Camshaft lsa and low end torque

[racin69z]

Ive been reading everything i can about cam selection and timing for the last 3 weeks. I am trying to learn, it is pretty overwhelming. Ive seen a few dyno test articles where they change the lsa but ran the icl at +4 advanced. The narrow lsa always seems make more low end torque. It seems like the flaw in the testing is that the later intake closing of the wide lsa cam causes less low rpm cylinder pressure. Is this where the torque goes?

I have heard experienced folks say that you pick the valve events you want and the lsa winds up being what it is. How in the world does a person begin to pick those events. Ive always picked the duration and lift based upon the intended rpm range and the lsa/icl based upon the commonly thrown around rules of thumb.

So what if you had a wider lobe seperation cam than necessary and just advanced it so the intake valve would close sooner. Would that mess up the exhaust end too bad?


Lynn

[pdq67]

It is proven that a narrow cam has a higher mid-range power peak, but lower ends. Whereas the wider cam has a lower mid-range power peak, but higher ends.

You want your power upstairs, make it wider and if you want it quick for more mid-range, make it narrower as I see it.

Crude, but seems to work.

I am always fascinated by engine combinations that are put together in such a way that both the power and torque curves are still going up past 5252 rpm! Talk about high-end rpm making big Hp!

pdq67

[gregsdart]

An uneducated guess is that a narrow lsa cam is great for low speed (relative to total duration) torque provided you aren't concerned much about engine manners below your chosen best starting point for torque.

[swampbuggy]

Most short to half mile circle track cams are on a 106 lsa with mid flowing heads an operate between 4000 to 7500. Nascar stuff with optimal heads for a single 4 barrel carb appx 1060 cfm is according to camking at 110, nhra pro stock with ultimate heads a ton of air flow at 9000 to 10500 limit ..........limit neing 10500 are at 115 to 120 appx ????? So this shows us the heneral trend. Marh h.....now

[swampbuggy]

General trend. Sorry for the typo.

[rfoll]

The trick here is that low end torque is relative. Low end torque for NASCAR is quite different than what I need for my pickup towing the car trailer.

[swampbuggy]

Every camshaft should be specific to the application and certainly that's why it should always be done by a qualified person at a cam company to get it correct

[hoffman900]

Most short to half mile circle track cams are on a 106 lsa with mid flowing heads an operate between 4000 to 7500. Nascar stuff with optimal heads for a single 4 barrel carb appx 1060 cfm is according to camking at 110, nhra pro stock with ultimate heads a ton of air flow at 9000 to 10500 limit ..........limit neing 10500 are at 115 to 120 appx ????? So this shows us the heneral trend. Marh h.....now

Then you go to a 4 valve head like an Indy car application and you're talking really narrow LSA (if you were to bother calculate it).

Here's a few 2+hp per inch engines to look at.
410" outlaw sprinter with big -12 heads: cam LSA 106 to 108
420" Dirt Latemodel with SB2 heads: cam LSA 106 to 108
377" Dirt Latemodel with SB2 heads: cam LSA 104-106

Here's a 3+hp per inch engine to look at.
2003 IRL Indycar engine: cam LSA 103

You are making a darn good case for the value of using narrow LSA's in really bad boy stuff, which supports the general idea that narrow is apparently the preferred way to go in high performance applications. Yet earlier you were basically saying Vizard was off his nut, and that you had come to different conclusions than him regarding the value of using narrow LSA's. But this agrees with Vizard's general preference for narrow LSA's.

You are also now agreeing with the SBC LSA comparison test done by that magazine awhile back, which showed the same thing, only on less potent engine. But I seem to recall that you were one of the biggest critics of that article.?

I don't know how you could get that from my post.
You're reading something that isn't there.

BTW, here are two more examples.
Nascar Nextel cup engine: cam LSA 110
NHRA Pro-Stock engine: cam LSA 117.5

How you could actually see some kind of pattern is beyond me.
Both articles are meaningless, and do nothing but confuse those readers that are struggling to understand how an engine works.

My opinion is that you should buy whatever Dave Vizard recommends, because you probably deserve it.......
Tell your cam man what LSA you want, and he will grind it for you.
This way, your car will run its' fastest.
However, I recommend everywhere from 107 to 118, just depending.

UDHarold

A certain 500 CID Hemi Pro-Stocker runs 310 int, 336 exh at .020, with LSAs in the 117-118 range.
For less overlap............
About 87* worth, more or less......

