The comp 268 has a nice idle with lope.

 

See my issue is that this is a daily driven 4wd truck. When I need the low end torque, I WANT IT! So needless to say im teddering between the 260 and the 268.......

 

If I were trying to decide between the comp 260 and 268 with low torque in mind...I would lean towards the 260H.

If I were open to suggestions...I might consider stock cam, higher ratio rockers, and port work to the head.

For the heck of it, here is comp cams description of the 260H and 268H

260H

The 260H is the perfect cam for vans, family sedans, pickups and tow vehicles. This cam provides exceptional power and a gas mileage increase, especially on the highway. With its great torque and throttle response, the 260H cam can also be used for O.E.M. replacement in most big block applications. The 260H's idle is smooth in large engines with stock exhaust systems. With headers, the 260H will produce a very slight exhaust sound.

268H

The 268H cam is Comp Cam's most versatile cam. It is a great high performance cam for small blocks and a powerful cam for big blocks. With its noticable idle and great all-around power, the 268H cam is great for daily driven performance vehicles. The 268H cam is an ideal cam for pickup drivers who want major power increases. It is also good for big blocks towing heavy loads equipped with lower optional rear end gears.

General statement on the Comp High Energy Camshafts

All high energy cams are designed to work with 8.1 to 9.1 compression. The unique lobe designs used on High Energy Cams allow them to build good cylinder pressure without the need for high static compression ratios. That's why they work so well and makes so much torque. Higher compression ratios will only work against the cam and possibly cause detonation and preignition.

 

Thanks. Yeah Ive read them both over and over. I probably should go with the 260. Its not a high performacne engine, just a dd with some occassional offraoding where low end is most important. The cam I have in there now sucks. Its a stock replacement and I stop making power at 3500rpm. Im looking for the power band to go to about 4500rpm. Mind you the cam in there now is basicly redlines at 3500.

 

The reason I say run the 260 with 1.7 rockers is because that will give you more lift without having to increase the advertised duration. As a general rule, the advertised duration controls the rpm where the torque starts and the duration @0.050 controls where it ends. With 1.7 rockers and the 260 cam you will get .475 lift which is well within the limits of the stock head. IIRC, on OI's cam the lift would go to .540 or something with the 1.7 rockers which is way too much without some significant head modifications. The 1.7 rockers will also add a few degrees of duration @0.050 which will carry the powerband out further on top. The faster a valve opens and closes the more air it will flow and higher ratio rockers increase the opening and closing rates. With 1.7 rockers you will probably have more low end and more top end than with the 268.

 

Someone give me a guesstop dyno a couple weeks ago...not saying take it to heart but I can tell you what its showing...


I am using to the best of my knowledge, accurate head flow (stock) and cam specs per cam.


Suprisingly, when I punch in the stock specs as accurate as I can get them, the peak hp is 145 and peak torque is 288, not quite identical to stock ratings but close.


If your interested, this is what its showing.


*Between the crane 503901 and the comp 260H w/t 1.7 rockers, there is a very slight difference at 2000 rpm within 5 lb-ft (advantage 260 H), around 2700 the crane 503901 start to walk away from the 260H, in both torque and hp.
*The 268H, after 3000rpm, really picks up more tq and hp as compared to the other two, however, it losses a little more torque on the bottom end than the others, so this one wouldn't be ideal for you.
*Suprisingly, when I punch in the 268H vs the paw/mellings/clevite grind, the graphs overlap with a slight torque advantage, under 2500 rpm, going to the paw/mellings/clevite.
*Now if I punch in an increased port flow on the heads, along with 1.7 rockers and a stock camshaft, the low end tq is much stronger than the others and it actually shows near identical upper rpm hp (as compared to the 268H) and much more hp as compared to the other smaller cams. This is however, if your able to get the head to flow 10 more cfm at .3/.4/.5 lifts, intake/exhaust.

Considering how close the crane 503901 and the 260H with 1.7 rockers appears, I might go with the crane for two reasons. While the crane is more expensive, your gonna end up with simillar out of pocket once you get the higher ratio rockers. Two, the crane cam is a newer grind, surely the design is much better and would allow for more hp/tq potential than the desktop guesstimator can take into account.

I would imagine, like an actual dyno, these numbers mean little at face value but if you take into consideration whats happening with each combination, maybe its a useful tool...maybe...

 

thats kinda interesting. when i used stock cam specs, the head flow specs i found on FSP i got dam close to stock numbers...perhaps i need to gather cam specs of the 260 and 268 now and play...

 

I may be using the same specs, what compression ratio are you using? I am using 8.5 being optomistic, if I drop it down to 8:1 it gets closer at 277 peak, hp stays pretty much the same.

 

im using 8.8:1 for an efi with 300 cfm intake volume...

 

wow that is really interesting. So you say go the crane way w/the rockers and I will see a little more top end if I need it than the 260. Both bottom end would be very close. I mean the crane is only maybe 10-$15 more so its not a big difference. I might just trow one the 1.7 rockers with the cam I've got now and see how satisfied I am with that. The I can save some money up and get the crane cam. Now is there a difference in the 2 different crane cams? The on for the truck as opposed to the other one? They both look pretty identical to me?

 

Well, we know the difference the rockers make with a stock cam. I wouldn't run a 1.7 rocker with the Crane. You are going to get into lift ranges that will require lots more money to be thrown at the truck.

FWIW, when I put the 3.8 rockers on my truck in the spring I put the numbers in DD2K and it showed that there was no difference at all. On the dyno there was definitely a difference.

 

Now thats odd, adding higher lift to a stock setup was the first thing I tried...


on my DD program, it shows roughly 1-6 lb/ft ...w/t 1.7 ratio ~ .423" int/exh


....wanna see something really interesting...take the stock 4.9 combination...then add an XE266HR cam....


cjbronco

I was saying use the stock ratio with the crane...you'd be ahead, out of pocket, not buying higher ratio rockers for the comp and close from a performance perspective, that and SS pointed out another good reason.

 

We might not be modeling the engine the same way. I used head flow figures that I found somewhere that produced number very close to stock and very close to what I have now with headers. IIRC, I told it a TPI intake, 600 cfm flow, 8.8:1, and small tube headers.

 

i think we should share DD2K files ;-)

 

What numbers do you have for head flow?

Otherwise, I'd say we are pretty close.