: Did your Northstar's Y pipe come obstructed from the factory? Mine did (with pics)

02-13-10, 08:40 PM
While I had my Northstar out to repair the headgaskets, I noticed that the Y pipe connecting left (front) and right (rear) exhaust manifolds came with a serious obstruction from the factory. Look at these pics:




From the looks of it, I would say that the cross section of the pipe was about 25% obstructed.

A few hours with a dremel tool with a dozen reinforced cut off wheels got me the following results:




That should get me a few HP back (at least closer to the advertised 300!).

Wonder if this explains why some FWD northstars are faster than others?

02-13-10, 09:00 PM
I never thought of that, but Northstar cars really vary when it comes to power. I've timed mine 5 or 6 times at a 0-60 time of 6.5 seconds. I've driven some STS's that seem quite a bit slower. Never taken mine to the track, but it's pretty damn quick.

02-13-10, 09:23 PM
I recall seeing that before. I don't think you are alone. I'll bet we all have that, but I'm not pulling mine apart to find out.

02-14-10, 11:07 AM
crap....i forgot to check mine.....

02-14-10, 12:49 PM
If you really want to, you can remove the Y pipe without dropping the cradle again, according to my service manual for 2000. Might require an assistant...

02-15-10, 10:50 AM
When I decided to do my exhaust, I figured I would do away with that Y pipe and make one. I don't have a picture of the Y pipe but here are some pics of what I did. I only replaced the pipe and catalytic converters, I kept the factory mufflers on it to keep it quite. I just wish there was something that could be done about the cross over pipe without loosing ground clearance.
Here is what I gained.

02-15-10, 10:57 AM
Interesting. Where is that in the pipe? On the engine side or the cat side?

I'm not taking mine aprat either put if it's ever apart for somehting else you can bet I'll address the issue.

I wonder why it's there to begin with? That's not an accident, it's there by design, but why?

02-15-10, 05:27 PM

Nice! Wish I had the welding skills to do that.


The area cleared up was on the engine side, before the flex joint. My opinion: GM did it that way to do it cheap, not do it right. stbtt's dyno chart shows that there are 12 horsepower at the wheels to be found fixing that, maybe less in your case (you already have the Corsa, so the gains will be limited to the Y pipe fix)

02-16-10, 10:00 PM
Is the flex underneath? Before it goes up to the head? I'm assuming so since you didn't say left or right bank.

So you're saying it's between the flex tube thing and the cat? Or on the flex tube end of the Y itself. I know that sound stupid but I can't really remember what it looks like under there.

Then the question is, what sort of effort would be required to get to it? Are we talking about dropping the cradle?

02-17-10, 08:53 AM

The obstruction is at the junction of the Y pipe - between the flex junction and the ends of the Y that bolt onto the exhaust manifold and crossover pipe.

According to my FSM, here's the procedure (the FSM calls it a front pipe):

1) raise the vehicle.
2) remove the catalytic converter to front pipe nuts (beware, you will need penetrating lube, 13mm 6 point socket wrench, possibly the use of a blowtorch, and they may be so rusted that they may be impossible to remove). Consult with Jake, he sees more northern cars with lots of rust. My Florida car did spend the first part of its life in the New York area, so it was a little rusty (used the pb blaster, didn't need a torch).
3) remove the front pipe to exhaust manifold bolts (more penetrating oil here).
4) remove the front pipe.

To get the necessary clearance, be prepared to loosen the rear engine cradle bolts and drop the cradle about an inch or so.

So it looks like you can do this without a full cradle drop.

02-17-10, 09:07 PM
I'm good with the Cat bolts, BTW if anyone cares, those studs, or what appear to be studs are actually threaded through the cat flange so don't try to smack them out with a hammer. All the heat in the world won't help you.

My cat went on with the Corsa so new bolts there :)

Thanks, maybe in the summer time I'll have this looked at.

02-18-10, 01:52 PM
the newer ones with the 4 bolt square piece that connects the flex to the cat are a b****. Ive taken apart those and the older style. Mine, we ended up just cutting it and replacing the flex pipe. The shop that did it had the exact same flex pipe and it was cheap. There was NO getting those bolts out. Unfortunatly i did not look to see if my Y pipe was obstructed like that, but i have 2 cars coming apart this month that i will check.

Actualy, i have an entire cradle, engine/trans still attached from a 98 concours and ill check it to see what it looks like. If its like that ill definitly be fixing it. I also want to have them take a good look at that crossover pipe. Im not sure what can be done with it, it has an added layer of metal on the pipe itself, for noise or heat disipation maybe?

I have a complete exhaust down pipe to tips from a 2000 STS. My 97 now has totaly custom muflers free of charge curtousy of mother nature. Wondering if i can get those mufflers from the 2000 on there.... i hear they are expensive :histeric::histeric: