Holy Crap.........

Thanks for all the replies, lots o' good info. I think you guys have a good point about the torque: nice for driving around, but unefective at the track, so screw it, if I do lose a little torque for a good hp increase, what the hay.

I am now more confused than ever on what size exhuast to do.

I still say theory is gravy, but the dyno is the true test.

4DRSS 355 hp - 364 hp and 389 lbs - 410 lbs That is a big gain over that exhaust by using cutouts at the collectors!!! Does the rest of your exhaust have an x-pipe or anything helping with scavenging? And is it just me or did this make it seem like freer is better?

Thanks again

-Chris

 

4DRSS, By 2.5 inch catback that would be a single 2.5 right? If so that is why you loose so much power. The stock cars should run bigger than that.

Ben

 

Oh, that would explain it. If it was single that would be why the cutouts help so much.

 

2.5in is fine. Why do you think the new 400hp Cobras use 2.5in piping? Thats all you need. Im not saying 3in would hurt but 2.5in will give your more room to work with. For instance im gonna lower my car with true duals. Not many people thought you could do this but if you tuck it up good enough you can. The lowest point on my exhaust is the header collectors.

 

Mine too, and I have a thirdgen. Look under a thirdgen(front subframes) and it will make a fourth look easy. I still have to have mine welded up. I just clamped it in the driveway and my car is not up and running yet.

Ben

 

You gotta realize too that the shorter the piping the less backpressure. If I would have went with my true duals exiting out the back then i would have went with 3in. But since the length of my pipes are only about 3-4 feet long 2.5in pipe off of each collector will be fine. I still feel like my exhaust is as open as my cutout was but with a tad more tq down low. Hopefully when the track opens i'll do some comparisons. A few runs with the duals and a few runs with open headers. Put it this way. I spin at the beginning of snatching 3rd gear now. Use to with the 3in y-pipe and cutout on the end i could only chirp. Seams like I gotta a tad more hp now. And its not because of the more torque because of course the rpms dont drop that low during full throtte goin through the gears.

 

I looked at your exhaust pics and a couple videos, and it looks like pretty much the same setup I have. I hope mine sounds that good when I get to drive it.

Ben

 

Do you have a 305 or 350? I'd like to hear true duals on a 3rd gen.

 

My car in stock form with a cutout and cold air, picked up 17rwhp, and 14ftlbs of tq all the way across the board.

Now my car has 306 cam, longtubes, 3" catback, cold air, 1.6 rockers, and I picked up 13rwhp and 10rwt all the way across the board with the cutout open.

The only thing I could do to get better flowing exhaust would be to run open headers.

After seeing my hp gains from the open cutout, I'm going with a 3" true dual setup, over the axle, out the stock locations.

 

350. I just made my sig. You can look at it.

Ben

 

Just so you know dual 2.5 has more area than a single 3.5 so you wouldnt have a lack of airflow with them. With that cam however, especially if you have heads dual 3 inch probably wouldnt be bad. All I am saying is you should match your exhaust to your motor. I have always heard that dual 2.5 is supposed to support up to around 450 hp pretty effeciently.

Ben

 

Impy's have duals stock. He's referring to 2.5" duals.

 

I didnt know that. I knew that the caprices needed the 9C1 police package to get duals or so I was told, but I didnt know about the impala's.

Ben

 

Personally, I have AS&M headers. These are known to be the next best thing to longtubes, and they make some pretty impressive power, just ask Injuneer. However, they only have 2.5" collectors. I did like Injuneer and ran 3" pipes butted up to these and then to a 3" x-pipe, then reduced to 2.5" duals back to the axle. Now, Fred and George Baxter both were running much more than 450HP through these headers, more like around 800 or so. If 2.5" collectors held up to that, I think it'll manage for the rest of us. And according to Fred, the AS&M's apparently made more power than longtubes at that horsepower level, it was only till the power was significantly increased that the longtubes showed benefit. If 2.5" is sufficient that far forward in the exhaust, where the exhaust gas is much hotter, it should work just fine for the rest of the piping. If you're really concerned about it, why not run 3" cutouts after the collectors? That way you'll have the track and the street covered.

 

Don't know many guys running mid-length or shorty headers in the top racing events. I'll have to look closer the next time one does a wheel stand but I'd say they're all using longtubes. Not only that, they're all using longtubes and tuning the collector with a merge or adjustable length slip-on collector. At least that's how we use to do it cause there's a bit of power to be found there.

-Mindgame