What size exhaust is best for 250 plus HP forced induction

[RedRez86]

Yes yes there are a few posts about this topic already but I didn’t get what I needed out of the answers so here I am lol. Don’t judge. So I ordered about a year back 2.5 inch down pipe and over pipe from VDS performance and am now after major set backs ready to piece my 86 together. I am going to run a supercharger on her and goal horse power is 300. If I get more then awesome. Question is I’m reading that a 3 inch cat back is what I would need to handle that kind of power yet I’ve seen 2.5 inch systems reach that horsepower or higher. Is their power being restricted? Could they get more with 3 inch? Is it the fact that our exhaust is dual so 2.5 inch is feasible? So reason for these questions is as I stated I already have 2.5 front and over pipe so if I went 3 inch cat back would that cause leak issues and is it even necessary? I think I’ve decided on going Perrin resonated and I think I have a choice of 3 inch or 2.5 with that catback. So I want to have the knowledge under my belt before I make a decision. I also down want obnoxious loud drone sounding car. So help! Lol ��

[Summerwolf]

Our exhaust isnt dual in the way its probably been interpreted by you. Its dual exit but it's a single exhaust. To be "true dual" each bank of two would basically run the length of the car and have their own mufflers.

To reach 300 you're probably able to do that with either exhaust size. 2.5 should be quieter.

It may be easier to hit that particular number with a three inch setup, depends on a lot of variable though. What is your entire setup going to be?

[RedRez86]

Well my setup will be when complete VDS UEL headers, Overpipe and downpipe all 2.5 inch piping (already ordered long ago). Perrin exhaust (2.5 inch resonated or 3 inch depending on which I’ll need) and HKS V3 supercharger.

[BigTuna]

Well if the over pipe and front pipe are already 2.5", doing a 3" catback won't gain you anything.

[weederr33]

Just get a 2.5" catback and call it a day. A 3" catback won't yield you anything spectacular other than noise.

[RedRez86]

Okay then I will be going 2.5 inch cat back if it really isn’t going to hurt my HP gains. I’m also thinking maybe going with Mxp comp rs catback since I can go 2.5 but I don’t want the car to be too loud. What do you guys think? Perrin resonated? Unresonated or Mxp comp rs?

[BigTuna]

If you want quiet, the Perrin 2.5 resonated is great. It's what's on my car, and I like it. Invidia Q300 is also known for being quiet. I don't have any experience with the MXP, but there are a few thread about it if you haven't already seen them.

[Summerwolf]

If you believe you will not be happy if you dont hit 300 and want room to grow get the three inch now. Your biggest bottleneck would then only be the OP and FP. You shouldn't have any leak issues and if you got a tamer exhaust, a lot of people like the deeper tones. All depends on your eventual goals though, there can be clearance issues and weight penalties for the bigger piping. Research everything.

What is the outlet flange size of your header?

Also, consider dezods new offering for a great sound / price.

[RedRez86]

So many things to think about... Well I would be satisfied close to 300 but maybe I might want to take it a little higher? Although I’m not sure I would want to do much more to the car other than full exhaust and supercharger. I don’t want to touch the engine and rebuild it. Maybeee fuel injectors, maybe fuel pump? That’s about as far as I would take it. And I was thinking Mxp comp rs because I like the sound of it I just don’t want it to be too loud. So you recommend go 3 inch.. thing is I have already bought these op and do a year ago and they are 2.5. Headers will also be VDS performance which I believe is also 2.5. This is why I asked you guys who are more knowledgeable on this. I only know so much.

[J1Avs]

Perrin 2.5 inch resonated is definitely quiet and I’m very happy with it. The CSG Spec MXP is also very quiet and I think it’s slightly larger than 2.5 but not as big a 3.0. Don’t quote me on that, but could be a happy medium and worth looking into.

I’m about to run a JRSC on all 2.5in and have no concerns of needing to go 3inch. IMO if you need a 3inch for power, you probably need to be doing some internals work also.

[RedRez86]

Okay I will not be doing any internals at all. Only injectors and fuel pump would be only other things I might do to add some HP. I Definitely don’t want to mess with internals. Well I don’t want it “quiet” I want it to roar and growl just not be stoned out or so loud I can’t hear myself think inside the care and waking neighbors lol. Maybe Perrin 2.5 catless?

[johan]

That power level is easy on the stock exhaust / front pipe. Your choice is irrelevant to the equation. You just need to pick based on style/sound and call it a day. Also, I'd recommend keeping a catted front pipe of some sort.

[JonAvalon]

Perrin resonated would probably be your best bet to keep it quiet but still have a bump in noise. Non-resonated for more noise. If you already have a header then everything else on the exhaust is just going to be your noise level preference. Hitting your power goals is all going to depend on your tuner, pulley/boost and fuel.

[RedRez86]

Alright so that settles it then. I’ll be going VDS UEL headers to 2.5 VDS over and down pipe to 2.5 Perrin resonated catback ��