Using Blair to spec a Cam

[GARY C]

Why don't you be more like your buddy Gary who I think is a good guy (he's reached out to me and we've chatted on the phone)? Blair's method is to develop a way for it to scale from a weedwhacker to a Rolls Royce Merlin V12. As such, it's a bit more complicated than using a simple rule of thumb. It however wasn't pulled out of thin air.



The difficult part is taking the time area and producing a meaningful valve lift curve that is realistic within the constraints of the mechanical limitations of a particular valvetrain.

That seems to be the issue I see with both, rule of thumb or models, you have to have some prior knowledge as to what your doing and then you have to have real world data to decide where you are going after that.

The beautiful part about having a pushrod engine with common tappet diameters (.842-.904") is that there are tens of thousands of camshaft lobes out there developed. It's a matter of creating the performance box you need and finding what fits. Likely, it's already been design and multiple iterations with varying amounts of aggressiveness exist.

The rest of the engine world isn't so lucky. The bucket lifter OHC builders are in better shape than the OHC rocker or finger follower builders, but nothing like what the pushrod engine builders have. I have some simulation tests going on. I'll post results later this evening.

Yes, that somewhat fits into what you said here (quote below) and how DV developed COS-CAMS, 128 and his article with the overlap chart, the later being very engine specific. I know most here don't like his name to be brought into any discussion but his work has merit to Cam Shaft Discussion... From what I have seen is it is very difficult to come up with anything that will best fit every style of engine due to so many different variations from engine to engine. You even see this with Fuel Injection with port vs DI systems due to the duty cycle that can be used on on vs the other it creates a new set of challenges.

If I had a camshaft business, I'd solicit all the feedback and dyno results I could. I could create a database and through some statistics and algorithms, I could really start honing in on some trends. You could probably hire a data scientist intern or a co-op for a summer to do this, and it would be quite easy for them as they're trained to work with datasets with MILLIONS of data rows. Bring on the machine learning!

[RevTheory]

Bob, that was friendly sarcasm. That's the problem with typed words on a forum; especially one where everyone has gone into their respective corners and are sitting on the edge of their seats just waiting to pounce. Voice inflection is gone.

You bet your ass that Jon will never and I mean never give an answer but I'm not going to blow up Stan's thread because I have zero respect for people like Jon that do little more than dance around a question but will never put their name on an answer.

[hoffman900]

Bob, that was friendly sarcasm. That's the problem with typed words on a forum; especially one where everyone has gone into their respective corners and are sitting on the edge of their seats just waiting to pounce. Voice inflection is gone.

You bet your ass that Jon will never and I mean never give an answer but I'm not going to blow up Stan's thread because I have zero respect for people like Jon that do little more than dance around a question but will never put their name on an answer.

I like Jon and I know exactly where he's coming from. He's also a really nice guy off the forum (most are), but I'll save my critique of other's work for another thread as I have a lot of respect for Stan and this should be a good thread.

So I did this in EngMod4t using the STA method. The J2 baseline is a measured cam I have. I then picked out a target BMEP (corresponding with a HP value at some rpm (7200)). I fortunately already had some valve lift profiles that fit and adjusted the centerlines some to match up as close as I could to the recommend STA values.



Baseline:


Approximate Match:


*note: it should be noted I cannot physically fit the better of these two in the head.

[RamblerRebel6]

I then picked out a target BMEP (corresponding with a HP value at some rpm (7200)).

I'm just a rank student, and maybe not the best one (for example, I never bring apples for the teachers), but I do have one question:
This would also be saying that you therefore have a target value for torque, right? I'm not saying peak torque, but a value for torque at horsepower rpm, maybe?

--Jim

[SchmidtMotorWorks]

Bob, that was friendly sarcasm. That's the problem with typed words on a forum; especially one where everyone has gone into their respective corners and are sitting on the edge of their seats just waiting to pounce. Voice inflection is gone.

You bet your ass that Jon will never and I mean never give an answer but I'm not going to blow up Stan's thread because I have zero respect for people like Jon that do little more than dance around a question but will never put their name on an answer.

Never give an answer to what?

[hoffman900]

Bob, that was friendly sarcasm. That's the problem with typed words on a forum; especially one where everyone has gone into their respective corners and are sitting on the edge of their seats just waiting to pounce. Voice inflection is gone.

You bet your ass that Jon will never and I mean never give an answer but I'm not going to blow up Stan's thread because I have zero respect for people like Jon that do little more than dance around a question but will never put their name on an answer.

Never give an answer to what?

They want you to pick out a camshaft in some cam catalog for the ST default 500hp, 383ci Chevy, with a single carburetor, AFR heads, and 10:1 compression. This will be for a street car, but we can ignore that because the dyno test won't start until 3500rpm and who cares below that point. AmIrightorwhat?

