ptuomov

Whether the stock cams or Simard's steel (4150M?) cams are stronger wasn't the question here. The question was whether Simard's cams are weaker or stronger with the gun-drilling option or without it. That's a purely theoretical question.

If we're interested in practically relevant questions, one of those would be how these different cam profile + cam material + lifter combinations wear. Even if I understoof how the maximum velocity of the profile relates to the lifter diameter and the cam lobe width and even if I understood how the lobe width and the lobe curvature relate to the stress on the nose and the oil film thickness, I still wouldn't know enough the cam and lifter materials and their hardening relate to the maximum allowable stress and oiling conditions. So there are many unresolved (to me) questions here that are of practical relevance.

blown 87

Ok, here is what I was told by some one a lot smarter than myself.

if you take a one inch torsion rod a foot long that is solid it will not hold as much torque as one that is the same that has a rifle drilled hole in it of say 3/8 inch.
I was told it was due to surface tension.

Like I said, I really do not know if it is true or not.

jon928se

If it is true the only reason I can think of is uneven shear flow in the solid rod. I suspect that it may be the more popular comparison between a tube and a solid rod of equal weight per foot.

RKD in OKC

Gun drilling is done to make a rod lighter weight NOT stronger by making it into a tube. You are removing material from the center where it does not have much effect on the overall strength. There might be some misconception of overall strength because the solid rod will start deforming before it fails, but the tube will fail first.

The main determining factor is the section modulus of the rod or tube. Section modulus is the cross-sectional area with a relation to the distance from it's center. A rod and a tube of the same diameter have the same maximum distance from the center but the tubing has less overall sectional area so it is weaker.

Google Beamboy for a calculator.

slate blue

Very nice cams, what lift and duration did you go for?

Greg

Speedtoys

So..im guessing that gun drilling out a cast iron cam..would be a -bad- thing, and these..are more created for this.

slate blue

Gun drilling a cast iron cam would be a disaster, they get their strength from bulk and the flexibility is very limited and the material is fragile.

Greg

ptuomov

A simple model assuming, among other things, that the material follows Hooke's law:

Angle of twist = (torque * length) / (modulus of rigidity *second polar moment of area)

For a pipe, second polar moment of area = (pi/32)*(outside diameter^4 - inside diameter^4)

In the limit where the id declines to zero, second polar moment of area for a solid bar = (pi/32)*outside diameter^4

Three observations.

First, under the assumptions, solid bar always twists less than a pipe if the od is the same.

Second, the pipe (with some id) is always more efficient if weight is any consideration at all.

Third, if the pipe id is small, the difference between pipe and solid bar is very small. Therefore, it's quite possible that making the assumptions more realistic will in fact change the conclusion that the solid bar always twists less than the pipe, as long as the id is small.

Caveat lector, internet engineering. I am not an engineer, I don't know the one and only true path of porsche hot rodding, I can't read dead people's minds, and I don't belong to professional societies (after I got booted out from the NBER). In other words, for all I know, the above could be total bs.

Darklands

My engine builder tells me that a great portion of rpm limitation of the 928 engine comes from the open deck concept.
So you can tune the valve train in the heads but your small block has the same limitations.
What is about using stabilisation plates on top of the bores .

ptuomov

In theory, torque / cylinder pressure limits maybe, detonation limits maybe, but why rpm limits from the open deck?

I am not an engine builder but my noob opinion that all this business about open vs. closed deck blocks is irrelevant on a well tuned engine. Look at what the 951 / 944 people are doing with their open deck blocks. Turbos are boosting to insanity and N/A are revving it as much as the largest cam that fits allows. Mostly with open deck blocks.

shmark

Somebody ping Mike and have him chime in here. I'm sure he can say exactly what's going on. Besides, not being a machinist, I would like to know how you do the actual drilling. That's a very long hole that's a significant portion of the diameter of the rod and it can't be easy to maintain stability during the drilling process. Not something an amateur could undertake, I suspect.

[edit] Oh and Sterling they look fantastic! Now that I've actually seen your car in person I would like to hear it run someday. Guess I'll have to plan another trip to Texas.

tv

I believe Mike S took care of that in his engine with those nice, drilled lips on the top of the cylinder sleeves that in effect create a top plate that also "beathes".

The only problem I can guess at is the movement in an open deck might stress the cylinder walls to a point of cracks developing. I thought I remembered someone pouring a pasty cement-like goop around the bottom of the cylinders to prevent this.

andy-gts

I have a set and the purpose was to decrease the rotational mass, less stress on the valve train and quicker and higher rpm......ah ...higher rpm safer !!!! He has already demonstrated it works all too well..( I think shelby used them also)

ptuomov

Take a look at the edm and other tools that his shop has:

ttp://www.simardtool.com/

He's got tools that can burn a passage inside a camshaft such that if you'd later split it in half along the axis the passage path would read in script font "this was easy."

shmark

I've been in his shop, definitely a cool sandbox. Just wondering about the mechanics of actually drilling something like that.