The 128 drama!

[David Vizard]

When I posted the 128 formula for establishing the LCA of 23 degree headed SBC with a 10.5/1 CR it created a big stir to say the least. The most vocal where those with negative criticisms. I let things lay awhile to calm down and that appears to have happened. With that I think I can now address some of the criticisms aimed at the 128 formula without bringing about a storm of contradictions.
What I want to address here is the often-quoted opinion that ‘the LCA is an output not an input’ so here goes.

What I have done here is piece the logic of several engine builders cam selection technique together that makes the claim that the LCA is an output.
One method goes something like this:-
First a decision is made as to when the intake valve should close. Next the exhaust opening point is chosen. Then the intake and exhaust are assigned a duration.
Let us say that that in this instance the engine builder decides on an intake closure of 76 degrees after BDC and an exhaust opening 87 degrees before BDC. Said engine builder then assigns duration figures of 300 for the intake and 306 for the exhaust. This works out to an event timing of 40-80-83-43.
To make life simpler let’s assume the cam is going to be timed in ‘straight up’. This produces an intake and exhaust centerline of 110 degrees. We get the LCA by adding the two centerlines together and then dividing by 2 so clearly this would be (110+110)/2 which equals 110. In this instance the LCA is an output but if any of the inputs were incorrect, and let’s face it at this point they were all guessed, the output ie. the LCA will be wrong. Which means the cam will be wrong! In computer parlance, this is very much a question of ‘garbage in =’s garbage out’!
There are other ways of generating the LCA as an output but because the figures used to generate this output are generally no better than an experience based guess the resulting LCA is equally no better than a guess.

Now let us assume we have a formula which can accurately establish the engines LCA requirement.
Well this I have, and it is the result of thousands of cam and rocker ratio dyno tests. Over about a 4-year period I, along with my small team, did some 19,200 tests for 4 cam companies. If you add to this number the tests I did before and after that period it would, I am sure, easily qualify as a record for the Guinness Book of World Records. What this means in practice is that anyone with differing conclusion to mine are basing such on far less cam testing experience.

OK on to the next step.
Let us assume that the engine builder who starts with a selection of the intake closing and exhaust opening points, then selects the duration has do such. They are now at the point where they can calculate the intake and exhaust centerline. This means the equation for the LCA looks like this:-
(Intake Center Line + Exhaust Center Line)x0.5 = Lobe Centerline Angle or in shortened form (ICL+ECL)x0.5 = LCA.
At this point we will spec the cam my way. If we know with near certainty what the engine needs for a LCA the formula can be re-arranged so – LCA =(ICL+ECL)x0.5.

From this we can see that if an accurate determination of the LCA is made in the first place it can be a very valuable input. This is exactly what my cam program – ‘Torquemaster’ does. If an accurate LCA can be established then everything else more or less falls into place.
DV

[swampbuggy]

Thanks David for taking time to post this information, hope you are doing good physically, and Don L. as well.

[Ian Riordan]

Hi Don, Dave and others.
A friend and racer (Dave) from Cranbourne in Australia put me on to this forum and subject.
I told him that I, with friends had attended a seminar where David Vizard spoke in Melbourne in the early 90s. If I recall correctly it was the Anchor and Hope (Lou Molina's) Hotel in Richmond, more on Lou later.
BTW, the bushfires here in OZ are quite bad, Fires 25 miles south of here and visibility down to 150 yards yesterday. At least no-one I know has perished.

Here is what I sent to Dave tonight.

