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Discussion Starter #1
I've recently become more interested in cam (and carb) voodoo. I know people will say, "get a custom cam," but I don't want just ask someone else what cam I need for my engine. I want to be able to know myself. Without back-to-back dyno results you can't really know for sure what cam will work anyway. I realize the "experts" may have put many engines on the dyno and this gives them experience but I want to understand more about the basic principles that they understand. Plus I take a certain amount of pride in being able to say, "I chose these parts, I built this, here are my results." I want to be a competent car builder- not for any reason other than I like to be good at the things I do.

I've just spent days researching LSA, looking at various magazine articles, reading forums, watching videos- all very good stuff. Now I'd like to more about the reasoning behind specific dual pattern scenarios.

So we all know that a dual pattern cam has more exhaust lift and/or duration (most of the time) to make up for the lower flow of cylinder head exhaust ports. But how is this difference determined? Is it just a shot in the dark? Is there some equation? A percentage? If you know your head intake and exhaust flow can you formulate your own perfect dual pattern cam? For instance maybe you'd choose an intake duration suitable for your desired RPM range- let's say you want 2500-6500 so you choose a [email protected] intake duration and a .545 lift. Your head head flows about 30ish% less on the exhaust at .600. How do you pick the exhaust lobe? If you follow the aftermarket it would seem that [email protected] and .565" lift is what you would pick. But why? They know nothing about your engine or heads. How do they do this? Do they just look at a few standard SBF heads and kind of know what the variance in intake vs. exhaust would be?

I don't want a bunch of people telling me I'm overthinking. Yes, that's exactly what I'm doing! And I don't want people to say, "just call this or that custom cam guy." If you want to dismiss the topic, do in your head. I want real talk from fellow gearheads who are interested in the science. Anyone can call a guy or order something out of a catalog.
 

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Some will say that more lift and duration for the exhaust isn’t necessary. The piston is pushing the exhaust out no matter what.
But I do prefer the split pattern.

What matters for cam choice is compression ratio, flow rate of the heads, and desired rpm range.

I chose gt40p heads.
Calculated CR to be 9.1:1.
Found some flow test numbers on the internet. Then chose the cam and valve springs.
 

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Of course you're overthinking, but that's OK. Much better than the more common "more is better" many folks use to choose a cam.

Depends a lot on the engine configuration. Cylinder head flow, manifold design, exhaust type.

The vast majority of 289/302 had a C3AZ-V cam, which is a dual profile. Probably due to the expectation that they needed a little help on the exhaust side. You will notice, though, that Ford's performance cams usually had a matched profile.
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Oddly, due to the cancellation of the 289HP engine, the 68 GT350 had a J code 302 with the C3AZ-V cam. Swap that J code engine to a C9OZ-C and it really wakes up.

The type of driving you plan, and drivetrain of your car have much more to do with cam choice. Are you driving to cruise night at Dairy Queen or doing an autocross on occasional weekends? Big difference.

If you get aftermarket heads, or even just do this to your stock iron heads, it'll really shake things up and reduce the chance you'll need a split profile-
Port Matching
 

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It's fun to learn about all the black magic that goes into a cam. To be real, if you talk to a good cam grinder, they have many decades of experience as to what works in the real world and what doesn't. You can't learn all that from Internet research.
 

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Discussion Starter #5
I hope to learn by doing, not just reading.

Right now I have an Anderson B-41 Cam.
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I'm thinking about going with a 108 LSA. Given that my engine ran out of steam at 6000 RPM I see no reason to run such a wide LSA. I'd rather have the 5-15 ft/lbs across the board below 5000 RPM (that's a guess) that a 108 LSA might offer. But I was thinking I might adjust the lift and duration a little as well. Maybe even go up a couple hundreths. I don't want to measure PTV again so I don't want to get carried away on exhaust but I think it will take about .600 / [email protected] no problem. Not that I need that much.

