Cam specs

[beanhead]

I "think" he wants to know if he can use math, to figure out overlap at, say, seat instead of just the overlap given at .050". I think.
The answer is....kinda?..May not be 100% accurate depending on lobe rates but the guys above know infinitely more about that than I do..maybe rates don't matter?
I know this thread's a little sideways by now but I like to learn miscellaneous info I'll probably never use, so correct me if I 'm wrong here----
Int duration + Exh duration = "X"
"X"divided by 4 = "Y" (4 is a constant)
"Y" minus LSA (112 in his case?) = "Z"
"Z" multiplied by 2 = a halfass close overlap number? (2 is also a constant)

 

[PRHeads]

I "think" he wants to know if he can use math, to figure out overlap at, say, seat instead of just the overlap given at .050". I think.
The answer is....kinda?..May not be 100% accurate depending on lobe rates but the guys above know infinitely more about that than I do..maybe rates don't matter?
I know this thread's a little sideways by now but I like to learn miscellaneous info I'll probably never use, so correct me if I 'm wrong here----
Int duration + Exh duration = "X"
"X"divided by 4 = "Y" (4 is a constant)
"Y" minus LSA (112 in his case?) = "Z"
"Z" multiplied by 2 = a halfass close overlap number? (2 is also a constant)

It’s 100% accurate for whatever the duration is at the specified lift point.

The problem so far is....... there are no duration numbers...... at any lift.

You need the duration and the LSA to determine/calculate overlap.

If you don’t know the lift point at which the duration numbers are derived from, then the overlap figure is somewhat erroneous.

Sure, you can speculate what the overlap at the seat might be based on duration@.050 numbers....... but without knowing the lobe intensity........ you’re looking at a “+/- 20 to 30 degrees” type of scenario.
You could pull a number out of thin air and be that close.

As an example..... two actual lobes:
Lobe A- 232@.050, 280* advertised

Lobe B- 232@.050, 302* advertised

Those two lobes, run as single pattern grinds on a 108lsa would have a difference of overlap at the seat of 22*(64 vs 86), yet they both have 16* overlap @.050.

 

[Kern Dog]

 

[beanhead]

It’s 100% accurate for whatever the duration is at the specified lift point.

The problem so far is....... there are no duration numbers...... at any lift.

You need the duration and the LSA to determine/calculate overlap.

If you don’t know the lift point at which the duration numbers are derived from, then the overlap figure is somewhat erroneous.

Sure, you can speculate what the overlap at the seat might be based on duration@.050 numbers....... but without knowing the lobe intensity........ you’re looking at a “+/- 20 to 30 degrees” type of scenario.
You could pull a number out of thin air and be that close.

As an example..... two actual lobes:
Lobe A- 232@.050, 280* advertised

Lobe B- 232@.050, 302* advertised

Those two lobes, run as single pattern grinds on a 108lsa would have a difference of overlap at the seat of 22*(64 vs 86), yet they both have 16* overlap @.050.

Ok thanks! Looks like I'm not a total loss after all

 

[old guys rule]

It’s 100% accurate for whatever the duration is at the specified lift point.

The problem so far is....... there are no duration numbers...... at any lift.

You need the duration and the LSA to determine/calculate overlap.

If you don’t know the lift point at which the duration numbers are derived from, then the overlap figure is somewhat erroneous.

Sure, you can speculate what the overlap at the seat might be based on duration@.050 numbers....... but without knowing the lobe intensity........ you’re looking at a “+/- 20 to 30 degrees” type of scenario.
You could pull a number out of thin air and be that close.

As an example..... two actual lobes:
Lobe A- 232@.050, 280* advertised

Lobe B- 232@.050, 302* advertised

Those two lobes, run as single pattern grinds on a 108lsa would have a difference of overlap at the seat of 22*(64 vs 86), yet they both have 16* overlap @.050.

I'm beginning to think I may be slipping myself...sorry guys. Duration @6 is 252/260. At 50 it is 210/214. O/L @ 50 is 12 and lift is 458/470. LCA is 112. Now did I finally say it right? If not just ignore the old coot, have a double shot of Jack and call it a night.

 

[BSB67]

I'm beginning to think I may be slipping myself...sorry guys. Duration @6 is 252/260. At 50 it is 210/214. O/L @ 50 is 12 and lift is 458/470. LCA is 112. Now did I finally say it right? If not just ignore the old coot, have a double shot of Jack and call it a night.

Well done! And yes you can calculate advertised overlap from those numbers. But after you made us work this hard, I'm not going to give you the answer. Beanhead already did the heavy lifting for you. Just follow his lead below:

Int duration + Exh duration = "X"
"X"divided by 4 = "Y" (4 is a constant)
"Y" minus LSA (112 in his case?) = "Z"
"Z" multiplied by 2 = closed overlap number (2 is also a constant)

Technically, I'd call it an "advertised" overlap, verses closed overlap, but that's nit-picking

 

[PRHeads]

Duration @6 is 252/260. At 50 it is 210/214. O/L @ 50 is 12 and lift is 458/470. LCA is 112.

Actually, 210/214@.050 on a 112lsa...... has -12* overlap @.050.

 

[BSB67]

Just to be clear, that's a negative 12°

 

[old guys rule]

Just to be clear, that's a negative 12°

I'm sure I'm boring you guys in dragging this out but I found the cam card. What do you think?

