Stepped piston hitting head, options and advice needed.

[nm9stheham]

According to that, 62cc =9.9 But, some one need to explain "affective head volume"?
Because, that term, to me, says that i should subtract 23.5cc from the head volume. aks 72-23.5=48cc WOW not thats some compression for a open chamber head!

In the case of KB piston specs, they mean that the 23.5 cc's is the net volume to be ADDED to the other volumes. In this case, it is the net volume of the dish and/or eyebrows below the compression height minus the volume of the quench pad above the compression height for this piston.

The number given is always net volume referenced to the compression height fer every piston Mfr I have checked; but the + or - conventions vary. For KB's, a + number is for an increase in volume and a - number is for reduced volume (like with a domed piston). Others, like JE, use the reverse convention, where a - number is for increase in total volume and a + number is for a reduction in total volume.

So you need to know the convention used by that particular mfr. The easiest way to tell is to look at a simple flat top with eyebrows for that mfr, which will always be an addition to total volume; and then just look to see if the mfr shows that as a + or a -.

 

[MOPAROFFICIAL]

So you're saying that that dome/step piston had less compression than a Standard Step/dished piston????? Im still missing something here

The pad is small, it's on one side of the piston that zero decks, thats also a small area....the rest is a 'below deck' dish. and 23.5 cc of volume HAHAHAHAHA

 

[nm9stheham]

So you're saying that that dome/step piston had less compression than a Standard Step/dished piston????? Im still missing something here

The D shaped dish in this particular piston (KB356) is 25 cc's and the quench pad is about 1.5 cc's giving a net volume increase of 23.5 cc relative to the compression height of the piston. The same piston with the quench pad milled off from the factory is the KB416, which has the 25 cc dish volume.

 

[MOPAROFFICIAL]

The D shaped dish in this particular piston (KB356) is 25 cc's and the quench pad is about 1.5 cc's giving a net volume increase of 23.5 cc relative to the compression height of the piston. The same piston with the quench pad milled off from the factory is the KB416, which has the 25 cc dish volume.

Ding ding.

 

[draginmopars]

If the op could mount the heads on his bare block and scribe the bores to the heads....he could get a shop to cut the chambers.

This was a poorly thought out build, costing more now for op.

I like to scribe the heads- remove sharp edges and to blend the head to the bore

 

[nm9stheham]

Took me a minute to figure out what I was lookin' at LOL. Man, those bores are shiney.... what finish grit is being used? That bore shine is not computing in my wee brain....

 

[yellow rose]

Took me a minute to figure out what I was lookin' at LOL. Man, those bores are shiney.... what finish grit is being used? That bore shine is not computing in my wee brain....

That looks like a 400 finish and a soft hone over the top. Looks fantastic.

 

[Cudafever]

OK now that i get it. looks like he will be fine at 9.8: with the positive step removed, rhs head and .039 head gasket.
Or keep the pop up/dome, run the stock 340/360 heads and and with the same gasket get 9.08.

This is assuming that your piston is at 0 deck(not including the the pop up part of the piston.)
With that info i change my tune. I would remove the piston, have the dome remove by someone that has a mill, reinstall and us the rhs heads.
installing your 340/360 heads you would only have check valve to piston clearance and your on you way.
Sorry about all that above. Just didn't think there was any way that dish was going to be deep enough to knock that much compression off of it............but i was wrong

 

[nm9stheham]

Yeah, they are pretty big.

The one thing I will give KB credit for is that they seem to have looked at 2-3 major applications with the most common heads that folks will likely use, and then tailored their pistons to get close to a good gasoline fuel CR for those 2-3 of major application types. They seem to have covered both street cams and bigger drag strip cams pretty well for quite a number of engine sizes, both stroked and not, and with closed and open chamber heads in mind.

The only other piston mfr that I have seen do this much was TRW back in the day; they had quite an amazing variety of specialized pistons in the 70's.

 

[popinsmoke]

 

[nm9stheham]

Sure does look like the KB356 illustration:
KB Hyper Piston - Chry 408 Rod 6.123 Quench Head 23.5cc 2V [KB356] - $462.70 : United Engine & Machine Co. Incorporated, Performance Pistons

Looks like the EQ LA heads setting on it now..... hence the thread.

 

[popinsmoke]

Pretty sure they are KB 356 piston will know for sure shortly, The heads in question are actually RHS/Indy LAX heads.

 

[MOPAROFFICIAL]

Pretty sure they are KB 356 piston will know for sure shortly, The heads in question are actually RHS/Indy LAX heads.

Yes. KB re designed it's hyperutectic 408 piston "kb356" . I assume they realized more people were building them and using newer closed chamber heads.
When doing this, they changed the 356's valve relief pocket from a slot ...to having a peak in the middle. All in one mold that they machine into the flat dish version, maybe the peak keeps the comp right at 9.1 still.

