Just got done putting a new intake and exhaust on and wiped a lobe. Just my luck. Here's what I've got:

350 .040 over
186 heads, 2.02 in and 1.60 ex bowl blended, springs good to .500
roller rockers 1.5 ratio
About 10:1 compression
1 5/8 short headers into 2.5 then single 3.0 all mandrel bent
Holley Street dominator intake 300-36
Holley 750 vac. secondary
Turbo 350 w/ shift kit and 2400 stall
stock rear end 2.73 gears (next on the to do list)

The cam I destroyed is a Comp XE274H. With the shallow gears the car is a dog off the line but an absolute blast on the highway. I don't intend on racing this car, just something that's fun to drive. I'm hesitant to change gear ratios because I only have the 3-speed auto and highway rpm is already somewhat high.

Anyway, I'd like a cam with good power up to 6 grand like what I have but would like more bottom end and better idle. Does anybody have any suggestions? How much top end would I lose with a XE268H? Has anybody tried the Xtrme 4X4 cams like the X4270H? They look to be set up a little better for what I'm looking for. I don't intend on changing any other engine components, maybe the valve springs if I could benifit from more lift.

 

I honestly don't have a liking to Comp Cams, I prefer Crane. I would look into the Crane Z-268-2 (113522) or if you want snappy performance with the 2.73 gears the Crane 113904 Truck power cam. The first cam makes peak HP about 5,500 and will pull well to 6,000 rpm. The later cam makes peak HP by 5,000 rpm and falls flat on its face at about 5,500. But they will sure get there quickly.

 

I'm guessing this is a non-roller camshaft? What kind of oil are you using? Did you use any break-in lube when you installed the camshaft? The oil companies have reduced the amount of zinc in their new formulas because of emissions and smog, but older non-roller camshafts need that zinc to keep from wiping the lobes. One of the big magazines did a story on this a couple months ago. Use oil made for diesel engines, as it still has the extra zinc.

I found the magazine story for you:
http://www.hotrod.com/techarticles/e...ech/index.html

Just another reason why I tell people use use later-model roller blocks and cams in their engines....

 

Non-roller, yes. I used to use synthetic 15w40 until the latest oil spec change, now I use Deisel engine oil for the zinc. Fully aware of the need for zinc. This engine was put together around 7 years ago and has 20,000 miles under it's belt. Now back to the original question.

 

And people in Hell would like ice-water, and we'd all like to eat our cake and still have it, too.

Seriously, that's THE trade-off in cam design, right there. High RPM power vs idle quality vs torque. Pick which one is most important TO YOU, and concentrate on it. Or, pick any 2, and sacrifice 1. Can't have all 3.

Anything you do to improve the idle, will cost one or the other; anything you do to improve mid-range torque, will worsen the idle or reduce high-RPM power; and anything you do to improve HP, will roughen the idle.

Kind of like, durable-fast-cheap: pick any 2. Can't have all 3, but you can have any 2.

Yes you could improve the idle by dropping the cam back a notch; you'll lose some top-end power. You have to give up on one thing to get more of some other.

 

I realize it is a balancing act. I'm looking for suggestions. Maybe I've got more cam than I can use with the rest of the components anyway? In which case a smaller cam might not hurt my top end much. Maybe cams have improved since 7 years ago? Maybe I should use the same cam as before installed a couple degrees advanced? Obviously if I new exactly what to get for a cam I wouldn't be asking. But, I only know enough to be dangerous (typical engineer). I let an engine builder pick this cam the first time and I want to see if I can get a little more real advice.

 

The cam you had is still pretty much state-of-the-art; although the Lunati Voodoo series is a marginal improvement over the XE series. But they're the same general idea: use computer modeling and finit-element analysis to push the absolute limit of how fast you can accelerate the valves without destroying things or being too noisy, the idea being, you want the valve open as far as possible for as much of the time as possible out of whatever the cam's duration is, and not spending any more time than absolutely necessary hanging out around the seat and lazily drifting open.

If you liked the way it ran, but just want to back it off a notch, the XE268 or the Voodoo that's 227° @ .050" would be logical things to look at.

IMO that combo you had was reasonably well-matched. That is, the RPM range of the cam, the compression, the head flow, and so on, all conspired together favorably. Nothing was out of place. I think your builder didn't do too bad. The 268 is still within that same window of a good match.

I wouldn't install the same cam on a different intake centerline (advanced or retarded). But you might consider getting one custom ground with the lobe centers wider; that will improve the idle and keep or improve the top end, at the expense of mid-range torque.

 

Alright! That's the kind of discussion I'm looking for. Thanks! Anybody else?

 

I was going to mention the voodoo one with the 227* intake. I had that briefly (wiped 4 lobes off it, do your break in very carefully). It's the 60103. I loved it though. I'd highly recommend it.

I hear you with the no-over drive and 2.73 gears. I have 3.23 gears and it's just borderline too much with no overdrive. 3300RPM on the highway cruising? Gotta have a quiet exhaust or good sound deadening. Looking at charts though, my top speed (based on gearing) is still much higher then i'd ever need, (like 150MPH), so I don't think it's geared too aggressively. Do you drive yours on the highway that much? I still get 20mpg on the highway if I drive it mildly (speed limit, cruising, not WOT'ing to pass people, etc). So I think a slight step up in gears would help your low end a lot. The TH-350 doesn't have a very steep first gear, so you kinda need an aggressive rear end unfortunately.

 

I like the look of that voodoo cam, it has a little more lift. Is there a way to test the springs on the heads to measure how much lift is ok?

 

You can rig up gizmo that'll bolt on instead of a rocker arm, and then "tighten" something down on your valve. Then use a dial indicator on your retainer say, and crank it down until the valve is open .500". If nothing is wrecked yet, crank it down to .550". If nothing is binding or hitting, you're ok.

 

Just as a data point for you, in the early 90s I built a 355 with the Comp Cams 268 cam, & was quite happy with it. Nice lopey idle, but it ran well & did well on the highway. I certainly wouldn't discount it if I were you, it worked well for me - and the newer lobe profiles are almost certainly even better!

 

the z cam pull well to 6000 do u think it fells on its face?