i just dropped my motor off at the machine shop and told them i wanted my motor bored from 84 to 84.5mm for my new pistons. my question is that should i get it bored out a little bit more and run looser clearance. i'm lookin to make 500-600 hp on a 35r and read in a few former threads that it may be a good idea to run a looser clearance to due heat expansion or something. does anyone have any insight on this?

 

IT'S ALWAY BETTER TO GO LOOSE FOR TURBO...BUT DEPENDING ON WHAT KIND OF PISTON U ARE USING.. IF FORGED PISTONS LIKE WISECO OR CP PISTONS, I WOULD WANT AT LEAST .040-.045 ON THE PISTON TO WALL

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by b20vtech &raquo;</TD></TR><TR><TD CLASS="quote">IT'S ALWAY BETTER TO GO LOOSE FOR TURBO...BUT DEPENDING ON WHAT KIND OF PISTON U ARE USING.. IF FORGED PISTONS LIKE WISECO OR CP PISTONS, I WOULD WANT AT LEAST .040-.045 ON THE PISTON TO WALL</TD></TR></TABLE>

lay off the caps. i think you mean .004", regardless you need to consult your piston manufacturer. its always better to be looser than tighter.

 

i am going to run wiseco's....does anyone know what the recommended clearances are on their pistons and how much more i should go over.

 

First off what kind of pistons do you have? What metal are they? There are many different things you have to take into account before you can go ahead and decide on you piston to bore clearance. It is a very important measurement when blue printing an engine. To much can be very bad and so can to little. If you go ahead and create to much clearance the piston will rattle in the bore (more pronounced when cold) and create premature wear also losing combustion pressure. To little clearance and the piston could expand into the bore and cause skuffing which will lead to oil useage and eventaully an blown motor. dont take this clearance lightly especially with the horsepower you are looking to generate a small thing like this could make or break your motor. Take you time and read the information supplied by the maker then decide from there.

The best thing to do is follow the guide lines set by the manufacture they didnt just pull those numbers out of thin air. You can always add or subtract from the base line they suppply based on your motor and what you have planned for it. If the pistons are ceramic coated you are able to run "slightly" tighter due to less heat in the piston and less expansion of it. You are also able to run "slightly" looser if you plan on extracting as much horsepower from the motor on A/F ratio tuning this will allow you that little bit of extra space for the increased heat but comes with a negative of increased piston rattle.

The bottom line after all that is only you can decide what you want! No one can tell yo that this is better than that and this will make more horsepower cause you are the only one that knows your motor and what you have planned for it and how you drive it. So do you research and im sure you will come up with the right answer.

"It took me 2 months to work out what piston to wall clearance i wanted for my motor" research research research

 

yeah i've been researching, but i dont actually have the pistons yet and the wiseco website doesn't have much specs. from what my research has told me, the recommended piston to wall clearance is built into the piston, so if i wanted to go from .0030(if that is the recommended clearance) to .0040, i would tell my machine shop to bore my sleeves to 3.328 inches because 84.5mm=3.327 inches and that would be .0010 over the recommended clearance.

 

If you dont have the pistons yet your machine shop is very wrong for even starting the work on the bore with out them. Each piston needs to be measured individually and the bore needs to be honed out to the spec of that piston.
I dont see anything wrong with going out just that little bit extra. Why have you decided to go with Wiseco pistons?
Basically your piston to bore clearance has nothing to do with who made your pistons. The area you want to concentrate on is the Metal composition of the piston. read the article below it will help you out alot on under standing the importance of this.

http://www.team-integra.net/se...D=183

 

ok i read the article, but it seems to be more aimed at high compression motors, i know things are similar, but it basically told me to use ctr pistons and that probably won't do much for me. it was informative, but i guess what i'm asking is what clearances people have used and been successful with from their experiences, especially from the well known tuners and builders on this site.

 

anyone else care to share some insight?

 

no one?

 

go the little extra, it has been stated by high end tuners on here, i would find the link but i dont really remember which thread it is. it was stated that preffered PW clearence is in the neighborhood of .0045-.005. if i were you i would go .0045.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Jared &raquo;</TD></TR><TR><TD CLASS="quote">

lay off the caps. i think you mean .004".</TD></TR></TABLE>
right .004-.0045 , thanks for the corrections!

 

alright well i talked to my machinist and decided to go with a .004 gap, we'll see how things go

 

if your gonna be in the 600 range i would prob go just a lil looser than that .0040 is better than .0030 but up to .0050 is ok, you may get some cold piston slap but piston slap never hurt anything, and you dont wanna find out you didnt do enough down the road. i think when i read a good thread on it the most common suggested was .0045, thats really microscopic compared to the .0040 though so its prob sufficient.

IM tony1 ask him, hopefully he will be of help i remember he touched on the subject and he really knows his stuff. he is a high end fabricator and tuner.

also IM Mr Wonderfull he lost a motor to not enough PW clearence and had to do a rebuild right after the initial build

 

all off the shelf pistons(je/cp/wiseco/etc) please just do .005-.006 guys/gals...this accounts for even most custom pistons... call the manufacture and they are even more clueless.... been there done that!!! pistons for 500whp+ you'll need more clearance then the typical .003-.0035!!!

good luck guy

 

wiseco reconmends .0025 P2W... that is squeezing the piston up and down the bore, and when it heats up, it's scraping it up and down the bore

 

i run .006 on my ross pistons..never had a problem

 

so should i go more?!?! this is getting confusing....

 

Follow the pw clearances that are recommended by your piston manufature. Call them for questions such as this

 

ugh haha....i feel like so many people have so many different opinions that it doesnt even make a difference

 

go with what the manufacture of the piston says, they put alot of time and money and they know the expansion properties why ask someone who didn't design the piston?

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by quicksilver1689 &raquo;</TD></TR><TR><TD CLASS="quote">go with what the manufacture of the piston says, they put alot of time and money and they know the expansion properties why ask someone who didn't design the piston?</TD></TR></TABLE>

Yes, call the manufacturer. You can not run the same clearances on all forged pistons...

 

Yes, but most forges pistons are in the 2xxx aluminum series. If you get a forged piston in the 4xxx series, like I did, you can run tighter clearances, but the piston is more brittle.

The higher copper content makes the metal expand more under heat in the 2xxx series. THe high silicon in the 4xxx series helps reduce the expansion and acts more like the OEM pistons where you can run a very tight gap.

Consult the maker and see where they recommend the piston-to-wall clearance for your HP rating. Also find out which alloy it is.

Is this car going to be a race car specific or a DD/race? If it's a race car then I'd go with slightly looser specs since you won't need to worry about the piston slap that much. If it is a DD, then go slightly tighter, because how often are you going to heat that piston up to 500-600 whp?

Just my thoughts though

I'm a chemist for an aluminum and metal finishing company with studies in metallurgy.


Modified by blaze the chemi at 12:45 PM 11/15/2007

 

well i talked to wiseco and they told me to just go .0010 more than the suggested .0025, so i'm just going with that i guess

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by .adam. &raquo;</TD></TR><TR><TD CLASS="quote">well i talked to wiseco and they told me to just go .0010 more than the suggested .0025, so i'm just going with that i guess</TD></TR></TABLE>
That's where my SRP's (9.9:1) are at. I get about 3 seconds of piston slap at startup and it goes away.

I deburred my cylinder walls (after confirming they were not out-of-round) on my rebuild and measured the piston-to-wall and they were catching my 0.0035 gauge and my 0.0040 was not moving. Although I'm no longer boosting, my engine is at 22K and still kicking ***. I took off my turbo about 4K miles ago.