I think some can't see the forest for the trees. To say "they figured all that out in the 70s" is a ludacris statement. You think nobody has learned anything in 40 years?

Modern stockers are over 1 second faster now that back then. Same parts such as heads intakes and carbs, yet the cars are way faster. The camshaft if the heart of any engine and what will make it run or be a turd. There is no current stocker record holder out there with a 70s grind camshaft in it. Will about bet the farm on that one.

The rod connects the piston to the crank, that's it. Doesn't matter in any other facet. People get WAY caught up in rod ratios and what's good and what's bad. Guys way smarter than me say it doesn't matter and I have found the same results.

People also do NOT understand the difference in intake centerline and lobe separation angle apparently. A 118 LSA cam installed at 116 does NOT always mean it is advanced. LSA is the intake centerline and exhaust centerline added and divided by two and is usually NOT the same as the intake centerline. Lots of big cams may have the intake ground on a 116 centerline and the exhaust ground on a 120 or wider centerline. That cam would have a 118 LSA but installed on 116 would make it straight up

As far as Don's deal, seems he told Scott before he ever tried it, that it wouldn't work. So he went into the experiment thinking it wouldn't work, so how much effort did he put into making the cam work. Did he do any carb changes, timing changes, maybe a converter? Just because you swap to this cam from another and the car slows early, doesn't mean the cam is wrong, just that it didn't like the current parts arrangement.

As AL has tried to point out, there is no magic PART........its the combination of ALL the parts and making them work right

The LCA is just a number derived from making the correct selection of the following. Pick the correct intake duration and closing point. Pick the correct exhaust duration and exhaust opening point. The numbers that end up are just that, numbers. Think about what happens to those two points and the LCA number when you go from a mild 230@.050 to a more aggressive 290@.050?
Doug

He knew I wasn't going to change anything in the combo. It was already sorted out Monte. Your right, I didn't think it would help. That doesn't mean I wasn't willing( in spite of that thought) to tear off the front of the motor and install it and give it a shot. It was at that time a heavy 3350 pound car with like 11.8 compression. It just wouldn't run as good. And yes, I did tinker with timing and such, trying to get the ET slip better. It isn't the first time I have tried something that didn't work. I suspect with a good bit more compression and convertor it might have worked better. But it didn't have that. I had what I had. And frankly saying it ran only a tenth off was being nice about it.
You missed a key point I made. He said it would run better with what I had, not if I changed everything around. It didn't.

Must be why they use those short rods in Formula 1...

The length of the rod is only part of the equation. If you have a 4 inch long rod and a 2 inch stroke, you still have a 2:1 rod/stroke ratio.

From the tech Archive from December 2010:

#828302 - 12/02/10 12:35 PM Re: Great info on rod ratio!! [Re: polyspheric]
Streetwize Online content
master

Registered: 01/20/03
Posts: 9419
Loc: Weddington, N.C.

While the (100% technical definition of) Dwell is instantaneous and constant, the rate of descent to and rise from that dwell is still measurably different between different strokes and rod combinations and it's effect may be 'mathematically' subtle...but one could argue that 2 different cam lobes with the same .050 durations are also subtle yet measurable...and since a crank is moving at 2X the speed of a cam the effects of those rates of change can be significant. 'Effective dwell' is the degrees of crank rotation on either side of the TDC and BDC where the piston is 'Virtually' parked as the crank rotates past those points (before reversing its direction).

So when discussing this (in practical and not NASA Science Lab terms) it really depends how much 'Fly Sh!t you want to pick out of the pepper'.


Very slight changes to anything effecting differential pressure (flow through a manifold and into a cylinder) can make measurable differences in power output....remember we're mixing fuel and air under pressure here!!....as correctly stated above you often "trade off"...bottom for top or vice versa...but a saavy tuner can usually work a particular combination to an advantage for the application he has. Short rods are generally more tolerant of a larger cam for a given CR as well in terms of attaining good part throttle drivability and street manners. Just a couple things that come to mind.

Typically for a given head flow a longer ratio favors top end breathing, a shorter ratio is advantageous for initiating low end torque...which in real world terms is likened to MOMENTUM...isn't it usually easier to keep something moving than to get it moving initially? (like from a standing start).

Short rods to me work best in motors that have a relative abundance of head flow...lets say race heads on a stock block where you don't necessarily want to (or need to) wring out every last potential drop of top end horsepower....or as in the engine masters type build where the sum of the Average torque across the powerband is more critical than the peak HP numbers.


BTW....Rod/stroke ratio is a misnomer....it should really be considered as R:1/2S as the rod angle can only be effected by 1/2 of the total stroke....in Pathagoreon terms 1/2 the stroke and the rod lengths are fixed (constants) and the 1/2 stokes rotation around its axis determines the (variable) triangle....which varies throughout the piston's motion.... any point other than TDC or BDC...where it is a straight line....but only for an instant.

I remember my shop teacher 35 years ago saying if you took a 1 cylinder motor and could park the trapped air fuel charge at precisely TDC and lit it off the explosive forces would be straight down and the crank wouldn't turn Well that's what starters are for anyway...to tell the crank which way it's supposed to go

Hope somebody captures this thread this time, it seems we have this same discussion every 6-8 months or so

Glad you pointed that out, I've forgotten it so frequently since first encountered... in 1964.
Let me guess: wheels are round, and water is wet?
Or must I use the <sarc> tag?

Then say it correctly. There is no such thing as a long rod, long tube headers and the like.

You keep tripping over your ego.
By "correctly", you mean "agree with you"?

Sorry to say, but you must include yourself, in not understanding LSA vs ICL.

A cams Exhaust and Intake centerline will Always Match the LSA angle in number When Centered equally or "Straight up" at piston TDC between the exhaust and intake cycle. It will only alter, when moved from that position, centered straight up position.

0 Degrees advanced or retarded. Straight up. Centered. Equal split left or right, dead center between the two lobes exhaust and intake when the piston is at TDC.

Its from this centered Reference point 0, that the cam can be measured advanced or retarded in relation to the crank, regardless of the LSA number.


Lots of people still feel straight up is when the dots are lined up, as did I at one time. But the true meaning is as I have described. Its a simple mechanical event, then measured from there. But not simply understood.


Also the term "Straight up" doesn't accurately describe the cams lobes actual position on measured cylinder. Lobes are actually pointing down away from said cylinder but equally in both cam degrees and crank degrees. But its a Visual left and right of a centered cams lobes in a graph showing a equal split in degrees for a better understanding.

Also a term just to describe 0 Advance and 0 Retard, of the exhaust and intake lobes Equally split in both Cam degrees and Crankshaft degrees at piston TDC as described above.