duckworth

i don't have a lot of experience with these 1uzfe engines yet, but so far in life, the same things apply to nearly every engine.......i'm gonna do some dyno comparisons since emissions isn't an issue here, because within the month i'd like to put an exhaust on......

the first 4.6 ford mustang gt benefitted from dual 2.5" pipes and that design is a bit archaic when compared to the 1uzfe isn't it? like i said, i don't know for sure and may be completely wrong, but for an engine that makes 250/260 with only 10:1 compression and no other tricks, the flow of air through the head shouldn't be an issue, and with a good exhaust, you'd have better scavenging with a dual 2.5" setup and hi-flo cats (one per side) and a good muffler........the increased airflow OUT would mean increased airflow IN and a cleaner burn.......the ONLY reason 2.5" duals would be too much is if the head wasn't capable of pulling equal amount of air in......a 2 liter 4 cylinder shouldn't be able to move that much air except for in race form (they'd still not use duals) but a 4 liter, 4 cam v8 SHOULD be able to.....maybe i'm wrong, i'll learn a lot when i hit the dynos after xmas, but logic says that the higher rpm will benefit a LOT more than the low end would suffer........i want headers too


they're raspy and obnoxiously loud due to them being 1.6-1.8 liters on average.....the higher the displacement, the deeper the natural tone.......a 4 or 5 liter v8 doesn't sound like a sub 2 liter engine no matter what you do............you get a bubbling sound with hollowed cats due to the turbulence and thinner cat walls..........i figured he meant that, but that bubble doesn't compare to the wide open weed eater sound a sub 2 liter engine makes with bad exhaust setup........

and i'm not saying i like an uncorked small displacement engine, i actually hate them.....i've been building 4 cylinders for 10 years, had some fast ones, but they sound awful when open......even boosted 2.3 liters just don't sound good without a good exhaust setup.....

i'd much rather hear a v8 anyday.........even my hondas with 12 second n/a setups had nice exhausts.......maybe not at 8k rpm, but it wasn't as loud as a 107hp d series with a cheap exhaust and muffler............they just sound trashy to me.....ewww....

JspecSC3

iTrader: (4)

Yes that is exactly what I mean.

JspecSC3

iTrader: (4)

Your emission laws are different than ours. I live in the state of California where everything is illegal. Muffler shops can only make them but they cannot put it on. Us, the customers have to put them on somewhere else. As far as having no cats goes..If you smog and they catch you without one they will automatically tell you they wont do it. Ive been to a couple shops that have told me that same thing.

The cutting of a GOOD cat is illegal like you said but when getting a test pipe made there is no need to cut anything off. Thats why it is a test pipe. Its just a pipe with flanges welded to the ends so you can bolt it on and off of the stock location. No cutting required.

JBrady

I understand your reasoning but it is the power RANGE that is critical. My engine has a single 55mm/2.18" OD center resonator from the factory and that supports 290hp/300tq. The GS400 with a 60mm/2.37" single center pipe is rated 300hp/310tq. Does this mean that for every 5mm center pipe size increase my engine will gain 10hp/10tq? Unfortunately NO. In fact as the pipe size increases the exhaust speed at any given flow volume decreases. Decreased velocity is a prime reason for loss of low-mid RPM power and responsiveness.

Adding 2.5" pipes to a stock 4.6 liter Ford making 235rwhp/250rwtq is a MUCH different situation than the same on a 4.0 liter Lexus making 175rwhp/185rwtq. That said a properly designed 2.25" system on the Ford would probably make the same or possibly more peak power and make more low-mid power. However marketing is another issue and it is much easier and therefore profitable to sell 2.5" systems than 2.25" systems due to the bigger is better mentality.

The bottom line is you want to use the SMALLEST pipe size that will support your peak power. In some cases smaller actually makes more peak power. This is NOT due to increase backpressure. In fact ANYTIME an engine makes more power due to an exhaust change at WHATEVER rpm there is less backpressure at the exhaust PORT. There are actually many reasons why bigger pipes can actually increase backpressure at the PORT at certain operating speeds/loads. Think about crossover sections be it X, Y or H pipe designs. They universally improve engine response and operating power under the curve. If the bigger is better theory were true you would simply run separate duals of very large pipe size and forget about crossovers. There is a lot more here than meets the eye and peak flow "capacity" is but a small part of the equation.

Lexmex

I live in Mexico City with my 99 RX. I have had two precats messed up by low grade gas (gas station said they ran out of Premium) and not another one around for 50 miles plus my 3rd cat got dinged by a rock and was rattling. Had to scrub the precats and put in a Maganflow cat in its place. No CELs to speak of and when I checked at my exhaust shop, my numbers would have been good enough to pass down here.

As I understand it, for your SC in NJ it is only a CEL issue, no tailpipe tests for OBDII.

I had a friend with a RAV4 down here who stripped out all cats (we are at 7,400 elevation and cars runs slow and have bad MPG) and did get a CEL.

A good highflow cat is really what you need, but yeah strip the precats...you won't have a problem.

700bones

Hell yeah, do it dog. My brother fitted his with test pipes and got like a 25 hp gain on the dyno.