K8600 vs. Comp 256XE

[mmcswain]

I have both cams is there really a choice or am I crazy not to use the 256? Please help.

[bushwood44]

Post the specs. of the Comp. cam.

[Chevelleguy]

The Comp has less lift, says it requires .150 longer push rods and screw in studs. I would venture to say it is a more technically advanced cam than the Summit.

[mmcswain]

http://www.compcams.com/Cam_Specs/Ca...x?csid=20&sb=2


Sorry here you go.

[JeepsAndGuns]

I have the comp XE256H in my 401. And I have the stock lifters/pushrods. I have had it in for several years, and the several years ago when I put it in, it said nothing about the screw in studs or longer pushrods.
Cant really help you much, as I have nothing to compare this too. I put the cam in on a fresh engine rebuild, and I dropped the 401 in place of a worn out 360.

I think the member plasticboob has one of these cams in his 401 too. Mabey he will post up. I think he swapped it in a already running 401.

[Elliott]

Originally Posted by JeepsAndGuns

I have the comp XE256H in my 401. And I have the stock lifters/pushrods. I have had it in for several years, and the several years ago when I put it in, it said nothing about the screw in studs or longer pushrods.
Cant really help you much, as I have nothing to compare this too. I put the cam in on a fresh engine rebuild, and I dropped the 401 in place of a worn out 360.

I think the member plasticboob has one of these cams in his 401 too. Mabey he will post up. I think he swapped it in a already running 401.

Did you run any oil additive for the break in or just use the cam break in lube?

[JeepsAndGuns]

Its been several years ago, so I cant really remember what I used. I cant remember if it came with some lube, or if I used some store bought assembly lube. But I used some type of assembly lube on it and all the other parts. Primed the oil system on the stand with the valve covers off to make sure I had oil out of all the pushrods. Then primed again right before I fired it up.
I broke it in with regular castroil 10w30, then drained it after the break in and have been running regular castroil 10w40 ever since. Nothing else ever added in. I think this summer, I may switch to rotella t 15w40.

[sappy76]

I'm getting ready to fire up my 401 with a crane cam. I used assembly lube, primed it and made sure oil in the pushrods as well. I installed a oil valley bypass line which will feed oil to the rear journals. I'm going to use Joe Gibbs break in oil, which comes highly recommended by a race engine builder here in town. Apparently the newer oils are really lacking for breaking in engines. (I hope all goes well, the previous owner lost a piston at start up due to improper ring gaps on the Keith Black pistons. Also, the cam lobes looked pretty worn for only having 10 miles on the engine. Most likely due to lack/poor oil at startup.)

[Chevelleguy]

The new oils are lacking for flat tappet cams in general. Run Rotella or Delo, the diesel oils have more of the stuff flat tappet cams need.

[addicted]

After I had to put a cam and lifters in my 04 GC 4.0 I broke it in with the stuff that came with the MOPAR Purple shaft I used and then changed it over to Amsoil full synth with extra zinc especially for flat tappet cams. A little more expensive but if you use their filters they warranty the engine from oil damage for 20,000 or so.

[dusty]

Originally Posted by Chevelleguy

The new oils are lacking for flat tappet cams in general. Run Rotella or Delo, the diesel oils have more of the stuff flat tappet cams need.

This is not true any more all diesel oils out there that you listed have upgraded (or down graded in my mind) fromt eh old CI-4 rating to the new CJ-4 rating the Zinc content in the CJ-4 oils is Not sufficient for cam break in any more.

John deere did not change their oil so their 15/40 is still a CI rated oil with higher zinc content, they did this because they proved in factory testing that there was a significant increase in engine parts wear when they tested out oils that met the new CI4 rating. all others if they have a CJ4 rating are too lo on the zinc which is what you need for cam break in..




Next question what motor a 360 or a 401? what compression ratio? what is the application?

the 8600 (the old PAW grind) is a great cam the wider lobe seperation will give youa wider torque curve vs the comp but not enough to notice. Id go for 256EX in a 360 with stock compression or a 401 with stock compression thought i think the 8600 is a little better on a stock compression 401 with the higher lift numbers. I think comp still leaves some power on the table with their lower lift numbers. Engle really has the high lift short duration thing down for our motors. the short exhaust duration on the comp will limit peak Rpm range the EX256 is pretty short legged IMHO I think with the 214/224 dur at .050 the summit cam will have a few more legs rpm wise than the comp cam but pretty darned close specs wise. heres a couple others for comparisons sake
all good on stock compression 401s I am running the lunati on my 9.8:1 401 with performer intake and TBI working out bugs but it's a stump puller. Don't look at the adv duration since everyone seems to measure a little differently look at the dur@.050 for a more accurate comparison. but the comp 256 has good agressive ramp profiles and every bit capable of making similar hp numbers to the 8600 and may yeild higher low end power numbers


