'89 CSX exhaust question

[pkpturbo]

The CSX I re-acquired recently has a new (stock) cat and the original 2.5" pipes and muffler. I'm thinking of removing the muffler and just going straight pipe after the cat; either 2.5" or 3".....what do you think? I'm concerned about over-boosting the VNT and want to hit the right balance for more HP and more "noise". Thanks.

Peter Paulson
CSX #216

[boxcar]

For what it's worth I have a completly stock VNT Daytona except for replacing the cat with a large high quality glasspack and replacing the stock muffler with a piece of 1 7/8" I.D. straight tubing that exits under the valance in the stock location. On warmer days (70-80F) the boost regulates as normal at 12 PSI but spools up quicker and the car pulls noticably harder through the gears. At idle and cruise the exhaust note is quiet but under boost it changes to a whistling roar, not super loud but definately louder than stock.
When the temps get cooler (30-50F) I have to restrict the exhaust with a 1 5/8" insert and the boost will still creep to 14PSI at 5000 but no cutout.
If you keep the cat in place but run larger pipe for the rest of the system you might be okay if its warm out but lose the cat with the large system and it will probably OB. I tried running my car with open ex. and it would OB @ 4000RPM in 3rd on a 65* evening.
Some additional info....Pressure in the ex. system mentioned above is 6PSI @ 5000 in 3rd, with the 1 5/8" insert it's 7 PSI @ 5000 in 3rd. The full stock system was 9.5 PSI @ 5000 in 3rd. Replacing the cat with the big glasspack and keeping the stock muffler in place was also 9.5 PSI @ 5000 in 3rd (but super quiet).
You might want to look at this other thread as well..Backpressure test on factory VNT exhaust

[sdac_guy]

I have a 90 Daytona VNT also. When I bought it in 2000 it was 100% stock. I noticed that compared to my other turbo cars, it had much better bottom end torque, but the top end was nothing, laying down above 4800 rpm. I could wind it higher, but it didn't pull at all like it did down low, or like my other normal T1 & T2 cars did in the upper rpm range.

The first mod I did was to install a stainless 2.5" cat back exhaust (keeping the cat & using a bullet muffler 2.5" in & out). I couldn't believe how much it woke the car up. It now continued to pull strong above 4800-5000, pulls good to almost 6K rpm.

But this didn't come without a price. Overboost was now a problem, especially on cool or cold days. If it was 75 or above, no overboost at all, but below 70 and it would start to come in at higher rpms. On a 30 degree morning, going down the freeway ramp, it would hit overboost cutout as early as 3500 rpm in 3rd. It was pretty aggravating.

I got a custom cal from a friend inside Chrysler and overboost cutout was disabled and it runs 14 psi max. I am delighted with the performance on the street now. It will light up the right front tire as soon as boost comes in, in either 1st or 2nd gear, and almost does it in 3rd. While that is great fun, it also makes it hard to drive aggressively without traction loss.

I haven't had it at the strip enough to learn a good launch technique. It's just tire spin all through 1st & 2nd.

So almost any exhaust mod you do will make the car more fun to drive, but the downside is that it is much easier to hit overboost cutout also.

Besides the computer & exhaust, I have made only one other mod. I was told that the 88 TBI cam would really go well with the VNT (by the guy that did my cal). I put one in last fall, and could tell the difference immediately. It is almost a different car. The next time we have a local dyno day I want to get it up there to see what it does.

Barry

[pkpturbo]

Thanks - Maybe I'll start by removing the muffler and installing a straight 2.5" SS pipe and see what happens. If it doesn't overboost, I'll keep on going....

PKP