Don't understand cams

[MopaR&D]

i put the lunati 701 in wifes 72 340 duster, very nice streetable cam, just a hint at idle there might be something in there, 727,323s, stock torque converter, it will positively fry 295/15 mickey thompsons

I got that same cam years ago and put it in my worn-out stock 318 with 4-bbl and duals. Woke it up for sure but it was still a turd on the bottom end (6000' elevation and 2.76 gears didn't help). The really interesting thing, I put the SAME cam in the 360 I have in my Duster now and it's got 10.5:1 compression and stock Magnum heads with 1.6 rockers. In the 318 the idle was a tad lumpy at times and you could feel it wake up once it hit 2500 RPM or so. In the 360 it idles really smooth but has a very raspy aggressive tone to it, almost like a diesel with straight pipes lol. It also has BRUTAL torque right off idle and the torque curve is super flat, almost too flat. Like everyone else is saying, matching the cam to the rest of the engine is critical; I know my 360 has a lot of potential HP waiting to be opened up if I get a proper cam custom-ground to match my exact engine/car specs.

 

[ir3333]

at what rpm does that 701 nose over or pull well to in your 360?
..wonder if the 702 would be a noticable improvement?

 

[MopaR&D]

at what rpm does that 701 nose over or pull well to in your 360?
..wonder if the 702 would be a noticable improvement?

The torque curve is so flat it doesn't even really 'nose over' but it seems to be ready to shift by 5000-5500 RPM. I would get the 703 cam in a heartbeat but it's too much lift for my heads with the 1.6 rockers. There are a couple 'off-the-shelf' grinds I've looked at that might work but I'd rather get a custom grind and get the most power/efficiency possible. I mean it costs the same (in most cases) so to me it's the way to go, and I wouldn't mind spending some time on the phone with an experienced cam grinder/engine builder picking their brain.

 

[ir3333]

The torque curve is so flat it doesn't even really 'nose over' but it seems to be ready to shift by 5000-5500 RPM. I would get the 703 cam in a heartbeat but it's too much lift for my heads with the 1.6 rockers. There are a couple 'off-the-shelf' grinds I've looked at that might work but I'd rather get a custom grind and get the most power/efficiency possible. I mean it costs the same (in most cases) so to me it's the way to go, and I wouldn't mind spending some time on the phone with an experienced cam grinder/engine builder picking their brain.

Do you think you can keep a strong bottom end using the 703 and improve hi rpm power?I am shopping myself and think the 702 may be what i need?I am looking for strong lo end torque and a smooth clean idle with power to 5500 give or take.I am not a fan of a rough idle.

 

[MopaR&D]

Do you think you can keep a strong bottom end using the 703 and improve hi rpm power?I am shopping myself and think the 702 may be what i need?I am looking for strong lo end torque and a smooth clean idle with power to 5500 give or take.I am not a fan of a rough idle.

The 702 should give you what you're looking for in a 360.

 

[roccodart440]

Who said what is wide and what is narrow?

I believe you said over 108 is wide to you. To me 112 and wider is wide. Certainly I'd agree on the subjectiveness of the statement.

Some of the characteristics you mention I wont dispute.


So the million dollar question is... How do you get 2 engines with cams of the same duration, but different LSA's to idle the same and have the same street manners?

[email protected] with 104 vs. [email protected] with112 LSA are the cams we'll use. I'd defy anyone to get these cams to idle the same.

As you can see I don't always ride the LSA like a 2 dollar ***** as I have both worlds in my garage. But man they are 2 different beasts.

Guess which on I like to drive? Guess which one has a sound that attracts people's attention?

Edit: both make similar power but the nod goes to the 104LSA for HP. Torque is very similar.

 

[yellow rose]

I believe you said over 108 is wide to you. To me 112 and wider is wide. Certainly I'd agree on the subjectiveness of the statement.

Some of the characteristics you mention I wont dispute.


So the million dollar question is... How do you get 2 engines with cams of the same duration, but different LSA's to idle the same and have the same street manners?

[email protected] with 104 vs. [email protected] with112 LSA are the cams we'll use. I'd defy anyone to get these cams to idle the same.

As you can see I don't always ride the LSA like a 2 dollar ***** as I have both worlds in my garage. But man they are 2 different beasts.

Guess which on I like to drive? Guess which one has a sound that attracts people's attention?

Jesus, do you like to argue?

I'll say it again so hopefully, someone will come along and read it and learn from it.

There is no such thing as a wide LSA or a narrow LSA. There is the CORRECT LSA and that is it. Your cam comparison is idiotic because you are not just changing the LSA, you are changing IVO and EVC to manipulate LSA. So what changed idle characteristics? LSA or the actual events? It's the events that have a much more pronounced affect on idle than does LSA. I run 255 @ .050 on 340 inches, on a 105 LSA. It idles no different than the 992 MP hydraulic it replaced. And that pile of dung is on a 110 LSA. My cam also has relatively fast ramps. It's seat timing is 280 at lash.

Again, there is more to it than LSA. But when you, or anyone else manipulates LSA to fix idle issues, you did it WRONG. Unless you think that an 800-850 idle RPM is not streetable, IDK what to tell you.

A junk cam is a junk cam. You can't manipulate LSA to fix opening and closing event errors.

FWIW, you can look at the heads and intake someone is using and pretty much be within a degree or two of what the LSA should be, just from experience. I know, for a FACT, if you tell me you spent a bunch of time increasing low lift flow, I know, for a FACT, you will have to open the LSA up. Because old wives tales never die, people spend incredible energy trying to increase flow where you don't want to increase it, at the expense of getting flow higher in the lift curve. I'd gladly give up 20% of my flow at .100-200 lift to gain 5% at .400-500 and with the correct cam, that head I'll make more power above peak HP, more torque below peak and require less at .050 timing than one that has better low lift numbers.

So to the OP, learning about cams is more than what rudimentary stuff you are reading. Learning cam timing encompasses everything about the cam, plus air flow, as in how much flow, port volume, shape of the curve, pressure recovery of the port and chamber and much more.

Overlap triangle is your friend. Learn to understand it, and how it interplays with what is happening when both valves are off the seat.

 

[roccodart440]

Now that was helpful.

While I'm not out for the max HP, the technical end of camshaft technology you posted is helpful to anyone who reads it.

I like to talk about engines. Not necessarily argue.

Here is an article that kind of proves both of our conversation points to be true.

Lobe Separation Angle Explained and How it Affects Horsepower

 

[318willrun]

I'll say it again so hopefully, someone will come along and read it and learn from it.

There is no such thing as a wide LSA or a narrow LSA. There is the CORRECT LSA and that is it. Your cam comparison is idiotic because you are not just changing the LSA, you are changing IVO and EVC to manipulate LSA. So what changed idle characteristics? LSA or the actual events? It's the events that have a much more pronounced affect on idle than does LSA. I run 255 @ .050 on 340 inches, on a 105 LSA. It idles no different than the 992 MP hydraulic it replaced. And that pile of dung is on a 110 LSA. My cam also has relatively fast ramps. It's seat timing is 280 at lash.

Again, there is more to it than LSA. But when you, or anyone else manipulates LSA to fix idle issues, you did it WRONG. Unless you think that an 800-850 idle RPM is not streetable, IDK what to tell you.

A junk cam is a junk cam. You can't manipulate LSA to fix opening and closing event errors.

FWIW, you can look at the heads and intake someone is using and pretty much be within a degree or two of what the LSA should be, just from experience. I know, for a FACT, if you tell me you spent a bunch of time increasing low lift flow, I know, for a FACT, you will have to open the LSA up. Because old wives tales never die, people spend incredible energy trying to increase flow where you don't want to increase it, at the expense of getting flow higher in the lift curve. I'd gladly give up 20% of my flow at .100-200 lift to gain 5% at .400-500 and with the correct cam, that head I'll make more power above peak HP, more torque below peak and require less at .050 timing than one that has better low lift numbers.

So to the OP, learning about cams is more than what rudimentary stuff you are reading. Learning cam timing encompasses everything about the cam, plus air flow, as in how much flow, port volume, shape of the curve, pressure recovery of the port and chamber and much more.

