Vortec 454 cam timing retard

[sreidmx]

ok I think I have figured out GM's reason for using a cam timing that seems really dumb in a bbc.
From what I've read and how I feel my burb drives there a delay in torque deliver that seems deliberate. I know torque management is part of the reason and have read that gm retarded the cam timing when installing it some 9 deg! Well towing a horse home tonight I was riding passenger and the wife was on the big hill maintaining 55 the rpm in second was around 3300, so the only reason I could imagine them doing this was for those times when fully loaded and maintaining 55mpg and gm not wanting to install a larger camshaft reducing drivability just to keep the torque curve growing at that rpm. Because if they installed it straight up or advanced the torque peak would be falling off which is bad once it has to downshift into second on a hill..

 

[Bent77]

Straight up and turbo!

And a standard tranny, not a 4L80!

 

[sreidmx]

85

 

[Bent77]

Whatever!

 

[sreidmx]

Mayo...

 

[Joe In Montana]

ok I think I have figured out GM's reason for using a cam timing that seems really dumb in a bbc.
From what I've read and how I feel my burb drives there a delay in torque deliver that seems deliberate. I know torque management is part of the reason and have read that gm retarded the cam timing when installing it some 9 deg! Well towing a horse home tonight I was riding passenger and the wife was on the big hill maintaining 55 the rpm in second was around 3300, so the only reason I could imagine them doing this was for those times when fully loaded and maintaining 55mpg and gm not wanting to install a larger camshaft reducing drivability just to keep the torque curve growing at that rpm. Because if they installed it straight up or advanced the torque peak would be falling off which is bad once it has to downshift into second on a hill..

There are so many other things that control your torque and horsepower curve than just a delayed cam. Of course, a cam that's retarded will drop off significant horses and perhaps it might increase the torque in another RPM range.

But you've got injector timing and pulse width, which controls the mixture to keep the Air : Fuel ratio near to13.7:1 for optimum combustion performance. The old adage is that a retarded cam - and all other things being equal - helps with off the line performance and an advanced cam helps high speed performance.

Here's an example concerning the Variable Cam Timing system in the 6.0 GM engines to help you understand

Variable valve timing using a hydraulic cam phaser to retard cam timing for low end torque and advance cam timing for high rpm horsepower
LINK HERE: http://gmpowertrain.com/Libraries/Marine_Engines/Vortec_6_0L_V-8_VVT_L96_Marine.sflb.ashx

Those 6.0s are pretty slick engines and in great demand in dune buggies and offroad racing where I came from. They are very noisy, but efficient.

Anyway - back to your problem......if you take the cam and advance it with after market timing gear/chain set, then you have to refigure the whole performance package because the ECM is going to try to undo what you've done.

There are chips and possible reprogramming options available - but I never had this conversation.

 

[Team208Motorsports]

Sorry but its cam advance for low end and cam retard for top end.

Significant retard at low RPM light load produces better fuel mileage. You are just changing when peak CYL pressure is being made.

What year BBC is it? I'll pull a file and have a look. GM really pulls ignition timing out of these during load. As is they will run them under 20 degrees at times.

 

[sreidmx]

It's a 99

 

[Team208Motorsports]

Yup. It's very low on timing. Just a reflash will wake it up.

 

[sreidmx]

That is what I thought.. kinda lazy feeling..