So Rev, take note. This isn’t about just yanking some camshaft out of a catalog. This is about breaking down an engine and looking at can we make more? Can other rules of thumbs (plural, there are a lot out there form multiple sources) maximize the combination? Does any given rule of thumb get you the maximum to what the combination is capable of? Is a good result good enough? This is Speedtalk, I think lots here are interested in the pursuit of more power, at least it use to be. It seems too many here are interested in some generic recipe magazine type build for some ancient architecure. That’s fine, but if that’s you, then too mucking up the threads for Thebes other guys. I know many in this thread are not interested in that. Is, for example, a 500hp 383ci pump gas engine good? Sure. Is it everything that I can be? I don’t known. We need to break it down and have a look.

Lots here come from other schools of experience or academics. If we see technical errors, we should be able to point them out. If the poster is willing to make their theories public, they should be able to take the critique and improve their product. All should be done without malice. So really, stop with the posting like you’re in the cesspool that is the political forum. You’re certainly capable of it.

Stan, I'll have some input later in the week when I get some more time to read up on this. I also want to try some other things with these two combinations (on the exhaust lengths and intake lengths - maximize overall power for both). Then we can break them down and see what's going on.

[SchmidtMotorWorks]

They want you to pick out a camshaft in some cam catalog for the ST default 500hp, 383ci Chevy, with a single carburetor, AFR heads, and 10:1 compression. This will be for a street car, but we can ignore that because the dyno test won't start until 3500rpm and who cares below that point. AmIrightorwhat?

The answer is, "it is a matter of taste" especially for a street driven car.

I design intake manifolds that are evaluated by dyno-testing and in-car testing.
The manifolds that make the best looking power curves are not the manifolds people choose in double-blind, in-car testing.
Generally, most people will choose a set of engine parameters that look worse on a dyno-graph but is better to drive. The power curves people think they want, are not what they like to drive.

A good example of this is the Coyote engine, when people drive it without knowing what manifold is on it, the F150 manifold gets high approval, when they choose from a dyno sheet, the F150 manifold is never chosen.

When you add to that, the requirements I deal with to pass emissions in all states, the problem is 3X more complex.

[hoffman900]

Motorcycle race engine builders / designers are sooo far ahead of everyone on that spectrum, and yet they’re still managing 3.0hp/ci+ from the factories on pump gas. Technology is pretty incredible. Anyway...

[SchmidtMotorWorks]

Motorcycle race engine builders / designers are sooo far ahead of everyone on that spectrum, and yet they’re still managing 3.0hp/ci+ from the factories on pump gas. Technology is pretty incredible. Anyway...

The Coyote engine is a nice piece. If it were not for emissions compliance, there is a lot of power on the table.
The cam timing maps can actually have negative overlap in some scenarios and still make decent power.

[RevTheory]

Bob, that was friendly sarcasm. That's the problem with typed words on a forum; especially one where everyone has gone into their respective corners and are sitting on the edge of their seats just waiting to pounce. Voice inflection is gone.

You bet your ass that Jon will never and I mean never give an answer but I'm not going to blow up Stan's thread because I have zero respect for people like Jon that do little more than dance around a question but will never put their name on an answer.

Never give an answer to what?

They want you to pick out a camshaft in some cam catalog for the ST default 500hp, 383ci Chevy, with a single carburetor, AFR heads, and 10:1 compression. This will be for a street car, but we can ignore that because the dyno test won't start until 3500rpm and who cares below that point. AmIrightorwhat?

So Rev, take note. This isn’t about just yanking some camshaft out of a catalog. This is about breaking down an engine and looking at can we make more? Can other rules of thumbs (plural, there are a lot out there form multiple sources) maximize the combination? Does any given rule of thumb get you the maximum to what the combination is capable of? Is a good result good enough? This is Speedtalk, I think lots here are interested in the pursuit of more power, at least it use to be. It seems too many here are interested in some generic recipe magazine type build for some ancient architecure. That’s fine, but if that’s you, then too mucking up the threads for Thebes other guys. I know many in this thread are not interested in that. Is, for example, a 500hp 383ci pump gas engine good? Sure. Is it everything that I can be? I don’t known. We need to break it down and have a look.

Lots here come from other schools of experience or academics. If we see technical errors, we should be able to point them out. If the poster is willing to make their theories public, they should be able to take the critique and improve their product. All should be done without malice. So really, stop with the posting like you’re in the cesspool that is the political forum. You’re certainly capable of it.

Stan, I'll have some input later in the week when I get some more time to read up on this. I also want to try some other things with these two combinations (on the exhaust lengths and intake lengths - maximize overall power for both). Then we can break them down and see what's going on.

Save the nonsense. Jon will never commit to a number. Talk it down all you want. Oh, I've talked to the big boys that actually race.

