All Small Six Dynamic compression

[DON]

I am starting a new thread so I am not stepping on another post. This info was posted:

Frank​

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• Today at 9:00 AM
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• #5

I haven’t calculated dynamic ever.
my static is about 10.2
What is stock rod by length and how is it measured?
How would you figure intake closing?

I don't know the rod length of the small 6's, but someone on here does, and I'm sure it's posted somewhere.
To calculate intake valve close point: Camshaft advertised duration (gross duration, not .050") divided by two. Add the Lobe Separation Angle. Subtract 180. This is the intake closing point after Bottom Dead Center on the compression stroke with a cam that is not advanced or retarded. Sense compression doesn't start until the valve is (nearly) closed, this calculation is critical to determine grade of fuel needed, etc. . Actual running compression is determined by the camshaft, the static compression is only a build foundation to match the cam selected. The more mild the cam, the higher the compression ratio and fuel grade required will be for a given Static Compression.
Example of finding IVCP: Cam specs say duration is 205*/260* intake duration, the LSA (Lobe Separation Angle) is 110*

260* divided by 2 = 130. 130+110(LSA)= 240. 240-180= 60 The intake valve on this cam closes @ 60* ABDC. This is with the cam straight-up. Most cams are ground with 4* advance built into the grind. The advance/retard is added/subtracted from this final closing point number. If the cam is advanced, subtract the *'s of advance from the total, if it's retarded, add the *'s of retard to the total.
From the example above: if this cam is advanced 4*the IVC point is 60-4=56* ABDC. If it is retarded 4* the IVCP is 60+4=64* ABDC Insert this final number in the last line of the calculator.

Ideally, the build plan begins with the camshaft chosen, and the target DCR known. Then work backward to determine the piston dish, piston compression height, and head volume. The UEM Calculator is the foundation for deciding what parts are going to produce a matched build- when starting with the camshaft, and the intake valve closing point.
End of post

I started by figuring intake opening point and the formula asks for lobe separation angle. My cam sheet gives lobe center but not separation. There must be a way to figure it? It is math

 

[aussie7mains]

All this stuff about Dynamic CR is basicly using the exhaust closing event to determine when the stroke begins, its like the debate on two stroke engines as to calculating the compression ratio from the top of the exhaust port. The problem with this is that the actual cylinder filling is fairly indeterminate given all the other things going on, VE varies with speed and load etc etc. For instance you could decide to calculate the CR at a semi closed throttle position at high temperatures, this would be in an area of low VE and therefore low BMEP, and at this point CR might be as low as 3:1, if the cylinder was only 30% full for instance. Are you going to consider this? All the usual quoted dyno tests are done at maximum load and max rpm, there is little concern for any other areas of operation, and you will all agree that the engines spend very little of its time at full load and speed on a road doing vehicle. As and example take aircraft piston engines, when flying they operate at relatively high load, they MUST be safe at this load, so they mostly operate on high octane fuel and lowish compression down in the 6-7 range. A car engine can get away with much higher compression than this as:- the consequences of failure are not severe, they rarely operate continuously at high loads, their fuel can be indifferent. So all the talk of dynamic CR being used to determine where the CR should be is fictious, NONE of the notable texts consider this (Ricardo for instance). Modern engines can get away with high CR even up to 11:1, most of them have knock sensing. My two bobs worth!

 

[Frank]

All this stuff about Dynamic CR is basicly using the exhaust closing event to determine when the stroke begins, its like the debate on two stroke engines as to calculating the compression ratio from the top of the exhaust port. The problem with this is that the actual cylinder filling is fairly indeterminate given all the other things going on, VE varies with speed and load etc etc. For instance you could decide to calculate the CR at a semi closed throttle position at high temperatures, this would be in an area of low VE and therefore low BMEP, and at this point CR might be as low as 3:1, if the cylinder was only 30% full for instance. Are you going to consider this? All the usual quoted dyno tests are done at maximum load and max rpm, there is little concern for any other areas of operation, and you will all agree that the engines spend very little of its time at full load and speed on a road doing vehicle. As and example take aircraft piston engines, when flying they operate at relatively high load, they MUST be safe at this load, so they mostly operate on high octane fuel and lowish compression down in the 6-7 range. A car engine can get away with much higher compression than this as:- the consequences of failure are not severe, they rarely operate continuously at high loads, their fuel can be indifferent. So all the talk of dynamic CR being used to determine where the CR should be is fictious, NONE of the notable texts consider this (Ricardo for instance). Modern engines can get away with high CR even up to 11:1, most of them have knock sensing. My two bobs worth!

