PSI 14-71 Boost Fluctuation

Have a 572 BBC with a 14-71 PSI HH. Boost runs fairly flat until I hit a certain rpm of 7660 rpm then it will begin to fluctuate close to 1.5 psi in each direction. Currentley making 27 psi of boost. It is real consistent at that rpm to fluctuate. Any advice or something I should not be concerned with.

Thanks

 

On current set up we are running 22% . When we ran 35% problem still existed. It is at the exact same rpm each time.

 

Possibly due to the ram air effect going down the track? ie, not mechanical but due to how the air is being crammed into the hat? is the boost increasing along with rpm/mph downtrack?

 

Whats your rpm limiter set at and are you sure that you arent losing a cylinder or spark varition? That will your boost slightly.

 

Bob69

Hi side is set at 8400. Phasing is right. Running a grid and all the logging on Grid looks good.

OJH

Boost increases at expected times at the hit and then shift point theres a slight fluctuation. Overall it is steady. Even before my shift at 7660 I can see boost moving around then when in Hi gear it is real noticeable

 

Yes, when I made my comment I was thinking only of highgear, after posting I realized and tried to delete the post.

 

Just a dumb question....
Have you tried a different sensor?

 

In my limited experience most blowers move air relative to eng rpm. When the blower gets to a rpm point were its efficiency falls off the boost will drop-usually, but not normally in a wave pattern.
When you have a weak spark (bad lead that breaks down at high RPM in high gear) your rpm line sometimes gets a bit jaggarded. Yours appears ok.
What is your seat spring pressure?
Do you run shaft rockers?
What wall thickness pushrods?

Sometimes you have to ask lots of dumb questions that may turn something up.

 

What boost did it make at 35 over?
I have seen that "wobble" in graph before. what square inch blade opening are you running?
When we increased the size of the blades it went away on our deal.
Also check that the back of the injector is lined up with the opening in the blower. the front is not nearly as important as the back is when it comes to lining up.