Please forgive me if this is in the wrong place. I am going to buy a set of 307 pistons for my upcoming build. All the ones that I see on ebay say the pin height is 1.655. If you look at GM archives they say the 307 has a pin height of 1.675 and the 250 height of 1.655. There are some NOS 307 pistons for sale part number 6271087. Does anyone know the actual pin height of these pistons? I would love to buy the Ross pistons that Tlowe sells but the budget says no. Thanks in advance for any info/comments. Jay 6155
Most aftermarket pistons are slightly shorter on the compression height to compensate for the rebuild processes such as overbore, head and block decking, etc...as to not let the compression or piston height to get out of control when its rebuilt.
I thought so. Enginetech even says that the sometimes take .010 off the top to make up for overbore ect. This would mean that NOS pistons would have a taller pin height. To me this means less or no decking of the block to get to "0" for quench and higher compression. Maybe I can get by with a small "clean up" cut on the block. Thanks CNC-Dude. Jay 6155
I see two types of cast replacement flat top pistons on Summit Racing, but they don't list the CC size for the valve reliefs. Anyone know what the CCs should be for 307 pistons?
Most SBC 4 valve relief pistons have a 4cc combined volume. Make sure that the pistons you select do not have the chamfer around the top edge of the pistons either.
The W295 and 1438 are for the Chevy 307 or 250, with a compression height of 1.655". The photo of each shows a chamfer.
The other two are for the Chevy 283 or 230, with a compression height of 1.780".
The W295 and 1438 are for the Chevy 307 or 250, with a compression height of 1.655". The photo of each shows a chamfer.
The other two are for the Chevy 283 or 230, with a compression height of 1.780".
Oh, I just searched by bore diameter. I wasn't looking at the other specs. So Summit doesn't offer anything piston-wise for 250cid owners. Anyone have an inexpensive source for replacement flat top 307 pistons?
I would suggest either Summit or Jeg's for the 307 pistons. I think that most of the 307 pistons sold in the last 10-20 years have probably been for 250's, I just can't see someone actually rebuilding a 307 on purpose.
Most of the guys I knew in high school with 307s just did top end rebuilds, anyone with a 307 block that was out to lunch would just replace it with the plentiful 350s.
Well Summit Racing only had those two Sealed Power pistons in their catalog which were chamfered. Jegs just has the same Sealed Power piston as Summit:
http://www.jegs.com/i/Sealed+Power/844/295P20/10002/-1I might be missing some in my search parameters, if anyone is able to find them please post a link.
Most SBC 4 valve relief pistons have a 4cc combined volume. Make sure that the pistons you select do not have the chamfer around the top edge of the pistons either.
What's the issue with the chamfer? Does it interfere with proper quench?
No, the chamfer is just really huge and kills a lot of compression off. It almost defeats the purpose of the flat top.
No, the chamfer is just really huge and kills a lot of compression off. It almost defeats the purpose of the flat top.
Ah, so it would be more than the 4cc for the valve reliefs. It's possible that the photo is not the actual 307 piston and may not have the chamfer.
I haven't had my head off yet to do some measurements on the factory head gasket, deck clearance or piston cc. When I play around with the compression calculator to try and achieve 8.1:1 SCR I assume 76cc chambers, .015" x3.875" gasket, .005" deck clearance and that comes up with a 16cc dished piston. Is that about right for the stock piston?
I have looked and looked and I can't find any 307 pistons that do not have the chamfer.(Unless you go to custom pistons like those made by Ross and others). From digging through GM archives it looks like the chamfer costs about .25 in lost compression in a 307. Has anyone actually measured in some way how many cc's that the chamfer adds.(Don't know how it would be done). This was done to reduce HC emisions in the early 70's. By the way,looking inside my 1980 truck 250 at the pistons they are also chamferd also. I have also seen 250 pistons advertised with .85 and.115 dish. How many cc,s are those dishes in the top of 250 pistons? Jay 6155
If you had an actual piston you could calculate the volume the chamfer was. I knew it was pretty substantial above and beyond the valve reliefs. The dish volume can also be calculated if you have some basic dimensions.
