I installed the stillen HFC onto my car... the exit on the hfc's are like 2.5" and the bassani x pipe inlet is 2.25"... this 1/4 " step I believe disrupts a smooth flow, as the exhaust flow will hits the flange. The power band doesn't feel smooth as before and I think I may have lost power. It seems to studder in acceleration at WOT. It also sounds louder than I'd like.

if this was a cat with a 2.5" exit and the exhaust was a 2.75" it would be fine, the air doesn't hit a wall that will obstruct smooth flow.

the question is. Does anyone have cats with larger openings than their exhaust mid pipes... port match the exhaust to reduce the exhaust disruption?

I'm thinking of gringing the inside of the flange from a straight edge to an angled one, to smoothen the transition and I'd hope doing so will make the exhaust sound better and smoother (less drone)

 

Just round the edges on the Bassani to smooth the transition from 2.5-2.25

 

Does anyone think it will work?

 

Smoothing out the edges seems like an easy fix, but in the end it still is a mismatch of pipe diameters.

This is one of those things you should have thought of before purchasing the cats. I don't know what to tell you.

 

I thought the stillens would have the same outlet as stock. no company ever posts specs.

 

Not a good idea. That will adversely effect the integrity of the weld and overall strength.

 

even if I just round the edges off? | to /

 

leave it alone, many members running 2.5 TP or HFC and 2.25 exhaust system, i never read any problems. If it's really bothers you change ur HFC or exhaust system, i think berk has 2.25? size. I had nismo/2.25 TP, and i'm switchin to 2.5 hfc and 2.5 Y-pipe.

 

i don't know if berks 2.25 on the back sides.

but I want to know if the pipe mismatch negates the gains of installing an HFC.

 

Do you feel gains?

 

Deleted, gsingh350z posted his picture.

 

Berk have a 2.25" inner diameter. I don't know what you mean by "back side", but if you're asking what the inlet/outlet diameters are - they are 2.25".

 

Don't worry.
Even if it does, you will not even feel it.

 

back side i mean outlet.

 

so both outlet and inlet are 2.25".

the stillen is a 2.25 inlet and the outlet is bigger.

 

I am pretty sure both inlet/outlet were the same size. Because if they were not then I would have noticed right off the bat.

 

very little gains in comparison to the Injen Intakes, but the car is a lot louder. The car studders on acceleration on WOT, something to do with the pulse of the exhaust? Stillen HFC's I thought would only make a slight difference in the sound, but it's pretty loud, I avoided test pipes for this reason. I'm a bit dissappointed.

 

I'll try re-aligning the exhaust and cats to be pefectly centered as possible. I'll use my die grinder to slightly round the edges of the bassani flange. I'll report back with information... this could become good research if all goes well.

 

You are grinding the edge of the flange not the weld. Grinding the flange edge will not effect the weld. The sharp edge will cause turbulence and lead to rasp. The smoother the transition the better flow characteristic.

 

There is some rasp now. I think it will go away with grinding the straight edges down to a smooth angle.