Now that the whole 'what is VE?' debacle is winding down, I'd like to start a new thread.
For all intensive purposes, I'd like to maintain the definition of VE as the air in the cylinder relative to the ambient air. This prevents altitude from becoming a factor, which I think will make calculations easier, and results clearer for everyone in the end. If you are wondering how altitude would affect your engine's performance, that formula could easily be added (I'm at a low enough elevation that I couldn't care less
).
Now, as we
all know, things like aftermarket intakes and exhausts don't necessarily add power, they just make the engine more efficient, thus increasing power output under identical conditions.
The main advantages the LD9 and LN1 have over the LN2 and V6 J's are their DOHC camfiguration and higher compression. The OHCs allow 4 valves per cylinder to be used, thus inceasing the volume of air that can move in or out of the cylinder. I don't think the compression of an engine would directly affect VE, but everyone feel free to correct me otherwise.
I'm now interested in whether anyone would be up to the task of trying to calculate increases in VE brought about by common alterations. Things like ideal port diameters and intake runner lengths would be something this board has never seen.
Event's post about maximum necessary TB sizes is a great example of how people are hurting their engine's performance by going overboard with add-ons.
How about things like ceramic coatings affecting cylinder temps, and therefore VE?
This would obviously be a TON of work, but the payoffs would be great for everyone.
And would I ever love to learn about the precise effects of different camshaft profiles
If anyone REALLY wants to go crazy, we could work on mechanical efficiency as well, and factor in energy lost to frictional forces, rotating masses, and heat transfer
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To begin to know where any changes are to be made you must know what you have. You must be able to figure out how much air flow you have and/or what the section area of a port or runner is. Here's a few of the fomulas that have help out alot and where they came from:
From HP Book'sAuto Math Handbook by John Lawlor,
Theoretical CFM:
rpm * displacement / 3456 =
theoretical cfm
example: 6000 * 134cid / 3456 = 232.6 cfm (as seen by Event's other post)
Volumetric Efficieny:
actual cfm / theoretical cfm * 100 = VE
example: 212 / 232.6 * 100 = 91.14%
From Edelbrock's web site and many catalogs:
CFM:
CID * RPM * VE / 3456 = CFM (note: this is the same as above but now we have included the VE to figure the actual CFM)
example: 134 * 6000 * 85 / 3456 = 197.7
Note: They also give carb rules, which can also apply the Throttle Body,
CFM * 110% to 130% for sinle plane intakes or plenums (such as the 2.2L/2200s) example: 232.6 * 1.1= 256cfm
CFM * 120% to 150% for dual plane intakes (or Hilborn type fuel injection systems)
All of the previous formulas have all been posted ans/or demonstrated in other forum posts. You will notice that in my examples, I used figures for the 2.2L/2200 motor
From Stock Car Racing Magazine:
To determine the peak torque RPM for header primaries:
Section Area * 88200 / Cylinder Displacement = RPM
to figure the section area divide the diameter by 2 to get the radius and then subtract the tube wall thickness(usually approximately 0.040" for most headers) to get the inside radius of the primary tube. Take that number square it and then multiply it by
pi(3.1429).
example: 2.2L OHV header w/ 1.5" primaries
1.5 / 2 = 0.75(outside radius)
0.75 - 0.040 = 0.71(inside radius)
0.71 * 0.71 = 0.5041(squared)
0.5041 * 3.1429 = 1.5843358(section area)
134 / 4 = 33.5(disdpacement of one cylinder)
1.5843358 * 88200 / 33.5 = 4171
So the torque peak RPM on this motor header combo is 4171RPM, which this happens to be the most common for these motors. Remember that this is only the peak, not where the torque band is. Header design(4-1 or 4-2-1) and primary length (longer for low end, shorter for high end )determines where above or below the torque peak the power band is. The PaceSetter primaries are approximately 21", which is about a shortie to mid length, which is why the power band is higher up.
These are just a few of the mathimatical fomula that will apply, I'm sure most ppl out the that are serious about engine design and building have these and many more.
As far as camshafts, most of the major cam manufacturers have tech/ FAQ pages for more information. You canalso call and talk to their Tech departments if you have further questions.
