calculating overlap?

STAR · 07-03-2002, 08:49 PM

I have two grinds that I'm trying to compare overall and want to start with overlap. How do I determine this? I have the cam card with all the valve timing events.

Thanks

Pony Killer · 07-03-2002, 09:57 PM

On the Cam Card, if it's got the seat to seat numbers it's much easier to tell..
Although sometimes they won't use the same terminology for the intake valve opening as the do on the Exhaust vavle opening.

Stare at it for a minute you'll figure it out 90* before Bottom Dead Center, and 90* degrees After top dead center are the same for example.

However long they are both open for is the overlap.

If the card's only got .050 numbers, If the cams got a wide lobe sep angle on it, and short duration, their may not be any overlap. If it's a healthy cam with a narrower Lobe sep angle you should see some overlap there.

Hope that helps

STAR · 07-03-2002, 10:41 PM

The valve events are at .050 on the card.
open close
int: 12 52
exh: 64 8

The cam is a 244/252/114 with very aggressive ramps. Its going in a 12.1 383ci stroker hopefully will run on pump gas.

rskrause · 07-04-2002, 12:08 AM

So the intake opens to 0.050" 12 deg BTDC and the exhaust closes to 0.050" 8 deg ATDC. This means that the overlap at 0.050" is 20 degrees.

Rich Krause

Quote:

<font face="Verdana, Arial" size="2">Originally posted by STAR:
The valve events are at .050 on the card.
open close
int: 12 52
exh: 64 8

The cam is a 244/252/114 with very aggressive ramps. Its going in a 12.1 383ci stroker hopefully will run on pump gas.</font>

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'95 Z-28 383 with Vortech, nitrous, etc.
"1FASTZ28"

jimbob65 · 07-09-2002, 07:29 PM

One more thing "STAR"
Overlap is more of a triangle shape (looking at the lobes).
Now that you have (.050 overlap) you may base duration overlap (if you have the spects). Add both intake and exhaust (base durations) and devide by two. Then take your lobe seperation and multiply that by two. Subtract lobe seperation from base duration.

Mine for example is 286/286 base with a 114 lobe seperation. So, I have 58 degrees of base duration overlap. You can tell by the curve that some where in the .075 tappet lift, overlap will be zero (in my case).

Oops, didn't read "Pony Killers" post all the way.....

More than one way to skin a cat right?

Jim
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94 Auto 396 Stroker

Tornado, Airfoil, Paper air filter........

[This message has been edited by jimbob65 (edited July 09, 2002).]