Overlap triangle is your friend. Learn to understand it, and how it interplays with what is happening when both valves are off the seat.

So, do you have a cam in mind (or at least what you'd be look'n for in a cam) for the Op's application? A certain area of LSA? Lift? Duration?

 

[yellow rose]

So, do you have a cam in mind (or at least what you'd be look'n for in a cam) for the Op's application? A certain area of LSA? Lift? Duration?

What the OP posted is too big. If he is running all stock parts, it's pretty hard to beat a stock cam.

If it was MINE, and I was running all stock parts, I'd be in the 220 @ .050 range, try and squeeze .500 lift out of if I could. And no wonder than a 108 LSA.

If the OP is willing to do a bit of work, with a converter and some gear, and maybe some adjustable rockers you could do a bunch more.

The OP should call a reputable cam grinder like Jim Doyle at Racer Brown or Cam Motion and get something from them.

Or Jones.
Or Bullet.
Or Controlled Induction.

 

[AJ/FormS]

I love this stuff. I'm still learning too, so I wanna join the fun;I'd like to revisit post#31, with the two 240* cams.
I love to play the numbers, and no I have no real,real-world experience.
So let me assume that these 240 cams were 284/284/108, and 284/284/112, advertised. But to make it easy, let's install them both at a 108 centers. This puts the ICA at 70*, for both, and both have 110* of compression, so the Dcr is the same for both.
But check out what happens on the other side;the 104cam ends up with 118* of power extraction, to the 102* of the 112cam. So I get that. and I get that most of the energy of the expanding gasses has been transferred by the 102*of the 112cam. So then the the 104 cam is doing not much for the next 16*, finally opening at 118*ATDC. I imagine there is quite a bit of energy left at 102After, with comparatively less at 118After. When this energy finds it's way to the tailpipe, you can really feel it, and hear it.
But hang on a second,by itself that don't mean much, but there's more.Since both these cams have 284* of exhaust duration, these timing event are translated to the closing moments too! With the 104* cam closing it's exhaust, 16* later than the 112cam. Well this puts the event well past TDC, well past the time that the intake begins to open,and Whoops! maybe the exhaust backs up right past the opening intake valve and up into the intake manifold.Well that would mess up the idle now wouldn't it. OK so which one is worse?Well that's a tough call. On the one hand we have the 112 cam that opened the exhaust valve early, dumped a load of energy out the tailpipe, and also closed early to send less exhaust into the intake. While on the otherhand , the 104* cam opened 16* later, and maybe couldn't get rid of all it's exhaust energy before the intake opened, so Whoops! into the intake manifold it goes.
But hang on, with headers it doesn't usually work like that.Manifolds yes, headers no. So what is going on at idle?
First,let's not overlook the seldom-discussed overlap period, which some call a cycle. And it really can be/is.
During this period, which is a lot,(in terms of time-at-idle,with a big cam like a 284),both the valves are open, and the piston is finishing the upstroke and beginning the down stroke; so it ain't moving a great distance. So what's going on?
Well this is where it all gets a little fuzzy for me. I understand that the 112* cam puts its exhaust closing event at 26* ATDC, and the 104cam closes 16* later at 42* ATDC.
And I understand inertial tuning in a primary pipe, and how the hot exiting exhaust gasses put a yank on the incoming charge at WOT.
But at idle, all this air motion under the carb is hard to get a handle on.
But since both of these cams,have identically timed events (because of the identically installed CLs) on the intake and compression "strokes",and we know they sure don't idle the same, the idle quality has to be related to the late closing exhaust.So if that's true, back up the bus aminute!
If most of the energy in the exhaust has been transferred to the crank by 102* ATDC, AND the idle is so much poorer with the late closing exhaust, why even bother with a 104*cam? The 112cam opens early, closes early; we're done right?
Well not quite, we gave up 16* of overlap didn't we; sux to be in my head right now.....
All right then how about attacking this from another angle. Suppose we had a 284 cam, in at 108. How could we change the exhaust side to do both; open early and retain the 76* of overlap. Well you can't. Something has got to move.Enter the split-pattern cam.Well you can too, but that would be a really goofy cam.
Yeah so I mixed myself up pretty good just now; I'm gonna go lie down for a bit.....
Truth is I don't care how my 276/286/110 idles, or why it idles like it does.It was easy to tune and goes like snot, at least fast/quick enough for me. And I like it a whole heap more than the 292/508/108 that I started with,back in 99.
I must say tho, that 292* had a power peak you could really feel acoming! It was like a 2-stroke dirt bike; whaaaM!
Comparatively, the 276* is a tractor.

