I have a question that I can't seem to find the answer. How do you determine what valve events are appropriate for a give displacement engine? Also how does stroke and bore play into that decision? Further into that, how do you determine what static compression is necessary/best for a given combination once events are determined? What order should these items be addressed?

 

This isn't a small question. A complete answer would be closer to a dissertation than a forum reply.
There are countless articles available online for this.

 

Could anyone provide a few links to some of those articles. My searches have not been fruitful.

 

I googled "Understanding valve events".
Here is the first result, which should get you started:
https://www.enginebuildermag.com/201...of-importance/

 

Please have a look at this article and video first and we'll be happy to answer your questions more specifically.

 

Please have a look at this article and video first and we'll be happy to answer your questions more specifically. This article does a lot to compare individual events between our different cam lines. You'll see the stages are incremental and it will start to make sense. You need to move the tables from left to right to see the individual events, so best viewed on a home computer.

 

Thanks everyone for the info.

 

Really the top concern is not even on your list - intended use. How you plan to use the motor is the single most important consideration when speccing a cam.

 

I agree. So help me with this. Street car, 3400lbs. Automatic 3.73 gear 28" tire 2800 stall stealthy idle 3" true duals 1 7/8" headers daily driven weekend warrior red light to red light. What valve events would you recommend for these 2 engines?
454 cid AFR 230 cathedral 11:1
416 cid AFR 230 cathedral 11:1

 

This is interesting because you've got a lot of cubes either way for torque. Generally we hear the other way around where it's a small engine and we need to conserve torque and idle.

For a daily driver with stealthy idle, We'd normally open the intake a couple of degrees after TDC to smooth the idle. Depending on your intake, those cubic inches can run a little later intake closing at the expense of a little bottom end torque. Something in the 47 to 52 range would be pretty common with a typical long runner factory "style" intake manifold.

As for exhaust, a little bit of that depends on your exhaust. You have a large free flowing exhaust and that makes it a bit harder to hide the note. Generally we'd aim for something in the 58-64 degree range for exhaust opening to evacuate for power, but if you wanted to dampen the note a bit; you wouldn't be losing too much with a 53 or 54 exhaust opening.

Exhaust closing is the final event and determines overlap. You have a free flowing exhaust and can get away with a bit later exhaust closing with decent scavenging, but that overlap is a balance of part throttle and WOT. With you daily driving, we'd back the exhaust closing back to 5 atdc and limit overlap to 2 degrees.

If we plug a 50 deg. intake closing, -2 intake opening, 54 exhaust opening and 5 exhaust closing; we get a 228/239 115 -1. This may sound "small" for the cubes (and it is compared to what a lot of guys run), but it will run good, be very stealthy and pull well with that taller tire and 2800 stall. We need to know more about your intake to tweak between the two cubic inch displacements. The 454 would allow us to sacrifice a bit more low end to pull that gear and move the powerband up. This is mostly a function of intake closing and earlier exhaust opening to a lesser extent.

If you want to think about a duration lsa numbers you had in your head, we can toss those in the calculator and describe what each change does to behavior. Here's the calculator so you can play around some yourself.

 

OK, I'll start with the 416. And I'll also state right now, I would go up in compression based on this post.

For the 416, I would be looking in the 49 range on IVC. With 11:1 compression, I agree with summit on opening exhaust around 54. Take the compression up and you can open the valve at 60. To me the issue is dynamic compression. You run a 49 IVC with that compression, and your dynamic compression is only 7.8, which could end up feeling lazy. Now a 4" stroke is going to make torque and you can get away with some of it, but I would be thinking more like 11.6 compression to get DCR up near 8.35 for more grunt all around. That will be 91 octane safe. Last concern is stealth. You need overlap to be negative for any hope at a stealthy idle. That puts a cap on max duration and a floor on min LSA. I came up with 228/234-118+5, which gives you -5 overlap and will have a better chance at being stealthy. It will want compression though to make the most torque and power it can.

For the 454, you have a bit more options, because the displacement will absorb some cam. But I wouldn't change the cam much from the 416 to the 454 if it's stealth you want. The 454 will sound tamer, but will make more torque. If you decided you wanted more cam with the 454, then I would look at 230/236-118+2 and then take compression up to 11.9 or 12.

