For my Chevy 250; the block is at the machine shop - on Monday they are going to tell me the size pistons I need to order.
This is going into my daily driver. My biggest concern are gas mileage and reliability.
Are 307 pistons worth the extra money over the 250 pistons, in terms of the additional low end torque I might gain with the compression bump? I think I can get the 307 pistons for about $40 bucks more than the 250 pistons.
Also, what brand rings do people like? For this engine I want trouble free miles...
Dan
I agree with Hank, you can't beat that price including the rings.
I called the store in MBHD's first link and was told that those pistons also had a chamfer around the edge.The photo sure doesn't look like it to me. If I have to go overbore those are the pistons that I am going to get. You can't beat that price! Even if the pin height is the same (1.655) you get rid of the dish in the 250 piston. Jay 6155
I'm back home. I'll dig the 307 set out today and get you the measurements. I know they are .040" over but I can beat that price! They do have a dish but not as deep as the 250 and only 2 valve cuts. There is no Chamfer and they are a bit taller than the 250s.
Here's the reason I'm asking - I did this little scenario to show an example. I think these are conservative estimates.
I drive 45 miles per day, 5 days per week, 48 weeks per year. That's a total of 10,800 miles.
I figured the price of gas to be an "average" of $3.42 per gallon for 87 octane.
If I were to get an average of 18.1 MPG with the 250 pistons I would spend $2038.32 per year in fuel.
If I were to get an average of 18.25 MPG with the 307 pistons I would spend $2032.89 per year in fuel.
The total savings after one year would be $14.43.
That isn't very much savings.
Now the 307 pistons may still be worth it...but if I have to pay around $40 more for the 307 pistons, will I even notice a difference?
Now the $40 isn't that important to me, but I have other things to spend money on as well, like potentially an intake (I only have the stock intake now), an aftermarket cam, maybe an upgraded carb like the Weber 2bbl, or even better a Megasquirt with throttle body injection (I've already successfully run megasquirt on a motorcycle).
Since I haven't driven a chevy 250 before and after a piston upgrade, I have no way of knowing how much of an upgrade this would be. I could get my block decked to improve my quench, and that would probably cost me $80 bucks. Would that be a bigger bang for the buck?
Dan
Beater ,thanks in advance for the measurements of the 250 and 307 pistons. Can you, if possible, also post what the compression height of the pistons from the box or sheet that came with them? Do you have more than 1 set for sale? I won't know if I really have to overbore until I get the engine apart. I understand that they might be sold before then and am fine with that. Str8shooter, I think that they would be worth it because the 307 pistons get you closer to 0 deck that you need for good Quench maybe not have to deck the block at all. Also there has got to be SOME increase in compression by getting rid of the dish in the 250 piston that is big enough to fill with water and scuba dive in. Jay 6155
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 havent 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.
So all the pistons are the same, and the rings fit them?
And its a set of 8?
Can you post a picture?
How much?
Dan
I posted this in response to Inrergrated's request but I should have done it on the other 307 piston thread . Sorry. I don't want to make a mess.
Yes the pistons are all the same and it is a set of 8. I guess this part should be on the Swap Meet forum or in a PM.
It's the one with the valve cuts.
LINK
I just wanted to update this thread now that I have the pistons in. These are the Silv-o-lite 307 pistons that I ordered.
I only measured one hole, but it looks like these pistons are .030 down in the hole. I do not believe that my deck has ever been machined, fyi.
I don't remember how far down the factory 250 pistons are for comparison.
Dan
ON ALL MY .040 ENGINES I HAD TO GO TO A H/D RADIATOR TO KEEP T COOL ENOUGH. JUST FYI
Can you post a picture of the pistons? Where did you get them? Thanks in advance Jay 6155
My 250 is .040 over with 307's and zero deck and .040 off the head. I have a 2 core Superior aluminum radiator with air here in this Texas heat with no problems...
Are those 2 fans in front of the rad the only fans that you are using? Looks like a very nice setup to me. Jay 6155
I use one electric fan on my 65 Wagon with a 250. 3 small ones on the turbo 292 Elco.
Two 10 inch fans do the job.. Had a big one till i added the ac cond. then the hood latch got in the way...