 

[RustyRatRod]

The OP has only responded once since his initial question. Why don't yall put your dicks away and actually discuss his question and address his post, rather than the length of your dicks?

Is that too much to ask?

 

[yellow rose]

The OP has only responded once since his initial question. Why don't yall put your dicks away and actually discuss his question and address his post, rather than the length of your dicks?

Is that too much to ask?

Discussions evolve. It's called learning. The OP will do what he is going to do. We've moved on to the more esoteric, nebulous stuff.

It's also called BULLSHITTING. It's what I do best.

 

[RustyRatRod]

Discussions evolve. It's called learning. The OP will do what he is going to do. We've moved on to the more esoteric, nebulous stuff.

It's also called BULLSHITTING. It's what I do best.

I think we all have a Phd in that, but it doesn't help someone who asked a simple question.

 

[yellow rose]

RE: post 36.....


aj, don't forget the time element, and lay it on top of valve lift.

Well, that's not clear is it?

When I look at overlap, I not only look at time, the time the valves are off the seat, but how FAR the valves are off the seat. If you look at the oft referred to comp drawing where they show the wider LSA having the valves off the seat longer, the valves ain't open very far. So really, when looking at overlap, you have to consider how far the valves are open, since, as a GENERAL rule, when th valve is further off the seat, it flows more.

Consider this....you have spent a long time porting your heads. And you spent a bunch of time working the seats to get low lift flow maxed out. Yes, you gave up some in the higher lifts, but damn, they flow like a striped *** ape at low lift, especially at overlap lifts. Since the air don't know what direction it's going, you can bet that the ports flow as well backwards as good as they do forward (this is critical because once the piston is on its way down, and the cylinder is gaining volume, therefore the air/fuel column is going to follow the path of least resistance), what stops your air/fuel column from going out the exhaust port during overlap? There is already a low pressure area in the header. There is virtually zero air flow moving into the cylinder at overlap, and what is moving is going to have an issue with the big *** piston in the way. So most likely, you will have some of the charge going into the exhaust, and some into the intake tract. Almost zero will make it to the chamber AT OVERLAP.

As a side bar, when you have intake reversion, you have a column of air move through the carb and it picks up fuel. Now, a little reversion shows up and the same air that just went through the carb and picked up fuel when it did, that same air turns around and goes backwards out the carb. The booster is stupid, and don't know what way the air is going, and as such, it picks up fuel AGAIN. Then the reversion changes direction, the air goes back through the carb for the THIRD time and picks up fuel AGAIN. We now have 200% more fuel in the same air. This is EXACTLY what happens at low speeds and idle.

You've got all this air moving at low engine speeds, in wrong directions, picking up more fuel, adding to a rich condition already, and now we slap a cam with a big overlap number or use a tighter LSA. You have just made the issue all the worse. So you take the big overlap/tight LSA cam out, cut way back on overlap and widen up the LSA and the engine responds so we all bless the wide LSA, market the **** out of it and get rich.

There is a flip side to this oddessy. What if you rethought your porting ideas? What if you took the time to flow your heads backwards, on both valves and learned how to do things to stop flow going the wrong way. We may lose a bit of flow all over going in the regular test direction. But we stopped flow going backwards.

So not only do we port to stop reverse flow, we port to kill low lift flow. Not to stop it, but knock it down a bit. And we now gain some in the mids and maybe a bit at high lift. Now we are getting somewhere. You can see how port flow can dictate cam timing, and the opposite is true.

Now, we decide that we not only are going to port to reduce reverse flow, and port to reduce low lift flow where reversion is at it worst, what if we play with the valve job? What if we can increase the bowl size as a percentage of valve diameter, but not use a bigger valve, which generally a big valve helps low lift flow? So now, we have the valve job helping to stop reversion.


