The original question was " Interested to see what some of the knowledgeable people on this forum think. I have seen them in circle track engines and a few of those guys around here swear by them, but have never used one personally. I have always preferred to put the time into balancing out the intake flow with the carbides and testing. In theory, it makes some sense; but I am looking to see if anyone actually has any first hand experience with them. So, are 4 pattern cams just Black Magic/ snake
oil or are they legit and based on sound testing?" the thread is even titled Dual Pattern cams... Black Magic or Legit.
An IR intake and programmable EFI was suggested as the fix. It definitely fixes the flow problem negating the need for different lobes on the intake side. A clean slate manifold with perfect matched cross-sections and lengths is likely not in the cards. It could be due to class rules or it may just be the way things are. So once again, its back to the original question of requesting knowledge on those 4 Pattern style camshafts. A statement was made saying lobe gymnastics do not fix the flow problem. That is true, bench flows are unaffected. But the cylinder doesnt see what the bench sees. The cylinder sees the whole picture because the lobes are the doors in and out of the cylinder, and they control the flow volume. Valve events (lobe gymnastics) absolutely change the game completely. Opening the door earlier or longer or faster or slower is how you optimize the flow volume to the cylinder. In cases where there are significant differences on the flow bench, the lobes can be used to bolster the low flowing ports, equalizing them with the better flowing ports. That’s the whole purpose of a lobe profile. Its not just duration vs rpm. Are cams that ’attempt’ to remedy flow variances warranted or cost effective or simply snake
oil is the issue?
The key take away of all this is: air movement through the cylinder is hardcoded by flow parameters and valve events; not flow only and not valve events only. Looking at a spider intake with shorter inner runners and longer end runners presents a flow difference on the bench. But the lobes are used to optimize flow to the cylinder. We see formulas that say xxx flow produces xxx hp. There is so much more to it. The valve events and ramp rates are what enable the flow to be realized at the cylinder.
Heres an example to see what lobe differences look like, compensating for flows. But instead of looking at the intake side because this seems to be causing problems in this thread, I am going to show it from exhaust side.
300cid V8, 10:1, peak hp 6000-6200 rpm.
The intake manifold will be the suggested fully equalized IR style with programable EFI. On the flow bench the full inlet path flows 250cfm (flowed with full inlet path, head with manifold attached and TBs). All ports flow equally. +++For simplicity of the example, Im only looking at peak flow and seat durations.
Now, let’s look at the exhaust. This set-up uses 1 3/4 diameter x ~30" header primaries. 7 of the 8 exhaust ports. On a flow bench, the complete exhaust flow paths (header attached to the head) all flow within 5% of 160 cfm (28").
But, one port has a hideous sharp bend on the header right at the head. why? because that is just how those headers are. They have to clear an obstruction in the suspension. This entire port length flows 140 cfm, greatly reduced from the other 7.
So how can you fix this flow problem? A new engine mounting position or new suspension to permit a better designed header is not an answer.
To recoup the flow potential in that cylinder requires a change in valve events for the cylinder to increase its outflow as the other 7 better flowing cylinders.
The valve events for the 7 cylinders would look like this
Intake 276 deg seat duration on a 106 intake CL
Exh 283 deg seat duration on a 116 exhaust CL
this calculates to a 111 Lobe Separation Angle.
The valve events for the ill flowing cylinder would look like this
Intake 276 deg duration ona 106 intake CL
Exh 290 deg duration on a 120 exhaust CL
calculates to a 113 LSA
This change in the exhaust valve events recoups the flow potential (decreases the exhaust restriction) in that cylinder. The flow capability thru the path hasn't changed, but the cylinder's outflow has now changed to match the other cylinders. (the door has been opened differently, earlier and longer) This was done thru increased exhaust duration and earlier activity.
This is an example of using a different lobe to equalize the cylinders' exhaust restriction across all cylinders. The cylinder sees inlet and exhaust as restrictions. it doesnt care whats attached, it only knows restrictions to its pumping volume.
In theory, you could have a cam ground with a different exh lobe on this cylinder. This is exactly what the 4 pattern style cams are attempting to rectify, in concept. However, the cam vender is primarily focusing on the intake side (with an open plenum spider intake) and not the full picture including the exhaust. That is a strike against the 4-pattern cam. The concept is correct and works, but does it go far enough. The exhaust weighs heavy in the picture too. If the exhaust flows are quite similar and the difference is solely due to the spider intake design, then it can work. But the valve events have to be correct or its simply a cam with a gimmick.
In practice, the easy band-aid for this low flowing exh port in the example would be to decrease valve lash on that valve to increase duration. OR add increased rocker ratio to increase duration at the valve. Both get the job done, not identically but similarly. But neither address the CL issue. Normally, you just accept that. OR you just treat all the exhausts the same (even though one is way out of family) and not worry about it and simply accept it. However, lash changes with a solid valvetrain are definitely a very easy change.
this is real world experience and actual numbers regarding what the concept of the 4 pattern style cam enables. I think this addresses the original question (again). but this time with a real world example of how differing lobes would be used.