Stroker questions, low CR 4.6 config

[jeepmkcomin]

Well I got a 4.0 block for free and decided I want to stroke it. I've been reading around a little bit and have decided what combo I'd like to put together:

4.6L Low-buck, low CR "rockcrawler"

~ Jeep 4.2L 3.895" stroke crank
~ Jeep 4.2L 5.875" rods
~ Keith-Black Silvolite UEM-2229 +0.030" bore pistons
~ Increase piston dish volume to 30cc
8.8:1 CR
~ Crane #750501 192/204 degree camshaft
~ Ported HO 1.91"/1.50" cylinder head
~ Mill block deck 0.035"
~ Mopar Performance 0.043" head gasket
~ 0.058" quench height
~ 2.25" exhaust
~ Ford 24lb/hr injectors with stock 39psi FPR for '87-'95 engines, stock injectors with stock 49psi FPR for '96 and later engines
~ 231hp @ 4400rpm, 327lbft @ 2000rpm

I have a couple questions regarding this combo:

I realize the 4.2 crank comes with 2 different numbers of weights on it. I hear the 12 wt is the better for torque at low rpms. What 258's had this crank as opposed to the 4 wt crank?
Has anyone who's tried this particular stroker combination run into any problems?
I heard something about clearancing a crankshaft or something, anyone care to explain?
Even with that combination will I need an aftermarket fuel pump?

And anything else I need to know.

Thanks ahead of time, will be checking in.

[Muad'Dib]

Well I got a 4.0 block for free and decided I want to stroke it. I've been reading around a little bit and have decided what combo I'd like to put together:

4.6L Low-buck, low CR "rockcrawler"

~ Jeep 4.2L 3.895" stroke crank
~ Jeep 4.2L 5.875" rods
~ Keith-Black Silvolite UEM-2229 +0.030" bore pistons
~ Increase piston dish volume to 30cc
8.8:1 CR
~ Crane #750501 192/204 degree camshaft
~ Ported HO 1.91"/1.50" cylinder head
~ Mill block deck 0.035"
~ Mopar Performance 0.043" head gasket
~ 0.058" quench height
~ 2.25" exhaust
~ Ford 24lb/hr injectors with stock 39psi FPR for '87-'95 engines, stock injectors with stock 49psi FPR for '96 and later engines
~ 231hp @ 4400rpm, 327lbft @ 2000rpm

I have a couple questions regarding this combo:

I realize the 4.2 crank comes with 2 different numbers of weights on it. I hear the 12 wt is the better for torque at low rpms. What 258's had this crank as opposed to the 4 wt crank?
Has anyone who's tried this particular stroker combination run into any problems?
I heard something about clearancing a crankshaft or something, anyone care to explain?
Even with that combination will I need an aftermarket fuel pump?

And anything else I need to know.

Thanks ahead of time, will be checking in.

We have a FAQ question... dont forget to check it out.

Here is one that will help you:

viewtopic.php?f=27&t=51

[jeepmkcomin]

Thanks! I guess I jumped in too fast... I will look through some more of the faq.

[dwg86]

You might want to consider using a different cam. From what I've been reading on the web, the crane cams have pretty big failure rate. The aftermarket cams are for the 258 (narrow lobes) and they do work in the 4.0. There is some difference according to the cam casting company that makes the cam blanks. Something about how or where the lifters hit the lobes... or something like that. I can't remember exactly what he said. They are suppossed to be making cam blanks for the 4.0 (wide lobe), but they won't be available for a few months. The mopar performance cams are made for the 4.0. I think the mopar performance 4529228ab camshaft is still available but the 4529229ab and 4529230ab have been discontinued. You might be able to find a 29ab or 30ab collecting dust in a dealership somewhere. There is a 4529229ab cam on ebay right now.

[Flash]

Personally if your looking for the heavy 258 crank for rock crawling..........the Crane cam is to big.
The small mopar cam that is left would give you a lot on the bottom end or low rpm torque.............Just don't expect it to rev higher then you stock cam.

The "catch 22" of this cam, is that it will bring you DCR UP!
So you Static Compression Ratio (SCR) will need to be considered carefully.

Flash

[jeepmkcomin]

Flash I'll be honest with you, I read through the faq on SCR and DCR but I'm still not sure exactly what you're telling me. If the dynamic compression ratio is always lower than the static compression ratio, wouldn't a ratio of 8.8 scr still allow a low DCR for the street? Or am I missing the point you're trying to make completely.

Or if you are speaking of the mopar cam?

The crane cam is too big as in clearance in the engine or as in the intake and exhaust valve durations?

---

dwg86: Are those part numbers for cams? I'm guessing wide and narrow lobe are different patterns used on the cams for the 258 and 242 for opening and closing valves? Does a narrow lobe work in a wide lobe engine?

Sorry I am completely new to this guys but am trying to learn as much as possible!

[Flash]

Flash I'll be honest with you, I read through the faq on SCR and DCR but I'm still not sure exactly what you're telling me. If the dynamic compression ratio is always lower than the static compression ratio, wouldn't a ratio of 8.8 scr still allow a low DCR for the street? Or am I missing the point you're trying to make completely.

