Camshafts, idle quality, driveability and LSA-REAL WORLD EXP and OPINION

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RAMM

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I didn't want to muddy up the other 340 thread with more camshaft discussion and really felt the need to share some of my experiences in this matter. Why? Maybe its the season or maybe its the Ceasars (Bloody Mary's for my US brethren)?

In my personal observations over the years I have observed the exact opposite concerning Lobe Separation Angle and duration. Warning: Blanket statement imminent.

LSA has a much greater impact on idle quality than duration does--Here's where it gets really good: CID Engine displacement means absolutely nothing! I bought into the whole "displacement eats up duration" BS for years until I kept running into the same scenario over and over and over. I've used the same tight LSA cams in every thing from a 318 to a 416 and guess what? The 416 didn't idle much better than a similar build 318 with the same cam. It really hit home when I had a chance to re-do a couple of 705 cube SuperMerlin Chevs in a Fountain boat. They had 250 @ .050" Comp solid rollers on a 106 and guess what? They idled like total garbage--very low manifold vacuum. I just want to get that out of the way. How come you can compression test a 318 with stock heads and observe 120 psi and then bolt on a set of 300+cfm race heads with the same size chamber and PSI doesn;t read any different? I'd think the mega heads would fill the cylinders better and show more cranking compression. Shouldn't they? They don't and I think I know why. I believe piston speed below about 3000 rpm just doesn't mean much.

A respected Mopar mag editor and I had this discussion a few years ago and I was the first to say---"I believe LSA has MORE to do with idle quality than duration does" He was in complete agreement and still is as far as I know.

Bottom line--tight LSA equals lumpy idle, wide LSA equals smoother idle. given same family of cam lobes.

J.Rob
 
Really?

From what I've done, LSA has very little effect on idle. It's the intake closing that causes low speed issues.

If the intake valve is still open, and the port can't overcome the upward movement of the piston, you get reversion. That reversion is where you get the dead rich idle you can't clean up.

Ever check the speed of the air at low lifts? If so, you know that at low lifts, the equal flow bench depression can be 120 inches or more.

Now, if you want me to believe you have an over scavenge condition at overlap, I can discuss that. Again, this is why you have to pay attention to things OTHER that maxing out low lift flow. I know David Vizard would disagree with me, but we agree more than not.

You can kill more things with ridiculous low lift flow numbers than almost anything else. I mean, do you use a radius valve job on the intake valve? I promise the correct radius valve job will outflow a valve job with angles every day of the week and six times on Sunday. But it will be down on power. Why?


One more thought. Back in the day, I was dealing with a customer with stage 6 heads. Someone else worked on them and the car was a pig. The first thing I noticed was the intake bowl was contaminated with exhaust. Hmmmmmm.


LSA is the RESULT of cam timing events. As I have said more times that I care to type, you can alter the LSA a bit AFTER the correct timing is set. The other thing is INTAKE CENTER LINE. You can install a cam 4,6,8 degrees advanced and change the intake valve closing. This will alter the idle and vacuum. The concept is not difficult unless Comp has brainwashed your mind.
 
I keep it simple. I never pick a camshaft based on how I think it will idle. I pick camshafts based on how I believe they will run, given a particular combination and let the rest fall where it may.
 
yellow rose said:
Really?

From what I've done, LSA has very little effect on idle. It's the intake closing that causes low speed issues.

If the intake valve is still open, and the port can't overcome the upward movement of the piston, you get reversion. That reversion is where you get the dead rich idle you can't clean up.

Ever check the speed of the air at low lifts? If so, you know that at low lifts, the equal flow bench depression can be 120 inches or more.

Now, if you want me to believe you have an over scavenge condition at overlap, I can discuss that. Again, this is why you have to pay attention to things OTHER that maxing out low lift flow. I know David Vizard would disagree with me, but we agree more than not.

You can kill more things with ridiculous low lift flow numbers than almost anything else. I mean, do you use a radius valve job on the intake valve? I promise the correct radius valve job will outflow a valve job with angles every day of the week and six times on Sunday. But it will be down on power. Why?


One more thought. Back in the day, I was dealing with a customer with stage 6 heads. Someone else worked on them and the car was a pig. The first thing I noticed was the intake bowl was contaminated with exhaust. Hmmmmmm.


LSA is the RESULT of cam timing events. As I have said more times that I care to type, you can alter the LSA a bit AFTER the correct timing is set. The other thing is INTAKE CENTER LINE. You can install a cam 4,6,8 degrees advanced and change the intake valve closing. This will alter the idle and vacuum. The concept is not difficult unless Comp has brainwashed your mind.
Click to expand...

Haven't used a radius VJ in years and years, sharp angles and above all round valve seats over here.

Not talking about valve jobs. Just overlap really. The discussion I would like to initiate here is LSA, not valve jobs angles or anything else to help idle quality AKA vacuum. I flow my heads in reverse all the time and almost every time they flow more up to about .250" lift backwards. I know how to help idle quality-most don't.

