I've pretty much decided on doing a custom build up for my '03 GS300which has an SRT intake. Ultimate goal is added horsepower without losing any more torque. I only want a subtle, refined sound improvement; leaning towards Magnaflow cans. Don't plan to do headers anytime soon. Have read hundreds of posts but need help......

1. What diameter is stock piping on my model now?
2. Will 2.25 or 2.5 piping perform better for my goals?
3. Other than increased sound, is there any reason not to reuse resonators?
4. Would combining a Megan B pipe with a custom Y pipe provide any enhanced performance? What else would work well infront of the Y pipe?

Thanks.

 

Not to rain on your parade or anything, but IMO it's not worth trying to make NA power out of a 2JZ. You can build the best exhaust and put in an aftermarket header and still, you're only going to gain around 20-25hp(with a tune on a piggyback). If you're really adamant on making NA power then you will need to upgrade to the 264(can use stock valvetrain) or 272(requires new valvetrain upgrade) Brian Crower camshafts, and then upgrade the ECU to a standalone so you can run a more aggressive tune and increase the rev limit to around 7500rpm or so. So basically, you can spend around $4k in parts and custom tune on the standalone. This will put you at around 250rwhp, stock HP is around 180rwhp or so. Now the question, is it worth $4000 to increase 70hp? Or would you rather spend that same money, turbo the car, and make 350-400rwhp?

 

I appreciate the "big picture" but I'm not looking for huge gains as I don't care to spend that kind of money. I would like to go ahead with exhaust system so if anyone can help with my questions, greatly appreciated.

 

Ok in that case.
1. Stock header has two 1.75" outlets. Then theres a mid-pipe(or what you referred to as a B-pipe) for the two outlets, and that ends with a 2.5" outlet.
2. Keep piping diameter at 2.5"
3. Resonators just to decrease sound, you can leave in if you want to be quieter or remove to be louder.
4. Adding in the Megan b-pipe will allow extra exhaust flow because you get rid of the rear cat. Also, the Megan b-pipe is more free flowing than the stock one.

Here's the numbers for you if you're wondering about the real performance gain. Axle back muffler upgrade will net around 2-3hp increase. If you build a full header back exhaust, expect to gain around 5-10hp depending on design. I consider it purely a cosmetic and sound upgrade because honestly you would be hard pressed to feel the 10hp difference. If you want something that will make more of a difference, consider upgrading the header, getting an FIC, and get the car tuned. If you do that plus the full exhaust, then you will gain a healthy 25-30hp or so. That's will be a difference that you will be able to feel.

 

I think JeffTsai was really trying to address your most explicit need to add horsepower. Believe me, when you say "I want to make power" he knows his stuff

Basically, buy an exhaust for the sound and/or look. You are not going to pick up anything more than a couple of ponies if you're lucky.

 

Thanks guys...I appreciate your openness and direct suggestions. What is an FIC and what headers would be appropriate upgrade if I chose to do? I'm only familiar with OBX and Mazzuri for the GS300.

 

FIC = Fuel Intake Controller, something like a APEX NEO, fuel rising rate regulator, external fuel pump within the fuel line, I'll let one of the HP ballers respond regarding tghat part.

I have to mention to you, which is along the line that JeffTsai is headed, if you want HP gains for the money you're better off going boosted instead of fooling along with your exhaust. I don't know any tuners in TN but there are a few folks down the road in ATL that can HOOK YOU UP with a baby turbo (5-7boost) and give you the HP gains you're looking for, less money than you'll spend the route you're taking.

 

I haven't heard of a "baby" turbo boost so what does that involve? How costly is it as I figured a custom catback exhaust to be around $500-$600 installed max?

 

What we're all trying to get at is...do you want to make the car fast or not. Fast does not equal 20-30hp gain. I'm talking at least 100-200hp over stock. So the question is do you want fast or just "a hair quicker than stock"? You can spend hundreds or thousands of dollars to try to make more power, but without going with a turbo of some sort...you will never be fast. You could build a baby turbo or budget setup for around $2000-2500 range(depending on parts chosen). That will put you at around 300-320hp range, which is roughly 100hp+ more than stock. I see that you have an SRT intake already, and planning to build a $500-600 exhaust. That puts you at nearly half of what it would cost to piece together a budget turbo setup. This is assuming that you're mechanically adept, if not then expect to pay a shop around $1000-1500 or so to install the parts and tune the car.

If you have no desire to go turbo, then the best you can expect is a car that has more exhaust sound and is just a hair quicker than stock. Don't go chasing after expensive exhaust, intakes, and other NA bolt on parts if you're trying to make the car fast...it's not going to happen. Not trying to put you down, just giving you the facts straight so you can decide what you want for yourself.

 

OK...my parade has been rained on enough. I'm not interested in a $2500 investment as I would trade before doing that. So,I'll pass on the turbo route.

Are there any others out there who've done custom exhausts coupled with SRT that have seen a nice mild....not significant...improvement.

 

I hope you don't feel like your parade was rained on, the folks here are just trying to set some realistic expectations for you before you spend a lot of cash going nowhere. With that said, here are a couple of exhaust recommendations.

Slight increase in cabin noise and slight increase:

Borla
RMM (I have one I would part with, see the classifieds)
L-Tuned (Infamous1 probably has one for sale, see classifieds)
HKS

Larger increase in cabin noise (fairly loud) with mild HP increase:

Tanabe MT
Pretty much everything else

This list is not complete by any means but you get the idea.

 

The Tanabe MT and their discontinued Hyper are really quiet. I would liken it to the Borla system.

 

Jeff I would love to turbo my GS3 too but I live in CA. It's impossible to pass the smog check.

 

Why is it so hard to give some info instead of all the money exhaust talks, it's pointless this and that, etc.. I think I know what you are asking for though. I've recently upgraded my exhaust pipes to 2.25" all over, removed all resonators, kept the stock mufflers, kept the cats on (there's only 2 cats right?), "h" pipe setup, and after driving over 100 miles in a few days, the CEL comes on. I'm thinking it's the "h" pipe setup that's driving the CEL. I will have the muffler shop add an "x" pipe instead and hopefully after I reset the ecu it'll take away the CEL. Watch out for droning as that's what I'm experiencing right now. I may have to throw in some high flow resonators to eliminate this problem. Also, can someone verify if there's 3 cat's or just 2 on these vvti 1uz's? Another thing is maybe the CEL is on due to the fact I remove the 3rd cat, which I thought looked like a resonator.