help ID these pistons

[baxsom]

i pulled a head off today
this is what i found.

there is a #30 stamped on top of the pistons.
does that mean that it is bored 30 over
and are these stock style flat top pistons or what

thanks

 

[JohnZ]

Definitely not stock pistons - those are .030"-over domed aftermarket replacements; different dome shape than the GM LS-7 pistons.

 

[baxsom]

Definitely not stock pistons - those are .030"-over domed aftermarket replacements; different dome shape than the GM LS-7 pistons.

i guess thats a good thing
everyone kept telling me that i need to get rid of the stock ls5 flat tops to build any real compression.

i am putting a set of 110cc chamber edlebrock performer heads on it along with the xe274 cam.

i guess i better check valve clearance now.
of course i took off 98cc 427 heads so hopefully the 110cc heads will work out ok. i guess its a good thing i didnt go for the 100cc high compression heads then.

how can i tell how much the dome is so i can try and work out a compression ratio?

 

[Copdogcorvettes]

Definitely not stock pistons - those are .030"-over domed aftermarket replacements; different dome shape than the GM LS-7 pistons.

His correct!! The only way to know what you really have is to look at the inside of the piston and maybe the maker's name and a part number can be found. Good luck :bash

Gary

 

[baxsom]

well, i was replacing the oil pan anway.
hopefully there are some markings on the inside that i can see from the bottom.


question
i have read that you can check valve clearance with pladough on top of the piston under the valves, is that with a headgasket in place or not?

 

[baxsom]

quick question
i have been told that those pistons pictures will not work with a 2.19 inch intake valve.

any insight since my edelbrock performer heads will be here tomorrow.

i dont want to break them out and then have to fight with summit to send them back if they hit the valves

 

[TimAT]

well, i was replacing the oil pan anway.
hopefully there are some markings on the inside that i can see from the bottom.


question
i have read that you can check valve clearance with pladough on top of the piston under the valves, is that with a headgasket in place or not?

You can check clearance with playdough- If you don't use a head gasket you pickup a touch more clearance than you measure- not a bad thing IMHO. Set the clay fairly thick on the pistons, set the heads on with a couple of bolts, then all the valve train on place. Rotate the engine a couple of revs, pull it apart and measure how thick the clay is where the valves hit it.

 

[baxsom]

cool
i am a little cautious to be happy right now. but if these higher comp that stock pistons will work then i will be happy.
i should have checked these as soon as i pulled the head off and noticed something strange but apparently the pistons are aluminum as well.
i couldnt find any markings on the bottom of them when i pulled off the oil pan just now though.

i really hope they clear my 2.19 intake valves on the aluminum heads i bought,

i just hope now that the cam i picked out is better than the one i am taking out of it.

if someone put domed aluminum pistons in place of the stock steel flat tops ones surely the cam is aftermarket as well.

since there was hardley any lope in it i guessed it was stock but now i am not so sure.

 

[Rodney Gold]

All pistons are aluminium , none are steel.

You have to CC the block to get the CR , IE seal the piston edge with vaseline , make a perspex plate to fit over one bore and use vaseline to seal it to the deck , use a pippette or buerette to measure the amount of water that goes in (making sure you have a small exit hole drilled to let air escape) when the piston is at TDC
Once you have that , it is easy to work out CR as you know the bore size (30 thou over) the gasket thickeness compressed (and can work out the CC of this) and the head chamber size.
I think you have approached this all wrong , you are making decisions based on assumptions and not concrete measurements.
If you have gone this far already , why not take out the engine and "refresh" it and while doing so , you can easily check the piston/bore/ring condition as well as all te bearings and rectify any problems and/or put in the correct pistons for your application...10:1 should be the goal

 

[baxsom]

the only assumption i made was that it had stock pistons in it.
i wasnt trying to raise the compression ratio.
8.5 to one was stock and as long as it maintained the stock ratio i was ok with that.
a small block might need huge compression but everything that i have read says that a big block does not.
even the crate engine 454sHOs only run 8.75.

 

[Rodney Gold]

But you have no idea right now WHAT the cr ratio is...I can assure you that fancy heads and a more potent cam will "work" with any engine...ie it will fire and will go...whether it will give you the increase in HP , driveability etc that you paid for is another thing.
You cannot make the best bang for the buck choices unless you know the CR of your engine...it's as simple as that.
The very least you can do is CC the block with the piston at TDC..at least then you KNOW a starting point
Now you have indeterminate pistons , you dont know whether the valves will clear on your new heads , you are taking off a small chambered head to put on a larger chambered one , thus effectively LOWERING CR ...its a mish mush....
Im not trying to rain on your parade at all , I have quite a bit of experience in building hi po motors for street use with both SB's and BB's and am trying to steer you in the right direction and give you advise to maximise your benefit from money spent.
It will not cost you a ton to redo the bottom end and at least know what you got and the condition of the rings and bearings etc...
At the end of it all, if you are happy with the output of a crate 454 HO , it might be a lot cheaper to drop one in