Don't care where the cam is installed the overlap period is the same regardless. Yes a cam can be installed way ahead to crutch idle but guess what? Now you have a stunted and F'd up power curve if everything else is correct.

I've used and observed an intake closing of about 46 deg @ .050" has nowhere near the effect on idle quality as does a wider LSA with the same intake closing.

Overlap is defined as the period of time that both the intake and exhaust valves are open. You do realize that in order for exhaust to be evident in the valve bowls of your Stage 6 example that the exhaust valve has to be open right?

The more overlap the poorer the idle. J.Rob
 
RAMM said:
Haven't used a radius VJ in years and years, sharp angles and above all round valve seats over here.

Not talking about valve jobs. Just overlap really. The discussion I would like to initiate here is LSA, not valve jobs angles or anything else to help idle quality AKA vacuum. I flow my heads in reverse all the time and almost every time they flow more up to about .250" lift backwards. I know how to help idle quality-most don't.

Don't care where the cam is installed the overlap period is the same regardless. Yes a cam can be installed way ahead to crutch idle but guess what? Now you have a stunted and F'd up power curve if everything else is correct.

I've used and observed an intake closing of about 46 deg @ .050" has nowhere near the effect on idle quality as does a wider LSA with the same intake closing.

Overlap is defined as the period of time that both the intake and exhaust valves are open. You do realize that in order for exhaust to be evident in the valve bowls of your Stage 6 example that the exhaust valve has to be open right?

The more overlap the poorer the idle. J.Rob
Click to expand...


Then the discussion is worthless. You can't parse out bits and pieces and get the whole picture. And to say moving the ICL is a crutch is not 100% true. It has been my experience if you have to move the cam more than 4 degrees to make it work, your cam timing is wrong to begin with. The 4 degree ahead bullshit is another COMP brainwashing marketing trick. The only reason to run the cam ahead is timing chain stretch. Comp made it something else.

So if you limit the area of discussion you can never learn. Cylinder head flow has as much to do with cam timing as anything else. You are making LSA the straw man for poor reasoning.


RRR actually gets it.
 
RustyRatRod said:
I keep it simple. I never pick a camshaft based on how I think it will idle. I pick camshafts based on how I believe they will run, given a particular combination and let the rest fall where it may.
Click to expand...

Most of the time that's beating a dead horse though. I can't TELL you how many times someone has said to me "Oh but I want the idle to sound like..." and pick your car. His dad's 66 whatever. His buddies 72 whoknows. The local street guys 69 thingamajig.

Hell, it's such a thing comp came up with it's own line of cam's just to target that idea. Nevermind those cams are out of wack. 235/249 duration at .050? With .497/.483 lift? Stupid.

People need to realize that when you build a strong motor. With planned out and matching parts. Then you get rewarded with that oh so sweet cracking rumble we love to call idle.

As for LSA? I always thought of it as working more in conjunction with duration to affect idle. Obviously a tighter LSA on the same duration increases overlap. And more duration on the same LSA also increases overlap. As for how much each affects it on it's own? Of that I am unsure.

Would be interesting to grind a cam. Vary the duration/lsa. And then run them all and see what you end up getting.

As for the race head's on a 318. It makes sense to me compression would stay the same. No matter how fast you fill a glass, it can still only be filled so much right? Same as a cylinder. If my analogy makes sense.
 
It's like I have always said and will stand behind forever. If you build a high performance engine, it will sound like one. You never build around what you want one to sound like, but rather, what you want it to run like.
 
Cams are picked for purpose. The purpose is determined by the owner/builder. Some to create low end torque, or to pull past 6000 rpms, or gas mileage, or just for sound. Yes, some folks really don't care if they get the ultimate performance, they just want the cool sound. In fact, there is such a demand for it (sound) that companies compete in the Thumper/Whiplash market.

Some miss their goal to meet their purpose due to mismatch components, or shall I say not getting the right cam for the rest of the engine and drive train.
Ironically, the most purposed cam sold giving the most smiles are the thumper/whiplash cams. Those who only purpose for sound are usually happy when the hear their thumper idle. Utube is full of smiling examples.
 
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Better discussing the finer points of getting the right amount of horseradish in your Bloody/Caesar. I agree it's the amount of that ingredient that makes or breaks them. Of course YR will say the flavor can't possibly only depend on that alone.
 
I have to totally agree with Ramm.In a small block I tried a 196-196 104lsa in at 104 vs 204-214 112 in at 107 cam they idled almost identical,but the 204-112 was heads above in power, but my point was you have to take away duration to clean up the idle(overlap) so you are giving up power/rpm.Also in another build with a tighter lsa I had more reversion and had to retard the cam to clean it up.Comp wasnt the first to build advance in a cam , I think it was crane (could be wrong but it wasnt comp) and their thumpers arent all that bad for what they were intended.YR seems to want to always create a **** storm and pound his chest to prove himself correct and some see through it and some dont . I dont really agree a tight lsa is the way to go. In some cases they also need more converter better exhaust,more comp,better intake and for the street with a dual plane full exh. low comp your shooting yourself in the foot not to mention worse idle,carb issues.You cant have both.Almost all if not all of these builds are street not race only.
 
