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Wider lsa for performance vs tight

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#62 ·
Roadknee said:
What are you wanting to achieve?
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Reason I had it speced was to see if I could broaden torque & get it to 60' a little better. Guy said it would pull better under peak since my converter stalls 12-1300 below peak tq.
In reality I probably wouldn't achieve anything except a slightly smoother idle & move peak hp up a bit. My thoughts.
 
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#63 ·
I've always stayed conservative with valve timing, tending to 106-108 ICL, which typically works well with a LSA at 110-112. I think what's missing most in this thread is the understanding and explanation that once you set the intake opening and closing points for the combination, you set the exhaust timing events, net is ICL and LSA. The discussion of wider LSA to bleed off cylinder pressure has nothing to do with LSA, it is ICL that causes that. I've ran 114 LSA cams, which typically install at 110-112 ICL, guess what, the idle changed noticeably at 104 ICL (intake opened early creating that bumpy idle). {FWIW, this was way before the days of information on the internet, this is what we did to try to wake up an engine and didn't have deep pockets to just go buy new parts}.
 
#64 ·
cstraub said:
Thank you sir for the DATA. See you next week.
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What's also impressive is how his 555 idles relatively smooth with, I think, a 107 LSA. It sounds more like a RV cam (said respectively).
 
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#65 ·
cstraub said:
...LSA......Advertised Duration...
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Chris, can you say if you spec your camshafts LSA off lobe "centerline" or "lobe peak"? I remember an argument about this on another forum and wonder what your thoughts are on this?


Also, can you say what lift you spec advertised duration numbers? Thanks-
 
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#67 ·
cuisinartvette said:
So what would be a happy medium of opening/closing events that dont beat things up, make power and have better idle quality than the proverbial tight lsa?

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Is that 232/240 a Jones grind?
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Good guess.
 
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#69 ·
There's an Excel spreadsheet over on a HP Tuners forum that I used to adjust fuel injector timing. You can enter different cam specs to see how that affects overlap. I've no idea how accurate -- or not -- the valve lift curves are in the graphs. As I said, we used that spreadsheet to play with injection timing, not cam design. I tried to attach the xlsx file but apparently files with that extension aren't allowed so I renamed it as a ".txt" file. This version of the spreadsheet has cam specs for a LPE GT9 cam that I'm using in a supercharged Gen IV LS.
 

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#70 ·
I just found a quote from the late great expert cam designer Harold Brookshire, that I had saved in my notepad, and this has to do with an earlier post I made in this thread. I guess i was getting the dur@.200 specs mixed up with dur@.020 specs which is what Harold often focused on to display what he called "MAJOR INTENSITY"of a cam lobe profile which is the difference in degrees between the Dur@.050" lift and the dur@.020" lift of any cam. The lower that this "major intensity" number is, then the steeper the ramps of the camshaft lobe are. What this means is, the closer in degrees that the dur@.050" spec is to the dur@.020" spec, the steeper the closing and opening ramps of the lobe is, and the bigger the "area under the curve" of the lobe profile is. This "major intensity" number of the cam lobe profile, represents how long and wide the valves are held open by the cam lobe profile. I have not found any racing cam lobe profiles with a Major intensity number lower than 27 with most high perf street cam lobes having a Major intensity number of 34-39 and going as high as 42. Harold's cam family that he mentioned here having a MI number of 31 represents some very intense lobe profiles which should make some major power in properly matched engine combinations. Here's is quote below: (BTW, I do not know what he ment by "Peak positive acceleration rates" concerning lobe profiles)....


"I have a family of cams in .725", .775", .825" and .875" that all have the same opening ramps, and the same closing ramps, even the same peak positive acceleration rates. I use the .725" lift cams as daily street drivers in 496-540 engines. All lifts are in every 4 degree spacings, and we have had no trouble in valve spring life, either on the street or the track.....
LSA for the stroke and stick transmission would be 114. This would flatten out your torque curve, so you could try to hook it up on the street. The torque curve would be very flat. A 499 with a 284/292 on a 112 had 625 ftlbs at 5000 and 7200, 689 at 6100.
You would have usable torque even at 2500.
This family of cams has 31 degrees Major Intensity, so a 276/288 at .050 would be 307/319 at .020. If you want to go smaller at .050, we should look at lower valve lifts, like the .775" or the .725" series."
 
#71 ·
My memory of going through lobe catalogs is they give you 0.050 and 0.200 durations, but not 0.020.

bradley67 said:
Help us understand how you came up with this assessment of the other cam grind after everything else you (and others) explained about how difficult it is to compare two cams?
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I shouldn't answer for Chris, but my guess is the 2 profiles are fairly close but the one with the larger LSA will spend less time with the valves closed, which typically lowers compression.
 
#73 ·
This is the 2 cams. Chris's cam closes the intake 4.5 deg. sooner that's where the higher cranking comp. would come in.
 

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#75 ·
WHT/73 said:
Bill, so the "MI" number is the .020 - the .050 number?
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Yes. And 31 is pretty intense. Most cam lobe profiles that I've looked at don't get that low with the MI number. I guess Harold found a way to design lobe profiles that are that radical to not beat up valve train parts. The guy was the best at what he did.
 
#77 ·
Wow.
Talk about acceleration rate!
Looks like it has inverted ramps and short duration.
Wonder what the rest of the valve train consisted of. Maybe the lifter just floated over the nose and that’s how it got more duration. :surprise:
 
#80 ·
MadmanMark said:
I have CC Xtreme Energy hydraulic roller profiles that are 52 deg between advertised and 0.050. 31 seems pretty aggressive.
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No Mark, the MI number, (in the example Harold was using is 31) is NOT the difference between the dur@.050 and "advertised" duration. It's between .050" and .020" and most "advertised" dur figures that I know of are taken at .006", and some at .009" lifts. I've never heard of a cam manufacture using .020" lift for their "advertised" dur figures. And even if any of them do, most of them do NOT as far as I know. So you cannot compare your Comp Cams piece using the advertised duration and the .050" unless you know for certain that Comp uses .020" as their advertised specs, (which I do not think they do).
 
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