Does this prove David Vizard's 128 lsa formula ?

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273

273

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The examples he give shows mid torque gains with going with a tighter lsa but was that really even in question ?
But to me the gains aren't large enough to say it proves DV's formula, if anything it disproves it cause to me for the formula to be valid being a few degrees off of calculated lsa in either direction should have huge losses, I'd like to see engines that the formula predicts wider lsa like 114-116 + and run 108 lsa and less against them and see if there's loses or gains, would be a better tests.

 
You are missing the point. DV has a number of sayings, two of which are:
- the right cam costs the same as the wrong cam.
- so why not do some homework & buy the right cam using 128 or derivative.
- as HP goes up from matching all the component parts to work together, changes in ideal LSA, [ & adv/ret the cam ] have a much greater loss of HP than a randomly chosen cam that is not optimised for the combo.
The 128 cam is for parallel valve heads, 9-10.5 CR. For canted valve heads, the number becomes 131.5. In his BBC book, he talks of engines that require wider LSAs, 114-116. And how as CR increases the LSA needs to be wider than the target 9-10.5 CR.
I have three Crane cam catalogues. DV tested 000s of cams for Crane . In the latest catalogue after the testing was done, there was a huge increase in tight LSA cams, 106 & tighter. So Crane must have been happy with the test results to make those changes....
 
Can somebody lay out Vizard's 128 formula so a dumbass can understand it?
 
Bewy said:
You are missing the point. DV has a number of sayings, two of which are:
- the right cam costs the same as the wrong cam.
- so why not do some homework & buy the right cam using 128 or derivative.
- as HP goes up from matching all the component parts to work together, changes in ideal LSA, [ & adv/ret the cam ] have a much greater loss of HP than a randomly chosen cam that is not optimised for the combo.
The 128 cam is for parallel valve heads, 9-10.5 CR. For canted valve heads, the number becomes 131.5. In his BBC book, he talks of engines that require wider LSAs, 114-116. And how as CR increases the LSA needs to be wider than the target 9-10.5 CR.
I have three Crane cam catalogues. DV tested 000s of cams for Crane . In the latest catalogue after the testing was done, there was a huge increase in tight LSA cams, 106 & tighter. So Crane must have been happy with the test results to make those changes....
Click to expand...
My point was say his formula recommends a 108 lsa then 110 and 106 should both should show drastic losses eg.. 30-50+ lbs-ft, what those test showed was fairly minor differences and going tighter then what DV would recommend still gain which pretty much what most would think anyways that tighter gives more midrange.
 
Sure.
Volume of one cyl in cu in. Divide that by the intake valve diam [in inches ]. Multiply the result by 0.91. Subtract that result from 128.
 
RustyRatRod said:
Can somebody lay out Vizard's 128 formula so a dumbass can understand it?
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Displacement / 8 / valve size x .91 then minus that answer from 128

340/8/2.02x.91 = 19.14, 128 - 19.14= 108.85 lsa for a 10.5:1 340 engine for every point of cr different add or subtract .75 lsa so for 9.5:1 340 108.1 lsa or 108
 
273,
DV gives the example of a 496 that has the LSA too wide by 1* & it will lose 10-15 ft/lbs. That would be a 2* change in a 720* cycle. Sounds about right to me. He also says that if the LSA is changed from optimal, the loss will be less if the LSA was tighter v wider....or words to that affect.
 
One Problem with that is it's based valve size so an stock X head and trick flow supposedly both require the same lsa. You could do worse than not following the formula but who didn't already think going 106-110 wasn't gonna give more mid range tq in a 340/360.
 
273 said:
Displacement / 8 / valve size x .91 then minus that answer from 128

340/8/2.02x.91 = 19.14, 128 - 19.14= 108.85 lsa for a 10.5:1 340 engine for every point of cr different add or subtract .75 lsa so for 9.5:1 340 108.1 lsa or 108
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Does the 8 represent number of cylinders?
 
Have you read his book?

That cam spec works for a 350 Chevy with a compression ratio of 9.5/1 to 10.5/1 only.
 
Bewy said:
273,
DV gives the example of a 496 that has the LSA too wide by 1* & it will lose 10-15 ft/lbs. That would be a 2* change in a 720* cycle. Sounds about right to me. He also says that if the LSA is changed from optimal, the loss will be less if the LSA was tighter v wider....or words to that affect.
Click to expand...
To me you need something that requires a wide lsa, like a 13:1 289 with a 2.08 valve, DVs would recommend a 112 then if every degree tighter loss 10-15 tq I be more inclined to believe it. But cause formula kind of recommends for most decent size engines under 110, an lsa range most would generally recommend if you want most out of your engine anyways.
 
273 said:
Now you done it leaving a truck load of tq on the table lol
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Naw, I haven't had it ground yet. The one in the engine in the car now is on a 108 so it's right, just by chance.
 
273 said:
Any Wedge head
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Well, not exactly. My understanding is any inline valve head. A Ford Cleveland closed chamber head for example, is a wedge head, but it is a canted valve head.
 
Bewy said:
273,
DV gives the example of a 496 that has the LSA too wide by 1* & it will lose 10-15 ft/lbs. That would be a 2* change in a 720* cycle. Sounds about right to me. He also says that if the LSA is changed from optimal, the loss will be less if the LSA was tighter v wider....or words to that affect.
Click to expand...
So you don't think a stock X head and a trick head might need different lsa?
 
273 said:
To me you need something that requires a wide lsa, like a 13:1 289 with a 2.08 valve, DVs would recommend a 112 then if every degree tighter loss 10-15 tq I be more inclined to believe it. But cause formula kind of recommends for most decent size engines under 110, an lsa range most would generally recommend if you want most out of your engine anyways.
Click to expand...
Book says add.75 LCA for every point of compression over 10.5/1.
 
You probable could do worse then his formula, but it basically recommends what someone trying to get the most would run anyways, and seen no evidence that being 1-4 wider is a huge loss and tighter seems generally to be a gain and he talks it up as 30-50 tq+ gain by following him, the only gains I've seen like that is when people are wider by 6-12*.

To me it's like this, say I said I came up with a formula for street strip cam duration , and said it was the **** you couldn't do no better then to follow it and it generally recommended cams in the 235-255 range basically what people generally pick for street strip and cause those are the cams people generally want and the performance is obviously generally good then I say see I told ya my formula is the ****, that's what I'm kind of seeing here.
 
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What I wonder is, say you figure the formula based on your combo. Like mine comes out to be 108. Is that what you need set in stone or is that a MAXIMUM or MINIMUM LSA?
 
Oh and when you say "valve size" in the formula, I am assuming INTAKE valve size?
 
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