[Stan Weiss]

Mark,
Most of the time you get what you pay.

What I am hoping to do is put a free entry level set of equations here for anyone to use. (The more I analyze this I am not sure that can be done). This I believe would cover many of the readers (lurkers) while the others as needed would buy the software packages you listed.

Stan

Is the spreadsheet the limitation?

Jon,
I have not yet been able to think of a way to translate/convert/what ever you want call it the STA into lift profile. Been busy all day and so have not even looked it since yesterday. All that be said, if i did come up with a method that was to complex for native Excel it is possible that some VBA code might to the trick.

If I was looking to do this for myself or someone was paying me for the answer. I would use some routines I already have. I would get some engine specs (RPM, intake and Exhaust valve sizes, ...). I would then input cam specs (max lobe lift, seat-to-seat duration, 0.050" duration, 0.100" duration, ...) , generate a lift profile every 1 degree, and then calculate the TA's. I would have the LSA and ICL (also if used rocker arm ratio) as separate specs so that I could adjust these while still using the same lift file. This would be a trail and error method of looking at this output against Blair's numbers and than going back and generating a new lift profile until they just about matched. I believe once I had done a few cams it would not take that long to get the needed TA's

Stan

[pastry_chef]

Bob,
My software is not an Engine Simulation program it is more like a Swiss Arm Knife.

I can read in a cam file and produce these stats.

Intake BTDC (IVO to TDC) =
Intake Pumping (TDC to BDC) =
Intake Ramming (BDC to IVC) =
Intake Overlap (IVO to EVC) =

Exhaust Blow-Down (EVO to BDC) =
Exhaust Pumping (BDC to TDC) =
Exhaust ATDC (TDC to EVC) =
Exhaust Overlap (IVO to EVC) =

I can adjust RPM, rocker arm ratio, advance / retard, open / close LSA.

Hi Stan,

How difficult would it be to translate those program outputs to an equivalent Blair BMEP for each segment?

[DrillDawg]

I then picked out a target BMEP (corresponding with a HP value at some rpm (7200)).

I'm just a rank student, and maybe not the best one (for example, I never bring apples for the teachers), but I do have one question:
This would also be saying that you therefore have a target value for torque, right? I'm not saying peak torque, but a value for torque at horsepower rpm, maybe?

--Jim

If you have a target HP peak, you have to have a target torque at HP peak as that is how you figure HP.

[Stan Weiss]

I then picked out a target BMEP (corresponding with a HP value at some rpm (7200)).

I'm just a rank student, and maybe not the best one (for example, I never bring apples for the teachers), but I do have one question:
This would also be saying that you therefore have a target value for torque, right? I'm not saying peak torque, but a value for torque at horsepower rpm, maybe?

--Jim

If you have a target HP peak, you have to have a target torque at HP peak as that is how you figure HP.

RPM, HP, Torque, BMEP, were all shown a long with some calculations in the first post.

Stan

[SchmidtMotorWorks]

Jon,
I have not yet been able to think of a way to translate/convert/what ever you want call it the STA into lift profile. Been busy all day and so have not even looked it since yesterday. All that be said, if i did come up with a method that was to complex for native Excel it is possible that some VBA code might to the trick.

If I was looking to do this for myself or someone was paying me for the answer. I would use some routines I already have. I would get some engine specs (RPM, intake and Exhaust valve sizes, ...). I would then input cam specs (max lobe lift, seat-to-seat duration, 0.050" duration, 0.100" duration, ...) , generate a lift profile every 1 degree, and then calculate the TA's. I would have the LSA and ICL (also if used rocker arm ratio) as separate specs so that I could adjust these while still using the same lift file. This would be a trail and error method of looking at this output against Blair's numbers and than going back and generating a new lift profile until they just about matched. I believe once I had done a few cams it would not take that long to get the needed TA's

Stan

I have never written anything complex in a spreadsheet, the latest versions of Visual Studio are easier to use than Excel once there is any decision making involved.

I think mechanically you have the right idea and it would be just right for the purpose of explaining the concept.

I think the most practical and valuable way to go would be to:

1. Use the list of lobes on Mike Jones web site to model a series of approximate curves. Maybe Excel interpolation can do that.
http://jonescams.com/hydraulic-roller-tappet/
Compute the profile values, save and use those rather than recomputing on every edit.

2. Make the spreadsheet or program so that it can choose from the catalog of profiles and also adjust their timing.

This way, the user can choose from readily available lobes and adjust their timing to spec a cam that they can order easily.

If you make it so that the coefficients of the formula can be refined for a particular type of application, then a professional engine builder can use it to create their own unique recipe (based on his knowledge) to spec similar cams for similar (but reasonably different) to other engines he builds.

That would be better than what most cam companies do.