One last point - your dual 3" exhaust will not be stealthy no matter how hard you try.

If you insist on staying at 11.0, then my inclination would be to move the IVC lower to increase dynamic compression. The problem is that it will run out of steam up top due to the early IVC. 44 is a great spot to aim for a 5.7 or 6.0, but a bit low for the 416+ engine, which is really going to like being int he high 40's to low 50's for a good blend of low and high end. Increasing static compression will fix that for you.

 

Thanks for your insight. I appreciate the info.

If one of these were going in a 4x4 with 35" tires and 4.56 gears at 6300lbs what would you change if anything?

 

Overall gear ratio is the nearly same, but the weight is heavy with more frontal area and a heavier driveline mass. Equates to more load at 1:1 and we’d pull the intake closing back to 39 degrees to pump up torque as we are spending more time lower in the rpm range. As Darth mentioned, static compression should be dropped in this case to as low as 10.2:1 due to the extra time spent with higher loads in high gear.

Our new monster truck pump gas highway roll race cam (assuming no wheel spin to get the engine up on wheel speed via a launch on Mud/dirt) now becomes a 216/236 113 +2 with everything else being equal.

At this point, the tires make more noise going down the highway than the exhaust and we should revisit exhaust opening and closing and that whole “sleeper thing “

 

I would not be concerned with the sleeper aspect with this vehicle. As you mentioned, tires would be the noise maker for sure.

 

That is a huge split.

 

The thing to remember is our engine doesn’t know math. The only thing it knows is what happens when you change the four valve events. Split means nothing. Duration and Lsa and advance are foreign concepts.

Ok, let’s get rid of the sleeper aspect and make this thing a little rowdy with more time spent at near WOT and the free flowing exhaust. 7 btdc intake opening, 39 abdc intake closing. 54 bbdc exhaust opening, 8 atdc exhaust closing generates: 226/242 111 + 4 if we round up 1/2 degree. Super Torque Monster with “ok” driveability with a 416+ at 2800+

if this thing was a 416 Cid rock crawler with more time spent off idle (1100 rpm) we’d open the exhaust later 8 degrees and reduce overlap by about 3 degrees per side for driveability which results in a 222/231 109 + 1. Unexpected numbers for someone expecting a 210 intake duration or a 112 Lsa, but we are adjusting just the events that need to be adjusted.

 

My "huge split" remark was not meant as derogatory. I'm a firm believer in "whatever works best" even if it looks/sounds/smells weird. If a w-i-d-e split works, ya work it!
I'm learning a lot here.

 

It's starting to make more sense now. I appreciate everyone taking their time to help me understand. Thanks!

 

G and JKD, this has been an enjoyable conversation. JKD gave us a fun twist on things and hopefully helps people really start thinking in terms of individual valve events and having trust in them. ...Even if the "duration, LSA, advance" etc. all seem to be out in left field.

 

I am on my phone so everything I am about to post is doing math in my head. If I am off a tenth or so on calcs forgive me. I would change a lot under this condition. 6300 lbs is a lot to get moving. Now with 35 and 4.56, you actually lose rpm at identical speed and gear. Not much. Maybe 200 rpm up top. Bottom line, this is when you do not want to sacrifice torque. Cam will be SMALL.

Once an engine is going to be loaded like this, compression needs to drop. 10.0 is a good number. But then, you really need an early IVC to get your DCR up. I would be in 36 degree territory. Again with a spreadsheet in front of me it might change a degree or two. I do think with an engine that big you can get away with some overlap without too much penalty.

Also with lower compression, the gases evacuate slower from the chamber. As a result, EVO needs to be late. I would be in 40 degree territory. So with those events at 36 IVC and 40 EVO, you have a cap on duration. Most of your duration comes from delaying IVC and making EVO earlier. This is opposite territory.

Now 6 degrees overlap should be tolerable, but it will have an aggressive idle. The overlap willl help keep it from falling on its face at 4000 rpm.

So that puts it at 220 intake on a 106 centerline and 222 exhaust on a 109 centerline. To make it easy, put it on a 110. So the spec is 220/222-108+2. Thats just off my head. With a spreadsheet and running DCR calcs it might be 220/222-107+2, or 219/223-107.5+1.5. But you get the idea. It might not be optimized, but its a good cam spec for that use and pretty close to what would be ideal.