Have a spare K24 block sitting in my garage. Trying to put it together for super cheap, that means honing it myself. Mic'd the pistons that came out of the engine and then measured the cylinders with a dial bore. The cylinders are a little out of round as they usually seem to be, and the sizes I got are on the absolute loose side of the factory tolerances as far as what the piston to wall is.

I have never ran a set of these pistons, but hear good things about them. I asked the seller of these pistons what a set of 87mm pistons typically measure out as. He told me that .0025" p2w clearance would be fine with these things and that they do expand a little. He also said that the clearance is built into the piston.

Someone with some experience with these things give me some info. Want to slap something together to put back into my car so I can drive it and do it for cheap I just don't have any experience with Nippon Racing Pistons.

 

https://honda-tech.com/honda-prelude...stons-3172361/ i heard alot of mixed reviews about them so i went ahead and bought a set. this was the end result for me. so from my experience go with oem or forged pistons

 

However, if the clearance is built into the piston, then that means they might actually be smaller than a true 87mm. Would they end up measuring smaller than a stock piston?

 

So no input on the .0025" clearance the guy said would be alright with these things?

Brand new stock should range between .0008 - .0016" and like I said the stock suggested service limit is .002".

 

People are usually going to lean toward the loose side to avoid black death of the piston. This is fairly hard to do on oe type cast pistons. If you are looking for a long lasting high quality rebuild then keep it on the tight side. If you start out loose the don't expect 150k miles before it gets tired. A home hone job is also not preferred because this will not eliminate the taper wear on the cylinder and is generally not the quality cylinder prep comparable to good machine shop equipment.

 

I was taught two thing when it came to setting piston to wall clearance: piston metallurgy and power output will determine clearances.

I am no engineer here, but I would be willing to bet the NPR pistons have a slightly different alloy content than an OE Honda piston.

I would be most concerned with taper and out of round as they would definitely limit reliability.

 

OP, I understand you maybe on a budget, but if you already have the block apart you may want to get better pistons.

The RS machine are a bit better and have larger valve reliefs in the case you'd like to run larger cams at a later date.

Also:

https://honda-tech.com/forced-induct...rance-2904081/


http://www.theoldone.com/articles/en...ata_sheet.html


Another good read:

https://honda-tech.com/all-motor-nat...stons-2721867/

 

im sure you can run .0025 with not immediate issues, but it may not last forever.

last year i daily drove an lsvtec (around 180-190whp) with nippon pistons at .0015. the skirts looked great very little wear certainly nothing abnormal. highest egt that motor saw was around 750C. id still be driving it today if i didnt suck some **** into the engine and scratch the cyl wall..

personally i try and set them up right between max normal spec and the service limit according to the helms

 

This engine is being thrown together with whatever parts I have in my garage. I don't have a decent set of pistons so this is basically my cheapest option. I don't plan on the engine running forever and as a matter of fact the car is not driven that much. I parted the setup that was in the car out, and was just looking for a quick option. I just do not have any experience with these Nippon pistons and thats the reason I asked.

The last shortblock I built should be sold this weekend and I am also getting a set of TSX rods in that deal. May end up doing the 87.5mm bore and letting the machine shop straighten the cylinders out better for those pistons.

As far as taper, that part is actually within factory spec because there is not a lot of taper between the top of the cylinder and the bottom. It's just the actual cylinder size is a little larger and therefore the p2w would be a little looser. Also, the cylinders are a little egg shaped as they often get. This engine/block was from a low mileage CRX, I am actually surprised on the measurements I got from it.