Well, the waiting was just driving me insane. I NEEDED to do a modification. I went to the Muffler shop to have the pre-muffler removed…I left with a Custom, True Dual Exhaust system. It all started when I asked about fabricating a Y-Pipe similar to the Top Secret design. “Well, why not do an x-pipe?” the fella asks me. That was it. We designed a system, and Rusty went to work building it.

Rusty over at Leonard's did all the work for me. He has been doing exhaust work for 30+ years.

System:

2 1/2” pipe
X-pipe
2 1/4” pipe
6” MagnaFlow mufflers

Sound

Idle: quiet, I think it is as quiet as stock
Light to Moderate throttle: Revving up to 4k RPM there is a wonderful deep sound. Kinda hard to explain.
More than Moderate: when cold there is a great deal of raspiness. When really warmed up, most, but not all, of that goes away.

I am still trying to decide about the raspiness. The majority of owners would not like the sound as it is right now. This system is a work in progress. I am leaning toward putting in a set of resonators to quiet down or eliminate the raspiness. If the sound stays nearly the same otherwise, I will be very pleased.

Performance

The car really feels different. The throttle response is ultra sharp. I felt like the power had raised across the board to some extent. Unfortunately, I did not do a pre-mod dyno. I have put about 600 miles on the car since the modification. So, today seemed like a good time to visit the dyno. I went to Colvin’s Automotive to use their in-ground Dynojet. Once they had strapped her down, they had a little difficulty determining where to clip on to the wire for the RPM. In the end, they used the blue and white wires off the number 1 coil. That done, they shoved the sniffer up the driver side tailpipe.

Run 1: The tech turned off the VDC and started accelerating the car up to speed. Once in fifth, he began the run. The run seemed to go off without a hitch. Hp 234.46 Tq 231.76 w/smoothing factor=1, 233.42/230.50 w/smoothing factor=5 When the car was back at idle the tech motioned for me to come over to the car. He pointed to the dash. At some point during the run, all the dash lights came on. The Brake, ABS, VDC Off, and SLIP were all on. Shutting the car off didn’t fix it either. The lights went off after the car was moved to the front of the shop. I don’t know if this is normal for the Z or not. We thought it might be the ABS computer not liking the rear wheels spinning and the fronts not. Any input on this would be greatly appreciated.

 

Run 2: We then ran a second sanity check run. Everything came out basically the same. 234.2/233.86 sf=5

 

Run 3: We let the car set for 30mins before the next run. The car had been running continuously for 10min prior to the first 2 runs that were done back to back. The cooler engine only produced a minor increase. 236.66/232.7

Would someone explain to me how it is decided which smoothing factor is used?

With a smoothing factor of 1, the dyno plots are jagged like 2003z. Also like 2003z, my numbers suggest no gain or a possible loss.

If you have any questions, ask away.

 

From the Catalytics to the X-pipe...

 

From X-pipe all the way back....

 

X-pipe behind brace...

 

Passenger side pipe going over the sway bar...

 

Close up of passenger side sway bar...

 

Pipe clearance

 

I would fathom that you lost a bit of hp from this, or maybe the ECU just took a crap and went into "save me mommy" mode. 230 seems pretty low. about 10 less than what Id expect stock.

the true test would be to stick a ecu in there when it comes out and do it again, see how much you can gain from it.

 

Low Rear view... From a normal view, the tips look very similar to stock.

 

ares,

I totally agree. I had hoped for roughly 250 rwhp.

I only wish AEM would release an application for us of their EMS. Then we could really see what these mods do.

JD

 

I don't know too much about exhaust, but a little about airflow, so here are a couple questions:

1. What is the purpose of the X-Pipe? Why not simply eliminate it and run reach pipe to a separate muffler? Is the purpose to allow the exhaust back pressure to equalize down both pipes so each cylinder bank sees similar pressures, or is it for better sound, or some other reason?

2. Do you have a picture of the X-Pipe before it was installed? It looks like it could be restricting the flow a bit.

3. The bends seem to neck down to a smaller diameter, which may reduce the flow a bit. Since I don't what the stock diameters look like, I don't know how the overall airflow would compare to the stock exhausts, but maybe it ends up about the same.

4. I've seem some people say those spikes on the dyno are due to predetonation and spark retard by the knock sensor. Did you notice anything like that?

5. The flashing lights sounds like "failsafe mode" which I've seen mentioned quite a bit, but I'm not sure exactly what causes it or how to stop it. My understanding is that it occurs when the ECU encounters a state that it doesn't understand, and will therefore default to a fuel mapping that is very conservative in order to prevent engine damage.

The design looks WAY cool though! Hopefully you can get the testing sorted out and determine if this mod really helped or not.

Either way, looks great!

-D'oh!

 

Have you done anything yet to give it more air? My understanding would be that less restrictive exhaust isn't going to be complete without more (or cooler) intake air. Maybe an Injen CAI would finish the package. I don't know if he's posted photos, but you should see the setup Thom Cameron has on his, with the Injen and a pair of straight pipes. Pretty sweet look and sound. I'll ask him Thursday at the Group Z meeting if he's done a dyno run. But your setup looks nice. Thom's is kinda odd, with the tips exiting at about a 45 degree angle. You'd have to ask him who did it. Personally, I prefer a stock look as well. That's why I put the HKS sport on my Z32-If you didn't know better, you'd think it was stock. But for those in the know....

