Very true.Yeah if I wanted peak power I would have put in a roller cam to start. Its a slippery slope as they say
Does this prove David Vizard's 128 lsa formula ?
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I'm sure it's a valid formula, in application, and certainly better than just guessing. I'd use it in a heartbeat to select a cam. I certainly don't have anything better to use and I wont purchase several cams in the pursuit of perfection. I think for most guys we just need it to be as close to "right" as possible, out of the gate. We're not gonna be swapping around a bunch of cams to test. So in that way, it probably works well.
All that said. I think it's far more a correlation, than a real explanation of some underlying principles at work.
All that said. I think it's far more a correlation, than a real explanation of some underlying principles at work.
I'm not saying that there's zero merit to it, I'd probably at least see what the formula say when shopping for cams.
This is what I'm thinking.
The point I was trying to make in the dudes video the dyno examples he gives as proof to me doesn't accomplish that, each dyno test basically shows that every few degrees you go narrower you gain a reasonable amount of torque even as you go pass DV's recommendation you still gain.
The formula has merit but it's just a guideline. Closer using it than ordering a cam because it sounds good. But, but, on the street that might be just what the guy wants.
I think the part that most miss, the part I like the most, is you supposed to subtract duration to keep overlap, eg.. Say your gonna go with a 286* on 114 but instead go 274* on 108 both should have similar overlap Idle etc.. The 274* 108 should have better bottom and mid range torque while I guess same overlap suppose keeps similar top end.
WHERE in the formula does it include duration? Or anything else for that matter?
Your suppose to calculate lsa, pick an overlap and calculate duration from the two. But other then a chart he really don't give much on how to pick the right overlap.
The way I see to use it, pick a cam like you normally would and then translate it to his formula, Say a 2.02 360 9:1 and gonna use a 340 cam, the formula says about a 106* lsa, so every 1* degree tighter is 2* less duration, so 114 to 106 = 8* so 16 less degrees of duration so 252/256 on 106 instead of 268/272 on 114.
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Yeah and that in and of itself disproves his theory right there. How many big block cars have been outrun by STONE STOCK 340 cars? A frikkin lot. So that tells me those 340s worked pretty dang well just like they were. ....and here comes the "yeah but they couldda been better" crowd. Horse ****. They were great like they were.
junkyardhero
Well-Known Member
exactly. i just ring 'em up and say: "gimme a 3/4" race cam" and call it done.
having raced my stock 340 on chit tires and the chit stock carb@80k miles 3.23 727 14.3@97 plus mph
the comp 218@50 454 lift 110 in106 much better then the stock cam better low mid high rpm no question
the 340 cam on a 110 would have been great
The reason they sucked the paint off good big blocks was a chit driver and traction
ho hum big blocks didnt stand a chance 396/325 396/350 390/335 383/335 400/350
350/350 327/300 289/271 330/310 350/325 302/290 etc
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Absolutely!
1978 Crane cams catalogue, SB Chev. Has 26 flat tappet grinds listed, hyd & mech. 8 are 108 LSA or tighter.
Fast fwd to the 2010 catalogue, which was after DV did the cam testing for Crane.
73 flat tappet grinds, hyd & mech. 32 were 108 LSA or less.
[1] Used SBC because there are more grinds gives a better numbers spread.
[2] The above cams do NOT include oval track grinds which are often on tighter LSAs.
[3] The numbers speak for themselves.....
Fast fwd to the 2010 catalogue, which was after DV did the cam testing for Crane.
73 flat tappet grinds, hyd & mech. 32 were 108 LSA or less.
[1] Used SBC because there are more grinds gives a better numbers spread.
[2] The above cams do NOT include oval track grinds which are often on tighter LSAs.
[3] The numbers speak for themselves.....
Everyone seems to miss the whole point of this thread, it seem most peoples responses are based on how they feel about DV, not the dyno results in the guys video I posted, doesn't seem like anyone has look at them.
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But if you go by DV when you go tighter lsa you also go with less duration which keeps the same overlap which should have similar idle driveability etc..
My take away that DV main point is, instead of sacrificing lsa for duration, sacrifice duration for lsa.
yes sir.
He takes exhaust valve size for calculating primary header tube.
DV never said a narrow LSA is better! You have to choose the right LSA for your engine combo!
My 493 cui with 2.14 intake valve (undervalved) needs a LSA in somewhere 100°, a 340 with 2.02 valves in the 110.
DV is also a detail freak. We all think why should i do a mod for 7 hp? If you are thinking 10 times that way, you lost 70 hp!
Which single mod gives you 70 hp for free?
DV never said a narrow LSA is better! You have to choose the right LSA for your engine combo!
