Cam talk (total noob)

[dodgerammit]

Okay, so in researching for my future engine build, I am first looking at cams. Well, reading till my eyes glaze over and I begin bleeding out my ears....

I am leaning more toward a custom grind.

Given, the Jeep has 2.73 gearing (and honestly, not looking to do the desired gear change/OD swap anytime soon, if ever), I am wanting to help all I can on the torque range.

A possibility of swapping axles to a 3.31 set is way more probable (even though OD/3.73s/Truetracs F/R would be a dream setup).

With my gearing and tire size (235/75/15), I'm running from 1500 rpms at 50mph to just under 2200 at 70. Focusing on that realistic range at highway speeds, I need a cam that makes max torque in that range. Correct?

So far, few are really designed for that low. Schneider comes in mind. Seems Engle cams falls in favor with the AMC crowd. Their 52-54 comes highly recommended. One guy on ifsja has this cam and loves it. Dyno numbers show a fairly flat torque graph through 3500 rpm, then it drops.

My only concern is the exhaust lift at .501 being above the magic .50 (yeah, barely) that they say you can safely run without heavier springs.


Here are the contenders so far:


Engle 52-54 (custom grind)
Duration:251/261
Lift: .482/.501
Duration @ .050: 208/216
Lobe Centers: 112
RPM range ?-3500

Lunati 260 (stock grind)
Advertised Duration (Int/Exh): 260/260
Duration @ .050 (Int/Exh): 210/210
Gross Valve Lift (Int/Exh): .470/.470
LSA/ICL: 110/106
Valve Lash (Int/Exh): Hyd/Hyd
RPM Range: 1000-4800

Schneider Cams 252-56H (custom)
Duration 252-256
Intake Duration (.050”): 194
Exhaust Duration (.050”): 204
Intake Valve Lift*: .424"
Exhaust Valve Lift*: .448"
Lobe Separation: 110
RPM Range: 1000-3500

According to babywag, the stock cam has 425/.425 lift. Of course, I know nothing else other than the duration being 196 (found on the interwebs, so may/may not be true).

Question about the stock cam. Why was it so horrid?

I've read the timing was retarded for emissions. Seems the few specs I see aren't bad when compared to the other low end power combos.




Next is what compression ratio I need. That is a whole other session of ear bleeding/glazed eyes.

It seems that CR follows the advertised duration with higher durations meaning higher CR.

So, given I'm looking at lower duration, I'm probably looking 8.5:1?

I understand (I think) the cam determines this for the most part, but can a decent set of pistons bump the CR to a respectable number?

Should I really concern myself with that?

Sorry for all of the noob questions, but I really want to do this right the first time.

Also, if you have real world experience with any of the above cams, chime in.

Thanks!

[dodgerammit]

Found on the obiwan Jeep Wagoneer page:

'74-78 304
'74-79 360
Lobe lift .266"
Valve lift (1.6x) .426"
Intake valve opens 14.75* BTDC
Intake valve closes 68.75* ABDC
Exhaust valve opens 56.75* BBDC
Exhaust valve closes 26.75* ATDC
Valve overlap 41.50*
Intake duration (adv) 263.50*
Exhaust duration (adv) 263.50*
Lobe separation angle
(computed by me, error-prone) 111*

[dodgerammit]

More reading, eye glazing, etc.

Found this thread: http://fsjnetwork.com/forum/viewtopic.php?t=8153

In one reply, REDONE stated this concerning compression:

One thing I would like for you to consider is that I wouldn't bother building an engine with the abysmal stock 8.6:1 compression, it's so incredibly inefficient! I'm not saying go overboard like I did with 12:1, but the smallest increases in compression yield the biggest gains in power and torque!

When you change your cam and carb on a stock (static) compression engine, you increase the DYNAMIC compression at a given RPM which is what gives you more power at that RPM.

With a cooling system working as good as a new stock system you can run 9:1 on low grade no problem, but I don't think that's really a selling point.

Right now the gas prices around here are $2.20 for low grade, and $2.35 for premium. On premium you can run 10:1. That's 15 cents difference a gallon so lets round up to 20 cents. Now lets say you have a 20 gallon tank. To fill up that $4 difference. That's two cans of Monster, half a pack of cigarettes or one BOMB burrito inside that same gas station. Chances are, your increased milage from the increased efficiency will make up for most of that $4 already anyways.

Followed up by a 2nd motion and addition by Tatsadasayago:

For towing, high lift and short duration is the ticket. Look for a centerline of 108 if possible. The reasoning is all the work is being done from idle to 2500 in most situations, so tailor the cam profile to match your RPM and load. Dual pattern cams with higher exhaust lift and duration compared to the intake take advantage of the dogleg exhaust port design of the AMC heads. And yes, I agree that a bump to 9.5:1 compression will surely make a difference down low.

So, the above posts have me leaning toward 9:1 to 9.5:1 compression and the Engle 52-54 cam. My thoughts being 9:1 compression, while lower, allows me to hit any 100% gas station and not worry about not having premium available. Most have 87 or 89 octane.

[dodgerammit]

And just like that, I found another contender.

Same company though.

Camshaft ,Engle 35018-H
Rocker Ratio,1.6
ILCL,109
LSA,112
Int. Duration @ .006,248
Exh. Duration @ .006,260
Int. Duration @ .050,207
Exh. Duration @ .050,216
Intake Valve Lift,466
Exhaust Valve Lift,496
Overlap,30
Hydraulic Intensity,41
Recommended RPM's,Off Idle - 4000

Looks like I'll be calling Engle up and weighing my options.

[dodgerammit]

Posting here for later study. Good CR info concerning piston choices and head displacement::

http://theamcforum.com/forum/amc-360-pi ... page2.html