LSA/LDA vs power production ??

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moper

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Ok, first, here is the Car Craft magazine article that talks about the Lobe Seperation Angle (or Lobe Displacement Angle as they call it) and Intake Center Line that was posted on another thread. I would like to have a decent tech discussion on this if we can. There is a lot of stuff to be learned from everybody here. So be thoughtful, and constructive and try to keep the feeling light.

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My own opinion is that when the entire system, rather than just the cam and crank, are taken into account; and when the reason for the build is a multi-use engine; then the result is the wider LDA will make more power. Not peak power, but more average. In terms of cylinder pressure as measured with the starter turning an engine with no plugs in it... The earlier the intake valve closes, the more cylinder pressure you will have. This means little in a running engine, but for the sake of "apples to apples" and diagnostics, this will always be the case. Simple physics. The lower the piston is when the intake valve closes fully on the upward compression stroke, the more air will be trapped in the swept volume, and therefore the higher measured pressure. A side note here, I think from Georges written posting he states the closer to Top Dead Center the piston is.. I'm pretty sure that's a typo... it's the further from Top Dead Center, or closer to Bottom Dead Center when the intake closes. I agree as was said in the other thread, there is no correlation between cylinder pressure and vacuum. The exhaust valve has nothing to do with cylinder pressure as measured, and will only have some affect once the engine is turning fast enough for the air to have enough inertia and the presure waves get strong enough to help (or hinder).
So let's hear the thoughts.. I have a lot more but I'm stuck at work and busy. No internet at the farm yet...
 
There's a lot of good information in there and it is true that for many of us the technical numbers outside of lift and duration of a cam are a gray area, any chance we may be able to get this stickied??
 
Good thread Moper. I know the basics of cam's and how certain numbers affect it's characteristics but not enough to add much of anything so I'd love to hear some more of your thoughts. And others thoughts as well.
 
I read that article and walked away from it thinking that this will confuse people and builds are going to get screwed up. In my '79 318, I choose a Crane cam with a 112 C-line for the idea of a broad powerband on a lower compresion engine.

If I was to disregaurd the smog era compresion ratio and cam it like a kid and a new hot rod toy while listening to a theroy of a narrower C-line of 110 or less for a peak power / top end pop, I'd be sucking wind the rest of the time thinking I'm fast.

Cam design, all around design has to be taken into account and thought out before on leaps and shouts "Brand X makes the best cam and I run it so should you because I go fast" statements are taken seriously.

Think twice, choose wisely before purchasing and installing the cam. Pro's are a phone call away.
 
You know, when I see the clarity & technical mastery displayed in these responses, I realize the error of my ways. I just cant hope to compete here, so from now on, I'll just listen & learn, and leave the tech questions to the real experts on this board.
 
I agree generally speaking a wider lsa is going to be better choice for a dual purpose engine,I do not like anything over a 110 personally because I think they tend to go to a point of neglible returns in a properly built n/a performance engine.I consider the bore stroke combo in addition to the vehicle weight and purpose.Most engines I build that are generally square or even oversquare get a 110 while my 340 (big bore short stroke) for my light,four speed duster is getting a 108.Its such a broad discussion and there are alot of variables but thats what makes it so fun picking a camshaft.

I should add for fun I dont really consider the company of origin when picking a cam but I find I mostly use lunati and comp for off the shelf grinds.
 
You know, when I see the clarity & technical mastery displayed in these responses, I realize the error of my ways. I just cant hope to compete here, so from now on, I'll just listen & learn, and leave the tech questions to the real experts on this board.

Oooooo, sarcasm is running rampant! lol. Easy buddy, Moper asked that we all be kind and I don't see why you're so upset about this. It's just a tech discussion on the internet for pete's sake. :thumrigh:

Now, the following has always been my understanding of narrow LCA's vs. wide LCA's:

Narrow LCA

Increases cylinder pressure
Has a higher tendency to detonate with high compression and pump gas
Pulls less vacuum at idle
Idle quality is worse for a given duration
Best for a low compression stock engine
Does not work well with electronic fuel injection
More low end torque
Peakier torque delivery

Wide LCA

Reduces cylinder pressure
Has less tendency to detonate with high compression and pump gas
Pulls more vacuum at idle
Idle quality is better for given duration
Better for a high compression, big valve/port build
Can work well with electronic fuel injection
Less low end torque
Broader torque delivery and allows a higher rpm potential IF the engine is built for it.