Armon (happystang) popped this cam in his 306:


He has KB twisted wedge pistons like me but they are flat top and mine are mild domes. I was thinking about having a cam ground that is similar to the Voodoo cam but on a 108 LSA. Also thinking about having my TFS heads ported by Fox Lake or TEA to bring them up to about where the TFS 190 11R heads are like Armon has.

I'm also switching to a toploader and Holley 650 XP Ultra very soon.
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Sometime after that I plan do swap in my 24" radiator and what better time to do the cam since the radiator has to come out for that too?
 

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My custom cam doesnt have more lift and duration on the exhaust. I have AFR heads and the exhaust doesnt need extra help.
 

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I commend you for wanting to actually learn rather than posting comments based upon what you believe or what you have heard here or on the web.
 

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Discussion Starter #9
That video is pretty good. Actually my engine seems to have more cam now than is warranted by my heads. It seems like something with around .500ish intake and .525-540 exhaust would be ideal. Still think 225-230 intake and 232-240 exhaust for my desired RPM range would be pretty good. Definitely want to try 108 LSA. Who will grind me a cam to MY specs for a decent price?
 

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The cam in my W stroker is .580 lift on intake , .577 on exhaust , 236 deg duration on intake , 242 deg duration on exhaust both at .050 lift. This is a custom grind for my application with AFR heads. Obviously with stock Ford heads the exhaust lift would be higher than the intake lift. Also you can have different lobe profiles for intake and exhaust with a custom cam for your application. I have also seen 1.6 rockers on the intake and 1.7 rockers on the exhaust.
 

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jdub, the very first thing you need to do is decide what you want from this motor. what rpm range will it spend 80% of its time in? that will be the basis of your cam choice for this engine. for instance if you are building a street engine for a daily driver, then you are going to be wanting a cam that operates best in the 1000-4500 or 5000 rpm range.

then you can decide on whether or not to use a dual pattern cam, single pattern cam, chose the valve lift, duration, overlap, etc that you want. remember the cam is the heart of the system we call an engine. the heads are the lungs, the intake is the esophagus, the exhaust is the intestinal track. each of these systems need to work in concert with the others for best efficiency.
 

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I found comparing what the maker claims helps to understand the why. Howards Ford 221-302 Hydraulic Flat Tappet Cams Look at the ones with the same lift and dur but different descriptions, RPM ranges, uses.

I also found it funny most of the split ones have about .020 difference even on big cams. The Ford C3 cam mentioned is 368/381, coincidence? There is another C3 with the opposite A or O 3rd digit, its square .381 and didn't last as long for a reason I suppose.
I went deep into some discussions that involved a few cam grinders including the CamKing and I think our political discussions were more civil o_O (You guys that are wrong a lot...) If they have different theories you will get different grinds and also have a good explanation for why they did or didn't do something. Its hard to favor the one that says "I build winning engines" when they all do.

After all the brain hurts from reading, I decided; pick a lift that sounds cool to say, pick a duration that will sound good out the exhaust(within the proper RPM range) and save the LSA and center-line for fine tuning if you are given a choice. Oh and fast bleed lifters so you can purposefully over do it :)
 

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Discussion Starter #13
jdub, the very first thing you need to do is decide what you want from this motor. what rpm range will it spend 80% of its time in? that will be the basis of your cam choice for this engine. for instance if you are building a street engine for a daily driver, then you are going to be wanting a cam that operates best in the 1000-4500 or 5000 rpm range.

then you can decide on whether or not to use a dual pattern cam, single pattern cam, chose the valve lift, duration, overlap, etc that you want. remember the cam is the heart of the system we call an engine. the heads are the lungs, the intake is the esophagus, the exhaust is the intestinal track. each of these systems need to work in concert with the others for best efficiency.
That may be good advice for someone, but not me.

This engine already put down 324hp to the tire through a C4. The converter flashes north of 4k RPM and stalls above 3500. This car exists to beat up on, have fun and experiment with. Here's my goal for the car: try a different cam and see what happens because hot rodding is fun and cams aren't that expensive. It's not even that I am unhappy with the current cam. I just think I can do better with more knowledge than I had before.

