128 my take, anybody see it like this ?

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Re: 128 my take, anybody see it like this ?

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skinny z wrote: Mon Sep 19, 2022 11:50 am How about the 128 rule in it's most directed application?
That would be a 10.5:1 SBC with a 2.02" intake valve (so looking at an average CoD) and 350 CID. The objective is maximum torque as observed on an engine dyno.
No area under the curve etc. Just maximum output.

EDIT: That question is probably unfair to ask and it isn't meant to put anyone on the spot.
I am curious as to any answer though.
FTR: The only spec to come out of that "formula" is the LSA. And in the case above, it falls in at 108.
It's not a formula, it;s a rule of thumb.
If you have a 350cid SBC with 10.5:1 compression, and 2.020" intake valves, the optimum cam for one application may be on a 108 LSA, but if you change the rod length, that will change. If you change the port size, that will change. If you change the desired RPM range, that will change.
BTW, the optimum cam for a 350 SBC with a 4.00" Bore and 3.48" stroke, will be different then a 350 SBC with a 4.140" bore and 3.25" stroke.
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Re: 128 my take, anybody see it like this ?

Post by skinny z »

CamKing wrote: Mon Sep 19, 2022 12:33 pm
skinny z wrote: Mon Sep 19, 2022 11:50 am How about the 128 rule in it's most directed application?
That would be a 10.5:1 SBC with a 2.02" intake valve (so looking at an average CoD) and 350 CID. The objective is maximum torque as observed on an engine dyno.
No area under the curve etc. Just maximum output.

EDIT: That question is probably unfair to ask and it isn't meant to put anyone on the spot.
I am curious as to any answer though.
FTR: The only spec to come out of that "formula" is the LSA. And in the case above, it falls in at 108.
It's not a formula, it;s a rule of thumb.
If you have a 350cid SBC with 10.5:1 compression, and 2.020" intake valves, the optimum cam for one application may be on a 108 LSA, but if you change the rod length, that will change. If you change the port size, that will change. If you change the desired RPM range, that will change.
BTW, the optimum cam for a 350 SBC with a 4.00" Bore and 3.48" stroke, will be different then a 350 SBC with a 4.140" bore and 3.25" stroke.
Understood Mike.
The TM program, which I believe has the 128 rule at it's core, also takes into account all of those variables you've mentioned.
I suppose this is why we have specialists like yourself.
And this is why I'll be in touch (in the new year).
Thanks.
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Re: 128 my take, anybody see it like this ?

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CamKing wrote: Mon Sep 19, 2022 9:59 am If it 's accurate for a Chevy, but not a Ford, it's not a formula, it's a rule of thumb.
If it's accurate for a Small Block, but not a Big Block, it's not a formula, it's a rule of thumb.
If it's accurate for a 350cid SB, but not for a 406cid SB, it's not a formula, it's a rule of thumb.
There is nothing that says a formula must be accurate in order to be classified as a formula. It’s just very very far from universal.

Newtons laws probably don’t work accurately inside a black hole or at a quantum level.

I find the formula interesting in the trend it implies.
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Re: 128 my take, anybody see it like this ?

Post by skinny z »

digger wrote: Mon Sep 19, 2022 8:48 pm I find the formula interesting in the trend it implies.
I reasonably certain that the formula was derived from a trend. That is if I understand DV's explanation of it's origin.
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Re: 128 my take, anybody see it like this ?

Post by hoffman900 »

digger wrote: Mon Sep 19, 2022 8:48 pm
CamKing wrote: Mon Sep 19, 2022 9:59 am If it 's accurate for a Chevy, but not a Ford, it's not a formula, it's a rule of thumb.
If it's accurate for a Small Block, but not a Big Block, it's not a formula, it's a rule of thumb.
If it's accurate for a 350cid SB, but not for a 406cid SB, it's not a formula, it's a rule of thumb.
There is nothing that says a formula must be accurate in order to be classified as a formula. It’s just very very far from universal.

Newtons laws probably don’t work accurately inside a black hole or at a quantum level.