Alright. Now, wouldn't there also be other factors such as cam profile that effect where peak torque lies?
Also, any idea where the number 88200 comes from? Is it just a generalization for an automotive engine, or is there something behind it that could vary with each engine?
With the measurement of VE, you could obviously measure the actual CFM on an already built and running engine with ease, but how about at the engine design level? I would assume you would need to measure the air's theoretical velocity at numerous points along its path, and multiply it by the cross-sectional area at the given point. And then, since a system is only as good as it's weakest point, the practical CFM would be the lowest number. And of course this would vary depending on RPM.
Obviously, if you had some test gerbal pieces to go off of, you could flowbench them after each modification, and find the best result to apply to the final piece. This would also give you measured CFM (but not necessarily for what RPM).
But if you don't have test pieces, how would you go about calculating the velocity (the basic model, not completely in-depth here. I'd assume a linear path of travel with varying areas)? You could assume the area swept by a piston on it's intake stroke will displace _____ sq in / s, but the velocity is relevant to the stroke position due to the crank having an angular velocity. So, if the piston is displacing air at varying rates, how do you determine what they are? Then of course you would have to factor in where the other piston is on it's intake stroke...or would the two in sequence produce a linear rate of displacement?
Now that I'm not even sure if I understand where I am, someone else please take a guess...
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That is what I call a very interesting topic.
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ELIOT. Now.....boosted.
Eliot wrote:That is what I call a very interesting topic.
I really injoyed Event's post, so I figured this would be the next step. Isn't it nice to have something beside "what intake is the best?" or "what exhaust sounds the best?" or "how do I get rid of the speed limiter?" or, of course, one of the generic ebay scam questions?
Am I correct in assuming that cylinder events are equally spaced (with respect to time) in sequence between cylinders?
e.g. @ 6000 RPM:
tdc cyl 1
(.0025s lapse)
tdc cyl 4
(.0025s lapse)
tdc cyl 2
(.0025s lapse)
tdc cyl 3
(.0025s lapse)
(repeat)
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Cam design has the greatest direct effect on where the engines power band will be.
Typicly the more lift generated by the camshaft or camshafts then the engine will make more low end off the line power. While conversly the more duration you add the more power the engine will have higher in the rpm band, at highway speeds as opposed to red light to red light. I can see what info I can get from LADDS headporting relateing on cam design and how everything actualy works if you would like me to.
The formula provided by Event is basicly from what I understand to be the way the manufacturers figure what size tb is needed for a perticular engine. But don't forget that the auto manufacturerers are going to cut costs where ever they can and if that means
they save $100.00 but sacrifice 2 hp then you can bet which way they're gonna go.
Now I may have completely blew it on the whole 100% v.e. thing but when you start talking cam design I do actualy know a thing or two about them and how they work in relation to rpm, compression, weather or not its forced induction or n/a and how the camshaft center line is sometimes more important then its lift or duration. As I said tho I'll be more then happy to go ask LADDS ( a VERY reputable local head porting and machine shop that has been aroud since ....... well since I can remember ) For any infomation you may need.
Semper Fi SAINT. May you rest in peace.
jackalope ( a.k.a. the prick ) wrote:Cam design has the greatest direct effect on where the engines power band will be.
Typicly the more lift generated by the camshaft or camshafts then the engine will make more low end off the line power. While conversly the more duration you add the more power the engine will have higher in the rpm band, at highway speeds as opposed to red light to red light. I can see what info I can get from LADDS headporting relateing on cam design and how everything actualy works if you would like me to.
This is how I've always understood it as well, which is why I raised the question after the header calculations. I'm sure it would play a role, I'm just not sure how big.
The last thing I will be doing with my engine (basically the only thing that's left) is a cam grind. I know this is where the power is going to lay, along with drivability. If you could provide any info as to matching a cam to head design (I think I still have the flowbench results from my ported head around here somewhere) and desired powerband, that would be great.
Also, one thing that's always stumped me is why everyone is constantly ranting about NEEDING low-duration profiles for turbo motors. I know the turbo drag engines are sure lopey as heck, so I'm assuming the only reason people say this is for low-end street driveability...However, once you need the RPM to spool a big turbo, you have to be able to shift your powerband up to get the required performance in the new useable RPM band (for a drag run). Now, you probably wouldn't want as much overlap as an NA engine due to problems with flow reversion, but you would need some extra nonetheless. Correct?
