Here's a thought;
Lets say you have a 268/276/114 cam It has a maximum overlap of
(268 +276)/2 less (2 x114)= 44
So to use all of the available overlap, you would install it at split overlap which is
(268/2) less 44/2=112, and so you have 44* of effective overlap, same as what's built in to the cam..
Your Ica will be;
(360 +22) less 268, less 180 and sign-change =66*Ica
Install that into a 10.0 340, and the pressure is predicted to be 159.3 at sealevel. The events are;
268/114/106/276/44; and in at 112= Ica of 66*
Now put it in an 8/1 340, still at 112, the events are exactly the same. But the pressure is now predicted to be just 120psi@ sealevel.
So what are you gonna do?
Well one guy on here might suggest to advance it a bunch.
Ok lets advance to 8* which would be in at 106. The new events are
268/120/100/276/ E-overlap down to 32*/Ica of 60*
and this will bring the pressure up to 127 in that 8/1 340; yahoo
In my opinion, that's a waste of time.
But ok, lets make it a 268 single pattern. still at 112LSA and at split overlap, the events are;
268/112/112/268/E-overlap is 40/ and the Ica is 68*
In the 10:1 340, this might make 155.8psi ....... hold on a sec, back up the bus, didn't the split pattern make 159.3? Why yes AJ your math said so.So what's going on? Well, the single pattern cam only has 40* of maximum overlap, so installed at split-O, the Ica comes in 2* later; namely 68* versus 66.
Ok/Ok; unfair you say.
Well, I'm trying to make a point here which is the blanket statement put forth above, that single pattern cams (almost) always make more low-end torque........... Which is possibly/ probably true, but at what cost to the top end? Notice the single pattern cam gave up 4* of Effective overlap. And the single pattern has 112* of power extraction, which is great for fuel-economy, but is a dead weight number at peak-power, especially for a head that has trouble getting rid of exhaust...... like the factory iron Mopar LA heads do.
Ok so, Lets see if we can actually compare two cams, one a split and one a single.
Since the intake duration is what ballparks the powerpeak, to be fair,we have to set that first. I chose 268*. So this time, lets try keep the extraction the same and lets toss that 114LSa cuz nobody runs that on the street. Let the LSA be tighter
Ok so lets work on a single pattern 268/268/110/48overlap, installed straight up at 110, and the events are;
268/116/116/268/48E-overlap and in at 110, the Ica is 64*... why anybody would want power extraction of 116* is beyond me. That might come in handy cruising at 65mph but is a good waste of time at peak-power. and the overlap is just 48*. It might also come in handy with a 2000stall TC.
Ok so how close can we get with a dual-pattern?
Well we gotta keep the 268. And I like a 6* split to allow some adjustment of the ICL; so that makes an exhaust of 274. And since I'm trying to target that stinking 116 power extraction, I'm gonna put it on a 106LSA. so what I get is;
268/274/106 and the events are ;
268/121/116/274/59* E-overlap/in at 105 for an Ica of 58*
Ok here it comes;from above;
268/116/116/268/48* E-overlap/in at 110 for an Ica of 64*
The split pattern has Plus 5* compression so maybe plus8psi CCA
The split pattern has Plus 11* more Effective overlap, for more midrange to peak, power
The split pattern has Plus 6* more exhaust duration, for the LA head.
The split pattern has a huge tuning window of +/- 4 or 5 degrees before the E-overlap falls to 48*
If you advance the split pattern another 3*, to in at 102/(4* advanced) the compression will go to 124*,(Ica of 56*) and the extraction will fall to 113. While the Effective overlap will fall to 52*, still 4* better than the single pattern.
So, IDK about you guys, but I know which cam I am choosing for my streeter.
But here's the deal;
Lets talk about the compression degrees Plus the extraction; I'll call it C&E. In the Single-pattern;
116 +116=232 which is a very good street number.
In the Split-pattern it is 121 +116= 237* a better number with the 268 Intake duration.
If, and I say IF, you were to compare these TYPES of cams using this C&E technique, then you might see a different picture.
Lets make a split pattern cam of 232* C&E, on a 110, with 48* overlap; the events are, or could be;
264/120/112/272/48 *Effective/in at 108 for an Ica of 60; compare this to; the single pattern from above;
268/116/116/268/48* E-overlap/in at 110 for an Ica of 64*
notice the C&E is 120 +112=232, same as 116 +116 =232
and overlap is still 48, and the LSA is still 110.
The exhaust duration has increased 4* while the intake duration has decreased the same 4*..
So how will this affect your engine?
Well; the split at 272 less 264= 8* which IMO, is excessive, even for stock LA heads. Be that as it may, maybe you can run 2" pipes,lol.
The Compression is 120 less 116= Plus 4* so again about Plus 6psi CCP
Extraction is 116 less 112= Less 4* but 112 is still a good number.
But the loss of 4* of intake duration means the operating rpm has come down about 100rpm, so I'll guess a loss of say 10Hp, over the peak. IMO the the loss of peak power, will be made up for by the increase in pressure, so it's a crapshoot as to ET from zero to 60mph.
So IDK, I'm not sold on a single pattern for street.
