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Discussion Starter · #1 · (Edited)
Disclaimer: this is for FUN! It is not in any way supposed to be the last word in anything. It's just a fun exercise to generate discussion. No you shouldn't take what you read here as the last work and spend money you don't have to burn. Yes you should get with a good reputable cam guy and listen carefully, then still don't spend money you don't have. No you will not suddenly go from running 12.20 to 8.90 by reading this thread. Yes you should go to another thread if you don't like open discussion.

Most of all, I like discussion, particularly technical ones, so take this for what it is: a fun exercise through technical discussion.

Disclaimer 2: in order of accuracy.... TRACK > REAL DYNO >>>> MODELS IN COMPUTER PROGRAMS. I know. Again, it's just a fun exercise.

So, with that out of the way, I decided to model a couple of different cams in Performance Trends Engine Analyzer Pro. Roots blown engines are interesting and ours takes a different approach compared to what I've traditionally been used to with NA, and even nitrous cars. So I'm trying to learn just like everyone else. Even the best engine builders in the world are constantly learning and software dynos are a fun risk free way to play around. They can be VERY wrong however with bad input data, so take all results with a grain of salt and a realization that this is just a model, on a computer, in my office, and not from "real world" data.

We talk a lot about cams and see lots of extremes on various builds here. The following doesn't go too extreme, but gives an interesting comparison ( I think anyway ) to two cams that are similar to what others are running. @random84 posted up here: Random's Post his cam card and I noticed it was very similar to one spec'd by PatG for my 427 build. I have no doubt Random is making good power and his data IS from the "real world" so again, take this as a discussion not a criticism or anything else.

The first cam is direct from Random's cam card (all specs at .050 lift).
Intake 234 degrees
IO 2.6
IC 51.8
Exhaust 252 degrees
EO 70.2
EC 2.2
LSA 119.3
Lift with 1.8 rockers .641/.648

Second cam is one that originally started out like Cam Motion's off the shelf 228/242 cam HERE but that I tweaked in EA Pro based on results
Intake 222 degrees
IO -2 (neg = ATDC)
IC 44
.630 lift w/ 1.8
Exhaust 236 degrees
EO 56
EC 0
.610 lift w/ 1.8
LSA 115.5

Engine modeled as:
427ci 9.75:1
WCCH AllPro LSW-3 (had to make assumptions about CSA as I don't have mine yet to measure)
2.20/1.60 valves
1.8 rockers
2" headers
Full high flow exhaust
Kong 2650 - 3.03 pulley ratio - 15-16# boost
108mm TB

Here is EA Pro's power graph:
150765


The interesting part comes when you start looking at events vs piston velocity/position, valve lift, and port velocity.

Here that is for the exhaust at 4300 rpm

150770


Here it is for the exhaust at 6100 rpm

150767


Now the intake at 4300 then 6100

150768


150769


That's a lot to take in I know. I have some thoughts about why the smaller cam with it's specific events does better...at least until 6150 rpm or so...but interested in other's comments first.

I know, I know....someone is going to say "But in the real world...." Still, there may be something to talk about here. If not, it was fun for me.
 

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Discussion Starter · #2 · (Edited)

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Discussion Starter · #3 ·
Oh and I modeled it with Ethanol.
Estimated idle vacuum with the smaller cam is 16.1"
for the larger 14.5". Give some general idea of "choppiness"
 

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Very nice post!

Even though I own the same software you are using, plus
Dynomation, PipeMax, as well as a couple of old
software packages written back in the 1980's, I have
never been able to get accurate data out of any of them
regarding an engine using a roots style blower.

While I commend you for your desire to characterize
one of these engines running a big roots blower, and
using Ethanol for fuel, I have a suggestion for you.

Start with an NA Engine first.
Use a 90% Throat, as that is the most common and
accepted throat size used to characterize most
Street / Strip engines.

Going beyond that, and you don't have much
room left to place a seat that will live on the
Street.

