Does this prove David Vizard's 128 lsa formula ?
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Newbomb Turk
Well-Known Member
I disagree. You’re plenty smart enough and with a good scientific notation calculator you can easily do it. I can’t do it without a calculator.
And there is math for about every damn thing you can think of and then some.
Once you figure your at .050 intake timing number, you use that to get your LSA, ICL and exhaust duration.
Plus, understanding the SEVEN (not 4 or 5) process model is a real eye opener.
I keep my copy right here by my chair. And the sub title is “Race Engines Optimized Through Hardcore Math”.
If that doesn’t get you sporting wood, you may want to check your pulse.
BTW, I do not believe the math is just for hardcore racing engines. I’ve used the math successfully for several street only cams and several street/strip cams.
Their even asking for less efficiency to go from stock less than 1 tq per cid to just over 1 not a huge askAnd that's where I thought these threads started out. (most any way) "I want a little more oomph from my Teen"
I just mean at my current level of understanding, I'm always looking to understand better, why I annoy people with these threads
and I like math.
Exactly! Like putting some parts together for a 300 horse 318. Such a nice engine for a cruiser type car. Built right and geared right it will be plenty snappy and still get decent mileage out on the highway. Most people would be happy with that.Their even asking for less efficiency to go from stock less than 1 tq per cid to just over 1 not a huge ask
Now you have at least twice that.
and so do I
o o o o. Find and post that.
I think it pays to be sceptical.
Someone asked for a DV story. I loved his early books, used his muffler testing and guidlines, and looked forward to his somewhat occassional posts on ST. Now I've posted this before so this the short version. I followed the recommendations in his books to improve my carb like the Carb Shop did for him. Carb Shop had closed so sent it to Quick Fuel (when they were just transitioning from modifying into making carbs). $400 and many months later I began my journey. It cost me a lot more money and time to understand better why things worked and didn't work. Without Shrinker, Tuner and Gregory and lot of time and data collection (and dyno pulls) that carb would be a door stop.
Does anyone ever regret a tigher LSA? Well I did. Went 108 instead of 110 and didn't do what I needed it to do. Again a learning and was able to crutch it with the v-max lifters but they have their drawbacks too - especially for what I wanted.
Well said Mike.
There was a post asking about starting points. Another early lesson for me was to know something about the intake flow and lift. While there are reasons to exceed the lift where there is max flow, that's not what I want to do (again) on an engine for my purposes. So that, and the rules of what I compete in (or think I'll be competing in) are starting points for me. Another critical starting point for me is the actual compression. We have some room here, but without actually measuring the volume its a WAG. I will never do that again!
I like the idea of reviewing the closest options for the effect dynamic compression. And one of those has to be a baseline. A real baseline that you personally are familiar with. Not a problem for the people posting in this thread but a big one for first builds.
I also like the idea of looking at the cylinder capture and will prefer a cam that works with the rod ratio of the engine.
So there's my 2 cents on that subject from someone who uses the dragstrip mostly as a means not an end, and in no way is an engine builder. Just a guy that doesn't want to get burned again.
My point was that in those dynos each degree of lsa was only worth about 3lbs-ft on average from 114-101, you'd have to be 10-17 degrees of lsa off to be losing the 30-50lbs-ft that DV implies and looks if you went tighter then recommend you'll still be gain.
Now I know those test are far from universal and not really setup to prove or disprove DV, my point is that the dude was using them as evidence and to me showed doubt, that's all the point I was trying to make.
Here ya go mattox
BTW.. i'm just being a dick... Andy only had like a year to setup his truck and it wasn't there yet...
and how many, how many, just how many times here do we try to tell folks that the build is just the begining. Most of the time? All of the time? the secret to good performance, never mind maximum performance is in tuning - tuning for performance.
Cost em 5k also..
It is a badass motor if you haven't seen it though.. 427 windsor with hammerhead hemi boss type heads and a tunnel ram.. crazy money but cool as hell
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That's really the dead give away isn't. When it doesn't work can they explain the whys and how's? DV is just scratching the surface.
Imagine being able to say this:
We’ve worked many a program where we used a record holding engine as a base line. In every instance, when the "soft" counterpart was tested, we’d gain perhaps only 8-10% more usable power, but the recovery time and acceleration rates were in a league all their own. As one would expect, the specific fuel consumption was always lower, but in every case the specific airflow requirement for the engine dropped considerably as well. So, now we’re making more power with the same displacement at the same or hopefully lower rpm ranges, and the engine’s consuming both less air and fuel. This not only verifies the fact that we’re achieving greater combustion efficiency, but the airflow relative to power notions that most believe in are no longer applicable
There's levels to this and DV's not very high up the chain in my view.
