LSA Question

[318willrun]

How in the world did my post turn into pro stock engines, 128 formulas of which I have no idea of what it all means and probably doesn't apply to my particular set of goals. I thought that I had asked a simple question concerning the lsa of cams for the street. I'm looking at Howard's cams and they have one that said it has very strong torque. I believe it's .479 / .494 x 255* / 261* duration at 0.050" is 204*/214*, lsa is 112*. I know that it's not much more than the factory 360, 318willrun did a 360 with similar specs and he got 12.80's from his 360. Any suggestions on a cam that's close to the 340 grind and that would help throttle response and low to midrange torque would be helpful and if a stall converter and gears are needed that's fine. I don't mean to sound disrespectful here or anything but my question blew up into something that I don't understand or even ever heard of. I hope that the rest of the comments will pertain to the question at hand. This is going to be nothing other than a street cruiser and no track time what so ever. I thank everyone for their help.

keep in mind, the cam in the 360 was going to have a stock torque converter and highway gears... started as 2.45's and now 3.23's. Better converter and gears, the engine would come to life with a better cam. It's why I say, if you do not plan to go to the drag way or race the car ever, just want low end torque, I think a factory 318 cam can deliver what you are hoping for. I would focus more on the tune of the ignition, quality timing set, a good valve job, etc

 

[Dale Davies]

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.

Billy Godbold's book Highperformance Camshafts and Valvetrains is a good book. I have read it once and as ou have stated you need to read it a few times.
For a person asking how cams can be advertised as both having strong torque, discussing IVC, IVO, EVO and EVC points will be probably past comprehendable until more of the basic knowledge is acquired. For this case, looking at David Vizard's Powertec 10 videos simplifies the procedure. There is one explains the 128 formula and another that explains what cam companies keep getting wrong.
The cam companies chose 110° LSA for shelf cams to account for the hot rod crowd that buys into the theory that if a bit of duration is good, a bit more will be better. Especially on the street a bit less duration and a tighter LSA will most likely give better performance. This limits the amount of overlap, for acceptable or good street running.

 

[Dale Davies]

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.

Pretty much all our SBM, SBC and SBF engines are head limited. The Boss 302 was one that had too much head for the street. That is one reason to replace 128 in the formula with 132 for LSA selection. Also why GM LS engines employ wide LSA on their OE cams. In the Chev Performance catalogue they list two cams for circle track use. I believe these are ground on a 108°LSA as idle quality is not a major concern when running between 3000 and 7000 RPM.
The LS engines have pretty good port flow right out of the molds.

 

[Spadman]

For a snappy throttle response, you can't beat a great combo, high cylinder pressure, and a sharp tune.

For most of us with SBMs, street cams are gonna fall into a small range of about 210 to 230/235 range, because after that, the rpm of peak power is gonna get expensive to build reliability into, and cylinder pressure is getting harder and harder to find, cheaply.. So yur looking at about a 3>4-size cam range.
Now;
You just can't stick any of those 3>4 sizes into the same short block, expecting a power increase at the top, to not negatively affect low-rpm and throttle response. And if you start mixing cam brands between the sizes, yur just looking for heartaches.