indeed. notice I said compression doesn't start until the valve is nearly closed. At idle, between vacuum and reversion, there's virtually no compression at all. . Calculation of DC is a ballpark which is useful on the ornery 300 with it's long stroke in a slender cylinder. As you said, actual cylinder filling varies more or less at all times, and in an automotive application is rarely maxed. .

 

[Frank]

I started by figuring intake opening point and the formula asks for lobe separation angle. My cam sheet gives lobe center but not separation. There must be a way to figure it? It is math

"Lobe Center" is the #. The "Center Line Timing Events" tells you the cam is ground with two degrees of advance in the grind.

274 over 2= 137. 137+108=245 245-180=65. 65*ABDC less the 2* advance= 63*ABDC intake valve closing point. That's a strong cam. Will have big low-end grunt with that tight LSA.

 

[DON]

Haven’t been home this am. Doing one of the two things in life you can’t get away from… and I didn’t die
Just looking at the last post, clay smith told me this cam was ground straight up, no advance

 

[DON]

And if I remember right when I time the cam, I have to retard it 2 degrees to get the lobe center

 

[DON]

So I would figure 67 degrees closing point, after bottom dead center

 

[pmuller9]

And if I remember right when I time the cam, I have to retard it 2 degrees to get the lobe center

So I would figure 67 degrees closing point, after bottom dead center

The cam card is asking you to advance the cam 2 degrees so the intake valve would close at 63 degrees ABDC.

This is a moderately aggressive camshaft for a 200 six. The engine won't start to pull until you get above 3000 rpm.

 

[Frank]

And if I remember right when I time the cam, I have to retard it 2 degrees to get the lobe center

No don't retard the cam, it's a strong profile already. As Pmuller9 said, the card shows the timing numbers 2* advanced. = 63* ABDC

 

[drag-200stang]

Remember that small sixes have to be degreed with a dial indicator and degree wheel. there is no way to know if it is right without checking.

 

[DON]

Ok, let me back up. Clay Smith said the cam was ground straight up. No degrees added. They stated RPM range is 1800 to 5700 RPM. ( 3000 is quite a bit higher) Installed with a double roller chain with adjustable crank sprocket. I used a degree wheel and the .050 before and after method, with the head off, to get the cam on 108 degrees. To get that, the crank sprocket needed to be on -2. When the sprocket was set at 0 it was 106 degrees. I still have my figures.
If there is numbers on the cam card indicating where the cam timing should be set, please explain. I never found anything that indicated a cam could be timed with out a wheel and using the cam card numbers as a goal. I am open to hearing it thou. I am always open to learning. I need to get this sorted, then we can work on dynamic compression.
Thank you for patience understanding. This is the first cam I have timed

 

[DON]

Just re- read the tec article on cam lobe center lines. Now I’m even more confused. It said install Clay Smith cam with 4 degrees advance. Is this regardless of numbers on cam card and degree wheel??

 

[chad]

echo’s vid on his 3.3 re-build really helped me (thank U bubs 4 assisting) @ the § he degrees in the cam. It seemed he did it so deftly (no fumbelin around) it made it real clear to me (as a 1st timer). Can any 1 cite the site for him (specific section I, II,II &/or min time place?)
EDIT:
went to uYube, just too much there & remembered bub’s stickies of our friend echo (RIP 4 both them)

200ci - Echo -1955 Rebuild's His 1965 Mustang 200 I6 Block.

