Piston massaging

Since we know the importance of an efficient head combustion chamber, as I see these pistons I can’t help but notice how much the air is going to bounce around due to the shape of this piston. Anyone ever smooth out the hard turns and sharp edges of this piston? Any idea how much it would affect the compression?

I am not an expert, but I would be more worried about the pistons being installed with the valve pockets on the wrong side.


Joe

You know I just picked up this car and pulled the engine out to see what was all inside. I hadn’t even noticed that yet. Wow haha thanks for catching that. Lol this is getting more interesting by the minute. Decided to pull the cam out to identify and found the crank had a ridiculous amount of end play. Pulled the engine out and found the crank side journal wiped out along with cam bearings. Obviously I will now have to go through the whole engine. That situation kept me so side tracked I didn’t notice the pistons. Oh well. Thanks again 👍🏼

Still interested on piston smoothing feedback

In a low compression N/A engine, it's not going to be an issue.

If it was a small chamber head, with a domed piston, I'd be wanting to remove any possible sharp edges and possible pre-ignition points. If it was an engine with several stages of nitrous, I'd be looking at enlarging the compressed area, to slow down the flame front.

A dished piston down the hole, with a factory chamber isn't going to encounter such issues.

Looks like there is 4 valve reliefs so they could be installed either way. I would have put em in the other way but it looks like they were made to go either direction.

Those are 2355 pistons, correct? Someone put a “D” dish in them

Softening the pistons and chambers is more for power adder combos, or very hi compression. You have neither so no need

I was just going to post that. Although I have seen TRW replacement forged pistons with two different configs from TRW. Can the OP tell a bit more of the history of that motor or what the car was used for?

The plan is to install some aluminum heads, get compression between 9.5-10.0. Install a 22X-23Xish cam and a 6bbl setup. With that being said, Would CR close to 10:1 warrant the need for removal of sharp edges? Honestly it’s something I’ve always done even if it’s just the very sharp edges but the face of this piston really surprised me. Terrible design IMO.



To answer the question of history of the engine, it is all unknown to me, I bought the car a few months ago and I felt it was overcammed, Removed cam to identify and pick something more to my liking and began to find multiple issues.

Do it if it makes you feel better, it's your time.

Is it going to make a noticable difference? No...

If you had 15 or 16:1, then it would be a must

I shoot for between 10.530 to 10.80 to 1 compression ratio on my non ethanol 91/93 octane pump gas BB builds with aluminum heads, that has work very well for me and my customers

Thanks for the advice unfortunately I have no access to non ethanol in my area.

they might work a lot better if they weren't installed upside down,.... . piston/rod assembly as a unit may be in backwards. i'd check for possible bearing/crank damage.

I think that was an old Dick Landy technique? It was said to make a little bit more power. I would be worried about bending valves/pushrods.

The pistons may actually be installed "correctly". The arrow pointing "front" does appear to be pointing to the front of the engine, if that's the engine stand I see on the right side of the pic.
Someone modified those L2355 "six pack" pistons by milling a dish in them...they are normally a 4 valve relief design. I've never seen a dish like that on the "top" side of the piston before, that would ruin any quench you may have had. It's possible whoever machined the pistons put the dish on the wrong side of 4 of them.
It really won't hurt anything, just not the normal way of doing it.

Thanks for the insight as far as why they may be that way. I agree, the surface shape totally messed with the quench, You are correct the pistons are facing the correct way in the engine. No idea what the thinking was behind this but what began as a quick cam correction is snowballing into a full blown overhaul.

I got way too many projects to add to my list LOL oh well, here we go!

If there are any boating areas around you check gas stations in that area for non ethanol gas.

Depending on the size of the dish, getting a lot of compression might be “difficult”…. Wouldn’t it be “better” if the dish was underneath the spark plug and the quench pad matched up with the chamber?

the pistons are just plain in upside down, peroid! i use a icon 836 with the same basic configuration, but installed correctly, and combined with an edelbrock rpm head is the best burning big block i've ever had. just a case of someone messing with something that has no business messing.

The pistons can be swapped side to side, which will properly orient the dish and quench areas so there could actually be some benefit when swapping to closed chamber heads.
The arrow would then be pointing towards the rear........ which some claim is beneficial as well.

This ^^^^^
Does that trw piston have an offset pin? It's been decades since I looked at one but i don't think it is offset. I would put them with the dish facing the chamber and call it done.

I don't know what the compression might be without knowing the deck ht. and the volumes of the dish, chamber and head gasket.

The valve relief depth show the valve stems inclined toward the exhaust side: wrong.

The dish was machined in those pistons after they were bought. When new, those pistons are flattops w/ 4 valve reliefs allowing them to be installed on either bank. You can see the remnants of the other two reliefs on the dished side.

If all 8 pistons had the dish cut the same way, then 4 of them will appear to be installed incorrectly if the directional arrow is pointing to the front.
The other bank may have the dish in the correct orientation.

One thing to remember is the piston is running away from the intake valve on the intake stroke, and then during the compression stroke some turbulence is good to keep the air fuel mixture mixed up. The reasons for quench pads on pistons and a quench area on closed chambered heads. I guess it must work as I don't know of and aftermarket wedge heads without a quench area in the chamber.

I always soften sharp edges. Smoother is better. Eliminate potential hot spots. Verify the extended tip plug isn't crowded.

If the cam, and especially the overlap window area, is smaller than optimum, radiusing & blending those sharp edges is helpful as it makes flow through the chamber more efficient.
If the cam is too big: leave it along.
Large chamber + low static CR: don't bother.

Ethanol in the fuel makes the fuel act like it has higher octane than it really does, compression can go higher with ethanol, the only concern could be fuel system corrosion but in nearly 20 years I have never had an issue running old fuel system components even my experiment with a bunch of parts and pieces in a sealed up peanut butter jar has not shown any degradation of the parts. It needs access to the atmosphere for extended periods of time to absorb moisture and that is what causes corrosion.

As for messaging the pistons I always round off all the sharp edges, you never know when you might get a bad batch of fuel or maybe they are out of premium and you got to run low grade in a pinch or the fuel delivery guy acidently put some diesel fuel in the tank in the ground, maybe you decide later on down the road to put some smaller chamber heads on and the work is already done without disassembling the short block or... it is just cheap/free insurance.