the chain gets pretty lose and starts a floppin way before 100k! add that stretch slop to your retard factor and it can be significant. what about that though, did trucks ever really get the retarded crank timing sprocket?
This is a simulation that I ran for someone a while ago. It is a 400+0.030 with 9.1;1 CR, 650CFM carb, dual plane, headers, and an XE256 cam.
Torque = 456 ft-lbs@2000 RPM, 456 t-lbs@2500 RPM, 449 ft-lbs@3000 RPM. HP - 317@4500 RPM.
If I retard the cam 4 degrees, I get:
Torque = 453 ft-lbs@2000 RPM, 450 ft-lbs@2500 RPM, 443 ft-lbs@3000 RPM, HP = 327.
I can't simulate fuel mileage, but I would expect the 'straight up' timing will produce the best mileage.
can you run that sim at +4? i wouldn't be surprised at all if +4 did better on the mileage, unless of course if the loud pedal was stuck to the floor the whole time the engine was running! the -4 position shows the torque dropping off. more torque, less pressure on the gas pedal.
If I run it at +4, I get:
Torque = 457@2000 RPM, 456@2500 RPM, and 448@3000 RPM. HP = 306@4000 RPM.
You might pick up some gas mileage at +4, but watch out for the Dynamic Compression Ratio. The intake valve will close 4 degreees earlier and increase the compression. You could need a higher Octane fuel.
looks like that one is optimised near "0", maybe it's the 9:1 factor that is negating any improvement at +4. is that with the EGR running? that'd keep mr knock knock down. for Gary in the next post, with stock squeeze the advance might show more improvement?
Danlee, based on what you're getting from you desk top dyno then in my situation, 400ci, =.030 bore, stock compression, edelbrock 3171 manifold, 600 Holley, DEH255 cam and headers, I would be best off to run the +4 on the cam as dynamic compression wouldn't be as much of a factor.
years ago i had a 79 bronco 351m and the timing was indeed retarded . i had the engine rebuilt , bored 30 over , with a good valve job and used all eldebrock performer parts in it , double timing chain and gears with the 3 key ways , i installed it at 0 or straight up . 4 barrell intake and 600 4 bbl carb , and cheapo headers , it would really run after that , night and day difference
I just finished degreeing my new cam. It's an Edelbrock 255DEH and I used an Edelbrock double roller timing setup. I installed the cam at the +4 mark on the crank sprocket when I put it together. Upon degreeing it today the cam is in fact now at a 0 degree valve timing. I guess that means that in fact my 400 was retarded 4 degrees.
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