Dan the man
Well-Known Member
Just a question, I'm trying to learn about cams. If a 108* lsa is good for torque, then how can a cam that has a 112* lsa said to have strong torque? Is it the duration at 0.050 "? Again, just a question. Thanks
LSA Question
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Dan the man
Well-Known Member
K. Thanks. Do you suggest any certain articles about cams?
It's combo dependent, doesn't mean 108 gonna make more low end torque than 112 in every application.
But generally the types of street, street strip engines most here are building a 108 probably doing better down low but don't mean the 112 is gonna be massively worse so in some cases the 112 can have strong torque and going 108 might make it stronger. Heads cid and rpm etc.. are gonna have huge effect on how a given cam reacts.
Better off looking real life examples, I'd watch Richard Holdeners videos on youtube see how the many different dyno combos react. Just don't watch the mopar ones, pay attention to the specs.
Here's a few to get you started
heres a search of his cam shootouts
https://www.youtube.com/@richardholdener1727/search?query=Cam shoutout
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That's actually a very good question. Think about IVC and its effect on cylinder pressure.
Newbomb Turk
Well-Known Member
Do you ever consider RPM? Or intended usage? Because that is what makes the difference.
Let’s take the first one. RPM. You lose some power past peak with a tighter LSA. If you can drive and hit your shift points it’s not a big deal. But if you can’t hit your shift points, you may want a wider LSA to let the power past peak carry longer.
What about intended usage? Well, a powerglide car will not want a tighter LSA. Especially if first gear is in the 2.0 range (or whatever the OE first gear was because it’s a PG and I don’t really give a single **** about those) because how far the RPM drop is.
With the wider LSA you will hurt power below peak torque, and for all the street guys who think blazing the tires every time you touch the throttle is cool then you want to keep the LSA tighter.
Then there is tuning. I read all the crap on hear about tight LSA’s and drivability and it’s all nonsense IF you can tune. IMO, it’s way quicker and far more cost effective to do the tuning on a dyno, but you can do it in the car. It’s just 10 times harder and takes at least 10 times longer in the car.
So the short answer is it depends. For most guys just buy something on a 110 and go. There is a reason why Comp uses that as the de facto LSA for most of their street and street/strip grinds.
I also find it somewhat comical that so many guys claim they don’t care about power numbers yet every car forum everywhere has guys asking the same thing. It IS about making power, where you make power and HOW it makes power. If it wasn’t, we wouldn’t be talking about this right now.
You‘d be far better off spending the money for Billy Godbolds cam book. Read through it. Several times. As many times as you need to. I’ve already read through the book 3 times and have read parts of it probably a dozen times.
If you are into math, you can go to speedtalk.com and buy one of the few remaining copies of “The Horsepower Chain”. That’s an eye opener.
And don’t forget, you can’t change the LSA of a cam in isolation. The only way to change the LSA is to move the timing events to get what you want.
LSA is lobe separation angle which is the angle between the intake lobe centerline and exhaust lobe centerline...
So if you isolate all other cam properties and just focus on lobe separation, here's what you can reason out:
A larger lobe separation angle has the lobe centerlines FARTHER APART, a smaller lobe separation angle is where the lobe centerlines are CLOSER TOGETHER... If the lobe centerlines are closer together, then there will be more overlap of the intake and exhaust valves being open at the same time together which will lower cylinder pressure... With the lobe centerlines farther apart, there will be less overlap of the valves being open at the same time and the cylinder pressure will be higher, therefore giving more torque...
The blanket statement that 108 lsa is good for torque is not an accurate statement.
Assuming friction losses have been minimized, air/fuel mixture quality is good and spark timing is optimal, there are two main factors that influence torque: compression ratio and volumetric efficiency. Get more air/fuel trapped in the cylinder and torque will increase.
Good cam specs are all about trapping the most air/fuel mixture in the cylinder in the desired rpm range. The 108 lsa has been shown to work well on an engine with a wedge style combustion chamber and a bore/stroke combination similar to a Chevy 350. A hemi style combustion chamber will want a different lsa. A large stroker motor may also want a different lsa.
It's all about VE.
Assuming friction losses have been minimized, air/fuel mixture quality is good and spark timing is optimal, there are two main factors that influence torque: compression ratio and volumetric efficiency. Get more air/fuel trapped in the cylinder and torque will increase.
Good cam specs are all about trapping the most air/fuel mixture in the cylinder in the desired rpm range. The 108 lsa has been shown to work well on an engine with a wedge style combustion chamber and a bore/stroke combination similar to a Chevy 350. A hemi style combustion chamber will want a different lsa. A large stroker motor may also want a different lsa.
It's all about VE.
TT5.9mag
Two atmospheres are better than one
Yes, any and all articles you can find. There are also many books written on the subject and that’s where you should start.
Here’s a good one.
https://www.amazon.com/High-perform...hnology-Selection/dp/1613257546?tag=fabo03-20
remytherat
Well-Known Member
Remember that LSA is a product of the other specs, not a defining spec itself. Changing LSA means changing when all valve events occur.
Newbomb Turk
Well-Known Member
Yup. That’s what I said.
The stock 340 cam had a 114 LSA.
B3422w5
Well-Known Member
Years ago I had a 107 lsa solid cam that Dwayne specced.
A certain cam guy that I hung around with a bit at the time and who sold and specced cams convinced me to try one of his cams( he swore by and likes 112+ cams)
He was well aware of exactly what my combo was. He designed a cam very similar to what I had regards lift and duration( old was 260-266, 623 lift) new was 259/268 620 lift.
