BXProject

[Vanny]

Erm, wait, am i missing something? For a 2litre 4 cylinder petrol engine the theoretical length of the exhaust should be around 1metre (based on the inlet track, cylinder displacement, number of valves etc) in order to harness Ricardos' wave principle, so you need soemthing to create the back pressure at that point (hence the resonator on the 16v). Surely the same basics apply to the diesel, if perhpas with a different distance, so removing the cross box restiction might make the turbo spool a little quicker (or adjust the waste gate FFS) but result in reduced torque around 2000rpm.

Strikes me that you want a fat pipe with calculated exhaust restrictor and side exit? Or better still, sod the diesel off and get a valver? I think what you do to the air intake will have a much greater impact!

Super charge a TZD mmm....

[Philhod]

Correct me by all means but I always understood that all experimentation using this theorem was on petrol engines only.
Because of the relatively low compression ratio's, it was used by honda, I believe, to look at fuel/air flow characteristics (rich/lean areas near the plug) and the effects on breathing of EGR valves, CAT systems and other fuel reducing and CO2 reducing measures.

The flow plan of Diesels, because of their much higher compression ratio's and very much higher fuel inlet pressure are far less affected by these measures and I have not seen any data as to Ricardo, but Bolinder did experiments on the different characteristics of diesel gas flow when the 2 stroke diesel was being developed in the 1930's

So, don't get a smelly inefficient petrol car, stick with the one that works better and is still being developed.

[Bx Bandit]

Certainly with turbo cars (in general) to get the best out of the turbo then the back pressure should be considerably less than on an N/A car.

I wouldn't know if it would be at the cost of torque circa 2000 rpm but I'd of expected the turbo to of compensated by then - that being based on more modern TDs using faster spooling turbos than the TZD....can you feel the turbo coming in at 2000 on the focus Vanny? I can't remember the Xantia that well tbh.

Interestingly, when I was driving around with no exhaust on at all on the XM, whilst I'm pretty sure the turbo did spool up faster, it certainly ran out of puff faster - it has a noticeably longer pull with the exhaust back on.

It's worth having a play with both air box and devil pipe I'd of thought.The other thing I can think of about this wots-his-name wave principle is petrol aside, does it have a relationship to RPM - diesel obviously revving much slower????

[Philhod]

It doesn't matter Bandit, From what I can remember of the paper on Honda's results, they did their testing at a steady 2000 revs to achieve best results over a measured flow. It was a Microcassegrain sensor they used for minute observation and according to their findings around that rev point gave readings that were compatible across the rev range.
The need for back pressure in a petrol engine, is to help equalise cylinder pressures and therefore maximise efficiency of each cylinder.
Diesels by virtue of their operation do not need back pressure as each cylinder is working well above the pressure that could be affected by this.
In terms of efficiency (ie extracting power from fuel used) Diesels are approximately 120% more efficient than petrol.

I notice that the 19 turbo Xant was crap around town, really sluggish till it could open up.
My BX would run rings round the Xant in traffic.

[mat_the_cat]

Interesting. I suspected it felt quicker to spool up, but that may have been due to the fact I'd just spent an hour welding up a different exhaust system and hence wanted to experience some reward for my hard work! Be interesting to see whether I notice any difference going back to the standard system.

[docchevron132]

There's no doubt the diesel in turbo form spools up quicker, and has more grunt minus the cross box, dad's car is much sprightlier across the rev range with the devil pipe.

[Philhod]

There is another set of data that works out the optimum length for an exhaust. It gives the right size of silencer to baffle down the slower gas as well.

I'll have a look round to see if I can find it.