first lets get something strait, theres two kinds of timing cam timing, the relationship of when the valves open and close relative to the pistons location at TDC and BDC and ignition timing which is the point at which the spark plugs fire in relation to the pistons position at TDC on the compression stroke.
cam timeing in the standard chevy V8 is set/locked in when the cam is installed and the relative timing of that cams lobe duration ,lift and LSA are set when the cam is ground/manufactured
ignition timing

http://www.centuryperformance.com/timing.htm

http://www.centuryperformance.com/vacuum.htm

http://www.boyleworks.com/ta400/psp/distcurve.html (pontiac but info the same for chevy)

http://www.73-87.com/garage/101s.htm

http://www.73-87.com/garage/hei.htm

here read this also http://www.victorylibrary.com/mopar/cam-tech-c.htm http://64.90.9.168/cranecams/pdf/276g.pdf
http://www.msdignition.com

how come its 180 degs out of phase? I get this question all the time, well heres something I see lots of guys don,t understand,ONCE YOUVE INSTALLED A CAM WITH THE TIMEING MARKS YOU MUST ROTATE THE CRANK 360 DEGRESS BEFORE DROPPING IN THE DISTRIBUTOR
... while its true that if the
timeing marks are possitioned so the crank is at 12 o,clock and the cam gear
is at 6 o,clock that the cam lobes will be in the possition that fires #6
cylinder that HAS NO EFFECT AT ALL (on finding TDC,) for aligning the degree wheel with TDC,or THE timeing tab pointer, for degreeing in the cam, the piston passes thru
TDC TWICE in every fireing cycle once on the fireing/power stroke and once
on the exhaust stroke, the cam rotates at exactly 1/2 the speed of the crank
so to make it easy to line up the marks they install it with the marks at
the closest point 6/12 for easy indexing, rotate the engine 360 degrees to
the #1 TDC power stroke and the crank gear will still be at 12 oclock 12/12
but the cam will be at 12 o,clock also, rotate another 360 degrees and your
back where you started. its simply easier to index the cam at the point
where the index marks align closely. look at how the cam lobes themselfs
open the valves when the cam is just installed the #1 cylinder valves are
slightly open and the #6 are closed
per "Lunati"
""YES YOU ARE RIGHT - WHEN CRANK IS AT TWELVE AND CAM IS AT SIX THEN #6 CYL IS FIRING
AFTER YOU LINE UP YOUR MARKS AND INSTALL GEAR THEN ROTATE YOUR CRANK ONE REVOLUTION AND THEN DROP THE DIST. IN - AT THAT POINT #1 IS FIRING""

cam timing
BR>Explanation of Crankshaft timing marks:

0 - Indicates standard cam timing A - Advances the cam timing 4° R - Retards the cam timing 4°

this is some of the best basic cam info youll find so read this first,
http://www.newcovenant.com/speedcraf...camshaft/1.htm (lessons 1-8

http://www.mercurycapri.com/technica...e/cam/lca.html
http://ctfba.tripod.com/main/technic.../cambasics.htm

http://ctfba.tripod.com/main/technic...raphAttack.htm

http://moparjimsgarage.virtualave.net/camvalve.html

http://www.federal-mogul.com/speedpr...speed_pro.html

some good general info here

look closely at the duration used for each MATCHING rpm range. ALSO KEEP IN MIND THE DCR AND OVERLAP MUST MATCH look here these are the valve timeing overlap ranges that are most likely to work correctly
trucks/good mileage towing 10-35 degs overlap
daily driven low rpm performance 30-55degs overlap
hot street performance 50-75 degs overlap
oval track racing 70-95degs overlap
dragster/comp eliminator engines 90-115 degs overlap
but all engines will need the correct matching dcr for those overlap figures to correctly scavage the cylinders in the rpm ranges that apply to each engines use range http://cochise.uia.net/pkelley2/Overlap.html

http://cochise.uia.net/pkelley2/DynamicCR.html

plug info

here you want plug info? we got plug info!

http://www.acdelco.com/html/pi_plugs_ident.htm

http://www.atlanticjetsports.com/_techtalk/00000005.htm

http://www.ngkspark.com.au/spark_plu...art_index3.htm


http://www.strappe.com/plugs.html

http://www.babcox.com/editorial/cm/cm59910.htm
http://www.ngksparkplugs.com/techinf...tnumberkey.pdf

http://www.eric-gorr.com/techarticles/sparkplugs.html

http://www.gnttype.org/techarea/engine/plugs.html


http://www.tsrsoftware.com/sparkplug.htm

http://www.racinghelp.com/read_spark_plugs.html

http://www.ngksparkplugs.com/techinf...overviewp2.asp


http://www.projectbasketcase.com/menus/ignition.html

why is there a need to advance the timing when the engine is higher in RPMS?