I'm gonna try to save you weeks of time by the following few statements;
1) choose your heads first, and Lordy let them be closed chambers. But if not, then whittle the quench into line.
2) choose you cam size , to support your intended usage.
...If you intend to go racing, go get a race cam.
...If you want to idle along in parades, get a parade cam
...If you are gonna spend 90% of your time in town, get a town-cam
... If you need to drive the thing on the hiway, criminy 45 hp will get any tank A-body to 65 mph! so forget about power at 5500rpm.
... if you need a lil of this and that, pic the smallest cam that will do the job
3) run the Cylinder Pressure up to the max for the fuel that you can afford, and tune it!
4) Make sure the beast gets oil, lots and lots of oil. Put an extra capacity oilpan on it, with baffles if you like to drive like me. Oil the crap out of it; on the street you don't care about a few couple of hp lost to the pump. Yur never gonna know it!
5) if an automatic, stall it right.
The bigger the cam, usually the higher the stall
the lower the cylinder pressure, the higher the stall
If you don't stall it right, yur just gonna be frustrated beyond thinking straight.
6) gear it right. If the tires don't spin in Second Gear, it better be geared right or it's gonna be slow until it hits the cam........ again.
If the cam is too big, and the gear is too small, it's gonna powerpeak at an mph that you cannot legally drive at! Where is the advantage in that?
7) To have a snappy combo, you gotta be financially prepared to marry all the pieces of the combo, and your stated usage has got to drive every decision you make.
If your usage calls for a 210 can, then don't buy a 220 nor a 235. I guarantee that you'll be sorry.
If burning rubber to 50 mph, is on the agenda, together with snappy take off, choose the biggest SBM there is.
If hiway fuel economy is a factor, together with a snappy bottom end, then choose more cubes over a bigger cam
If fuel economy is a really really Big factor get a smaller engine. Marry the combo to the usage.
If you need an overdrive to cover all your bases, either get one, or change your stated usage.
8) if you have a financially challenged combo, then start with the stall and gears. I can't tell you how many guys will say, "I can't believe the difference 4.10s and a 2800 stall made to my stock318! I'm not suggesting BTW that you rush out and get some 4.10s....... lol

Man I was just gonna quickly dash off a couple of things, sheesh, here I am again, an hour later.

Excellent common sense explanation. I like it.

 

[Dale Davies]

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?

Your duration is still fairly short, so it should be close to stock idle quality. I replaced the cam in my 1982 Blazer with the lopo 305. Factiry cam was something like 192°/196° @ 0.050. Intake lift was 0.375" and exhaust was 0.396". I looked at the TRW catalogue and chose the cam two up from the dtock 350 cam snd fourth up from the stock 305. The guy did not want to sell it to me for the 305 as he thought it was too much. 204°/214° @ 0.050" with 0.42" and 0.48" lift. I think the LSA was 110°, but this cam was the RV 350 cam. Gosh did it improve vacuum, driveability and fuel economy. Idled rock solid.

 

[Dale Davies]

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.

Especially when you add say 0.030" lift in with that cam timing. As with any cam swap, piston to valve clearance must be checked. This can be done without removing the head by putting #1 on TDC and putting air into the cylinder to hold the valves shut. Then the valve springs can be replaced withight checking springs. Remove the air pressure and put the rockers back on. The closest exhaust will be about 10° BTDC and intake will be about 10° ATDC. A dial inducator on the edge of the retainer and push down on the rocker over the valve stem will indicate the clearance. You may have to check a few degrees before and after the 10° point mentioned.

 

[Dale Davies]

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.

204° @0.050" lift on a 108°LSA cam is not much more than stock. An "RV" cam. It will likely benefit with some minor adjustment to the tune, but even the stock cam may benefit with the additional TLC of a tune.

 

[Mean416]

For reference, I built a basically stock 360 last year (you can find a thread on this site). It had a comp 265 deh. Definitely a significant upgrade over stock. That thing had miles of valve clearance. It was over.200 at the tightest point, if I correctly recall. Mopar likes putting those pistons waaaay down in the hole.

Obviously always check clearance. Just throwing this out there.

 

[Dale Davies]

How in the world did my post turn into pro stock engines, 128 formulas of which I have no idea of what it all means and probably doesn't apply to my particular set of goals. I thought that I had asked a simple question concerning the lsa of cams for the street. I'm looking at Howard's cams and they have one that said it has very strong torque. I believe it's .479 / .494 x 255* / 261* duration at 0.050" is 204*/214*, lsa is 112*. I know that it's not much more than the factory 360, 318willrun did a 360 with similar specs and he got 12.80's from his 360. Any suggestions on a cam that's close to the 340 grind and that would help throttle response and low to midrange torque would be helpful and if a stall converter and gears are needed that's fine. I don't mean to sound disrespectful here or anything but my question blew up into something that I don't understand or even ever heard of. I hope that the rest of the comments will pertain to the question at hand. This is going to be nothing other than a street cruiser and no track time what so ever. I thank everyone for their help.

