Just looking for those with experience with non sleeved, forged builds setup up for moderate to high boost applications -> more specifically 15-20 psi on a APS/Greddy TT type setup. what type of piston to wall clearances do you run?

2.5?
3?
3.5?
more?

Also, what are your experiences with running a slightly looser than normal motor?
More power?
Less Power?
Less life expectancy?
Longer life expectancy?

 

give away my secrets??? hehehe


it depends on A LOT of things, materials of pistons, if nitrous will ever be ran on it, boost levels, cars applications (track, drag, ect)

i would talk to your local machine shop that will be doing your work...

 

more power with shorter life ,pistons tend to rock in bore.piston clearance isnt the only factor in how tight or loose an engine is..the definition of a loose motor is usually being at the maximum allowable clearance in several areas in an attempt to reduce friction

 

Stock bore pistons were used on my first engine build , and the cyl. walls were just cleaned up . So I would think the wall clearances were on the edge of being exceptable . I had piston slap so bad that it sounded like a diesel engine even after it warmed up all the way . It got better , but still was noticable

 

You have PM.


Go-Fast,
at this point, in terms of how loose or tight, I am only concerned with piston to wall clearances.

 

Stock bore is one thing, but were the cylinders mic'd and spec'd to a given clearance? I too have stock bores in my car right now, but the cylinder walls were taken to a given clearance. I wouldn't say my car has excessive piston slap, but it is audible to those that know what to listen for

 

That is something I left up to my machinist, pick/talk to one that not only does machining but actually has experience with the use of the engines, mine does engines for race teams so I deferred to him on that stuff. Another area to look also is the bearing clearances.

 

You should follow the piston manufactures recommended piston to wall clearnaces. Every piston type will have a slightly different clearanced, based on the bore size, the material used, etc..etc.

What pistons are you using?

 

at this point, I plan on going with arias ED pistons

 

.004-.005 and it will also be listed on the job card.

Too tight, and you will skuff the piston skirts and damage your cylinder walls. Too loose, and the engine will be noisy, and the pistons will not last as long, due to the rocking in the bores.

 

+1 on what sharif said. you can take a couple other things into account also of how the motor will be used. if you are just using it for street (bottom of spec on clearance) or hitting a road course (upper end of clearance) most every piston will come with a recommended clearance card and list weights too (if it is a higher quality one)
all that being said, i don't remember the actual numbers right now, lol.

 

Why not let GRD worry about all of that stuff?

 

Dont forget piston ring end gap, this too is VERY critical with higher HP. Too little end gap and as the rings heat up and expand the ends will touch and cause the ring to press hard against the cylinder wall and this can cause a ring land to crack as the piston moves and the ring drags. Call your piston/ring manufacture and tell them your target HP and type of power adders. Any time you add nitrous they end gaps get much bigger. IIRC on my built VQ35 for my Maxima, CP Pistons recomended end gaps of .021. I was shooting for 600 crank hp using boost and a 100shot of nitrous. Normal end gaps were .017 I think for the low compression CP pistons.

 

complicated - 400 miles between us, adds another variable to the mix. We will see, they may be the ones to go through it, but not sure at this point. I want to talk to a local machine shop and see what I have for options

 

There's always BuiltZmotors or GTM

I'd let them do the worrying, and just swap their motor right in. Just my opinion though.

 

there are too many variables for a universal answer,but you can narrow your needs down by knowing silicon content of piston ,intended use ,how much piston slap (noise) is acceptable and how long you plan on running the engine before its next tear down.

 

My engine has some piston slap with Arias ED Pistons. It also uses some oil due to loose clearances. About .5 to 1 quart every 3000 miles depending on how hard i drive it.

 

Those are two vary viable options, but really the motor is fine. I most likely could get away with dropping in a single piston. I can still see the cross-hatches on the cylinder walls. That said, I think I am going to opt to put in a set of ED pistons since the motor is apart. I am just trying to get a feel for things with this thread if I take it to a local machine shop so I have a frame of reference to talk about it with them.

Everything in the motor looks mint. rod bearings, rods, cylinder walls, just one f^cked up piston with broken ringlands. If I were 10 minutes from any of these shops, I wouldn't even be posting about it, but the reality is, I am hundreds of miles away. I have a local guy I trust to assemble it, but he wanted me to look into clearances before we went any further

 

I would like the engine to last as long as the turbos - so 80-100K miles if that is realistic

 

Follow the piston to wall spec sheet that comes wit the box.

Nobody knows the piston and the specs/properties of the forge itself better than the manufacturer. A very knowledgable machine shop comes second < VERY important factor. Somebody who deals with nissan motors very often.