How much advance for a less than optimal cam ?

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Tom68
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How much advance for a less than optimal cam ?

Post by Tom68 »

Lets say you've decided you want a 226 234 110 cam fitted 4 degrees advanced.

BUT you have a 230 230 110 cam that you'll use for whatever reason, time budget whatever, how much advance would you fit it with to try and keep the performance as similar as it can be to the first cam ? lets not worry about differences under 3,000 rpm.

Open headers.

I'm thinking 6 degrees advance.
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Re: How much advance for a less than optimal cam ?

Post by Geoff2 »

I do not have the answer & I doubt anybody will unless that exact combo has been tried by someone else.
What I can tell you is what Crane cams said in one of their catalogs: a minimum change of 4 crank degrees is needed for the butt-meter to tell the difference; & 4* shifts the rpm range approx 200 rpm.
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Re: How much advance for a less than optimal cam ?

Post by F-BIRD'88 »

You'd want to move the 230/230 cam ahead by 2 more degrees.
Now it has the same intake closing point and the same exhaust opening point as the 226/234 cam.

The butt dyno can be decieving.
This may not be the best possible position for best perf overall of either cam in the vehicle but its not bad.
From there you have to trial and error for actual effect.

Generaly if you have to move a cam more than 8 degrees + or -. you're getting beyond the truth.
But adjusting the cam installwd position can be very effective to tweek the overall torque/power curve.

Yup sometimes you have to work with what you got.
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Re: How much advance for a less than optimal cam ?

Post by mag2555 »

I think a great start would be to note your average cranking compression you have across 8 cylinders now and then get as close to that by messin with the new cam.

I must say that if I did not have the bigger cam already and my valve springs could take it, I would just run higher ratio rockers which would keep the low end power you have now and add some top.
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Re: How much advance for a less than optimal cam ?

Post by F-BIRD'88 »

"open headers". Incombination with tweeking the installed position of the camshaft you can really boost up the low/mid range torque output with collector extentions and or choke type/merge type header reducer/extentions added to your open headers.
This effectivly makes the engine think the headers are longer. and increases the velocity of the exhaust gas exit.
This greater exhaust gas speed (velocity) tends to return a stronger negative exhaust pressure PULSE back to the combustion chamber to kick up the scaveging effect .
Better evacuates the exhaust in the chamber and gives a pull on the intake port , on the overlap cycle.
Air likes to move from (relative) high(er) pressure towards a lower pressure so if when the negative return exhaust pulse arrives at the chamber at the right time it really helps get the intake flow moving just after TDC.
More exhaust gas out and more net intake flow in equals more power output in that range of rpm @WOT.

If you are running open headers and want MORE low and midrange engine torque, collector extensions can make a big difference in how well the car accelerates.

Oh , no I want less torque. Said no one ,, ever....
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Re: How much advance for a less than optimal cam ?

Post by Stan Weiss »

mag2555 wrote: Sun Sep 25, 2022 9:24 am I think a great start would be to note your average cranking compression you have across 8 cylinders now and then get as close to that by messin with the new cam.

I must say that if I did not have the bigger cam already and my valve springs could take it, I would just run higher ratio rockers which would keep the low end power you have now and add some top.
Given what information we have I agree. It seems people only like to look at 0.050" numbers anymore and don't care about adv. duration and events.

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Re: How much advance for a less than optimal cam ?

Post by F-BIRD'88 »

Stan Weiss wrote: Sun Sep 25, 2022 11:05 am
mag2555 wrote: Sun Sep 25, 2022 9:24 am I think a great start would be to note your average cranking compression you have across 8 cylinders now and then get as close to that by messin with the new cam.

I must say that if I did not have the bigger cam already and my valve springs could take it, I would just run higher ratio rockers which would keep the low end power you have now and add some top.
Given what information we have I agree. It seems people only like to look at 0.050" numbers anymore and don't care about adv. duration and events.

