Okay, so I'm wanting to do a custom cam for my build (258 L6 with a 4.0 head, street car) and had a question on cam lobes. I know I want something in the 265-270ish advertised duration and the 258 uses a .904 lifter. I've been looking at the Comp lobe catalog and these are what I'm looking at so far:

The Xtreme 4X4 hydraulic:
lobe 5904
adv duration:266
.050 duration: 221
.2 duration:138
lobe lift:.325
valve lift, 1.6 rockers:.520

XFI:
int lobe 5086
adv duration:268
.050 duration: 224
.2 duration:138
lobe lift:.325
valve lift, 1.6 rockers:.520

exh lobe 5103
adv duration:272
.050 duration: 223
.2 duration:134
lobe lift:.308
valve lift, 1.6 rockers:.493

XE:
int lobe 5444
adv duration:270
.050 duration: 226
.2 duration:139
lobe lift:.321
valve lift, 1.6 rockers:.514

exh lobe 5103
adv duration:270
.050 duration: 224
.2 duration:133
lobe lift:.313
valve lift, 1.6 rockers:.501

The easy part of this is that it's likely the Xtreme 4X4 (cut for Mopar lobes) and the XFI will probably make more power than the XE. The questions that become a bit more complex are:
-Is the valvetrain life worth the power gains?
-Even if they're not optimized for .904 lifters will the XE and XFI lobes have increased durability if cut on the correct cam blank
-Will any of these make a difference on idle quality? Overlap will be 50-54 degrees so I suspect it will be pretty hot.

The cop out for this is that I go buy an Isky Mega 270 and toss it in. The lobes on that would probably be out lazy to any of the above truthfully but it would probably be easier on moving parts.

 

What are you planning to do with the vehicle? What trans? Gears? Turbo? Can't pick a lobe without a lot more info.

That said, I don't think you're looking at a massive change in power or torque between the 3.

 

Trans will be a Torqueflite 998 (which is a HD 904 trans)

Gears are going to be 3.54s, I have the front axle need to get some for the back still. It will be a Chrysler 8.25 or exploder 8.8. Not sure yet unless a Dana 35 with 3.54s falls in my lap. As of now I have malaise era gears which absolutely will not do. Stock converter which is supposedly about 2000 stall which obviously means little.

Turbo's going to be a legit Turbonetics T66 with a P trim turbine that has a .69 housing. Real old school stuff.

Head/intake will be a 94 Jeep 4.0 head. I'd have to get the guides cut down some (or DIY that.)

In terms of head flow the intake flows about 208-220 at .500 depending on where you look and exhaust is 128CFM. Debating on porting or not. The documentation I've seen on porting these heads is pretty involved but gives really good results.

 

From that info, I would go with the Xtreme cam. I don't think ant of them would be an issue with the .904" lifters as those seem fairly mild for a lifter that big.

 

You say street car but that could be a 20k mile engine car or a 200k mile engine car

If you want 100k or 200k miles from the springs and valvetrain with low maintenance use the lowest lift with the slowest ramp and the weakest spring possible
for example I use
TFS30602001 with PAC1218 springs, OEM lifters & OEM rocker trunions

This cam have extremely slow ramps for superior valve control, weak spring will last 100k or more, easy on lifters especially good for OEM lifters, easy on guides, good for longevity, and supporting 500-800rwhp easily forced induction for daily drivers
In the future I will use even lower lift lobe than that for similar output figures, might as well.

Some fancy cams with advanced lobe design use springs that only last 20k miles and must be replaced periodically, and harsh on lifters, guides, etc... valvetrain under stress and difficult to control at high RPM.

= Not necessary with forced induction at street car power levels

 

Some very good points mentioned in Post #5.

Tom V.

 

I will say this isn't exactly an LS engine, I think that some cam work will be required to make up for the head honestly. If I make it to 250HP N/A I'll be happy with that.

If I drove 50K miles I'd be surprised. I'm also not talking an engine that makes 275-300hp stock, but one that makes 115ish and has a VE of somewhere around 60% stock. I'd like to see 450ish flywheel hp out of it on pump gas if plausible and more on E85 if I can get it (seems to be in short supply in my location now that I moved.)

Also, being a split port L6 with a non-adjustable valve train it's at the moment anyways fairly easy to work on and would likely not be terrible to do springs on. I did head bolts on it in an hour and a half or so.

I absolutely understand that aggressive lobe profiles lead to valve train life being lower all else being equal, but I guess where I'm trying to go with this is "how much?" Engineering is the art of compromise but at the same time I'll admittedly say I don't know what I'm gaining to what I'm giving up and that's what I'm trying to figure out.

If I'm giving up 5HP for 60K miles in valve spring life vs 50HP for 10K miles in valve spring life it's two different matters in making a decision.

 

The comp lobes are always aggressive, and not great with today's oils for low maintenance. Power wise, I don't think you'll see a real advantage in either of the lobes over the other. Because it's ft, and changing cams sucks... I'd personally look for a lazier lobe. Add another 10 or so degrees to the advertised. I think you'll loose very little hp with stockish head flow.

 

Takinganother hit at this, how about this? I pulled some stuff out of the Howards Catalog and came up with this:

Int:
1hf213300
267 adv
[email protected]
[email protected]
.300 lift

Exh:
1hf221313
275 adv
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[email protected]
.313 lift

The game plan would be a 108 LSA with this. I do realize I'd have to pay attention back pressure doing that as well.

 

Scared a copy of Desktop Dyno up. Not the most accurate thing in the world, but likely there's worse base lines. Compared to a "shelf" cam I am about +8-10HP with the Howards Cam as spec'd above, and compared to any of the Comp Lobes above I'm down maybe a couple HP if not up a couple all else being equal. I think this is the one, at least until I start trying to toss around the idea of head porting which won't be any time soon.