i have a question...im getting a set of wiseco 81.5mm pistons and i need to bore and hone my block..my question is..do i get it bored to exactly 81.5 mm which is 3.209 inches??? or do i get it bored larger to accommodate for the piston to wall clearance spec??

 

If you bored your cylinders to the exactly same size as the piston it wouldnt work lol, your pistons have the recommended p/w clearance right on the sheet inside the box. Depending on your hp goal you increase the clearance from spec to handle the piston expansion.

 

Depends what the piston spec sheet says, read that before you have the block machined. I had a machine shop make the mistake of mis-reading wiseco's clearances and ruined my block, they made it up buy replacing it though.

Take your advise and do it "right", take everything to the machine shop when your ready

 

I ran Wiseco's in my old motor and they recommended them to be run a little tight, I am assuming that is due to the coating on the skirts which wears off.

 

id like to run them at .003 instead of the recomended .0025...if i do this, then wut do i use as the bore number to put into the equation to achieve my ring gap?

 

i mean, do i use the 3.209 for the 81.5mm bore even tho its bored out larger than that?

 

i thought the clearences was in the pistons?..if u had 81.5mm and they called for .0035 that when u honed the cyl to 81.5mm it would have the .0035 clearence???
i might be wrong tho?

 

Most of the time you want to run the clearance the mfg. suggest, but if you're throwing big boost on it, then you should go about .0035 - 004.
You can also talk it out with your Engine Builder.

 

ALWAYS have the machine shop check on the actual piston itself on the exact bore. you want to base your calculations from the measurements of the pistons, not from the "number" you think the bore size is. There's always mistakes by machine shops thinking the clearances are already built in to lets say the 3.209/81.5mm or they're not. So to prevent any misunderstandings, make sure just provide the piston when you get the block machined so they can double check and mark the piston to each cylinder.

 

yea i understand that...but does that mean it has to be bored more than 3.209 and wut about calculating the ring gap? do i use the 3.209 to calculate it, no matter if i decide to use mfg suggestion or if i go all the way up to .005

 

Unless your ordering file fit rings your pretty much stuck with the ring gap built into the rings.

 

so ur saying theres no way to gap my rings from wiseco?

 

You can special order file fit rings. The rings on an off the shelf Wiseco box are set up for the bore they recommend (not that they shouldn't be checked).

 

Order your pistons. Once they come in, take the pistons and your block to the machine shop at the same time. Tell your machinist what bore and p2w clearance you want/need, and let them do their job.

It's really not that hard, Lol...

 

So how would I find the ring gap? Do I have to actually measure the bore with the dial bore indicator to get the exact bore size? Or can I just use 3.209?

 

If you want to assume its 3.209 then just throw it together, otherwise it has to be measured. No offense but all this is common sense, you seem to already know these answers.

Here dude.... watch all 3 parts.

http://www.youtube.com/watch?v=mpy_By5aIxM

http://www.youtube.com/watch?v=MtTXA9_a8sI

http://www.youtube.com/watch?v=JE7U5l_MoP8&feature=fvst

 

This is some good info since I'm about to do my first build. My machine shop did a hone on my cylinder walls, but I haven't got my pistons yet. The walls looked good enough that they said I could just get by with a hone.

BUT, should I get the 81mm pistons or 81.5mm?? I'm assuming that I need to have the block checked and bored/honed again. But should I assume that the bore now isn't TOO big for the 81mm?? Or do I need to take it by the shop and have the bore checked before I make the order for the pistons??

Not trying to thread jack either, but I just figured it would be relivant.

 

You should never do a damn thing until the pistons are in your hand, bottom line.

Ill repeat for you what I and others have repeated for the OP in this thread...

Take the pistons and the block to the machine shop and let them do their job, without measuring nobody can help you... if the shop didnt bore the block it should still be 81mm but with an excessive P/W... this is all speculation of course you shouldnt of had them hone it for no reason without pistons in hand.

Take the block to the expert and let them do their job, thats what you pay them for.

 

Lol this thread is funny. It reminds me of talking to a brick wall.....

 

Actually the first step IS taking the block to the machine shop to find out if the block needs or has already been bored. From their recommendations you should order pistons and WHEN they arrive the machine shop can measure the pistons and bore or not bore the block.

 

 

lol common sense at its finest. A stock motor cant be any other bore size than 81mm unless its a B20 or a K, so no need to take it to a machine shop to verify. I cant recall anyone running Forged 81mm pistons (that had any sense) so if the block is untouched it has/should to go to 81.5mm... no reason in the world I can think of to just hone an 81mm stock bore and stick a stock size replacement piston in there unless you cheap or lazy or both....

 

it's weird the machine shop would hone it for you without any pistons present. at least any shop that gives a damn.

 

wrong! take your block to the machine shop first, have them measure it all first and let them tell you which pistons to order, for me a i bought pistons first for my 81.5 mm b18c5, so i ordered some wisecos then took it to the machine shop only to find out my piston to wall clearence was 0.0055 double the manufacture specs, so now i have to jump up to either a 81.75 or 82 mm becasue my power goals are less then 400 hp