Have a customer with a Quad Whipple that keeps popping or backfiring through one compressor, never the other.

Primarily if the throttle is held in one position or on a reduction of power.

What could be the cause?

Its an EFI set up. Driving him crazy, which is now doing the same to me as my engine never did this and i am not much help!!

is it at around 3500 rpm if it is i heard it could be the fuel damper that on the fuel rail

It seems to be almost anywhere. If you keep increasing throttle it sounds and runs fine. When you stop or bring it back to idle, POOF!!! It blows through the starboard compressor.

Im a 2 stroke person, but dont 4 strokes backfire from a lean condition when you lift?

i had the same problem the boat only ran good at full speed but at low and mid range rpm it pops call whipple and see what they say

Tried...no luck so far.

Someone has had to experience this.

Whipple offers a by pass valve, does your system have one ?

The symptoms you describe is what the by pass is designed to correct.

There are bypass valves on both sides of the superchargers. We tested the diaphrams and the operation, all appears normal.

They rigged it into a different boat, but the componenets are all the same.

Its on a stand and still doing it.

The Whipple was resealed, rotors never were removed, just the intercoooler to manifold resealed. No leaks as they dont see much movement on a vac gauge and sprayed starting fluid around the intake seal to check for leaks...nothing.

Try to send Dustin a PM , he is always on OSO some where I'm sure he would be glad to help . Just my 02

The guy has been on the phone with Dustin and we sent him email. I'm sure hes busy and we understand.

This cannot be the first time this issue has happened. It only backfires (for a lack of a better term) out of one compressor. If it were common in the manifold it would do it from both compressors right?

What would cause one to respond or act different from the other?

Engine has been thouroughly checked with compression test and leak down - all is well.