Sunday I got the full 3" exhaust from busher in along with the Air intake. I am going to put in the AFC and manual boost in the next week or so. Good sound coming out of the exhaust but I am getting a suction sound when I hit the gas and it seems to be concentrated in my defrauster vent on the driver side. My guess is that the intake is causing alot of suction under the hood and there for causing some kind of negative backpressure in the air vent resulting in a annoying sound in the cabin thus adding even more cabin noise. Any thoughts on this, is my thinking off is it the BOV but if so why is it causing a sucking sound in the vents? When I put my hand over the left defraust vent it is moving the air back. Very strange... should I wait to put in the the AFC and manual boost to see if this goes away? I am ready to put back the stock box and see if it goes away if it does the cone air intakes are not for me to much noise to the already noisy cabin. Thoughts anyone or solution

 

That's purely the noise of the intake through the new cone air filter. I have one myself. Personally, I like the sound. If you got an Evo to be a quiet daily driver, you got the wrong car. It's going to be loud.

 

Well I think it was the initial difference of the wide open 3" exhaust and the cone filter suction, I have gotten more use to it but what I am going to do is lay some Dynamat extreme and this is mostly so I dont have to crank the music up so loud, and I did not get the wrong car I researched this car carefully and I am making this an awesome machine of power, looks and balance. I will post pictures in the future once I am done I believe you will agree.

 

noise, schmoize...

HOW IS THE POWER?

 

Well I think for the real power to come to life I need to finish the other two steps manual boost control which will be set to 18psi across the whole rpm range for safe reliable going fast on 92 pump gas and the S-AFC set up by Bushur. Just with exhaust and intake I lost some low end torque and at the higher RPMs it feels better more open but I would not just do this upgrade with out the other two which i will be doing the following weekend. I wanted to do this in stages to see the difference and test reliablity. Stock set up has better low end punch and it is pretty tight through out. Pretty impressive for stock. So dont bother with just exhaust and intake unless you go all the way with boost and AFC not worth taking the hit its sounds cool though.
If you only plan to do exhaust and intake only stick with a 2.5" exhaust it creates the necessary back pressure in its stock state to keep the torque right and you will gain a few Horses and the sound.

 

tried closing the climate control vent (hit the recirculate button) to see if the noise stops?

 

That is true for a normally aspirated engine, but not a turbo and if your car has lossed some torque on the low end, then something else is going on. That 16g should pull harder throughout the power band. Bigger is better.

Speedlimit.....

 

The only reason to go with a 3" is if you are going to raise the the stock boost and or upgrade to a bigger turbo in the future otherwise its wasted in its stock state. The 2.5" can more than handle the stock horsepower and the stock turbo setup does benefit from the backpressure on the low end torque. It changes on the upper RPM's bigger exhaust is then better. Ask the major tuners if you only do intake and 3" exhaust on the EVO you will lose a little low end torque but gain HP on the high rpm. Small sacrifice but I dont plan to stop there I am doing the SAFC and manual boost next week so I will gain alot more on the low and high end.

 

Hi,

Congratulations on the Buschur exhaust by the way.... good choice!

I agree that a 2.5" exhaust is fine for stock horsepower. I dissagree that a 3.0" exhaust only will reduce low end torque. If it does, I don't understand how.

Here is quote from an engineer who designs turbo's for Garrett:

Remember, a turbine operates via a pressure ratio. For a given turbine inlet pressure, you will get the highest pressure ratio across the turbine when you have the lowest possible discharge pressure. Again, less pressure downstream of the turbine is goodness. This approach minimizes the time-to-boost (maximizes boost response) and will improve engine VE throughout the rev range.

This is why larger exhausts make such big gains on nearly all stock turbo cars-- the turbine compounds the downstream backpressure via its expansion ratio. This is also why bigger turbos make more power at a given boost level-- they improve engine VE by operating at lower turbine expansion ratios for a given boost level.

As for 2.5" vs. 3.0", the "best" turboback exhaust depends on the amount of flow, or horsepower. At 250 hp, 2.5" is fine. Going to 3" at this power level won't get you much, if anything, other than a louder exhaust note. 300 hp and you're definitely suboptimal with 2.5". For 400-450 hp, even 3" is on the small side.”

Speedlimit.......

 

Speedlimit,

I certainly agree that bigger is better for max HP under most conditions with forced induction applications.

However I'm not sure that translates when operating under partial throttle openings combined with sustained low boost pressures (read normal driving). Under these conditions, the larger diameter exhaust, due to its increased volume, might enable the formation of an exhaust reversion pulse of greater volume and pressure than that encountered with the stock system. If the reversion pulse and pressure are sufficiently greater than that encountered with the stock exhaust pieces, could it possibly overcome the low boost pressure and adversely impact air flow? Under these limited circumstances low end performance characteristics and drivability might be degraded. There are many other variables including cam lift, duration, timing, and overlap, that will be contributing factors in determining whether and to what extent exhaust reversion might influence performance at a given rpm range.

I believe that under these conditions your assertion might warrant additional consideration....or not.

FWIF, just my $0.02.

 

Profec B spec and Buschur turbo back + test-pipe + air filter, yes, the 16g pulls quite nice now in the upper rpms. And the sound is just music to my ears.

 

Well, although the theory of "biggest is best" for turbos is correct, the reality is a little different. I put a 3" turbo-back system in my WRX and I also put a larger than stock, no muffler pipe in my turbo charged Miata.
Both cars lost power at the low end. I think it is because at lower speeds and lower rpm, the turbo is not spooled. You get hit with a double whammy: turbo lag (although the bigger pipes help this somewhat), and the loss of back pressure when the car is really not under boost. Results? a weaker feel in the low end.
On the other hand, the power gains at the top end are quite noticeable. I'm not sure what I'll do with my EVO. I think that I'll probably do something with a Ralliart product just because they are the real deal. I do think that guys who put the big pipes in their cars will definitely benefit from it.
As far as the intakes go, I really am opposed to messing with them until I know for absolute certain that the ECU will operate properly. Same goes for the blow-off valves that vent to the atmosphere. I don't know how the EVO is on this respect, but the WRX responds badly to intake mods unless a lot more work is done with electronics.

 

Hi,

I have seen this discussion before, however, I wonder if the effect is so subtle as to be unnoticeable at low RPM? When I upgraded the stock exhaust on my 93 Talon (16g turbo), there was a very noticeable increase in torque throughout the rpm range. I would expect the same on the EVO. Maybe it is 'cause I don't spend much time with a vacuum in the manifold!

Speedlimt.......

 

Hey, you mioght be righ there ... But there was a noticeable drop in low end torque (albeit small) in thw WRX and the Miata... I will say however, that both cars were definitely faster after the upgrades

 

When I decide to finally buy the 25g for my EVO, then I'll go with the 3inch... Till then a 2.5 is just fine to take the little 16g into the high 11's...