The 128 drama!

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Re: The 128 drama!

Post by hoffman900 »

digger wrote: Mon Jan 06, 2020 6:30 pm OEM considerations (emissions, economy etc) for their camshaft choice is probably not the purpose of this thread where the stated method is for WOT performance
It isn't, but check out to the two Honda figures showing overlap changing as a function of engine speed and load (which I assume would be torque production by the engine).

They show increased overlap for power below torque peak, it varying between peak torque (judging by the other graphs) and as the torque curve decays increasingly (so likely around peak power), it reduces overlap.
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Re: The 128 drama!

Post by Orr89rocz »

On new gm LT1 motors, playing with the variable timing advance/retard is worth a good bit of power. Cam lca is same but clearly the events change and results are favorable. But those engines are well overdeveloped. Stock they can make 370 at the tire. With just the typical bolt ons like air intake headers and exhaust with computer tuning and vvt changes they do 460’s at the tire. Damn near 100 hp difference.

In contrast it would take a huge cam to make 460 in the ls3 which has same displacement, similar heads i think and intake.
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Re: The 128 drama!

Post by digger »

hoffman900 wrote: Mon Jan 06, 2020 6:33 pm
digger wrote: Mon Jan 06, 2020 6:30 pm OEM considerations (emissions, economy etc) for their camshaft choice is probably not the purpose of this thread where the stated method is for WOT performance
It isn't, but check out to the two Honda figures showing overlap changing as a function of engine speed and load (which I assume would be torque production by the engine).
Yes if you have variable cam phasing then the ECL or ICL (i.e. LSA) or are not going to be fixed vs rpm at WOT for optimization of VE at each rpm.

This does not mean that in the case of fixed timing engine that there isn't a cam phasing that’s optimum for a specific (consistent) set goal.

I ran a bunch of cam options in ENGMOD4T single pattern cam straight up various ICL/ECL (i.e. LSA) on same engine with no other changes.

It showed that with various durations (5 of them and each on 5 centrelines) there was an LSA that made best average power in the rpm band that would match something like the EMC 3000-7000rpm band irrespective of whether it was a 270 cam or 310 cam (seat to seat durations) which happened to be very tight like 102 IIRC

this seems to agree with David’s work about the LSA being “fixed” (not that I agree with the methodology put forward as i would have separated out ICL and ECl and looked for trends in those separately rather than LSA with more time)

There are a number of flaws with my test, as I did NOT:
- optimize exhaust and inlet configurations (lengths, pipe sizes, configuration) to suit the different cams that would tend to want to operate at different rpms.
- raise the CR with increasing duration
- advance or retard the cam. I just ran straight up single pattern where ICL = say 102, ECL =102 and therefore LSA also 102
- I was calculating best average power over a very wide rpm which is not always the goal for every application e.g. a high rpm narrower rpm band would be able to use a wider LSA but only slighty.

from some of the test ive done I don’t think this invalidates the sims e.g. a change in runner length hasn’t seem to warrant a change in centerlines but thought id put it out there that this isnt a conclusive set of answer merely a trend.
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Re: The 128 drama!

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digger wrote: Mon Jan 06, 2020 7:01 pm
hoffman900 wrote: Mon Jan 06, 2020 6:33 pm
digger wrote: Mon Jan 06, 2020 6:30 pm OEM considerations (emissions, economy etc) for their camshaft choice is probably not the purpose of this thread where the stated method is for WOT performance
It isn't, but check out to the two Honda figures showing overlap changing as a function of engine speed and load (which I assume would be torque production by the engine).
Yes if you have variable cam phasing then the ECL or ICL (i.e. LSA) or are not going to be fixed vs rpm at WOT for optimization of VE at each rpm.

This does not mean that in the case of fixed timing engine that there isn't a cam phasing that’s optimum for a specific (consistent) set goal.

I ran a bunch of cam options in ENGMOD4T single pattern cam straight up various ICL/ECL (i.e. LSA) on same engine with no other changes.

It showed that with various durations (5 of them and each on 5 centrelines) there was an LSA that made best average power in the rpm band that would match something like the EMC 3000-7000rpm band irrespective of whether it was a 270 cam or 310 cam (seat to seat durations) which happened to be very tight like 102 IIRC

this seems to agree with David’s work about the LSA being “fixed” (not that I agree with the methodology put forward as i would have separated out ICL and ECl and looked for trends in those separately rather than LSA with more time)

There are a number of flaws with my test, as I did NOT:
- optimize exhaust and inlet configurations (lengths, pipe sizes, configuration) to suit the different cams that would tend to want to operate at different rpms.
- raise the CR with increasing duration
- advance or retard the cam. I just ran straight up single pattern where ICL = say 102, ECL =102 and therefore LSA also 102
- I was calculating best average power over a very wide rpm which is not always the goal for every application e.g. a high rpm narrower rpm band would be able to use a wider LSA but only slighty.

from some of the test ive done I don’t think this invalidates the sims e.g. a change in runner length hasn’t seem to warrant a change in centerlines but thought id put it out there that this isnt a conclusive set of answer merely a trend.
I have done similar tests and I agree with them. In the real world, we also use camshafts around 104 LSA (installed 2* advanced) on road race engines that peak out around 7000rpm.