 

It appears to me that the pipes are not mandrel bent, with areas of restrictions. I am not sure if this would cause that much of an HP loss, but it's plausible. Also, did you use the same diameters that Top Secret used? I believe it was 60mm x 2 by 80mm.

 

Try to address some of the comments above based on what I understand of exhaust systems (I am no expert, just a backyard mechanic... so I may get corrected on a point or two...)

D'oh Question #1 - An X-Pipe is used to equalize backpressure on each cylinder bank. I know uneven back pressure can create a rough idle... I believe the problem is magnified as RPMs rise. With a well-tuned motor (such as that on a new car), an X-Pipe will likely only show minimal gains.

D'oh Question #3 - A 2 1/4" pipe should be sufficient for exhaust flow on the Z's stock configuration (2 1/4" is the size arcticfury stated his pipes were after the X-Pipe). If anything is done to boost motor output above stock (basically over 300hp), I'd personally look for at least a 2 1/2" pipe all the way back... maybe 2 3/4" for a BIG power gain.

D'oh Question #5 - Hmm.. if you are right about the lights and "failsafe" mode, then what Ares suggested is probably true. I bet the ECU took a dump and went to a default setting that is more conservative than stock. Result, lower HP & Torque figures. I bet with an ECU mod, arcticfury's set up will net him some HP gains...

fdao comment - This is one I don't know the specifics on, but not having Mandril bends probably does increase back pressure... may be contributing to the HP loss, but I think the ECU is the big culprit.

arctic fury - very nice looking set up! I like the effort put into the pipes just before the outlet... very professional! Keep us posted on future mods that help this set up work for you!

 

I love the setup! It is beautiful, however, like McDuck said, I don't think we are going to see any gains until the ecu upgrade is out. Bone stock I was at 242, then dropped 4 with an injen and exhaust, so it is possible that injen is correct and the intake adds 5, but that my exhaust is costing me about 10hp or more.

As for smoothing, they use 3 at my dyno place.

 

I like the idea, but there are few issues with implementation I see right away:

1. Bents are not mundrel. Descrease in diameter/change of profile are clearly seen on every bent.

2. X-pipe is quite far from cats.

3. Cheap MagnaFlow X-pipe use wich is quite restrictive.

I guess, you'll be better off with crossower like shown here

The idea is the less bents the less restrictive flow is. Currently you have one bent where stock Y connection was. Then you have one bent on the entering X-pipe, and one bent on exiting X-pipe.
In total that makes 3 bents per each side. Crossover like in the link above has only 1. By the way, 300zx use to have such a crossovers very often on custom dual exhausts.

4. Whole system has too many seams. I can imagine that disturb airflow quite a lot. expecially around X pipe.

5. I know it's not simple but if you can fit smaller mufflers along the way of pipes instead of 90 degrees, you can shorten the whole way, and make it less restrictive again. Probably you can try shorter mufflers, and then 2-in/2-out resonator in plase of old resonator.

6. Don't forget to spray seams with some ceramic silver paint. Joints give up to rust first since they steel structure modified and they are not stainless anymore.

Considering all above. I can see how your current setup flows can offset all the goods true dual can give.

And last thing. You did a big mistake for not going to dyno BEFORE installation. As it was agreed here before, all dynos are different, so the only menaingful data is the difference between before and after mod. So without knowing what dyno looked before on that particular machine, you can't say what you gained. And you can't compare it to any other dynos taken on different dynomometers.

At least know you have some base to see how new changes will affect your power.

 

...I agree. The only real way to see modification results is to have a baseline dyno before every mod....still, nice settup!!

 

Everyone thank you for your responses.

I know that this is not the absolute optimum solution. Mandrel bent would be preferred, except there is not a shop in Austin that can do true mandrel bends. I would also be interested to see if someone could provide some hard data regarding how much benefit mandrel bends would be on this setup.

The X-pipe is most definitely not as good as an X-pipe that is part of a mandrel bent stainless section of pipe. Again, we were working with what we could readily get. I understand the concept of the less bends the better, but you also have to make due with what the car gives ya. I guess I don't get the point about how the Corsa system uses less bends. If you look at the picture there are the same three bends, although nicer due to mandrel bending, but still three bends. As for nicer due to mandrel, see above.

This system will not be the end all, be all of exhausts on the Z33, but it will be a nice one for now.

As for the pre-dyno, I know, I know, I know. Truthfully, I really don't care about being able to say my exhaust system gave me X amount of power.

2003z,

I agree about the ECU. I know the IS300 guys started using S-AFCs and ITCs. I understand the concepts and use of these, but have never dealt with actually installing and using them.

mcduck,

Thanks for your help answering D'oh's questions.


I hesitated to post this system, because I knew that 90% of the responses would be "Well, it's ok, but you should have done mandrel bent." or "If you had done mandrel bent you would have gotten a gain." or more along those lines. But I decided that the other 10% made it worth posting.

Thanks again for all the comments,

JD