UDHarold

A certain 500 CID Hemi Pro-Stocker runs 310 int, 336 exh at .020, with LSAs in the 117-118 range.
For less overlap............
About 87* worth, more or less......

UDHarold

yep,
one of my Pro Stock guys is doing pretty well with a 277/300 @ .050" on a 117.5 LSA.
I can't imagine how fast he'd be if I went with a 106.

... NO exact LSA will always be best even on same size and brand motor due to different needs or usage.

Actually, size, brand, needs have very little to do with LSA.
LSA really doesn't do much. Its terms used for manufacturing or checking a camshaft. The valve events, themselves, are what defines the real relationship; the openings and closings and ramp rates.

To me, LSA is not a design criteria, its a calculation from the timing events, and a manufacturing criteria. But I dont want to start that discussion, for fear of missing out on all the conversations, if I cant check the site.

So, I will just simply talk in terms of the relationship of the intake and exhaust lobe (LSA). LSA is the relationship of the intake lobe to the exhaust lobe, and that is not a design criteria, brand criteria, or usage criteria. It is based on the inlet and outlet parameters and their relationship to the displaced cyl volume within the intended rpm criteria.

In general, a restrictive motor (defined as a limited flow capability in comparison to the displaced cylinder volume and very high port velocities) do not require early exhaust valve activity. Therefor LSA will trend narrower. The real answer will be driven by E/I system relationships.

An unrestricted motor (defined as a LESS restrictive flow capability in compariosn to the cylinder volume and decreased port velocities) will trend towards earlier exhaust valve activity. Therefore the LSA will trend wider. Once again, the actual answer is a function of the inlet and exh systems and the cylinder geometry.

A motor that unrestricted in lower rpms, can become restricted at higher rpms.

ITs all relative, narrow for one combination, may be wide for another.

but the design of the test was actually perfect for what they wanted to test.

The test was perfect for selling Comp cams to people that believe every thing they read. That's all it was good for.

If you're going to test the engine with a 2-plane manifold that'll restrict the peak power to 6,200, run a hydraulic roller that's designed for 6,200.

With that manifold, you should run a cam around 238/242@.050" for a 6,200 power peak.
If they ran that test with that cam, it would make more overall power on a wider LSA. It would also be a lot more driveable then the cam they ran, and wouldn't need as much stall.

When you run an oversized cam, it'll normally like the tighter LSA.
Except for selling cams, the test was useless.

540Rat,

That shows how old I am.......

I NEVER figure overlap when I am designing cams. I only calculate it when a customer requests it, or asks for a cam card.
How COULD I have gone for 34 years without realizing the real importance of overlap?
How much better would my cams have been if I had realized this importance?
I alwas thought it was the design of the cam lobe, and where it was placed that mattered, not the overlap.
BTW, since I do only unsymetrical cams, I am faced with this dilemma:
300* symetrical cam on 108 LSA---42-78-78-42, for 84* overlap
300* unsymetrical cam on 108 LSA---39-81-75-45, for 84* overlap

Do you think the engine sees these as the same thing, as they both have 84* overlap.
No, the ICL/ECL are the same numbers, 108. the difference is called off-set, and different families of unsymetrical cams sometimes have different off-sets.
Why didn't Comp discover this before they made so many Xtreme Energy cams on 110 LSA, for about 15 years? At least, when doing the VooDoo series, we tested with different LSAs, sometimes counter to what Sales wanted.
What we found out was what I already knew: big cams do not like low CRs and tight LSAs. We tested on 108, 110, and 112 LSAs in a 9.3 CR 355. You will notice that the small cams ended up on 112 LSA, for idle vacuum, and low-speed drivability, bigger cams on 110, preferably with over 10:1 CR.
Super Stock roller cams in the old days, when they used unported cylinder heads, used 104 to 106 LSAs, and even 102s on occassion. four-speed cars were generally around 108.
Pro-Stock cams now are running around 116 to 118 LSA,and bigger CID NO2 engines are pushing 120, or more.

We must be very careful about taking one magazine article and deciding it is the sum of all knowledge.........

UDHarold

It was looking like a person running tight LSA's were just victims of magazine propaganda.

That's not what I was trying to say.

I'm just saying the test is a joke when they make statements like this:
" We've got a very clear demonstration of the advantages-namely a more usable powerband-of running a narrow LSA."

That's a rediculous blanket statement to make from this test.
There are many cases where that is flat-out false.