Summit 8600
Advertised Duration (Int/Exh): 272/282
Duration @ .050 (Int/Exh): 214/224
Gross Valve Lift (Int/Exh): .472/.496
LSA/ICL: 112/108
Valve Lash (Int/Exh): Hyd/Hyd
RPM Range: They say 1500-4500 is the operating range which is pretty much what the XE256 does with the XE256 the range seems to be 1000-4000 with it falling off around 4500 rpm the 8600 seems to reva little longer

Comp Cams XE256H
Advertised Duration (Int/Exh): 256/268
Duration @ .050 (Int/Exh): 212/218
Gross Valve Lift (Int/Exh): .477/.484
LSA/ICL: 110/108
Valve Lash (Int/Exh): Hyd/Hyd
RPM Range: 1200 to 5200



Lunati 64501
Advertised Duration (Int/Exh): 256/262
Duration @ .050 (Int/Exh): 213/220
Gross Valve Lift (Int/Exh): .484/.507
LSA/ICL: 112/108
Valve Lash (Int/Exh): Hyd/Hyd
RPM Range: 1200-5500

Engle 5054H
Advertised Duration (Int/Exh): 260/260
Duration @ .050 (Int/Exh): 214/214
Gross Valve Lift (Int/Exh): .501/.501
LSA/ICL: 112/108
Valve Lash (Int/Exh): Hyd/Hyd
RPM Range: 1200-5200 R.P.M.

[PlasticBoob]

Originally Posted by mmcswain

I have both cams is there really a choice or am I crazy not to use the 256? Please help.

Yes you are crazy! It's no contest, the 256xe is AWESOME. I have so much torque it's unbelieveable.

Here are some Desktop Dynos - don't pay attention to the actual numbers, just compare the differences and see which makes more power, and where:
Summit 8600: http://home.off-road.com/~plasticboob/t1/amc401cam-sum-8600.jpg

Comp Cams 256XE: http://home.off-road.com/~plasticboob/amc401chart.jpg

[PlasticBoob]

Originally Posted by Chevelleguy

The Comp has less lift, says it requires .150 longer push rods and screw in studs. I would venture to say it is a more technically advanced cam than the Summit.

WHAT? My instructions didn't mention any of that at all! That means I'm probably not making maximum power, right? I'm not using stock pushrods, but don't know if they're .150 longer than stock (it's been years, can't remember any of it - I just know they're Summit rods). Time to go measure I guess...

[PlasticBoob]

Originally Posted by JeepsAndGuns

I think the member plasticboob has one of these cams in his 401 too. Mabey he will post up. I think he swapped it in a already running 401.

First I installed the Edelbrock Performer intake on the stock engine, and noticed a slight improvement. But after I swapped in the 256XE cam, I noticed a huge improvement in low/mid range torque! I never have to rev the engine (not that I had to much before), but I can accelerate "briskly" to say the least and not even have to get above around 2000rpm. I also did my "curb test" before and after the cam swap, and noticed that I could climb a curb at significantly lower RPM than with the stock cam. I was also worried that this cam wouldn't play nice with fuel injection, since I had repeatedly read on the internet that "cams with lobe separation angles less than 112* don't work well with MAP sensors". I didn't have that problem at all, I just richened up the idle mixture a bit and things are great. I'm a very happy camper with this cam!

**I don't know all that much about cams so this is just my subjective, practical, real-world experience with this cam...I did some Desktop Dynos to help me choose it, here they are: http://home.off-road.com/~plasticboob/cams.htm

[JeepsAndGuns]

Originally Posted by PlasticBoob

WHAT? My instructions didn't mention any of that at all! That means I'm probably not making maximum power, right? I'm not using stock pushrods, but don't know if they're .150 longer than stock (it's been years, can't remember any of it - I just know they're Summit rods). Time to go measure I guess...

Yea, mine didnt say anything about that either. I am running stock lengh pushrods and stock rocker arms. Still runs good for me.

[dusty]

Originally Posted by PlasticBoob

WHAT? My instructions didn't mention any of that at all! That means I'm probably not making maximum power, right? I'm not using stock pushrods, but don't know if they're .150 longer than stock (it's been years, can't remember any of it - I just know they're Summit rods). Time to go measure I guess...

some do some don't but thats with roller rockers not stock bridges. prime the oil system and turn the engine over doubtful you need longer pushrods if you are running stock rockers. my engine needed 10 thou longer but that was because of my roller rockers not the cam.

[JeepsAndGuns]

Originally Posted by dusty

John deere did not change their oil so their 15/40 is still a CI rated oil with higher zinc content, they did this because they proved in factory testing that there was a significant increase in engine parts wear when they tested out oils that met the new CI4 rating. all others if they have a CJ4 rating are too lo on the zinc which is what you need for cam break in.

I find this very interesting. Mainly because I now work at the local john deere dealership , and just noticed the shelf full of their 15w-40 diesel engine oil. I am thinking I might see if I get a discount on it, and might start running it. I dont think it would hurt anything. I run some rotella-t in my 246k 4.0 in my YJ and it run just fine.