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If you can give me a copy of your flow chart I'll take it to Ladds and see what they would recomend for you and your driveing style. As for the question of the turbo cams, Its not the duration your worried about as it is the lobe seperation. When you look at a cams specs it gives you lift, duration, and the cams center line. The lift is important for a couple reasons. 1st you dont want the valve to smack the piston top. And 2nd you need to watch out for coil bind in the valve spring as the bind will do one of 2 things. 1st break the spring and possibly damage the engine ( not good ) 2nd it could "wipe" the cams lobes off and then our back to square one in needing a new cam. Duration is how long the valve is held open for. I'm used to dealing with V-8's so forgive me if the nubers I use may seem off in relation to the 4 cylinder we have. There are 2 basic ways to look at duration, Advertised ( bad ) actual ( good ) Advertised duration is how some manufacturers like to "rate" there cams. they'll say it has for example (we'll just use the last cam I had in my big block ok ) the cam has 292 degrees of duration. BUT what your concerned with is not advertised specs as they are useualy totolaly meaningless YOUR concerned with what the duration is at .050 as this is the actual duration on the camshaft BEFORE you figure in your rocker arm ratio. So to see what the TRUE duration is just multiply the duration at .050 by the ratio of you rocker arm and that number is the cams TRUE duration. Center line is VERY important ! This is what allows the engine to build cylinder presure. I know you all heard the very loppy
big block that sounds like its about to stall out at anytime right? Well thats because of the cams center line allowing cylinder presure to be bled off into the exhaust system so that the high compression monster can idle at all. The lower the center line number is the more cylinder bleed off you get because the exhaust valve is still open a little as the intake is starting to open. Most big block cams you'll see run a center line around 106 degrees to 110 degrees its just basicly an easy cam to set up. Turbo cams center lines are more broad to make sure the exhaust valve is FULLY closed before the intake opens so the turbos presure doesn't just go out of the exhaust. On a dedicated turbo cam don't be surprised to find a center line starting at around 115 degrees and going up into the 120's. Now n/a engines can also make use of a broad center line as they to will run better / make more power if the exhaust valve is closed before the intake opens. BUT be carefull TOO much seperation can lead to detonation as cylinder presure can go too high. Yes you can have a 9.5 to 1 engine but have cylinder presures so high that it can't run on pump gas at all. Take my old engine as example again useing what I just told you you should be able to get a better picture of how nasty it really was. It was a 427 cubic inch Pontiac engine running 10.5 to 1 compression
the cam I had was running a full roller valve train with 1.65 roller rockers. The cams specs were as follows lift at the valve was .550 duration at .050 was 298 degrees and its center line was 114 degrees giveing the engine a cranking compression of 225 psi per cylinder. basicly you could stand 10 feet behind the thing and at idle you'd still feel the exhaust hitting you in the legs. No lope at all so to speek but Tons of usefull compression.
This post is too long and I'm tired so I'm going to bed. Find me your flow chart and let me know EXACTLY how everything on your car is set up and how you intend to truthfully use it and I'll tell you what cam to look for. Deal?
And if anything I said conused anyone please let me know so I can clear it up.
Semper Fi SAINT. May you rest in peace.
Okay, so does the shorter seperation (at the same duration) effectively raise the powerband? This would induce more overlap, correct? Also, why does this actually affect how much power is made at what RPM? Seems odd to me...
Thanks for the offer w/ Ladds. Unfortunately, I just took a trip through the various cavities of my garage and couldn't find the flowbench results. I might have accidently thrown them out when I cleaned up a little a few months back. I'll pursue a more thorough search & rescue this weekend.
I also need to test my valve springs to determine the spring rate, as I'm sure Mantapart wouldn't generously give out that information.
Anybody know the piston to valve clearance on a stock LN2? I have spec sheet that's not too clear. There's a number around 44mm, but that can't be right. Of course, it also lists the exhaust valves being wider than the intake, so I should probably ignore it...
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Notec, Jackalope,
You are correct, the cam will have the greatest affect on the power band. I was just staring you off with a few formulas to get the discussion going.