My 493 cui with 2.14 intake valve (undervalved) needs a LSA in somewhere 100°, a 340 with 2.02 valves in the 110.
DV is also a detail freak. We all think why should i do a mod for 7 hp? If you are thinking 10 times that way, you lost 70 hp!
Which single mod gives you 70 hp for free?
True but most would generally calculate what most would consider tight lsa, A small displacement with big valves and high cr would have a fairly wide lsa. EG. a 13.5:1 289 with 2.08 valves = 115* lsa and even that's not that crazily wide.
273,
I am not missing any point....& most others aren't either. DV claims that cams sold by cam companies are generally too wide with LSA....because the cam company wants to save the hotrodder from him/her self, so they widen the LSA. DV says the correct way to moderate the function of the cam is to reduce duration.....not widen the LSA because power will be reduced; he has dyno tests in his books. How many dyno tests does he have to do?
Richard Holdener did a LSA comparison on a 5.3L LS engine [ three cams, identical except for LSA ]. The tight LSA cam made more average hp everywhere & IIRC, it actually made a little more at peak hp. So modern engines also like tight LSA. Maybe someone can link it.
Every test I have seen shows tight LSA is better. The late Joe Sherman was quoted as saying 'The tighter I went [ with LSA ], the more power I made '.
Here is yet another LSA test. Long before the 128 rule was known. Three big duration cams in a 350 Chev. Isky cams identical except for LSA: 106, 108, 110.
The 110 made 3 peak hp more than the other two : 583 [110 ], 578 [ 108 ], 580 [ 106 ]. The 106 made peak HP 500 rpm earlier. Average tq through to 7000: 106 was highest, 108 was down 13, 110 was down 23. In percentage terms, the 110 was down 5% on the 106 in average tq.
Much to much criticism of the 128 rule. It was created so that hot rodders didn't have to guess LSA. DV wants you to buy his software program, which gives more accurate results. 128 was a freebie...
I am not missing any point....& most others aren't either. DV claims that cams sold by cam companies are generally too wide with LSA....because the cam company wants to save the hotrodder from him/her self, so they widen the LSA. DV says the correct way to moderate the function of the cam is to reduce duration.....not widen the LSA because power will be reduced; he has dyno tests in his books. How many dyno tests does he have to do?
Richard Holdener did a LSA comparison on a 5.3L LS engine [ three cams, identical except for LSA ]. The tight LSA cam made more average hp everywhere & IIRC, it actually made a little more at peak hp. So modern engines also like tight LSA. Maybe someone can link it.
Every test I have seen shows tight LSA is better. The late Joe Sherman was quoted as saying 'The tighter I went [ with LSA ], the more power I made '.
Here is yet another LSA test. Long before the 128 rule was known. Three big duration cams in a 350 Chev. Isky cams identical except for LSA: 106, 108, 110.
The 110 made 3 peak hp more than the other two : 583 [110 ], 578 [ 108 ], 580 [ 106 ]. The 106 made peak HP 500 rpm earlier. Average tq through to 7000: 106 was highest, 108 was down 13, 110 was down 23. In percentage terms, the 110 was down 5% on the 106 in average tq.
Much to much criticism of the 128 rule. It was created so that hot rodders didn't have to guess LSA. DV wants you to buy his software program, which gives more accurate results. 128 was a freebie...
I tend to agree with that statement.
Are they available to us ?
It's one of the dyno results the guy uses, no one is arguing with that going tighter generally makes more mid range torque that's common knowledge, the question is does the formula get you optimal lsa and does this optimal lsa gain you 40-50 lbs-ft and get you near the 1.40 lbs-ft DV claims over the 110-114 most cams are ground on? What was the gain of this eg., like 10 lbs-ft or so 108 vs 112 most would be glad to lose 10 for driveability.
No one arguing that, like saying does more duration tend to make more hp, question is does running tighter lsa then the formula recommends are you still gaining torque? And in the eg.. The guy shows seems you will, if that is true how's the formula recommendation optimal ?
Which is the whole bases of me posting this.
Just like everyone would expect, the question isn't does tighter lsa give more torque, it's does the formula give optimal lsa and more important match the claims of being up there choosing cams like 1% of engine builders.
Like said before you could probably do worse than using the formula as a guide line.
And I like the basic idea of tighter lsa less duration for same type cam as you would normally pick.
And these aren't setup as a real test, to do that 1st you'd have to run recommended cam and a bunch of cams on either side of the lsa while keeping overlap the same, maybe in that scenario we'll se the 40-50+ gains for 1% builder type torque. But what evidence I've seen so far I'm a bit doubtful, so until then I'll take it with a grain of salt.
And the main problem with his formula is picking overlap which the next main step so you can figure out duration.
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