I havn't done this yet - here's my plan

[MacaveliMC]

ok, excellent, I put in numbers using KB944 pistons, over sized 0.030", using the 258 crank and the 242 connecting rods, decking the block 0.020 and plaining the head 0.010.

With the crane cam and a gasket thickness of 0.043 I am reading from the stroker calc, a SCR of 9.78:1 with a quench of 0.0505. The smaller gasket brings the quench to 0.039, which seems dangerously low to me.

Putting the numbers into the DCR calculator and my local altitude of about 900 feet, I am seeing a DCR of about 7.88, which I believe can easily run 87 octane

I am wondering if I should even try to bring the DCR up, by maybe plaining the head. I still don't think I understand plaining the head. If you are taking metal off the head, how is that not lowering the quench? Maybe I am thinking of the wrong surface.

[Flash]

ok, excellent, I put in numbers using KB944 pistons, over sized 0.030", using the 258 crank and the 242 connecting rods, decking the block 0.020 and plaining the head 0.010.

With the crane cam and a gasket thickness of 0.043 I am reading from the stroker calc, a SCR of 9.78:1 with a quench of 0.0505. The smaller gasket brings the quench to 0.039, which seems dangerously low to me.
Are these ### with the the head and or, block decked?
Putting the numbers into the DCR calculator and my local altitude of about 900 feet, I am seeing a DCR of about 7.88, which I believe can easily run 87 octane
8.1 (in DCR) is considered at the hight end of streetable compression, so 7.88 may reqire 91 to be happy.
I am wondering if I should even try to bring the DCR up, by maybe plaining the head. I still don't think I understand plaining the head. If you are taking metal off the head, how is that not lowering the quench? Maybe I am thinking of the wrong surface.

I had a hard time with this as well.

Quench is the distence between the top flat part of the piston and the flat surfice of the head. if you shave .010" of the head. Compression will increase equally for SCR as well as DCR.....however, Quench has NOT change at all.The piston is still the same distence to the flat surfice of the piston to the flat surfice of the head..........compression has went up becose there is less cc of space in the combuston chamber of the head but Quench is unchanged

Now, if you shave or Deck the block .010", the head now is closer to the piston at TDC, which means the quench is now now tighter by .010" BUT the compression ratio has also when up as the piston is higher in the bore (less cc at TDC)

You could shave .100" of the head and the compression would be extreamly high.........but the Quench would be un changed.
If you don't need to shave the head don't........Unless your after HIGH Compression.


Make sence?

[MacaveliMC]

Thanks Flash that makes perfect sense now. So I have my crank, cam, and pistons picked out, as well as my gasket thickness. What I really need to do now is figure out what other new parts I need to order. Any recommendations on parts I should upgrade instead of just getting stock replacements? I was thinking about maybe getting mopar springs to make sure I don't ever float the valves, though it would be more for off-roading anyway. But besides that I am still debating on what else I need to replace or upgrade from my 4.0.

Anyone had any experience with using stock fuel injectors instead of upgrading? How about changing timing? What about changing the MAP to 5.0V? I read about that on cheromaniac's personal build site, but I have no idea what that means or if I even need to do it as well.

[Flash]

I would build the stroker, then see if you need the extras after it running.

So what piston/rod combo did you decide on. If KB did you go with the 9.1 or 10.1?
What cam did you decide an?

The computer need to know how much air is entering the eng and it use the map (as well as others such tps) to now this.
the map receives 5v and then send a resisted voltage to the ecm to tell what pressure (or Vac.) is in the manifold by varying the voltage to the ecm. a map adj simply fooles the ecm into adding more fuel then normal, or less then normal.

That's basically whats going on. others can explain it in more depth

Flash

[MacaveliMC]

I believe I am going to keep my stock 4.0 rods, and go with KB944's, 0.030" oversized. I believe my SCR is going to be around 9.94, do you think I should go with the 10.1 then?

Thanks for the info on the map voltage, any idea on how to actually change it?

I would like to do pretty much a full engine rebuild, including rod brgs, cam brgs, oil pump, lifters, timing components, frost plugs, and obviously all new gaskets.

[Flash]

I'm just guessing here sence no one has installed a piston to measure piston to deck height and actual cc of the dish, but I'm guessing that that 9.9 is going to be a lot lower in the end.

when i figured it up in the "KB944 piston" thread.

Flash

[MacaveliMC]

Well according to the stroker calc. those are the numbers that come up. Obviously the DCR is going to be lower.

Also Flash, in an earlier post you said... "8.1 (in DCR) is considered at the hight end of streetable compression, so 7.88 may reqire 91 to be happy."

