Don Terrill’s Speed-Talk

The images below are from the book "Design and Simulation of Four-stroke Engines.

https://books.google.com/books/about/De ... e=kp_cover

These pages are a small sample from a huge book about the mathematics involved in simulating many activies that happen in an engine.

The section that these pages come from is different than most of the book. This chapter is about "empiricism", in other words; collecting data from real engines and making use of that data to make formula. (These formula are much simpler than the computation involved in the 1D simulation that most of the book is about)

These images tell about a set of well-developed engines that span a very wide variety of applications.
The data in the charts is about the flow area made by a combination of the valve and the cam (over-simplified).
This data was used as input to make the set of formula for the STA system.
If someone used a different collection of engines and re-did the same steps to make the formula, they would have different numbers (that fit the new engines).

You can see that the data in the charts and tables are rather scattered, even though all of the engines are considered "well-developed". A ~30% difference from one engine to another.

I found the same thing to be true with even with relatively small changes made to one 5.0l Coyote engine (manifolds, intake tubes, throttle bodies, headers).
It is a pleasant engine to test with because the cams can be timed to anywhere in the adjustment range and change at any RPM (and other circumstances) all while sitting in a chair. No carburetors, so fuel can be tuned easily. The stock cams (of course) have less duration than the highest performance can be achieved, but it can make over 500HP, pass emissions testing and an 80 year-old grandmother would be comfortable driving it 200K miles.
One of the biggest opportunities when tuning this engine is that the ideal cam timing can change 20 degrees inside of 1,000 RPM and back again. With the short duration, there are circumstances where the optimum tune has no overlap.

Its interesting to see how much the LSA changes on those through out a power pull considering everyone says LSA doesn't matter yet the only real change is LSA while the lobe profiles remain the same.

GARY C wrote: ↑Wed May 16, 2018 2:53 am Its interesting to see how much the LSA changes on those through out a power pull considering everyone says LSA doesn't matter yet the only real change is LSA while the lobe profiles remain the same.

The ICL and ECL changes are to optimise the events for best cylinder fill on variable cam timing engines .

As you say the LSA changes with rpm as a result of that ( chicken vs egg) so much for there being an optimum LSA for all rpm like some claim .....

digger wrote: ↑Wed May 16, 2018 2:57 am

GARY C wrote: ↑Wed May 16, 2018 2:53 am Its interesting to see how much the LSA changes on those through out a power pull considering everyone says LSA doesn't matter yet the only real change is LSA while the lobe profiles remain the same.

The ICL and ECL changes are to optimise the events for best cylinder fill on variable cam timing engines .

As you say the LSA changes with rpm so much for there being an optimum LSA for all rpm like some claim .....

No the LSA is required for ICL and ECL.

GARY C wrote: ↑Wed May 16, 2018 3:00 am

digger wrote: ↑Wed May 16, 2018 2:57 am

GARY C wrote: ↑Wed May 16, 2018 2:53 am Its interesting to see how much the LSA changes on those through out a power pull considering everyone says LSA doesn't matter yet the only real change is LSA while the lobe profiles remain the same.

The ICL and ECL changes are to optimise the events for best cylinder fill on variable cam timing engines .

As you say the LSA changes with rpm so much for there being an optimum LSA for all rpm like some claim .....

No the LSA is required for ICL and ECL.

If you ever tune an engine with individual inlet and exhaust cam with vvt on both you will understand why LSA is the result

It's impossible to teach someone who doesn't want to learn...........

This is what I would expect though isn't that the point of VVT or VTech or whatever the application wood be.

Now when it comes to GM with a LS design isn't there VVT more of an illusion instead of being able 2 change timing events they're just shrinking or expanding their event timing by reducing or increasing the lift and duration from a fixed Lobe location

VVT is what I would considered the next step in evolution of a Modern Performance Engine. But on the platforms that we've been working with so many years it's a limitation that we've had to work with that limits the span of the useful intended performance level.

