I have no evidenced to back it up from what understand that might explain why cube don't eat duration if flow ratios cfm per cid and intake and exhaust that a cam should act similar between different displacements as long as these ratios are similar. So for example if you take a 273 and 340 which have similar port flow to cid ratio it should take the same amount of time (duration) to fill the cylinders at a certain rpm say 6000 rpm for this example. But take 273 vs 318 since they both have same head a 318 will need more time (duration) at 6000 rpm or same cam will act smaller but if swap 340 heads on the 318 and compare it to a 340 the 318 will need less duration at 6000 rpm or the cam will act larger. I've seen evidence in a lot of the builds I've read but also sometimes theres ones that don't.
Camshafts, idle quality, driveability and LSA-REAL WORLD EXP and OPINION
- Thread starter RAMM
- Start date
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I have no evidenced to back it up from what understand that might explain why cube don't eat duration if flow ratios cfm per cid and intake and exhaust that a cam should act similar between different displacements as long as these ratios are similar. So for example if you take a 273 and 340 which have similar port flow to cid ratio it should take the same amount of time (duration) to fill the cylinders at a certain rpm say 6000 rpm for this example. But take 273 vs 318 since they both have same head a 318 will need more time (duration) at 6000 rpm or same cam will act smaller but if swap 340 heads on the 318 and compare it to a 340 the 318 will need less duration at 6000 rpm or the cam will act larger. I've seen evidence in a lot of the builds I've read but also sometimes theres ones that don't.
Or to say it another way a lot of the hot street strip engine are running similar flowing heads no matter the cid or brand. So say the average build has a 300 cfm @ .650 lift a bigger engine is gonna need more help to fill the cylinders so tighter lsa which will give more overlap (time) since duration probably gonna be similar between builds .
famous bob
mopar misfit
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roccodart440
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While I agree with that statement. I would never build an engine to sound a certain way, I certainly think pretty damn hard about how the cam will affect street driving and functionality. Street driving most often being idle to 3000RPM.
I agree with the above statements... "build with the cam that will work the best, perform the best". But that's me......
However, is it really wrong if somebody wants to build for a sound, and couldn't care less about performance??? What if they only like the mean sound, but have no interest in ever opening it up???
- Is it wrong if somebody mounts a dual snorkel hood scoop that's not functional but only for looks?
- Is it wrong to put wide tires with traction bars on a stock slant six car though it's not needed, but does it for looks??
I say we all have different desires and interest for our cars.
However, is it really wrong if somebody wants to build for a sound, and couldn't care less about performance??? What if they only like the mean sound, but have no interest in ever opening it up???
- Is it wrong if somebody mounts a dual snorkel hood scoop that's not functional but only for looks?
- Is it wrong to put wide tires with traction bars on a stock slant six car though it's not needed, but does it for looks??
I say we all have different desires and interest for our cars.
I remember some years ago, there was a mid 70's Camaro in a neighboring town that had a rough idle cam with connecting gears. You could hear him whining 2 blocks before you saw him. It had ladder bars and wide tires in the back. Rumors were it was a 11 second car, 12 second car, and whatever. However, he never would race anyone, just lumped around town whine whine whine like a full blown funny car.
He sold it and the guy that bought it came to my house. He took it to the drag way and it ran 15.20's (best run).... LOL.
You see?? One guy had it built to what he wanted... a mean look'n and sound'n car that he never intended to race.
The other guy was majorly disappointed. LOL ....
He sold it and the guy that bought it came to my house. He took it to the drag way and it ran 15.20's (best run).... LOL.
You see?? One guy had it built to what he wanted... a mean look'n and sound'n car that he never intended to race.
The other guy was majorly disappointed. LOL ....
RAMM
Well-Known Member
Nothing wrong with doing any of those things--IF and its a BIG IF--They TRULY are happy with the result.
I've done things in the past for customers that assured me up down and sideways they would be happy, and guess what? They weren't! But they wouldn't admit to their friends and family that it was THEIR call would they? Of course they would! -NOT They would never bad mouth the builder who was the last guy to touch it would they? You betcha. Now on the flip side of this coin I have had customers who were very happy with their mean sounding , NO power, NO efficiency engine but they are few. Of course there are exceptions to every rule but this is the toughest part of this whole deal. J.Rob
Robb,
I wish I had more time to get into my opinions and experiences for you, but I would probably end up writing a book, lol.
There is a lot of confusion on this subject, and some of the marketing and "rules of thumb" out there muddy the waters even more. I see a lot of emphasis on one aspect or another of cam selection, but the whole combination of parts is going to determine the cam selected, right down to the size of the tires on the vehicle, if someone is really looking for the best possible choice.
