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128 my take, anybody see it like this ?

General engine tech -- Drag Racing to Circle Track

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Tom68
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128 my take, anybody see it like this ?

Post by Tom68 »

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

Post by Tom Walker »

The idea of using what you have has been a basic philosophy of hot rodding since day one and I do it myself, but I think we must admit that way of building engines or anything is filled with compromised results. It is what it is at that point.
To apply a theory or formula that’s purpose is to achieve near optimal results, I would think requires an assumption that all the planning and parts would meet near optimal characteristics if we expect the desired optimal results.
I have not studied the 128 theory much, but I would not expect it to achieve great results if in the process we use parts that are not really the greatest pertaining to compatibility.
But regardless, I say let’s continue to use what we have when we need to.
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Re: 128 my take, anybody see it like this ?

Post by mag2555 »

If your interest is really to maximize the VE of any given size motor and end up with widest power band possible be it Tq band or Hp, or the combination of both then what needs to be focused on it the amount of overlap and critical to that where that overlap duration is placed.

This assumes that for your motors cid that you already have a well thought out intake tract and a exh system that scavenge’s well which is one of the main keys to High VE numbers.
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Re: 128 my take, anybody see it like this ?

Post by juuhanaa »

I dont have first hand experience about 128 formula, but here's an formula that doesn't get any simpler.. i have tested and it worked, although it's not the optimum for me.

Screenshot_20220917-151016.jpg
Screenshot_20220917-151150.jpg
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Re: 128 my take, anybody see it like this ?

Post by skinny z »

Tom68 wrote: Fri Sep 16, 2022 11:24 pm 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.
I believe it was explained by Vizard that the 128 rule tends to be very specific.
A quote from his paper explaining how it works:

Now before it becomes a subject of posting questions let me say that the ‘128’ number is for parallel 2 valve engines such as SB Chevy’s, Fords and Chryslers with typical (average) discharge co-efficient’s in the 0.000 to about 0. 200 thou valve lift range. It is also for a base 10.5/1 CR engine but I will explain that and how to cater for other CR’s later.

Venture outside of that arena and you're on your own with respect to having that handy formula.

Further to that, his Torque Master program follows a similar principle. I had this discussion with Stan Weiss when DV posted up in his "128 Drama" thread.
As an example, when using a compression less than the ideal 10.5:1, (still Gen 1 SBC with a 2.020 intake valve) the resulting duration numbers don't follow the usual trend of getting smaller so as to preserve cylinder pressure. Usual at least to the more common folk like myself.
When I asked DV what was going with the trend towards increasing the duration with less compression here at Speed-Talk, his reply was something along the lines of " if you can't compress it enough you better be sure that you have enough time to fill it" or words to that effect.

Even the rule has rules.
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Re: 128 my take, anybody see it like this ?

Post by F-BIRD'88 »

No its not a perfect formula.
Its a guideline formula to get yiu close to create a strong running sbc.. If the formula say calls for a 104° LSA cam and you don't got one find a cam that is close eg: 106, 107, 108, 110 LSA , and has suitable duration for the intended running rpm range where you want the power and torque to happen.

EG: a 218@.050" .450" 106 LSA is pretty close. Now install it so it has the same INTAKE CENTERLINE, as what that 104° cam would have.. Get it close.
EG: 100 to 104 installed intake C/L
It will run close and make good power and torque..
If say you got a 218 to 224 ° cam on 110° LSA again install it with the intake CENTERLINE as close to what that 104 cam wants . EG install at say 104/116 phasing (110° LSA). [ It is 6° advanced] You cannot change the LSA. , but you CAN adjust the installed intake centerline as required to get it close..

Of course a 114°LSA cam is not going to quite work as well as say a 108° LSA or a 110° LSA cam that you may have kickin around. The point being is to get the installed intake centerline as close as you can.
It will run good as lobg as the duration is in the ball park fir the job.
"Poor man's custom cam". If you them care to test it you can move the cam around +/- to fine tune it . It will be as good as it can be.
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Re: 128 my take, anybody see it like this ?

Post by F-BIRD'88 »

Further: Nothing too much stopping you from digging thru you buddies collection of heads to find a 1.84" valve 305 head to use instead of that 1.72" 350 smog head.

Bigger intake valve,+ smaller combustion chamber.
Responds very well to home hand porting for low buck power additional airflow.
Your Buddy will likely give you the heads.
Now say you got a 230/230. .480"/.480" 109° LSA cam kickin around. 1.84" valve on a 350 calls for a 106° LSA°
Your cam is 109° LSA..... So install that cam at the same inake C/L as that 106° LSA cam will want for best torque..
Try a 102 to 103° intake Centerline. That makes the 109° cam 6 to 7° advanced... Just right for best torque where you need it on this budget build 350.
Will it run as good as the 106° cam.. Maybe not BUT IT WILL BE CLOSE.. It will run good.
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Re: 128 my take, anybody see it like this ?

