Gained 11hp after the work was done. Also gained 4mpg in use afterwards. Torque was increased below 1500rpm by nearly 40lb-ft. Yes, 40lb-ft! That's on a 2003 Astra 2.0DTi.

Funny results those.

You gained 40lb.ft-in an area where the turbo is virtually inoperative-without increasing the fuelling?? riiiight

but you only gained 11hp? Well 40lb.ft@1500 RPM gives you your 11hp.

But since any back pressure problem gets worse as air flow increases, any credible results would show a trivial gain at low speed, which gradually got larger as RPM increased.

The dyno operator(s) pulled a fast one on you mate.

I did say that EGR delete would yield a small gain in economy.

However, OP's engine is an n/a IDI diesel. Unlike dI engines, IDI's breathe very well on the intake side. The exhaust side is totally irrelevant, since the only major restriction is the early closing valve. Which nothing can be done since the valve would kiss the piston.

The engine is gutless because it is naturally aspirated. It was offered as a cheap alternative to the HDi engine. Simple as that.

Edited by unthrottled on 19/01/2012 at 16:36

People will believe what they want to believe-even if that means thinking that the people who designed the engine were idiots.

Aftermarket companies make lots of money selling shiny induction kits (cones on sticks) and big f***y exhausts. Gullible drivers equate noise with power.

The back pressure 'problem' is always at the top end of the exhaust system ie across the valve, through the port and manifold.

Downstream of that, the problem is normally quite trivial. That is why engine designers are happy to have an exhaust full of bends-because it makes very little difference.

Take a reality check: A 3" exhaust pipe costs no more than a 2" one-so if there was a back pressure problem, they'd just put a bigger exhaust on!

71hp isn't bad for a 1.9 n/a diesel. VW only got 67 from their SDI. However, An IDI can make a bit more power than a DI engine, so try turning up the pump a bit. You might get 80hp before the smoke becomes unacceptable.

Bolt on bits rarely give much extra top end power and more often than not rob you of mid range power and thus torque where you need it most. Manufacturers have huge R & D departments that spend millions trying to beat or even match the oposition, why not sack all the people and go to Halfreuds or Demon Thieves and buy a few bolt on goodies just like Lada did in the 70's and 80's.

I'm sure. But I imagine that understandably Citroen probably didn't throw much time and energy at getting the most out of a NI diesel engine when they also had an HDi to sell.

There is a logic behind my questions.

No. Because the engine was at the end of its life. It had already had much time and money thrown at it-and it had reached the end of its useful life. In its day the XUD was at the top of the field in terms of naturally aspirated diesels.

That is a b***** good point, cheers! You're right.

I wasn't arguing, just wanted to get more than the usual 'why bother' answers, I just wanted to optimise what's there, not race tune it :-D