Figuring out what I am going to do next keeps me interested in the car. I'm not trying to build a daily driver or something that I pick all the right parts for and then its done forever. I finally figured that out. Researching and tinkering and trying (and maybe failing) is what I want. The car itself is just an avenue for learning new things and having fun.
 

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David Vizard has published theories about the optimal LSA, which he claims is dominated by the intake valve size relative to the displacement. The smaller the relative valve size, the smaller the LSA. His explanation is that the vacuum in the cylinder that occurs during the first halve of the intake stroke can never be fully compensated by late closing and that the valve should therefore be opened as much as possible, as early as possible. For a stock valved 289, the LSA should be ~108 deg, IIRC, according to his tables.
That is a valid point, because the maximum piston speed occurs at 75-80 deg after TDC, so the ideal intake lift centreline should also be 75-80 deg from that perspective (which is not practically possible without resulting in way too much overlap, so a compromise is needed). Also, the displacement at that point for a single cylinder is about 80% of the average flow of the engine (example: 302 CID, 6000 RPM, 302*6000/3456=524 CFM, displacement at maximum piston speed ~420 CFM), so vacuum during the intake process will occur in just about any naturally aspirated engine.
Unfortunately, David Vizards articles tend to be half very specific and well explained and half vague, so you never get the full answer. For example, does he mean the LSA or the ICL (intake center line) and what about the exhaust?
So, now I need to go on and do other things J
 

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I know you simply want to talk cams but since you are going to this level of detail, I do not see how your carb, Intake, (you mentioned heads) and even exhaust/mufflers play into these decisions unless you are saying lets hold everything constant and play with the cam as opposed to lets make the motor do what I need it to. My suggestion if you really want to play with the cam is to download a good desktop dyno and there you can play with all of these or keep them constant and just play with cam profiles and see how they impact the output. Numbers may not be exact but the trends are likely to give you an idea input to output response. There was a free one that let you play with values but you had to pay to be able to download values such as flow rates for performer RPM heads etc...
 

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Your sig says 289 with iron heads, but you mention TFS heads. Are the TFS heads on the car? if not thats why the car stops pulling at 6k because of the iron heads. That duration of cam on a 108LSA won't be much of a driver but its all in what you want.
 

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Discussion Starter #17
The sig is a joke. Here's the real setup:

306
10.75:1 Compression
TFS 170cc heads with Anderson Valve Springs
Anderson B-41 Cam (0.544/0.568, 228/236 112 LSA)
1-3/4" Headers
Edelbrock RPM AirGap
Holley Street Avenger 670, 1" Open Spacer
Pertronix Distributor and Coil
JBA 2.5" side exit with glasspacks and H-Pipe
 

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Latest Engine Masters episode had a good test on LSA, where they switched out cams with the exact same intake and exact lobes, with differing LSA’s (106, 112, and 118).

Fascinating test, although I would have liked to see them explain the opening and closing events of each cam and how they differed (i.e., in each successive widening of the LSA, how are each of the centerlines moved in relation to the previous cam?). I imagine that moving just one centerline to achieve a desired LSA has a different effect than moving both centerlines and equal amount to achieve the same LSA.

I’ll post some screen shots if you cannot access it.


Sent from the interwebs... where else?
 

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... how is this difference determined? Is it just a shot in the dark? Is there some equation? A percentage? But why?
...High Performance is another thing entirely. Change one factor,.and you have just negated in most cases, the need for that longer exhaust lobe. Why... insist on running a cam with longer exhaust duration regardless of what equipment is employed? The answer is "habit". Most of them have been somewhat successful in doing it their way and will probably never change unless virtually forced by circumstances to do so.
Ed Iskenderian


Good explanations without the math here.
 

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I actually bought a cam from Dema Elgin, but that's not why I posted the link. Since you are really digging deep, I found this article to be enlightening on cams. The section "Engine Cycles and Cam Timing " will probably be very interesting to you.

Hope it helps.

Allen
 
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