KB pistons

[kris]

Pin height puts piston .023" below top of stock deck. Guess they had to put some clearance so you can deck your block without your piston sticking out the top.

They got the stroke wrong "3.905"? Maybe that's were some of the clearance came from.

They have the stroke wrong and also the deck height...
The "Mopar Jeep Engines" book lists the deck height at 9.450-9.456. The deck on the 9.1 pistons is listed as 9.433" and the 10.1's is listed as 9.443.
So which one is it ?
My math on the 9.1's came out to.0145" in the hole. When I asked if the "pin height was high", I meant on the piston, which would lower the top of the piston and increase chamber volume.

So, check my math...
3.895"stroke/2=1.9475"
1.9475"+6.123" rod+the pin height of 1.358=9.4285"
their listed height of 9.443"- the actual height of the piston and rod of 9.4285 =.0145" down.

Now if you go by the "book" and call it on the short side of the deck spec at 9.450" deck, you would have .0215" in the hole.


Either way, assuming that the stroke is a typo, it looks good. It gives some wiggle room to play with quench and CR with decking the block and head gasket thickness. Much better than the "zero deck" that had been mentioned...

When can I buy a set ?

kris.

[oletshot]

So, check my math...
3.895"stroke/2=1.9475"
1.9475"+6.123" rod+the pin height of 1.358=9.4285"
their listed height of 9.443"- the actual height of the piston and rod of 9.4285 =.0145" down.

Now if you go by the "book" and call it on the short side of the deck spec at 9.450" deck, you would have .0215" in the hole.


Either way, assuming that the stroke is a typo, it looks good. It gives some wiggle room to play with quench and CR with decking the block and head gasket thickness. Much better than the "zero deck" that had been mentioned...

When can I buy a set ?

Math looks good to me, but you knew that. I think I would wait until they get their spec page straightened out. Not only stroke wrong, but piston dish is unclear as flash mentioned, 60cc's?
One of the biggest questions for me still unanswered is price. Time will tell. It's exciting to see this becoming a reality.

[Flash]

So, check my math...
3.895"stroke/2=1.9475"
1.9475"+6.123" rod+the pin height of 1.358=9.4285"
their listed height of 9.443"- the actual height of the piston and rod of 9.4285 =.0145" down.

Now if you go by the "book" and call it on the short side of the deck spec at 9.450" deck, you would have .0215" in the hole.


Either way, assuming that the stroke is a typo, it looks good. It gives some wiggle room to play with quench and CR with decking the block and head gasket thickness. Much better than the "zero deck" that had been mentioned...

When can I buy a set ?

Math looks good to me, but you knew that. I think I would wait until they get their spec page straightened out. Not only stroke wrong, but piston dish is unclear as flash mentioned, 60cc's?
One of the biggest questions for me still unanswered is price. Time will tell. It's exciting to see this becoming a reality.

My math said that there is only 4.15cc above the piston if its .0215 below the deck........that meant that there would still be 55.8cc of piston dish volume. According to my figures, that is a quench height of.0575(.043 head gasket) and a static compression ratio of 7.10:1 ..........good turbo or blower compression ratio 60cc CAN NOT BE RIGHT no matter how you look at it! I mean, ....look at it this way, our heads cc volume is 57 to 59cc.......THATS ONE BIG SOUP BOWL, FOR A PISTON!!!!!!!!


Flash

[dwg86]

Ok, got an email from kb pistons today. The stroker pistons part #944 has 20.9 cc dish(9:1), and the part #945 has a 10.7 cc dish(10:1). I think they have a few typos on their website also. According to my calculatios the pistons would be .024 in the hole.(rod+comp distance+half stroke- deck hieght... 6.123+1.358+1.948=9.429 9453-9.249=.024).

[gradon]

Thanks for the info. Did you tell him to update the site with correct info? I will be going with the 20.9cc dish, deck .020, and use the .043 gasket, to achieve an SCR of 9.88:1 and a DCR of 8.42. I never cc'd my CC so I'm going with the 57cc#(even though I polished the chamber and unshrouded the exhaust valves). I guess the 10.7cc dish would be good for someone that is just doing a rebuild and not stroking their engine, otherwise the SCR would be in the high tens without decking.

[dwg86]

Thanks for the info. Did you tell him to update the site with correct info? I will be going with the 20.9cc dish, deck .020, and use the .043 gasket, to achieve an SCR of 9.88:1 and a DCR of 8.42. I never cc'd my CC so I'm going with the 57cc#(even though I polished the chamber and unshrouded the exhaust valves). I guess the 10.7cc dish would be good for someone that is just doing a rebuild and not stroking their engine, otherwise the SCR would be in the high tens without decking.

Yes, I did tell them about the wrong info. Hopefully they correct it soon. Now if we only had a price....