I find the formula interesting in the trend it implies.
I get hung up on how people have given great engineering / science based principals, backed up with empirical evidence, on a number of topics here, ans get glossed over for rules of thumb and other folklore that just won’t go away.

It reminds me of a racing friend / engine builder who won a lot about when I asked him why he doesn’t keep secrets “because they won’t listen to me and misconstrue what I say even though I’m beating them”
-Bob
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Re: 128 my take, anybody see it like this ?

Post by skinny z »

hoffman900 wrote: Mon Sep 19, 2022 9:08 pm I get hung up on how people have given great engineering / science based principals, backed up with empirical evidence, on a number of topics here, ans get glossed over for rules of thumb and other folklore that just won’t go away.
Is this in support of 128 or suspect of it's credibility?
Curious only.
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Re: 128 my take, anybody see it like this ?

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skinny z wrote: Mon Sep 19, 2022 9:12 pm
hoffman900 wrote: Mon Sep 19, 2022 9:08 pm I get hung up on how people have given great engineering / science based principals, backed up with empirical evidence, on a number of topics here, ans get glossed over for rules of thumb and other folklore that just won’t go away.
Is this in support of 128 or suspect of it's credibility?
Curious only.
128 is a rule a thumb for a narrow range of application. I’m in support of it for what it is, but it’s not based o sound engineering principals and teaches you nothing about how engines work, or how to really develop them. It’s a formula David backed into by data fitting dyno testing he did for a 350ci, 10:1 compression, single carbureted, with decent but not great cylinder heads, vintage Chevy.

I like race engines, learning about developing them, and going faster. I wish there was more of that here because copy pasta street vintage small block Chevy’s have been done a million times and just aren’t exciting. You can do a good job at this point just copying a package out of one of many books and magazine articles and apply some rules of thumb, but they aren’t really all that exciting.
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Re: 128 my take, anybody see it like this ?

Post by digger »

hoffman900 wrote: Mon Sep 19, 2022 9:27 pm
skinny z wrote: Mon Sep 19, 2022 9:12 pm
hoffman900 wrote: Mon Sep 19, 2022 9:08 pm I get hung up on how people have given great engineering / science based principals, backed up with empirical evidence, on a number of topics here, ans get glossed over for rules of thumb and other folklore that just won’t go away.
Is this in support of 128 or suspect of it's credibility?
Curious only.
128 is a rule a thumb for a narrow range of application. I’m in support of it for what it is, but it’s not based o sound engineering principals and teaches you nothing about how engines work, or how to really develop them. It’s a formula David backed into by data fitting dyno testing he did for a 350ci, 10:1 compression, single carbureted, with decent but not great cylinder heads, vintage Chevy.

I like race engines, learning about developing them, and going faster. I wish there was more of that here because copy pasta street vintage small block Chevy’s have been done a million times and just aren’t exciting. You can do a good job at this point just copying a package out of one of many books and magazine articles and apply some rules of thumb, but they aren’t really all that exciting.
there are some potential points of discussion from the claims of the equation and implications implied. E.g. for a given engine the relative phasing of the inlet and exhaust should remain fixed even when adding or subtracting duration and thus increasing the communication between the inlet and exhaust sides during overlap.
By extension you might also say that if increasing the inlet lobe duration the opening and closing points should both change the same amount, or in order to close the inlet valve later you need to also open it sooner for it to work properly. When i looked at this in ENGMOD4T this seemed to be reasonable provided you were only looking at WOT maximum average power in the 3-7k rpm range.
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Re: 128 my take, anybody see it like this ?

Post by GARY C »

Tom68 wrote: Fri Sep 16, 2022 11:24 pm I was thinking about 128 cam selection (whilst avoiding work that needed to be done).

So if I had a 1.72 intake 350, I get 105 degree LCA, if I use a moderate overlap for a stock converter and good idle, I'll end up with a wee little cam that has good low range power (matching the heads) but obviously won't make power over say 3500 rpm.

