Spawne32

iTrader: (3)

So im a bit lost here as to how I should size the P2W with the replacement pistons. If you may or may not know, I had some light skirt wear that was progressive from #1 to #4 cylinders likely from some issues with leaky seats/guides causing the first cylinder to run hotter then the others. I was using 4032 forged aluminum (low expansion) supertech pistons, with short tapered skirts. I ditched the JRSC after the tear down and am going to run all motor for a period of time, with the potential to run a small turbo down the road.

However because I could not save the supertech pistons at price I deemed reasonable for what I have budget wise, i decided to go with a fall back set of YCP cast pistons of the same dome size/shape. However the YCP pistons are not tapered skirts, and have full size skirts as well. This seems to now be presenting itself with the new P2W clearances.

On the old supertech pistons with the skirt wear i was measuring up to .0050 on cylinder #1 and .0030 on cylinder #4, taking measurements from right around the middle of the skirt per supertech's recommendations, which is about the widest point.

However on the new pistons, measuring a half inch from the bottom of the skirt, im getting P2W's of between .0010-.0015, much tighter then with the supertech pistons.

Now from what I understand from reading about vitara D series builds using these pistons, most people recommend running stock P2W clearances as the service manual indicates, as they are designed to be "OEM replacement" pistons with a added teflon coating. However I have also been reading people running crazy P2W's with these anywhere from .0050 to .0080 for...what reason I have no idea.

So im trying to decide what is going to be too tight, and what is going to be too loose. Service limit from honda states .0020 to be the maximum for OEM cast pistons, with a range of anywhere from .0004 to .0016. Given the fact that these are T6 heat treated AC8A (336) cast, do I have to worry about thermal expansion as much as the other alloys? From all the research I have done thus far, the thermal expansion rates at 100C for 336 is 19.2% and 4032 is 19.4%.

wantboost

iTrader: (2)

Give me super techs and I fix ? :p

I don't remember anything about cast pistons anymore

Spawne32

iTrader: (3)

i was going to have them recoated at swaintech, but the turnaround time vs the cost, it was just cheaper to go back with heat treated cast. I probably will eventually have them fixed with the coats again and resell them or use them in another project, once im confident they are all uniform in size again.

rich7777

I'd get in contact with the company you purchased them off. All new pistons should come with a spec sheet with the piston to wall clearance on ideally. If they don't then you need to find it out.

Go with what the manufacturer/shop you brought them from recommends.

Spawne32

iTrader: (3)

No way im gonna be able to get an answer from YCP, I might be able to use RSmachines as a comparable piston to go by, as they are virtually the same thing. Only real info I have to go by as they are designed to be an OEM replacement, which means....OEM P2W's are recommended. But with the option of a turbo down the road, what range of OEM P2W should I be shooting for...closer to .0020? Or stay within the .0004-.0016 range?

blackeg

when i ran the cast vitaras i had set my ptw at .003 because i went 75.5mm. the motor ran 18ish psi around 250-275hp with no problems for the 12k miles i owned it. its still in the car today a few owners later has to have a good 50k miles. the outrageous ptw people run with vitaras comes into play when they go 75mm on just a rehone. the ptw is built into the pistons making them undersized so if u hone out a 75mm and the pistons are a bit under 75mm the tolerance gets big. since you currently have a tight tolerance of .001-.0015 you can open it up no probs without having to start over at a different bore.

build a motor too loose and only you know it with a bit of slap at cold start. build a motor too tight and everyone knows when it breaks. i remember hearing that a while back and am becoming a big believer in it.

Spawne32

iTrader: (3)

Where exactly are you folks measuring on the piston skirt for the P2W, supertech's guidelines for measuring were a bit wacky with the tapered skirt. My measurements would vary from .0070 to .0030.

h2.4

if you're gonna boost it later, I would set it .0022" .0025" range, assuming they have similar expansion rates at the vitaras. But you're gonna have some slap when it's cold. But usually will go away shortly.