[Steve.k]

Whats your census on duration split between exh and intake and why. It used to be with the poorer flowing exh you used to see cams with 8-10 degrees more duration on exh. Now you see cams cut tighter or nearly identical. What’s your reasoning for cutting the same or giving the exh extra.

 

[cstraub]

A good starting point is 75% I/E ratio....starting here if the number is lower add to Exhaust, if the number is higher add to Intake.

 

[Shawn Finn]

Its just about valve events, the splits are just a result. It took me a long time to understand that but once you can wrap your head around it and start coming up with a cause/effect for the #s it is much better. Every event is managing pressure, different engines and how they are operated need to manage the pressure differently.

 

[stuska1]

The answer to this question is different for every engine
There is no David Vizard formula that covers every combo
You have to look at many different factors that affect the pressure in the cylinder, fuel type, stroke length cylinder head design and the rabbit hole is a deep one

 

[Steve.k]

So with that said Stuska you must have a rough idea on engine group. It seems sbc likes the a closer split where bbf or Clevelands like a wider.I’ve noticed the cams I’ve asked to get ground he’s tightened that up. Trying to figure out why.

 

[Geoff]

Go to the Isky Cams website, Tech Tips: Is extra exh duration really necessary?

 

[600" BBF]

Go to the Isky Cams website, Tech Tips: Is extra exh duration really necessary?

Tech Tips 2000™

iskycams.com

 

[Warp Speed]

RPM......

 

[ndmp40]

It seems sbc likes the a closer split where bbf or Clevelands like a wider.

I dont think that statement is accurate nor useful. Especially given the large variability in aftermarket cylinder heads.

 

[Chris Uratchko]

There's no such thing as a duration or a split. That is all cam grinder talk.... not engine talk.

Some may say respond that it's just being picky or wanting to get attention for steering the conversation away from durations and splits but I truly believe that this is the exact reason, 99 percent of engine builders and end users have nearly zero understanding about camshafts... because they are focusing on numbers that don't mean anything to the engine... so of course there's no understanding. The level of understanding is trying to attach a duration and a lobe separation to a running engine and the mind goes numb and the eyes roll in the back of your head because...... it's not real.

Instead, the industry has been attached to these numbers for so long that we have developed a system of trying to make these numbers fit into the design of the engine. And you can reasonably and successfully get there with these formulas and developed experiences .... but at the end of the day, these numbers don't mean anything.

And that is why after 60+ years of hot rodders and engine builders messing with the pushrod v8 engine they still just don't understand cams.....and most will admit it.

 

[BBF612]

Open and close the valves where they make the most HP/best torque curve for your application.

 

[russxr67]

So we should be looking at valve event numbers rather than duration and lobe splits.
That’s all good and well but how does one learn a better understanding of how to pick those numbers?

 

[BBF612]

Get what you can out of this Banks video.

 

[Chris Uratchko]

So we should be looking at valve event numbers rather than duration and lobe splits.
That’s all good and well but how does one learn a better understanding of how to pick those numbers?

You can develop and understanding of open and close numbers based on experience and education. Those numbers directly correlate to managing pressures and filling the cylinders.

 

[Shawn Finn]

So we should be looking at valve event numbers rather than duration and lobe splits.
That’s all good and well but how does one learn a better understanding of how to pick those numbers?

Experience

Or take the duration #s and lobe seps that you are familar with / understand and plot them out to get the events. Start comparing the events and you start to get a better idea of what is going on.

I used graph paper at first to better visualize what is going on. Makes it easy to see piston speed/location in relation to valve lift without standing at the engine.

 

[Chris Uratchko]

The other problem is that you have cam grinders turned engine experts. I need a cam so I am going to have a cam grinder design it. That's because..... a cam grinder is an engine expert? There are some... but knowing how to grind a cam, or even knowing how to design a cam lobe has nothing to do with knowing how to manage a 4 stroke engine. It's like saying because I know how to hone a cylinder in a block that I am an engine designer.

We have machinists confused with engine builders/designers and that has been the course for decades. Some are, some aren't but we have this belief that the two are one and it's the farthest thing from the truth.

None of this makes sense when you start actually laying this stuff out in a discussion.

 

[Chris Uratchko]

A the end of the day we are all chasing Data. We observe, and react. It doesn't matter whether it's Valve Events, or Durations and Splits.

But, at the end of the day we can come to conclusions based on valve events. You can probably try to defend coming up with conclusions based on Durations and Splits, but the data within those durations and splits are the real numbers..... so making conclusions and following trends of durations and splits, is really self deceiving in the end.

 

[novafornow]

You may ruffle some feathers with that one Chris. Absolutely true though.

 

[scott foxwell]

The other problem is that you have cam grinders turned engine experts. I need a cam so I am going to have a cam grinder design it. That's because..... a cam grinder is an engine expert? There are some... but knowing how to grind a cam, or even knowing how to design a cam lobe has nothing to do with knowing how to manage a 4 stroke engine. It's like saying because I know how to hone a cylinder in a block that I am an engine designer.

We have machinists confused with engine builders/designers and that has been the course for decades. Some are, some aren't but we have this belief that the two are one and it's the farthest thing from the truth.

None of this makes sense when you start actually laying this stuff out in a discussion.

Most "cam guys" aren't even cam designers and have zero knowledge of the math involved in designing an actual cam lobe nor have the ever ground a cam. They work off iteration programs that use a library of existing lobes.

 

[Ed Curtis]

RPM......

but... but... but... "128"

🤪