Thanks, cooking dinner a bit late tonight.
Essentially, I think he's trying to work on a streetable overlap for a daily driver and the 23 degree 10.5:1 package are a giveaway to that. He wrote about this in the late 80s.
As a rough guide your best streetable maximum overlap is no more than 60 degrees. I concur with this, I once replaced a #151 350hp 327 cam with a custom cam that was a Sig Erson 1H but ground on a 105 LCA. It had 72 degrees overlap versus around 60 for the #151.
At full throttle it came on 500rpm lower than the Duntov, even though it had 14 more @.050 on the intake alone. Full throttle launch (no 2 foot braking) it would smoke the tyres in my HQ ute with a 350/2000 converter/T400/2.75 gear and FR70/14s. With the #151 you needed a left foot or a puddle to boil 'em.
In this form, the 3500lb HQ ute felt like a strong low 13 ride with a freeway gear, at least to 6600 in first and second.
But at anything less than 3/4 throttle it was a bad mannered pig. Worse, as a car used in city traffic it'd draw cops like flies to horse shit. After a couple of weeks of that behaviour, I settled on that tiny Cam Dynamics cam with 204 and 214 @.050. Less power and torque than the Sig cam, but more power and torque than the Duntov. As you know, that little cam just flat works in everything. It's LCA is 114. 107 intake and 117 exhaust, so I have always set it up 2 before in a 350 and 5 before in a 400 to suit the shorter rod/stroke ratio.
I never ran 0-30 or 0-60mph on them all, but I reckon the Cam Dynamics unit would eat them all in this range.
I think from memory it had about 56 degrees of overlap, I'll check when I unpack some of the stuff I've got packed in case of bushfires. Remember that for every degree you take from the LCA you add 2 degrees to the overlap. Bad on the street.
On the track however, a "tight" LCA will give you shyteloads of midrange if the package has sufficient compression, gearing and airflow. In the distant past, I used to get a lot of cams ground by Motor Improvements near the Greyhound Hotel (opposite St Kilda town hall), when Rocky was the counter salesman. I can't recall who did the grinding, but I got a lot of SBC cams ground on a 105-108 LCA.
The comment was always the same "That would be a hell of a dirt track/ski race cam". Nitrous was getting big then in Melbourne in the early 80s, so I suppose the 112 -114 cams were more popular.
Now, if I was doing an N/A 434 I'd go 104-105, and for Blown/Nitrous/Turbo it would be a 348 or 377 with a 4.125 bore and a 116 LCA

[mag2555]

Thanks David and I hope your doing better each day!

[Orr89rocz]

Let us say that that in this instance the engine builder decides on an intake closure of 76 degrees after BDC and an exhaust opening 87 degrees before BDC. Said engine builder then assigns duration figures of 300 for the intake and 306 for the exhaust. This works out to an event timing of 40-80-83-43.

I’m confused?? If they want a 76 deg closing why is it 80? If they want a 87 deg opening why is it 83? Where did those numbers come from?

Wouldnt 300 deg duration just be 300 - (76 + 180) or intake opening of 44 deg ?? Exhaust closing would be 39.

When you have those numbers the only way to arrive at those events is if the icl is 106 and the exhaust centerline is 114. That makes a 110 lsa or lca. That is what it is based on the 4 events chosen. What am i missing?

Now however one decides IVC or EVO or any of the 4 events for a given application, thats the magic and seems to vary among cam people. Some of it is experience some of it is calculation.

[BLSTIC]

I remember reading about that on here somewhere. It seemed to make sense to me that adding duration without changing LCA gave more overlap, later IVC and earlier EVO, all suited to high rpm. What surprised me is that it on an engine with given low-lift flow the ideal points would give the same LCA, as in my limited experience and knowledge can't come up with a reason for the almost perfect correlation. It also can't come up with a reason it shouldn't be true, so I can't in any capacity argue against it.

I'm curious, have you got other "128" numbers to suit, say, 4v engines, or perhaps a more universal one that goes off actual flow data to compensate for any particular design?

Ian - this HQ with the part throttle problems seems like the ideal recipient of anti-reversion tricks. Did you try any?

[steve316]

that's a lot of dyno testing; about 23 tests a week for four shops for 4 years. All working on the 128 formula ? You know and I know this may work in some cases but not all. So are you saying this works in every engine in every application, or just some of them.

[David Vizard]

Let us say that that in this instance the engine builder decides on an intake closure of 76 degrees after BDC and an exhaust opening 87 degrees before BDC. Said engine builder then assigns duration figures of 300 for the intake and 306 for the exhaust. This works out to an event timing of 40-80-83-43.

I’m confused?? If they want a 76 deg closing why is it 80? If they want a 87 deg opening why is it 83? Where did those numbers come from?

Wouldnt 300 deg duration just be 300 - (76 + 180) or intake opening of 44 deg ?? Exhaust closing would be 39.

When you have those numbers the only way to arrive at those events is if the icl is 106 and the exhaust centerline is 114. That makes a 110 lsa or lca. That is what it is based on the 4 events chosen. What am i missing?

Now however one decides IVC or EVO or any of the 4 events for a given application, thats the magic and seems to vary among cam people. Some of it is experience some of it is calculation.

Sorry guys - I was working on this about 1 am and had initially chosen to show a cam with 4 degrees advance, Factor that in on the events shown and you will see how the 76 degree closure came about.
DV

[David Vizard]

that's a lot of dyno testing; about 23 tests a week for four shops for 4 years. All working on the 128 formula ? You know and I know this may work in some cases but not all. So are you saying this works in every engine in every application, or just some of them.