If I had a 2.2" valve you get a wider lobe center so even for a similar idle etc you get a bigger cam that will then get the benefit from the better flowing head.

So it's a nice formula to help pick a cam to suit your combination. That's cool.

Where I see a deviation from it would be say a motor where being a tight ass you use an old 1.72" valve head on a 350, assuming a decent size carb (coz you had one) but you want to still rev it to a gob smackingly high 4500, you'd have to close the intake later to get any cylinder fill but you don't want to compromise the idle so you have to widen the LSA (later LCA), yes you'll lose power from idle to 3000 odd.

i.e, it may be a valid formula for a perfect world, or even just a clean sheet build, but some of us like to make combinations to suit our rev range desires, or have a lopey idle etc, with stuff we actually have at our fingertips and only need to add a Cam and gasket set to throw it together.

Or am I living on another Planet all by myself ?
viewtopic.php?f=1&t=55269
This is a 1.94 valve head with a 52% seat giving the effect of a smaller valve with a 238/248 cam on a 104 LSA, it made over 490 hp from 5700 through 6500. Some of the specs are talked about on page 6.
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Re: 128 my take, anybody see it like this ?

Post by skinny z »

digger wrote: Mon Sep 19, 2022 11:06 pm When i looked at this in ENGMOD4T this seemed to be reasonable provided you were only looking at WOT maximum average power in the 3-7k rpm range.
I think this is also fundamental to the rule.
Although, peak torque may be more of an emphasis. The average would fall into place. Of course, there are exceptions.
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Re: 128 my take, anybody see it like this ?

Post by hoffman900 »

skinny z wrote: Tue Sep 20, 2022 8:21 am
digger wrote: Mon Sep 19, 2022 11:06 pm When i looked at this in ENGMOD4T this seemed to be reasonable provided you were only looking at WOT maximum average power in the 3-7k rpm range.
I think this is also fundamental to the rule.
Although, peak torque may be more of an emphasis. The average would fall into place. Of course, there are exceptions.
I think the first thing people need to do is to create a histogram rpm plot on how they drive. We use 104-106 LSA (104/104 centerlines, or around 102/106 centerlines) on road race engines. Work great, make a lot of power for something that redlines around 7200rpm, but no way would I call that streetable and I bet most people with these kind of Chevy’s are spending most of their time below 3000-3500rpm (where most dyno pulls start). The 128 rule of thumb also only works for symmetrical valve lift profiles. It’s not going to work with Harold’s lobes, some of Mike’s, and a handful of Comp’s lobe families.

Also, I need to caution about lobe profiles when you simulate. You really need the actual lobe / valve lift profiles you want to test. I have bought cams specifically to have CamDr’ed for simulation work (and sold them). You can kind of rough in one, but it’s not the same and you will be missing a bunch.
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Re: 128 my take, anybody see it like this ?

Post by skinny z »

hoffman900 wrote: Tue Sep 20, 2022 8:56 am
skinny z wrote: Tue Sep 20, 2022 8:21 am
digger wrote: Mon Sep 19, 2022 11:06 pm When i looked at this in ENGMOD4T this seemed to be reasonable provided you were only looking at WOT maximum average power in the 3-7k rpm range.
I think this is also fundamental to the rule.
Although, peak torque may be more of an emphasis. The average would fall into place. Of course, there are exceptions.
I think the first thing people need to do is to create a histogram rpm plot on how they drive. We use 104-106 LSA (104/104 centerlines, or around 102/106 centerlines) on road race engines. Work great, make a lot of power for something that redlines around 7200rpm, but no way would I call that streetable and I bet most people with these kind of Chevy’s are spending most of their time below 3000-3500rpm (where most dyno pulls start). The 128 rule of thumb also only works for symmetrical valve lift profiles. It’s not going to work with Harold’s lobes, some of Mike’s, and a handful of Comp’s lobe families.

