JakeFusion

iTrader: (7)

So, I decided to write a little something on cam valve events as I've been thinking about it over the last couple of days.

As a general rule of thumb, very late IVC will contribute to terrible low end. So will opening the exhaust valve too early and allowing the charge to escape. And as will excessive overlap. You can't build cylinder pressure if all the intake charge is being pulled through the exhaust at idle or reverting burnt fuel back into the intake manifold.

For anybody looking to make torque... in a 5.3L keep the IVC around 36-38 degrees to build cylinder pressure and bring the overall peak HP down a few hundred RPM (same stroke as a 346, but you have to offset the missing displacement and bore). And the 346 would be around 40 or so. Then you set your EVO properly to carry power past peak or to enhance the torque peak. And that relies on the cylinder head exhaust efficiency, the exhaust valve size, the headers, and exhaust itself. As a good rule of thumb for most street engines is if the I/E ratio is 75% you need a single pattern cam at .050". If for every % below that you need about 1.5 degrees of split favoring the exhaust. For every % above that you need to add 1.5 Degrees to the intake.

The intake is fairly well set with the long-runner plastic manifolds. Their harmonics create a 4800 peak torque and 6300 peak HP number. So trying to push the valve events too far away from those ends up with dog turd performance. In either direction.

But let's take a balanced set of cam events for a 347. That peaks at 4800 with torque and 6300 with power. Carries it out nicely, but generates a lot of off-idle torque. What would that look like?

Well an IVC of around 45 in a 347 creates that 6300/4800 peak with an EVO of 55 carrying it out another 500 or so RPM while maximizing torque as an example of creating a profile that makes power everywhere. If you set your EVO at 53 or 51, it'll build more torque at the expense of carry past peak. And there's many ways to get there to create the total overlap wanted (which affect drivability and total performance). More overlap means more power at the expense of being able to drive the car but increasing the efficiency in the upper RPM range. But all of the profiles below would generate similar cylinder pressures with the same compression.

The overlap and the IVO/EVC tell us where those cylinder pressures occur: higher overlap and overlap that biases toward the intake makes power later (but may not move the peak - just carry better), whereas lower overlap that biases it toward the exhaust will make a little more torque down low (but retains similar peak torque and peak HP RPM areas, but would fall off up top faster). And if you center your overlap you'll make good power everywhere without enhancing or exaggerating either end of the powerband. But then the trick is to get the overlap right for the power and drivability desired.

So what about the 45 IVC and 55 EVO combo? Here are 5 cams that produce the same valve events. We now can play with IVO and EVC to get the duration/LSA needed to achieve a stated goal.

240/248 108+3 28 degrees of overlap biased toward the intake - monster cam that produces explosive topend
234/242 111+3 16 degrees of overlap biased toward the intake - top end screamer
230/242 112+3 12 degrees of overlap biased toward the exhaust - explosive midrange
226/234 115+3 0 degrees of overlap balanced - excellent street manners and good power everywhere
224/224 118+5 -12 degrees of overlap biased toward the exhaust - stealthy with a lot of torque

All would work best with 11.5:1 CR assuming using the same lobe (50 degree .005 to .050" ramp rate).

That's the best way for me to describe how you can affect torque and drivability using different cam profiles. And all would peak around the same 6300/4800 range in the same motor. But would drive differently and either carry the power out longer as with the two bigger cams or generate more explosive midrange or lowend grunt with the smaller cams. But again, that's with the same IVC/EVO. You can play with those to get huge swings in performance too.

So as the last example, a 42 IVC cam would need less compression. So it may not make more torque than the smaller cam above with more compression. So it comes down to what you want. Maybe you want a chop in the idle and don't want to run high compression? Or you have a 5.3L? Then move the IVC down to get the cylinder pressure building early. And go through the same exercise again to set overlap how you want it to achieve the outcome you'd like in terms of drivability and where the power comes on the hardest.

Darth_V8r

iTrader: (4)

Nice write up, Jake.

Observation - since you held the line at 45 IVC and 55 EVO, you're pretty much guaranteed an 8-12 degree split, unless you go way off center on the overlap. Personally, I like the overlap to be basically centered on most street car builds, because it makes good power everywhere. Now, personally, i'm not one to really look too much at splits, LSA, etc. I tend to say if the valve events are correct, and the split and LSA just ends up being what it is.

Question - IF you are concerned with split, where do you tend to make the sacrifice? Do you make the overlap more intake biased, or do you bring the IVC up closer to the EVO, or do you bring the EVO down?

Tuskyz28

Thanks for the information as always Jake.
Now I have to pick at your brains a little bit.

