Revised build plan - please proofread - High DCR

[sudo chop]

I have been doing a lot more research since I first came on here with my long rod build plan. I also found out my block was cracked and had to pull another at the junkyard, so now I am back to short rods and H802CP pistons.

I want to zero deck the block for good quench, because I want to run high DCR ~8.5:1-9:1. However, I am not familiar with how well the combustion chamber on these jeep heads respond to compression.

Is this too much compression? Anyone else running this? I seem to remember reading a post at some point where someone discussed being able to achieve this kind of CR with good quench but now I can't find it.

Also, I want to discuss the use of the OEM HO camshaft.

At zero deck the calculator gives me
9.03:1 with Comp 231-4
8.8:1 with Comp 232-4
8.5:1 with OEM HO

Now, aside from their yielded DCR, what are the major benefits/ disadvantages of using each of these? I have sometimes heard that the OEM cam will produce more torque, but I can't see any reason why this would be true. If i stick with the stock cam, will I be missing out on a whole bunch of power? It certainly has the benefit of being the cheaper route to take.

I also want to detail my plans so that those with experience can point out any pitfalls.

1998 XJ AW4
3235477 crank
4.2L Rods
Sealed Power H802CP pistons .040
Sealed power Moly rings
0630 head
Block zero decked bored .040
99+ intake manifold bored out to 63mm
63mm TB from Leigh
Borla header
ford racing 24lb/hr injectors

Thanks guys!

[Cheromaniac]

I have sometimes heard that the OEM cam will produce more torque

Depends on which cam you're comparing it to. Compared to the Crane 753905 cam that I previously had in my stroker, the OEM cam only produces more torque below 1600rpm. Idle vacuum and fuel economy is also slightly better with the OEM cam.
With your plan the SCR will be ~10.1:1 so you could consider a longer duration cam such as the CompCams 68-235-4.

[sudo chop]

Are you recommending that cam just for the lower DCR? Is the DCR of 9.03 with the 231-4 too much even with the .043 quench?

Thanks man.

oh and idk if our figs are different but i am getting 10.33 in the calculator

[gradon]

Read this:
http://www.empirenet.com/pkelley2/DynamicCR.html
You're not going to want to be above 8.5:1 DCR. The reason the stock cam would have more torque than some others is that the overlap is short in duration, so compression begins earlier. A lot of the long duration cams have more overlap, so compression starts later, thus the dcr is lowered.

[sudo chop]

I've been throwing stuff into Dyno 2003 and I like the way the 235-4 looks. Any major disadvantage to using this cam? This is going to be a DD.

If I need to get my DCR down without losing tight quench, what is the best way to do so? Can I have my machinist take some material out of those pistons? Is there a better way?

I don't want to lose too much compression though. I want the power of course. I really would like to know what people's real world experiences have been with tight quench and high DCR on these AMC engines. Of course how much cylinder pressure an engine can take is different for each, like my Integra Type-R has a DCR around 10.5:1 but thats possible only because of some serious engineering. So what DCR can this combustion chamber and head handle?

[Shark]

Speaking of Dyno 2003, what are you using for the block entry drop down menu?

[sudo chop]

Speaking of Dyno 2003, what are you using for the block entry drop down menu?

I did:
chrysler->6 cylinder->225 slant 6

Then obviously change the bore and stroke.

[Shark]

Speaking of Dyno 2003, what are you using for the block entry drop down menu?

I did:
chrysler->6 cylinder->225 slant 6

Then obviously change the bore and stroke.

thanks, thats what i was using too. /hijack

[Cheromaniac]

I've been throwing stuff into Dyno 2003 and I like the way the 235-4 looks. Any major disadvantage to using this cam? This is going to be a DD.

It'll be a nice streetable cam and with a 10.1:1 SCR, you'll have gobs of power and hopefully not have to run premium gas so you can have your cake and eat it. The only disadvantage will be noticeable valvetrain noise at idle due to the fast ramp rates of the cam. Use stock valve springs for the cam break in and then swap in a set of Mopar Performance 5249464 springs (rated to 0.525" lift). You might also want to consider a set of shaft-mounted roller rockers e.g. Harland Sharp and a set of Crower chromemoly pushrods for long term valvetrain stability and reliability. You'll need shorter pushrods anyway if you're going to mill ~30 thou from the block deck.

[sudo chop]

Dino, I put the 235-4 into the CR calculator just now, and I am getting 8.93 DCR. Isn't this too much? I was thinking about running the Isky 133127 cam, It makes good low end torque on DD2003 (not as good as the 235-4) and kicks my DCR down to about 8.3:1 which from a couple posts I've read is just flirting with the higher end of 87 octane pump gas on this engine.