On this engine, with these parts, with these cam profiles, with this compression, and with this fuel, it liked a tighter LSA.
That's the only conclusion that can be drawn from this test(advertisement).

Comp Cams' top guru Billy Godbold provided the cams for this test. And the guy is no idiot, he is one of the top cam guys in the nation. And he knows more than most of the rest of us will ever know about cams. He knew full well what he was doing with this cam comparison.

You're 100% correct
Billy's not stupid.
He knew before the test started that if he used a cam with more duration then the manifold and hydraulic lifters wanted, the tighter LSA version would make the most power.
He knew how to make those 107 LSA thumper cams look good, and designed the test to make them look good.

Like I said before,
if the test was run with cams with 10 degrees less duration, it would have liked a wider LSA, but that wouldn't help sell thumper cams.

Back in my old UltraDyne days, my most popular roller cam was the SB288/296R. It was 288/296 at .020, 255/263 at .050, 176/183 at .200, and .626"/.626" gross valve lift with 1.5s.
With 83 degrees of overlap, it dominated the NDRA for 2 years, driven by Jeff Purvis. IVO 43 BTDC IVC 65 ABDC EVO 76 BBDC EVC 40 ATDC
With 80 degrees of overlap, it won a LOT of races for 20 years.
IVO 41 BTDC IVC 67 ABDC EVO 77 BBDC EVC 39 ATDC
With 76 degrees of overlap, it won 2 of the 3 UltraDyne national wins in the Winston Amatuer National Championship. IVO 41 BTDC IVC 67 ABDC EVO 81 BBDC EVC 35 ATDC
These overlap numbers mean that this cam is either a Street/Strip cam, a Race cam, or a Pro Competition cam, although it is always the same cam, on different LSAs.
Of course, the overlaps are different. Did I decide on the overlap first, then firgure out what the LSA should be, or did I decide on the LSA, then calculate the overlap for the customer?
If you really get into the study of overlap, then you will realize that the area under the overlap curves is more important than the overlap number itself. Obviously, rollers have more Area under the curve than flat tappets, who have more area under the curve than hydraulics, even though the overlap is the same in all the cases.
The area under the curve on the intake opening portion of the overlap has the most overall influence on cylinder filling.
The area under the curve on the exhaust closing portion of the overlap influences the engine mostly at very low engine speed, and it is mainly a function of how many milliseconds after TDC the exhaust valve is open, to allow reversion into the cylinder.

30-60-60-30 270/270 105 LSA 60 overlap
30-70-70-30 280/280 110 LSA 60 overlap
30-80-80-30 290/290 115 LSA 60 overlap

Normally, one would expect these 3 different cams to produce different results, but they all have identical overlap, so??????

UDHarold

540 Rat,

I hope Billy NEVER changes his views on cam design. If he believes overlap to be the main thought, good, let him think so forever.
Because YOU do not understand a lot about overlap, though, I thought I might give you some thoughts. You can reject them, you can say I don't know what I'm doing, but my thoughts have been making cams that have been winning since 1974.
Overlap should never be figured for .050" lobe lift/duration.
Why?
Because the valve opens AT THE SEAT DURATION, not at .050".
When I was Comp Cams cam designer, I wrote a full-page ad for National Dragster that asked the question, What is the most important degree in your camshaft?
It is the degree BEFORE the intake valve opens!!!
If we could determine the amount of exhaust gas left in the cylinder, and its' pressure, we could predict how the intake lobe would fill the cylinder.
Playing a little 'numbers' game, if you have 2 cams, with the identical durations/lifts, either single or dual-pattern, but on 2 different LSAs, and both identical intake lobes are installed on the identical intake CL, guess what?
The cams have different power curves. They have the identical opening and closing points on the intake. Only the exhausts are different timing points.
Yet the cylinder is filled differently by the same intakes on the same ICL.
It is because of this difference of exhaust volume and pressure that exists before the intake valve starts coming off the seat.
The further before TDC that the intake valve opens, the higher this exhaust volume/pressure is, and the more reversion enters the intake port.
Air does not begin entering the cylinder until the piston has quit PUSHING the exhaust out the cylinder, the piston reaches TDC, and then begines the intake stroke. The more exhaust gas that has blocked the initake, the later clean air flow starts in the intake tract.
Using this theory, I beat Billy by 10 BHP at peak in the Dodge Hemi Truck engines, on my FIRST SHOT. The cam designs I sent in as a resume.
The engine builder sent me a check for $1000, he liked them so much.
My 10,500+ ProStock cam has 88 degrees of overlap at .020". It opens at 41 BTDC(Intake), closes at 47 ATDC(Exhaust). This is seat duration, not .050" duration.
It runs in the mid-6.60s, and has been nr 1 P/S qualifer a lot this past fall.
It was my first shot a a ProStock cam in over 20 years, and not a bad first try.
I think I'll stick around and keep doing cam designs the way I do.
Again, I hope Billy keeps doing cam designs the way he does.

