cam timing using cranking pressure

[MadBill]

Just to know that 4°A. is commonly but not universally ideal, I observed a test of a big Hemi with a 116° LSA cam, initially installed 4° A., per the grinder's direction. Moving it to straight up was worth over 25 HP peak, with gains starting at ~ 2,000 RPM lower.

As has been stated before, If moving the cam around +/-4° has no significant effect, you've got the wrong cam. (But if it does, that doesn't guarantee that it's right.)

[Bucky]

What does the split have to do with where you install a camshaft? Do some use the lsa number to degree a cam??? When we say that a manufacturer recommends advancing the cam 4 degrees......4 degrees from what?

[MadBill]

4° from 'split overlap', aka 'intake centerline the same as exhaust'.
It can get confusing with different durations for the two lobes, as some incorrectly think the intake opening and exhaust closing angles should then be the same at the straight up/split overlap position.
(Hopefully no one will bring up the "what-if" of asymmetrical lobes... )

[Stan Weiss]

The graph is for 327

Doesn't matter; except for a minute effect due to rod/stroke ratio.

Here is the difference for the 327 with the 5.7" rod and a 5.0" and 6.4" rods

Stan

IVCCGPCR2.gif

[Dan Timberlake]

Ron Isky - Advancing the cam a few degrees looking for an increase in cranking compression is very popular among some circle track racers, presumably because of an advantage in mid range acceleration off corners.

Joe Sherman reports most engines want 2-4 degrees advance. Apologizing to Joe in advance if I'm wrong, I'm guessing best HP and torque numbers are among the things Joe is looking for.

So advanced at least 2 and perhaps as much as 8 degrees from certified "straight up" is good for "everything."

So now I'm wondering why cam grinders don't simply grind cams like that in the first place.
Also makes me wonder if the other events also work "better" advanced, or if the intake closing just kind of drags them along.

respectfully,

Dan T

[Warp Speed]

Why is the IVC event always presumed by the masses to be the most important?

[MadBill]

Ron Isky - Advancing the cam a few degrees looking for an increase in cranking compression is very popular among some circle track racers, presumably because of an advantage in mid range acceleration off corners.

Joe Sherman reports most engines want 2-4 degrees advance. Apologizing to Joe in advance if I'm wrong, I'm guessing best HP and torque numbers are among the things Joe is looking for.

So advanced at least 2 and perhaps as much as 8 degrees from certified "straight up" is good for "everything."

So now I'm wondering why cam grinders don't simply grind cams like that in the first place.
Also makes me wonder if the other events also work "better" advanced, or if the intake closing just kind of drags them along.

respectfully,

Dan T

First, the operative word is "most, not "all" Second, most shelf cams are ground with 4° advance. Given all the variables, even within a class of engine/application, the odds of any shelf cam having all four events within a couple of degrees of ideal for a specific application are at least 100:1, so A-R adjustments are useful for achieving the 'least bad' compromise.
The "ideal" cam will have all four events optimized at some particular A/R index and power will suffer significantly with any change. However, [/i track performance may still be helped by advancing/retarding as this can somewhat tailor the power curve to track conditions.

[MadBill]

Why is the IVC event always presumed by the masses to be the most important?

Despite the title, a major discussion re relative importance of valve events runs through this thread: viewtopic.php?f=1&t=38480

[Dan Timberlake]

.............Second, most shelf cams are ground with 4° advance.

So, even ground 4 degrees advanced (from ???) MOST cams want even more, maybe an ADDITIONAL 4 degrees?
So why aren't most cam ground 8 degrees advanced ( from ???)

Sure hope Cam King is willing to check in on this one.

[lorax]

.............Second, most shelf cams are ground with 4° advance.

So, even ground 4 degrees advanced (from ???) MOST cams want even more, maybe an ADDITIONAL 4 degrees?
So why aren't most cam ground 8 degrees advanced ( from ???)

Sure hope Cam King is willing to check in on this one.

Many do grind them 4* advanced,
When you look at the early days of hot rodding, and cam grinding, they all ground cams straight up/split over lap. It was "assumed" the builder knew where he wanted it installed, and not necessarily the job of the grinder to make that decision. Not saying they wouldn't make a recommendation, but the cams were ground in a "neutral" position.

No matter how many papers and booklets Ed Iskendarian, Jack Engle, Howard Johanson, or Chet Herbert wrote on cam timing and the effects of advancing and explaining the overlap period, and IVC or anything else, the vast majority of cams were installed dot to dot, straight up, or so they thought. The timing marks said they were.

Along comes the original trio from RHS and they decide they want to market cams to compliment their heads, and they realize 2 things. Timing sets are being made 4* degrees retarded(early smog era) and almost all engines were being over cammed, plus they almost always ran better if advanced, and very few customers were bothering to check the true timing. So they started grinding them advanced and wa la, instant success for a simple no cost concept.

Some companies jumped on the band wagon and started doing the same thing. But with most true racing cams I buy, they are still ground straight up, and I believe should be.
Street cams like Comp Cams when they started selling cams, is another story, and more and more street/strip oriented cams from others are ground advanced,

[Dan Timberlake]

To clarify -

When I say a cam is installed advanced X degrees, or straight up, etc it is because I checked (measured) the timing events with a degree wheel and a verified TDC relative to the piston motion and compared them to the specs on the cam card. if I found that timing events indicated the cam was advanced or retarded my first inclination would be to use offset cam sprocket bushing or an offset key or an alternate keyway on the crank sprocket to bring it back to a true "straight up."

If someone on this board says they installed a cam advanced X degrees I would hope/expect that means they did the same, and did not just pick a different keyway on the crank sprocket, etc.

I repeat my question, modified a little bit.
So, even though reportedly MOST cams are ground 4 degrees advanced (from ???) MOST cams want even more, maybe an ADDITIONAL 4 degrees?
So why aren't most cams simply ground 8 degrees advanced ( from ???)

I Sure hope Cam King is willing to check in on this one.

[MadBill]

No. Advance is measured from straight up, aka with the intake centerline angle the same as lobe separation angle. The likely 'sweet spot' is 4°advanced from straight up, or as-ground (or at least intended to be) by many suppliers. In other words, if everything is completely to print, installing such a cam 'dot-to-dot' will yield 4° advance.

[DaveMcLain]

Straight up cam timing is NOT necessarily the same as split overlap. Split overlap is when the lift at TDC is the same for both valves. This means that if the cam has different lobes between the intake and the exhaust split overlap will not happen at TDC when the cam is installed "straight up" with the intake centerline at the same number as the LSA.

[lorax]

Yep, split overlap at straight up only occurs with single pattern symmetrical lobe cams

All of which makes one wonder with all being written about "the hot setup" being installing the cam 4* advanced, just how many are installed that way by guys not actually timing the cam in, not knowing that the cam is already ground 4* advanced.
I have NEVER seen a timing card that stated a cam should be installed 4* advanced, only that it should be installed XXX* intake centerline, even though it was already ground that way.(nominally)
I can just imagine how many cams are installed by Johnnie Racer 4* advanced using a multi index crank sprocket, and end up 8* advanced.

[3window]

Guilty!!! Last cam I put in I didn't degree in, just used the dots. Car felt sluggish for what it was, but I knew it was over cammed (cam was originally bought for a larger engine). When I replaced the cam with a custom grind, I did degree it per the company's recommendations and found that dot to dot the cam was roughly 8 degrees retarded!!! when I found this, I checked it several times, yep, way off. New cams in where it belongs and I can't wait to drive it. Makes me wonder how terribly the old cam affected the engine seeing that it was too big to start with and then retarded possibly 8 degrees!