I am going to buy a cc test kit and check and post what the actual cc's of the chamber, stock piston ect really are. With a little math we should be able to figure out what volume the chamfer is and what it costs in compression. Even though my 1980 truck engine has a advertised compression of a blistering 8.25 to 1 I bet reality will be lower. Probably be lucky to break 8 to 1 in the real world. Jay 6155
Yeah, that's my plan too. CC the original head and pistons, measure deck clearance, and try to measure the compressed thickness of the factory head gasket, then share my baseline findings. That won't be until I get a new head, valve job, and clean up the casting a bit. As soon as it warms up, I'm going to check the factory cam and see what the ABDC and the rest of the opening closing points are. Then I'll not what the real starting point is on compression.
I got into this mess while trying to find pistons for my 153 4 cylinder build. Same combo as a 230. When I threw a 181 Mercruiser crank in the mix the 307 pistons came into play. The stock pistons were .050" down the bore. I got a few sets that should have worked but all came up shorter than expected. That could be the .010 discussed earlier as a rebuilder cushion. The chamfer on some are way more than the valve cuts and are more equal to the dishes. I go a set of tlowe's 250 pistons but still need to get them on the 181 rods so I can measure. Any way I have a couple of sets of rebuilder 307s for cheap.
I got into this mess while trying to find pistons for my 153 4 cylinder build. Same combo as a 230. When I threw a 181 Mercruiser crank in the mix the 307 pistons came into play. The stock pistons were .050" down the bore. I got a few sets that should have worked but all came up shorter than expected. That could be the .010 discussed earlier as a rebuilder cushion. The chamfer on some are way more than the valve cuts and are more equal to the dishes. I go a set of tlowe's 250 pistons but still need to get them on the 181 rods so I can measure. Any way I have a couple of sets of rebuilder 307s for cheap.
I got a lot of people on the NastyZ28.com forum asking me about my L6 Camaro, thinking of getting or doing something similar for an economical daily driver car and saving their V8 car for weekends or racing. But the 153cid sounds like it might be a good alternative for a daily driver. You can hook it up to a TH350 and I presume it fits on the same motor mounts as the V8/L6 with just a lot of space between the radiator and the pulleys. I should make that suggestion to them.
What are the specs for those pistons? Pin height,chamfer,make,ect Jay 6155
They came in some Chevy IIs. I wouldn't want one in a car heaver than that but a little '62 two door post with a built 4 cylinder would be fun. Probably not much savings in the build but different. Start with a 181 Mercruiser and you are already at 140 HP.
They came in some Chevy IIs. I wouldn't want one in a car heaver than that but a little '62 two door post with a built 4 cylinder would be fun. Probably not much savings in the build but different. Start with a 181 Mercruiser and you are already at 140 HP.
So something under 2800 lbs. Not even the early '70 to '74 2nd gens fall into that range. The early 3rd gen Camaros had a 4cyl option, but I'm not sure what engine that was, but I know they were lighter than the later 2nd gen Camaros.
Mine is going in a '26 Chevy roadster and my goal is as close to 1500 lbs as I can get.
Here are some pictures comparing 250 (dish) and 307 (valve cuts) pistons.
LINK 250 and stock pistons with 181 crank (3.60" stroke)
LINK 2Ross 250 from tlowe & stock 153
Wow! I have never seen even a picture of a 307 piston that only has 2 valve reliefs and a dish. I am talking about the first link. Did you measure how deep the dish was on both pistons? How far down the hole did each one sit? Are these the ones for sale? Very interesting. Jay 6155
I can try to measure it again when I get home. I in Hank's area right now. Those are in he 153 block with the 181 crank. the 181 has a 3.60 stroke which puts them .035 higher than a 250 would. The stock pistons with the 153 crank were .050 down the hole. It is the same stroke as the 230 at 3.25".