UDHarold

Randy331,

Sorry about taking so long to answer your questions, but they were kinda hard, and you desirve a good answer.
I consider EVO and IVO to be the 2 most important timing events in the cam cycle.
As far as what I use to determine IVO, ready for another fight to start?
I use the unsymmetric opening side opening at .020", and the ICL. I found the ICL by what LSA I am using to accomplish what the engine builder wants the engine to do power and torque-wise.
I find the IVO AFTER I determine what intake lobe I am using, and what LSA/ICL. I do not design the other direction---decide what IVO I want, and design a com from that.
The way an intake port flows backwards certainly influences the effect of reversion, and reversion affects the starting point for clean airflow, AFTER TOP DEAD CENTER. BTDC the piston is pushing exhaust out of the cylinder, not sucking clean air in.
The less reversion, the sooner clean airflow starts, the higher the intake port velocity, and the better the intake port fills the cylinder.

This is enough.......I am getting too sleepy to continue......

UDHarold

I would have liked to get in on this one a while back. I did not read thru all the pages of this post. In the ones that I did read, it seems there is a lot of this cam versus that cam, but without any real look at what the valve event requirements for the motor should be. Then which of the cam configurations matches those requirements t the closest.

Running a cam or component swap test and make global generalizations is pointless. the only validity is in engine combinations that are nearly identical. to apply this to another motor that has a differing inlet,outlet, and cylinder volume relationships is pointless. Valve events are relative to the specific combination at hand. To say this LSA works and another doesn't, without considering the engine specifics may or may not yield the desired response. It could be completely backwards. Whats narrow for one motor could be too wide for another.

If they are holding the intake CL constant for all the cams, then it should not be much of stretch to find where the optimum placement for that exhaust lobe should be and if it matches the results, or atleast follows the trends correctly.

Hopefully, I can snag the mag on my way home from work.

So how do we define low end?

For a street car, low end is 900rpm-3500rpm or so. This is below where most dyno tests start - certainly in the magazine world.

For a 12,000rpm 450cc motox bike, low end is 6000rpm.

Tighter LSA's will have more overlap. Tighter LSAs will certainly hurt power on an application that runs from 900rpm-3500rpm the majority of the time.

As said above, LSA is just a machining term.

[CamKing]

Just got off the dyno with my 355ci SBC for my boat.
It's 10:1 with ported 492 heads, Performer RPM, and Holley 600.

RPM---TQ--BHP
3200--436--266
3400--443--287
3600--445--305
3800--444--321
4000--443--337
4200--440--352
4400--440--368
4600--441--386
4800--441--403
5000--432--411
5200--422--418
5400--412--423
5600--400--426

The cam is 216/220, on a 112 LSA, and 108 ICL

LSA, by itself, is meaningless

[swampbuggy]

Hey Mike would you disclose the opening and closing numbers

[rustbucket79]

Nice numbers Mike, shows what can be done with a tiny camshaft. Are you planning to utilize the numbers above 4500 RPM or is it just a by product of a well designed marine engine? What would happen if the duration numbers were 5 to 10 degrees less?

[MadBill]

Yeah, and whose cam is it?

[swampbuggy]

???????bill??

[MadBill]

Well (Settling my Captain Clueless cap more firmly on my head..), don't we always ask that?

[racin69z]

CamKing that is nice torque for a 355.

The specs of the cam in your 355 are similar to one i have setting on my shelf. I have a 218 224 on a 113 lsa. I was thinking of using it in my 360ci sbc. I also have a 202 206 on a 115.

It seems like combos that require torque at 1200 rpm are a little tougher to nail down than something with a 4500 converter. Ive used cams with anywhere from 240 to 270 @.050 duration all on a 106 in my camaro without a huge change in ET. I know i could stab a stock cam in and have decent torque at 1200, but finding that cam that will be ok at 1200 and then really pick up at 3000 is hard.

Lynn