BruceH
BBB Big Bore Boss 322
First off there are a number of online calculators for this. However, I'm looking for experienced input on the subject. I did some data logging with my current combo and it's peaking at around 41-42 pounds of airflow. I'm getting the airflow from the maf signal so it's dependent on the accuracy of the other tune parameters (maf xfer and injector data mostly) and how accurate the wideband reporting is. Basically it's a measured ballpark estimate.
Here's the background: I have a 322 cubic inch 3 valve motor. Bore and stroke are 3.701 x 3.750. The heads are rated to flow 280 cfm at .600" lift and 273 cfm at .500 lift for the intake runners. The cams have an intake lift of .535". Intake manifold is stock 4.6 3v and throttle body is stock 55mm that should flow 875 cfm if I have the correct info. The air intake is a Bullitt 87mm that should flow 1390 cfm if I've done the calculation correctly.
In the past the peak airflow numbers were consistent with what I'm seeing now when using the stock intake manifold. The only differences are that I have cmcv, stock tb, and slightly smaller cai housing (87mm vs 95mm previously) now. Also in the past the motor was able to move more air in the higher rpm range with a FRPP intake manifold. Peak numbers increased from around 5000 rpm to the redline of 7200, they increased about 3-4 pounds per minute with the FRPP intake.
It is my belief that the stock intake manifold is holding back airflow during higher rpms. I'm reluctant to go with a FRPP intake due to the loss of low end power I've experienced in the past.
I'm wondering if different cams could mitigate some of the airflow reduction? Specifically what I'm looking at is a lower lift cam with more duration. Something like Comp Thumpers. For reference my current cams have .535/.550 lifts and .050" durations of .229/.236.
Does it sound reasonable that a lower lift cam with more duration would provide more airflow at higher rpms? I don't think that the higher lift of these cams makes much of a difference for what I'm doing. The current cams are locked out at 108 icl and have an lsa of 113.
I could also go with Comp 127500 and 10 degree limiters. They have an icl of 102 and lsa of 112, lifts are the same as what I have now. I would be able to retard them in the tune for more airflow at higher rpms while gaining a little bottom end with the 102 icl.
I'm also contemplating have Comp grind me something. I'd probably go
with around a .500 lift, 111 lsa, and durations of .235 and .245 @ .050".
So, I know that we have some experienced engine guys on here, what do you think I'd gain with Comp thumpers that have durations of .236 and .254 with a 98 icl and 109 lsa? Anything or maybe even a loss? How about a custom grind? From what I understand they are about the same price as off the shelf cams. Has anyone contemplated or gone through with a similar idea?
Thanks,
Bruce
Here's the background: I have a 322 cubic inch 3 valve motor. Bore and stroke are 3.701 x 3.750. The heads are rated to flow 280 cfm at .600" lift and 273 cfm at .500 lift for the intake runners. The cams have an intake lift of .535". Intake manifold is stock 4.6 3v and throttle body is stock 55mm that should flow 875 cfm if I have the correct info. The air intake is a Bullitt 87mm that should flow 1390 cfm if I've done the calculation correctly.
In the past the peak airflow numbers were consistent with what I'm seeing now when using the stock intake manifold. The only differences are that I have cmcv, stock tb, and slightly smaller cai housing (87mm vs 95mm previously) now. Also in the past the motor was able to move more air in the higher rpm range with a FRPP intake manifold. Peak numbers increased from around 5000 rpm to the redline of 7200, they increased about 3-4 pounds per minute with the FRPP intake.
It is my belief that the stock intake manifold is holding back airflow during higher rpms. I'm reluctant to go with a FRPP intake due to the loss of low end power I've experienced in the past.
I'm wondering if different cams could mitigate some of the airflow reduction? Specifically what I'm looking at is a lower lift cam with more duration. Something like Comp Thumpers. For reference my current cams have .535/.550 lifts and .050" durations of .229/.236.
Does it sound reasonable that a lower lift cam with more duration would provide more airflow at higher rpms? I don't think that the higher lift of these cams makes much of a difference for what I'm doing. The current cams are locked out at 108 icl and have an lsa of 113.
I could also go with Comp 127500 and 10 degree limiters. They have an icl of 102 and lsa of 112, lifts are the same as what I have now. I would be able to retard them in the tune for more airflow at higher rpms while gaining a little bottom end with the 102 icl.
I'm also contemplating have Comp grind me something. I'd probably go
with around a .500 lift, 111 lsa, and durations of .235 and .245 @ .050".
So, I know that we have some experienced engine guys on here, what do you think I'd gain with Comp thumpers that have durations of .236 and .254 with a 98 icl and 109 lsa? Anything or maybe even a loss? How about a custom grind? From what I understand they are about the same price as off the shelf cams. Has anyone contemplated or gone through with a similar idea?
Thanks,
Bruce