Stan
Thats because the .050" specs are a accurate way to reference the relative position of the camshaft in the engine and then to move it +/- as desired, with accuracy

Moving the camshaft +/- will have a much more profound effect on the engine power curve than does +/- changes in thw rocker ratio.
The cost of getting high(er) ratio rocker arms can exceed the cost of aquiring a new different camshaft.
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Re: How much advance for a less than optimal cam ?

Post by Stan Weiss »

F-BIRD'88 wrote: Sun Sep 25, 2022 11:15 am
Stan Weiss wrote: Sun Sep 25, 2022 11:05 am
mag2555 wrote: Sun Sep 25, 2022 9:24 am I think a great start would be to note your average cranking compression you have across 8 cylinders now and then get as close to that by messin with the new cam.

I must say that if I did not have the bigger cam already and my valve springs could take it, I would just run higher ratio rockers which would keep the low end power you have now and add some top.
Given what information we have I agree. It seems people only like to look at 0.050" numbers anymore and don't care about adv. duration and events.

Stan
Thats because the .050" specs are a accurate way to reference the relative position of the camshaft in the engine and then to move it +/- as desired, with accuracy

Moving the camshaft +/- will have a much more profound effect on the engine power curve than does +/- changes in thw rocker ratio.
The cost of getting high(er) ratio rocker arms can exceed the cost of aquiring a new different camshaft.
Really! And here I am thinking I can degree a cam in at lets say 107.5 ICL without having a cam card. :shock:

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Re: How much advance for a less than optimal cam ?

Post by PackardV8 »

F-BIRD'88 wrote: Sun Sep 25, 2022 11:15 am The cost of getting high(er) ratio rocker arms can exceed the cost of aquiring a new different camshaft.
Yes, No, Maybe.

Yes, if one can do his own work, just get the best cam for the combo.

No, if one has to pay a shop to pull and replace the cam.

Maybe, run some dyno simulation software and quantify the results of all the options. Sometimes, we're just pickin' the flyshite out of the pepper and there's very little to be gained.
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Re: How much advance for a less than optimal cam ?

Post by F-BIRD'88 »

Stan Weiss wrote: Sun Sep 25, 2022 11:25 am
F-BIRD'88 wrote: Sun Sep 25, 2022 11:15 am
Stan Weiss wrote: Sun Sep 25, 2022 11:05 am

Given what information we have I agree. It seems people only like to look at 0.050" numbers anymore and don't care about adv. duration and events.

Stan
Thats because the .050" specs are a accurate way to reference the relative position of the camshaft in the engine and then to move it +/- as desired, with accuracy

Moving the camshaft +/- will have a much more profound effect on the engine power curve than does +/- changes in thw rocker ratio.
The cost of getting high(er) ratio rocker arms can exceed the cost of aquiring a new different camshaft.
Really! And here I am thinking I can degree a cam in at lets say 107.5 ICL without having a cam card. :shock:

Stan
You don't need a cam card.. You can determine the phasing of the camshaft by measuring that in the engine and the .050" open close events are the best most accurate way to do that then to move it accuratly.
You can have a cam and a cam card in hand but from there you still have to referenxe its position in your engine, to se
1. is it in there correctly?
2. How much does it might need to be move ,+/- to adjusts its perfomance in that engine?
Did it get moved accuratly?

Measuring the .050" lifter rise events is the best way to
do all this.
And it does not matter who is paying who for that.

It is your best method.
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Re: How much advance for a less than optimal cam ?

Post by hoffman900 »

F-BIRD'88 wrote: Sun Sep 25, 2022 12:07 pm
Stan Weiss wrote: Sun Sep 25, 2022 11:25 am
F-BIRD'88 wrote: Sun Sep 25, 2022 11:15 am

Thats because the .050" specs are a accurate way to reference the relative position of the camshaft in the engine and then to move it +/- as desired, with accuracy

Moving the camshaft +/- will have a much more profound effect on the engine power curve than does +/- changes in thw rocker ratio.
The cost of getting high(er) ratio rocker arms can exceed the cost of aquiring a new different camshaft.
Really! And here I am thinking I can degree a cam in at lets say 107.5 ICL without having a cam card. :shock:

Stan
You don't need a cam card.. You can determine the phasing of the camshaft by measuring that in the engine and the .050" open close events are the best most accurate way to do that then to move it accuratly.
You can have a cam and a cam card in hand but from there you still have to referenxe its position in your engine, to se
1. is it in there correctly?
2. How much does it might need to be move ,+/- to adjusts its perfomance in that engine?
Did it get moved accuratly?