 

[popinsmoke]

Been busy getting ready for Irma but once that passes will be measuring to see exactly what I am working with and plan the next step from there.

Assuming I don't have bigger problems from the storm!

 

[moper]

Take care and good luck to you guys. Looks like a powerful storm...

 

[nm9stheham]

Ditto.

I am in the NC Outer Banks a lot and it looks like it is FL's turn this time. No fun looking forward to that; hope all works out OK for you and others like CharrlieS.

 

[popinsmoke]

We were blessed very little damage to the house, but lots of landscape damage. A limb falling and creasing the hood of my 78 magnum, 5 days without power and a week out of town on business, to come home to 3 days worth of clean up with a chainsaw and brush pile 4 pickup loads deep.

Back to the engine I have a dial indicator on order and will be measuring the protrusion of each piston above deck, with this information I should be better armed with the information needed to decide which option is going to work the best for my goals (custom head gaskets, mill piston quench pad, or run different heads altogether.) Frustration is high but I am also counting my blessings as so many were hit much harder and lost everything. Thanks for the advice and well wishes, I am sure I will be back soon for more advice!!

 

[nm9stheham]

Glad you survived with so little damage. Dang, you weren't too far from the center of the path!

 

[popinsmoke]

Dial indicator and base showed up, so should have some numbers this weekend!

 

[yellow rose]

Dial indicator and base showed up, so should have some numbers this weekend!

Wow...stuff must have traveled on donkey express. Last post was a week ago. I live where the hoot owls and chickens fornicate and even I get stuff quicker than that.

Can't wait to see the numbers.

 

[popinsmoke]

So assuming I measured correctly, (and the is a BIG assumption) The numbers are as follows #1 .070 #2 .090 #3 .070 #4 .075 #5 .098 #6 0.95 #7 .099 #8 .095 averages out to .086 above deck which seems to jive with the advertised quench pad height of .085

Now I am concerned that I didn't get the dial indicator in the correct position for accurate and repeatable results. I am going to study up a little on how to use it and the magnetic base, but these are the numbers I came up with at first blush.

Edit, it has become obvious I need to spend more time with learning to set up the dial indicator and magnetic base, to achieve accurate and repeatable results

 

[MOPAROFFICIAL]

So assuming I measured correctly, (and the is a BIG assumption) The numbers are as follows #1 .070 #2 .090 #3 0.70 #4 0.75 #5 0.98 #6 0.95 #7 0.99 #8 0.95 averages out to 0.86.5 above deck which seems to jive with the advertised quench pad height of 0.85

Now I am concerned that I didn't get the dial indicator in the correct position for accurate and repeatable results. I am going to study up a little on how to use it and the magnetic base, but these are the numbers I came up with at first blush.

Rods resized can account for some variance.
Center of piston is where you want to read from, note max rise...then measure the quench head .
This is what I would use along with a couple dial indicators...
www.summitracing.com/parts/pow-pow101310?seid=srese1&cm_mmc=pla-google-_-shopping-_-srese1-_-powerhouse-products&gclid=EAIaIQobChMIkISjp9_i1gIVj4l-Ch3QzQlNEAQYASABEgKt8vD_BwE

 

[yellow rose]

So assuming I measured correctly, (and the is a BIG assumption) The numbers are as follows #1 .070 #2 .090 #3 0.70 #4 0.75 #5 0.98 #6 0.95 #7 0.99 #8 0.95 averages out to 0.86.5 above deck which seems to jive with the advertised quench pad height of 0.85

Now I am concerned that I didn't get the dial indicator in the correct position for accurate and repeatable results. I am going to study up a little on how to use it and the magnetic base, but these are the numbers I came up with at first blush.

Did you buy a mag base or did you buy a deck bridge? Much easier to use a deck bridge to measure piston height.

Also, you can get some variance in height because piston to wall clearance. If the numbers are as far off as you say, you need to deck the block and correct it.

 

[Cudafever]

Decking the block isn't the problem #1 .070 #3 .070 #5 .098 #7 .099 Now this is with me giving the benefit of doubt and keeping all the decimal point in the same place............ If that deck jumps from .070 to .098 from cyl 3 to 5..........coolant would just port out out at that point.

All the piston domes should be EXACTLY the same height(from "wrist pin" to dome)

O.P. just need to spend some more time using the tool and getting use to it.
check a piston.....remove tool and then set it up to check that same piston. When you get the same Number Three time. You now know how crucial the "setup" is and are now ready to check the next piston.
I'm not scolding, just trying to help. Every one has a learning curve when it's the first time using a tool that can measure in .001 (1000s of a inch)
Go back out and play with it. Have some fun with it! U will get it.
The Bridge suggested above is easier to use but a dial indicator on a mag base is just as accurate............Just requires a little bit more set up time.....To be accurate.

 

[popinsmoke]

I agree 100% I need more time with the tool, I am going to play around with it some more tonight and see if I have get an accurate and repeatable result.