ok lets look at it
lets use a mild high performance cam in a 350, at idle the engine is spinning about 800 rpm
now every other rotation /stroke is a power stroke as it compresses and fires the cylinder, thats 400 power strokes a minute, v-8 chevys make most of the cylinder presure and useable power over about 22-24 degrees after TDC but at idle it take about 5 degrees advance in the ignition spark timing to get the flame to cross the cylinder, building pressure to effective levels and it takes roughly 40 thousands of a second to light and burn the compressed mixture
60 seconds /400 power strokes=.15 seconds per power stroke (but thats 360 degrees)of which 22 degrees is burn time =.0091 seconds) now with about 5 degrees needed to get the ignition going and building pressure we have .002 seconds needed to get good ignition in the cylinder started.
now lets increase the rpms to 6000 rpm thats 7.5 times faster so in theory if the ignition time nessesary needed to stay the same for the flame to cross the cylinder and build effective pressure we would need 7.5 times as much advance in the ignition timeing or 37.5 degrees to maintain that same .002 burn time before the piston passes TDC and the cylinder pressure reaches useable pressure to push the piston down the cylinder efficiently.
now in the real world there are several other factors involved here but you should get the basic idea, it takes time for the cylinder to ignite and burn the compressed mixture, the time stays almost the same at any rpm COMPARED TOO the vastly SHORTER TIME AVAILABLE DUE TO THE INCREASED RPMS , THUS A GREATER LEAD TIME IS NECESSSARY IN THE IGNITION POINT TO BUILD PRESSURE TO THE SAME USEABLE POINT in the cylinders ROTATION.
look here
http://www.iskycams.com/ART/techinfo/ncrank1.pdf

youll notice the piston is only about 1/4 inch down the bore bye the time the cylinder pressure starts to drop.

http://www.geocities.com/ljaya6390/analysis.htm

and yes your correct as the rpms increase the cylinder swirl and tumble also increase as does the pulse strength and speed of the fuel trapped in the quench area of the combustion chamber, its normal that at some point the cylinder burn time is substantially shortened in time due to the increased speed at which the flame crosses the cylinder,due in part to the quench area throwing a increased jet of burning gas acrossed the cylinder helping speed the combustion, remember the faster the burn the the lower the time and the less advance necessary in the ignition point ideally youll have dual quench areas that squirt dual opposeing jets into the center of the combustion chamber and a centrally located spark plug for an extremely fast burn time, keep in mind that any pressure before TDC requires wasted energy to compress it as the rod swings past TDC





[Modified by grumpyvette, 8:37 AM 2/23/2003]

 

Eh, kinda. With a given cylinder head design (assuming you don't move the plug or valves, etc, etc) there is really only one major determinant in combustion speed....turbulence. If you look at spark ignition curves, you have a spark advance curve that starts at idle and goes to usually around 3200 rpm or so. At this point, the rate of increase of turbulence in the cylinder and the corresponding decrease in burn time balance with the increased piston speed, and therefore at full advance the burn duration can be discussed in terms of degrees of crank rotation. Up until that point, the decrease in combustion time will not cancel out the effect of increased piston speed, which is the reason for the timing advance curve. As far as burn durations go (at full advance), if you can find a wedge head that can burn at 22 degrees, you will make a TON of money....the best we've ever seen here at the research lab is ~27-28 degrees. Now, a 10-90% burn time of 22 degrees is common, but there is a HUGE difference in these two values. Also, the importance of the location of peak pressure (which usually coincides with the CA50, or 50% burn point) is in terms of making the best use of your combustion pressure. Too early, and as you say, you'll be fighting combustion pressure trying to reach TDC. Too late, and the energy you're releasing from the combustion is not generating the optimum amount of pressure. What's interesting to see is an overlay of a timing sweep while collecting IMEP data. When you find your location of peak pressure, and mark that crank angle and pressure value, and then advance the timing a little, you'll notice that your peak pressure value is higher (as is the magnitude of your pumping loop...bad...), but that your pressure at your location of peak pressure from optimum timing is of the same magnitude....In other words you do not perform any more work from your optimum CA50 down the line by advancing the timing, but you do increase the magnitude of your pumping loop, which causes a loss in brake power.

