They don’t show the cam card on there site?
Single Pattern vs Dual Pattern Camshaft
- Thread starter srduster340
- Start date
-
I don’t believe that to be true but it could certainly be mostly true. I think it could be combination dependent and by that I mean the cam timing events.
At of all the tests I remember seeing on camshafts, and there’s not enough of this testing being done, I myself would and do rather say is it has the propensity to make more low and torque.
I believe that to be true. The extra exhaust duration helps with all the crazy dynamics going on in making power upstairs.
They only show the duration, lift, lsa, intake centerline.
On the web site? That sucks. Hummm.
Well, on the cam card they show what you’re looking for but that’s in the too late category. My solid roller below.
duster 344
Well-Known Member
My understanding of the dual pattern cam, has to do with flow of the heads. Horse power depends on the flow of the intake ports, this can be hindered by an exhaust port that flows less than 75 percent of the intake. By adding more lift and duration to the exhaust can increase potential for horsepower. Depending on the goals of your build. That’s one explanation I’m sure there’s other reasons for a certain cam
They used to show the whole card. I'm like you though, I cannot find them now.
mderoy340
Well-Known Member
Cam cards have the events. They are also very helpful on the tech line. My cam card attached.
AJ/FormS
68 Formua-S fastback clone 367/A833/GVod/3.55s
- Joined
- Jan 19, 2014
- Messages
- 25,856
- Reaction score
- 13,165
One thing not yet mentioned is what happens to the overlap cycle, which, the more generous it is, is gonna help power production.
Here's what I mean; take your generic hi-po street cam, say something around 270 degrees;
Make it a 270/270/110. Installed at split-overlap, the events are;
270/115/115/270/50 overlap/Ica of 65*
In the order of
<intake/compression/extraction/exhaust/overlap/Ica>
Ok
now lets add 8*to the exhaust, to make it a split-pattern, and again install it on split overlap, the events are
270/117/109/278/54 overlap/Ica of 63*
compared to the Single pattern
270/115/115/270/50 overlap/Ica of 65*
You see what happened here? She gained 2 degrees of compression, lost 6* of extraction and gained 4* of overlap. Installed like this, this is a completely different cam!
Lets retime this split-pattern cam, to Ica of 65* like the single-pattern example, the events are;
270/115/111/278/54overlap/Ica of 65*
compared to the Single pattern
270/115/115/270/50 overlap/Ica of 65*
the intake and compression are now the same, but we traded away 4 degrees of extraction to get the additional 4 * of overlap; this being a good trade!
The front end is the same, but the extra overlap is gonna make a difference, with the loss of extraction making no real difference to power-production.
Ok
if that's true, lets tighten up the LSA to 108, which David Vizard says is correct for a 2.02 valved 360; and lets keep the Ica at 65*. This allows plus 2* intake duration so, The events are:
272/115/115/276/58 overlap/Ica of 65*
Compared to the single-pattern
270/115/115/270/50 overlap/Ica of 65*
What happened? For the same compression and extraction; we gained 2* intake duration, gained 6* of exhaust, which together gave us the extra 8* of overlap, which is about the overlap that you would typically expect on a cam at least one size bigger , but the Ica is still 65*, so no loss of low-rpm performance. That extra 8* of overlap is gonna make a lil more power thruout the rpm range, and make a nice lil bump-up over the nose.
Now;
this 272 cam begs to be advanced to better center the overlap. lets change the Ica from 65* to 63*, and the events are;
272/117/113/276/58/Ica of 63 *
compared to the Single-pattern;
270/115/115/270/50/Ica of 65*
oh yeah another good trade, and Ima liking that 272/276/108 split pattern..
jus saying.
Here's what I mean; take your generic hi-po street cam, say something around 270 degrees;
Make it a 270/270/110. Installed at split-overlap, the events are;
270/115/115/270/50 overlap/Ica of 65*
In the order of
<intake/compression/extraction/exhaust/overlap/Ica>
Ok
now lets add 8*to the exhaust, to make it a split-pattern, and again install it on split overlap, the events are
270/117/109/278/54 overlap/Ica of 63*
compared to the Single pattern
270/115/115/270/50 overlap/Ica of 65*
You see what happened here? She gained 2 degrees of compression, lost 6* of extraction and gained 4* of overlap. Installed like this, this is a completely different cam!
Lets retime this split-pattern cam, to Ica of 65* like the single-pattern example, the events are;
270/115/111/278/54overlap/Ica of 65*
compared to the Single pattern
270/115/115/270/50 overlap/Ica of 65*
the intake and compression are now the same, but we traded away 4 degrees of extraction to get the additional 4 * of overlap; this being a good trade!
The front end is the same, but the extra overlap is gonna make a difference, with the loss of extraction making no real difference to power-production.
Ok
if that's true, lets tighten up the LSA to 108, which David Vizard says is correct for a 2.02 valved 360; and lets keep the Ica at 65*. This allows plus 2* intake duration so, The events are:
272/115/115/276/58 overlap/Ica of 65*
Compared to the single-pattern
270/115/115/270/50 overlap/Ica of 65*
What happened? For the same compression and extraction; we gained 2* intake duration, gained 6* of exhaust, which together gave us the extra 8* of overlap, which is about the overlap that you would typically expect on a cam at least one size bigger , but the Ica is still 65*, so no loss of low-rpm performance. That extra 8* of overlap is gonna make a lil more power thruout the rpm range, and make a nice lil bump-up over the nose.
Now;
this 272 cam begs to be advanced to better center the overlap. lets change the Ica from 65* to 63*, and the events are;
272/117/113/276/58/Ica of 63 *
compared to the Single-pattern;
270/115/115/270/50/Ica of 65*
oh yeah another good trade, and Ima liking that 272/276/108 split pattern..
jus saying.
Last edited:
What is being seen & done a lot in recent years [ but rarely seen 20+ yrs ago ] is lower ratio rockers used on the exh. Allows the effective exh duration & lift to be reduced on a dual pattern shelf grind.
-
