4.7L stroker build happening soon, time to pick cam

[Rinkrat456]

For a 4.7L stroker using a 12ctw crankshaft and long rod forged pistons, what do you folks think is the best camshaft for an '89 XJ? This will be my wife's daily driver and we can run up to 91 octane but it would be nice not to have to every day.

Here are the build parts:

-'97 4.0L block and head, stock valves but head 0.005" decked
-Icon KB forged pistons, 0.060 over
-70's 12ctw AMC 258 3.895" crankshaft
-4.0L 6.125 rods
-'97 intake manifold (if possible, otherwise we can re-use the '89 stuff)...

This is for an '89 XJ my wife will daily drive and wheel/off road quite a bit later on. Reliability and low end torque are the main goals. I was hoping to use factory valve train parts to keep everything easy to replace and timid. I found this web link with cam info...
http://www.angelfire.com/my/fan/Jeep4.0Camshafts.htm

And I'm thinking of using one of the factory camshafts...new hopefully, if I can find one. Using the '87-'95 cam specs (270/270 adv dur, 197/197, 0.424"/0.424", 112LSA 120ICL) and using a factory head gasket, I calculate a compression ratio of 9.53 with a DCR of 7.02...does that check out? Sounds pretty good of a choice to me for a daily. The other two versions of the factory camshafts seem like they get more emissions-happy and less powerful for a 4.7L stroker that doesn't need to meet emissions.

Any thoughts ?

[IH 392]

If using a stock cam I would run the '97-'99+ OBDII cam over the OBDI cam, dyno sim's show it to be much better and if the earlier cam was/is so good why did Chrysler change it?
And I wouldn't go any more on the over bore than to clean it up, going all the way will get you NO more power and if something should happen there is no possibility of fixing it!

[Rinkrat456]

The block is already 0.060 over and all the machine work has been completed.

If you look at the OEM cam's, the duration gets shorter and lift decreases on each revision until the end of the 4.0L all together when Mopar decided to use the 3.7L V6 for better emissions.

[ruffy01]

I ran a dyno sim on both cams for you.
It shows the earlier cam makes more power after 5000RPM, pretty useless, and loses out before that.

Jeep 96 vs 87 cam.jpg

[IH 392]

I lost all my engine simulations in a computer crash! but IIRC? neither of the "RENIX" or "OBDI" cams was really worth a crap!??, the way my '97 engine pulled right up till the rev limiter shut it down!
Try a sim with the OBDII cam advanced 4* and look at the torque curve.

[Rinkrat456]

I suddenly have my eye on the 81-90 4.2L cam. Seems like it fits in between the early 4.0l cams well and keeps cylinder pressures within the range of 87 octane.

Thanks to the USAF, my wife and I now live on the east coast at Dover AFB where I've heard the humidity is horrid. Perhaps not Florida horrid, but worse than we're used to. This Jeep may see up to 3500lbs of trailer weight behind it and 90+ degree days of high humidity, so I'm just trying to pick a cam she can drive every day without wondering "if the engine can handle it"...

4.2L '81-'90 cam specs: 262/262, 191/191, .405/.405, 114lsa and 113icl...makes for 9.57:1 compression and a 7.73:1 DCR. I've been under the assumption 7.5-8:1 DCR is best for 87-89 octane, and lower if we're at sea level towing on a hot muggy day.

[Rinkrat456]

If anyone wants the full size image...

[Cheromaniac]

Those curves don't look right and the reason is that you've entered a seat-to-seat duration of 262 degrees. If you enter a 0.050" opening duration of 191 degrees which would be the correct way to do it, the results will be very different (lower rpm peaks for HP/TQ).

[Rinkrat456]

Those curves don't look right and the reason is that you've entered a seat-to-seat duration of 262 degrees. If you enter a 0.050" opening duration of 191 degrees which would be the correct way to do it, the results will be very different (lower rpm peaks for HP/TQ).

Interesting catch. What do you think about using a 4.2 cam instead of the early 4.0 cam?

[IH 392]

Actually running the 258's back in the day! I wouldn't take one of those shitty cams to use for a tent stake!, those emission cams were absolute CRAP!

[Cheromaniac]

What do you think about using a 4.2 cam instead of the early 4.0 cam?

I wouldn't bother. The 4.2 cam has too little duration & lift and the performance in a stroker would fall off dramatically above 4000rpm. The early 4.0 cam that I'm using is a much better choice and my dyno numbers speak for themselves.

[Rinkrat456]

What do you think about using a 4.2 cam instead of the early 4.0 cam?

I wouldn't bother. The 4.2 cam has too little duration & lift and the performance in a stroker would fall off dramatically above 4000rpm. The early 4.0 cam that I'm using is a much better choice and my dyno numbers speak for themselves.

Though this engine will very rarely see 4000rpms or higher, I think you're right on the short duration. I found a good $100+ shipping cam option though after making a few phone calls today. My buddy works at a machine shop near my home town and can get an OEM replacement Melling brand camshaft. Specs are for 87-91 4.0L's, though these specs don't match up 100% to the ones listed on this website.

270/270 advertised duration
197/197 duration at 0.050"
.397/.397" valve lift
112 Lobe Sep Angle
112 Intake Center Line

Cam works out to 7.7:1 DCR, still fine for low octane pump gas.

It's supposed to be a stock replacement camshaft so I'm hoping it will have the wider lobes and work nicely with my Federal Mogul OEM lifters.

[Rinkrat456]

Melling part # MC809. Ordered and paid for today. I ordered it through my machine shop contact for $105 bucks and they're going to ship it to me for another $20 or so. Should use the wider OEM lobes and work with stock springs.

Final specs (same as above)...

270/270 advertised duration
197/197 duration at 0.050"
.397/.397" valve lift
112 Lobe Sep Angle
112 Intake Center Line

Using the Icon 944 0.060" over pistons and stock MLS headgasket (0.051 compressed 4" bore) and zero deck height I come up to a compression ratio of 9.77:1 and a "DCR" of 7.70:1 now that the cam is factored in.

We shall see how this goes.

[Cheromaniac]

Final specs (same as above)...

270/270 advertised duration
197/197 duration at 0.050"
.397/.397" valve lift
112 Lobe Sep Angle
112 Intake Center Line

The lobe lift is 0.265" so those valve lift numbers would coincide with a 1.5 rocker ratio. The actual stock rocker ratio is 1.6 so the valve lift should be 0.424".

[Rinkrat456]

The lobe lift is 0.265" so those valve lift numbers would coincide with a 1.5 rocker ratio. The actual stock rocker ratio is 1.6 so the valve lift should be 0.424".

Thanks for the heads up. I'm more of an LS-engine builder so the finer details of the Jeep stroker are still new to me. I'd change the specs above but I can't edit it.