how to measure piston bore depth?

[1BAD68]

I'm trying to find out how far my pistons are in the hole and I took a dial indicator and measured 0.120"
I know its not very accurate but am I reading my dial indicator wrong? I've read they usualy are about 0.085" down.
These are Federal Mogul 285NP 318 cast pistons

[Challenger340]

On an unmilled 318 Block, those Pistons should be around .100" down from the deck, mathematically speaking.

Now, given Piston "rock" in the bore on a cold engine, you may very well be seeing close to the .120" mark if measuring on the downside of the Piston,

or

Given factory block variances, Crank grinding, Rod resizing in the past, etc., they may just be indeed further down the hole, on your particular engine.

Either way, they are a very low compression Piston.

Why are you measuring ?, and what are you trying to do ?

Bob out.

[1BAD68]

Thanks for the reply
When i bought the car the previous owner had about $2000 in reciepts in this engine. It runs fine but is a dog on the low rpm range so I figure I would tear it down and see where the compression is at and chamber volume, etc.. and see what I can do to get more power out of it.
Its bored .030 over and still has the cross hatching from honing, the bottom end looks fine but I need more compression.
I'm thinking taller pistons and different heads should be all I need.

[Challenger340]

More compression will help out power everywhere, however, best look into everything in the combo first.
, lest you not get what you're expecting.

wee-18's just aren't that great off the line anyways, none of the 3.31 stroke engines including the 340 are either.

Is the power OK for you from a roll ?  What Cam ?

Maybe all you need is a bit more convertor ?

I found this, http://www.moparchat.com/forums/showthread.php?t=101140

[1BAD68]

I wouldnt say its good from a roll but from 2000 rpm and up its great, I think your right about the convertor, I'm using the stock one now so that would definately help.
The cam is a Comp Cams 260 .440
Using the calculator I found on that link, I have compression ratio of 7.9:1 right now. If I installed KB167 pistons my compression would be 9.29:1 with no machining done.
What torque convertor should I be looking for?

[firefighter3931]

Why not use a set of the later 302 swirl port heads ? Those will bump up the compression....if the shortblock is that fresh i wouldn't be in such a hurry to rip it apart. There are other ways to perk it up. 

A cam swap to something more agressive with faster valve action will also help. The converter needs to be matched to the engine's powerband. The cam being used has a big influence on the converter....they need to be matched properly or it will be sluggish off idle. 


Ron

[Plumcrazy]

Why not use a set of the later 302 swirl port heads ? Those will bump up the compression....if the shortblock is that fresh i wouldn't be in such a hurry to rip it apart.

Ron

The 302 heads are easy to find.  You get more compression and a more efficient combustion chamber design.

[1BAD68]

convertor is definately on my list, can anyone recommend one for that cam?
also, I think the cost of rebuilding a set of 302 heads would equal the new pistons (I think?) would I be better off with heads instead of pistons because of the better flow?
Or would a nice do it yourself port job on my stock heads be good?
I'm on a tight budget with Christmas coming up so I just want to raise the compression and match up a torque convertor.
Thanks for all the info