Dan, you asked a question. Part of the answer is to find the video from David Vizard on his Powertec 10 channel. He explains very well and simply in two separate videos; What the Cam Manufacturers Get Wrong and there is another that discusses the 128 formula. In his book How to Build Horsepower David goes through the formula. It is very easy to understand. Some on here have posted about IVC and its relation to cylinder pressure. To understand the valve event timing requires a lot more knowledge than what you appear to have. Now I am not intending to be insulting by that statement, only expressing what you appear to know and not know.
The formula is 128 - (displacement of one cylinder ÷ (intake valve head diameter × .91)). This breaks the starting point for LSA down to a simple choice to understand.
A number of years ago I called Engle Cams regarding a cam for a 351W for my 1980 full size wagon for strickly street driving and intended to try to increase fuel economy. I had been looking at the prevailing noise indicating going to a 112° LSA. The tech talked me through it and suggested they grind on a 109° LSA. This worked out very well.
210°/210° @ 0.050, 256°/256° seat timing and 0.472" lift on both, ground with 109° LSA and 4° advance. I eventually parked the car and a friend talked me into selling the car to another friend to use mechanicals for his 1948 Mercury truck. Only thing was the first friend was adamant to rebuild the engine which ran well and did not burn oil. I insisted to get the cam and lifters back. I have the lifters stored in a 2 x 4 labeled fon and rear so the lifters can go back on the same lobes.
So on the 351 with the 1.78 emission intake valves it works out like this;
128 - (43.875 ÷ (1.78 × .91)) = 128 - 27 indicates 101 LSA. Pretty tight.
Now let's try that on my 0.020 over 289 and installing LS 1.9/ 1.55 valves:
128 - (36.43 ÷ (1.9 × .91)) = 128 - 36.3 ÷ 1.73 = 128 - 21 = 107° LSA. Now that cam lifts the intake valve fairly quickly and with 1.72 :1 roller rockers definately is guick off the seat. According to David Vizard this allows to increase the LSA by about 1°. With a back cut on the intake valves we can increase it a bit more. I also plan to increase the CR to about 11:1. So now the LSA is looking to be close to optimal for the 289.
I hope this makes some sense out of this for you.
Billy Godbold's book on highperformance cams and valvetrains is informative, but much of it passes over my head. I need to read it a few more times. Through his extensive knowledge earned by being a leading engineer with Comp Cams, he approaches the topic from opening and closing events. Without that intense knowledge we are peeing into the wind.
David Vizard is a friend of Billy Godbold due to years interacting in the high performance industry and says he intends to read Billy's book when he can find time. I am interested to know his opinion. It would be interesting to here them discuss their thoughts on eachother's selection process.

 

[Dale Davies]

keep in mind, the cam in the 360 was going to have a stock torque converter and highway gears... started as 2.45's and now 3.23's. Better converter and gears, the engine would come to life with a better cam. It's why I say, if you do not plan to go to the drag way or race the car ever, just want low end torque, I think a factory 318 cam can deliver what you are hoping for. I would focus more on the tune of the ignition, quality timing set, a good valve job, etc

318 cams are wanting a bit. A 360 cam is likely going to perk it up a bit and still keep a smooth idle. A 340 cam may introduce a bit of lope to the idle. This is really where the tune comes into play.

 

[318willrun]

318 cams are wanting a bit. A 360 cam is likely going to perk it up a bit and still keep a smooth idle. A 340 cam may introduce a bit of lope to the idle. This is really where the tune comes into play.

I've ran all 3 in 318's. Yes, they'll make a difference, but, neither of those offer any more off idle stomp than the 318 2bbl cam, results are seen once you get it going. I've had 318's that took some getting used to for a new driver because they would lay rubber at the tap of the gas, and that's with stock converters and highway gears.

 

[Bewy]

DVs videos on the 128 rule are EXCELLENT, as are all of his videos. But the video I mentioned in post #73 is even better because it actually tests & and validates the 128 rule. So do not take DVs word, look at independent testing; maybe somebody with better computer skills than me can post it....

