Wide Lobe separation angles

la360 · Post by **la360** » Tue Nov 09, 2004 6:40 am

I have noticed in recent years a trend with some camshaft grinders, of running less duration @ 0.050" than we would have done in the past, on a wider lobe separation angle. What is the thinking behind this?
Do these camshaft profiles have more duration @ 0.100" and 0.200" than a similar grind on a conventional designed camshaft
Thanks
AL...

Guest · Post by **Guest** » Tue Nov 09, 2004 9:44 am

My guess would be because heads are much better this day and age. I beleive that is why we see the wider LSA? Someone correct me if I am wrong.

speedtalk · Post by **speedtalk** » Tue Nov 09, 2004 11:57 am

The less duration trend is because of the use of higher rocker ratios.

bsfc9 · Post by **bsfc9** » Tue Nov 09, 2004 8:32 pm

don, can you elaborate on that?

speedtalk · Post by **speedtalk** » Tue Nov 09, 2004 9:05 pm

Sorry about that. Rocker ratios have increased for the last 10 years. If you just throw a higher ratio on the same lobes you end up with more valve duration, so you need to shrink down the duration to get back to where you started.

la360 · Post by **la360** » Wed Nov 10, 2004 1:39 am

I can understand that point Don, but I am seeing guys go away from running 106 and 108 lobe sep, to 112 and 114 lobe sep, plus running around 10 degrees less than some other companies would . An example-
Comp cams may suggest a 275/280 @0.050" , 0.700" w/1.6:1 rockers on a 108 lobe. Someone like Straightline Perf may suggest a camshaft with similar lift on a 112 lobe sep, with 265/270 @0.050"
I have started to see more companies starting to offer profiles like this, even Harold (Ultradyne) who is at Lunati , is starting to grind these.
No one has really been able to give me a reason why people are starting to run these profiles over more conventional tighter lobes, other than "they make more power"
AL...

Guest · Post by **Guest** » Thu Nov 11, 2004 3:45 pm

As cylinder head technology gets better it allows for the use of wider LSA's. Most engines do not need the use of big overlap cams to get the job done. As you widen the LSA, you can in turn shorten the @.050 number to achieve the same RPM range with a lot less overlap. But remember the @ .050 is only 1/2 the equation. The lift is going up too. This is exactly what Don was saying. Rocker ratios have grown through the years. Better flowing heads, higher rocker ratios, smaller at .050, wide LSA's. Gotta love it!

Jay Allen · Post by **Jay Allen** » Thu Nov 11, 2004 3:47 pm

Anonymous wrote:As cylinder head technology gets better it allows for the use of wider LSA's. Most engines do not need the use of big overlap cams to get the job done. As you widen the LSA, you can in turn shorten the @.050 number to achieve the same RPM range with a lot less overlap. But remember the @ .050 is only 1/2 the equation. The lift is going up too. This is exactly what Don was saying. Rocker ratios have grown through the years. Better flowing heads, higher rocker ratios, smaller at .050, wide LSA's. Gotta love it!

Sorry all. I posted this. I just forgot to Log-In before I did.

joe · Post by **joe** » Thu Nov 11, 2004 4:19 pm

in the early going they sold cams using descriptions like 1/2 3/4 and full race , then they came up with catchy names like "monarch" and "fireball " . In the early 70's hot rodders would use seat duration figures too brag on the size of their cam , chevy had a big block ,can't remember which one, that had 340o duration ! hot rodders just ate that stuff up ! I don't think people are so conscious of outdoing one another with duration as they once were , they've learned a thing or 2. I hope !

shawn · Post by **shawn** » Thu Nov 11, 2004 8:10 pm

When i worked in a parts store in the old ages, we would get guys coming in wanting a "3/4" race cam.The old owner used to say " 3/4, that's pretty big, you sure you don't need the 5/8's?". Still makes me laugh.
Shawn