, as the near edge of the valve is really close to the chamber wall. That side simply won't flow anything, and (more important) also biases the direction leaving the port. Unless volume is really critical (1" valve, 500" motor) this looks like a case where the largest effective valve is perhaps whatever OD clears the bore edge by at least 1/2 valve lift.
I don't remember seeing it explorer but the current philosophy (Jon Kaase) is that the intake valve should be:
1. as close to the center of the bore as possible
2. as large as possible
3. the exhaust valve gets whatever is left
This means moving the guide, rocker stud, etc. over and pushing both valves towards the exhaust side - example only: move the intake 1/8" and the exhaust 3/16". This may not be possible since moving the port walls hits water, but you get the idea.
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"Would you install a 2.15" intake valve?" Sure for racing,, w/an engine that you know will come apart shortly.
MBHD The reference to installing that large a valve in these heads was only made, because in another post about head work, someone cautioned the person that installing intake valves larger than 1.84 would likely strike water. I was pointing out that we frequently and successfully installed valves that large and never hit water, and was just clarifying that point, and not suggesting that the user attempt to put those large a valves in his head, and even said that in the open remarks originally.
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Just out of curiosity, as I have never tried to order a set, but don't several piston manufacturers sell pistons with 'blank' crowns (ie unfinished). Nex, your are right, but most of the blanks still aren't thick enough in the crown area to make an adequately large enough dish for the 292's. The piston companies typically have (3)different style of piston forgings, dish, flat top and dome. Most dome forgings are of the hollow dome variety ,and just don't have enough mass on the underside to create a dish or pocket, and most of their flat tops are also too thin to allow for much of a dish or pocket to be created, the dish forgings are made specifically for this, and getting them in an unfinished form isn't feasible, because they can provide them to you finished cheaper than you can finish them yourself, and put whatever size dish in it you need for no extra charge as well, but they still cost as much as a dome piston. I think the perfect scenario would be a blank flat top with a real thick crown to allow you to custom tailor the dish to whatever specific volumn was needed for a particular application. Maybe we need to just go from A-Z on the piston manufacturers and see if any of them can provide us with this type blanks.... Even in blank form the dish and dome pistons are much more expensive than a flat top blank,so thats why I felt the thick flat top would be more cost effective in the end to try to find....
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I was wondering about that because I have heard of some pistons having really thick crowns, so you can cut crazy deep valve reliefs. I understand that the small thinner area of a valve relief isn't going to react the same as a larger carved out dish, but it was something I had to ask.
Thank you.
My, what a steep learning curve. Erik II#5155
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Many of the TRW forgings have very thick crowns and solid underneath.
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IIRC, I cut .100 out of the underside of my TRW 307 pistons,just to lighten them up.
They are thick,,, I have used Nitrous ,then switched to a supercharger,no problems.
MBHD
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I was thinking TRW, thank you. 
Last edited by Nexxussian; 04/10/09 02:08 AM. Reason: smileys didn't stick
My, what a steep learning curve. Erik II#5155
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An LS1 piston for stock LS1 rods has a slightly higher deck height at 1.34 than the one you referenced earlier. With a 6" rod that puts you at 9.105, which is within decking range. Although those JE pistons were 100 apiece sold individually, which is what you guys were quoting for custom pistons, so maybe you aren't buying yourselves anything here.
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"Overkill is underrated."
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Any concerns with the short piston skirts of the LS1 pistons? Some LS1 engines had piston slap during warm up and oil consumption, due to excessive piston ring movement in the piston grooves caused by the piston rocking in the cylinder. The pistons were made of hypereutectic aluminum alloy. Very tight piston to cylinder wall clearances are required with the LS1 piston to prevent issues, tighter than for standard eutectic pistons. Why run a piston on the edge of the design requirements unless necessary? Any one make LS1 pistons with a slightly longer skirt?
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CP pistons has several LS forgings available... The three brothers that run it all were previously at JE for many years each, so they might not be as well known of a brand, but they came from the best, and are very sharp. "Snake" is the brother to contact at CP, he can advise you on any issue regarding the skirt design or any other for that matter....
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i think another thing to consider for the ls pistons. the ls engine was designed to have every cylinder be identical. therefor the intake vale notch could be in the wrong place with every other cylinder if used in our engines.
does that nmake sense. tom
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No, not really, the 307 4 valve relievs are not made for our engines either. wrong angle, SBC 23 degrees as to our inlines like 15 or 18 degrees???
Plus the valves are of different spacing between the intake & exhaust.
When I checked for piston to valve clearance ( Chevy 250)on a cam I ran w/.585 lift, & 248 degrees duration @ .050 I had a mile of clearance, really not even close.
I never ran a cam w/huge lifts or big overlap, so I really do not know when the valves would get close to the pistons???
CNC Dude,Twisted6? Chime in. :-)
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You would also possibly have to correct the valve location as well, and not assume the ones that were the same I-E configuration have the same valve centerline and position on the piston as the 250/292 head has. This is where a true flat top piston with no valve pockets at all would be nice, you can just put your own reliefs in there. When you are degreeing your cam and checking P/V, you will have to center punch (2)pistons to get one for each orientation. You might get lucky and not have to cut any at all either....
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