Gm vvt on ls motors i thought just changed intake centerline. More advanced at low rpm and may go slightly retarded at high rpm

Given the roughly 30% difference in the values for the cams in the variety of engines, I think it is fair to say, that the best universal cam formula possible from a few engine parameters will be within 15% - 30% of optimum for some engines.

digger wrote: ↑Wed May 16, 2018 2:57 am

GARY C wrote: ↑Wed May 16, 2018 2:53 am Its interesting to see how much the LSA changes on those through out a power pull considering everyone says LSA doesn't matter yet the only real change is LSA while the lobe profiles remain the same.

The ICL and ECL changes are to optimise the events for best cylinder fill on variable cam timing engines .

As you say the LSA changes with rpm as a result of that ( chicken vs egg) so much for there being an optimum LSA for all rpm like some claim .....

Agree, very dynamic.

Yet many Pontiac folk insist on 112 LSA.
Regardless of RPM range, engine size, head type / port size, compression ratio etc.

Jon,
I am not sure why you keep doing this. Everyone who has been reading these threads knows exactly what you are saying here.

No xxx is not a universal cam formula. But if you would have read and understood the mission statement and scope that was posted at that time that was made clear to everybody.

You danced around and posted nothing of an value in my thread about Blair's method.

How much of that ax that you are grinding do you have left?

Stan

Orr89rocz wrote: ↑Wed May 16, 2018 7:34 am Gm vvt on ls motors i thought just changed intake centerline. More advanced at low rpm and may go slightly retarded at high rpm

The lift is varied by regulating the oil pressure to the lifter which manipulates event timing by changing the Lash. To change only the center line a mechanism would have to be designed to rotate only half of the lobes on a single cam shaft

B Original wrote: ↑Wed May 16, 2018 10:48 am

Orr89rocz wrote: ↑Wed May 16, 2018 7:34 am Gm vvt on ls motors i thought just changed intake centerline. More advanced at low rpm and may go slightly retarded at high rpm

The lift is varied by regulating the oil pressure to the lifter which manipulates event timing by changing the Lash. To change only the center line a mechanism would have to be designed to rotate only half of the lobes on a single cam shaft

I thought it was rotating the entire cam since it is one piece lol i could be wrong

You can see that the data in the charts and tables are rather scattered, even though all of the engines are considered "well-developed". A ~30% difference from one engine to another.

Years ago when I had a strong interest in TimeArea analysis, Blair's approach was very informative and insightful, but subject to your observed data scatter. This was primarily due to the wide range of engines being examined.

When an engine group with greater similarity is used as a basis (L4, 2v, NA) the scatter is less pronounced but remains evident. However, TimeArea, or rather SpecificTimeArea remains one of the most useful analysis tools available
for predictive engine evaluation.

Using the SpecificTimeArea tool, it is possible to predict, with some accuracy, the changes in cam lift/duration, valve size that will be required as engine displacement, power and engine speed increase.

I have also found an application for STA in the design of two-stroke engines. However, while the inlet and exhaust TA were quite accurate, the transfer port timings were not. While STA provides a useful quantitative insight, it does not include parameters such as Cd and resonant tuning effects.

Nonetheless, a great, quick evaluation tool.

Orr89rocz wrote: ↑Wed May 16, 2018 10:58 am

B Original wrote: ↑Wed May 16, 2018 10:48 am

Orr89rocz wrote: ↑Wed May 16, 2018 7:34 am Gm vvt on ls motors i thought just changed intake centerline. More advanced at low rpm and may go slightly retarded at high rpm

The lift is varied by regulating the oil pressure to the lifter which manipulates event timing by changing the Lash. To change only the center line a mechanism would have to be designed to rotate only half of the lobes on a single cam shaft

I thought it was rotating the entire cam since it is one piece lol i could be wrong

you're incorrect with the ls although at one time I don't remember the name of it but someone in the aftermarket offered a mechanism to do this exact thing on a gen 1 small block it operated off of oil pressure and varied a chain snubber that either relaxed or put pressure on the timing chain itself changing the cam timing