Rebuild 65 200 I6 Block. I bought my 65 in 65. I brought it back to life in 98. I had to repaint it a couple months ago because my prized 100 lb Lab played catch me iffen ya can wid a 10 lb cat. Their playground was the top of my FB. Scratched the paint all the way down to metal. This is where...

fordsix.com

right on the site... go to post 16 @ that link. I bet his vids are the red at bottom of post (in sig?)
Not sure which shows degree - in. U may not need it. All the readin I did just threw me off.
Try the 2nd vid. It may even B documented - like a table of contents by min of his sequence of
operations in the vid...
HTH, GL
One more, one more time:
min 9:15 of vid III

 

[Frank]

Don, if it clocked @ 106* intake LCL with the gears @ 0* advanced, then the cam has 2* advance built in. 106* is what your cam card says, and that's +2*. That's good results! A fair % of the time the cam is not timed where advertised. Including the one I have just installed, was -5* from the card.
Also verify the other specs on the card. Valve opening/closing @ .050" lift should match the card. If everything agrees (within a *), the cam is the grind it says, and is where it's designed to be. Now, for intake closing DCR calculation, roll past the .050" intake closing to .006" lift. this should be close to 63*ABDC. Whatever it is, that's the # to plug into the calculator.
Take your time and repeat the test as necessary. I'm sure you did, but being sure the degree wheel is exactly on TDC is critical, otherwise all readings are erroneous.

 

[Frank]

Just re- read the tec article on cam lobe center lines. Now I’m even more confused. It said install Clay Smith cam with 4 degrees advance. Is this regardless of numbers on cam card and degree wheel??

Install it where ever you need to for your build. Advancing lowers the RPM range, and vice versa. there's no "rule" that it has to be advanced.
Mine is "supposed" to be 4* advanced, and it's set @ 1* retarded for this particular build.

 

[DON]

Ok guys, I think some of my confusion and what you are telling me is based on me giving you wrong info. I used the lobe center number of 108 to degree the cam and not the intake center line timing events number: 106. The good news is I know where to set the timing chain/ sprocket to get that: 0

What I need to decide now is if it is worth pulling the timing cover off to change it. My plans are to use this car for local driving, within 100 miles,maybe a few road trips. I plan to put a five speed tranny in it and rear axel that the gears can be changed. I want high gear to be pretty high. 2000 rpm’s or less. The post about starting to pull at 3 grand worries me. I can live with starting numbers below 2000 as clay smith advertises. I think I would rather lower the power curve and sacrifice top end

 

[pmuller9]

I want high gear to be pretty high. 2000 rpm’s or less. The post about starting to pull at 3 grand worries me. I can live with starting numbers below 2000 as clay smith advertises. I think I would rather lower the power curve and sacrifice top end

We put a Howards 221 degree cam (Yours is 224 degrees) in Goldies 200 mustang.
It has a C4 tranny with a 2500 stall converter and pulls hard from there.
It has a 3.08 rear and cruises all day long around 2000 rpm and gets 23 mpg and does well against the 289/302 Mustangs.
They were talking about going to a 3.55 rear to up the performance.
You will be fine with that cam.

 

[DON]

We put a Howards 221 degree cam (Yours is 224 degrees) in Goldies 200 mustang.
It has a C4 tranny with a 2500 stall converter and pulls hard from there.
It has a 3.08 rear and cruises all day long around 2000 rpm and gets 23 mpg and does well against the 289/302 Mustangs.
They were talking about going to a 3.55 rear to up the performance.
You will be fine with that cam.

Thank you! That makes me feel better
New day, more positive outlook

 

[DON]

Install it where ever you need to for your build. Advancing lowers the RPM range, and vice versa. there's no "rule" that it has to be advanced.
Mine is "supposed" to be 4* advanced, and it's set @ 1* retarded for this particular build.

After sleeping on on it, I think I am going to pull the cover and set it at “0”. That puts me at 106, right where the manufacturer recommends, it will keep power curve a little lower, which is where I want it.
I also checked dyn comp, it was just over 8. I used the 67 and 65( I think ) and they were both under 8.5 and the static was the same as I figured it before, just over 10, less than 10.5. I will re-check and document it. I want to run ethanol free gas which we can get at 91 octane, more frequently available at 89. Does that sound doable at, let’s say, 8.3 DC

 

[drag-200stang]

Any change should also be verified again with the degree wheel.