GMCtrk

iTrader: (27)

Eventhough I have a magnaflow "straight thru" muffler welded in, when I cap my cutout my low end just goes to ****. I'm not a physicist or anything, but in medicine when talking about the vascular resistance, the single most important factor in resistance to flow is the radius (of the pipe in this case). It's in the denominator to the 4th power. So even a small change can make a big difference. Length of the pipe also plays a factor. What I'm trying to figure out is will going to a 3.5" catback get me the same power as my cutout? Is the magnaflow muffler killing power? So theoretically going from the stock 2.75 to 3.5" cutout will offer a ~260% decrease in resistance to exhaust flow. I'm curious what everyone else is running after the 3" Pacesetter Y pipe. Thanks!

cellulis44

iTrader: (11)

3" flowcrapster

fastnblu

iTrader: (2)

While I don't have a Pacesetter Y, I have the following to say. Who offers a 3.5" catback? Most of the usual systems are 3". Not the diesels, they're BIGGER!
A 3" should fit your needs. Going too large kills torque. Not what u want to do on a truck, unless going for sound. On a truck, u don't want horsepower, u want torque. Torque moves our heavy trucks.

viciousknid

iTrader: (8)

stay with 3". no reason to go bigger. You lose enough low end tq with LTs and 3".

GMCtrk

iTrader: (27)

Going to a bigger catback is not going to make me lose low end lol. Losing low end with LTs/exhaust is stupidest myth out there.

skyhighsami

iTrader: (8)

Uh, not really. If you have too little back pressure you will lose low end. Still think it is a myth, take a truck and pull the muffler off and drive around straight piped and tell me what you think

Mangled03gmc

iTrader: (95)

I totally agree, I def lost low end on my truck when I first put headers, lost the cats. It isn't a myth

John

GMCtrk

iTrader: (27)

Oh boy.

Let's think about this for a second, if you have more resistance to removing exhaust flow from the combustion chamber (what you are calling "backpressure) you are increasing the resistance to piston movement. Thus, the crankshaft isn't rotating as forcefully. Your power output goes down. As far as I understand it exhaust flow is all about VELOCITY. So if anything, any "loss" of power with headers is due to a mismatch of too large a header primary to too small of an engine (too little exhaust coming out for the size of the pipe). Get the right sized header primary and I guarantee you that you will gain power all over the powerband just as I have experienced.

JakeBrakeIH

iTrader: (22)

same for me...with i open the cutouts it feels doggy down low but good on the top end...once i got tuned it helped a lot but i feel low end loss with an open exhaust...

viciousknid

iTrader: (8)

I lost low end with mine.
I've seen dyno runs lose 5~ hp from opening a cutout. It's not a myth, it really just depends on your setup.
At our dyno day a person was there with the same truck as mine except he had a cam, tune and Straight pipe compared to my Stock cam, full exhaust and tune. I made about 40hp more than he did.