Think about how all this affects cam timing. If the head flows more overall, you can reduce @.050 timing yet turn the same RPM. This helps with bottom and mid range power with no drop off in HP. But what if we could run a bit more @.050 and because we have reduced reversion and reverse flow, we can add a bit more @.050 to the cam, but we don't have the effects of reversion.

But we want the RPM range to not go any higher, and more duration will make it RPM higher. Now, you can move the LSA a couple of degrees tighter. You get a big boost in the middle, which helps in the gear change, and th narrower LSA will keep the engine from RPM'ing higher than we want.

The point is, it's not all about the cam. It's about what you can do to make air do what you want and then how to take advantage of it.

I think some head guys spend way too much time worrying about low lift flow and it handicaps the engines ability to use a narrower that accepted LSA, and leaving power on the table.

 

[yellow rose]

I think we all have a Phd in that, but it doesn't help someone who asked a simple question.

What the hell was THE question??

I'll have to go look.

 

[Johnny Dart]

Is this cam good to use in a 72- 340 with factory style rockers, lifters and push rods ?
Also, will this make my engine have a real lumpy idle ?
Sorry for a stupid question, but I've never understood camshaft, lifts and nodurations.
What would factory specs be for a 1972- 340 engine?View attachment 1714985708

Suggested a cam. Didn't mean to confuse you.
Never mind.

 

[Johnny Dart]

.

 

[norton]

All that I know, is that I'm more lost now than when I first asked the question. Somehow the topic went in some other direction.

 

[yellow rose]

All that I know, is that I'm more lost now than when I first asked the question. Somehow the topic went in some other direction.

I'll get you back on the plantation.

I would NOT use that cam. I would never do it on stock rocker gear. You need at least 9:1 compression, at least a 3.55 gear, at least a 3k converter.

So like I said way back many posts ago, pick up your phone and at 5 PM or 6 PM eastern time, call Jim at Racer Brown and get something he suggests.

Or build your engine to fit that cam. An idea that I don't care for.


Welcome back.

 

[T-N-T]

Make sure you mention what altitude you are at too. I would use 9.5 to 10:1 static compression ratio personally.

 

[AJ/FormS]

YR
I think I understand pretty much all that you posted, And some of those ideas I actually referenced during my build. But since I am, and will always be,a streeter,I was never really interested in top end power, well not after the 292/508/108 error. But I figured out pretty quick, what I didn't need,and what I did need. And so my combo evolved quite a bit over the first 5 or so summers.
Whenever you increase the intake event you always have to steal duration from somewhere else. At first the manufacturer steals it from the compression cycle and as the cam gets bigger and bigger, the intake opening point eventually moves into the exhaust cycle. Since the piston is kinda dwelling there, it's not initially a big deal, and it gives the cam some time to get the valve going, while not much is happening. But as the cam gets still bigger, this hang time starts to be a problem at idle. And eventually off idle and in the street-extreme The tuner has his hands full.
The biggest cam I have tuned was that 292,in a 360, and I didn't think it was that big a deal.I just found that cam had traded away too much low-rpm grunt, for a serious top-end-charge that I never used. The power rush didn't begin until well over 50 mph, and in the meantime I was slipping the clutch out like farm truck hauling potatoes off a soft field,lol. Yeah, no; that cam wanted more gear, like 4.30s or better,and that took it out of the realm of being street-friendly.
Back on topic,tho; It ends up that the overlap period becomes a kindof dumping area, cuz to not do so, you end up stealing so much from the compression and power cycles. Take a Mopar 312/312/106 for instance. This bad-boy has 100* of overlap.If you install it at 106* then you end up with an ICA of 82*,leaving just 98* for compression. This guy will need some serious Scr to even just to get moving. I mean that piston is about an inch and a quarter up the cylinder before compression even starts! But worse is the other end, where the intake opens 50* BTDC! That's an awful lot of degrees, and a long time and the valve is probably near 20/25% open, when the exhaust valve finally closes at 50* ATDC.That's a .588 lift cam, with a .028 cold lash, so that's alotta lift already.
Yeah I see that as tough tune alrightee. It ain't gonna pull itself around the parking lot at 500 rpm, no how,lol.