Frankly, with most of the so called porters, the heads
come into the porters shop, and leave without changing
the throat size by much, or if any at all.

They make things look shiny, and do a
multi-angle valve job that directs the
mass charge to what 'They Think' is the
correct side of the valve / cylinder.
***However, the flow through the port changes
sides, after the valve reaches convergence lift.
***With these engines, most guess correctly,
as convergence lift is 0.541", and most cams
sold for these engines don't generate a net
lift at the valve, which is higher then that.
***To control that shifting from one sided to
the other, many 'Real' cylinder head porters
put a 'Fin' on the bottom of the floor which
forces the mass charge to enter the cylinder
on the correct side of the valve.

-below are the values measured for an LS3 Head-
CSA at:
intake flange...... 3.23 sq./in.
push rod pinch... 2.90 sq./in.
throat................ 2.693 sq./in. (87% of 2.16 valve size)

--------------------------------------------------

You wrote:
"The interesting part comes when you start looking
at events vs piston velocity/position, valve lift, and
port velocity."

Yes, continue researching the above, as that is
where you will find many of the answers to your
questions.

You can fill a cylinder by increasing either
Lift or Duration.

But I begin by fitting the duration to the 'Mean Piston Speed'.
I then fit the lift, relative to the size of the cylinder.

--------------------------------------------------

Again, I would begin with an NA Engine.
I would use gasoline as the fuel.

Plug in different lifts and change Engine RPM.
***As you know, piston speed is directly related
to your engine rpm and the stroke of the crank.

Then begin to change the duration number.
***Do the same thing as above;
change duration numbers and / or engine rpm.

--------------------------------------------------

Also, these low entry LS Series of heads go
into velocity choke at far lower velocity speeds
than do 'High Port' heads.

So I would suggest that you hand calculate the
velocity at the MCSA, which should be the
valve throat on these heads.
***These low entry port cylinder heads choke,
at a velocity far less than what most use within
there simulators.
***They don't even come close to the 146 CFM
per Sq." of flow that many use.

The math to do that is in my signature line.

If you have any questions relative to that
math, I would be most happy to help you
with it.

Finally; relate everything back to BMEP.

----------------------------------------------------

While I think what your attempting to do will
reward you once you get a 'Handle' on things,
this subject matter is far above most on this
forum.

But I would suggest that anyone that has an
interest in this subject matter, post up your
questions, and you might find your answers here..:)

Cheers,
Bruce
 

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Your lift data with my rockers is wrong I think. It should be .641 / .648

Also, you need more pulley. Something closer to a 3.5 ratio!

And i wonder about ramp profiles- could be similar (since PatG knows his stuff), could be a big difference?




Well, get your build together and we'll test them out! :D


Sent from my SM-G991U1 using Tapatalk
 

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Regarding the cams: 2nd cam has less duration and more overlap - essentially a lower dynamic compression ratio. Would that not lead to a loss of intake charge and cylinder airmass in real world conditions, in addition to having a narrowed exhaust duration in a setup that typically needs it?

The mid RPM torque gain could be from the earlier IO / IC events, but that's the tradeoff for higher RPM power.

These cams are really not that aggressive compared to almost anything else out there so when you start thinking cylinder fill at 6k - even under boost - I'm surprised the calculations don't show a bigger difference at 6500 RPM.

FWIW, between two otherwise similar setups, I'd take the power gain over 6k, as we will already be traction limited at WOT in 3 or 4 gears on the street... so more HP on top will assist at the track when your RPM range is 5500 - 7k!

