Improved TOP-END w/ 2.5" section on 3" system PICS

[astro49]

Cut off a 1 foot section from the end (tip) of my 3" exhaust pipe and replaced this also with a 1 foot long 2 1/2" pipe. Top end Power has now improved by at around 15%!!

Accelerating from 120kph going up to 145kph is now a breeze unlike with the all the way 3" pipe, 120 to 140 was a slow slow drag! And low end engine responsiveness has also improved!!

Now I'm really happy with the outcome of this combo pipe ;D Can't wait to go up the mountains this Monday

Btw.. fuel consumption has increased! but this is mainly because the MU now is so fun to drive that my foot is always mashing the gas pedal ;D


Here was my evaluation when I had the 3" pipe installed (posted on another exhaust mod thread)

To continue my evaluation of the newly installed 3" pipe (all the way to the tip starting after the dump pipe):
1. Improved low to mid end torque. This is noticeable on uphills. I now seldom downshift to from D to 2 (automatic transmission).
2. Degraded top end. With the stock pipe and muffler, I could go gradually speed up to 140 kph. Now with the 3", from 120 to 140 kph takes quite a long time.
Note: I've already increased turbo boost and mixture even while using the stock exhaust pipes and muffler. These settings were untouched after the 3" pipe install.
3. No noticeable improvement in fuel economy though I would say there even was a slight increase in consumption. This is driving on 60% unpaved mountain roads and 40% paved

I think a 2.5" would be the best and the 3" an overkill (for a low reving 2.8 diesel). What I plan now is to cut the end of the tip a approximately 12" and have a 2 1/2 in. pipe as the tip to restrict the exhaust a bit. This might solve the top end problem.

Just a personal experience and my 2 cents......







Fujisuba 3" straight through muffler and LSD diff






Steel braided brake line and Load Master helper leaf spring

[dasnoboarder]

Sounds like you've found the magic combo...

So for when I get around to doing mine, the best plan is:
3" dump pipe
3" mandrel bent exhaust
One straight through muffler
Going into tail section of 2.5"?

Is that your exact system (except dump pipe)?

What does it sound like?

[Graham]

The 2.5" tip might have a logical explanation - as the exhaust gas gets to the end of the exhaust, it has cooled and therefore contracted, taking up less volume. Since the pipe is the same size, but there is less gas, it moves more slowly. By reducing the size of the pipe, the exhaust gas might be moving faster, and provide a better tuned exhaust system.

I wouldn't think that it would be as noticeable as you report, but maybe your exhaust just hit the perfect harmonic balance to become one big extractor

[astro49]

dasnoboarder
Yes that's exactly what my setup is except for dump pipe which is still original. In addtion, my injection pump's mixture was also richened (even before the exhaust upgrade) and its timing is I guess now too advanced (due to maybe an assembly error when I had its timing belt replaced).

The exhaust now roars quite a bit but though not annoying loud. But what's weird is that everytime I'm accelerating, then suddenly release the gas pedal, there this quite loud and low pitched whistle that eminates also from the exhaust tip. I'm guessing its must be coming from the turbo. Its a sound much louder than a turbo whine while accelerating.

Graham
Thanks from your explanation! You are right it wouldnt be as noticeable improvement IF we're talking top end power, which could effectively mean my MU could already hit 160-170 kph. What I actually meant (sorry and please let me correct my initial observation) was a more or less 15% improvement accelerating to Top End speed. As compared to the 3" all the way pipe which verrry slowwly accelerated from 120-140 kph, as to now with the 2.5" tip it accelerated steadily and swiftly to 140 (though I'm quite sure it could still hit 150 but twas already quite scary since there was already some front end vibration, more than likely because of my unbalanced tires).

[geeves]

What is that device on your spare tyre?

[astro49]

Hi geeves!

Those are traction clamp ons by Bridgestone. You can see them in detail here
clubisuzu.proboards29.com/index.cgi?board=Other&action=display&thread=1157253357