Yellow Rose is not off base, although he is very passionate, and comes off pretty strong with his opinions. Heck, I think he could be passionate about a bowel movement! (Sorry Tim) I understand it though. I'm just as passionate about valvetrain geometry, and some people think I'm being a jerk, when I'm only trying to help them. Btw, that plays a huge role in the selected cam working the way it's supposed to. That being said, I'm not a cam genius, and most times I will select a shelf grind that gives me 95% of what I'm looking for, and when the need arises I go custom.
I personally don't care much for tight LSA's on pump gas engines for a few reasons. While a limited cylinder head will respond to a tight LSA vs a good cylinder head, the increased cylinder pressure from the early intake closing increases the chance of detonation on sketchy fuel, and the work against the piston after combustion is lessened because the exhaust valve opens early causing combustion pressure to blow out the exhaust before it is done working. The overlap reversion then dilutes the intake charge, and causes the loss of bottom end power and driveability. Once the rpms increase enough to overcome the reversion and the overlap is actually drawing the intake charge, cylinder pressure spikes, and before you know it, the motor is rattling itself to death, whether you hear it or not.
As Yellow Rose said, the timing events can be moved to where they need to be, but the cylinder pressure spike is going to be more prevalent the tighter the LSA gets. It will also lay down earlier, which is why they are better for a limited head that can't feed the motor at a high rpm anyway. Make the most power you can, before the cylinder head runs out of steam. And more duration won't be much help. Once the port goes sonic, it's done filling the cylinder, and it won't rpm any more.
As far as idle characteristics go, the idle will be similar if the intake closing and the overlap degrees are the same, regardless of the LSA. Maybe not exact, but similar. To keep those parameters equal, the duration would have to decrease with a tighter LSA, or increase with a wider LSA, on the intake or exhaust, or both.
Man, I swore I was only going to type a couple lines. I've got to get back to work.
I wish I had more time to get into my opinions and experiences for you, but I would probably end up writing a book, lol.
There is a lot of confusion on this subject, and some of the marketing and "rules of thumb" out there muddy the waters even more. I see a lot of emphasis on one aspect or another of cam selection, but the whole combination of parts is going to determine the cam selected, right down to the size of the tires on the vehicle, if someone is really looking for the best possible choice.
Yellow Rose is not off base, although he is very passionate, and comes off pretty strong with his opinions. Heck, I think he could be passionate about a bowel movement! (Sorry Tim
) I understand it though. I'm just as passionate about valvetrain geometry, and some people think I'm being a jerk, when I'm only trying to help them. Btw, that plays a huge role in the selected cam working the way it's supposed to. That being said, I'm not a cam genius, and most times I will select a shelf grind that gives me 95% of what I'm looking for, and when the need arises I go custom.I personally don't care much for tight LSA's on pump gas engines for a few reasons. While a limited cylinder head will respond to a tight LSA vs a good cylinder head, the increased cylinder pressure from the early intake closing increases the chance of detonation on sketchy fuel, and the work against the piston after combustion is lessened because the exhaust valve opens early causing combustion pressure to blow out the exhaust before it is done working. The overlap reversion then dilutes the intake charge, and causes the loss of bottom end power and driveability. Once the rpms increase enough to overcome the reversion and the overlap is actually drawing the intake charge, cylinder pressure spikes, and before you know it, the motor is rattling itself to death, whether you hear it or not.
As Yellow Rose said, the timing events can be moved to where they need to be, but the cylinder pressure spike is going to be more prevalent the tighter the LSA gets. It will also lay down earlier, which is why they are better for a limited head that can't feed the motor at a high rpm anyway. Make the most power you can, before the cylinder head runs out of steam. And more duration won't be much help. Once the port goes sonic, it's done filling the cylinder, and it won't rpm any more.
As far as idle characteristics go, the idle will be similar if the intake closing and the overlap degrees are the same, regardless of the LSA. Maybe not exact, but similar. To keep those parameters equal, the duration would have to decrease with a tighter LSA, or increase with a wider LSA, on the intake or exhaust, or both.
Man, I swore I was only going to type a couple lines. I've got to get back to work.
I have absolutely no problem with a builder refusing work because they don't like the scenario.
And, engine builders are not alone.
Go to a well known body shop and tell them to slap some bondo over the rust and shoot it real quick. They will refuse. Why? Because every car they paint is a rolling billboard. If they can't do their quality of work, they refuse the job.
Folks can build their car with their money the way they want, and folks can run their business the way they want. Should be no hard feelings either way.
just curious.... if someone was going to build a mild street 360 at 8.5 compression (let's say 350 hp), what LSA would you be marketing for that build???Robb,
I wish I had more time to get into my opinions and experiences for you, but I would probably end up writing a book, lol.
There is a lot of confusion on this subject, and some of the marketing and "rules of thumb" out there muddy the waters even more. I see a lot of emphasis on one aspect or another of cam selection, but the whole combination of parts is going to determine the cam selected, right down to the size of the tires on the vehicle, if someone is really looking for the best possible choice.