Sent from my SM-G991U1 using Tapatalk
 

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ive got the pipemax and the dynosim6 just for some visual look at the affects, it is interesting to see all the small changes affecting the curve, one thing i noticed tho is with PD boost (havnt tried any turbo layouts) but if i add say 5psi more boost it will only add power to the top of the curve where realistically it should add to the majority of it especially down low, not sure if thats a glitch the RD has mentioned with the roots blower calculation, i have my old dyno run which i have adjusted the program offsets to suit it so ill see once my new build is done how close the new changes actually are compared to the program estimation
 

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ive got the pipemax and the dynosim6 just for some visual look at the affects, it is interesting to see all the small changes affecting the curve, one thing i noticed tho is with PD boost (havnt tried any turbo layouts) but if i add say 5psi more boost it will only add power to the top of the curve where realistically it should add to the majority of it especially down low, not sure if thats a glitch the RD has mentioned with the roots blower calculation, i have my old dyno run which i have adjusted the program offsets to suit it so ill see once my new build is done how close the new changes actually are compared to the program estimation
Which version of PipeMax do you own?
I am still on v3.98, as I did not want to
upgrade to the latest version.

I might end up keeping v3.98 and purchase
the latest version and install it on another
computer. . . .

Here is what I am thinking you might do. . .
If you have the time (which I don't right now).

Take both of those camshafts that the OP
posted, enter them into PipeMax using
his 427 CID Engine, having the 2.204"
Valve. You of course will also require
the static compression ratio.

PipeMax will show the 'Calculated' operating
RPM Ranges for each of those camshafts.

It makes no difference what the throat size
or MCSA is, as we are just looking for the
differences between the two cams.

But the OP must also supply you with
information regarding if those cams
are ground with an advance.

Also, set the VE% for 100%.

What do you think...o_O

Cheers,
Bruce
 

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Discussion Starter · #11 ·
I'm swamped at work but am taking notes of requests and ideas. I have the newest pipemax and will see if I can also do that tonight. I have dynosim6 as well but not as much of a fan.

I modeled on ectual cam events from the card. I could play with advance and centerlines.

I will respond more later
 
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I'm swamped at work but am taking notes of requests and ideas. I have the newest pipemax and will see if I can also do that tonight. I have dynosim6 as well but not as much of a fan.

I modeled on ectual cam events from the card. I could play with advance and centerlines.

I will respond more later
I am a big fan of PipeMax, as it gives you the required
areas, to optimize your port sizes to for both CFM and
Velocity.

I basically use PipeMax to verify a program I have
written over the years.

If I was still racing, and looking for 5 - 10 fwHP,
then I would spend time with Dynosim and
other so called simulators.

However, all of the racing I did was NA, and that
is what so called simulators like Dynosim are
optimized for.

Some years back we had a discussion on Speed Talk
regarding how to calculate the fwHP of an engine using
a Roots Blower.

Many of those people are absolute genius' on that forum.
As I recall, it ended like this; they all agreed to disagree..lol

Cheers,
Bruce
 
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Discussion Starter · #13 ·
I think I read that ST thread LOL. fun stuff
 
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I think I read that ST thread LOL. fun stuff
One of the members is a mathematical genius.
He has a little program he sells, and it is well worth the money.

He also has a website, where he has many calculators,
which one can use for free.

I have much respect for this member!

But his calculator for FI Engines, was not calculating
the fwHP correctly. This occurred (as I recall) as
someone provided Dyno numbers that did not correlate
to his calculator.

I go up to his site now and then, just to see what's new.

In my opinion, his calculator used to calculate HP for
an FI Engine, using a roots style blower, is still not
accurate. .lol

As this thread moves along, and after we 'Connect' all
of the dots for an NA Engine, then we might begin to
uncover the 'Why's' of the engine using a roots blower.

Let's see how this goes / progress'?

But we can't rush this type of thing, as there
are many, many 'Confusing' variables, we must
quantify first, via an NA Engine (JMHO)!

Cheers,
Bruce
 

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Discussion Starter · #15 ·
Your lift data with my rockers is wrong I think. It should be .641 / .648

Also, you need more pulley. Something closer to a 3.5 ratio!

And i wonder about ramp profiles- could be similar (since PatG knows his stuff), could be a big difference?