With this said, please read this next article by David Vizard. He brings some points up that I haven't thought of and adds more fuel to the fire.

http://www.stockcarracing.com/techarticles/scrp_0612_lobe_centerline_angles/index.html

Comments george? Please don't be shy. :) We're all adults here and there's no reason why we can't have a contructive discussion and all learn something new.
 
Oooooo, sarcasm is running rampant! lol. Easy buddy, Moper asked that we all be kind and I don't see why you're so upset about this. It's just a tech discussion on the internet for pete's sake.

Yea, maybe, but, that's what chattin is all about.

lead69, that's about how I follow C-lines when I build them. Performance wise. Bigger the engine , lower the C-line as well.
 
Sorry guys, as I have little time lately to answer my own stuff...lol. The thing that appears in both articles is the assumption of a good flowing intake port (recall this is from the carb to the valve) and an exhaust with little or no back pressure. In the first article, the engine's peak torque is 5500. No street engine intake length will show peak torque at 5500. They are looking at race engines. The typical 1 5/8 header, or 1 3/4 header, coupled with 8' of pipe and mufflers also is not zero or low restriction when compared next to a race engine and properly designed headers. Herein lies my disagreement. The LDA controls the way that 5th cycle works. How strong or weak, and therefore the rpm, peak reached, and the peakiness of the torque in an engine is affected that way. But most street engines dont reach the 100% efficiency mark due to consessions made to get it in a car chassis, under a hood, and/or quiet enough for the law. So I would like to get more into the "what ifs" that are associated with things the typical hobbyist sees. It is in that sector of engine performance where I say the opposite is true. Because my moving the LDA and ICL, you can use tailor the cam and the lack of that 5th cycle to make the best power within the parameters of a street car build. I think that little "set of givens" in the articles is a huge point of contention.
 
5500 is way to high for a street engine IMO and I think it's closer to 3000 RPM's give or take 500 on ethier side for a street driven machine. That's more real world to me. I know theres guy's out there driving cars on the street that make crazy power and peaks @ 5500 or better, but that isn't really a street driven car by the average driver of a hot rod.

The exhaust and head issue is another part of the article that just assumes a "Stage" of build they think is more likely to be on the street over a stock headed engine.
In chassis engines and performance parts are allways limited to the cars sheetmetal and of course, there performance potential.
 
Sorry guys, as I have little time lately to answer my own stuff...lol. The thing that appears in both articles is the assumption of a good flowing intake port (recall this is from the carb to the valve) and an exhaust with little or no back pressure. In the first article, the engine's peak torque is 5500. No street engine intake length will show peak torque at 5500. They are looking at race engines. The typical 1 5/8 header, or 1 3/4 header, coupled with 8' of pipe and mufflers also is not zero or low restriction when compared next to a race engine and properly designed headers. Herein lies my disagreement. The LDA controls the way that 5th cycle works. How strong or weak, and therefore the rpm, peak reached, and the peakiness of the torque in an engine is affected that way. But most street engines dont reach the 100% efficiency mark due to consessions made to get it in a car chassis, under a hood, and/or quiet enough for the law. So I would like to get more into the "what ifs" that are associated with things the typical hobbyist sees. It is in that sector of engine performance where I say the opposite is true. Because my moving the LDA and ICL, you can use tailor the cam and the lack of that 5th cycle to make the best power within the parameters of a street car build. I think that little "set of givens" in the articles is a huge point of contention.

As you know, torque is just cylinder pressure, and HP is a mathmatical equation of such at a given rpm.

Given this as a start to my next point, cranking compression as George has stated is higher with a narrow LDA. This is in my experience with DOHC motorcycle engines (where I can adjust it with slotted sprockets) as it has been with my v8 builds.

Now, to your point which I believe is valid but no real way to test barring a dyno with a "hat" which would give us real time VE and BSFC. Like I said, what you say is valid and that is "Running Cylinder Pressure". Like you say, this is dependant upon the combination and I agree 100%, although the basic differences I stated above regarding narrow vs. wide LCAs still generally apply.