 

[baxsom]

But you have no idea right now WHAT the cr ratio is...I can assure you that fancy heads and a more potent cam will "work" with any engine...ie it will fire and will go...whether it will give you the increase in HP , driveability etc that you paid for is another thing.
You cannot make the best bang for the buck choices unless you know the CR of your engine...it's as simple as that.
The very least you can do is CC the block with the piston at TDC..at least then you KNOW a starting point
Now you have indeterminate pistons , you dont know whether the valves will clear on your new heads , you are taking off a small chambered head to put on a larger chambered one , thus effectively LOWERING CR ...its a mish mush....
Im not trying to rain on your parade at all , I have quite a bit of experience in building hi po motors for street use with both SB's and BB's and am trying to steer you in the right direction and give you advise to maximise your benefit from money spent.
It will not cost you a ton to redo the bottom end and at least know what you got and the condition of the rings and bearings etc...
At the end of it all, if you are happy with the output of a crate 454 HO , it might be a lot cheaper to drop one in

the big question is ccing the block.
with flat tops it seems easy just do the same thing as with the chamber in the head but how do you do it with the domes sticking out past the deck on these pistons.
that is the part i am not sure on.

 

[Rodney Gold]

You can CC below TDC , so that the dome doesnt project past the deck and then measure the distance the piston travels from that point to TDC and subtract that swept vol from the total.

 

[Peer81]

Maybe an idea to measure the cc's. First measure with a dial indicator if the piston it self is below deck or zero deck. I think the piston self is flat so you can calculate "cilinder" that is below deck (encluding the dome). Then what you do is make a "print" from the dome with clay, now you can cc the clay print. Substract the clay print cc's from the "cilinder" and you have the cc's below deck. For the cc's besides the piston and the pistonrings you can take a fixed number (which i don't know...) This is not so important because it's a very low in cc's. I don't think you want to make a compression ratio from 12:1 or higher?
Then use this site to calculate the DC ratio:
ProjectPontiac.com - Static/Dynamic Compression Ratio Calculator

It has everything you need to know. Not on the 0.01 cc's but again, that is not to important I think

Groeten Peter

 

[baxsom]

i have decided to go ahead and replace the pistons.

machine shop recommended the keith black pistons to go with the heads i have ordered
Keith Black/KB Pistons KB203-030 - Keith Black Hypereutectic Pistons

on the pistons website it estimated a 9.75 compression ratio with a .039 headgasket and the heads i picked out.

desktop dyno estimates 450 hp/511 ft/lbs

even if its off a few % points i guess i will have to live with it

 

[damoroso]

I looked it up because I didn't know....

As information, hypereutectic pistons are aluminum with silicon added to make the alloy more stable with regard to expansion. Hypereutectic means there was as much silicon added to the aluminum that can be and still have it join with the aluminum molecularly. To much, and the aluminum gets grainy and brittle. This is basically a "stabilizer" that makes the aluminum piston expand less as it gets hot allowing a better cold/hot fit. The technology came about because in the early days of smog motors, aluminum pistons were used (for various reasons) and because of the expansion when they got to operating temp, they had to have a fairly loose cold fit. This allowed unburned fuel to sit in the rings and eventually the crankcase then venting unspent hydrocarbons to the atmosphere. Getting the pistons to expand less and closing up the cold gap using hypereutectic technology eliminated this.

If this was common knowledge, I appologize!!

 

[Rodney Gold]

Now you talking....excellent choice
To give you some idea ..assuming you only get 375 of those HP at the RW and traction -- your vette should do the 1/4 mile in the low 12's which is very very fast for a street car ..there is very little out there that will match that

 

[baxsom]

how does this sound.
i have been talking to the local machine shop
according to them, since there isnt a ridge in the top of my cylinder walls, they say that i can take the pistons out with the block still in the car and as long as the bearings are ok (not scored, etc showing the the crank is messed up) i wont need to pull the block to remove and reinstall the pistons.

that would be great if it were true. what do you guys think?

 

[TimAT]

That's correct- As long as there's no ridge, you can knock the pistons/rods out with no problem. I did Ol' Red a year ago- just like that. The biggest trick is getting everything clean.

BUT- (always has to be one of those) just getting new pistons does not necessarily mean they fit. You said you're looking at hyper-u-whachcallit pistons- the piston clearance can be run tighter to take advantage of the different piston material. You can't really correctly hone to fit without taking a chance on nicking the crank- not saying that it can't be done, but there is that chance.
the swap I did was forged to forged and the pistons I put in had been there before and were marked as to what hole they went in.

Unless $$ is really an object, I think I'd look at going with forged pistons- some issues- clearance is looser so they might rattle a little bit cold, but the overall strength is better,

 

[Rodney Gold]

You might well regret not removing the engine , if you have gone as far as new heads , cams , lifters and so forth , go the whole hog and pull the motor and check and refresh everything and do it right.