[Flash]

Them numbers came out a lot better.....
Doing it with the assumed deck height of .0215, .043 head gasket, 59cc head and 20.9/10.7cc piston dish
Came out to 9.18:1/10.19:1 s.c.r. .....things are starting to look much closer

Now, i figured it with 3.895 bore and stroke (.020" over bore)

With a 3.905 bore the compression ratio was 9.22:1/10.23:1.......
3.905 bore and .051 head gasket............9.08:1/10.05:1

.043 head gasket, quench .0645
.051 head gasket, quench .0725"

Sure would like to see just a little bit better quench and cc of the dish to match it!!!!!!

[gradon]

Hey Flash, where did you get the 59cc volume from your head? Are you adding in the gasket volume? I see on Summit's site that KB forged pistons average about $50 a pop for the Chrysler/Dodge engines. I'd rather deal direct if they let us and skip the middleman. So, I'm in. . .1
who else?
edit. I googled KB and came across this good read from Popular Hot Rodding:
http://www.popularhotrodding.com/tech/0 ... index.html

[Flash]

Hey Flash, where did you get the 59cc volume from your head? Are you adding in the gasket volume? I see on Summit's site that KB forged pistons average about $50 a pop for the Chrysler/Dodge engines. I'd rather deal direct if they let us and skip the middleman. So, I'm in. . .1
who else?
edit. I googled KB and came across this good read from Popular Hot Rodding:
http://www.popularhotrodding.com/tech/0 ... index.html

I ported a set of 4.0L head(renix) and cc the combustion chambers before and after i clean the combustion chambers up.
before they were 57-58 cc, after unshrouding the exh valve and clean off any sharp edge, smoothing the rough casting(slightly)
I gain one hole cc 58-59.

So when i do figures i usually call it 59 cc but actually i should go with 58 as that would be the average.

And no, that's not including the head gasket thickness.

If you go to "Stroker Basics" and click on the subform FAQ section, then "Compression Ratio FAQ". I give a mathematical
Equation where you can figure out your exact compression ratio as well as a lot of info on thing like Quench, and DCR and how to figure it out! ( how using a different cam will change you running compression)

The reason I'm telling you this is that you can us that same equation to figure out cc for a head gasket. Example: The gasket bore is 4.00" the thickness is .043" or.051" You now have your "bore" and "stroke" of you head gasket! Now with the equation you can find out how many "cc' are in that gasket, or how many cc above the piston at T.D.C. do i have if the it set .020" down in the bore or .030" or .040" with this equation you can answer all of these questions.

NOTE: the math is sound!!!!! but the example it not quite right When i did my examples i figured it with 3.875 stroke......the stroker or 258 crank is "3.895"........SO the numbers i came up with(In my examples) are not quite accurate or exact......but there still close

Flash

[gradon]

I will stick to the 57cc# since it'll give me the worst case scenario(not necessarily, but you know what I mean w/ a 9.88:1 SCR and a 8.42 DCR). I could've sworn I saw somewhere that the renixes head CC was in the 60+cc range.

[cherokee]

It's in the mopar jeep engine book
89 engine spec lists combustion chamber as 64.45-67.45cc
99 engine spec lists combustion chamber as 52.22-58.22cc

[Flash]

It's in the mopar jeep engine book
89 engine spec lists combustion chamber as 64.45-67.45cc
99 engine spec lists combustion chamber as 52.22-58.22cc

Hmm thats interesting i own 3 89 xj with 4.0L in them.....Have only pull the head off of one.......but......just when out and double check as i used magic marker to right the cc down for each head.....58-59cc.....Maybe mine got shaved before i owned it........But i real don't thing so.

[cherokee]

That is pretty odd then... Any carbon buildup when you cc'ed it? I suppose there's always the possibility it's a factory oddball too. Would the factory have shaved it if the gasket surface wasn't even enough?

[Flash]

That is pretty odd then... Any carbon buildup when you cc'ed it? I suppose there's always the possibility it's a factory oddball too. Would the factory have shaved it if the gasket surface wasn't even enough?

Any carbon that would have been on the head was remove with my grinding and polish of the combustion chamber.........which only changed the chamber volume by 1cc.

I just really don't thing there was a cc difference between years or there would be a lot of talk of,........ us this head if the compression its to high or using this head will help lower compression on a stroker exc.
I could be wrong, but you would think there would have been discussion on it before now if it was true

Could it be the 64 to 68cc head, was a 258 head?


Flash

[cherokee]

Sort of right it seems... Same book has 81 and 90 4.2 stats...
81 = 67.84-70.84cc
90 = 64.45-67.45cc

Although that does beg the question of why no one has attempted a compression ratio fix by using an early 4.2 head doesn't it?

I've got a renix head (many miles though), what's a good reference point we could measure depth to as a comparison? I have nothing to measure cc's at the moment or I would do that.

There's still other possibilities as well... Inaccurate information in the book, a misprint, there's even the possibility that the factory measured differently than your method. Not having cc'ed a head myself, I'm not sure how much variance is possible when cc'ing a head.