I've got many more formulas to work with, but I was multi-tasking at the time I was writing that post (looking up the formulas, taking care of and helping my child with home work, hunt & peck typing, etc...).
The number 88200 is a constant that was developed through research, that is used as a conversion factor for the individual cylinder displacement and the "ideal" exhaust flow velocity of 260 - 280 feet per second. This velocity is where the exhaust molecules can flow fastest without crating undue back pressure if front of the exhaust pulse and developing a maximal negative pressure (vacuum) behind the pulse.
The peak rpm formula is intended to show how you can help tune your engine's power band for optimal performance. You can also rewrite the formula to find out what section area will be needed for the torque peak you are looking for. For example: you want your torque peek at 3500 RPM, what size primary would you need?
Section Area = RPM * Cyl. Vol. / 88200
3500 * 33.5 / 88200 = 1.329365
You would need a header with a primary section area of 1.329365 sq. in.
As you Know, tubing generally comes in 1/8" o/s diameters and the tubing that comes closest to this section area is 1 3/8", with a section area of 1.317680 sq. in., assuming the tubing has a wall thickness of 0.040".
For those interested, if you feel so inclined as to make your own header or have one made,
J Tuners makes a header flange in stainless steel and
Headers By Ed has mild steel and stainless steel J-Bends and can make or already has a collector for this application, if you feel you need other size headers.
Hope this clarified some of the info I posted above. Since my deployment, I'm still trying to sort out the mess my now Ex, made around here. I'm still trying to recover allot of data I used to have, some of which I will never recover.
Alright MadJack, that's what I figured. The 'ideal' exhaust velocity intrigues me, as it would be highly dependent on EGTs and head port shape (wonder how they determined the size and shape of that little bump in the exhaust ports?
) Maybe I'll be able to find out a little more about the specifics of the 88200 as well.
Would you happen to know an approximate percentage the header plays in the equation of peak torque? Also, anything dealing with factoring in the specific primary length and the effects on the torque curve (what length for peak torque at about 50% of torque curve for example)?
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I'd also like to note that a techarticle at cirlcetrack.com also presents this formula for measuring the intake manifold's contribution to peak torque location in the powerband. The only difference being they suggest taking the average ((inlet+outlet)/2) cross-sectional area of the runner (not really applicable to the header primaries) instead of a single value.
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Ok sorry work is being an ass about the internet use lately so I'll answer about the centerline confusion.
In the easiest terms the more lift the more off the line power. The more duration the more power higher up in the power band. The centerline has to do with cylinder presure and doesn't change the power bands peek points . A higher numarical centerline will take better advantage of the V.E. thats actualy avaible to the cylinders by keeping more of the intake charge in the cylinders as opposed to alloweing it to just go into the exhaust system.
If you have any more questions on cam design feel free to ask. Once we get this part nailed down we can move onto exhaust and intake designs and how things such as short tube, long tube, or tri Y headers work. See this is the type of stuff I've done since I was 16 so I have collected a fair knowledge on how this stuff works in the real world and not just on paper.
Not that the equasions are important but its just as important to know WHAT to actualy expect and this is where experence comes in.
( Disclaimer : If at any time I'm starting to sound like a "prick" or that I'm all knowing
please don not hesitate to let me know. I'm only trying to help and teach you guys what I know so you can get your cars to run as good as humanly possible. In no way do I think I know all there is to know about engines but what I do know can yeild you some nice power gains. )
Semper Fi SAINT. May you rest in peace.
Jackalope,
I presume you are talking about the Lobe Separation Angle(LSA)?
In simplle terms, the LSA determines where the torque peak occurs and to some extent the breadth and peak value of the torque. I know you said most of this above, but maybe this is stated in simpler terms.
A narrow LSA (about 106-110 deg) will produce a torque peak the comes in sooner in the popwer band and is peakier, but also produces a lumpier idle. This lumpy idle is caused by the reduced vacuum and reduces fuel atomization which is difficult for the O2 sensor to read. Also the lumpy idle charachteristics can trip the knock sensor, retarding the ignition timing. A narrow LSA also bleeds off too much pressure on a boosted motor, allowing the boost to go out the exhaust, instead of staying in the combustion chamber.