Yellow Rose is not off base, although he is very passionate, and comes off pretty strong with his opinions. Heck, I think he could be passionate about a bowel movement! (Sorry Tim
I personally don't care much for tight LSA's on pump gas engines for a few reasons. While a limited cylinder head will respond to a tight LSA vs a good cylinder head, the increased cylinder pressure from the early intake closing increases the chance of detonation on sketchy fuel, and the work against the piston after combustion is lessened because the exhaust valve opens early causing combustion pressure to blow out the exhaust before it is done working. The overlap reversion then dilutes the intake charge, and causes the loss of bottom end power and driveability. Once the rpms increase enough to overcome the reversion and the overlap is actually drawing the intake charge, cylinder pressure spikes, and before you know it, the motor is rattling itself to death, whether you hear it or not.
As Yellow Rose said, the timing events can be moved to where they need to be, but the cylinder pressure spike is going to be more prevalent the tighter the LSA gets. It will also lay down earlier, which is why they are better for a limited head that can't feed the motor at a high rpm anyway. Make the most power you can, before the cylinder head runs out of steam. And more duration won't be much help. Once the port goes sonic, it's done filling the cylinder, and it won't rpm any more.
As far as idle characteristics go, the idle will be similar if the intake closing and the overlap degrees are the same, regardless of the LSA. Maybe not exact, but similar. To keep those parameters equal, the duration would have to decrease with a tighter LSA, or increase with a wider LSA, on the intake or exhaust, or both.
Man, I swore I was only going to type a couple lines. I've got to get back to work.
RAMM
Well-Known Member
All of this in the above quote is extremely accurate. I didn't want to GO there 'cuz like you said a book could be written. Very informative post--for those who don't already know this read the above two paragraphs over and over until a light bulb goes on. Thanks, Mike. J.Rob
Time for my dumb question. I have been following along in this thread and I have a question for you cam guys. Assuming and engine is 340 CI and is running "Cam-X" and it works great. Now let's make that same engine 400 CI. IF we got to the new CI by a longer stroke, wouldn't you need a longer duration cam to take advantage of the longer stroke? Now the second part of my question: let's say that we got to 400 CI by boring the cylinders and keeping the stroke the same. It would seem to me that the original "Cam-X" would be ok since the piston/valve timing would essentially be the same as stock. BUT, you would still need some way to fill the larger hole. Could you not keep the duration basically the same as "Cam-X", but increase the lift to accomplish filling the cylinder? I know that is pretty basic info and there are many variables, but I was trying to get the idea concerning the different ways to get larger Cubes and how the difference between increasing bore-vs-increasing stroke affects cam selection.
Too many variables left, and LSA wouldn't be the first consideration. But,...assuming oem iron heads with a little bowl work, the quickie combo would be something like a Comp XE262, with a 1.6 rocker and correct geometry. That grind is on a 110, and will have decent area under the curve, and build cylinder pressure in a usable rpm range with the low static CR. Obviously, a better combo could be had, but it takes a lot of info to make the best choice.
ir3333
Well-Known Member
Now let's make that same engine 400 CI. IF we got to the new CI by a longer stroke, wouldn't you need a longer duration cam to take advantage of the longer stroke?
wouldn't the piston travel still fill the cylinder at the same rate?
wouldn't the piston travel still fill the cylinder at the same rate?
When you switch from 340 to 400 I'm assuming the cylinder heads are gonna be the same.
Let's say stock edlebrocks now peak power is gonna be different for both engines. So say the 340 peaks at 6500 rpm the 400 may peak 5500 rpm so both engine will be pumping the same amount of air/fuel (hp) through at those rpm so cam duration and lift needs are probably similar. But since the 400 is under headed compare to the 340 it could use a tighter LSA from what I understand. And for your for your big bore short stroke vs small bore long stroke I'm sure playing with opening and closing points could maximize performance from each but that's a level few probably play at. That's why NASCAR engine cost a lot they got to dyno thousands of variables.
Ya I think since the longer stroke would be operating at a lower rpm but the piston has to travel further than a the short stroke but higher rpm both would probably need similar time (duration) to fill the cylinders during each stroke.
roccodart440
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Correct me if I'm wrong but a stroker piston travels faster from TDC to BDC. This should pull very hard on the port and also send a good signal to the carb. My guess is they would be a little more forgiving on camshaft size.
Actually, no.
Longer stroke=higher piston speed=more depression (vacuum)=higher port velocity=lower peak rpm. To maintain rpm, an increase in duration or cylinder head capability is needed.
For a larger bore, same thing.
larger piston=more area=more depression (vacuum)=higher port velocity=lower peak rpm.