Some other stuff I have already purchased besides those H802CP pistons is the Victor .043 MLS head gasket, and clevite77 bearings for all. Are these good bearings to use? If im not mistaken, those are the cam bearings SilverXJ had some trouble with.

[SilverXJ]

clevite 77 bearings are fine. My bearing failure isn't bearing dependent. I have a set of Clevite cam bearings and a set of Durabond bearings. I like the clevite finish better.

[4.whoa]

Everyone's always so worried about octane and detonation. How many of you have notched your bores? the CC overhangs even on my .060 over block,after having my head milled .040. I notched the bores and haven't had any problem with the dreaded ping. It's not only about cfm/flow, but better swirl and an almost guaranteed hot spot. I use 87 in normal driving and it's been ok even when i stomp on it. (granted i use 91 when i go to the track, but why take the chance when you're beating the snot out of it) I must admit i'm not sure of my correct scr/dcr as the shop said my cc's went UP to 68(?!?) after milling the block so I cant trust his #'s(I no longer use that shop)
Oh i'm running a 68-231-4 adv 4* (4.0 not a stroker yet) Supposed to be zero deck, .043 mls hg .no chamber or port porting or polishing.

Not trying to tick anyone off, just saying there are other ways to avoid pinging

[sudo chop]

clevite 77 bearings are fine. My bearing failure isn't bearing dependent. I have a set of Clevite cam bearings and a set of Durabond bearings. I like the clevite finish better.

Good to know. Thanks man.

Everyone's always so worried about octane and detonation. How many of you have notched your bores? the CC overhangs even on my .060 over block,after having my head milled .040. I notched the bores and haven't had any problem with the dreaded ping. It's not only about cfm/flow, but better swirl and an almost guaranteed hot spot. I use 87 in normal driving and it's been ok even when i stomp on it. (granted i use 91 when i go to the track, but why take the chance when you're beating the snot out of it) I must admit i'm not sure of my correct scr/dcr as the shop said my cc's went UP to 68(?!?) after milling the block so I cant trust his #'s(I no longer use that shop)
Oh i'm running a 68-231-4 adv 4* (4.0 not a stroker yet) Supposed to be zero deck, .043 mls hg .no chamber or port porting or polishing.

Not trying to tick anyone off, just saying there are other ways to avoid pinging

I hope there is some discussion sparked about this, I haven't heard of anyone else on this board mention this. Do you know how much overhang was notched off? I'm not going to argue about how much that helps swirl and flow, because it probably does a great deal. And eliminating that hot spot sounds even better. Hell I'm probably going to ask my machinist to do it. I am sitting here with Alexander Graham Bell's "Four Stroke Performance Tuning" (which has been my bible since I started playing with honda's a couple years ago) and I don't see anywhere in here where he addresses CC overhang. It could be that he assumes it is taken care of by default for anyone building a performance engine.

Still, notching would remove enough material to make your CC size go up at least a few cc, which would lower DCR.

Sounds like a totally awesome and valid option to a noob like me, both for better gas flow and for lower CR.

Perhaps I will just have the block zero decked and notched and THEN choose a cam. I've been messing with DD2003 all day and I am in love with the curves of the 239-4 and 235-4.

[4.whoa]

The notches aren't big,you can measure everything of course, but i read a easy article in engine masters a while ago, and followed it.
You mark the deck with dye then put the head on the bare block(i used a piece of cardboard to not nick anything)and snug it. then using a hanger bent like a fish hook and the little end sharpened,scribe the deck along the inside of the CC (from the bottom of course) when you take the head off there will be your mark. next put the HG on with several bolts to keep it where it needs to be and scribe the bores. then check the distance from the top of the piston to the top ring and put a mark in the bore. those are your limits!! do NOT sand past those!!and if in doubt , leave some extra there.Don't be aggressive, it doesn't take long to make the notches.And use a finer grit so it doesn't get away from you. I doubt the notches are even 1 cc per bore total.
Note: on my block not every cly needed both sides done( int/exh) core shift,I guess.
I'm planning on doing this again to an engine i'm building now. I wonder just how much (cfm)it helps with but i've been running this one for 2yrs and am happy with it.

Edit-to get an idea http://www.jeepstrokers.com/forum/viewt ... 26&start=0
the 1st pic shows where the chamber overhangs,and the 2nd gives an idea how big-or small the notches are

[sudo chop]

I found this also, looks like a pretty good DIY writeup.



i'll be doing this.

I want to brave the 239-4's DCR of 8.7:1. If I end up having to use like 89 or 91 or 93 or whatever, I would be ok with that I think.