JWRENCH

Just got my copy of the new Car Craft mag. It has a four page article on lobe seperation angle. Pretty good info. Looks like Lunati and Crane both say the higher the seperation the more the bottom end loses torque, and the powerband is shifted up.

Direct quote: "Interestingly, at the very top of our test, well past peak-power rpm, the wide cam actually caught up and surpassed the other two grinds by a marginal amount".

I feel much more informed now on lsa and feel a few other fellas on here should check it out to get a better understanding on the issue... <img border="0" title="" alt="[Smile]" src="gr_stretch.gif" />

LS171Malibu

Which month is it? October...November?

LS171Malibu

Which month is it? October...November?

RaNsOm

iTrader: (2)

</font><blockquote><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><hr /><font size="2" face="Verdana, Helvetica, sans-serif">Originally posted by JWRENCH:
<strong>Just got my copy of the new Car Craft mag. It has a four page article on lobe seperation angle. Pretty good info. Looks like Lunati and Crane both say the higher the seperation the more the bottom end loses torque, and the powerband is shifted up.

Direct quote: "Interestingly, at the very top of our test, well past peak-power rpm, the wide cam actually caught up and surpassed the other two grinds by a marginal amount".

I feel much more informed now on lsa and feel a few other fellas on here should check it out to get a better understanding on the issue... <img border="0" title="" alt="[Smile]" src="gr_stretch.gif" /> </strong></font><hr /></blockquote><font size="2" face="Verdana, Helvetica, sans-serif">sooo...between a 112 and a 114....the 114 is a higher seperation?

JWRENCH

Sorry, it's the November issue, Page 72, and they test three cams with exactly the same specs exept for a 106,110,and 114 lsa. <img border="0" title="" alt="[Wink]" src="gr_images/icons/wink.gif" />

SSLink

Once again, testing bears out that on a street engine, tighter LSA effectively lowers powerband and raises peak torque. Tighter powerband overall shows up at higher RPMs, where wider LSA shows advantages (beyond where they are useful to most of us).

AFTICA

iTrader: (8)

This has been my opinion all along.Since I had people like Thunder Racing,Raughhammer, Colonel & now Crane & Lunati agreeing with me,I felt pretty confident posting in other threads what I remembered from the old days.....Wider LSA moves PEAK power UP.

HITMANSS

This is pretty much the opposite of what Comp Cams says in their Timing Tutorial.

Guess GM must have it backwards too. They insist on using extremely wide LSA's for the LS1, & yet they run out of HP at 5500 RPMs. Maybe their computers have bugs.

I selected a 114 LSA for the smooth idle, lower emissions, and usable torque. What a surprise to learn that I also benefit from better high RPM performance too! Maybe I should have gone with a 120 LSA!

SSLink

GM's goals are smooth idle and low emissions. Stock LS1 cams are the worst of both worlds: low duration means weak top end; wide LSA means weak low end torque and off idle bog when you drop the clutch on an M6. I now run the 218/218-.563/.563-112LSA Comp cam and both low and high end performance have improved markedly, at the expense of a little rougher idle.

SSLink

HITMANSS: I haven't seen the issue yet but will look for it. Were there any graphs or or documentation of torque/horsepower at various RPM's? I am curious as to how the cams compare other than just at peak. For example, at 4400RPM and below 106LSA is not at peak torque, but is it still higher than that of 112 LSA? How do the areas under the various curves compare? When does power really start to come on for each? Is this how the article's writers reached their conclusion?Interesting stuff.

HITMANSS

We's all friends here, so you can call me HITMAN, or Gary --- your choice.

Unfortunately, the article did not include a detailed graph or chart for the 3 different LSAs. I too am interested in seeing the detailed numbers, including those below 2500 RPM. My experience with lumpy, tight-LSA cams is that can be real pigs at low RPMs, then the power comes on fairly abruptly. This is great for racing, lousy on the freeway.

After reading & digesting all the various comments, theories, and info I think we'd all agree that the tighter LSA narrows the power band somewhat, and raises peak power. Whether the power band gets moved higher or lower is a bit subjective, as there is conflicting evidence. It also depends on how you define the "range". The article analyzes two different power ranges --- 2500-4000 RPM & 2500-6300 RPM. In both cases, average TQ & HP were higher with the tighter LSA. As I said, I'd like to see the average TQ in the 1700-3000 RPM range.

LSA is only one of many variables that cam designers use, and it's simplistic to try to narrow down its effect into a simple "rule". But it's certainly fun to try! <img border="0" title="" alt="[Big Grin]" src="gr_grin.gif" />

As the article points out, the LSA will have a different effect on an engine with high flowing heads, compared to a stock-headed engine. Also, these tests were done on a Vortec SBC, not an LS1.

nuzee

iTrader: (2)

Hope its not too late to jump-in. These are some of my personal beliefs & experiences from first generation small block Chevys flat tappet cams:

1. Tighter the LSA, the peakier the torque curve. Good mid-range punch. Lose some of the off-idle pull. Upper rpm pull drops off more noticeably past power range.

