LSA/LDA vs power production ??
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:
