I am trying to match up the size of my header, cat delete test pipe, and cat back that i would like to purchase. I am finding it hard to piece these together. I was looking to have everything be 2.5" in diameter. I am going to purchase the Yonaka catback.

 

I know that everyone has their own ideas, and I'm not here to change your mind, just consider a few things.

1 - Removing the cat with a straight pipe will make the car smell terribly and will not gain you any horsepower. You are more likely to have issues with the computer. I would simply suggest a high flow cat, you can get them for under $100 on ebay. Just a thought

2 - I wouldn't get too caught up with it being 2.5 exhaust for similar reasons. You will gain little to no horsepower, as that exhaust diameter is enough to flow a 400 horsepower car. So, getting a bigger diameter isn't doing anything but adding weight to our cars. I can understand wanting a certain sound out of your car, in which I would focus on the muffler for the sounds, not the pipe size.

Now, if you tell me that you are running at the track, need every ounce of power, and have a turbo or other things not mentioned, then I understand more what you are doing. But if you are like most of us here, this is a stock car and the exhaust is not a big gain in horsepower, no matter what you do. IF anyone wants to argue that, show me a dyno sheet with the improvements, because otherwise it's all subjective. I've dynoed a lot of things, and that's where I am coming from, I've seen many sad faces from stock cars with exhaust and being stunned they got maybe 1 horsepower.

Other than that, good luck with your build, it's still good to see a car getting some love.

 

I agree with your premise but your info may be for a dual exhaust setup. dual 2.5" on a RWD V8 or similar would be good for 400-500hp.

OP: a full length 2" (non-crush bent) system is not going to be your bottle neck for power (unless as stated- turbo). and you're probably bending stock rods before you need more than 2.5".

 

We can discuss exhaust flow extensively, my point is it's not going to provide any benefit (agreeing with above). If anything, you creating a smelly car, putting more damaging exhaust into the air, probably over scavaging your engine with an overbig exhaust,it's more weight, and it's probably not going as well as you think. Finally, that's money you could use for something else more productive or valuable.

I love gearheads, I love tinkering with a car, but I feel that as someone on the board, if it seems like it's not going to be of a benefit, I should say something. I'm not going to insult the person, just state what I think.

At the same time, I would want someone to tell me if I was doing something I thought was beneficial or not, at least as kindly as possible. And, I also don't know what else is going on. For all I know, you are bulding a racecar, it is a 300+ horsepower car, and you need everything you can because of the regulations of the race you've entered into. Then, ok I get it.

 

I just wanted a new exhaust....why has it become a discussion about forced induction applications and saving the planet...can we please keep this on topic?

 

I think what they are saying in the nicest terms possible is that we are all tired of the 90hp **** boxes with fart cannons abusing our ears and stinking up the joint when you can make all the power the F22 is capable of with quiet and smallish diameter exhaust and a catalytic converter.

I love performance cars and modifications but I also demand that my projects remain quiet and don't stink like unburnt fuel. Plus you can rip around and not draw attention when you are stealthy. 100% worth the 1-2hp lost to not being annoying.

 

Ran 2.5" header collector and 2.5" exhaust all the way to the exhaust tip on my 96 F22B2 no cat. It helped gain throttle response and I loved the sound. This was in conjunction with a proper intake manifold and throttle body setup. More air in requires more air out. There was no exhaust gas velocity stall/tumble adding 0.25" diameter. Have to remember that the stock F22B1 Accord (EX/EX-R) exhaust is already 2.25" from the cat back. so going to 2.5" is not going to be a big deal. If your exhaust is too loud, add a resonator and if it smells of raw fuel, you will require tuning or it could be as simple as doing an ignition tuneup. When tuned properly it won't smell of raw fuel, maybe a NOX smell if you are running a premium fuel. As far as the smell, IMO it smells great! That is a personal opinion of course....

As far as measuring and matching, what size is your header collector at the moment? 2.25" or 2"? If that is the case you can probably purchase a 2.25" to 2.5" test pipe, or have one made at a local muffler shop. If your header collector is 2.5" that makes everything easy. First things first you need to measure what you have on the car now.

Header collector Dia =
Converter inlet Dia = (should be the same size as your collector now)
Converter exit Dia =
Converter length from flange to flange =