Well, get your build together and we'll test them out! :D


Sent from my SM-G991U1 using Tapatalk
Getting parts has gotten impossible!!! It looks like it's going to be forever before mine is together. Just know reading your build helps feed my lack of patience to get mine going LOL

I fat fingered the lift #s on the post but modeled it correctly. Edited first post with correct lift #s

The lobes modeled were less aggressive: 27.74 inch * deg intake / 30.16 inch * deg exhaust. I'll have to play around and see what overall impact to the comparison that makes. Pat has a lob he uses that he worked with Cam Motion to develop and it's hard (impossible?) to really get a sense of what he chose without profile the cam on a fixture. IMO that's somewhat overkill for looking at comparisons like we are doing here as we are just trying to understand valve events vs pressures vs port velocity vs piston velocity/demand.

A 3.5 ratio puts the boost 19-20# in the software. Curious what you have actually seen to compare to what it is deriving. One swag I had to make is intercooler core flow efficiency which directly impacts boost drop across the core.

The higher boost benefits each cam where they are strongest. The smaller one sees even more low end torque since the lower overlap doesn't loose as much boost out the exhaust with the higher pressure differential. The bigger cam likes it way up top. The smaller cam could get trickier down low with timing due to the higher cylinder pressures, so there are a lot of variables here.

150787
 
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Discussion Starter · #16 ·
Regarding the cams: 2nd cam has less duration and more overlap - essentially a lower dynamic compression ratio. Would that not lead to a loss of intake charge and cylinder airmass in real world conditions, in addition to having a narrowed exhaust duration in a setup that typically needs it?

The mid RPM torque gain could be from the earlier IO / IC events, but that's the tradeoff for higher RPM power.

These cams are really not that aggressive compared to almost anything else out there so when you start thinking cylinder fill at 6k - even under boost - I'm surprised the calculations don't show a bigger difference at 6500 RPM.

FWIW, between two otherwise similar setups, I'd take the power gain over 6k, as we will already be traction limited at WOT in 3 or 4 gears on the street... so more HP on top will assist at the track when your RPM range is 5500 - 7k!

Sent from my SM-G991U1 using Tapatalk
The second cam has slightly less overlap. It has a higher dynamic compression ratio and higher max cylinder pressure than the larger one. It has less intake charge loss (what EA Pro calls "short circuit %) and higher BMEP. This actually means with the higher boost, it'll be trickier to tune timing with pump gas. It's all a balance.

I generally shoot for a more rounded (i.e. power under the curve) goal. It's all about that midrange power under the curve, or at least from post shift rpm drop up, with a nice bias for me toward the middle between shift and drop. Not that yours isn't, it is just biased to the top end and that cam would likely be happier up pretty high so you can spin it.
 

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I have 400" and pretty good heads, with a 9.55 / 3.00 (3.2 ratio), I pull almost 19psi in 60* air on the street.

Sent from my SM-G991U1 using Tapatalk
 

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Discussion Starter · #18 ·
The fun thing for me is playing around with the actual events in different scenarios and seeing the general trend. Overall it's super complicated and nothing beats a bag full of cams and lost of engine dyno time to kill. I do think some of the tendencies of certain valve events in a given scenario, that is the trends from shifting them, can shed a light on what cams are in that bag and maybe help some see beyond the marketing for some cams that are out there. These software packages are not only based on complicated math and stats, they also, in most cases, have a lot of the creator's empirically derived knowledge baked in. Larry Meaux with Pipemax has spent decades tweaking based on what he saw on the dyno. I bet if he or Larry Atherton or any of the rest of them had spent decades only dynoing roots boosted engines, their programs would have that empirical knowledge embedded in the way their formulas work. It's unfortunately too complex to "nail down" in software, though I do believe it allows us to understand trends and get going in the right direction.

But onward....

