so i pulled one of my heads off today to see what kind of pistons were in the car.

this is what i found. are these stock pistons?
there is a 30 stamped on the top of each one.
does that mean that the engine has been bored 30 over?

thanks

 

If the pistons are stamped .030 then it has been bored .030 over. Not sure if this is a SBC or BBC but SBC have a standard bore of 4.000 so with .030 pistons it would be 4.030 bore. Those pistons do not look like stock replacement pistons, the pistons you have are aftermarket and are pop up" or domed pistons which increases compression vs. flat top pistons. I would be happy if I took my heads off and saw those sitting in there..

Good luck...Chris.

 

Yes & pistons replaced.

 

thats some great news.

it is in a 454 so whats that 460 now.

everyone kept telling me that when i do my head and cam swap i should put some domed pistons in to build some compression.

i guess that wishful thinking does work.

now i just need to figure out the size of the domes so i can work out a compression ratio.

 

Yes, those are replacement style pistons. You can see the double valve relief where the piston can be swapped side to side.....unlike stock ones with only one relief. Good news is they are higher than flat tops or sumps...bad news is they are lower than regular 10.25 style ones would be.

You can also see the blue fel pro gaskets were used...about .040 or so thick. Check to see how far the pistons are below the deck at TDC. Stock is around .020 or so...often replacement ones are .030-.040 below the deck. That messes with compression too.

You can get some .015 gaskets from Cometic to help bring compression up with your new heads.

Need to check Piston to valve clearance closely with the new heads. Those pistons are not designed for 2.19/2.250 or larger intake valves.


JIM

 

regular pistons on the ls5 is 8.5:1 with flatops so wouldnt any domed piston bring up the compression.

thats not good. the new heads have a 2.19 intake. i dont want to have to send them back. what am i looking for to make sure that i can use them


as far as the below the deck distance at TDC. the picture i posted of the full piston is the #1 at TDC.
i am guessing that you mean how far the flat part of the piston is at TDC and not the dome.

 

i am not sure if i did this right but the flat top of the pistons is .05 inches below the deck according to my dial calipers whatever that means

 

Here is a real, live LS-7. Right bank.

And then looking from the right side across the deck to #1

 

that is as close as a picture as i guess i can get of what my #1 piston looks like. i put it at TDC before i took the engine apart.
the one pic of multiple pistons. the one that is up is pretty much what i am looking at.


magnet test shows that mine are aluminum as well. is that good or bad.

i pulled the oil pan and couldnt find any markings at all other than that 30 stamp

is there a normal spot for manufactur stamps on these things

 

at deck height. Then swing it around where the indicator is on the flat of the piston. The distance is your amount of piston-to-deck height. Usually stock is .032 or so in the hole (below deck height). Your biggest concern will be making sure your piston domes don't hit your valves. My guidelines are .080 clearance with an automatic tranny and .120 with manual tranny or aluminum rods. Various head gaskets of different thicknesses can get you to the clearance you need or you can have the valve seats cut deeper. Last resort is to flycut the piston eyebrows.
Some use Play-doh but I prefer using a warmed up Tootsie roll miniature to squash with the paper still on it. Easier to measure than Play-doh plus you get to unwrap and eat the Tootsie Roll afterwards. All our Play-doh is ground into the carpets in my house. Check me out first on these specs - my brain is fried.

 

Lay a straightedge of some sort across the flat part of the piston..let's say the top side in your pics. Push down on the piston to *rock it* and measure the distance with some feeler gauges. Now push down on the opposite side of the piston to rock it upwards and measure the clearance in the same place you did before. The difference between these two measurements will give you an idea of deck height. Hopefully they aren't .050" down in the hole. Make sure you are at TDC...look at the balancer while on #1 piston.

Yes, anything is better than what the low compression LS-5 had..so you're probably doing better.

You just need to check valve clearance. That's common procedure with any build. It's easy to do with some modeling clay. It depends on the cam as much as anything...not so much the lift....but the duration and LSA and installed intake centerline. Depth of pockets will likely be fine...but you will want to double check the *radial* clearance around the edges of the pockets. Better to spend a few minutes checking than end up with shrapnel.

Your pistons are aluminum...they all are. Those appear to be cast aluminum replacement type.

TimAT..now THOSE are some pistons! That was the good ole days for sure!

JIM

 

.020 and .035 PV clearance will likely get you some issues unless you are REAL lucky!

JIM

 

thanks for the all the help.
i was ready for stock pistons and picked out heads that would work with the stock pistons. now i am playing back up and rethink so it gets fustrating. (especially now that one head is laying on the garage floor.
cam isnt majorly radical .552/.555 lift.

i was going by what was on there. with the tiny chambered heads that were on it, i based part of my decision on that. with those domed pistons and 98cc chambers 427 heads i am curious as to what the CR was running at.

at this point i wonder if i should get those ported out and put them back on.

 

You need to check for sure the part number on those pistons, to bad that you only can see that if it is pulled from the block. The reason would be those are Silvalite pistons most likely and that style of dome was used in 396, 402, and 427 motors not 454's that I recall. They were replacements for the 10.25 comprestion engines but these were reduced to around 9.2 with that modified dome. Total deck of the piston was advertized as .015 lower than the stock piston also.

 

man, here i was all happy that i had dome pistons instead of the flat tops and now it looks like i may have to pull them out anyway.

that 427 reference makes sense now.
it had the heads off of a 427 on it (one of which is now on the floor)

the new heads have a larger chamber but 2.19 intake valves.
i need to cc those pistons somehow to work out my new compression ratio but most importantly check clearance to make sure the .17 larger valves wont hit.

damn, it almost seems like it would have been easier if the pistons in it were stock

 

No, it wouldn't be easier....they would be just as tight.

Put piston at bottom of stroke and measure it. 3-3/4" is a 427or a 396/402...4" is a 454. Need to measure bore size too...should be 4-1/4"...not just a little over 4".

The valve notches on cylinders look like a 396/402 type cylinder..usually don't see that on larger bores unless someone adds them.

Let's verify what you have first.

JIM

 

Them are not the good OLD days there Boss. That's TODAY! 12.5 and I run VP 110. Not cheap, but man what FUN! Smells nice too.

 

i decided to just go ahead and replace the pistons so i know exactly what i am working with.

i talked to the local machine shop and then confirmed it with a tech at summit that they would work.

they recommended a set of keith black pistons with enough clearance for the 2.19inch valves.
the keith black website says that with my heads and a .039 headgasket compression should be 9.75.

 

Piston to valve clearance shd be .080 with automatic tranny and/or steel rods. It shd be .120 with a manual tranny and/or aluminum rods.
Hope nobody swallowed a valve with my earlier specs.

 

Did you figure out the bore and stroke? Are you going to bore it again or at least TQ plate hone it? Are you getting forged or Hypereutectic pistons? Forged are a good investment for the future.


JIM