The other thing I wanted to mention has to do with the flame propagation. Very quickly, it's squish, not quench (VERY common misnomer). Quench is when the flame is extinguished, usually due to contact with the relatively cold cylinder wall. Anyway, the main point is that unless you have ported gas jets into the head (specifically from the combustion chamber into the squish area), you will NOT have a massive jet of flame moving across the cylinder. What you WILL have is a massive jet of end gas (end gas is the term for unburnt air/fuel mixture) that will fly across the cylinder, greatly increasing the amount of turbulence, part of which will pass through the kernel at the spark plug which will being flame propagation. Basically, squish induces mixture motion which helps to mix the air/fuel mixture and generate turbulence. The flame begins at the shear planes between two eddy currents in the end gas, which is why you will notice little rings of fire when you look at high speed film of cylinder combustion. You will further note that the flame burns inward from the shear planes of the eddy currents until it has burned to the center of that particular eddy current and that part of the flame extinguishes due to a lack of air/fuel mixture to burn. As this pocket is burning, the mixture motion induced from swirl, tumble and squish will cause this pocket to move around the cylinder, coming in contact with other shear planes of other eddy currents, igniting them so that that may burn from the outside in. One source of knock is when the temperature/pressure gradient inside the cylinder gets high enough that a pocket of end gas ignites due to the temperature and pressure, rather than coming into contact with the flame. This type of end gas ignition results in an explosion rather than a burn, causing sharp rises in LOCAL pressure and temperature, which can further increase the temperature/pressure gradient in that location. Typically, when one sees a pitted piston top, this type of knock has been present in the motor, as the local temperature and pressure can literally soften and blast away little tiny pockets of aluminum from the surface of the piston. It's VERY common in high CR race motors to have this as a normal fact of life.

For those of you who want to read a VERY good textbook on engine fundamentals (which has an excellent section on combustion models, mixture motion, knock theory, etc, etc) read Heywood's "Fundamentals of Internal Combustion Engines". It's definitely not a light read, but for those who really want to know, it's an excellent source.

 

CorvetteZ51Racer
thanks for the imput here,:cool: (I really enjoyed reading that)
its obvious that you know as much and quite possibly more than I do on this subject , but I hope you realise Im trying to keep this extremely simple in concept as Im sure theres at least a few people here on the site that are not retired engineers (mechanical)(like myself):cheers: (Ive found that the less technical I make the explanations the fewer peoples eyes glaze over) :D and if I got into things like rod lengths, piston dwell times, heat reflective coatings, piston pin off-set angles,aux. oil cooling the underside of the piston , higher ring locations , and gas ports to supply cylinder pressure to the rear of the top ring and reading burn patterns on the piston surfaces there would soon be an extemely limited audience reading this.
btw what do you think of these http://www.theoldone.com/articles/Ci...rl_Power_2.jpg http://www.theoldone.com/articles/Ci...rl_Power_3.jpg http://www.theoldone.com/articles/Ci...rl_Power_4.jpg http://www.theoldone.com/articles/Ci...rl_Power_5.jpg
http://www.theoldone.com/articles/Ho...ng_Heads_1.jpg http://www.theoldone.com/articles/Ho...ng_Heads_2.jpg http://www.theoldone.com/articles/Ho...ng_Heads_3.jpg http://www.theoldone.com/articles/Ho...ng_Heads_4.jpg http://www.theoldone.com/articles/Ho...ng_Heads_5.jpg http://www.theoldone.com/articles/Ho...ng_Heads_6.jpg http://www.theoldone.com/articles/Ho...ng_Heads_7.jpg

 

Wow! Good Read!
Its been a WHILE since there has been anything this technical and interesting posted, especially the head & swirl write up. Glad to see there are still people more interested in technical information. Keep it coming.

89'Bowtie




[Modified by 89'Bowtie, 10:17 PM 2/22/2003]

 

Grumpy, no prob :cool: I guess sometimes I look so much at the letter of the word that I sometimes forget the intended audience that may not have had the benefit of working with IMEP data, or watching high speed combustion film, etc, etc or even those who care about those types of details.

As fas as some of the info in the articles...