Post by juuhanaa »

Okay now, if we have a wrong cam and porting is allowed, how can we address and fix possible too wide lsa? :D
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Re: 128 my take, anybody see it like this ?

Post by F-BIRD'88 »

juuhanaa wrote: Sat Sep 17, 2022 1:42 pm Okay now, if we have a wrong cam and porting is allowed, how can we address and fix possible too wide lsa? :D
How much too wide LSA.
99% of the time the cam you got will respond to advancing it if when more low end torque is desired.
Yes its a trade off. Low mid torque VS peak horsepower..

If the cam LSA is not that far off. EG 108 to 110 LSA. VS say a 114 LSA cam it can be moved to a better intake C/L for effect.
But the 114 LSA cam will also respond.
A 114 LSA cam in on say 105 to 107 in C/L will make more low end grunt than if its in on 110.
Yes you may give up a bit if peak hp.
Most low budget builds with modest cylinder heads especially if a modest converter stall will usually accelerate better if when advance is dialed into that not quite right cam. on hand.
If you are willing to play with it you can +/- the installed position to goid effect.

The very common popular off the shelf 110 LSA cams
respond very well to playing with the installed position to dial in the overall torque curve of the engine in the car.
Nothing wrong with moving that 110 LSA to a 101-105 intake C/L for effect if more low end torque is desired.

or running it "straight up" 110-110 if a big top end charge is desired.
Find the sweet spot for that cam in that engine in that car.
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Re: 128 my take, anybody see it like this ?

Post by F-BIRD'88 »

On a hyd cam you can try a bit of running valve lash for tuning effect if say the duration is a bit too much.
This effectivly shortens the valve event duration.
There is definatly a limit to whats practical when running a bit of valve lash with a hyd cam.
I recomend you keep it less than .010" lash
.004" to .006" running lash works well.
The sound of the valve train at idle is not a bad clue.
Mild lifter noise is passable (like a correctly lashed solid lifter cam sounds at idle.
Excessive valve noise at idle is a good clue the lash is just over the top too big. Its hard on the valves.

A solid lifter cam generally allows for a bit more valve lash variation +/-.
Again excessive valcetrain noise at idle is a good clue you have gone too far looser valve lash.

Some people run solid lifters on hyd cams with a bit of running lash for effect to good results. Just keep it real.
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Re: 128 my take, anybody see it like this ?

Post by F-BIRD'88 »

I have found that with those "old school" design hyd cams with longer easy ramps "lazy" that this tuning by running a hair of running valve lash does effectivly liven up the net valve motion. A bit of lifter noise but more snappy.
One, I just did the 8 intake valves for valve event effect.
This cam was 111 LSA and 111/111 in/ ex phasing and the engine compression ratio was low.. 8.2:1 ish. .
Moved the 111LSA cam to 104/118 phasing and added a bit of lash to the intake valves only and it became a lot more of a toque monster.. Ran a lot better than before.
Car had gears but a stock converter and a low compression ratio. It made a nice difference.
Sometimes you got to make the best of what you got.
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Re: 128 my take, anybody see it like this ?

Post by juuhanaa »

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.
I did small comparison using a torque master program. I changed the intake valve size and compression ratio, so that the program gave the same dynamic compression ratio and cranking cylinder pressures.

I also tested different exhaust valve sizes for both examples and i noticed the program recommended different advance. What you guys think about this?

SBF 302 109LSA.cam.png
SBF 302 108LSA.cam.png
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Re: 128 my take, anybody see it like this ?

Post by skinny z »

I'm going to say that the 10:1 result isn't possible. With an IVC of 51° the DCR will be in excess of 11:1.
Something is off with the calculation. Maybe the intake valve size is causing a problem?
I'm also curious as to why there are commas rather than decimals in the appropriate places in your Torque Master screenshots.


SCR.jpg

Cam.jpg

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

Post by RevTheory »

I've learned that the smaller the valve size for a given cubic inch, the more it'll really swallow up overlap. I did a hyd/flat cam for a 406 with 2.02 intake valves several years ago and with the cam ground on a 107 LSA, had 49 degrees of overlap. Damn thing idled like a kitten and pulled 18 inches of manifold vacuum.

It would've been a different story had it been a 350.
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Re: 128 my take, anybody see it like this ?

Post by skinny z »

RevTheory wrote: Sun Sep 18, 2022 11:58 am I've learned that the smaller the valve size for a given cubic inch, the more it'll really swallow up overlap. I did a hyd/flat cam for a 406 with 2.02 intake valves several years ago and with the cam ground on a 107 LSA, had 49 degrees of overlap. Damn thing idled like a kitten and pulled 18 inches of manifold vacuum.

It would've been a different story had it been a 350.
I believe that's one of the guiding principles of TM. As the CoD of the intake valve goes up, the LSA will spread. And vice versa. The same with more CID.

Question though: What were the specs that gave you 49° of overlap?
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