Cam Debate

[brokenujoint]

ok i've sat back on my build for a few yrs and I'm starting it up again. When i left off everyone was going with Crane and Comp cams. they kept wasting lifters because the lobes were to thin.. after hearing about this i decided to go to a stock 97 4.0 cam.. i dont care for snap your neck performance really i just want a new, pepped up, long lasting (most important) engine. Is there a proven cam that is recommended?

[gradon]

Get a mopar cam that has the same wide lobes as the stock. I got mine(the 30ab) from www.mopartsracing.com / www.jeepconnection.com . If you can only get the 28, consider using 1.7:1RRs to bump the lift. They all have less overlap compared to other cams, so they will build torque sooner(so definitely calculate your DCRs!) Also, the 30ab's powerband starts a little later than the 28 and 29(pulls hard to redline), so if you like the bigger lift, but want power earlier, consider advancing it(which also raises DCR).

[1bolt]

If you can wait I intend to compare a bunch of off the shelf cams using Engine Analyzer Pro... part of the wait is me not having a hell of a lot of time and part of the wait is finding true accurate and comprehensive data on the cams, EAP uses a lot of info on the cams and some makers don't supply it, or they supply slightly different data, which is confusing and often mixed in with other more desirable data... Advertized duration (useless) for instance is often quoted right before "seat" duration, and lobe center line and separation often don't actually jibe with the .050 lift duration data. Sometimes its hard to tell if the numbers are advertised (when they are not clearly denoted) or one of many other common duration measurement standards.

[jffffl]

Just another option, if you old cam is still servicable. Have it reground, to the specs your desire.
My 92 had the wide lobes, unlike the after market cams, and it reground and then re-hardened.
So it should be like a new, better I hope, than the alternatives. We'll see when we turn the key
this evening!!! It will still be interesting to see how the cams sort out on the simulator, are you
doing a short rod vs long rod, like your time isn't valuable.

Russ

[Cheromaniac]

When my Crane 753905 cam failed after 34k miles, I replaced it with my old '92 stock cam. The performance loss was so small I could only detect it with a stopwatch 'cause I couldn't feel it by the SOTP. The stock cam actually produced better part-throttle response and I even saw a small mpg gain.
Then when I swapped my old '92 intake manifold for an '01 XJ version, I recovered some of that lost performance and gained even more mpg, so now my engine performs almost equally with the stock cam as it did with the Crane and with better fuel economy.

[brokenujoint]

since i already purchased a 4.0 stock cam i am happy to hear what you just said.

[PolloLoco]

So the CompCams have thin lobes which can contribute to premature failure? That's a real kick in the pants. It looks like I'll have to go with a Mopar cam and 1.7 roller rockers to bump up the lift a bit.

[dwg86]

I talked to Reed cams about this a while ago. The way he explaned it to me was...The bottom of the lifter is round, like a basketball for example. It doesnt matter how big the surface is you set the basketball on, it still has the same contact point. It makes sense to me.
I would make sure you use a good break in oil, make sure your valve springs don't bind, the valve spring retainers don't hit the guides, pushrods are correct length, and spring pressure is not ecessive.
If you want the wider lobes but more of a performance cam, you can always have yours reground(smaller base circle). If you are going with 1.7 roller rockers, buy a pushrod length checker and make sure your pushrods are the correct length. I used 1.6 crower roller rockers, zero deck, and shaved the head just enough to make sure it was flat. My pushrods ended up 9.350 long. That is almost .300 shorter than the stock pushrods. When you are changing to a roller rocker, decked the block, shaved the head, there is no telling how long your pushrods will end up. The pushrod checker is only $20.00. Custom pushrods aren't that expensive. I paid something like $5.18 a piece for one piece for .080 wall, 4130 chrome-moly pushrods. Total shipped to my door in 3 days was something like $65.00.
http://www.trendperform.com/
http://www.trendperform.com/misc/TrendP ... og2008.pdf

[PolloLoco]

I talked to Reed cams about this a while ago. The way he explaned it to me was...The bottom of the lifter is round, like a basketball for example. It doesnt matter how big the surface is you set the basketball on, it still has the same contact point. It makes sense to me.
I would make sure you use a good break in oil, make sure your valve springs don't bind, the valve spring retainers don't hit the guides, pushrods are correct length, and spring pressure is not ecessive.

I thought that flat-tappets were flat?





maybe not...

I found this article to be an interesting read:
http://stockcarracing.automotive.com/49 ... index.html
It answered my question "why 15W-40, isn't that a diesel oil?" and explains what makes a good [break-in] oil.

Another good read:
http://www.hotrod.com/techarticles/engi ... index.html
It mentions "crown radius" a couple times. I guess there is an ever-so-slight crown to the "flat" tappet.

The lesson of both articles?

• Get good lube! Diesel and "for off-highway use only" oils are your friends, they have more ZDDP
• Aggressive lobe profile can contribute to premature failure
• Lifter bore grooving is a good idea (SilverXJ, got that tool handy for rent?)
• Proper break-in is key, to include assembly lube

[dwg86]

Yes they are a hydraulic flat tappet (non roller), but all flat tappets have a slight convex curve. If you hold a straight edge on the bottom, you can see it. It is because of this curve and a slight tapper of the lobe that makes the lifter spin. If the lifter doesn't spin, you will wipe out a cam real fast.

[PolloLoco]

Yes they are a hydraulic flat tappet (non roller), but all flat tappets have a slight convex curve. If you hold a straight edge on the bottom, you can see it. It is because of this curve and a slight tapper of the lobe that makes the lifter spin. If the lifter doesn't spin, you will wipe a cam real fast.

My post was edited after you posted this. I found out that there is a slight crown.

I think I'll stick with my original plan of the COMP 68-231-4.

[PolloLoco]

[/hijack]

ok i've sat back on my build for a few yrs and I'm starting it up again. When i left off everyone was going with Crane and Comp cams. they kept wasting lifters because the lobes were to thin.. after hearing about this i decided to go to a stock 97 4.0 cam.. i dont care for snap your neck performance really i just want a new, pepped up, long lasting (most important) engine. Is there a proven cam that is recommended?

From the articles that I already referenced your "years ago" happened at the time of the "death" of the flat-tappet camshaft design. Several factors contributed to the failures including decreasing ZDDP levels and poor-quality lifters. Things seem to have calmed down now, but then I also found this thread that talks about thin lobes:
http://www.jeepstrokers.com/forum/viewt ... 46&p=12178
It seems that aftermarket cams are fine, just ensure that you use good lifters and good lube. If you want the wide lobes then go with Mopar.