There are people on the net like Hoffman & Schmidt who criticise DV's cam selection methods. DV has challenged them many times to show their method....& we are all still waiting....

 

[AJ/FormS]

@Dan the man
Here are some theoretical cams, to show you what happens to LSA/etcetera, whilst adjusting the overlap period.
this is just an exercise.
all are in at split overlap.
I set the Ica to 62* for a compression period of 118, which is typical street
I set the intake/exhaust split to 4* for a power extraction of 114* .
I set the overlap to be 20* on the first example and increasing by 8* in each successive one.
Watch what happens to the LSA, and intake/exhaust durations

1) 252 intake/118 comp/114 power/256 exhaust/20 overlap/LSA of 116
2) 256 intake/118 comp/114 power/260 exhaust/28 overlap/LSA of 115
3) 260 intake/118 comp/114 power/264 exhaust/36 overlap/LSA of 113
4) 264 intake/118 comp/114 power/268 exhaust/44 overlap/LSA of 111
5) 268 intake/118 comp/114 power/272 exhaust/52 overlap/LSA of 109
6) 272 intake/118 comp/114 power/276 exhaust/60 overlap/LSA of 107
All of these cams can be installed into the very same short block,
and because the ICA has NOT changed; you can expect
very similar cranking cylinder pressure, bottom-end power, throttle response, and among any three or even four cams in series, even similar steady-state fuel economy. Furthermore the stinking pushrod length can be set just the first time.
Thus , for street
you can build a zero-deck 318 with closed chambers and set the Q with the Quench-pad/gasket and adjust the compression with a step-D cup ,
then have at it.
Hey, it wasn't my idea to start with a 318 ............... lol
OR
still for street;
you can start with a 360, in the which the deck height might fall together at .012 down, slap on a gasket of .028 which takes care of the Q using a closed chamber head, and just choose what ever head has the right sized chamber, no decking required, no piston work, Easy peasy.... 1-2-3
And finally, if the cam you have chosen doesn't work out, just slide another one in with the same Ica except a different overlap; smooooooth.

Just for reference and not specifically related to the above, as to the idle sound;
20* overlap idles like a factory 318
30* overlap idles like a factory 360
44* overlap idles like a factory 340, and is barely noticeable
52* is a lil more than barely noticeable
60* is starting to sound like something is going on under the hood
68* is loping, just a nice warm gentle cadence
76* is very noticeable, especially if you run it with retarded idle timing.

Up to 44* requires no special tuning skills
52 and up will depend on your base ignition timing.
68 and up, the engine will want some bypass air, no big deal
I have not tuned for more than 76*
IMO,
None of theses are particularly difficult to tune. You just gotta give the engine what it wants, and not just throw a buncha timing at it. I mean that sorta works with an automatic, which has a higher than stock stall, but that don't mean it's the right thing to do on the street, and especially not in a DD.

 

[Dale Davies]

DVs videos on the 128 rule are EXCELLENT, as are all of his videos. But the video I mentioned in post #73 is even better because it actually tests & and validates the 128 rule. So do not take DVs word, look at independent testing; maybe somebody with better computer skills than me can post it....

There are people on the net like Hoffman & Schmidt who criticise DV's cam selection methods. DV has challenged them many times to show their method....& we are all still waiting....

True enough on comparing on youtube vids. But you have to admit that DV's consulting record with Cup Car teams, F1 teams, the General along with his race and pole winning record kind of proves he knows a few things. When his information is closely aligned with people like Mike Jones, you can assume they know what is going on. You do not have to agree with them. If you have your own method that works for you, carry on. This is not directed at you but a lot of other nay sayers.

 

[Bewy]

Dale,
I am not a DV nay sayer, quite the contrary. Do not know what gave you that idea. He also has numerous patents to his name & his record speaks for itself.

 

[Dale Davies]

Dale,
I am not a DV nay sayer, quite the contrary. Do not know what gave you that idea. He also has numerous patents to his name & his record speaks for itself.