Why don't we see more single pattern cams these days vs previous years?
​​​Almost every cam I see spec by a cam guy the cam have a split no matter what the head selection may be.

Overlap- why is a bigger valve head such as a 2.16 LS3 intake valve is very sensitive to overlap vs a cylinder head with a smaller intake valve such as a 2.08? Big valve heads can be VERY PICKY when it comes to dialing in the cam specs.
Seems like to me the bigger valve will be easier to cam and will always make more power but that's not the case....

And one more question... Martin Smallwood said lobe separation angle doesn't matter, remember? What is your thoughts about that Jake? Let's say I was running a 346ci with some ported 243s with a Ls6 intake... Nothing special about the combo.
Let's say we had a choice between two cams 224/230 600 lift on a 112+4 LSA vs 224/230 600 lift on a 115+3 LSA
Which one would you choose and why ?

JakeFusion

iTrader: (7)

Well, that was the example valve events to show how much things can change. And it showed 5 different cams with those events. Obviously, if the heads are super efficient, you want to bring that split closer together. You still pick the IVC first based on the motor size and stroke, intake manifold, and intended RPM range, and then the heads themselves. Then you pick the EVO based on the head, exhaust valve, and exhaust setup, and intended usage. So a street/strip 408 with cathedral or even rectangle port heads wants an IVC of 50 for example. But are the heads LS3 or Cathedral? What's the I/E Ratio there? A really efficient head might want a much later EVO since it can evacuate the exhaust quickly. I think you see that a lot with Tony Mamo's heads. He prefers a 4 degree split and a much later EVO because the exhaust port flows so well.

And we see so much of a split with the LS3 stuff because they flow like 65%. Given that, you end up wanting like a 15 degree split. And when you look at the events on 416, a 50 IVC is still about right but now your EVO needs to be closer to 65 to open the exhaust valve sooner to aid the exhaust. And then you can play with the IVO and EVC based on other factors to get the cam where you want it.

The split is there because almost all heads are less than 75% I/E ratio efficient. The newer stuff is even further away. So you need the split. Ported stock heads don't improve the I/E ratio... they just pump up both numbers. You have to look at aftermarket castings to see a difference. Most still stay in that 70% range, because they dedicate more of the bore to the intake valve.

A larger valve tends to be more sensitive to overlap because it slows down airspeed. You create a bigger hole and the vacuum remains the same, the airspeed decreases. Or think of it another way... overlap becomes a problem because where is the spent charge going? Out the exhaust or back through the intake? Where is there a greater pressure differential?

So how do you counter it? More bore. More CID. More vacuum. So the intake to bore ratio is a big number a lot of people forget. There's a reason the LS3 stuff works better on the 4.065" bore vs a 4" bore. I think this is also why you see more conservatively cammed stock LS3 heads doing very well and why a 2" header is really beneficial for the LS3 even at 376 cubes.

And yeah, LSA doesn't matter. Look at the five cams in the example. They all have different LSAs. But the valve events will produce similar dyno graphs just moved up or down in terms of overall power and the ability to affect the areas above peak HP and below peak torque.

A.R. Shale Targa

iTrader: (2)

I've read stuff from Mamo, Tooley, and Smallwood where they seem to share the opinion of more Ex. timing(4,8,or12); even in a well balanced head, carries the power out longer after peak(assuming stable valve train is in place) Shift extensions are raised which keeps the air pump moving faster after the gear changes.
Overlap being when both valves are opened simultaneously, as Jake mentioned; bigger In. valve/runner does affect port speed, however the space between the
valves is also minimal. bigger valve; bigger bowl; closer to exhaust valve. Mamo has eluded to playing with the exhaust seat height; relative to the intake in order
to negate some scavenging with a near 80% E/I ratio head on an NA app
Most would pick the 112/108 ICL (40 ABDC IVC) for a crispier low/mid range POP and a schnizzle idle
I'm not enamored with idle bump and would opt for the 115/112 ICL (44 ABDC IVC) which reduces peak torque, flattens out the ends (wider torque band) and in your example would prolly carry out 2-300 more rpms after peak

Rise of the Phoenix

iTrader: (27)

I think looking at intake and exhaust flow of heads is the most important thing to look at when specing a cam. In my case, the heads I have flow more on the exhaust side than any other cathedral port head on the market, so the cam needed to be spec'd accordingly. The original cam I had was not good at all with my setup. The new cam, spec'd accordingly, is way better. More power under the curve and more top end power.