However, these have 12.1+ compression and do NOT idle at anything less than 1800rpm.

Not what I would recommend for a typical street engine. It will idle and sound like an old 9:1 compression Busch GN engine...
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Re: The 128 drama!

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There’s a Ford paper on restricted intake engines. Compared to unrestricted intake engines, the overlap remained almost the same but exhaust duration had to be reduced a lot and intake duration less. Would this mean that restricted intake would call for a tighter LSA?
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Re: The 128 drama!

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ptuomov wrote: Mon Jan 06, 2020 7:16 pm There’s a Ford paper on restricted intake engines. Compared to unrestricted intake engines, the overlap remained almost the same but exhaust duration had to be reduced a lot and intake duration less. Would this mean that restricted intake would call for a tighter LSA?
If that's what happened, then yes. Can you share that paper? I’m assuming the RPM’s dropped a lot?

Oldie but goodie with Harold Brookshire, Mike Sloe, and Mike Jones:
Cam design basics ?
viewtopic.php?f=1&t=6807

They talk about restrictor camshafts.
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Re: The 128 drama!

Post by ptuomov »

hoffman900 wrote: Mon Jan 06, 2020 7:25 pm
ptuomov wrote: Mon Jan 06, 2020 7:16 pmThere’s a Ford paper on restricted intake engines. Compared to unrestricted intake engines, the overlap remained almost the same but exhaust duration had to be reduced a lot and intake duration less. Would this mean that restricted intake would call for a tighter LSA?
If that's what happened, then yes. Can you share that paper? I’m assuming the RPM’s dropped a lot?
Can't post it but the paper is here: https://www.sae.org/publications/techni ... nt/962514/
Paradigms often shift without the clutch -- https://www.youtube.com/watch?v=cxn-LxwsrnU
https://www.instagram.com/ptuomov/
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Re: The 128 drama!

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ptuomov wrote: Mon Jan 06, 2020 7:39 pm
hoffman900 wrote: Mon Jan 06, 2020 7:25 pm
ptuomov wrote: Mon Jan 06, 2020 7:16 pmThere’s a Ford paper on restricted intake engines. Compared to unrestricted intake engines, the overlap remained almost the same but exhaust duration had to be reduced a lot and intake duration less. Would this mean that restricted intake would call for a tighter LSA?
If that's what happened, then yes. Can you share that paper? I’m assuming the RPM’s dropped a lot?
Can't post it but the paper is here: https://www.sae.org/publications/techni ... nt/962514/
I'll have to look at it later, but being from 1996, I have some questions.

I've posted this before, but here is a screenshot from a presentation Brian Kurn did while at ECR (now at Roush Yates, formerly of Bill Davis Racing, Hendrick Motorsports, Roush-Fenway, LG (Lou Gigliotti), Barton, and Reher-Morrison):
Untitled.jpg

Full presentation:
https://www.slideshare.net/slideshow/em ... 7FaKNdNBMN

Brian's Linkedin profile:
https://www.linkedin.com/in/briankurn/

This was for the Daytona Prototype engine. The rule change meant 5L engine to 5.5L engine and a sonic restrictor. Peak horsepower appears to be somewhere in the 7000-ish rpm neighborhood

So what happened here?
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Re: The 128 drama!

Post by ptuomov »

Visually the same thing, intake restrictor left the overlap duration and area about the same while the duration and area of both lobes were reduced?
Paradigms often shift without the clutch -- https://www.youtube.com/watch?v=cxn-LxwsrnU
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Re: The 128 drama!

Post by peejay »

hoffman900 wrote: Mon Jan 06, 2020 6:33 pm
digger wrote: Mon Jan 06, 2020 6:30 pm OEM considerations (emissions, economy etc) for their camshaft choice is probably not the purpose of this thread where the stated method is for WOT performance
It isn't, but check out to the two Honda figures showing overlap changing as a function of engine speed and load (which I assume would be torque production by the engine).

They show increased overlap for power below torque peak, it varying between peak torque (judging by the other graphs) and as the torque curve decays increasingly (so likely around peak power), it reduces overlap.
Overlap is just a side effect of getting enough valve duration while also maintaining a good IVC.

The downside is poor part throttle drivability.