Steve316

I have said on many many occasions that this 128 deal is for a SBC with a 10.5/1 CR. I coverd this several time in previous posts. These posts gave the corrections for various changes in CR. Maybe someone can direct you to that/those posts.
DV

[David Vizard]

I remember reading about that on here somewhere. It seemed to make sense to me that adding duration without changing LCA gave more overlap, later IVC and earlier EVO, all suited to high rpm. What surprised me is that it on an engine with given low-lift flow the ideal points would give the same LCA, as in my limited experience and knowledge can't come up with a reason for the almost perfect correlation. It also can't come up with a reason it shouldn't be true, so I can't in any capacity argue against it.

I'm curious, have you got other "128" numbers to suit, say, 4v engines, or perhaps a more universal one that goes off actual flow data to compensate for any particular design?

Ian - this HQ with the part throttle problems seems like the ideal recipient of anti-reversion tricks. Did you try any?

Different engines require a different number to the 128 one. this is mostly due to how much cross flow occurs during the overlap for any given lift.For instance a BBC has a base number of 132 ish.

These numbers ie 128 and 132 etc are just something I threw out there for folks to calculate the LCA easy. The result of my extensive dyno tests is a universal program on which I have based my TorqueMaster program which is extremely comprehensive in as much as it not only calculates what cam is needed but it also matches this to heads, intakes, carbs, cranks, pistons etc,

DV

[ptuomov]

How do car factory designers choose camshaft timing for engines that don't have variable valve timing? I was under the imagined impression that the idle and/or emission considerations determine the overlap (given the displacement and the heads). Then, the redline rpm and head flow will determine the intake and exhaust duration. Whether the cam is advanced or retarded doesn't matter much because the factory heads usually flow so well for the rpm*displacement. Lobe separation angle ends up being whatever it ends up being, if that's the design procedure.

[hoffman900]

How do car factory designers choose camshaft timing for engines that don't have variable valve timing? I was under the imagined impression that the idle and/or emission considerations determine the overlap (given the displacement and the heads). Then, the redline rpm and head flow will determine the intake and exhaust duration. Whether the cam is advanced or retarded doesn't matter much because the factory heads usually flow so well for the rpm*displacement. Lobe separation angle ends up being whatever it ends up being, if that's the design procedure.

https://www.hondarandd.jp/

Search "cam timing", "camshaft", etc. It's way more involved than anyone here could hope for. They have to account for a lot more than anyone here could hope for as well.

Development of Valvetrain for Formula One Engine, 2009
http://www.f1-forecast.com/pdf/F1-Files ... P2_09e.pdf

Only mentions opening and closing.

Also attached from their converting the IRL engine into a restricted ALMS/IMSA/LeMans engine (circa 2007):

Untitled.jpg

[ptuomov]

How do car factory designers choose camshaft timing for engines that don't have variable valve timing? I was under the imagined impression that the idle and/or emission considerations determine the overlap (given the displacement and the heads). Then, the redline rpm and head flow will determine the intake and exhaust duration. Whether the cam is advanced or retarded doesn't matter much because the factory heads usually flow so well for the rpm*displacement. Lobe separation angle ends up being whatever it ends up being, if that's the design procedure.

https://www.hondarandd.jp/

Search "cam timing", "camshaft", etc. It's way more involved than anyone here could hope for. They have to account for a lot more than anyone here could hope for as well.

Yeah but is that a reasonable approximation of the process, namely that idle emissions dictate the maximum overlap regardless of the peak power rpm?

[hoffman900]

How do car factory designers choose camshaft timing for engines that don't have variable valve timing? I was under the imagined impression that the idle and/or emission considerations determine the overlap (given the displacement and the heads). Then, the redline rpm and head flow will determine the intake and exhaust duration. Whether the cam is advanced or retarded doesn't matter much because the factory heads usually flow so well for the rpm*displacement. Lobe separation angle ends up being whatever it ends up being, if that's the design procedure.

https://www.hondarandd.jp/

Search "cam timing", "camshaft", etc. It's way more involved than anyone here could hope for. They have to account for a lot more than anyone here could hope for as well.

Yeah but is that a reasonable approximation of the process, namely that idle emissions dictate the maximum overlap regardless of the peak power rpm?

I guess it depends on what other technologies they are controlling emissions, but you would think so to a certain extent. Check out the third page where through the use of high tumble ports, they increase overlap for increased EGR to heat up the catalyst as well.

For variable, check this out:

overlap.jpg

Figure 11 is interesting.


Another white paper:

overlap2.jpg

overlap3.jpg

Figure 13 is interesting as well.

[digger]

OEM considerations (emissions, economy etc) for their camshaft choice is probably not the purpose of this thread where the stated method is for WOT performance