Diesel exhaust

Maisie · 19 Jun 2003, 11:45 (Ref:636501)

My camper van's just failed its MOT on the exhaust, which has finally given me a catalyst to go get a nice shiny stainless replacement. I've been given a quote of £200 for a Powerflow exhaust from Topgear in Burnley which I think is reasonable. Now, should I go for a slightly wider bore than standard? It's to go on a 2.0 Perkins Prima diesel engine, which is currently a little down on power to how it should be. Would a slightly tuned exhaust make much of a difference to a diesel?

garcon · 19 Jun 2003, 11:59 (Ref:636514)

Well it certainly won't make it any louder...

Bluebottle · 19 Jun 2003, 20:58 (Ref:636998)

Not sure, but I would say probably not. Not that I know.

woodyracing · 19 Jun 2003, 22:59 (Ref:637107)

MINE is a Powerflow exhaust from TopGear Burnley..
top place, top bloke, but boy is my exhaut LOUD.

i went for largest bore, straight through all the way etc.

Im not sure what it will be like with a diesel, but tbh i'll be glad to get rid of mine and escape an ear ache.

Performance wise, it will shift the powerband further up, meaning it will need more revs and might be slightly dosile at low revs but should be better higher up.

my mate also had a Powerflow exhaust fitted, it sounded nice but it spoiled the sound of his expensive music system.

Tristan · 19 Jun 2003, 23:46 (Ref:637142)

Now here's a related question that I've always wanted to know the answer for - not always but often, diesel exhausts droop downwards to the ground whereas petrol ones are always straight. Why do exhausts on diesels droop??

woodyracing · 20 Jun 2003, 01:49 (Ref:637184)

some petrols droop down too. like my new car.

GTV27 · 20 Jun 2003, 03:32 (Ref:637206)

is the engine a turbo diesel - in which case a less restrictive exhaust could be quite an advantage?

Maisie · 20 Jun 2003, 09:12 (Ref:637364)

Nope, not a turbo. I don't want anything massively overbore, or loud (as garcon says, the engine's loud enough, in a really endearing daggadaggadagga sort of way

), the main object is to look a little better against the paint job than the current rather sad and rusty effort! However, a little performance increase would be nice.

Warwick · 20 Jun 2003, 09:25 (Ref:637374)

Do it,due to the higher compression ratios in a diesel they actually have a larger volume of gas to shift a bigger bore exhaust will certainly give an increase in power,but don't go to large or it may make it drone a bit without putting a extra muffler in.

I went from a 2inch to a 2 1/2 inch on my 2.3 litre SD23 Nissan and got a definite boost in midrange,you can also buy Headers/extractors off the shelf for a lot of diesels and the exhaust guys tell me diesels show a bigger percentage gain in power than a equivalent size petrol with these mods,they also respond well do a large airbox especially if you can duct cold air into it.

Maisie · 20 Jun 2003, 09:30 (Ref:637380)

Cool, cheers

Right, I'll book the appointment to have it done and ask a little more about it when I get a minute today. Then I need to get the engine working properly, ie to get rid of whatever problem (compression?) is leaving it woefully down on power at the mo, and maybe get an uprated air filter.

Dave Brand · 20 Jun 2003, 16:19 (Ref:637763)

Quote:

Originally posted by Warwick
Do it,due to the higher compression ratios in a diesel they actually have a larger volume of gas to shift

Compression ratio has nothing to do with airflow requirements. The amount of air an engine can breathe is purely a function of the pressure difference between the cylinder & the air inlet. As this pressure difference is produced by the increase in cylinder volume during the induction stroke it's the same for any given swept volume irrespective of the thermodynamic cycle. Assuming an ideal Otto cycle, for a given engine speed a diesel will move just as much air a petrol engine; the difference is that, under low-load conditions the petrol engine will be throttled while the diesel is not.

The maximum airflow rate for a diesel will be significantly less than for a similar-sized petrol engine as, due to limitations of the combustion process, the maximum engine speed of a diesel is much lower than for a petrol engine.

Mattracer · 21 Jun 2003, 00:57 (Ref:638130)

Quote:

Originally posted by Tristan
Now here's a related question that I've always wanted to know the answer for - not always but often, diesel exhausts droop downwards to the ground whereas petrol ones are always straight. Why do exhausts on diesels droop??

Possibly to direct the gases away from the surrounding paint on bootlids and rear of the vehicle which stain and discolour the paintwork?

Warwick · 21 Jun 2003, 02:12 (Ref:638147)

Interesting Dave,wrong assumptions on my part,I was thinking of it as stuffing more air in a smaller space but its the same amount of air but compressing it more?

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