Why would a lower compression require a higher octane gas to be happy. I thought the higher the compression dictated whether you needed higher octane gas or not.

[Flash]

Well according to the stroker calc. those are the numbers that come up. Obviously the DCR is going to be lower.
Yes DCR will be lower ### then SCR Always!
The reason I say that it will be lower is that the spec on the KB sit is not correct as far and the block DECK HIGHT. so, it Seam that the compression is going to be lower what you figured
Also Flash, in an earlier post you said... "8.1 (in DCR) is considered at the high end of streetable compression, so 7.88 may require 91 to be happy."
Before we learned or new about the more accurate DCR, we all have learned that 8.1 (SCR) was for low octane and 10.1 would require premium. "DCR" at 6.1 would be the low octane and 8.1 work require the premium.....Make sence?
7.88 would take less octane then 8.1, I was just trying to make the point that 7.88 was close to the max recommending compression ratio for premium gas
Why would a lower compression require a higher octane gas to be happy. It Won't I thought the higher the compression dictated whether you needed higher octane gas or not.

That is correct!


Flash

[Cheromaniac]

Here's another good DCR calculator:

http://www.kb-silvolite.com/calc.php?action=comp

According to that calculator my stroker's SCR is 9.25:1, DCR is 8.03:1, and I can run it on 89 octane without pinging.
When my stroker had the Crane 753905 the DCR was 8.42:1 (earlier intake valve closure) and it had to run on 91 octane.

[Flash]

Yes, this is the one you need to us, if the only cam spec is "@.050"

The problem with that calc.( or any @.050 Calc) is that if you have a cam spec where it give you both seat to seat and @.050........the numbers don't match I fill the seat to seat is the most accurate of the two.

Vary interesting, about the octane requirements, and a cam change. Good example of how a cam change, can change octane requirements, with out change SCR

Flash

[MacaveliMC]

hmmm, interesting, I gotta buddy who's friend has a 4-stroke snowmobile, that has a 10:1 SCR and a stock cam, plus 8 pounds of boost and he runs 87 octane no problem. i wonder what the difference is.

[dwg86]

Here's another good DCR calculator:

http://www.kb-silvolite.com/calc.php?action=comp

According to that calculator my stroker's SCR is 9.25:1, DCR is 8.03:1, and I can run it on 89 octane without pinging.
When my stroker had the Crane 753905 the DCR was 8.42:1 (earlier intake valve closure) and it had to run on 91 octane.

WHAT CAM ARE YOU RUNNING?

[MacaveliMC]

I was definitely thinking about grabbing the crane cam. It would bring my SCR to about 9.78 with the 0.043 gasket and the following info:

Bored out - 0.030"
Crank Stroke with 258 crank - 3.895
Decking Block - 0.020
Plaining head - 0.010
Custom Piston - -21.7 (KB944 9.1)
4.0 rod length - 6.125"
Piston Height - 1.353 (kb944 9.1)

I used this DCR calc (http://www.wallaceracing.com/dynamic-cr.php) with these numbers:

# of cylinders: 6
Bore in inches: 3.905
Stroke in inches: 3.895
rod length: 6.125
static compression: 9.78:1
inlet valve closes ABDC: 61
boost pressure: 0
altitude: 900

This gives me a DCR of 7.88:1

This is obviously using the crane cam, hence the 61 degrees ABDC.

I looked at your other DCR Cheromaniac, but I didn't know what to put in for all the values, maybe you can help me out with those and see if I get different numbers.

[Flash]

It not that your doing any thing wrong with either calc..........It's the info the KB is giving ..........well i think its a little bit inaccurate. And is why a few of us are dying for some hard spec of these new pistons.

Read the first two pages of this link. it may help understand why i say the compression ratio will probably be a little bit lower then you have figured.

viewtopic.php?f=15&t=225


Flash

[MacaveliMC]

Flash, I read that whole post, I am really interested to see what happens when he puts the pistons in. I am not extremely concerned about compression, especially if it is lower since that definitely means I can run 87 octane. I have a buddy who's a mechanical engineer, a engine guy working for Polaris, and he is convinced up and down that my hypothetical build so far will have no problem running 87 octane, but of course I want to consult multiple sources. I also want a good quench, so it will be interesting to see what Reelm n Rubi comes up with when he installs.

On an off note, I am probably still a couple months away from actually ordering parts and tearing down my engine, since I am just about to get a job here and need a little bit of time to save. But When I do get there I'll definitely be keeping you guys updated on the process. Plus I'll probably have tons of dumb questions to ask you since it will be my first time rebuilding an engine