Just like driving,....folks keep dickin' with the next great thing & keep changing/upsetting the car, never getting anywhere. If They just stop, get what They have dialed in, & take the time to learn drive the damn thing....They'd be shocked at just how fast They are already....
More exh with more cubic inches, 1.600" exh valve. Yes true, but there is also more pressure in the cyl to 'push out' the exh gas.
Cams for turbo engines often have less exh duration, yet make more HP than a NA engine, so more exh gas to be removed.
Cams for turbo engines often have less exh duration, yet make more HP than a NA engine, so more exh gas to be removed.
Newbomb Turk
Well-Known Member
NA you will kill power and RPM and not adding exhaust duration. Already proved that more than once.
And I'm not talking abut 4 degrees like Comp loves. I'm talking 12-15 degrees more exhaust timing. Making the engine pump out remaining exhaust gases is a sure fire way to kill RPM and lose power. Pumping losses are real.
Dale Davies
Well-Known Member
What the 128 formula does is simplify cylinder volumn and port flow calculations. Canted valve and hemi heads require a wider LSA due to flows. SBF engines with factory heads use 127. Good seat forms and fast off the seat valvetrains increase LSA due to increased low lift flow.
DV also states final LSA for a race engine shouldbe tested on a dyno using a number of LSA cams to zero in on what works best with the build combination.
For canted and hemi think it more to how effective air travels through the head, in and out, intake and exhaust then port flow. Apparently max effort wedges are efficient to around 9,500 rpms and hemi 12,000+ rpms and canted are in between depending on the angle.
Dale Davies
Well-Known Member
If the formula recommends a 108°LSA, DV states there will be more loss using a 110°LSA cam than a 106°LSA cam. This is a base to start. High compression over 10.5:1 dictates an increase of 0.75° per compression point increase. So going from a 10.5CR to 13:1 would be 0.75 × 2.5 = 1.875° increase in LSA. Quick off the seat and high flow at low lift dictates more LSA. You need to watch Richard Holdner's video dynoing 4 LS cams. The tighter LSA cam beat the others across the whole RPM range tested. Get and read DV's book, How to Build Horsepower.
Dale Davies
Well-Known Member
Yes. But it is seat diameter that the calculation uses. Thus intake valve head diameter × .91.
Dale Davies
Well-Known Member
Dale Davies
Well-Known Member
Works for Ma Mopar also. SBF use 127. Canted valve such as BBC, Cleveland Fords and the 385 series and the Mopar polysphere use 131 or 132 for base calculatuon.
What makes you think I haven’t, I got them all them or close to it, I’ve read them a ton of times especially his Performance with Economy.
Dale Davies
Well-Known Member
That is the base to start with. Higher CR and greater low lift flow indicates more LSA.
Well in those dynos buddy uses as evidence they gain the tighter you go, from 120 to 101 at an average of 3 lbs-ft per degree, So if your example followed that trend 108 would make about 6 lbs-ft more than 110 and 106 would of made 6 lbs-ft over 108 and 104 would make another 6 lbs-ft, but the gains as they got tighter the gap did shrink but there was gains.
If those held up to lose 30-50lbs-ft + over recommended 108 you'd have to run 118-125 + lsa.
Like I said doesn't necessary disprove maybe cast a doubt but certainly doesn't prove.
Especially when most use a 116 at worse and more like 108-112 and the formula generally recommends 105-110.
Somewhat repeating myself here, but I've spent my dollars on DV and one has to assess both his strengths and his weaknesses of not just his understanding, but in the time and space available for his explanations. There's a reason one gets much more out of an HP Book than an SA Book. There are other things going on but
lets get back to the topic of picking of cams and the role of LSA.
Rod stroke makes a difference because it changes the time the piston will dwell at the top vs bottom of the stoke. The valve openings and closings ought to work with piston dwell and take advantage of it rahter than fight it.
Those are interesting observations regarding reversion and chosing valve closing and opening points from a guy in the trenches involved with everything from motorhomes and commercial trucks to motorsports. Because a guy who focused on combustion and tuning mostly for racing (but also to meet Aussuie emissions rules) explained that same thing although from a slightly different perspective.
Shrinker wrote:
A wide LSA creates high vaccum at idle for sure but it also does other things. I prefer to think of LSA in the old ways of overlap because at least calling out the overlap amount at TDC defines the actual event rather than you having to calculate it. The overlap of the valves allows the exhaust to supply gases to the intake system depending upon the physics of what is happening in the exhaust at the time. I have done tests that indicate that large cam motors actually run on substantial amounts of air inducted through the exhaust backwards into the intake manifold. Decreasing the overlap reduces this and allows better controll of the mixture. Quite a lot of the time the exhaust system functions as a uncontrolled carburetor, in as far as it has combustible gases in it that are drawn into the engine.