Thanks for checking when you get time. Please tell me if I am figuring the math correctly. The stock 153 piston sits down in the hole .050 with a 3.25 stroke. You swap in a 3.60 stroke 181 crank all other things being the same. 3.60-3.25=.350 increase in stroke. .350 divided by 2 (half of the stroke increase is at the top half at the bottom)gives a upward movement of the stock piston of .175. .175-.050 leaves the stock 153 piston sticking out of the hole .125. Just a tiny bit too much positive deck IMHO. So the next thing tried is a stock 250 piston. 3.6 -3.53=.070 half of which is .035. Do I understand this correctly? If I have the math correctly and if you can tell me where both the 250 and 307 pistons come from and take measurements I can tell where your 307 pistons will sit in my 250 block. Are the pistons oversize? I realize that this is old hat to a lot of people here but some of us (me) are trying to learn. Jay 6155
I think you have it. In the second group of pictures the one sticking out is the stock 153/230. The dished one is a 250. All my pistons are .040 over. What messed with me is that none of the ones I bought had the compression height advertised. I think now it is what CNC was saying about lowering the top .010" to allow for truing up the deck or head. I haven't been able to try the Ross flat top 250 because the pins have to be fitted. They are a little taller and I have high hopes for them. This project has been sitting too long. My goal is to have this engine running on a stand by the end of May. (20140)
Headed home tomorrow.
Looking at the first set of pictures, it seems that the 307 piston sits down in the bore more than the 250 piston. I guess we will know when they get measured. Do all of the 307 pistons that you want to get rid of look like the one in the picture? If they are like the pistons that I see around here, the 307 will have a pin height of 1.655 and the 250 will have a pin height of 1.640. That should make a .015 difference.(A little hard to see in a picture). To me at least, this is very interesting because I have heard as much about 307 pistons as I have the 194 head over the years. The wonderful thing about this site is sooner or later the facts come out and myths are dispelled. Jay 6155
The tough part of this site is that a lot of us are friends. Some of us actually know each other. Even the ones we disagree with are not our enemies and the groups don't stay the same. Facts are plentiful but truth is elusive.
Looking at the first set of pictures, it seems that the 307 piston sits down in the bore more than the 250 piston. I guess we will know when they get measured. Do all of the 307 pistons that you want to get rid of look like the one in the picture? If they are like the pistons that I see around here, the 307 will have a pin height of 1.655 and the 250 will have a pin height of 1.640. That should make a .015 difference.(A little hard to see in a picture). To me at least, this is very interesting because I have heard as much about 307 pistons as I have the 194 head over the years. The wonderful thing about this site is sooner or later the facts come out and myths are dispelled. Jay 6155
I thought the 307s were the only stock replacement flat top pistons for the 250cid? Does anyone else make a flat top cast replacement? I've only been able to find the stock dished pistons on Summit's site:
http://www.summitracing.com/search/Part-...ine-6-cylinder/
Beater,
Just put your nose to the grindstone and get to work. We all know your not getting any younger or will have more energy. Heck, that describes me!
The 307 pistons are not direct replacements. 250 pistons are made and sold.
They have just been a reliable choice of a cheap alternative piston choice.
Beater,
Just put your nose to the grindstone and get to work. We all know your not getting any younger or will have more energy. Heck, that describes me!
The 307 pistons are not direct replacements. 250 pistons are made and sold.
They have just been a reliable choice of a cheap alternative piston choice.
I've only been able to find cast flat tops for the 307cid V8. The cast pistons I've found for the 250cid L6 are all dished about 0.085" and chamfered. Are there flat top 250 replacement pistons?
No, just custom is the only way to get a flat top for the 250. That's why the 307 piston is such a popular swap, its cheap and not expensive like a custom piston is.