But I think us streeters should care very little about overlap making us go fast. Our cams typically have only 50 to 75 degrees, and that cycle doesn't start to be helpful until you get near peak torque, and only with a sealed header and a free-flowing exhaust; so that's a lot of ifs already.And peak torque is gonna be up around 4000 to maybe 4500, so with 3.55s that would be about 36mph in first gear with a stick-car.With minimum tirespin, it's a bit of a pull, before it's helpful.Maybe.If your headers are new and tight.And your exhaust system doesn't plug the collector.
No, us SBM streeters should think about the heads;just as you say. Make the heads do the work, and let the cam put the work at a decent pulling rpm. So you can hammer down in second gear and blast off.
Or just install a stock 440,lol.They do that all the time with 3.23s yet. Hah! you wanna have fun, take a ride in an old BB NewYorker. Hey that reminds me of a story.
Back in highschool this one kid's dad had one of those more-door tanks . You know the 16 passenger model 14 girls 2 guys,lol.And he was always bragging on it, and egging me on. See I was the go-to guy, The one with the "fast" Swinger that pounded nearly all comers. That car wasn't actually 1/4 mile fast, posting just 98mph at 14.4 seconds. But on the pavement from 20 or 30mph hang on!Anyway back to the story. So one day he gets up in my face about his Daddy's 440 tank, and I finally stoop to racing a family car. We line up and the flag falls , and AJ is.... G-O-N-E! And after I get out a bit I see him in my mirror and I'm killing myself laughing. I pull second and hey, he doesn't seem as far behind as before.So I pull third and oh man this guy is moving up on me! And I ain't laughing anymore.Well We get up to 85 and I see the finish-line, and he's nearly on my bumper, and I'm starting to sweat! This guy is really moving. Here comes the line and it's .......AJ for the win! But it weren't no thing to brag about cuz another second or so and it coulda gone the otherway.
Well I learned something that day; stay away from big-blocks-barges, I might get my azz handed to me!
I don't know what this has to do with anything but it's a cool memory.At 63 I gotta hang on to memories when they come, cuz there's a lotta living gone by,between me and hi-school

 

[yellow rose]

YR
I think I understand pretty much all that you posted, And some of those ideas I actually referenced during my build. But since I am, and will always be,a streeter,I was never really interested in top end power, well not after the 292/508/108 error. But I figured out pretty quick, what I didn't need,and what I did need. And so my combo evolved quite a bit over the first 5 or so summers.
Since whenever you increase the intake event you always have to steal duration from somewhere else. At first the manufacturer steals it from the compression cycle and as
the cam gets bigger and bigger, the intake opening point eventually moves into the exhaust cycle. Since the piston is kinda dwelling there, it's not initially a big deal, and it gives the cam some time to get the valve going, while not much is happening. But as the cam gets still bigger, this hang time starts to be a problem at idle. And eventually off idle and in the street-extreme The tuner has his hands full.
The biggest cam I have tuned was that 292,in a 360, and I didn't think it was a big deal.I just found that cam had traded away too much grunt, for a serious top-end charge; that I never used. The power rush didn't begin until well over 50 mph, and in the meantime I was slipping the clutch out like farm truck hauling potatoes off a soft field,lol. Yeah, no; that cam wanted more gear, and that took it out of the realm of being street-friendly . She liked 4.30s or better.
Back on topic,tho; It ends up that the overlap period becomes a kindof dumping area, cuz to not do so you end up stealing so much from the compression and power cycles. Take a Mopar 312/312/106 for instance. This bad-boy has 100* of overlap.If you install it at 106* then you end up with an ICA of 82*,leaving just 98* for compression. This guy will need some serious Scr to even just to get moving. I mean that piston is about an inch and a quarter up the cylinder before compression even starts! But worse is the other end, where the intake opens 50* BTDC! That's an awful lot of degrees, and a long time and the valve is probably near 25% open, when the exhaust valve finally closes at 50* ATDC.That's a .588 lift lobe, with a .028 cold lash, so that's alotta lift already.
Yeah I see that as tough tune alrightee. It ain't gonna pull itself around the parking lot at 500 rpm, no how,lol.