Also, I need to caution about lobe profiles when you simulate. You really need the actual lobe / valve lift profiles you want to test. I have bought cams specifically to have CamDr’ed for simulation work (and sold them). You can kind of rough in one, but it’s not the same and you will be missing a bunch.
In this case, it'll be a tale of two engines.
One would be the typical street/strip/highway deal. As such, the approach to development may be a little different from engine number two. That being a more dedicated racing engine.
From my experiences, and even from the modest simulation work I've managed to do, there doesn't seem to be a lot to choose between what one might get custom ground or something I pull off the shelf with respect to engine number one's performance. The application is too broad I think to be able to determine that any one performance metric is better than another. I.e. drivability vs drag strip results vs fuel economy, etc.
Engine number two on the other hand, would be more defined. RPM range tightened up, and outright power the ultimate goal given the collection of parts already in hand. All that remains is a cam spec really. Then maybe some of the usual experimentation with carb spacers and or carbs, intakes, etc.
This is why I'm intrigued by the TM program because the results provided are quite different from what been spec'd from those aforementioned multipurpose engines.
Anyway, this is all part of the process. The feedback and dialogue are at this time, what's driving the project forward. Scheduling is preventing this from moving along in the hard parts sense until the new year. Maybe a little sooner.
As for simulations, with my limited access to the best programs, I'm typically looking for trends more than anything. All well documented by others but I still look for what happens with a tighter LSA or a split pattern vs a single pattern. Or a small change in CR as examples.
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Re: 128 my take, anybody see it like this ?

Post by CamKing »

digger wrote: Mon Sep 19, 2022 8:48 pm There is nothing that says a formula must be accurate in order to be classified as a formula.
Um......OK
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Re: 128 my take, anybody see it like this ?

Post by ClassAct »

hoffman900 wrote: Tue Sep 20, 2022 8:56 am
skinny z wrote: Tue Sep 20, 2022 8:21 am
digger wrote: Mon Sep 19, 2022 11:06 pm When i looked at this in ENGMOD4T this seemed to be reasonable provided you were only looking at WOT maximum average power in the 3-7k rpm range.
I think this is also fundamental to the rule.
Although, peak torque may be more of an emphasis. The average would fall into place. Of course, there are exceptions.
I think the first thing people need to do is to create a histogram rpm plot on how they drive. We use 104-106 LSA (104/104 centerlines, or around 102/106 centerlines) on road race engines. Work great, make a lot of power for something that redlines around 7200rpm, but no way would I call that streetable and I bet most people with these kind of Chevy’s are spending most of their time below 3000-3500rpm (where most dyno pulls start). The 128 rule of thumb also only works for symmetrical valve lift profiles. It’s not going to work with Harold’s lobes, some of Mike’s, and a handful of Comp’s lobe families.

Also, I need to caution about lobe profiles when you simulate. You really need the actual lobe / valve lift profiles you want to test. I have bought cams specifically to have CamDr’ed for simulation work (and sold them). You can kind of rough in one, but it’s not the same and you will be missing a bunch.
Most of my stuff is 11-12:1 pump gas and I haven’t used over a 108 LSA on any of them. My own engine is on a 105 in at 105. None of them are bad or hard to drive on the street. They idle clean and will idle down to 700 if I let them.

That’s GM, Ford and Chrysler small and big block. My engine will go on the pump late this winter or early spring. I’ll test it with some other cam if someone wants to pay for the cam and lifters. I’ll do the dyno for free and post the results here.
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Re: 128 my take, anybody see it like this ?

Post by skinny z »

ClassAct wrote: Tue Sep 20, 2022 11:16 am
Most of my stuff is 11-12:1 pump gas and I haven’t used over a 108 LSA on any of them. My own engine is on a 105 in at 105. None of them are bad or hard to drive on the street. They idle clean and will idle down to 700 if I let them.

That’s GM, Ford and Chrysler small and big block. My engine will go on the pump late this winter or early spring. I’ll test it with some other cam if someone wants to pay for the cam and lifters. I’ll do the dyno for free and post the results here.
I'd like to know what CID and cylinder head/ intake valve size (or any trick valve job)?
Those are the 128 inputs and kind of the centre of attention with this thread.
Thanks.
Kevin
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