If i had a intake, and a 3" downpipe with a high flow, and the replaced my 2nd cat with a highflow and ran a cat back would i be in danger of running to lean??

 

you can't get a downpipe with a cat in it, unless you go with a stock one. read the newb stickies at the top of the FD forum, it may be a ****-ton of reading, but it will stop people from bitching at you for asking "dumb" questions (i have dumb in quotations because the info is there, and if you ask the questions that means that you're too lazy to help yourself, and no one is going to answer it because it's a stupid question). you will run lean because you changed the volumetric efficiency of the engine. this means that it's easier for the engine to pull in and push out air, which will in turn make the turbos spin faster to keep the stock boost. the stock boost is measured by a MAP (manifold air pressure) sensor, and the computer will keep the WG closed until you reach 10 psi at the manifold, which requires much more air than stock, because of the increased volumetric efficiency. mods to do before intake, dp, hf cat, and exhaust are: MAKE SURE YOUR CAR IS IN GOOD RUNNING ORDER BEFORE YOU **** WITH IT, radiator, aluminum AST, DP, stand alone fuel computer, medium-sized stock mount intercooler, THEN intake, hf cat, cb

 

thanks for the info

 

read faq

in anycase, its not adding an exhuast which will kill your motor, its running too lean such as running too much boost. you can have stock exhuast adn still blow your engine if your running too much boost... that or if anything fuel related dies like an injector craps out on you

 

if you dont have a boost controller you should definetly get one. you wont be in danger of running lean if you can control boost at safe levels.

 

that was an ignorant comment. 10 pounds of boost with all stock components is not the same as 10 pounds of boost with an intake, dp, hf cat, and cb exhaust. this has always been my problem with quoting how much "boost" you're making. ya, you're changing the pressure at the throttle body plate when you have a supercharger/turbocharger, but what really matters is the VOLUME of air that you flow through the engine. (i'm going to just pull numbers out of my *** for this analogy, because i don't know how much volume the stock turbos on a FD will flow, or how big the throttle body is, etc.)

Let's say that you have all stock components on your engine. at stock boost, 10 psi, let's say you're pushing 200 cfm of air through all stock components. now, let's say you try and push the same volume of air (200 cfm) breathing through an upgraded intake, dp, hf cat, and cb exhaust. the upgraded parts will let the engine flow, let's call it 15%, better than stock. that means that for the same given volume of air, you are only going to have to push 8.5 pounds of boost to move the same volume of air, to ensure that you don't run lean and blow your engine.

 

ok thanks for explaining it

 

You can get a downpipe with a cat in it. Tri-Point sells one, and you could easily make a custom one. One or more of the HF cat makers specifically produce "pre-cats".

-Max

 

you can get an aftermarket high-flow pre-cat? really!?! i've never heard of this, is it a ceramic or metal core? how does it flow vs. a downpipe?

 

no problem, what the guy above me said was correct to a point, but i don't think that either manual or electronic boost controllers will go low enough for you to run those mods safely with the stock ECU, plus you'd have to do a flow test comparison to see which aftermarket part would flow with the least improvement over stock, and caculate how much boost you should run to keep the same AFR. in short, it's way too much of a headache to try and keep the stock ECU with those mods, because of the time and money that you'd have to invest to flow test all of your stock parts, all of your aftermarket parts, and then figure out some way to safely regulate your boost at lower-than-stock values to keep your engine in tact. If you prop the WG open, as far as i've read, you'll only push 7.5 pounds of boost, so if you are dead-set on getting those mods first, then open up your WG so you don't have to drop the coin for a new engine.

 

no problem, what the guy above me said was correct to a point, but i don't think that either manual or electronic boost controllers will go low enough for you to run those mods safely with the stock ECU, plus you'd have to do a flow test comparison to see which aftermarket part would flow with the least improvement over stock, and caculate how much boost you should run to keep the same AFR. in short, it's way too much of a headache to try and keep the stock ECU with those mods, because of the time and money that you'd have to invest to flow test all of your stock parts, all of your aftermarket parts, and then figure out some way to safely regulate your boost at lower-than-stock values to keep your engine in tact. If you prop the WG open, as far as i've read, you'll only push 7.5 pounds of boost, so if you are dead-set on getting those mods first, then open up your WG so you don't have to drop the coin for a new engine, and don't stand on it until you can get a PFC or equivalent.

 

I dont know if I am reading your example right or what, but I just want to clear something up. In your example adding the intake, dp, hf, and cb it is not as simple as running 8.5psi of boost to keep the same AFR's as stock running 10psi. The reason is the MAP sensor. The stock SCU bases your fuel injector duty cycle on the MAP, RPM, and several other sensors that dont really matter for this discussion. If you simply reduce your boost then the MAP sees less pressure and the ECU in turn keeps your injector duty cycle lower. You can still have the lean problem, it will just be limited to the 8.5psi and below partion of the fuel map.
If the FD ran a MAF then the ECU would know how much air was in the system and reducing the boost to 8.5psi would prevent you from running lean. That is the one main advantage of a MAF system over the MAP.

 

The main thing to be concerned with regarding boost is spike (at transition) and creep. Keeping a high flow cat in the mix (vs open exhaust) will keep creep in check and will usually minimize spike. The problem is the stock internal wastegate and it's inability to divert enough exhaust energy away from the turbine wheels when you run dp/mp/cb.

 

i have a catback, dp, and intake going on soon..i bought an avc-r until i buy a new ecu...what will i have to set my boost at to stay safe for now

 

about .5 kg The acv-r I had was in metric and I ran .5kg or about 7.2psi. The only thing is that when I set it up I would set the target boost and then have to slowly work the inj duty cycle up until the desired boost is set. from there you can change the rpm based boost to maybe help with lag earlier on and spike later on.

 

very true, i didn't even think about the ECU only seeing 8.5 psi. of boost and cutting the injector duty cycle. damn, i still have alot more to learn before i buy a FD. thanks for the correction.