The overlaid graphs that they have at the beginning of the Circle Track article is kind of funny....the one they list as the typical curve isn't remotely what a typical curve looks like. It's not nearly that peaky, and it doesn't fall off that fast either.
They mention cylinder-injection engines being the wave of the future....diesels have been done this way FOREVER, the Audi R8 LMP900 cars in the ALMS series are direct-injected engines, as is the engine in the new BMW 745i.
There are some things in the circle track article which are good but don't apply to racing despite what they say, and some that don't make much sense. If you're burning more before the exhaust valve opens, you will have higher EGTs, because the more you burn, the higher the temperature and pressure gradient gets. If the temperature/pressure gradient is now higher because you've burned more, then the temperature of the gas leaving the engine will have that same higher T/P gradient. Now, they don't say where they're measuring the EGT, but quite frankly I don't believe an EGT of 300 deg F was taken anywhere near the heads.
Next, they say all of this nice stuff about high swirl intake ports, etc, etc. That's nice. Any experienced head porter will tell you the same thing about high swirl ports....they kill flow. I have worked with a top NASCAR head porter and watched him go back and forth between the porting bench and the flowbench (equipped with swirlmeter). EVERY single time his swirl went up, the flow dropped. Now, remember this is on maximum effort race heads I'm talking about, but I assume that Circle Track mag is referring to the same type of deal. That's why the race engine designers work to induce swirl inside the cylinder, using just the piston crown and head. The idea of ducting the air/fuel mixture over to the exhaust side has a very beneficial effect, one which they COMPLETELY missed in the article...the exhaust valve is typically the hottest point of the cylinder. If you get your wet, unburned fuel over to the exhaust valve, it will evaporate into a gaseous form. Once in a gaseous state, it can better mix with the air. That's also why fuel injectors are optimally aimed at the back side of the intake valve and they fire with the intake valve CLOSED...using the head of the valve to help vaporize the fuel for mixture purposes.
Oh, and the other thing I was wondering about in that article. They talked about high mechanical compression ratios....ok, what fuel are they testing with? The professor that runs the graduate racing engine design program here has a Chevy 358 that's running 15.5:1 CR. So what? He's running on 116 Octane. That's safe, there's nothing wrong with that. And yes, higher mechanical compression ratios will yield better burns, BUT you reach a point of diminishing returns above 16:1 on spark ignition gasoline engines, AND NASCAR is limited to 12:1.

On the Hot Rod article....
On the interview with Widmer....if you're not showing a gain in power on a steady state, but you are with an inertial dyno, you have a lighter rotating assembly (usually). The whole point of doing steady state dyno pulls is to see how much power you're making...that's it. Steady state removes variables such as rotating assembly weight, etc, etc from the equation.
Also, when he says "we had to run that cam to run that compression", what he was doing was admitting to using the cam to drop the dynamic compression down to manageable levels. You remember when NASCAR didn't have compression limits on the restrictor plate motors? They were running 20:1 on 110 Octane. Because of the size of the cam and the horrible flow of the restricted manifold, the dynamic CR at speed was around 10-12:1. If you fell below race speed, the motor would blow itself apart from detonation. That's why it used to be common to see people either blow a motor or blow a clutch when leaving the pits after a pit stop. It was a fine line between feathering the clutch too much or not enough....too much and you fry the clutch, not enough and you blow the motor apart. High CR...from what he's saying about the motor....so?

Oh, also, I don't remember which article it was in, but they were talking about high port heads...yeah, so? The air is moving so fast with so much momentum that it doesn't want to turn in the port. If you can't change the angle relationship between your intake valve and your head deck, you raise the intake port to increase the radius of the bend, allowing it to turn more easily.

The other thing that's funny is seeing the technology they had to work with back then.... a 1.94" intake valve on a Winston Cup motor? Good Lord you've got to be kidding me! Um, they're now running 2.15-2.20's with flow numbers upwards of 360 cfm and lifts over 0.750" on a small block head (I know for sure what they're running, but I can't tell you specifics...doing research for NASCAR is fun)

 

One of the most satisfying posts I've read in a long while. Plenty of links for good knowledge. As a former ME/current nuke guy, I love the technical explanation.

Now, since I've got the experts here... let's do something simple. Give me your expert opinion on timing and fuel to make a mild LT4/Hotcam setup run at under 45kPa MAP smoothly enough to prevent misfire detection by the crank sensor :) . After much tinkering, I don't think it can be done reasonably. If you can provide a solution to this then you'd have many a happy emission restricted performance nuts worshipping you :)

But being reasonable, what are your thoughts on smoothing out the idle/low MAP qualities of higher than stock overlap cams?