Can someone tell me if apexi gt spec from a turbo 2 will be good on a s4 N/a that has stock ports and pacesetter headers?

 

NOPE! Piping is way too large for an NA, best bet is 2.5in piping or MAX 3in.

 

Is it a 3" inlet? If so, it won't work since the header probably has a 2.5" in outlet. If they do match up, then go for it. As long as the catback is large enough in diameter (this one definitely is) then they have very little effect on power.

 

OO ight I guess I wouldnt buy it then. I wish it was 2.5 tho, cause the **** is right around the corner from me guy is sellling it for 200 I think

 

This thread has the potential to blow up into a 7-8 page argument that'll go way off topic. I suggest you do an advanced search for exhaust and specify RotaryGod in the username field. You'll find some good info but you'll also see what I mean.

Basically you can go with a 3" catback like Sideways7 said and you'll get the least amount of backpressure and maximum power high in the powerband BUT you'd be better off with a 2.5". The reason being exhaust velocity. The best way I've heard it decribed is imagine 2 pipes, a 2.5" one and a 3" one. The 2.5" pipe flows 250cfm and the 3" pipe flows 300cfm. Let's say your engine flows 250cfm at redline. At redline both pipes are large enough to not cause a restriction. (Imagine what a 2" pipe that flows 200cfm would do; cause backpressure and hurt power.) But in the lower rpm's, your engine isn't moving as much air. The 2.5" being smaller causes the exhaust gases to move faster than they would in the 3" pipe. This exhaust velocity helps make power in the lower rpm's. Then as you approach redline, the 2.5" and 3" basically become the same. So you want to go big enough without going too big and the word on the street is that 2.5" is the optimal size for a stock port n/a.

Of course the numbers I used are arbitrary and I probably used some terminology wrong as well but you get the idea.

 

Generally speaking, most of the exhaust gas velocity decided before the catbacks, though (in this case, in the header.) I realize this isn't entirely true, but for simplicities sake it will work about the same.
If it really is a 3" inlet, then it really is too big since the rest of the exhaust system would be too big to accommodate it. Stick to a simple 2.5" inlet catback.

 

So say I do some modifications to this 3inch exhaust so that it can hook up to my stock cat will that be good or will it still be to big? Thanks for the help also

 

i would go go with a custom 2.5" --> 2 canisters of your choice. stock cat and header. you need backpressure. im running 2.5" behind the cat with 2 mazdaspeed canisters. it sounds clean and has no negative effect on power or aux ports.

 

^ sounds good. Might just stick with simple 2.5 but I want single out the pass side. thanks for help everyone.l

 

i was wondering about something. do you get better gas mileage with a smaller exhaust? and would emissions be better on a smaller exhaust or would it be better on a bigger exhaust? i was lookin at the electronic valves for the exhaust. i had in mind to put one in for SOUND-GAS-EMISSIONS purposes. but dont know what the ill-effects are. what if i went with a 3" also... i think i know which exhaust he's talking about.. i was actually wanting to get it too but i was mostly getting bad feed back so didnt go through with it. anyways, with that valve installed, would it make it "okay" to run the bigger 3" exhaust?

 

man, im telling you from experience. i have an apexi gt with a bonez straight (ALL previous owner, what a ricer -_-) on an N/A, its loud as F&$K. TOTALLY useless on an N/A. if you are going with an open exhaust, run RB true duels. BEST way to go. they sound good, have great flow, not too restricted not too big. although expensive, best way to go hands down. hell, its a great exhaust on any 7 IMO.

peace

 

Nor does a full racing beat system, header back. Looks better, sounds better, and performs better. I wouldn't do custom anything unless you need special bends or piping diameter.

Buy whatever exhaust you want to. If the GT is cheap, buy it and use it. If you don't like it, sell it. I think the GT is overkill for the n/a but it's not my car.


There is no such thing as Mazdaspeed "canisters." They never made them, never will.

 

Yea Im just wait till I find someone selling a nice pass side exit catback. Thats right for the N/a Thanks.

 

 

RB is great, but it is $600 for just the Y pipe and mufflers. You can get custom piping done by a muffler shop for less then $100 and you can then add on the muffler(s) of your choice for however much you want to spend and the style you want.

 

Doesn't the GT Spec have a 65mm inlet for a connection to a stock cat?

I may be wrong however?

 

As of the systems Iv seen, start at 2.5" to fit up to the stock cats.

 

yes, my GT has the same ID as my midpipe, so i would imagine its 2.5

 

Well, the OP said that it was a 3" turbo catback, and I took this to mean that it had a 3" inlet made for a 3" turbo-back exhaust. He never did clarify if that was the case, though. If it it indeed the standard 2.5" inlet, then he should go for it since thats a pretty good deal on the GT.

 

The Catback is welded on to high flow cat that is 3in inlet. also

 

Ah, ok, that changes everything. I personally would never mess with a system that has a cat welded onto it because what happens when you have to replace the cat? You have to cut it and either re-weld the new cat on, or put on a flange. Too much trouble IMO.

 

You are correct. I purchased an Apexi GT Spec exhaust system new and installed it on my 87.5 Sport (overkill) and it indeed bolted up to the stock cat. There was a noticeable decrease in low-end torque, with functioning 5th and 6th ports, but the increase in high-end pulling power was equally noticeable.

Regardless, the GT is the sexiest, best sounding exhaust on the market if you ask me. I plan to purchase one for my T2 in the near future.

 

That's good to know. I was going to get the N1 for my 87 sport, but rx7.com currently has the gt spec on sale for the same price, and I was going to pick it up if they still had it. I was also going to run a racing beat header and presilencer.

 

I have the RB header/presilencer with an Apex N1 and it sounds great, though it can get a bit annoying on long trips.
One thing to consider is that you will hear a slightly different sound with it being on the drivers side as opposed to the pass side, especially with the windows down.
http://videos.streetfire.net/video/6...58001f0db8.htm

 

Well I know it's really the drivers preference, but what would you recommend, the n1 or the gt spec? I would like a passenger side exit, but the gt spec was on sale for the same price, so I was interested in it.

Would like to add this is for a daily driver sport. Would have the rb header and presilencer also.