 

[old guys rule]

Just to be clear, that's a negative 12°

Sorry, this thread has been a real slog for you I'm sure. It's just that I find this stuff very interesting. Thanks guys

 

[PRHeads]

What do you think?

I think it’s a pretty small cam.
That series of lobes from Engle are pretty well liked however.

Should be good in a lower CR combo with mild gearing and a stock converter, in a heavy-ish vehicle.

A factory high CR combo with a cam that small will likely have detonation issues.

There are a couple of slight errors on the cam card though...... anyone else see them?

 

[old guys rule]

I "think" he wants to know if he can use math, to figure out overlap at, say, seat instead of just the overlap given at .050". I think.
The answer is....kinda?..May not be 100% accurate depending on lobe rates but the guys above know infinitely more about that than I do..maybe rates don't matter?
I know this thread's a little sideways by now but I like to learn miscellaneous info I'll probably never use, so correct me if I 'm wrong here----
Int duration + Exh duration = "X"
"X"divided by 4 = "Y" (4 is a constant)
"Y" minus LSA (112 in his case?) = "Z"
"Z" multiplied by 2 = a halfass close overlap number? (2 is also a constant)

I "think" he wants to know if he can use math, to figure out overlap at, say, seat instead of just the overlap given at .050". I think.
The answer is....kinda?..May not be 100% accurate depending on lobe rates but the guys above know infinitely more about that than I do..maybe rates don't matter?
I know this thread's a little sideways by now but I like to learn miscellaneous info I'll probably never use, so correct me if I 'm wrong here----
Int duration + Exh duration = "X"
"X"divided by 4 = "Y" (4 is a constant)
"Y" minus LSA (112 in his case?) = "Z"
"Z" multiplied by 2 = a halfass close overlap number? (2 is also a constant)

 

[old guys rule]

I'm getting 27 degrees advertised overlap. Pretty low but probably close. Ok though, I want to daily drive it starting next winter. (Florida)

 

[beanhead]

Your advertised overlap is 32 degrees using the figures on your cam card. With basically none @ .050. Smooth and lots of vacuum..

 

[beanhead]

I think it’s a pretty small cam.
That series of lobes from Engle are pretty well liked however.

Should be good in a lower CR combo with mild gearing and a stock converter, in a heavy-ish vehicle.

A factory high CR combo with a cam that small will likely have detonation issues.

There are a couple of slight errors on the cam card though...... anyone else see them?

Using the valve timing numbers I get 220 intake duration @ .050"? And the valve lift figures are off by a couple thou using a 1.5 RR is that what you're talking about?
Hold on. The way they show a (-) in front of both intake opening and exhaust closing is throwing me off. I thought that meant those events happened before TDC. But then on the other end both numbers show as a positive. Does that mean the exhaust opens after BDC? I expect the intake to close after but shouldn't they put a (-) next to the exhaust number if it's opening 'before' BDC? That would change the exhaust duration @ .050 also then. Hell I don't know..this is good stuff to learn though!

 

[Hemirunner]

I think it’s a pretty small cam.
That series of lobes from Engle are pretty well liked however.

Should be good in a lower CR combo with mild gearing and a stock converter, in a heavy-ish vehicle.

A factory high CR combo with a cam that small will likely have detonation issues.

There are a couple of slight errors on the cam card though...... anyone else see them?

1/2 a degree off on exhaust valve events and the lobe lift to valve lift math is off..no mention of ICL at 110 unless it’s cut off

 

[PRHeads]

1/2 a degree off on exhaust valve events and the lobe lift to valve lift math is off

Those are what I was referring to.

Bean-
As for the overlap @.050 being listed in negative numbers.......
-6 BTDC is........ 6 ATDC

Forget the terminology and just use the event points as they are shown....... in this case “-6”.
The intake duration@.050 for that cam is 208*.
(IC)34 +180 (IO)-6 = 208

 

[beanhead]

Those are what I was referring to.

Bean-
As for the overlap @.050 being listed in negative numbers.......
-6 ATDC is........ 6 BTDC

Forget the terminology and just use the event points as they are shown....... in this case “-6”.
The intake duration@.050 for that cam is 208*.
(IC)34 +180 (IO)-6 = 208

Aah got it. I was going by the picture and visualizing it as the crank turns..the 6 btdc, then 180, then 34 after bdc and adding them all. Thank you!

 

[old guys rule]

Using the valve timing numbers I get 220 intake duration @ .050"? And the valve lift figures are off by a couple thou using a 1.5 RR is that what you're talking about?
Hold on. The way they show a (-) in front of both intake opening and exhaust closing is throwing me off. I thought that meant those events happened before TDC. But then on the other end both numbers show as a positive. Does that mean the exhaust opens after BDC? I expect the intake to close after but shouldn't they put a (-) next to the exhaust number if it's opening 'before' BDC? That would change the exhaust duration @ .050 also then. Hell I don't know..this is good stuff to learn though!

I agree. Cam is the attitude of the motor. FYI Power Pro Series has a good book on camshaft and valve trains called how to build and modify Chevrolet small block V8 camshaft and valve trains. Makes interesting reading. Sorry about the bow tie part.

 

[old guys rule]

1/2 a degree off on exhaust valve events and the lobe lift to valve lift math is off..no mention of ICL at 110 unless it’s cut off

The cam is installed in the block 4 degrees advanced