Re: Re: Overlap Calculation
 

:D

WELL I EXCUSE ME (quote from Steve Martin)

I held the exhaust as a constant and the 454/502 Mag cam as the reference.

I almost went on about exhaust but I figured some intelligent soul would do this.

FYI Look up proportional

:)

How about 226/235 with 108° and wet exhaust... runs and sounds great!!!

As LC decreases and duration increases the overlap increases My last example (my cam I had to look it up) has 2 degrees of overlap at 0.050. At 0.050 is where the lift become significant

Overlap can be calculated in the overall sense. My cam is as follows:

Intake duration @ 0.050 = 228
Intake duration overall = 280

Exh duration @ 0.050 = 232
Exh duration overall = 284

Overlap @ 0.050 = +2 degrees
Overlap total = 54 degrees

I also run Stainless Marine Captain's call (short)

14.5 You better have long (kingsize) risers!

And then the cam timing comes into play too.

I'm lost.:(

What about 216/228 112 Lsa?

Thanks for the replies,
First off, I did talk to Comp Cams.... not much help, more interested in selling me a new cam. B.S.

Camshafts to me are like an unknown science. I have water in the oil and just trying to rule out variables. Any more info would be great. Keep it coming!

Bajalion,
I am an engineer(propeller head) and very interested in the origin of your formulas for cam overlap.

If there is negative overlap, I assume the chance of reversion is eliminated?

Paul

If it is coming from reversion you will see it on your spark plugs. Pull one right after letting the motor idle and see if you see residue.

:eek: OUCH!!! I'm busted!!! Technically, I think you are correct, but as a practical matter, it isn't likely. In a dry exhaust system, I have heard that the danger is sucking a bit of cold air into a hot cylinder and warping a valve. The chances are fairly slim if you have a properly working exhaust system. However, if you have an exhaust leak near the cylinder or a great deal of overlap and a large amount intake vacuum with a short exhaust system such as a set of "zoomies" it could happen.

I stand (sit) corrected. :drool: :drool: :drool:

By the way, Bajalion -- overlap CAN be proportional to reversion. Your statement was "IS proportional". But then I guess it depends on what your definition of what the word "IS" is.:D :D :D

(Someone please kill me -- I just quoted a Democrat.:D )

hey guys I'm not here to make judgements just a little education on Cam profile and what it is.

KAAMASCARAB30 and Formula31 are both correct you have other factors. I understand engine attitude and exhaust attitude are also involved. Formula31's knowledge of boats and engines makes me look like a dunce.

Cuda, Unless you have standard merc exhaust I bet your OK. Even if so your still pretty mild.

The best way to check for reversion is to pull off a riser after idling as low as she'll go for a while. Turn off, remove a riser. Do you see water down in the bottom of the manifold? If not no problem.

If you have water passing through the manifold to the riser (no hose bypass). You may need to drain the manifold first.

PB-reversion probably would not cause water in the oil. A leaky head gasket will.

Of course a rod through the side of the block will do it too:D :D :D but I guess that's my problem