Or if you are speaking of the mopar cam?

The crane cam is too big as in clearance in the engine or as in the intake and exhaust valve durations?
The crane cam move its HP and Torque range higher in the RPM range were as the Mopar cams Hp and torque curve would be at a lower rpm(were you want it if you a rock crawler)---

dwg86: Are those part numbers for cams? I'm guessing wide and narrow lobe are different patterns used on the cams for the 258 and 242 for opening and closing valves? Does a narrow lobe work in a wide lobe engine?

Sorry I am completely new to this guys but am trying to learn as much as possible!

Dynamic Compression ratio is tough to grasp with the first bite, but as you chow on it, it will make more sence.

IF you get you SCR down to 8.8(which would require a deep dish) and you installed the mopar cam, you DCR would be higher then(because the intake valve would be closing sooner) if you installed the Crane Cam(intake valve would close later, making essentially a shorter compression stroke......They would both be below the scr of 8.8
Just fictitious numbers here........but if you had SCR of 8.8 the the mopar cam would come around 8.1 and the Crane came would be at 7.4......................
SCR in the machanical compression ratio and DCR is what the eng See's when it running. you can't start to make compression until both valve are closed and the piston is in a upward direction...........No mater what cam you install the IVC will be after the piston has started up the bore on the compression stroke.

The "CATCH 22" is if you were running say 9.5 SCR and you were using the Crane cam. Your DCR would be low enough that it wouldn't ping or Knock on pump gas................Remove the crane cam and install the Mopar cam.......now you DCR has go up to the point that you must run premium all the time as you have raised you DCR up........Evan thow you SCR has NOT changed

Make sence? or did I confuse ya more?

[jeepmkcomin]

It's starting to get clearer. Would a dcr of 8.1 be okay for pump gas?

Also which mopar cam specifically are you looking at; I'd like to try plugging in the durations bore stroke etc into your formula on the faq page so I can work through it myself. Not that I dont trust your numbers but I think I would learn more that way.

[EDIT: ivc = intake valve closed]

Thanks so much for the advice and help thus far.

[Flash]

It's starting to get clearer. Would a dcr of 8.1 be okay for pump gas?

Also which mopar cam specifically are you looking at; I'd like to try plugging in the durations bore stroke etc into your formula on the faq page so I can work through it myself. Not that I dont trust your numbers but I think I would learn more that way.

[EDIT: ivc = intake valve closed]

Thanks so much for the advice and help thus far.

From all that i have read, DCR of 8.1 is about the limit. for a street eng. you would be better of in the 7s if you want to run low octane fuel................and like i said in the fact, were you live(altitude) will vary how much DCR you can get a way with.

MPP yous to sell 3 levels of performance, now the smallest of them is the only on available. P4529228AB

I wouldn't trust my numbers either, as i just pull then out of the air for examples
That's what i did. go to different cam sights pull the info of the cams you like, take the IVC spec and start plugging them in, and start watch what happens.

Happy to help any way i can

Flash

[Flash]

on your search, go to Comp Cam's, do some figures with there 231 cam......That would be my choice
Also, the stock cam would work, just fine in a low rpm crawl rig.

Just making your 4.0L into a "stroker" will increase your low end torque a bunch, with out changing your cam, or any thing else.........and, the heavy crank just adds to that.

Flash

[dwg86]

Yes the 258 camshaft or narrow lobe will work, but there has been problems. Check out this link http://www.jeepsunlimited.com/forums/sh ... =crane+cam
Some people havn't had any problems, but after reading this link, doing some research, and talking to a company that makes camshaft cores, there could be a problem. The camshaft company also said that cheap lifters and low zinc in the oil is also a contributing factor in camshaft failures. If you can't wait until the new 4.0 cam castings are done, and don't want to use the mopar performance camshaft, I would make sure the lifters that you use are MADE IN USA!!! I also like the crower cam saver lifters (They are also made in the USA).

[John]

Ok you are thinking of building a 4.6L Low-buck, low CR "rockcrawler", Could I ask what your end use of this motor will be? Rockcrawler or low buck emphasis? What vehicle are you planning on using? It will steer some of the information you get from the board membership.

John

[jeepmkcomin]

I obtained a 4.0 small block for free that really only needs to be honed. I want to keep it cheap but it will be used for rockcrawling so I like the idea of a torquey motor rather than a high rpm hp one. That's why I targeted that configuration on one of the many stroker "combo" sites. It will still see mud but it will be purposed for rocks.

Flash you mentioned I could use the stock cam... the stock 4.0 cam or the stock 4.2 cam? I would love to keep the majority of the torque in the low rpms.

Also I found this:



Is this too far gone to clean up and use? I can get it from a friend locally for $20... media blasting?

Thanks again guys.

[John]

Use the stock 4.0 camshaft, and it is unlikely the crankshaft in the picture is salvageable. What year is the 4.0 block that you are working with?

[Flash]

I will 2nt John's thoughts.


The rust is too deep and would require machining deeper then there is bearing available.

Cranks tend to warp when there laid on there side instead of strung up by there neck.
It only takes several thousands of warp to make it junk!!!!!!!!

Trust me, it's not worth 5 buck!

Flash