Measuring the .050" lifter rise events is the best way to
do all this.
And it does not matter who is paying who for that.

It is your best method.
Assuming that the events below .050” is the same is a big assumption.

The engine sees seat-to-seat duration, not .050”. You can’t compare a Mike Jones designed lobes to Billy Godbold designed lobes to Harold Brookshire designed lobes look at .050. Mike’s cams look smaller at .050” than they run to, Harold has “unsymetrical ness” and Billy has symmetrical cams to non symmetrical cams, same with many of the designers, and they all use different lash ramps. It’s all “it depends”.


This makes this very obvious:
https://youtu.be/K1DFrWcvTuc
Last edited by hoffman900 on Sun Sep 25, 2022 12:43 pm, edited 2 times in total.
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Re: How much advance for a less than optimal cam ?

Post by skinny z »

hoffman900 wrote: Sun Sep 25, 2022 12:21 pm
Assuming that the events below .050” is the same is a big assumption.

The engine sees seat-to-seat duration, not .050”. You can’t compare a Mike Jones designed lobes to Billy Godbold has designed lobes to Harold Brookshire designed lobes look at .050. Mike’s cams look smaller at .050” than they run to, Harold has “unsymetrical ness” and Billy has symmetrical cams to non symmetrical cams, same with many of the designers, and they all use different lash ramps. It’s all “it depends.
This is my understanding as well.
Or even between a Jones lobe of 286 adv with 234@.050' (or 288 with 242@.050"!) vs one his 286 adv with 226@.050".
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Re: How much advance for a less than optimal cam ?

Post by hoffman900 »

skinny z wrote: Sun Sep 25, 2022 12:34 pm
hoffman900 wrote: Sun Sep 25, 2022 12:21 pm
Assuming that the events below .050” is the same is a big assumption.

The engine sees seat-to-seat duration, not .050”. You can’t compare a Mike Jones designed lobes to Billy Godbold has designed lobes to Harold Brookshire designed lobes look at .050. Mike’s cams look smaller at .050” than they run to, Harold has “unsymetrical ness” and Billy has symmetrical cams to non symmetrical cams, same with many of the designers, and they all use different lash ramps. It’s all “it depends.
This is my understanding as well.
Or even between a Jones lobe of 286 adv with 234@.050' (or 288 with 242@.050"!) vs one his 286 adv with 226@.050".
Looking at .050 and peak lift is like deciding what a house looks like based on a measurement 5’ off the ground and the roof peak, and ignores everything in between.
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Re: How much advance for a less than optimal cam ?

Post by F-BIRD'88 »

hoffman900 wrote: Sun Sep 25, 2022 12:21 pm
F-BIRD'88 wrote: Sun Sep 25, 2022 12:07 pm
Stan Weiss wrote: Sun Sep 25, 2022 11:25 am

Really! And here I am thinking I can degree a cam in at lets say 107.5 ICL without having a cam card. :shock:

Stan
You don't need a cam card.. You can determine the phasing of the camshaft by measuring that in the engine and the .050" open close events are the best most accurate way to do that then to move it accuratly.
You can have a cam and a cam card in hand but from there you still have to referenxe its position in your engine, to se
1. is it in there correctly?
2. How much does it might need to be move ,+/- to adjusts its perfomance in that engine?
Did it get moved accuratly?

Measuring the .050" lifter rise events is the best way to
do all this.
And it does not matter who is paying who for that.

It is your best method.
Assuming that the events below .050” is the same is a big assumption.

