3" exhaust. necessary or trendy?

[Redlined]

Seriously, Maybe im lacking in understanding of turbo technology or something but... 3" exhausts? I see 3" exhausts on a four banger and I think somebody is being flashy. I'm looking to upgrade Angels Exhaust system before I add a bigger Turbo and Inter-cooler and want to have a clue what I'm looking for and why.

Ive seen a 600 horse 440 in a 1969 charger pushing through 2 1/2" duel pipes and mufflers. (( with full Try Y headers, and a 2" equalizer pipe )). It didn't seem to be wheezy in the least.

Just seems like 3" exhaust on a.. what? Ill be optimistic and say 225-250 horse 4 banger (Modded , not stock) seems to be overkill. (( In my opinion of course ))

Now I AM new to the Turbo circuit so my knowledge of these things is pretty limited. So please enlighten me.

Thanks in advance!

[Legacy777]

Turbo engines move a lot of air through them.

You could probably get by with 2.5", however I don't think that's much bigger then stock. 2.75" might be more ideal, but I don't know if that's an odd-ball size.....which is why you probably see a lot of people go 3"

[555BCTurbo]

I used 3" because I figured that while I was going to be spending the money and time to build new exhaust, why not have it flow as well as it possibly can...


And let me tell you, it sure woke the car up!

[skid542]

I went through this personal debate when I decided to upgrade my exhaust.

First thing to consider is what are the ultimate power goals. If 250-260 at the crank it all you're after, then no you don't need a 3" TBE. But if you're going to be chasing the 300-350+ WHP then yeah, you're going to need it or you'll be spending a lot more time and money on other components to compensate for the power lost through a more restrictive exhaust.

And monetarily, it doesn't make much sense to spend money on a 2.75" system if you know you'll have to upgrade later and spend a bunch more money.

As you said, these are four cyl. engines and they require more work and refinement than the large V-8's and such that can get away with smaller exhausts because they have the displacement to make up for it. Yes the STi runs a smaller exhaust, but it has more displacement, larger turbo, and most importantly - EM that has been tuned for more power. You look at the Honda world, a lot of those guys are running 1.6L - 2.0L motors. You can't push the power they do on those tiny motors without exhaust support.

So to answer your question, I believe some of the exhausts you see are a result of 'being trendy' but many of them are a result of pure performance drive both now and for the future as the car continues to get built.

And as Nick said, the 3" TBE and a TMIC really spiced things up without having to touch anything else. I'd say, rough estimated, I'm now sitting around 200-220 CHP with a few extra pounds of boost out of the stock turbo. That's a pretty subtantial gain over stock.

[AWD_addict]

Ive seen a 600 horse 440 in a 1969 charger pushing through 2 1/2" duel pipes and mufflers. (( with full Try Y headers, and a 2" equalizer pipe )). It didn't seem to be wheezy in the least.

A naturally aspirated V8 does not necessarily want the same exhaust as a turbocharged H4. An NA engine wants a little backpressure, a turbo does not. Although an engine can be thought of as an air pump, there is not a set ratio of X hp to Y exhaust diameter.

[93forestpearl]

^ This.

A turbo charger gets its energy from the pressure differential across the turbine wheel. Remove any backpressure from after the turbo and it makes the some boost with less effort. Ideally you'd run zero exhaust after the turbo, but in reality thats not an option.

[Redlined]

Lots of great info! Thanks all!

Second question. Just a quick verification really. Found an '06 STI exhaust. From what Ive found on the BBS, an STI exhaust SHOULD fit with a 6-9" extension.

I ask because the gent says he bought it to put in a legacy but it required to much modding.

Thanks again!

[asc_up]

Well maybe he's just not mechanically inclined...? Haha j/k.

But yes. It will fit with that extension. I also had to cut off an exhaust hanger and re-weld it into a new spot. No big deal.

[BXSS]

+1 on what 93forestpearl said - turbos do not like an exhaust.

I saw an exhaust comparison on a STi a while back & 3" (outer diameter) TBE made power over stock, 3" (inner diameter) TBE made power over 3" (outer diameter tubing), & a 3.5" APS TBE made more power than all of the other exhausts.

We are using 4" exhaust on the "Welfare Racer" Rotary Starlet this year (to match the 4" V-band e-housing on the GT45R turbo upgrade) & its motor is just 68cubic inches (1.1l).

Funny thing is we crashed a V8 Test/tune day once with this car & after seeing everyone advertise there bigness (440 ci, 454ci, 502ci ...) I advertised our smallness (68 ci).

We raced a 502 CI back-halved Chevelle (?70) with our car running just 12psi & starting in 2nd gear (as the car could not be shifted from 1-2) & even though we started out slow we whooped that ass....

We ran 11.319 @123.59MPH vs his 11.357@115.66MPH & had a crowd of V8 guys amazed @ how the carb & turbo was bigger than the motor...

[93forestpearl]

Carburated and turbocharged? I've heard stories of such crazyness. Do you blow-through or totally encapsulate the carb with pressure? Or are you drawing fuel through the turbo?

pics please

[Legacy777]

Yeah that sounds like an interesting setup!

[BXSS]

The "Welfare Racer" uses a turbonetics Carb-plenum & 2x450cc + 2x560cc injectors run off a MAP Based additional injector controller that I ghetto tune based on EGTs on a 32x32 load/rpm map for each pair of injectors.
This car has run 9.97 & 9.98 @ 20psi with a good tranny (one that could be shifted from 1st-2nd).

There are a couple draw-through (carb in front of the turbo inlet - turbo pulls air & fuel & forces it into the intake manifold) systems running around that my buddy fabbed up.
He put one together for his brother also in a KP61 Starlet / 12A Rotary swap - that car ran a Buick G/N turbo & @ about 20+ psi it would run 11.81 1/4s, with no electronics - just a carb+turbo+stock 12A.

In PR turbo-carbed cars were pretty common - 3 of my 3tc (1.8l Toyota Hemi headed motor) friends run/ran 58psi of boost through weber carbs running a best time of high 8's - on carbs....
I of them has gone stand alone & has yet to beat his 8 second best time.

I'll try to look for some motor pics, but think I only have some from a Suzuki Samari that has the same set-up as the Starlet on a bigger (80CI) 13B motor.

[BXSS]

http://bbs.legacycentral.org/viewtopic. ... automobile

Here is a pic on the car in last year's small turbo (from an 18 wheeler), small I/C, small exhaust trim.
It ran a best time of a 9.98s 1/4 mile in this event (95*+) coasting through the lights in N as the car did not shift to 4th about 100' from the traps.
I believe the best 60' this car has done with its little tires was 1.2x seconds on a 13B / 250HP shot of NOS bridgeport, 5.57FD set-up.

I have no pics of the motor, but do have pics of the Suzuki's set-up under construction that I can give to someone to post.

[aspect]

I am pushing around 350 dynojet whp on a 2.5" system with a resonator and a prodrive axleback. That being said, I think it's restricting the power a little bit up top. I'm going to throw on a silly loud N1 3" system just to see what the difference is and take it to the dyno, so we'll see if there really is that much difference!