I don't think you'll learn anything by blowing through a 3" pipe.....however, my situation is a bit different, but similar. My streetported motor is 'missing' around 70-80 hp, and we've been trying to 'find it' and one of the things I've checked is my hi-flow cat (an ATR). I took it off and visually inspected it (it has less than 1,000 miles on it), and it looked clean. To check the flow through it, I used an air flow meter that I had laying around from my Porsche 911 days- it read air flow through the 3bbl Weber downdrafts so that you could synchronize the dual carbs. To check the cat, I first checked the flow rate through a 3" PVC pipe by using a smaller vacuum at one end, and the flow meter at the other, and noted the readings. I then setup the cat in the same way, and checked the flow, and they were the same. Conclusion? No clogged cat, and 70-80 hp still missing.....

 

Nice. Are those flow meters expensive (as if I have to ask)?

I wonder now if a shop vac hooked up as a blower and a pressure gauge might do it. If you read the pressure between the shopvac and the exhaust inlet, the higher pressure would indicate the more restrictive part. If the shopvac is big enough, I imagine it would make for very good comparisons.

Dave

 

here is something I've found out after driving for awhile. VERY VERY WEIRD!

When I accelerate the boost comes on 0.9kg as I re-adjusted, but after that the primary stops working.

For example: Say that I accelerate from 4th all theway to the 7,000rpm and then shifts to the 5th. At 5th, I'd let go the acceleration and let it cruise going about 80mph. Then steps on the gas pedal to speed up alittle.
At this point, primary should come on and have a boost, but what I would get is 0.0kgs. The boost would not build up at all even if I keep on pressing and releasing the pedal and so on. Theres change in exhaust tone also. Its deeper than usual. If I down shift and let the secondary to come on, then the boost would build up the boost to 0.9kgs no problem. This problem goes away afer 30sec to 3min, it just has it's own mood.

1) 4th with 7,000rpm shift up to 5th and I'd loose the primary boost, but when its above 4500rpm, the boost does build up.
2) When that happens, the exhaust note gets deeper. When the boost starts to build on the primary the exhaust note changes back.
3) Problem goes away after but almost everytime I let the secondary to come online, the primary goes out and it wont come back for awhile
4) I let the car idle when the primary stoped working. The exhaust tone at idle was deeper than usual.

Now, isn't that wierd? Is this the common symptom of clogged cat? I'm sorry about my crappy explanation, but hey! I was raised in Japan!

 

I'd take a look at your check valves, sounds like it could be an issue with one of them.

 

This never happened untill the exhaust setup was changed...but symptom does sound like its one of the check vaulves since the reading on my boost guage is 0-0-0.9kgs...

 

ok just to end this thread here is the update. I gutted out the Bonez HF Cat and I'm now using it as a mid-pipe. Boost problem is solved. The cat was clogged eventhough it was "really clean". Now the cat is gutted, theres big increase in response and high range power and lost somewhat of low torque. Overall I'm happy with it

 

got pics of the exhaust?

i never seen good clear pics of this exhaust on an FD