Camshaft spec lt1

i have actually found they don't need to be cut, just straightened. at least with the CC pro magnum roller rockers

The off the shelf cams are OK, but they tend to have too wide an LSA. What happens is most folks want the most horsepower from the biggest cam they can stand. So what has happened over the years is that the cam companies realized that most hotrodders pick too big of a cam and then call the cam company back up and complain because they lost too much bottom end and they don't like the idle. So, instead of arguing with their customers, the cam companies just assume you're going to order too big of a cam for your needs, and so they've widened the LSA to save you from yourself. Widening the LSA reduces overlap, makes the car idle more smoothly, and gets better mileage on the street. The trade-off is you give up 20 to 30 ft/lbs of torque through the midrange.

Instead of getting a sub-optimal cam, do the smart thing and order a smaller cam on the optimal LSA. The cam you listed in your post has 42.5 degrees of overlap at 0.006". This is a great number for the street - it makes a great towing cam, in fact. You can get the same amount of overlap, which will give you the same mileage and idle of the off the shelf cam, and pick up another 20 ft/lbs of torque over that cam:

206/206 @ 0.050
258/258 @ 0.006
LSA 108
42 deg overlap
4 deg advance (Intake center line @ 104)
Recommended lobe: Comp Xtreme Energy 3311 which would give you .480"/.480" with 1.5 rockers

That cam has 42.0 degrees of overlap, so it's going to idle almost exactly the same as the 212/218 cam. The cam you listed uses Comp's Xtreme Energy lobes, so looking at Comp's master lobe catalog, the lobe closest to the 212/218 cam's lobe lift is lobe# 3311. It's got .480" lift using a 1.5 rocker vs. .488". If you want a little more exhaust duration, you could go with the following:

206/212 @ 0.050
258/264 @ 0.006
LSA 108
4 deg advance
45 deg of overlap
.480"/.488" lift with 1.5 rockers
Intake lobe: Xtreme Energy 3311
Exhaust lobe: Xtreme Energy 3312

That is one lobe smaller on the intake and exhaust than the cam you listed - your 212/218 cam uses Xtreme Energy lobes 3312 on the intake and 3313 on the exhaust.

By being smarter than the average hotrodder and going one catalog number smaller on the lobes, you'll be able to use the optimum LSA of 108 and still retain a nearly stock idle. If you're very concerned about idle quality, I'd stick with the single pattern 206/206 cam. It will give you the exact same idle and rpm range as the 212/218 cam since it has the same overlap, but with better midrange torque and similar peak horsepower. If you'd like a little more high rpm performance, go with the dual pattern 206/212 cam. Even with that cam, the idle's still going to be very mild.

To show you that I'm not just blowing smoke, here's an article where they made 447 hp on a 350 SBC with iron vortec heads (same exact ports and combustion chambers as the iron LT1 heads) using a Comp Cams 224/224 with 108 LSA. Vortec Small-Block Build - Popular Hot Rodding Magazine

BALLSS said:

Watched an Engine Masters episode the other day on using same lobe cams but different LSA to see what difference was. Tighter LSA made more HP up top but the wider LSA cam had a broader HP/TQ curve (flatter) than the tighter LSA but did make less HP up top

Comments were for a "street car" where it isn't about WOT only use the wider LSA even though it made less peak HP would "feel" better on the street as the TQ and HP was in at a lower to mid RPM range that is the majority use of street car driving

Click to expand...

Of course they're going to get that result if they use the same lobes for each cam. When you widen the LSA and keep duration the same, you decrease overlap. And it's overlap that determines idle quality and where peak torque is going to occur, NOT duration. The design of that test is flawed.

You can't really blame the magazine guys, though. 99% of hotrodders are fixated on duration, so of course their test had to focus on duration to connect with their audience. That's why the cam companies have to widen the LSA in the first place - to keep their customers happy; not produce the best engine numbers.

Just out of curiosity, what were the specifications of the cams they tested? I'd like to compare them to the numbers they got in that Popular Hotrodding article I linked above; particularly since it was the same group of guys (Steve Dulcich, et al) who did both the EM test and the PH test, and on the exact same dyno. The heads will make a difference as well, but we can still get somewhat of a comparison by looking at the dyno curves.

One thing the EM test does prove, since the duration was the same for all cams, is that it's overlap, NOT duration, that determines the power curve and idle quality.

Since everyone but the hard core guys pick their cams based on idle quality and every day driveability and NOT peak hp numbers, it would make a lot more sense to test cams that have the same idle qualities but different LSA's and lift durations. We can use the OP's cam to start with and go from there.

206/206 dur @ 108 LSA = 42 deg overlap (at .006")
206/212 dur @ 108 LSA = 45 deg overlap
212/218 dur @ 112 LSA = 43 deg overlap (OP's pick)
218/224 dur @ 116 LSA = 43 deg overlap

Using Comp's Xtreme Energy cam lobes #3311 (206), #3312 (212), #3313 (218) and #3314 (224), all of those cams would have pretty much identical idles because their overlap numbers are all nearly the same. So the only reason to choose one over the other would be their performance on the dyno. If you were able to notice any difference at all in idle quality, the 206/212 cam would have the cammiest idle of the four, although the difference is so small I doubt most people could tell which cam was which.

For comparison, the stock overlap in the LT1 vette is 41 degrees and the LT4 is 46 degrees. So all of these cams will idle about like a stock C4 corvette.

Just FYI, Vizard put out another video talking about his method of spec'ing cams yesterday. Same info as before, but they did a better job this time. The poor guy editing the video was struggling to correct Vizard's rambling, and did a creditable job of it. But Vizard's still got the same issues as before that don't have all that much to do with cams - namely, he's upset that so many people in the industry think he's full of it, and he spends the first 30 minutes of the video going over his CV. This includes the fact that he tested over 22,000 cams over the course of his career, mostly in the 1980's; he was a consultant on Jim Clark's Cosworth F1 engine; and he's done a lot of Pro Stock consulting.

Once he gets past his qualifications, this is the best video yet of how he goes about spec'ing a cam. Unfortunately, he doesn't spell it out completely. He starts to go into detail in a couple of places as to what factors go into it, but then they cut ahead and move on. I don't know if they thought he was getting into too much detail for a video, or if they were trying to protect proprietary information. Either way, it was kind of frustrating to hear him begin to talk about it and then they cut ahead.

Still, there were a couple of interesting bits. He says Brian Tooley is full of it. Which is only fair, because they showed a video of Tooley basically trashing Vizard's method at the beginning of the video. Ironically, one of BTR's BEST blower cams follows Vizard's design specs. When I asked Tooley about it on the phone, he stated, "it's a coincidence". I kid you not, that's what he said. Apparently they don't like each other professionally.

They did give out some more interesting tidbits towards the end of the video. Vizard listed a number of camshafts, with their part numbers, available from various cam manufacturers. He also listed several people whom he thinks develop great cams.

The first 6 minutes are kind of interesting because you see Tooley trashing Vizard's method and then Vizard saying Tooley doesn't know his a$$ from his elbow (albeit very politely, <lol>). Then there's about 25 minutes of Vizard stating why you should take him seriously. If you haven't heard it before, it's pretty impressive. But if you want to just get to the meat of it, start at about the 35 minute mark.