Someone asked about tweaking the LSAs of the cams, and leave everything else the same. That would be interesting if we were stuck with a certain lobe with a certain duration, but we can do better. Since this is all make believe we can actually change the valve events themselves. The intake centerline, exhaust centerline, overlap, LSA, "advance" (that an be a misleading word btw) are all just derived from when the cam opens and closes. That's what matters. These other things are a nice way to sort things in our head, but not necessary. For example, we know a wider LSA has less overlap...well maybe...depends on the duration of the lobes of each cam...and that comes from the cam events...and so on. So we'll focus on cam events and how that relates to when things are happening with the pressures/velocities

And that leads me to the most interesting part. Pressures. You don't really "push" air. You create a pressure differential and air moves from higher to lower. That's because mother nature has zero tolerance for imbalance. The bigger the pressure differential, the more potential air will move. Air then has to deal with the gauntlet of physical things trying to keep that from happening. Valves in the way, the physical port shape, and other impediments (too much velocity, too little velocity, waves and pulses hitting at the wrong time, and on and on). So you want to time the valve events to optimize the differentials so the air has the most potential and can take full advantage of the imbalance. But then you realize air also has mass and momentum. So it's gotta get moving, and then it takes some time to stop moving. So if you time the intake closing just right, you can use that momentum to keep filling even when the piston is on the way up. Or you can use the exhaust still flowing out during overlap, which causes a pressure differential and "pulls" the intake charge so it starts moving before the piston is really moving down and creating it's own demand. Boost complicates that period as there is already some greater than normal differential waiting on the back side of the intake before it even opens, causing the charge to not only get moving, but maybe moving right out the exhaust during overlap. Then there is velocity. I'll stop though. I don't know why I am going on and on. You guys know this already.

So anyway...we play around with valve events to maximize the pressure differentials, maximize velocity, and use as much momentum as we can so we capture as much intake charge in the cylinder and get the exhaust out as quickly and completely as we can. That's all. Easy peasy. LOL

And one more note...all of this is a massive compromise. Just like in our two example cams, you give one part of the power range to get in another. If you are good, you can strike an amazing balance and really get the most "area under the curve". But EVERYTHING with an ICE is a compromise.

By far the most interesting thing in these softwares is to graph piston velocities, piston movement, pressure diffs, and air velocities and start to see how cam timing interacts. It's not always what you guess.

Oh and I didn't even mention optimizing waves...recommend you move to Speed Talk if you want to dig deeper. It's awesome stuff.
 

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Discussion Starter · #19 ·
I have 400" and pretty good heads, with a 9.55 / 3.00 (3.2 ratio), I pull almost 19psi in 60* air on the street.

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I somehow thought you had a 427.
 

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Which version of PipeMax do you own?
I am still on v3.98, as I did not want to
upgrade to the latest version.

I might end up keeping v3.98 and purchase
the latest version and install it on another
computer. . . .

Here is what I am thinking you might do. . .
If you have the time (which I don't right now).

Take both of those camshafts that the OP
posted, enter them into PipeMax using
his 427 CID Engine, having the 2.204"
Valve. You of course will also require
the static compression ratio.

PipeMax will show the 'Calculated' operating
RPM Ranges for each of those camshafts.

It makes no difference what the throat size
or MCSA is, as we are just looking for the
differences between the two cams.

But the OP must also supply you with
information regarding if those cams
are ground with an advance.

Also, set the VE% for 100%.

What do you think...o_O

Cheers,
Bruce
yea ive got the v3.98as well as the 4## newest one and yea id recommend to keep the 3.98 i seemed to like that one more layout wise but now cant find a download for it to get it back, the newer one had alot more inputs but just seemed harder to navigate, then i got the dynosim6 as it has the graph i like see like a dyno readout, strange thing i noticed also when i put all my engine data in and i then swapped head flow data (mine is cathedral port dart pro1 also cnc'd) with a known cnc'd LS3 head data with bigger intake valve and more flow it actually showed a loss in power with the better flowing heads, bloody laptop died so i cant use the pipemax until i find a way to get it on the new one as i think they are linked to a single computer, ill see if i can get it working on the dynosim
 
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