The engine sees seat-to-seat duration, not .050”. You can’t compare a Mike Jones designed lobes to Billy Godbold has designed lobes to Harold Brookshire designed lobes look at .050. Mike’s cams look smaller at .050” than they run to, Harold has “unsymetrical ness” and Billy has symmetrical cams to non symmetrical cams, same with many of the designers, and they all use different lash ramps. It’s all “it depends.


This makes this very obvious:
https://youtu.be/K1DFrWcvTuc

The real difference in modern sbc hyd flat tappet cams
That work in these engines are NOT THAT DIFFERENT.
the physics and mechanics of the job in the engine is the same.. The cams are MORE ALIKE THAN DIFFERENT.
The advertized published durations would like you to think different.
A Crane HMV cam is near identical in desgn to a Comp XE cam..
When get one and measure it you will see.
They are more a like than different in design.
If you were to lay the graphed lift curve of each hyd cam of same .050" "shoe size" on top of each other you will see. they are MORE A LIKE THAN DIFFERENT in actual design..
If you want to determine the relative position in the engine. ACCURATLY.. use the .050" method.
The other " shoe size" sizes are just relatively bigger or smaller lobes. Inreference to the .050" "shoe size" spec.
One 234° hyd flat tappet cam will operate more like another, than different when on simular same same .050" events.
The small differenes in seat to seat and open close ramp design. between them DOES NOT MAKE THAT MUCH DIFFERENCE..

Crane cams are measured at .004" lifter rise... Comps are .006" Neither use the SAE standard of .006" + Lash @the valve.

I'm not even real sure what the ISKY advertized duration reference is.. (.007" open .009" close) ????

The real difference between these 3 hyd flat tappet designs when measued at the same reference point on the cam lobe is NEAR IDENTICAL.
Cam Kings Hyd Flat tappet cams will be NOT THAT DIFFERENT.
They all are dealing with the same mechanical practical limitations of the engine valvetrain.

Use the .050" lifter rise events to practical method compare one to another.
Use the .050" specs to determine the installed position and to adjust that as desired, ACCURATLY.
Last edited by F-BIRD'88 on Sun Sep 25, 2022 1:12 pm, edited 3 times in total.
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Re: How much advance for a less than optimal cam ?

Post by F-BIRD'88 »

hoffman900 wrote: Sun Sep 25, 2022 12:40 pm
skinny z wrote: Sun Sep 25, 2022 12:34 pm
hoffman900 wrote: Sun Sep 25, 2022 12:21 pm
Assuming that the events below .050” is the same is a big assumption.

The engine sees seat-to-seat duration, not .050”. You can’t compare a Mike Jones designed lobes to Billy Godbold has designed lobes to Harold Brookshire designed lobes look at .050. Mike’s cams look smaller at .050” than they run to, Harold has “unsymetrical ness” and Billy has symmetrical cams to non symmetrical cams, same with many of the designers, and they all use different lash ramps. It’s all “it depends.
This is my understanding as well.
Or even between a Jones lobe of 286 adv with 234@.050' (or 288 with 242@.050"!) vs one his 286 adv with 226@.050".
Looking at .050 and peak lift is like deciding what a house looks like based on a measurement 5’ off the ground and the roof peak, and ignores everything in between.

In practical terms in real use in a typical engine like the sbc. This is just not true..
A 234° cam will run very similsr to another 234° cam wether the max valve lift is .450" or .,485" or .512"
Yes the upper lobe Area is a bit different. BUT the 2 234° cams will run very close to the same..
The difference in the .050" open close events MATTERS THE MOST. (These) Events matter more that lift area or dynamics in a typical sbc. Especially in terms of the hydraulic flat tappet cams.

Knowing the .050" specs tells you ALOT about how that cam will perform VS another typical SBC hyd flat tappet cam.. " Don't sweat the small stuff"
Last edited by F-BIRD'88 on Sun Sep 25, 2022 1:07 pm, edited 1 time in total.
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