A wider LSA(112-116 deg. for N/A) will produce a torque peak that is higher up in the power band, dosn't have quite as high of a peak, but spreads the torque over a broader range with in the power band. It will also increase the vacuum, resulting in a smoother idle, which is why the cams for computer controled cars usually has a wider LSA. A boosted motor would use this wide ore even wider to prevent the boost pressure from being blead out the exhaust.
When you state Centerline, I think of the Intake Centerline, which determines where the power band lies, which can also be benificial in fine tuning the power band. I.e., advancing the cam 4 deg will move the rpm of the powerband down about 200 RPM. Retarding the cam 4 deg will move the power band up about 200 RPM. I have yet to discover a way to advace or retard the cam on the current cam gear, but if you use the old 1.8L roller set and change the dowell pin on the cam to a small block pin, you can use a small block bushing set to set the timing.
Hope this clears things up a little.
Jackalope, I also thought you were talking about the lobe seperation angle at first (hence my asking about it moving the powerband), but the intake centerline would make more sense ('centerline', duh, how'd I miss that?). Got ya now, my terminolgy was just off
(nice disclaimer
)
Also, I read on an LS1 site I think about someone mentioning setting the torque peaks from the intake manifold and header to opposite sides of the cam's torque peak in order to broaden the curve. I never thought about this before, but it would make a lot of sense for anyone who's building a racing/performance engine, and not a dyno queen.
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Madjack, I've always just called it the cams center line but yeah thats what I was refering to thanks for maybe helping clear it up a little. Now that it looks like we're all up to speed on cams do we want to talk headers now?
Semper Fi SAINT. May you rest in peace.
Ok I have a really crazy off the wall question that should really be in the boost forum but I think it would also apply here as well. Nitrous oxide is simply a mixture of nitrogen and oxygen(I am a total noob when it comes to boost) if am correct. And is a way to increase VE by forcing the mixture into the cumbustion chamber. I am guessing it is mixed this way because pure o2 in the engine may burn to hot or cause an explosion in the cumbustion chamber that our cars are not able to handle.... I know that liquid o2 is available and as one would expect extreemly cold. This is where things start getting off the wall. What if you could in fact spray the liquid to the intake? The liquid being injected would expand into a gas and and fill the head. The air would be more dense and would also obviously O2 rich. Sorry if this is a stupid question I know I dont have the knowledge to answer this question and I am also pretty sure that this has been tried and the reason why we have nitrous but I just thought I would throw it out there for you guys to tell me what a noob I am.
/\ /\ /\ What "NAWZ" is is an oxygen bearing gas by introducing it into the engine it basicly leens it out by stuffing in more air this in turn makes more power. But throw in too much and the engine gets too lean things tend to go boom. This is why when you start spraying you need to throw in more gas as well to make sure things don't go boom. Now I'm by no means an expert on nitrous as I never liked it or even run it because of its tendancy to break things of which I can do all by myself without any extra help. So I think maybe you are better off asking this in the nitrous forum but if you guys know the answers to his question go for it.
Semper Fi SAINT. May you rest in peace.
IIRC, pure oxigen is HIGHLY unstable, which is why the nitrogen is added (N2O), to stabalize the gas and prevent it from exploding (as it would if injected in pure form) without spark (preignition). This would shatter your engine as the force and heat produced would be so extreme. Also, it would take a rediculous amount of fuel to compensate and prevent a lean mixture.
This is the way I remember/understand it. But I have zero experience with the go-juice, so I could easily be way off.
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/\ /\ /\ was I confusing again? Damn I'm sorry
Header design anyone, anyone at all?
Semper Fi SAINT. May you rest in peace.
Alright, header design. What ya got for us?
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What do you want? Remember I'm at work so i can't get too into it cause I don't want to get busted on-line.
Semper Fi SAINT. May you rest in peace.
BlackCav wrote:
What's that supposed to mean?
Jackalope, I'm at work to, just posting in my free time, no rush.
The main thing I'm still looking at regarding header design is specific effects on the powerband due to different tube lengths, as well as collector design.
Also, what should be done differently in a turbo header in order to maintain as much heat as possible to keep exhaust velocity high and help prevent reversion?