I agree with RAMM 100%. I previously ran a Crane hydraulic flat tappet cam in my 400. That was a great street cam. It had 222/234 duration and 114 lobe centers. It idled great and made lots of vacuum. It also made 415 HP and 450 TQ in a very mild 400. I stepped up to a 500 stroker, and read all about cubic inches masking the effects of a larger cam. I put in a Comp hydraulic roller with 236/242 duration and 110 lobe centers. It has a noticeable lope at idle and pulls about 8.5 inches of vacuum in gear. The rest of the car is built to accommodate it so it is not an issue, but I expected better with the increase in cubes.
 
yellow rose said:
Then the discussion is worthless. You can't parse out bits and pieces and get the whole picture. And to say moving the ICL is a crutch is not 100% true. It has been my experience if you have to move the cam more than 4 degrees to make it work, your cam timing is wrong to begin with. The 4 degree ahead bullshit is another COMP brainwashing marketing trick. The only reason to run the cam ahead is timing chain stretch. Comp made it something else.

So if you limit the area of discussion you can never learn. Cylinder head flow has as much to do with cam timing as anything else. You are making LSA the straw man for poor reasoning.


RRR actually gets it.
Click to expand...

If you have to move your cam more than 2 degrees to get what you want-whatever that is--it's the wrong cam! I agree with you there. To be clear I'm no fan of Comp but I do use them for custom 'cuz I email the form and get my cam a week or so later the way I want it--no questions asked. For catalog grinds I usually turn to Lunati.

Not trying to limit the discussion at all but to introduce cylinder head "tricks" into this will convolute the whole purpose of the thread so fast it would be crazy.

I'm actually a fan of tight LSA's as they tend to produce such a huge wallop of midrange power its hard to argue with them. For the bulk of my customer base I'd say less than 5% can actually tune and set up their vehicles to handle a tight LSA and the radical idle and "light switch" power delivery. I'm also getting older and don't care for coming to a stoplight with both feet working the pedals-unless its a stick. J.Rob
 
RustyRatRod said:
I keep it simple. I never pick a camshaft based on how I think it will idle. I pick camshafts based on how I believe they will run, given a particular combination and let the rest fall where it may.
Click to expand...

I agree Rusty when I build an engine for myself its different. When building for a customer you have to almost guess at what that particular customer is willing to put up with. It's a tough call most times. J.Rob
 
moper said:
Better discussing the finer points of getting the right amount of horseradish in your Bloody/Caesar. I agree it's the amount of that ingredient that makes or breaks them. Of course YR will say the flavor can't possibly only depend on that alone.
Click to expand...

Love a good spoonful of HR in my Ceasar. J.Rob
 
Hmmmm.... what is new about LSA effecting idle? Look at all the torque and low RPM cams ever ground..... 112 or 114 LSA.

As far as cubes versus LSA, I am surprised to hear this. /6 and 360 and 440 cams all get ground on the same basic LSA's and all react the same way to LSA changes. As well as Chevvies, Fords, Opels, etc....



Real world experience? I had a low duration, high lift 114 LSA cam in a 351C that passed all emissions except NOx, idled like stock but would beat factory 440 GTX's in B bodies all day long. Torker manifold (gasp!) and 1-7/8" (gasp again!) and it still idled with 18-19" of vaccum. The lift and the heads made it breathe so duration and overlap could be sacrificed and idle improved.

Not sure I understand this statement; is it talking about reversion during intake closure on the compression stroke? How can that contaminate the intake with exhaust?
yellow rose said:
If the intake valve is still open, and the port can't overcome the upward movement of the piston, you get reversion. That reversion is where you get the dead rich idle you can't clean up.
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Did you mean to say "If the intake valve is already open..."?

This is going into a different topic, but just an observation: I would not put too much faith in flow bench numbers revealing what will truly happen with reversion and during overlap. Flow benches are steady state tests, and real operations are anything BUT steady state; real operating flow is start-stop-start-stop ad infintum, and the air mass in the intake has to be accelerated from a dead stop each and every time. The MASS of AF mix in the intake tract (heads and intake up to the plenum) IMHO dictates a that behavior more (and perhaps much more) that low lift steady state flow. As well as compression ratio, which effects suction pressure as well as compression pressure, and also impacts total cylinder clearing of spent gases. (Another topic.... I'm out of control! LOL)
 
It has been my experience with ex-wives, that the person who uses the most words, disparaging comments and screams the most or uses the most capital letters is to be declared the winner of a........ah.......discussion? I left behind the last, "You are so stupid, who can talk to you?" partner so many peaceful years ago and I will not go back.
 
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