2. Wider the LSA, the broader the torque curve. Adds more off-idle pull. Good for automatic tranny. Feels like the motor can pull & pull (the drop off is less noticeable).

3. Cam DURATION dictates where the powerband will be. If you want a higher rpm powerband, you choose a cam with more duration, & vice-versa.

4. The cam lobe profile & timing events (intake/exhaust open/close) dictate the cam characteristics. The duration & LSA are just indicators of those timing events. For SBCs, you cannot generalize duration or lobe separation between different cams let alone different cam manufacturers for comparison purposes. Maybe you can for LS1 cams as there are not that many profiles to choose from, I don’t know. But the practice of comparing cams just by duration or LSA can be very misleading.

5. Valve overlap should be a key factor as it takes into consideration the cam timing events. Add that into your evaluation of particular cam grinds and you’ll see a more clearer picture.

HITMANSS

Nuzee --- well put, Bruddah! <img border="0" title="" alt="[Smile]" src="gr_stretch.gif" /> Very nice summary!

SSLink

Thanks, Gary. I agree that what happens when you narrow LSA and increase overlap the powerband is narrowed and the peak torque increased. On a street engine with a powerband to 6500 RPM I believe this effectively lowers the torque range because it starts coming on faster and stronger from about 1500 to 2K RPM and up. It probably also comes off more and faster after 6500, beyond where we typically spin our engines. I say this effectively lowers the torque range because for most of us what happens below 1500 RPM or so isn't very important because we don't spend much time there. However, for anyone who likes to lug around in 6th gear at 1200 RPM, it could have an impact. Regardless though, I believe we are splitting hairs comparing the effects of 112 and 114 LSA's on cams in the range of 218 to 224 duration. We're probably talking about a few HP
and torque here and there. What is noticeable is that with 112 LSA cams you will get a rougher idle.

SSLink

Thanks to you too, Nuzee. I agree completely. By the way, though, why is it that 110 to 112 lobe centers are pretty tight for LS1 use and medium to wide for SBC use? Is it the difference in the heads? Imagine a 106 LSA in one of our cars! You'd probably have to bump the idle to 1500 RPM...

nuzee

iTrader: (2)

<img border="0" title="" alt="[Cool]" src="gr_images/icons/cool.gif" /> <img border="0" alt="[cheers]" title="" src="graemlins/gr_cheers.gif" />

"why is it that 110 to 112 lobe centers are pretty tight for LS1 use and medium to wide for SBC use? "

I've wondered why that is too. That seems to apply to all roller-cam grinds for SBC & LS1s. I do believe that the optimum LSA gets tighter as displacement increases.

Colonel

I look at the "power range" more as a definition of where I should shift for best results. Going by this we should be able to agree that due to the power dropping off slower after peak HP (would anyone argue with that?) the shift point is going to be higher with a wider LSA.

Why does GM use a super wide LSA for a low RPM engine? Simple, for clean emmisions, outstanding idle quality, and great low rpm drivability. Keep in mind that the intake duration has FAR more impact on the shift point than does the LSA. That's why the stock engines have low shift points despite a super wide LSA...they have a super low duration to go with it.

HITMANSS

At lunch today I went out & got the Car Craft article, & read it through thoroughly. It's fascinating how many different conclusions can be reached by reading the same data.

First, which LSA produces the highest peak HP? Here are the #'s:

106 LSA 433.7 @ 5900 RPM
110 LSA 434.0 @ 5500 RPM
112 LSA 428.5 @ 5500 RPM

So which is better for high RPMs --- wide LSA or narrow LSA? Looks to me like the tighter LSA produces more peak HP at a higher RPM.

Next, which LSA produces the highest peak TQ? Here are the #'s:

106 LSA 454.9 @ 4500 RPM
110 LSA 448.8 @ 4400 RPM
114 LSA 440.0 @ 4400 RPM

So which is better for high RPMs --- wide LSA or narrow LSA? Looks to me like the tighter LSA produce more peak torque at a slightly higher RPM.

You decide......

nuzee

iTrader: (2)

"Going by this we should be able to agree that due to the power dropping off slower after peak HP (would anyone argue with that?) the shift point is going to be higher with a wider LSA."

No argument here! <img border="0" title="" alt="[Big Grin]" src="gr_grin.gif" />

Base engined SBC during the 70s used a short duration and lift,108 LSA cam. Smooth idle. Made good off-idle torque. But, when you rev'd past 4000 rpm, the engine would start wheezing, couldn't breath, power would just drop off. Obviously, that was one of the first things that got replaced whenever doing a performance build.

The factory performance cams from the 70s used wide LSAs with a good amount of duration and relatively low lift. That produced a relatively smooth idling cam with mild lobe profiles that wouldn't stress the valvetrain too much. They would pull pretty good to redline. Aftermarket cams typically made more power with more aggressive lobe profiles, at the risk of stressing the valvetrain.