Installed new cam per spec, went to the track, and wow….
new cam killed 60 foot and ET. talking about 12-14 in the 1/4.
the only item that didn’t suffer was MPH. In fairness, it was virtually unchanged..
I didnt have a ton of compression(11.5) vert was 5200) and car was heavy 3350.
this was a 416 Eddie headed motor I had swapped the top end off of and went to W5 heads, beginning of the season. Ran it half the season, then in late June made this cam swap.
Conclusions I drew( right or wrong) was that if I had a lot more compression, and a good bit more vert, car might have actually ran as well or quite possibly better, but with what I had, it most definitely didn’t.
I believe wider LSA belongs more on a street car for better idle quality, or a light car, or a car that is going to use a power adder.
narrower LSA cam is more for a head challenged car, class car, etc.
A certain cam guy that I hung around with a bit at the time and who sold and specced cams convinced me to try one of his cams( he swore by and likes 112+ cams)
He was well aware of exactly what my combo was. He designed a cam very similar to what I had regards lift and duration( old was 260-266, 623 lift) new was 259/268 620 lift.
Installed new cam per spec, went to the track, and wow….
new cam killed 60 foot and ET. talking about 12-14 in the 1/4.
the only item that didn’t suffer was MPH. In fairness, it was virtually unchanged..
I didnt have a ton of compression(11.5) vert was 5200) and car was heavy 3350.
this was a 416 Eddie headed motor I had swapped the top end off of and went to W5 heads, beginning of the season. Ran it half the season, then in late June made this cam swap.
Conclusions I drew( right or wrong) was that if I had a lot more compression, and a good bit more vert, car might have actually ran as well or quite possibly better, but with what I had, it most definitely didn’t.
I believe wider LSA belongs more on a street car for better idle quality, or a light car, or a car that is going to use a power adder.
narrower LSA cam is more for a head challenged car, class car, etc.
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Go to Don Terrell's Speed Talk and read the conversations with Mike Jones (CamKing, thanks Hysteric!) and David Vizard and study the 128 cam formula. They say that LSA has the most effect on peak cylinder pressure during the combustion cycle and that one degree of LSA is equal to at least four degrees of intake valve closing event. CattledogGarage has some videos where he talks in depth on the subject and cover it in better detail. He also gives the formulae for rocker ratio and compression. It takes several veiws to filter it all but it's worth watching.
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David Vizard’s YouTube channel or any of his books.
Dan the man
Well-Known Member
K. Thanks everyone for your help
Dan the man
Well-Known Member
I've started to read about camshaft timing events. Would a cam that has a 108* lsa and duration of 204* / 214* @ 0.0.050 " have a rough idle?
No.
But it really depends on what you qualify as "rough". I personally don't think cams sound all that radical until you get up in the 250s.
I also *hate* when a guy idles down his engine really low to try to make it lope. Sounds god awful.
But it really depends on what you qualify as "rough". I personally don't think cams sound all that radical until you get up in the 250s.
I also *hate* when a guy idles down his engine really low to try to make it lope. Sounds god awful.
Dan the man
Well-Known Member
My intended goal is to have good throttle response and low to midrange torque. As some have said that I maybe satisfied with the way it already is and if so then I'll concentrate on the tuning of the ignition and carburetor. I'm looking forward to the learning curve
A cam upgrade from stock is still a good idea. The factory cam balances a bunch of considerations, having nothing to do with good power and torque production.
A mild cam, under say 215@50, will significantly pick up midrange torque and allow it to rev out nicely to 5000+. Without sacrificing much at all on off idle response.
Newbomb Turk
Well-Known Member
No. 90% of idle is tuning. Your timing curve and carb tuning.
You know how I know that? Because Jim at Racer Brown called me out on my tuning. So, I went and figured it out. And he was dead right. My cam is [email protected] on a 105 and it was in at 105 and it will idle down to 750 all day long. I don’t let it do it, but it can.
Rather than reading up on cam timing, maybe, just maybe if you ask him nice (I’d ask but he may not do it for me lol) @Hysteric may be able to post some links to what Shrinker wrote about carb tuning. And maybe some stuff Tuner wrote about it.
And maybe, if we ask nice, @Mattax will post some links to where ever he gets his information on ignition timing and all that.
Thats where I’d start. Because if you can’t tune or can’t learn it or don’t want to learn it or maybe you don’t want to pay to have it done then that right there is a big clue about what to do about cam timing.
You‘d be surprised how fruitless your effort will be worrying about mid range torque and the like.
Pick your compression, cam it accordingly and tune it up. Worrying about made up **** like “mid range torque” and “throttle response” will drive you mad because none of what you are looking at affects those things.
That stuff falls under the category of “drivability” and very few of the good drivers I know are even capable of taking a car out, evaluating what’s happening and then being able to explain it so it can be tuned.
That’s why if I don’t drive it I don’t tune it any more. It’s too damn hard to try and tune around what other people say, let alone the things they do even after they are told not to.
That really depends on a bunch of things, off the top of my head, 3 big ones are,
Valve overlap, how many degrees the intake and exhaust valves open at the same time. Smaller overlap,smoother idling.
How your exhaust port and exhaust system flows. The second the exhaust valve opens, exhaust is super sonic till about.1-.15 lift. Better flow, smoother idle.
The better the exhaust scavenges and the less reversion, smoother idle.
What your kind of talking about with rough idle is overlap when both valves are open, bigger the overlap the less it likes to operate at very low rpms. So a 108 204/214 will have more overlap than a 113 204/214 but will have same as a 113 214/224 which would be on the mild side still.
dave ellis
Old guys
Get yourself a copy of the power pro series how to build and modify Chevrolet small block V8 camshafts and valve trains. You'll be a cam pro. Chevy, but info is across the board
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