No, just custom is the only way to get a flat top for the 250. That's why the 307 piston is such a popular swap, its cheap and not expensive like a custom piston is.
Yeah, that's what I thought. It should still be an improvement in compression for the 307 flat top over the 250 dished, since both types of cast replacement pistons seem to be chamfered. It might be my only option when I decide to go the final step on my project and rebuild the short block and shoot for improved lower end durability and maximizing compression.
They came in some Chevy IIs. I wouldn't want one in a car heaver than that but a little '62 two door post with a built 4 cylinder would be fun. Probably not much savings in the build but different. Start with a 181 Mercruiser and you are already at 140 HP.
I put the 153 in my 47 CJ2A Jeep. The engine was carefully rebuilt ;.023 shim gasket to get quench at .043....steel tube header, modified distributor advance and rejetted stock carb.
The Jeep weighs about 2200 pounds, stock 5.13 gears, 4x4 and 3 speed. The engine runs great and the performance is better than the original 60 HP Red Devil flattie but just still adequate at best.
Maybe in a 2000 pound car with a 5 speed , hotter cam, more compression and carb you might have something until the next punk in a old 4 cylinder Interga blows ya off
Beater, I am very glad that people on this site are friends. People have disagreements all the time, After all there is just more than one way of doing things. I am sure that no one wants to willingly run an intergrated head but me. That just proves that I am crazy not unfreindly. If I have offended anyone please forgive me. Please tell me what brand those 307 pistons are.
intergrated j 78
You are not the only that has or does use that head but many cut both intake and exhaust off of it. And to the best of my understanding the factory built a small lump into the head. I never got my hands on one yet! to cut the intake & exhaust off one to see for sure. But anyway you can still clean the bowl and Some vary little but a little of the port over the short turn area.
Wow! I never thought of cutting a head like that. If I ever end up with a cracked one I will saw it and "see whats inside" Do you know which head was cut, 1 or 2bbl? Jay 6155
intergrated j 78
You are not the only that has or does use that head but many cut both intake and exhaust off of it. And to the best of my understanding the factory built a small lump into the head. I never got my hands on one yet! to cut the intake & exhaust off one to see for sure. But anyway you can still clean the bowl and Some vary little but a little of the port over the short turn area.
Wait, you literally mean there were people that cut the integrated intake manifold off the side of the head and machine the intake/exhaust face for use as a non integrated head?
YES and as to the 1 or 2b I don't think it mattered once they got done with it. Mind you most of these were used mostly for Racing.
YES and as to the 1 or 2b I don't think it mattered once they got done with it. Mind you most of these were used mostly for Racing.
I'm saving my integrated head now!
YES and as to the 1 or 2b I don't think it mattered once they got done with it. Mind you most of these were used mostly for Racing.
My understanding is that the integrated head with the intake portion cut off becomes a 12 port head, as the intakes ports aren't siamesed inside. The monojet head is restricted by the single barrel mounting point, but it does have a 2.25" exhaust manifold. So with a 2bbl with adapter, good valve job, increase in compression, basic street cam/springs, and 2.25" single exhaust it would still be a pretty good street engine. I think the 205 truck integrated head would be better yet with it's two barrel carb mount and the duel 2" exhaust outlet manifold. Nothing wrong with an integrated head for a daily driver street application.
OK. I stuck this on the other 307 piston thread. I get confused easily. I was doing this in response to Intergrated j 78's request.