JakeFusion

iTrader: (7)

Geoff @ EPS loves to do a 12-degree split and center the overlap. He does it to make more topend power at the expense of a little less midrange torque. I think most folks would agree that's the way to go.

And between those two, I would do the 115+3 and run more compression given an LS1 or LS6 head. That car would drive better, idle better, and carry the power uptop better. It may peak at the same HP number (just a little later RPM) and might actually make a little less peak torque, even with more compression. But it'd be faster with the right gearing/shift extension/RPM range.

I'd actually rather do a 112+2 with more compression. IVC is a little later, EVO is a little later as well. So you'll build more torque with the later EVO instead of opening the exhaust too early. And you maintain the same overlap number. And overlap is power.

Tuskyz28

Jake, you mentioned Geoff @ EPS loves to do a 12 degree split... on what cylinder heads ? Rectangle or cathedral?
A 12 degree split on a good flowing cathedral head such as a AFR/TFS head unless you plan on running some juice....

I've seen Pat G run 6-8 degrees with a TFS cathedral head on some naturally aspirated builds with great success.

JakeFusion

iTrader: (7)

He ran them on the TFS 245s with the nitrous port... that's an efficient head.

LS3 is greater split.

Darth_V8r

iTrader: (4)

FWIW, Tusky, LSA doesn't matter in the same way displacement doesn't matter. of course displacement matters, but what really matters is the underlying bore and stroke. 402 is really just short hand for 4" bore and 4" stroke.

LSA is sort of the same way. of course it matters, but morein the sense that it describes the underlying valve events, which are what REALLY matter.

Sort of the way I look at it anyway

Tuskyz28

very very interesting thread here and I'm loving it.

Martin Smallwood

iTrader: (2)

The reason why big valve heads are sensitive to overlap is due to their low lift flow numbers. The valve is the major restriction in the cylinder head at low lift, not the port because the valve at that point in the lift curve is the restriction. So when you increase the valve diameter the low lift numbers increase as well. This has the same effect as increasing valve overlap. When the head can flow more air at low lift and you have too much overlap, even higher amounts of reversion and charge loss occurs. You'll always have some reversion and charge loss on a performance based camshaft. Airspeed also drops as Jake mentioned so you do not have as favorable a pressure differential from intake port pressure to cylinder pressure during the IVO event. Overlap occurs at low lift, so if the head flows better a low lift you use less overlap.

For example, a 4 valve mod motor head has incredible amounts of valve area due to it having 4 valves. For example, a stock Coyote head has the equivalent intake valve diameter of a 2.150" valve and the equivalent exhaust valve diameter of a 1.800" valve!!! This is on a 300" engine!!!! Can you imagine a LS3 sized intake valve on a 300" engine and a BBC sized exhaust valve on a 300" engine?!?!?

This is why the 4 valve mod motors do not need anywhere near as much camshaft and overlap as a 2 valve push rod engine. Also because the valve train is much lighter due to the OHC design.

For example:

TFS 245 intake flow numbers:

.100= 69
.200= 146
.300= .237

TFS 245 exhaust flow numbers with N20 exhaust port:

.100= 55
.200= 122
.300= 199

4 valve GT500 ported head intake flow numbers:

.100= 94
.200= 179
.300= 245

4 valve GT500 ported head exhaust flow numbers:

.100= 80
.200= 160
.300= 205

As you can see there is a HUGE difference in low lift flow between the two heads.

Now, you can negate low lift flow by altering the valve job angles as well. If you go to a steeper valve job (say a 50*) it will lose flow at low lift and gain it at higher lifts.

I/E % is important, but it's not the most important or only thing that needs to be looked at. There are a lot of other factors that play into how a cam should be ground and of course if you ask 5 different people you'll probably get 5 different answers.

00pooterSS

iTrader: (40)

I wanted to add a little bit of laymans terms here to help. If this is wrong please edit and I'll go back to watching the pro's discuss.

Pulse Red

Very interesting topic, for choosing a cam I had just picked up little bits of info over the years that were helping me decide what to go with. I didn't really understand IVC or EVO. These kind of threads are helping me learn.

I had been looking for a cam for my 346 LS1 that has a bit of a different combo to most down here. It has CNC Ported cathedral port heads, Mafless tune, OTRCAI, ported stock TB and stock LS6 manifold. However it has short extractors and twin 2.5" exhaust rather than the long tubes and twin 3" most people use. It also uses 3.9 diff gears and a stock T56 Manual transmission. I was aiming for street performance so below the curve power in a heavy car (Pontiac 2004 GTO equivalent) thus the choices above.

I came to the following cam: CamMotion 218/226 .595" .587" 116 (or a similar CamTech 216/226 .600" .598" 116).

