View Full Version : Stock exhaust and header really that restrictive?

10-28-2010, 08:39 PM
i have an 03 Si, stock a3 motor.

I recently put a jrsc race kit on it, with the hondata reflash. The only other engine mods i have is a comptech air box. anywho, i put the car on the dyno and checked a/f. the afrs were in the mid 12s on the initial hit and trickled down to the mid 11's at redline. prefect IMO for a boosted motor. moderate power and yet reliable ratios.

well the numbers were no where near what i was hoping for. it made 165whp and 148tq... eek! way way less than i was expecting. i have ran it with a boost gauge and it hold 7-8psi all the way to redline, so its not a boost leak... also, power tappers off at 7000rpm instead of peaking at 7500 as whats shown on hondatas site. im thinking the stock exhaust just isnt flowing enough at high rpm, and choking up the motor.

i started doing research which got me here. seems like EVERYONE else seems to make 220ish with the race kits. but they ALL have a header and exhaust. so, is there really a hidden 30-40whp in just a header and exhaust?

another bit of helpful info, the motor is healthy because not too long ago it made 138whp without the SC. which is right on par with all other stock ep3's.

10-28-2010, 08:48 PM
yeah man of course it is. .

10-28-2010, 08:54 PM
most people who go with the race kit also team up with a race header to 2 1/2-3" piping...i've heard the stock axle back exhaust has pretty good flow so i left it for a stock look and sound..I'm positive you'll have the numbers you seek with a race header and aftermarket exhaust...

10-28-2010, 10:39 PM
Its the reflash that is hurting you. Get Kpro and get tuned. Before I got tuned I dynoed 170whp and like 140trq. After the tune: 205whp and 160trq. supporting mods are AEM V2, Megan shorty 4-1 header, OEM cat, and Comptech exhaust. The tuner told me I could make another 15hp if I deleted the cat and ran a raceheader

10-28-2010, 11:16 PM
The ep stock midpipe is sad, its like 1 1/2", its really small. With all that forced air going in, you have to get in out just as fast. And reflashes arent the best way to go.. with my first turbo setup i made 205whp on the hondata rev hard tune and once dyno tuned made somewhere around 260whp.

10-29-2010, 11:10 AM
i knew i was gonna hear alot about go kpro. when i originally bought the kit, i bought it with a kpro, but a friend needed it, so i sold it.

i really cant see tune making a 35whp gain when the air fuel is where it is. i mean, timing is one thing, but their map would have to WAAAAAY off. typically in all of my tuning experience, if timing is off a car in the power range will pick up 4-7whp per 2 degrees. and thats only IF the timing is off. i doubt their flash would be 10 degrees off.

looking at the kmanager tune, it looks like depending on cam angle, timing is anywhere from 19-22 degrees. hondatas upgraded 91oct tune on the stock a3 is 23-24 degrees. soooo, it doesnt look like they pulled out hardly any timing, even with adding boost.

im not arguing that kpro wouldnt make more power, but im saying for the power im looking for and mods i plan on. $1000 for kpro just isnt justifiable to me.

so, the verdict im getting from everyone is; header and exhaust will dramatically help my setup?

10-29-2010, 11:19 AM
The stock exhaust is VERY restrictive, untill you get to the muffler section. That and the fact you do not have Kpro, that is were the decent gains will be found.

First off get Kpro then go with a Krusher header, Car-Sound cat, 2 3/8ths to a 2.5" typeS midpipe, vibrant resonator and stock axle back or OBX loop muffler.

10-29-2010, 11:24 AM
Going from a stock midpipe to Megan Midpipe car really opened up a bit for me.

10-29-2010, 11:34 PM
timing on a boosted car adds an unbelievable amount of power.. one more example, my built boosted setup; hondata tune on 10psi made 265whp, adjusted the timing (didnt adjust boost or anything) made 345whp and later with vtc adjustment made 398 on 10psi...
But do one thing at a time.. get a better flowing exhaust and if your still not happy get kpo. I would say get kpro right away but that shits expensive (but worth it!).

Lucid Moments
10-30-2010, 06:40 AM
Exhaust is critical to a supercharged motor. It needs to be as free flowing as possible so that it lets the supercharger do its work. It doesn't need to be fancy and high dollar like you might want on an all motor car either. Exhaust scavenging isn't the issue for a s/c setup that it is for an all motor car.

10-31-2010, 11:23 PM
Exhaust is critical to a supercharged motor. It needs to be as free flowing as possible so that it lets the supercharger do its work. It doesn't need to be fancy and high dollar like you might want on an all motor car either. Exhaust scavenging isn't the issue for a s/c setup that it is for an all motor car.

Yes and no. I'm not diving in head first right now as I'm going 3" for my S/C setup because I'm looking at the long term. It'll be worth it when the A3 gets replaced with a K24A1.

I also went with a different race header in addition to the exhaust again looking at the long term.

Thread starter go with a Kpro, RH, and exhuast then get retuned. If you don't pick up a solid amount of power I will pay for your tune (provided it's tuned by someone reputable).

You say the Kpro isnt justifiable with the power your looking for now, things change man. Get a Kpro - you won't regret it (Not to mention the car).


11-01-2010, 08:09 AM
There is a lot of solid info here, most given to you by peeps with proven SC'd setups. Exhaust is very important. Header design, not so much. In other words, you dont need some $1200 custom header. A race header to 2.5" midpipe to stock axle back is really all you need. Anything bigger will cause you to lose TQ and midrange... something the a3 already lacks. Anything smaller... well youre already familiar with those results.

Take your 'tuning expertise' and chuck it out the window. The fact you went with a reflash, and not a fully tunable option, was kinda of silly on your part... especially if you had 'race kit' performance expectations. KPro, and all the other parts mentioned are worth the WHP you are missing. The sum of all the smaller parts combined, is what you are looking for.

If you want more than a daily driven 300whp...

1)The JRSC is not your kit.
2)The a3 is not your engine.
3)The reflash is F to the AIL.

Those are basic guidelines that will help you decide based on your goals, what you need to do. Knowing your goals will help you spend $$$ on the RIGHT parts, the first and ONLY time.

11-01-2010, 10:59 AM
Ba82ep3...what is up man..?? I have been callN you. we need to get up soon and check out the EG swap.

Back to topic,
**reflash sucks, Kpro = 15-25whp depending on mods, but always gives you more as you build it
**exhaust size is tricky and is sized according to engine's desire
**I didn't get a gain from a Greddy evo kit, I got the gain from the race header on my k20a3
**It is all about having as much mid-range as possible in a 160HP engine

11-01-2010, 04:59 PM
reflash is terrible. i ran it for maybe 2 weeks and bought kpro soon after. noticed a hell of a difference. boost and reflash is like jesus and satan