Hello I've dumped about 2000 in all new parts and interior on my vehicle. I bought a flow master 2.5" high flow cat and figured I'd buy a new downpipe while I'm at it. Did the upend delete and resanator. It's 2.5" back to the y-pipe. I wanted to throw a 2.5" downpipe in but have questions. Is the 3400 series and 3800 series downpipe the same exact thing or is there differences? I see all these down pipes for 3800s but 1 for the 3400 and that's an eBay one for $120. Any help would be greatly appreciated. I've come a long way with this car and don't plan on stopping lol. Should I get a 2.5" or 3" downpipe? Has k&n air filter.
I own a 2001 monte carlo ls 3400

 

Anybody have any inputs on this topic?

 

They are not interchangeable. The original exhaust was 2-1/4", but since you've already upsized to 2-1/2" I would stay with that. 3" is too big, you need a little backpressure.

 

I'm mostly going for sound. Where can I get a good 2.5" downpipe with no cat attached? Most I find have one welded to it already.

 

Anything but a stock setup is gonna' be hard to find off the shelf for a 3400. It's not as popular when it comes to mods as the 3800. Are you planning to add a turbo?

 

As Plumbob mentioned, the 3400 in the w-body is not as popular to mod (but in your N-bodies like the Grand Ams, it's very popular).

Here's a link to some 3400 info (I know there is a mention about the down pipe):
https://montecarloforum.com/forum/fw...p-power-46071/

If you are going for a different exhaust sound, a cat back system would be the way to go. Unfortunately, I don't know any to recommend for the 3400. As for a down pip without a cat or U-bend, you might need a custom exhaust shop to build that.

 

What What a big help thank you The_Maniac! No I do not plan on boosting this engine. I'm running it till she blows then swapping in an l67. The l67 I'll be doing major engine work too. I'd like to bore the blocks for slightly larger and slightly higher compression. Cams, rockers, valves. I'll end up boosting this one when I get to that point. Exhaust (headers to mufflers). Kyb struts too and so on.

 

If you don't have plans to go crazy with mods on the 3.4 and eventually get a L67, then here is what I would do on the cheap:
- Delete the resonator and the U-Bend. Leave the rest of the exhaust stock (unless it has a problem). Worry about other exhaust changes when you get an L67. Or one step further, get an SS exhaust (it's just a Y pipe and dual mufflers).
- Get L67 coils. OEM coils (used are fine)
- Fabricate a fender well intake, gut the air box or buy a cold air intake.

Outside of that, keep up on maintenance. Those mods should be cheap and give it a little more (not a lot) get up and go.

 

2 years back I had cut out the u-bend and fitted straight pipe in there. Then I went to a junkyard and pulled a SS impala exhaust with y pipe. I had then made it 2.5" from the cat outlet, cut the resonator out and continued the 2.5" up to the y pipes first bend. Can't remember what size the y pipe is and if I put a reducer from the 2.5" to the y pipe.
Quick question, can I weld a new cat onto my stock downpipe being it's double walled? I may just save the bucks since she's at 160k right now and once it blows I'm going to the boneyard to pull an l67 and start from the oil pan up to the manifold lol

I've had this car sitting in my garage for awhile due to BCM issues. I bought the replacement and got it in (which really, really sucked btw) now tell me, is it 30 minutes on and 10 seconds off or 5 seconds off? And does it mater if I'm 1 second off?

 

I don't see why an aftermarket cat can't be welded to the downpipe (that's how the factory one was done). Just make sure the welds are solid and all around, no leaks, should be good.

Treated right, that 3400 can last a LONG time. I know someone pushing a 3400 Grand Am to 300K (he has over 250k on it now and just keeps changing the oil and it keeps going). Those 60* v6's are pretty durable and reliable engines.

Now, the BCM. If you got a replacement BCM, you should really get that properly programmed with a GM Tech II scan tool (that computer contains various information about the options of the car).

As for the PCM relearn process, here it is from the shop book:

1. Turn ON the ignition, with the engine OFF.
2. Attempt to start the engine, then release the key to ON (vehicle will not start).
3. Observe the SECURITY telltale, after approximately 10 minutes the telltale will turn OFF.
4. Turn OFF the ignition, and wait 5 seconds.
5. Repeat steps 1 through 4 two more times for a total of 3 cycles/30 minutes (the vehicle is now ready to relearn the Passlock™ Sensor Data Code and/or passwords on the next ignition switch transition from OFF to CRANK).

Important: The vehicle learns the Passlock™ Sensor Data Code and/or password on the next ignition switch transition from OFF to CRANK. You must turn the ignition OFF before attempting to start the vehicle.

1. Start the engine (the vehicle has now learned the Passlock™ Sensor Data Code and/or password).
2. With a scan tool, clear any DTCs if needed (history DTCs will self clear after 100 ignition cycles).