As I stated that part was intended more for those that discredit DV, and are nay sayers.

 

[krazykuda]

Tighter lsa makes more cylinder pressure because of earlier intake closing. Assuming all other specs are the same.

Intake closing is determined by the intake lobe centerline and intake duration...

You can bump the intake centerline forward or backward and keep the same lobe center.... The exhaust centerline will follow if the lobe centers are kept constant/equal...

You can pick a lobe separation and then tune in when the intake closes by establishing the intake lobe centerline... You can have a lobe separation of 108° and bump the intake centerline as needed to close the intake valve wherever you want it to affect your cylinder pressure/dynamic compression....

It takes two parameters/degrees of freedom to lock in the intake valve closing and lobe centers....

 

[340six]

keep in mind, the cam in the 360 was going to have a stock torque converter and highway gears... started as 2.45's and now 3.23's. Better converter and gears, the engine would come to life with a better cam. It's why I say, if you do not plan to go to the drag way or race the car ever, just want low end torque, I think a factory 318 cam can deliver what you are hoping for. I would focus more on the tune of the ignition, quality timing set, a good valve job, etc

Nothing new about this thread. Reminds me of back in 1978 drinking a few beers with friends. After a few to many on of the guys who was looking at a RV Cam ( so he can have A/C and power brakes work in his cruiser ) to put in his junk yard low mile motor.
And one of the guy's there says WOW the bottom of the page cams look good.

 

[dadsbee]

I'm not sure he's old enough yet to be drinking beer though...

 

[Dale Davies]

Intake closing is determined by the intake lobe centerline and intake duration...

You can bump the intake centerline forward or backward and keep the same lobe center.... The exhaust centerline will follow if the lobe centers are kept constant/equal...

You can pick a lobe separation and then tune in when the intake closes by establishing the intake lobe centerline... You can have a lobe separation of 108° and bump the intake centerline as needed to close the intake valve wherever you want it to affect your cylinder pressure/dynamic compression....

It takes two parameters/degrees of freedom to lock in the intake valve closing and lobe centers....

Do not forget the main person here is the person that asked a question, the OP. For cam selection he is a neophyte, so KISS is required. This is why I recommended he watch DV's cam select videos or get a copy of How to Build Horsepower.
For more experienced builders we can get down and dirty with opening and closing events, and the whys.

 

[krazykuda]

Do not forget the main person here is the person that asked a question, the OP. For cam selection he is a neophyte, so KISS is required. This is why I recommended he watch DV's cam select videos or get a copy of How to Build Horsepower.
For more experienced builders we can get down and dirty with opening and closing events, and the whys.

I understand...

I'm trying to correct mis-information from getting passed along and someone falsely believing it...

I was replying to pentastar's post that tighter lobe center will make more cylinder pressure with the intake valve closing when they are not related... The OP's question was about lobe separation, not intake valve closing... I don't agree with him responding to my reply on lobe separation that tighter lobe separation will make more cylinder pressure - that's incorrect... Tighter LSA will make lower cylinder pressure than larger LSA because of more overlap of the intake and exhaust valve open - it's simple physics...
Stating that tighter lobe separation will make more torque because of earlier intake valve closing is like asking "do you walk to work or pack a lunch"...

Larger lobe separation with early intake valve closing will make the higher cylinder pressure and more torque... If you make the lobe center smaller and the intake valve close later, that will decrease cylinder pressure and reduce torque...

Intake valve closing is completely independent of lobe separation and can be moved to achieve any intake valve closing that you wish... Intake valve closing and lobe separation work together to determine the cylinder pressure of an engine...

I've done cam calculations forward, backward, inside out, and upside down and found errors and conflicts with many cam manufacturer's published information and corrected it in my charts... I have tried to simplify the question that he's answered and break it down to basic physics and the math on how those parameters will affect the performance of the camshaft and explain it in layman's terms...

 

[Bewy]

KK,
Your statement that smaller LSA will reduce tq [ & vice versa ] is incorrect & has been proved with various tests on different engines. Watch the 33 min 'Cattle Dog Garage' video, & below.

