I have all the goodies to manage a straight pipe.

I have a MP and wondered if a hollowed out Main cat will sound better (deeper?) and will it positively/negatively impact HP/TQ compared to a MP?

Is it hard to hollow it out?

what techniques are used?

 

It sounds like total ****. Why would you think it would be better then your mid pipe. If you have a mid pipe why would you waste your time reaming the stock cat?

 

I gutted the stock cat, since I couldnt afford a midpipe and it was clogged anyways. It made the stock muffler sound quite deep, but with an aftermarket exhaust I have no idea. im not getting boost creep or spike because the stock cat is 2.5 right?

 

Buy a resonated midpipe from Jason. Sounds good and deep, and it's pretty quiet. The straight pipe was loud as hell and backfiring was also obnoxious!

Alain, coming to the dyno day on 6/6?

 

^^ will the resonated one cut back on backfire?

 

My main cat is gutted and I have an HKS DP. The tone is very subtle and deep at idle. Road noise drowns out exhaust at about 50mph with my all-weather tires.

 

I think i'll make a resonated MP with my curent MP.

 

Do what you can afford. Obviously a hollowed cat on a 2.5 inch pipe will not give you the flow of a true 3 inch mid-pipe. I hollowed one once on a 2nd gen. I cut the whole thing in half right through the catalatic core then cleaned it totally out, then I mig welded it back together. Maybe you should just buy a 2 foot piece of 2.5 inch exhaust pipe and weld it in unless you are worried about a visual emissions inspecction.

I once had a full 3 inch exhaust on my FD (DP, Res MP, Cat back) and it was VERY loud. At idle is was tolerable but at road speeds it was terrible and would drone through out the car going down the highway.

 

i have the MP already.

but the idea of the hollowed out cat sounds appealing since the cops will look underneath the car.

 

I would think a hollowed cat wouldn't flow that well, because of the rectangular dimensions of it. Possible adding backpressure as well. Because you would be going from straight pipe to a chambered section, and the pressure would get backed up on the inside edges when the exhaust tries to exit at certain rpm's creating a lag effect. You would be better off just welding in a straight pipe inside of the cat imo, that would be the best of both worlds.

 

I'm with you on that...I also live in Cali and the thought of cops checking for cats is a nightmare...

I was thinking maybe going the resonated MP way and somehow covering the muffler on the MP with the stock cat shield. Kinda like a MP in disguise...haha, sounds funny, but might just work for visuals.

Edit: Or what he said^^

 

>>>>>esebueno ^^ will the resonated one cut back on backfire?

It did for my car. The backfires were much quieter. And after I installed me pullies disconnecting my airpump, the backfires stopped completely. I didn't do any additional tuning. Maybe someone else can explain this...

>>>>>BATMAN I think i'll make a resonated MP with my curent MP.

I was going to have a resonator/muffler welded inline with my old straight pipe. But the cost of the RX& store res MP was just easier and cheaper.

My 3" SS Straight Pipe: $112
Borla XR muffler: $239+/-
Labor (welding): $35-100

Rx7store: $269

 

esebueno ^^ will the resonated one cut back on backfire?

It did for my car. The backfires were much quieter. And after I installed me pullies disconnecting my airpump, the backfires stopped completely. I didn't do any additional tuning. Maybe someone else can explain this...

BATMAN I think i'll make a resonated MP with my curent MP.

I was going to have a resonator/muffler welded inline with my old straight pipe. But the cost of the RX& store res MP was just easier and cheaper.

My 3" SS Straight Pipe: $112
Borla XR muffler: $239+/-
Labor (welding): $35-100

Rx7store Res. MP: $269

Sold 3" SS MP: -$90

 

I wonder if the hollowed out cat might serve as an expansion chamber, thus increasing in HP from a pseudo negative pressure.

John, the reason why disconnecting the air pump eliminates/ minimize backfires is that u aren't supplying O2 to heated unburnt fuel for a post-combustion event.

 

Ahh, I see....thanks Batman.