Obviously treatments such as jet-hot coating will help keep heat in.
I read on one site where someone was talking about how offsetting the runners either above or below the ports will effect different flow characteristics. I believe if the runner is set slightly above the port it helps keep velocity high, as the gasses exit the head at an angle above the horizontal, and this keeps them from having to 'bounce' off the pipe with such a drastic effect. However, if you offset the pipe low, it helps guard against reversion, as the gasses trying to travel back up into the head ports will hit the side of the head instead of actually entering. Of course, you could also run an oval opening to take advantage off both characteristics, but I think then you would have to worry about the gasses losing velocity due to the increase in the cross-sectional area and the expansion causing the gas to become less dense.
Any thoughts?
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That sounds like you are talking about a raised runner head. The raised runners help keep the velocity up buy giving the gases a straighter shot out of the chamber. This is done on many aftermaket race heads. Usually they can maintain the stock bolt / port pattern, so special headers are not required.
As far as header design you need to decide on what the pupose and operating range of the motor will be. We've already discussed how to determine what the torque peak will be, by the primary tube diameter. There are basically only two designs of header available for any of the 4 cyl Cavi's, a 4-1 mid-length, and a 4-2-1 or tri-y. All of the headers I've seen, so far, have a primary tube diameter of 1.5" which leaves only one torque peek for what is in production. From this point you need, if your using a prodution header, you would need to decide on which design is best suited to your needs from the motor.
To decide what your car needs from a header lets look at some of the designs and sub-catagories and how some of the sub assemlies affect the power band.
1. 4-1 HEADERS, the most common design. Here the power band is affected by how they are designed.
A. Long Tube Headers are good for a realativly broad torque band that favors low to mid range torque. This is the design most people think of when you mention headers, they are typically made for the V8 cars and truckswhich usually have plenty of room underneath the chasis. The longer the tube, the more it favors the low end, to a point of diminishing returns.
B. Sortie Headers are good for more top end power, compared to long tubes. They are commonly used whre space is at a premium, such as hot rods and really cramped compacts.
C. Mid-Length Headers fall in between a long tube and shortie. This is what is typically used on most designs for the J-Bodies, because its a compramise between a full length and the some-what tight clearances under the chasis/engine.
D. Dual Diameter Primary Headers are an attempt to broaden the torque band by using two different size primary tubes. You get some of the benefits of the smaller tube and some of the benefits of the larger tube. They usually work to a point, but usually not quite as well as their advertisements suggest. The peak torque of the small tube is usally down, the power of the large tube is also down, but you do get a slightly broader power band.
E. Stepped Diameter Headers try to do the same thing as the dual dia.s try to do, buy add a largwer section of tubing about 8" down the primaries. They too seem to broaden the torque some what, but tend to favor the low slightly more than the dual diameter headers.
F. Equal Length Headers are typically a race only type header. All the primary tubes are the same length. These are for a very tight power range, typically on racecars that work in a very narrow power band, such as a dirt late model circle track car or sprint cars.Also used on "dyno queen" motors to bboost the torque and / or Horse power numbers.
2. 4-2-1 or TRI-Y HEADERS. This design is got for boosting the low to mid-range torque, in fact, more than long tube 4-1 headers. Originally designed for trucks, but have found their way into full-sized (read heavy) cars and compacts, to boost the low end torque. What made them so popular with the compacts is you cant always fit the longer tube under the chasis of a compact and that most of the compact 4 cyl. motors typically lack the low end torque needed for quick launches or for powering off the corners in auto-x.
One final item that is often over looked, with the production headers, is the collector. The collector is probably the second most important part (torque wise) of the header after the primary tubes. The same pricipals that apply to the primary tubes also apply to the collectors(larger dia, top end; longer, more low end). The length of the collector is often sacraficed so the header will fit in the car. But, the is a little cavat here, most people who put headers on thier cars also do the full exhaust and that is usually the same diameter as the collector, or the down pipe is the same diameter as the collector, which effectivle adds to the length of the collector.
I know most of the headers describe above are not available for the J-Bodie, but there isn't anythig stopping some one talented enough from making what ever design to fit thier pupose.
Well, I've just type my longest post yet. I hope this helps