So the Honda graph makes sense - they are altering the IVC relative to RPM, but they are also compromising IVC at part throttle in order to reduce overlap. Different situation different priority. At part throttle, the main goal is efficiency not power - you can open the throttle more if you want more power. And with drive by wire, the driver doesn't have to notice what is going on while all this is happening - the pedal is a torque request, the computer moves the cams and throttle position to what it has been mapped for that speed and torque. You might have the pedal at 15% but the throttle plate might be 50% or more. For some engines the throttle plate is only there for idle and as a safety backup.
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Re: The 128 drama!

Post by GARY C »

Then you have the latest 2000's technology Mazda using High Compression High Swirl to achieve lean burn.
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Re: The 128 drama!

Post by GARY C »

hoffman900 wrote: Mon Jan 06, 2020 7:10 pm
digger wrote: Mon Jan 06, 2020 7:01 pm
hoffman900 wrote: Mon Jan 06, 2020 6:33 pm

It isn't, but check out to the two Honda figures showing overlap changing as a function of engine speed and load (which I assume would be torque production by the engine).
Yes if you have variable cam phasing then the ECL or ICL (i.e. LSA) or are not going to be fixed vs rpm at WOT for optimization of VE at each rpm.

This does not mean that in the case of fixed timing engine that there isn't a cam phasing that’s optimum for a specific (consistent) set goal.

I ran a bunch of cam options in ENGMOD4T single pattern cam straight up various ICL/ECL (i.e. LSA) on same engine with no other changes.

It showed that with various durations (5 of them and each on 5 centrelines) there was an LSA that made best average power in the rpm band that would match something like the EMC 3000-7000rpm band irrespective of whether it was a 270 cam or 310 cam (seat to seat durations) which happened to be very tight like 102 IIRC

this seems to agree with David’s work about the LSA being “fixed” (not that I agree with the methodology put forward as i would have separated out ICL and ECl and looked for trends in those separately rather than LSA with more time)

There are a number of flaws with my test, as I did NOT:
- optimize exhaust and inlet configurations (lengths, pipe sizes, configuration) to suit the different cams that would tend to want to operate at different rpms.
- raise the CR with increasing duration
- advance or retard the cam. I just ran straight up single pattern where ICL = say 102, ECL =102 and therefore LSA also 102
- I was calculating best average power over a very wide rpm which is not always the goal for every application e.g. a high rpm narrower rpm band would be able to use a wider LSA but only slighty.

from some of the test ive done I don’t think this invalidates the sims e.g. a change in runner length hasn’t seem to warrant a change in centerlines but thought id put it out there that this isnt a conclusive set of answer merely a trend.
I have done similar tests and I agree with them. In the real world, we also use camshafts around 104 LSA (installed 2* advanced) on road race engines that peak out around 7000rpm.

However, these have 12.1+ compression and do NOT idle at anything less than 1800rpm.

Not what I would recommend for a typical street engine. It will idle and sound like an old 9:1 compression Busch GN engine...
More to do with a big head on a small engine than the effect of cam shaft alone.
The first car in this vid (Chevy II) is a 434 with a 106 cam and idles just fine at 950 and cross the traps at 7000 with a 4500 converter with exhaust and mufflers.
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Re: The 128 drama!

Post by digger »

I don’t think the port size has much to do with idle (other than low lift curtain area ) it’s mostly the overlap and associated curtain area , cylinder size and cross talking which is not the same as looking at LSA saying it will idle poorly . Small duration and 100LSA can idle fine, the same IR will tolerate More overlap
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Re: The 128 drama!

Post by GARY C »

digger wrote: Mon Jan 06, 2020 10:40 pm I don’t think the port size has much to do with idle (other than low lift curtain area ) it’s mostly the overlap and associated curtain area , cylinder size and cross talking which is not the same as looking at LSA saying it will idle poorly . Small duration and 100LSA can idle fine, the same IR will tolerate More overlap
What cam does an F1 engine run that causes it to idel at 7000 rpm?

I am sure the cam plays a part but I ran the same cam, heads intake and carb on a 306, 357, 379 and 382 and less idle speed was needed as the displacement went up, all things equal the 306 was around a second slower naturally aspirated and would bog slightly at a 7500 rpm shift.

I later changed the cam 10 degrees less and 8 degrees wider to dyno the 357 on nitrous, it did nothing for the idle quality and without the nitrous the tq was shitty to say the least.

It just seems less displacement requires more rpm to overcome reversion, or a really late opening small cam to bandaid it.
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Re: The 128 drama!

Post by digger »

Gary, I never disagreed about changing the displacement that’s kinda different. F1 cars have a ton of curtain area and cams are about 270@0.040” for 4v not exactly small don’t have CL data It’s the curtain area not the port area. Fill in the ports 25% and the idle will not magically become good.
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