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Discussion Starter · #1 ·
What is the difference in performance between a stock LT1 with 1.6 to 1 rockers, and the same setup with an LT4 cam with 1.5 to 1 rockers? Can the LT4 cam be used with 1.6 to 1 rockers?
 

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Discussion Starter · #2 ·
Found a sticky with most of the info that I need.
 

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Discussion Starter · #4 ·
LT1 camshaft/valve train selection guide
 

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Discussion Starter · #6 ·
I am installing it in another engine and need basic information about the valve train. I may even use a different cam.
 

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I downloaded some catalogs from Vizard's website yesterday that had the part numbers for some Lunati cams he designed. Lunati currently doesn't have any of them listed on their website, although the 2nd gen LT1 cams they do list use the exact same lobes. I'm guessing his cam designs were too radical for most hotrodders and didn't sell well. I bet Lunati could grind one custom for you if you asked, though. I wish he had some designs for LS motors, I'd sure love to see what kind of difference they made.
 

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I am looking for a streetable cam with a reasonable amount of power.
 

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I am looking for a streetable cam with a reasonable amount of power.
One thing everyone notes about Vizard's cams is how well they idle. Even the radical ones will usually idle below 900 rpm, and the tame ones around 450 rpm. The key is he lists the minimum compression ratio needed for each cam.
 

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*FYI: Vizard uses the term LCA (Lobe Centerline Angle) to identify what most of us know as LSA (Lobe Separation Angle). So in the formula below, he's not talking about the intake centerline. He's talking about the overall LSA.

Vizard has a strange way of calculating the cam specs. "Strange" in that the required duration is a derivative of other factors, rather than the seat of the pants guess we usually make when trying to optimize street manners vs. performance. If you guys look at the cam catalog I posted above, he specs different cams not only based on compression ratio but also displacement. Going on the interwebs shows why: He has a formula to calculate the LCA (Lobe Centerline Angle) that uses engine displacement as one of the variables. The optimum LCA for a smallblock chevy can be calculated as:

Purple Sky Font Violet Magenta


Vizard claims this can result in torque outputs of as much as 1.4 ft/lbs per cubic inch. So, for a 2nd gen LT1, that works out to:
128-(350/8/1.94*0.91) = 107.5 LCA (LSA). Are you starting to see why people have such a hard time accepting his claims? (LOL)

Next, you need to determine where in the rpm band you want that torque to occur:

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10-1. This chart shows a typical spread of overlap for various applications. The middle of each range represents the amount for a typical two-valve engine having 21.6 ci of cylinder displacement for each inch diameter of intake valve. This puts multi-valve engines at the lower overlap of each range and big-displacement under-valved engines at the bigger overlap values of each range.

1) is for street towing
2) is regular street
3) is street performance
4) is street-strip
5) is race
6) is full race
*Note that these numbers are at .006" lift

So assuming we want something mainly for the street, the amount of overlap is 50-75 degrees, so pick 60 degrees overlap. I got lazy and just used the Wallace Racing cam overlap calculator to figure out the required duration. The answer is a 276 degree lobe. At 0.050", that means the 218/218 cam on the catalog page at 108 LSA. I note that Vizard specs it at 4 degrees advance. this is identical to what most cams are ground to.

This also explains why so many modern cams have split durations. Since most modern cams don't run that tight of an LSA, in order to get the required amount of overlap, they have to run more duration on the exhaust.

Now, how to test that? I went back to Lunati's website and clicked on their 2nd gen LT1/LT4 page. I found the cam that uses the 276 intake lobe. It happens to be the first cam on the page. Its specs are listed as 218/228 at 112 LSA at 0.050". Hey, whaddaya know, Lunati has their own version of the LT4 HOT cam. But check it out. The specs at 0.006" are 276/286 at 112 LSA. Going back to the Wallace Racing calculator, that works out to 57 degrees of overlap. Bingo. Now we know why they run more duration on the exhaust on so many cams. It's so they can get the correct amount of overlap.

So, according to Vizard, if you feel like the LT4 HOT cam is the cam for you, by going with Vizard's 218/218 @108 LSA version of the cam, it can net you as much as 20 ft/lbs over the regular HOT cam while actually running LESS duration.

Camshaft Overlap Calculator - Wallace Racing
Chevrolet Small Block LT1 and LT4 (1987 - Up) - Chevrolet/GM - Camshafts & Kits - Products

It apparently works on LS engines as well:

There are plenty of guys out there running the LT4 HOT cam. I'd LOVE to see how this cam stacks up against it, assuming the other mods are the same.
 
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Incidentally, if Vizard's claim of 1.4 ft/lbs per ci is anywhere near true, that means an optimized engine running one of his cams would see something like 490 ft/lbs at the crank. Knock off 20% for rear wheel dyno, that still comes out to over 400 ft/lbs at the rear wheels.
 

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Some thing I note watching every Engine Masters episode. Only the big block mopar with a 107 made something just over 1.3. All their other motors with wider LSAs are in the 1.2 ranges.
 

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I remember people running the 218/218 Lingenfelter cam in mildly ported LT1 AL head 350's in our tanks. Did pretty good at the track and idle was very close to stock

I had a Comp custom grind 214/220 on a 112 LSA with LT1 AL heads with 2.02/1.60 heads using 1:6 RR with Comp 987 springs that made 350 RWHP/351RWTQ in my otherwise stock bottom end

smaller cams car really rock
 

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Yep. And note for the Lunati cams there's a note it's for 2.02 - 2.08 valves. 1.94's would want a touch less separation. Like pick a displacement one level bigger.
Yeah, using his formula it came out to 107.5 LSA.
 

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I tried this formula on my 07 vette. 408 ci LS2 with 6 lbs of boost. Wasn't sure how to calculate boost, so I just multiplied the intake valve diameter times the boost over atmospheric: 2.00x(6+14.7)/14.7 = 2.82
128-(408/8/2.82x0.91)= 111 LSA.

A lot of LS catalog cams are on a 112 LSA, meaning I could probably use one of those. I'd like to hear what Vizard's take on how boost affects this formula. And what the constant is for LS engines.

I messaged Vizard on Facebook, maybe he'll answer. If he does, I'll spec a cam and install it in my vette.
 

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The theory works on LS engines like the video implies. I just wonder if the formula is exactly the same. Or do you just adjust for the better heads. Better heads need wider LSA. For SBF, he uses 127 and for big block chevy's i recall 132 being the number. But they all work out to about same tight LSA. Which books do you have? In his Camshaft and Valvetrain book, he goes over the how boost, supercharger and turbo and even nitrous how it would affect the cam selection. Worth getting if you don't have that one.
 
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