Again, this is assuming all else is the same except how the cubic inches are achieved. That's not saying the final cam selection might not vary between the two, but the trend is going to be the same to get the same result.
yellow rose
Overnight Sensation
This is exactly my point. Why are you picking LSA as the ONE point you care about? That's as rediculous as it is silly.
The LSA is a FUNCTION of all the combined events. Damn.
yellow rose
Overnight Sensation
Robb,
I wish I had more time to get into my opinions and experiences for you, but I would probably end up writing a book, lol.
There is a lot of confusion on this subject, and some of the marketing and "rules of thumb" out there muddy the waters even more. I see a lot of emphasis on one aspect or another of cam selection, but the whole combination of parts is going to determine the cam selected, right down to the size of the tires on the vehicle, if someone is really looking for the best possible choice.
Yellow Rose is not off base, although he is very passionate, and comes off pretty strong with his opinions. Heck, I think he could be passionate about a bowel movement! (Sorry Tim
I personally don't care much for tight LSA's on pump gas engines for a few reasons. While a limited cylinder head will respond to a tight LSA vs a good cylinder head, the increased cylinder pressure from the early intake closing increases the chance of detonation on sketchy fuel, and the work against the piston after combustion is lessened because the exhaust valve opens early causing combustion pressure to blow out the exhaust before it is done working. The overlap reversion then dilutes the intake charge, and causes the loss of bottom end power and driveability. Once the rpms increase enough to overcome the reversion and the overlap is actually drawing the intake charge, cylinder pressure spikes, and before you know it, the motor is rattling itself to death, whether you hear it or not.
As Yellow Rose said, the timing events can be moved to where they need to be, but the cylinder pressure spike is going to be more prevalent the tighter the LSA gets. It will also lay down earlier, which is why they are better for a limited head that can't feed the motor at a high rpm anyway. Make the most power you can, before the cylinder head runs out of steam. And more duration won't be much help. Once the port goes sonic, it's done filling the cylinder, and it won't rpm any more.
As far as idle characteristics go, the idle will be similar if the intake closing and the overlap degrees are the same, regardless of the LSA. Maybe not exact, but similar. To keep those parameters equal, the duration would have to decrease with a tighter LSA, or increase with a wider LSA, on the intake or exhaust, or both.
Man, I swore I was only going to type a couple lines. I've got to get back to work.
I agree with all of this, even the bowel movement part. Definitely passionate about that.
Other than that, I'm still stumped that people think LSA is the make or break datum point of cam design. Comp says that a narrow LSA decreases overlap. Now that I write that, I may have that wrong. Comp says so much **** that's backwards I can't keep it straight.
I'll have to read the post that roccodart provided. I will say that while I personally like Chase Knight, we have never had an agreement of cam timing. Especially on blown alcohol stuff. So I'll have to see what he said.
I'm still waiting for two things.
1. I want it explained to me how I can get a 900 RPM idle out of a cam with 255*'s duration at .050 and still have enough vacuum to run power brakes. I don't let it idle that low, but I can.
B. If two cams have the same duration at .050 lift, does it know if it's a HFT, HRT, SFT or SRT? To me, at .050 is at .050 and seat to seat is seat to seat timing. Once the clearance is taken up, the lifter has no idea.
yellow rose
Overnight Sensation
That's why when building induction limited circle jerk engines you run the longest rod you can get, with the shortes stroke. When the induction system is less limited, R/S ratio is less of a factor.
I'm glad you took the BM comment for what it was, a desperate attempt at humor.
As far as your #1 question, it's because you run a fair amount of static CR. It helps the vacuum and idle, but on pump fuel it gives me the willys unless the tune is perfect. Most guys cant, don't, or won't get it there.
#2, it doesn't know or care.
yellow rose
Overnight Sensation
Ok, I hate tests like this. It just fucks up everything. Why use a 104 LSA on a SBC? I have no idea. That head is good enough to use a 107-108 LSA. Of course, they didn't test THAT.
Second, the 104 LSA kicked the **** out of the other two for low end grunt, without giving up top end power. I thought that's what all you guys wanted...low end grunt.
Third, no where in that entire article is it said where each cam was installed. That is total bullshit. I'd have taken the 104 LSA and shoved it in at 100, or even 98*'s so 4-6* ahead. That would have helped the idle, because it shuts the INTAKE valve earlier and it would have moved peak torqu down a bit.
And still the 104 kicked the **** out of the other two cams, and it wasn't the right LSA for that engine.
For the final and last time, the LSA is a function of all the other camshaft properties. That test was at least misleading, if not an outright fraud. I say that because we all know that 104 is too tight for the engine, just like 114 is too damn wide. So was 110. I'd love to see the same test with every thing the same, and do it on a 107-108 LSA, a degree or two ahead for timing chain retard. That would have been the best.
And yet and still, the 104 kicked ***.
Damn.
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