yellow rose
Overnight Sensation
It was great humor. Too many guys around here take this **** way too literal.
See what I did there.
Camshafts, idle quality, driveability and LSA-REAL WORLD EXP and OPINION
- Thread starter RAMM
- Start date
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It was great humor. Too many guys around here take this **** way too literal.
See what I did there.
yellow rose
Overnight Sensation
Sorry, it was IQ52 that posted the links, not roccodart.
My bad.
My bad.
yellow rose
Overnight Sensation
Did anyone read the Austrialian Crane cam article?
They say in the text that the intake closing is what is affecting idle.
Didn't I say that? Damn, I need to print that thing off and look it over very close.
Just like I have said, the correct LSA will NOT affect the idle as much of the rest of the parameters are correct. It's all about intake closing.
And just like I've said, guys are pissing away a bunch of horsepower and torque right where we all want it.....MID RANGE.
They say in the text that the intake closing is what is affecting idle.
Didn't I say that? Damn, I need to print that thing off and look it over very close.
Just like I have said, the correct LSA will NOT affect the idle as much of the rest of the parameters are correct. It's all about intake closing.
And just like I've said, guys are pissing away a bunch of horsepower and torque right where we all want it.....MID RANGE.
mopowers
Well-Known Member
LOL Yeah right.
yellow rose
Overnight Sensation
We'll see.
The article that IW52 posted actually verify X what I have been saying the whole time. I don't like the article because of the way it's written, and how they didn't give all the info they should have, but in the end, it shows exactly what I'm saying. It's even in the text of the
article.
It's simple really.
RAMM
Well-Known Member
So we can ignore the overlap period altogether? Idle vacuum is all about how long (duration) and how high (lift) BOTH the intake and exhaust valves are open. This is viewed on a cam graph as the overlap triangle. The overlap triangles area (how large or small it winds up) is a by product of the LSA and what determines idle characteristics of that cam to a very large degree--even more so than duration, IME. J.Rob
RAMM
Well-Known Member
YR maybe I'm posing the wrong question. Would you explain what causes a rough idle ? J.Rob
yellow rose
Overnight Sensation
Intake valve closing has a bigger affect on idle than does LSA.
If you read the article that IQ posted it says that right in the text.
As I said, the article has faults, such as using a 104 LSA on those heads. If I was shopping for a cam and someone spec'd that LSA, especially with a split duration, they'd have some serious explaining to do.
That engine with a 107-108 LSA and a single pattern cam would have whooped all comers, had a better idle than the 104 and just as much or more big end HP than all the others.
Again, it's about the combo, not just LSA.
Read the article. Closely. You find it supports my points to a fault.
yellow rose
Overnight Sensation
BTW, overlap is critical. Never said it wasn't. There is so much bullshit being posted, like moving the LSA by moving the exhaust lobe. Who does that, and why?
Does anyone change the ICL and test that? I have. It show exactly what I say it does. Advancing the cam closes the intake earlier, thus, increases low speed power and increases idle vacuum.
RAMM
Well-Known Member
I've tested advancing the ICL many times in an effort to build score for the EMC--guess what? It shifts power curve down and lops it off at the top--predictable-big deal. It doesn't help idle vac that much either, ever record it after moving the ICL? It also doesn't build score in case like EMC if you get cylinder pressure too high either but I'm not getting into that here. J.Rob
RAMM
Well-Known Member
Im kinda surprised that no one has really mentioned the driveability aspect and how LSA effects it--not even me and its in the thread title--LOL. B3Re has touched on it a bit--Tight LSA's lend themselves well to power delivery that hits like a sledgehammer and while impressive is not always satisfying or the fastest way from A - B (traction). Tight LSA's are total crap at part throttle or just off idle. Tight LSA's are a nightmare with stock converters and highway geared rear ends. Tight LSA's on the street require a hot plug in order to burn off all the crap the builds up on them too but you can run into pre-ignition and detonation due to the higher than normal cylinder pressure @ and below peak torque. Look I build a few circle track deals and tight LSA's are employed here and its almost the tighter the better too. They have their place just not in my street car. J.Rob
I'll throw in my 2 cents of personal experience between two cams I've ran with a similar LSA but very different intake closing events and overlap. Original cam was a solid flat tappet mid 500's lift, mid 250's duration @ .050, and 107 LSA. The cam was made to "pump up the cylinders" so to speak (over 225 psi cranking pressure). With a Holley 950 HP carb, idle quality didn't seem to be an issue at all. Rebuilt the engine with a mid 600's lift, 266/273 @ .050, and 106 LSA solid roller. This cam was custom ground to bleed off cylinder pressure to get the DCR down to run 91 octane and it cranks 150 psi. When I changed to this cam, the idle quality went to hell. I spent hours and hours drilling and tapping holes in the metering blocks, changing the diameter of the emulsion holes, PVCR's, idle air bleeds, etc etc until it wasn't running extremely fat/lean all the time and idle was tolerable. I've finally got it to where I don't have to double foot the brake and gas at the same time at a stop light (this is my street car after all). Part of that was float level being too high, but that was only an issue when braking hard and fuel coming over the vent tube and flooding it. But anyhow, it does seem to me that after reading what some have stated here and seeing the difference in these two cams, that the intake closing/overlap event probably does have more impact on idle quality than the LSA does.