But I think us streeters should care very little about overlap making us go fast. our cam typically have only 50 to 75 degrees, and that cycle doesn't start to be helpful until you get near peak torque, and only with a sealed header and a free-flowing exhaust; so that's a lot of ifs already.And peak torque is gonna be up around 4000 to maybe 4500, so with 3.55s that would be about 36mph in first gear with a stick-car.So with minimum tirespin, it's a bit of a pull, before it's helpful.Maybe.If your headers are new and tight.And your exhaust system doesn't plug the collector.
No, us SBM streeters should think about the heads.Just as you say. Make the heads do the work, and let the cam put the work at a decent pulling rpm. So you can hammer down in second gear and blast off. Or just install a stock 440,lol.They do that all the time with 3.23s yet. Hah! you wanna have fun, take a ride in an old BB NewYorker. Hey that reminds me of something. Back in highschool this one kid's dad had one of those more-door tanks . You know the 16 passenger model 14 girls 2 guys,lol.And he was always bragging on it, and egging me on. See I was the go-to guy, The one with the "fast" Swinger that pounded nearly all comers. That car wasn't actually 1/4 mile fast, posting just 98mph at 14.4 seconds. But on the pavement from 20 or 30mph hang on!Anyway back to the story. So one day he gets up in my face about the 440 tank, and I finally stoop to racing a family car. We line up and the flag falls , and AJ is G-O-N-E! And after I get out a bit I see him in my mirror and I'm killing myself laughing. I pull second and hey, he doesn't seem as far behind anymore.So I pull third and oh man this guy is moving up on me!And I ain't laughing anymore.Well We get up to 85 and I see the finish-line, and he's nearly on my bumper, and I'm starting to sweat! Here comes the line and it's .......AJ for the win! But it weren't no thing to brag about cuz another second or so and it coulda gone the otherway.
Well I learned something that day; stay away from big-blocks-barges, I might get my azz handed to me!
I don't know what this has to do with anything but it's a cool memory.

You are so close you can taste it. You are exactly correct on overlap, and why it causes issues.

My point it you can help with overlap by doing the things I suggest. Ultimately, guys tend to end up with way too much low lift flow, and a duration number that is too big for the low lift flow and you get severe reversion. If you taylor your low lift flow to reduce flow at overlap, you can make a much bigger cam behave, without moving the LSA so wide you have to remove intake timing(or add exhaust timing depending on who you ask) to keep the RPM range where you want it.

That's why I try and run as much lift as the valve gear will take. If you can only fit .500 lift in there, you have to start looking at flow by .200 or so, maybe .225 at the latest. If you can get .600 lift, you can start looking at 275-.300 lift and work on reducing forward and reverse flow below that.
I have done heads and intakes for net 1.000 lift. I didn't even start flowing until .400 lift once I got the valve job where I wanted it. Unless I was flowing the port backwards.

 

[frosty_the_punk]

Nope. Idle quality is MOSTLY a tune up issue, and seat timing. LSA gets bitched at, but really affects idle very little. It is very important though.

Oh brother.

That's just bad advice. If you can't give good information then don't give any.

OP, Please ignore everything in that post.

When you select a custom grind can you will select the lobes you want based on their duration, lift and ramp velocity. They are listed in the catalogue. Some are race only and assume a short lifespan of massive abuse. Some are like factory spec and will last a million miles. there's everything in between.

You will usually pick different lobes for the intake than the exhaust as they require different function. Exhausts are subject to more heat and abuse often have slower ramp speed. Exhaust air is pushed out and intake air is pulled.

Air is much more stretchy when it's being pulled than pushed. So a faster operating intake lobe is a good choice.


For the same reason Most engines are designed with exhausts ports which don't flow as much air as the intake. Or more accurately, they prefer to make the intake flow as good as possible, and the exhaust just has to be good enough!

To help compensate for this. In a performance application the exhaust lobe often has more duration than the intake. (Meaning it's bigger)

Figuring out where the lobes will go is the next part. This includes lobe separation angle.

For a street/strip camshaft, overlap is a big consideration. Too much Overlap can makes your engine idle rough and feel soggy at low rpm.

