stealth71

iTrader: (15)

That is one sick ride you've got there. I guess I need to talk to Lou for a H/C package for my Chevelle LS1.

cantdrv65

iTrader: (3)

The G5X3 cam used here obviously makes EXCELLENT torque throughout the rpm range.... What LSA is this cam?

J-Rod

Its a 112. Nothing special, just the standard X3 package. Anyway, don't get hung up on one dyno graph. Point is, you can make 1.25X with a stock bottom end.

bichin95redta

This is probably the single, most complex topic when it comes to discussing power production. There are literally countless combinations of duration, lift, lobe separation angle/overlap, intake centerline, single/dual pattern, and valve event timing.

Some general rules-of-thumb:

Increased duration means the valve opens sooner, and closes later. The longer the valve is held open, especially the intake valve, the more top-end power the engine will make, because there is more time to fill the cylinder at high RPM. The downside is that longer duration cams tend to give up some low-to-mid-range power. This is because the later closing intake valve allows air & fuel in the cylinder to escape back into the intake manifold at low engine speeds. This is generally known as reversion, and occurs because the pressure in the cylinder, is greater than the pressure in the intake manifold. The faster you can open and close valves, the longer you can keep the valve open near maximum lift, which trasnslates to more air flow into the cylinder.

Lobe separation angle is the angular displacement between the centerlines of the intake lobe, and exhaust lobe. As LSA is increased, overlap is decreased. A 116* LSA will give a smooth idle, and a broad torque band. A "rumpety-rump", or "choppy" idling cam is a direct result of overlap. Valve overlap is measured in crankshaft degrees, and occurs as the piston approaches and leaves TDC, extending from the exhaust stroke of one cycle, to the intake stroke of the next. LSA directly affects overlap. Overlap is also influenced by duration. Given the same LSA, as duration increases, valve overlap increases.

Duration, overlap, event timing, and LSA are all interrelated; it is not possible to "tune" each of these characteristics independently for a single cam engine. Because of the compromise nature of single cam engines, if valve duration and overlap are increased past a certain point, all additional top-end power will be produced at the expense of low-end performance.

A typical cam card will list 4 opening/closing points: intake opening, intake closing, exhaust opening, and exhaust closing. Pay close attention to the intake closing point. This determines the point at which the rising piston starts to build cylinder pressure. High cylinder pressure results in improved torque production.

What the hell did I just say?

This is why, when it came time to select a cam for my stroker set-up, I left the choice up to my engine builder. He tried explaining the above points (and more, that just went in one ear, and out the other, it was SO over my head) to me so I would have some idea as to the technical reasons he was choosing my particular cam grind. After he was all done, I just said, "Sure. Okay." God, some of the valve event diagrams this guy was drawing, and the techno-speak he was using, made me think I was sitting in on a physics class.

Anyone who has a full understanding of the dynamics of cam selection, and its relationship to valvetrain events, and HP/TQ production at low, mid, and high level engine speeds, has my undying respect.

chevyhighrider

Would it be possible for someone to post up two dynographs of engines with similar peak horsepower, one with good power under the curve, and the other with just good peak power? That way we would have a good visualization of some of the explainations that were given. Thanks.

MadBill

For an illustrative (albeit unreal) example, envision two geometric shapes drawn on a typical HP graph, with the X axis being HP and the Y axis RPM: Representing a nice broad, fat power curve, the first shape is a half circle, arcing up from zero RPM/zero HP to a peak of 400 HP at 3,500 and back to zero HP at 7,000. The second, representing a narrow, peaky power curve, is a triangle formed by a straight line rising from zero RPM/zero HP to a similar peak of 400 HP at 3,500 and straight back down to zero HP at 7,000.

To simplify terms, let's say 1" = 100 HP on the 'X' axis and 1" = 1,000 RPM on the 'Y' axis.

So for the half circle, the "area under the curve" will be 1/2(Pi x R squared), or 1/2( 3.14 x 4 x 4) = 25.1 sq. in. Dividing this by the length of the 'Y' axis, 7,000/1,000 or 7", gives 3.59" = the average height on the 'X' axis (HP) or 359 HP average over the entire RPM range.

For the triangle case, the area will be 1/2 the base x the height: 1/2(7 x 4) = 14 sq.in, or an average output of only 200 HP.

HOWZAT?

Old SStroker

ZAT is a great visual, Bill!

Only one correction to offer: You said "Pie are square". Cornbread are square, Pie are round.

FieroZ34

iTrader: (1)

It is a good visual I guess, but it doesn't mean anything about performance.

MadBill

Boston Cream Pie are square...

MadBill

It means everything. If you accelerate through the entire RPM range in any gear, the 'circle' power curve will provide 359/200 or almost 80% more total accelerative force than the triangle one. It also means that if your gear ratios are such that the RPM drops 30% when you shift, you will be operating in a much higher average power range (shifting at 4,100 RPM and dropping to 2,900).

Another way to put it is that with the triangle 'curve', the acceleration will be worse at every speed except 3,500 RPM, where it will briefly be equal.

joecar

I thought "area under curve" meant area under the torque curve, and hp then follows from multiplying torque by rpm.

MadBill

It can mean either curve, but usually it is the HP that is of greatest concern and whose area most determines potential performance.

Ric

McDonald's apple pies are kinda square... more rectangular, though.

Ric

And I've ate round cornbread before, too. So don't go thinking ALL cornbread are square, now.

Old SStroker

It depends on where y'all hail from, I reckon. I'm fixin' ta' get me some cornbread for dinner. Yum!

Engine Masters Challenge used average torque plus average power for scoring. "Average" was the value every 100 rpm or so added and divided by the number of increments. That's a fair approximation of area under the curve. EMC weighted avg. torque and avg. hp equally. Of course making the torque curve fat at the top end helps the avg. hp curve a lot.

AngryJ

iTrader: (1)

exactly... find a curve fit equation and integrate it