RAMM
Well-Known Member
So you went a single degree tighter on the LSA and added over 10 degrees @ .050" and in the process dropping 75 psi cranking and winding up @ 150 psi and you were surprised that idle was so much poorer? Not surprising in the least.To sum up--You had a big cam on a tight LSA and then you installed a much bigger cam on an even tighter LSA and you witnessed a much poorer idle? You don't say? You are obviously an astute tuner and a cam with a tight LSA is probably right up your alley anyways. The intake valve closing is important for sure but what it AND the exhaust are doing at the same time is more important-at least in my observations. J.Rob
Never said I was surprised. I just flat out didn't know what to expect being a novice to hot rodding. This car is my first muscle car, the first time I had ever had an engine rebuilt, first time tuning a carb the way I did, well first everything really. I had a steep learning curve and knowing what I do now, the outcome doesn't surprise me looking back. If I had the chance in the future, I'd tweak the cam to have better idle characteristics. But other than that, the car runs like I want it to. Seems like the more I try to learn, the less I feel like I actually know!
Silly?... Only if you keep assuming things.
I know, you have repeated all about the events, functions and LSA and all this, that, and the other in multiple threads. I've stayed out of all the arguements. I haven't needed help in picking a cam in 20+ years. I picked that question because of a private PM I received from another member. That's ok, isn't it? Or did I break a forum rule.... RAMM
Well-Known Member
I have a build planned this winter for my autocross/roadrace themed , D150 Shorty. Currently building a 371 inch, 11.0 comp, Eagle steel crank, Scat I-beam rods, Icon Flat-tops ,BigMouth RPM's, SuperVic intake, and solid flat tappet cam. I don't trust solid rollers in an engine that I plan to put thousands of km's on per season-hence the solid flat tappet. As a sole result of this thread I have had an idea: In 2015 I ordered a pretty aggressive flat tappet cam from Comp for EMC 2015 use--It featured lobes that I don't fully remember now but it was something like 251/255@ .050" on a 104 LSA .600" with a 1.6 rocker , fully nitrided. Now because I have that cam already and will likely never use it or sell it --why don't I at least try it? Here is what I propose if anyone really cares- Since I know I would hate that cam the way I intend to use my vehicle, I will get a custom cam ground on the exact same lobes except I will specify a much wider LSA , something like a 113-115. Testing would be cranking comp, full dyno testing, and idle vac @ a common RPM. I should also state that I want and fully intend for this engine to be a 7000+rpm piece, preferably with a peak HP @ 6900-7000 and power that hangs on 'till 7400-7500 rpm.
This is the rotating assembly to be used in a different 360 block with the only difference being lifter bore bushings for better oil control.J.Rob 360 Street/Strip Bruiser-Dyno results
This is the rotating assembly to be used in a different 360 block with the only difference being lifter bore bushings for better oil control.J.Rob 360 Street/Strip Bruiser-Dyno results
Those two cams are apples to oranges regardless of the similar LSA's. I can clearly see which one is going to idle like a truck!
RAMM
Well-Known Member
This is why I like discussions like these. You have said a mouthful with this sentence. I'm not saying you can isolate LSA from duration. I'm saying when choosing an engine's "personality" I do consider LSA before duration. I could choose valve timing events based on what I know works for BALLS to the WALLS power but when you give LSA some serious thought then your perspective on RAW duration changes and things become a little clearer--at least the way I now see things. I consider duration and LSA somewhat interchangeable and know how to take some from here and stack a little over there to get what I want. Setting the events where you want and letting the chips fall where they may is a good way to the utmost in power potential but leaves so much more lacking-:refer to the title of this thread as to what will be lacking. J.Rob
If you can pick cam from its opening and closing points and use that to guide your lsa and duration picks I would imagine that's probably the ultimate way if you have the knowledge and experience. I would have no clue that way.
For the average guy most can pick duration and lift for the basic application and since most cams are ground on a few lsa it's a pretty simple affair. That's as far as I go into help picking when asked. For myself Id pick a range for lift and overlap and plug many different cams as can that fall into those criteria into my dyno software and use it to narrow my decision.
For the average guy most can pick duration and lift for the basic application and since most cams are ground on a few lsa it's a pretty simple affair. That's as far as I go into help picking when asked. For myself Id pick a range for lift and overlap and plug many different cams as can that fall into those criteria into my dyno software and use it to narrow my decision.
mopowers
Well-Known Member
I'm just glad I'm not the only one who feels this way. These camshaft know-it-alls sure make me feel good about leaving my camshaft decisions to a professional.
RAMM
Well-Known Member
What is actually scary is I still feel the same way! When I finally think I have a solid handle on something--Wham! An example comes along and turns almost everything I know on its head. Back to square 1. J.Rob
Many of
Don't over engineer. Most of us just want more performance but we don't care if it puts out maximum horsepower for the size of engine. Many times we have to work with what components we have. (Intake, heads, compression, etc. How many here have built too much and it's not fun to drive. Maximum power isn't always the best.
RAMM
Well-Known Member
I should be more clear. Cams: LSA trumps duration when considering things like vacuum- vacuum equals = part throttle tip in, mileage, ease of tuning, part throttle torque under peak torque, and a much wider and user friendly power band.
Also again:Increasing LSA has a much greater impact than reducing duration in order to achieve a certain idle/power curve/drivability.
Corollary : Narrow LSA will negatively impact idle vacuum, narrow/abrupt power curve and make driveability/tuning difficult--To a MUCH GREATER DEGREE than a wider LSA will.
Look all of this is in countless publications and all over the place. All I am saying is what I said in post #1----Cam 2 cam and duration 2 duration the cam with the wider LSA will be the better choice for the street bound crowd. Also given the choice I would prefer to widen the LSA than reduce duration to target a given HP goal AND retain any kind of manners. J.Rob
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