Lots of lobe Duration is great for high rpm but makes the engine inefficient at lower rpm. Particularly idle.

Overlap increases as a cam's duration increases.

Duration is often measured as crankshaft degrees in which the valve is lifted a minimum of .050" from it's seat.

This is expressed as "degrees at 50 thou" Before this point the valve isn't really functioning in any significant way.

A cam lobe with 190 degrees duration at .050" lift is very small. Like a factory camshaft.

A camshaft with 290 degrees at .050 is very very big. Like max effort " rebuild every dozen drag strip passes" type big. Think top fuel engines.

A narrow lobe separation is considered 103-107. It makes an engine operate with higher peak torque output. (Not necessarily peak horsepower) But It takes a bit from the low end of the torque curve and adds it to the peak torque. As a result idle quality can suffer. Also chance of detonation is higher. This limits compression ratio.

A wide lobe separation does the opposite. It takes from the peak of the torque curve and adds to the areas below the peak. Idle quality is superior and chance of detonation is reduced. Meaning a higher compression ratio can be used.

Typically wide separation is favored for electronic fuel injection engines with high compression. As well as forced induction applications.

 

[T-N-T]

Oh brother.

That's just bad advice. If you can't give good information then don't give any.

OP, Please ignore everything in that post.

When you select a custom grind can you will select the lobes you want based on their duration, lift and ramp velocity. They are listed in the catalogue. Some are race only and assume a short lifespan of massive abuse. Some are like factory spec and will last a million miles. there's everything in between.

You will usually pick different lobes for the intake than the exhaust as they require different function. Exhausts are subject to more heat and abuse often have slower ramp speed. Exhaust air is pushed out and intake air is pulled.

Air is much more stretchy when it's being pulled than pushed. So a faster operating intake lobe is a good choice.


For the same reason Most engines are designed with exhausts ports which don't flow as much air as the intake. Or more accurately, they prefer to make the intake flow as good as possible, and the exhaust just has to be good enough!

To help compensate for this. In a performance application the exhaust lobe often has more duration than the intake. (Meaning it's bigger)

Figuring out where the lobes will go is the next part. This includes lobe separation angle.

For a street/strip camshaft, overlap is a big consideration. Too much Overlap can makes your engine idle rough and feel soggy at low rpm.

Lots of lobe Duration is great for high rpm but makes the engine inefficient at lower rpm. Particularly idle.

Overlap increases as a cam's duration increases.

Duration is often measured as crankshaft degrees in which the valve is lifted a minimum of .050" from it's seat.

This is expressed as "degrees at 50 thou" Before this point the valve isn't really functioning in any significant way.

A cam lobe with 190 degrees duration at .050" lift is very small. Like a factory camshaft.

A camshaft with 290 degrees at .050 is very very big. Like max effort " rebuild every dozen drag strip passes" type big. Think top fuel engines.

A narrow lobe separation is considered 103-107. It makes an engine operate with higher peak torque output. (Not necessarily peak horsepower) But It takes a bit from the low end of the torque curve and adds it to the peak torque. As a result idle quality can suffer. Also chance of detonation is higher. This limits compression ratio.

A wide lobe separation does the opposite. It takes from the peak of the torque curve and adds to the areas below the peak. Idle quality is superior and chance of detonation is reduced. Meaning a higher compression ratio can be used.

Typically wide separation is favored for electronic fuel injection engines with high compression. As well as forced induction applications.

View attachment 1714987273

It's actually not bad advice, you need to read and understand the rest of the posts he made. Like everyone says it's all about the overall combination. Many combinations aren't correct for a real tight LSA but if you get the combination right they flat out work. Admittedly he is talking about higher horsepower engines then most of us build, that doesn't make him wrong either. Faster yes, wrong no. Think of it as an advanced camshaft class. You are talking algebra, he discussing advanced calculus.

His advice isn't for everyone, it's to advanced for everyone to understand. He did a great job of explaining in in the short posts he made. There is more to the combination need then he posted, my guess is he didn't feel like writing a book as a post.

And no I'm not arguing with what you posted, your post is just about a totally different overall combination. It actually applies to many builds, kinda like what the OP is asking about.