OK, Here's what I got. My measurements are somewhat crude but should give you an idea. I used a caliper as well as I can. The 307 pistons are .040 over as marked on top. There is a dish and two valve cuts. The dish is 2.995-2.93 wide and .050 -.058 deep. Without the valve cuts that about 5.8cc to 6.4cc. That is probably a little bigger than the 250 dish but it does not have the hugh chamfer that the 250 and some other 307s have. The rim on top is about .045" wide and would give a nice quench area. To get the pin height I measured from the top of the pin hole to the top of the piston and added 1/2 of the pin diameter. The 307 measured 1.64856" -1.65365" and the 250 was 1.63875". It could be closer to the 1.655" advertised. So the 307 is roughly .010" taller with a more efficient design. I think it would help some but not a lot. The box they came in may not be the original box. It may be worth more a sports memorabilia than the pistons are worth. It says Zollnor and Fred Zollner was the founder of the team that became the Detroit Pistons. There is a hand written part number on the box. It is a Sealed Power number. 295 AP 40 is the one with 4 valve cuts. The rings are Sealed Power KromX. I mounted one to check it in the 153. The rest haven't been messed with. The pins are stuck from dried lube but will come right out with some degreaser.
I'm not in the piston business so if you want them I'll make you a good deal and there is no hurry they are not going anywhere till you know if you can use them.
Thank you for taking the time to measure those pistons for me. Everything that I have read about new 250 pistons either say that the dish is either .085 or .115 deep depending on brand of replacement pistons. The pin measurements match the published specs for both pistons. If I need to overbore I would be interested for sure. Maybe str8shooter will need them sooner. While the tools are out can you please tell me how deep the dish is on the 250 pistons that you have. Jay 6155
I'll do that tomorrow. I don't think the dish on the Silvolite 250 is that deep but we'll see. We'll see what you and Dan want to do.
Found this data in a Sealed Power catalog that can be helpful. It lists(2) pistons as replacements for the 250.
L2314F- C/H is 1.672,Flattop w/4 reliefs and a volume of -2.5cc and also a -.025" deck height.
L2396F- C/H is 1.655, .073" dish and chamfer with a volume of -11cc
The first one sounds interesting. In my 4 cylinder build that would be really close to zero deck and less expensive than the Ross pistons I got but also not forged if I go to the next step. Crap it's taking years to get to the first step.
CNC-Dude there are 2 of theL2314F pistons (std) on ebay for 39.99 each. They are forged. Napa,Autozone does not list them. I called my friend at Advanced auto parts It's a good number but they can't get them. Haven't checked anywhere else. I will let everyone know if I do find them at a different parts store. I looked on the sealed power web site and they don't show them either. (Maybe I am just not using the sealed power website the right way). Beater thanks in advance for checking the 250 piston for me. Jay 6155
Sorry, Long day and I didn't get out there. Get it as soon as I can.
No problem. I don't mind waiting at all. Jay 6155
Jay, What is going on with your build. Are you still waiting on me to measure something? I got lost. I made a test pin so I could check the height of my Ross pistons and they are perfect. In the pictures the Ross 250 is shown with the 307.
Beater, I waited until today because my Grandson was coming over and we could work on the engine together. Sometimes time with him is limited as I work and he is very busy. Today we tried to get the head off so I could check for bore wear and measure the stock pistons. We got as far as just the headbolts and dist left to go when we ran out of time. I could do this myself very quickly but that is not the point. He gets out of school soon and we may be able to go faster. I did find out that the exhaust manifold is cracked. Will take it to work and see if we can weld it as it has dual exhaust outlets. Those Ross pistons are purrrdy. Jay 6511
Beater, I waited until today because my Grandson was coming over and we could work on the engine together. Sometimes time with him is limited as I work and he is very busy. Today we tried to get the head off so I could check for bore wear and measure the stock pistons. We got as far as just the headbolts and dist left to go when we ran out of time. I could do this myself very quickly but that is not the point. He gets out of school soon and we may be able to go faster. I did find out that the exhaust manifold is cracked. Will take it to work and see if we can weld it as it has dual exhaust outlets. Those Ross pistons are purrrdy. Jay 6511
Damn the 2bbl integrated exhaust was cracked. That was one of the focal points of the project. Hope it welds up easy.
I probably have a extra. They usually go into the iron pile.