I like your premise to speak of the "average" street/strip driven car on pump gas, naturally aspirated with a street exhaust and how should these theories can be implemented to benefit us. I'll give you some real life experiences plus some "book" theory I've had over the years. This is obviously up for debate as that is what this thread is all about!! I've only had about 25 years experience and know that there is always more to learn. :thumrigh:

1: The cam is the brains and the short block is the heart of the engine. Too much compression and too small (duration/LDA) will lead to detonation. Not enough compression and too big a cam will suck on the street and run like crap, although it might sound good (racy) at idle.

2: Too small a carb/manifold combo will run and be responsive as hell in traffic, but right where the combo should be pulling hard it chokes.

3: Too big a carb/manifold will suck around town but haul *** on the entrance ramp and dragstrip. :)

4: Buying a cam with a .600 lift when your head flow stalls at .500 is pointless.

5: Duration @ .050 matters more than LDA in an average street/strip motor. This changes on a big valve, Indy/W2 headed high comp stroker.

6: Altitude matters! The higher you are (no jokes please, lol) the more compression you can run safely and breathing means everthing. :thumrigh: Most calculations I've seen pull 2% to 5% for every 1000' of altitude. I've seen over 9000' of density altitude at bandimere!!

OK, now for some real life crap. I'm running 10.2 measured comp ratio on a 360 bored .040 over with KB pistons and a Lunati cam with a 112 LDA to bleed off some low speed cyl. pressure, 213 degrees intake duration @ .050 and iron J heads, 2.02 valves and home porting w/34 degrees total advance. Even though I had the block milled to give me 0 deck, the heads milled to 68 cc, and a .040 Cometic gaskets, my quench is minimal with the open chamber heads. Keep in mind that this is at 5280' altitude. This thing is neck snapping right off throttle and pulls to 5.2k before I get valve float from the Crane springs. This is in a 5 thousand+ pound truck with full time 4WD NP203 transfer case, 3.55 gears and 33x12.5 tires and steel wheels. Mind blowing to most Infinity and BMW SUV owners although I think Porche cayenne SUV owners would kill me, lol! UNTIL we went offroad..... :p

Now here's another of many expierences. I had a '75 Torino with a 400M. Don't laugh, a very, very experienced engine builder just won the engine masters challenge with the same engine (4.00x4.030) stroke and bore. Sounds familiar doesn't it. :)

Hold on, I'll back in a few minutes. :thumrigh:
 
I think George agrees with this sentence by his other posts... You cannot look only at cylinder pressure and relate it to torque production. In my opinion, it's like testing the done-ness of steak with finger pressure. It's a great way to roughly tell and the better the cook (or more experienced) the more likely the surmising will be correct. But really you should measure the internal temp. So defining torque simply as a function of cylinder pressure at 150rpm is vague at best, and totally off base at worse. This is because we mearsure at 150 rpm or so, and the engine doesnt run there. If simply building more pressure in it was the key, there would be much different camshafts being developed. It's the dynamics that make the package. Then inertia of the intaek charge, the heat soak or lack thereof of both the mixture and the port/chamber/piston materials and shape, the pressure wave tuning and scavenging of the exhaust. And THAT'S where the LDA comes into play. Because that is where all the dynamic pieces either work together and help, or work against each other and hurt the result. And to me, the key to the input values for the dynamic stuff mentioned, is piston speed. Meaning crankshaft stroke and intended rpm range of the engine. Note I said range, not peak. A point I made to George offline was that the LDA is the difference between the centerline of the intake lobe vs the centerline of the exh lobe, and with asymmetrical lobe designs where the peak lift or longer duration on one ramp may not be the true center of the lobe, and the fact that you can advance or retard the lobes in relation to the designed LDA, means the LDA becomes less of an easilly defined number.
 
OK, if this is still alive on the weekend, I will chime in with my thoughts. Glad to see some serious thinking going on here. Ramcharger & I are pretty much along the same lines on this.Sorry I havent really responded offline Ramcharger/Moper, cranky kid and a dinner guest last night. Man, now that i have a kid, I'm starting to wonder where i will find the time to work on a car!
 
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