 

[cpearce]

I understand...

I'm trying to correct mis-information from getting passed along and someone falsely believing it...

I was replying to pentastar's post that tighter lobe center will make more cylinder pressure with the intake valve closing when they are not related... The OP's question was about lobe separation, not intake valve closing... I don't agree with him responding to my reply on lobe separation that tighter lobe separation will make more cylinder pressure - that's incorrect... Tighter LSA will make lower cylinder pressure than larger LSA because of more overlap of the intake and exhaust valve open - it's simple physics...
Stating that tighter lobe separation will make more torque because of earlier intake valve closing is like asking "do you walk to work or pack a lunch"...

Larger lobe separation with early intake valve closing will make the higher cylinder pressure and more torque... If you make the lobe center smaller and the intake valve close later, that will decrease cylinder pressure and reduce torque...

Intake valve closing is completely independent of lobe separation and can be moved to achieve any intake valve closing that you wish... Intake valve closing and lobe separation work together to determine the cylinder pressure of an engine...

I've done cam calculations forward, backward, inside out, and upside down and found errors and conflicts with many cam manufacturer's published information and corrected it in my charts... I have tried to simplify the question that he's answered and break it down to basic physics and the math on how those parameters will affect the performance of the camshaft and explain it in layman's terms...

COMP Cams Effect of Changes In Cam Timing and Lobe Separation Angle - COMP Cams®

 

[Dan the man]

I understand...

I'm trying to correct mis-information from getting passed along and someone falsely believing it...

I was replying to pentastar's post that tighter lobe center will make more cylinder pressure with the intake valve closing when they are not related... The OP's question was about lobe separation, not intake valve closing... I don't agree with him responding to my reply on lobe separation that tighter lobe separation will make more cylinder pressure - that's incorrect... Tighter LSA will make lower cylinder pressure than larger LSA because of more overlap of the intake and exhaust valve open - it's simple physics...
Stating that tighter lobe separation will make more torque because of earlier intake valve closing is like asking "do you walk to work or pack a lunch"...

Larger lobe separation with early intake valve closing will make the higher cylinder pressure and more torque... If you make the lobe center smaller and the intake valve close later, that will decrease cylinder pressure and reduce torque...

Intake valve closing is completely independent of lobe separation and can be moved to achieve any intake valve closing that you wish... Intake valve closing and lobe separation work together to determine the cylinder pressure of an engine...

I've done cam calculations forward, backward, inside out, and upside down and found errors and conflicts with many cam manufacturer's published information and corrected it in my charts... I have tried to simplify the question that he's answered and break it down to basic physics and the math on how those parameters will affect the performance of the camshaft and explain it in layman's terms...

I'll use a 268* duration cam for how to calculate the inv. I've tried this formula several times along cams that have their inv closing listed and it's dead on. cpearce also included a post from comp cams. He we go. 268*÷2=134*+112*=246* - 4* advance =242 -180 = 62*inv. 268*÷2=134*+108*=242- 4* advance = 238 -180 = 58* ivc. None of the formulas included the valve overlap. So going by their formula for finding the inv closing point the lsa does affect the ivc, I couldn't find or figure any way to get a wide lsa and get a sooner inv point.

 

[Dan the man]

Everything that I've read up to this point all pretty much said the same thing, a tighter LSA will help close the inv sooner. The formula that I used earlier showed this to be the case. I'm not saying that I'm a 100% right as I'm simply going by the formula given to figure the inv closing point of a camshaft. And every place that I've read all gave the same thing. Advertised duration divided by 2 + the LSA minus any camshaft advance minus 180 equals the inv closing point. Is this formula accurate for figuring the inv closing point? I read that the camshaft and the compression have to work together or you could have to much cylinder pressure which causes detonation, or to little cylinder pressure in which both can cause a power loss and possibly engine damage. Have I been learning anything here or am I miss understanding something? I wasn't trying to say or prove anyone wrong, as I was sharing what I've read and if I miss read or miss understood something please let me know. I thank all you guys for your help.