First time build - calculations help

[madmax79]

I've been working with the calculator on this site and I'm not sure where to get some of the numbers to plug in. I was thinking of using Keith Black forged KBB944's, 4.2 crank and rods in a '92 block and cyl head. I need an expert to please look at the number below and tell me if I'm missing anything. The calculator had some default numbers that I left in but I'm not sure if they're correct. I couldn't figure out the piston ring height and piston to bore from the KB website. think this would affect the deck clearance so I'm not sure of that either. Alsso, I picked the Mopar cam kinda at random. Should I pick another?

Here's what I have so far...

Bore: 3.905 (.030)
Stroke: 3.895
Combustion chamber: left as 58
Deck Clearance: left as .0215
Gasket thickness: left as .051
Gasket bore: says 4 is normal
Dish: 21.73
Piston ring height: ?
Piston to bore: ?
Connecting rod length: 5.875
Cam: Mopar P4529228AB (duration:240, Lobe sep: 108)
Advance or retard: 0

Gives me...
Liters:4.59
SCR: 9.09
DCR: 8.11
Quench: .0735
Intake valve closing angle: 48

[Muad'Dib]

The sections to the right of where you input the information in the calculator tell you about that particualr section. If you read it it tells you that Piston Ring Height and Piston to Bore Clearance have little effect on the result. Just leave them blank if you dont have the information.

Your calculations are correct... however i got 8.13 for your DCR... not 8.11.

Even with that low of a compression ratio... i would consider getting the quench down. Use a thinner head gasket, deck the block, and or shave the head. All will raise your compression ratio and lower your quench.

Consider getting your DCR around 8.5 with as low of a quench as possible.

[jsawduste]

I`d use the longer 4.0 rods. This will move the piston higher up in the bore. Giving a much better quench.

[Muad'Dib]

i totally forgot that he was planning on the 944's... they are made for the 4.0 rod not the 4.2.

[madmax79]

i totally forgot that he was planning on the 944's... they are made for the 4.0 rod not the 4.2.

You're right. However, I did use the connecting rod length in my calculations as 5.875. I went back and changed it to 6.123 but it didn't change the numbers much. It dropped quench to .0725

So from what everybody is saying, it looks like a do-able build?

[jsawduste]

:doh: i totally forgot that he was planning on the 944's... they are made for the 4.0 rod not the 4.2.

You're right. However, I did use the connecting rod length in my calculations as 5.875. I went back and changed it to 6.123 but it didn't change the numbers much. It dropped quench to .0725

So from what everybody is saying, it looks like a do-able build?

First I will admit to NOT having played with the calculator(s) here.

The purpose (as I understand it) of the 944`s was to be able to use a 4.2 crank in a 4.0 block with 4.0 rods and achieve a zero (or close to it) deck height. With a nominal compression ratio of mid 9`s. With a .04x head gasket your quench will be in the sweet spot for a good running engine.

MadMax-someone will chime in and help you (us) out. Plenty of engines have been made with the 944`s so the knowledge is out there. Did you see Corey`s build on PBB ? He used 944`s as I recall.

Did you happen to see the Hesco RVOB cam ? Not sure of the numbers off the top of my head but it seems to be a well respected stick.

[PolloLoco]

Does anyone know of a build using KB945's or am I the only one?

[Muad'Dib]

Im sure not many people have chosen that piston .. only because they are usually trying to keep compression ratio down. WIth the small dish of the 945's .. that just isnt an option for alot of people.

[jsawduste]

:doh: i totally forgot that he was planning on the 944's... they are made for the 4.0 rod not the 4.2.

You're right. However, I did use the connecting rod length in my calculations as 5.875. I went back and changed it to 6.123 but it didn't change the numbers much. It dropped quench to .0725

So from what everybody is saying, it looks like a do-able build?

What you are missing from your calculations is the pin height of the 944`s. That is one of the main reasons 944`s were made for strokers. It moves the piston up in the bore at TDC/BDC. Reducing quench and deck height. Then the "larger" dish of the piston itself averages compression out to a tolerable level.

[SilverXJ]

Pin height for the 944s and 945s is 1.353" AKA compression height.