My reasons for choosing these cams despite being told I should only use bigger cams with no split? Based on my understanding it was the following:

1. Trying to keep the cam stealthy. So it needs somewhere around -10 overlap.

2. I want ZERO bucking/ surging at low RPM. In an LS1 manual it needs a low Intake (212-218)

3. Hoping for the least possible valvetrain noise. Lobes play a part but keeping the lift around 600" or less helps.

4. Wanting a smooth idle. Less advertised duration @.050 helps with this.

5. Looking for more under the curve power rather than top end. Lower duration is better here.

6. Cathedral port heads (even when ported) work well with an 8-10* exhaust split.

7. When using short headers and a smaller exhaust split pattern cams of at least 8* split work best.

I now wonder how accurate the above is that lead me to my decision.

JakeFusion

iTrader: (7)

You can run up to about 4 degrees of overlap and keep the bucking at a minimum to zero.

You will need more exhaust duration with that exhaust. You'll need a crutch.

If you want it stealthy, anything under about -4 will get you there but closer to -10 will really have little chop.

I'd honestly do a 218/230 .612/.595 115+4. IVC of 40 and EVO of 54. -6 degrees of overlap. So not far off from what you were looking at.

Pulse Red

Thanks for the response, its interesting, part of the reason I believed the claims about surging/ bucking is that it was backed up by cars I tested. ONLY in manual 346 cars (autos and newer engine cars were fine) did I find that while it was mostly ok you couldn't completely remove these attributes with the bigger cams, so for example you can't roll around just above idle with the clutch out like you can in a stock car. You could drive around this but it was still there. The cams with lower intake didn't seem to have this issue

The exhaust duration comments are interesting, I initially thought this too but apparently with the CNC ported heads it wasn't needed?

My current cam has -7 overlap and its ok but I think less would be what I'm after, so I feel that -10 may indeed be the magic number. So that one may be right.

Tuskyz28

Surge/bucking..... allot of that comes down to the tune/tuner on the car. Youll be amazed what a great tuner can do.

Pulse Red

Most certainly, however the kind of things I am talking about were present in larger cam, manual, 5.7 cars tuned by those considered top of their game. They were not things that may bother most people but I am looking to avoid them.

z-maro

iTrader: (18)

Love all the info. I was wondering how you think my new setup will perform, just need pushrods before I start it up. I have AI 232cc heads (82.5% average I/E ratio per the flow data on their website compared to 71.6% average for their 226cc), 62cc chambers then milled .003" with stock MLS gaskets (11:1ish CR). Mamo ported FAST 102, stepped headers and hooker catback.

Geoff set me up with a 226/230-113+2, goals are to not lose any power from my bolt on only setup at low rpms and just a fun overall street car. Thoughts, peak HP and TQ rpm's to expect?

JakeFusion

iTrader: (7)

I'd say probably 450/410. The catback may hurt you. True Duals pick up torque. Especially at lower and mid RPMs.

I would have brought the IVC down a little more for a street car (6-speed I assume?). The 226/230 111+2 would have come on a little stronger in the midrange and still drive well (maybe not perfect but not bad at all). But it would die out somewhat uptop after peak (tho the 232 runners will help). But so would the 113+2... the exhaust is opening too late - so it should make good torque at the expense of some high RPM carry. But that's fine for a street car.

I looked at the AI 232s... the 226s are flowed without an exhaust fixture. The 232s use a 1-7/8" fixture. So it inflates the exhaust flow. I would take the flow numbers from the 226 (since the exhaust is untouched between them from what I understand) and use that for your E/I ratio. 212/305 = 70% ratio. They also flow well above .600... so I'd try to use the .629 or .637 lobes from Cam Motion that Geoff would use. Anything beyond that and you may have issues with the stock rockers.

So using my own logic...I'd do a 226/234 .629/.604 111+2. 8 degrees is where I'd say the cutoff is for a really streetable car. And I'd run more exhaust because you have larger runners in the head and more flow. So you might need a little more exhaust assistance (especially running a 3" y-pipe configuration).

And just to throw a wrench in there... here is the 227/244 115+5 (that I run) as a cam only graph (and before he did this, he said he swapped in an S60 and lost 21rwhp - so this is 405rwhp with a stock LS1 intake and LS1 heads and carries to 6900). This shows the power of a very early EVO combined with a relatively mild IVC. Peaks at 6300 and carries 600 RPM past. Put a FAST 102 and a ported LS6 heads on that... and hey what do you know, you end up with my combo. I think he would have been around 405/390 without the S60. And is at 385/365 with it.