Advancing Cam and cylinder pressure

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Slantsix64

Slantsix64

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Hey guys, so i finally know how to degree a camshaft my question now is, my buddys slant 225 has a 268 duration clifford camshaft headers 4 barrel all that nice stuff. but he is only cranking out 120PSI at each cylinder evenly so im guess his compression ratio is around 7:8- 8:1. Motor is over cammd not much low end but decent top end but i was telling him what if we advance that same camshaft 4 degrees what would the cylinder pressure rise to? Slants need more torque. My question is if we advanced his camshaft 4 degrees would he be able to build at least some decent pressure or should we just start milling that head
 
Slantsix64 said:
Hey guys, so i finally know how to degree a camshaft my question now is, my buddys slant 225 has a 268 duration clifford camshaft headers 4 barrel all that nice stuff. but he is only cranking out 120PSI at each cylinder evenly so im guess his compression ratio is around 7:8- 8:1. Motor is over cammd not much low end but decent top end but i was telling him what if we advance that same camshaft 4 degrees what would the cylinder pressure rise to? Slants need more torque. My question is if we advanced his camshaft 4 degrees would he be able to build at least some decent pressure or should we just start milling that head
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Maybe. Put a compression gauge in it when you advance it and see how much higher it goes. That's how I always degree camshafts. With the degree wheel AND a compression gauge. Because sometimes that 4* just isn't enough.
 
Slantsix64 said:
Hey guys, so i finally know how to degree a camshaft my question now is, my buddys slant 225 has a 268 duration clifford camshaft headers 4 barrel all that nice stuff. but he is only cranking out 120PSI at each cylinder evenly so im guess his compression ratio is around 7:8- 8:1. Motor is over cammd not much low end but decent top end but i was telling him what if we advance that same camshaft 4 degrees what would the cylinder pressure rise to? Slants need more torque. My question is if we advanced his camshaft 4 degrees would he be able to build at least some decent pressure or should we just start milling that head
Click to expand...

On a slant setting the cam to 100 ICL is typically optimal.
However with that large of a cam you need static compression.
I would pull the head, measure piston recession, cc the head to get the chamber size, put that with the bore and gasket size to see where the compression is currently.
Is the 268 advertized or @.050?

If you are starting with stock slant six compression, you will not get enough of a dynamic compression bump by advancing the cam by itself to make it really run. You will need static in the 9’s to 10’s to get there.
 
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Just pull the head and mill it .060

that will address the real issue a lot better and not negatively affect the gas mileage.
 
MOPAROFFICIAL said:
Just pull the head and mill it .060

that will address the real issue a lot better and not negatively affect the gas mileage.
Click to expand...

.060 may not be enough, depending upon the vintage, slant sixes were all over the map for piston recession and cylinder head combustion chamber size.
Measure, use an online CR calculator and you can nail it.
IIRC you mill .0069 from the head for each cc reduction.
 
my68barracuda said:
.060 may not be enough, depending upon the vintage, slant sixes were all over the map for piston recession and cylinder head combustion chamber size.
Measure, use an online CR calculator and you can nail it.
IIRC you mill .0069 from the head for each cc reduction.
Click to expand...
By your figuring, .060 would be around 9cc's..Whats that, a full point?
what are they, 58cc? so 49cc, 120psi turns into about 150psi?
 
MOPAROFFICIAL said:
By your figuring, .060 would be around 9cc's..Whats that, a full point?
what are they, 58cc? so 49cc, 120psi turns into about 150psi?
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Then advance the cam to 100 and it goes to 180. lol
 
well maybe its 170..maybe its 300, im not doing the math. I said .060 because it would fix the lack of adequate compression and still use the push rods.
Advance it, idgas. lol
 
Slantsix64 said:
Hey guys, so i finally know how to degree a camshaft my question now is, my buddys slant 225 has a 268 duration clifford camshaft headers 4 barrel all that nice stuff. but he is only cranking out 120PSI at each cylinder evenly so im guess his compression ratio is around 7:8- 8:1. Motor is over cammd not much low end but decent top end but i was telling him what if we advance that same camshaft 4 degrees what would the cylinder pressure rise to? Slants need more torque. My question is if we advanced his camshaft 4 degrees would he be able to build at least some decent pressure or should we just start milling that head
Click to expand...
no. Most slant six cams are around 104-106 ...so 4° isn't really going to do **** and even if you took it to 100, what's 6° ? so maybe you've gained 20psi, maybe you'd only gained 10 psi...still soggy.
figure it out.
 
Yeah i was wondering cause i heard people advancing and retard camshafts By 4 degrees adding from 10PSI-15PSI or losing as well if they retard when taking before and after Comp tests
 
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Slantsix64 said:
Yeah i was wondering cause i heard people advancing and retard camshafts By 4 degrees adding from 10PSI-15PSI or losing as well if they retard when taking before and after Comp tests
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Wallace Racing has a nice selection of online tools.
I have used online calculators that give a dynamic cranking cylinder pressure dependent upon intake centerline.
 
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The Desktop dyno has a BMEP pressure reading. (Brake Mean Effective Pressure)
Although generated by the program, there are compression increases when you advance the cam.
 
toolmanmike said:
The Desktop dyno has a BMEP pressure reading. (Brake Mean Effective Pressure)
Although generated by the program, there are compression increases when you advance the cam.
Click to expand...

Yes and it CAN BE more accurate than most think. You know the old saying garbage in garbage out? It works the other way too. lol
 
Slantsix64 said:
Yeah i was wondering cause i heard people advancing and retard camshafts By 4 degrees adding from 10PSI-15PSI or losing as well if they retard when taking before and after Comp tests
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Based on your train of thought, you already expect about 10psi increase... so the current stated 120psi goes to 130-135psi. The other guy said the 150psi from milling the head around .060 would be too low still...That is just an opinion, mine ran 155psi. I had the .460 solid, 6 into 1 , 350 holley and iron 2 barrel, blended vj 177 /[email protected]
So what are you going to do?
pull the front off and mess with that pita front pan seal and possibly have a leak... or 9 nuts & collector , fuel line and hang it to the side, alt bracket, 2 hoses, 6 plug wires. all easy...hardest part is on your back from bending forward and picking up the 85lb head arms stretched out.lol Use a hoist, work smart!
 
There's more to it than advancing a cam to just get some more cranking compression.
You'll also run the risk of making the cam work outside of it rpm-range even more, turning the engine into a turd even more.
 
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