...
How this all relates to idling is that the LSA is the un-throttled connection of the inlet to the exhaust. If the exhaust gas is going gang busters and doing all super scavenging stuff and being nice and not blowing up the intake then you can get high manifold vacuum. High manifold vacuum helps you to turn the fuel into a gas before it gets compressed.
Theres not much gas being compressed inside a cylinder when the engine is idling so you dont get much compression energy. An engine wont run at all unless the fuel is turned into gas and its the amount of gas at ignition time that determines the quality of the burn and the quality of the burn is what causes the exhaust to behave properly or be a pain in the butt.
...
Measuring it as LSA is a modern thing that I think confuses the issues of the overlaps effects. Ed Iskendarian got it right when he said its the fifth cycle [overlap]. And thats the best way to understand it, you have to know the ramps and imagine the effects etc. I fully realise that you can have different durations with the same LSA and therefor you get a different overlap.
I was talking in terms of varying the LSA without changing the duration. We were discussing the idle vacuum verses duration which is of course not the most important influence on the vacuum; its predominantly the overlap that affects idle vacuum. As the overlap is an "unthrottled" inlet to the inlet manifold.
LSA is a useless number in my opinion as you have to calculate what the overlap and bottom fills are but its convenient to use for advertising reasons i suppose and its whatever you get used to.
So this is a deeper explanation of why I think LSA can be useful for comparing cams but the valve events for the specific engine should be the main focus. Also very very important is what the engine needs to do. A circle track cam can focus on a narrow rpm range whereas other applications are going to want a much broader power range.
lets get back to the topic of picking of cams and the role of LSA.
Rod stroke makes a difference because it changes the time the piston will dwell at the top vs bottom of the stoke. The valve openings and closings ought to work with piston dwell and take advantage of it rahter than fight it.
Those are interesting observations regarding reversion and chosing valve closing and opening points from a guy in the trenches involved with everything from motorhomes and commercial trucks to motorsports. Because a guy who focused on combustion and tuning mostly for racing (but also to meet Aussuie emissions rules) explained that same thing although from a slightly different perspective.
Shrinker wrote:
A wide LSA creates high vaccum at idle for sure but it also does other things. I prefer to think of LSA in the old ways of overlap because at least calling out the overlap amount at TDC defines the actual event rather than you having to calculate it. The overlap of the valves allows the exhaust to supply gases to the intake system depending upon the physics of what is happening in the exhaust at the time. I have done tests that indicate that large cam motors actually run on substantial amounts of air inducted through the exhaust backwards into the intake manifold. Decreasing the overlap reduces this and allows better controll of the mixture. Quite a lot of the time the exhaust system functions as a uncontrolled carburetor, in as far as it has combustible gases in it that are drawn into the engine.
...
How this all relates to idling is that the LSA is the un-throttled connection of the inlet to the exhaust. If the exhaust gas is going gang busters and doing all super scavenging stuff and being nice and not blowing up the intake then you can get high manifold vacuum. High manifold vacuum helps you to turn the fuel into a gas before it gets compressed.
Theres not much gas being compressed inside a cylinder when the engine is idling so you dont get much compression energy. An engine wont run at all unless the fuel is turned into gas and its the amount of gas at ignition time that determines the quality of the burn and the quality of the burn is what causes the exhaust to behave properly or be a pain in the butt.
...
Measuring it as LSA is a modern thing that I think confuses the issues of the overlaps effects. Ed Iskendarian got it right when he said its the fifth cycle [overlap]. And thats the best way to understand it, you have to know the ramps and imagine the effects etc. I fully realise that you can have different durations with the same LSA and therefor you get a different overlap.
I was talking in terms of varying the LSA without changing the duration. We were discussing the idle vacuum verses duration which is of course not the most important influence on the vacuum; its predominantly the overlap that affects idle vacuum. As the overlap is an "unthrottled" inlet to the inlet manifold.
LSA is a useless number in my opinion as you have to calculate what the overlap and bottom fills are but its convenient to use for advertising reasons i suppose and its whatever you get used to.
So this is a deeper explanation of why I think LSA can be useful for comparing cams but the valve events for the specific engine should be the main focus. Also very very important is what the engine needs to do. A circle track cam can focus on a narrow rpm range whereas other applications are going to want a much broader power range.
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