Feelin' frisky, I thought I would re-dyno at 5° cam advance today.

It did lower the rpm where the torque peak was, ~3500, as I expected, but the peak was slimmer and the peak was almost 20ft lbs less than at 3°, horspower too! The 5° torque plateau was only 500+rpm wide, versus 1000+rpm at 3°. TQ, then HP dropped like a rock after 4500rpm.

I could have sworn that it felt more aggressive. But I guess it was just louder. Reset to 3°, it idles better, and accellerates more smoothly.

Anway...

Without benefit of dyno testing, I'm extrapolating that effective retard will be also be limited to 3°, but might just put my little 4.5 over the 200WHP (240 crank) mark. (190/222 at 3° advance, 195/217 at 0°, 200/212 at 3° retard?)

Should I even bother thinking about a 6° variable cam system, for 10WHP?

 

On further reflection, I should have realized before that there is only 5 or 6° of movement, regardless of possible HP, given the length of the belt.

...

Side note: my dyno results to date suggest a 200RPM displacement in TQ and HP for +-1° of cam movement. IE. with 3° advance, the start of useable torque/hp and the peaks are 600RPM lower.

 

Wow! At 5 degree advance 20ft lbs reduced TQ means the 4.5L is extramly sensitive to cam changes. I just wish someone made a good cam grind for the 4.5L. Are you running the Euro throttle body?

 

What do these numbers represent?

They look like duration numbers to me, and if that's the case then they're incorrect. A cam's duration will remain the same regardless of it's timing in relation to the crankshaft. However, by altering the timing by advancing and retarding the cam, what you are doing is changing the position where the lobe events occur, and duration remains as before.

You can get the Euro cam for your car.

 

Lagavulin, those are RWHP/RWTQ numbers.

 

Doh! Thanks Jon...

Ok, those numbers show the engine responding exactly as it should.

Advancing the cam lowers peak hp but beefs up torque because of the earlier closing intake valve. This creates less intake reversion and creates more cylinder pressure, but has less time to fill the cylinder at higher RPM.

Likewise, retarding the cam delays intake closing which hurts torque (..more intake reversion and less cylinder pressure), but improves peak hp since the intake valve is held opened later on the compression stroke which improves high speed breathing.

Thanks for sharing the results!

 

200/212 at 3° retard?

Just to clarify, the retard figure is a guess, to really answer my question I have to drop some coin and keep dynoing.

These are the tested values for my car:
~170/~200 at 5° advance, 190/222 at 3° advance, 195/217 at 0°

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toofast928,

The cam lift on the L-Jet cars is the worst, so I would assume that there isn't much room 'in the zone'.

No Euro TB for me. I don't know if the larger TB would help, perhaps when retarded?

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Lagavulin,

It would make more sense to use a variable cam movement with a Euro grind; better numbers to play with, or at least a US 78-79 cam.

 

Porken, can you imagion the bigger throtal body hurting?

Do the conversion, keep you old suff, and if it doesn't help, maybe I'll buy it off you for a discounted price.