parkertseng

The exhaust was provided from a company base in Netherlands.
Owner asked me they have a new design and see if I want to try it for my stock 3.6 engine.
Didn't realize the length, sizing and matching until the 3.8 upgrade.
It seems my headers longer than most of other provider.
But isn't long header will provide less back pressure and good rpm?
Could it be size of tubing after the collector is too small, too long, too restrictive and too much bend?
Thanks

-nick

Typically longer primaries increase torque. Stock exhaust piping is 2.75”. Your 2.5” might choke upper rpm power if anything. None of this accounts for the torque dip.

No point in speculating without wideband o2 info. I believe that’s where you’ll find your answer.

Welding that octopus is impressive!

jonathant

Re the exhaust design, and taking a few flyers here but: it *looks* like the cat bypass (straight pipe) is too small. Normally once the individual headers come together at a collector, that collector pipe is larger. Not massively larger, since you want to help extraction, but also need to account for gas expansion. That larger size then carries through the muffler(s).
I would have moved the primary mufflers (your small ones) into the place where the cats would be, then dumped them together into a center secondary muffler that could also serve as the Y, with a dual outlet. That would cut some overall length, and more or less parallel the 993 design, but with long tube headers (and the Y collection much later in the flow; 993 does this just before the cat).

The whole thing is a resonant system though, with various parts driving each other, so it’s not easy to sort. Thus my earlier black art comment.

parkertseng

Thanks,
That is one of the option on table at moment.
To fabricate two silencer each side after the collectors with either 3 or 3.5 inch pipe and then to join together at the rear bumper for a single outlet design.
Local work shop suggested to 3 inch piping after the collector.
It seems my piping is either 2 or 2.5 inch, by looking at the picture the exhaust tip is 3 inch(took the measure yesterday), and the piping before looks like 2.5 till after the two primary silencer and 2 inch from primary to the collector.
So wondering would 3.5 pipe too large
My tuner said there is a section of low end rpm that the engine couldn’t suck enough air with some felt startle when on full or large gas pedal
input, so he adjusted to make it leaner and the startle becomes less.

I speculation is the exhaust piping is too small restrictive to deteriorate the scavenging effect which needed for the my high lift and duration cam?

Does it sound reasonable?

thanks

jonathant

Sounds reasonable to me, but I’m not doing any math over here, so don’t make any big bets. 😀 best starting place is your tuner, a dyno, and the air-fuel mix. Seems like he’s on the right track.

BLACK3.2

it sounds reasonable but to avoid any guesswork I worked consult an experienced exhaust fabricator who knows these engines and can work with your tuner.

what does the manufacturer of this fancy exhaust have to say about your odd results?

ras62

Something wrong with those curves. You normally bhp and torque cross over at 5250 rpm. As for the drop off in torque that is most likely due to ITB setup and imbalance between cams/exhaust gas flow through the heads. Its a complicated subject where engine builder experience is key

parkertseng

-nick

These maps are unusual in so many ways. I won’t second-guess your tuner, but I would be asking a lot of questions-

#1 Ignition is drastically pulled back from stock. At 100% throttle, stock is ~25° by 3500rpm then settling down to ~15° after 4500rpm. Your map shows 16° in the 3500rpm range. At 2000rpm your timing is pulled by ~5° from stock. Where did this timing map come from? Timing issues will destroy a motor fast.

#2 Why the extreme change in volumetric efficiency (assuming fuel map is VE) between 2500-3300rpm? That map isn’t based in reality.

#3 The dyno lambda is definitely showing too rich. It looks like rich misfire starting at 2250rpm but the timing and fuel are so far off that who knows what is happening. At 75% throttle it is wildly rich from 3k-6750rpm.

#4 Why was the dyno run at <75% throttle? Was this on purpose to map that range? It’s usually best to map 100% throttle then work backwards- unless the maps are so far off that you’ll damage the engine at 100% throttle.

That’s just the most obvious bits. It looks setup for 100% tps / alpha-n which is a debatable for partial-throttle in a street car.

Wish you were closer, it wouldn’t take much to get you 80% of the way with just common-sense tuning without a dyno. I’d do it just for a good taco & tequila dinner. These maps look post-tequila rather than pre-tequila