Exhaust performance

[sheerwater]

Sorry to butt in on the performance boys but maybe somebody can give me advice on my exhaust. 1997 940 estate b230ft engine.
I had an exhaust fitted under warranty at my dealer. They stated that it was the third attempt to get an exhaust that would fit but Volvo had assured them that it was the correct one. You dont take much notice of exhausts really but what was noticeable was that the tailpipe was much smaller bore ????? Funny I thought as Volvo kits come as an out of the box as a bolt and fix kit made for the job. So why the small tail pipe.
Measuring the exhaust starting at the turbo which is the original 3"
through the cat the pipe then starts to get smaller down to 6cm then it goes through the first box. It then flattens and ends up 6.5 cm wide and 4cm deep before reverting to 5.5cm . The tail pipe ends as a 5cm. Now looking at this from a laymans point of view having a large turbo outlet pipe of say 7cm gives a cross section of 36 sq cm. If the pipe narrows to 5.5 cm the cross section is 24 sq cm and then to a tail pipe of 20sq cm. I would consider that the flattened section is probably less than this. Now I know exhausts are not perfect having to change through joints,bends,boxes etc but if the engine needs a 7cm tube out of the turbo why narrow it down to 5cm at the end of the system? Has anyone any comments to help on this one from experience.Much appreciated. Nigel ps all dimensions approx

[Peter Milnes]

You have probably been given parts from a 440/460 exhaust which is approximately the dimension you have given for the tailpipe. The exhaust should be at least 2.5 inches (6.35cms) diameter at the tailpipe for your engine. This is why I replaced my exhaust with a tailor-made stainless steel version which uses free-flow silencer boxes. Your restriction will come mainly from the Catalytic converter which is the first box from the turbo. If this is faulty from new or of the wrong size it will impose a lot of restriction on the exhaust gas flow. All parts of the exhaust should carry the Volvo stamp and IIRC for your year should be of stainless steel in any case (including the catalyser). If the dealer is up to the mark he should have no difficulty in obtaining the correct fittings and parts for your car. OK mine is diesel but has the same size engine (give or take a gnat's ****) but the exhaust is 3 inches diameter all the way through. They all will have the flattened bit which goes under a chassis member at that point.

All the best, Peter.

[tonyflynn1]

Approximateley what are the tolerances of the gnats appendage Peter?!!?

[sheerwater]

Thanks Peter,
Just gives me more ammo against the dealer with other arguements I already have. I was rather surprised at the tiny replacement exhaust and to be honest the performance seems to be slightly lacking which cold(or of course could not) be as a result of a smaller diameter exhaust. I just wonder how many other cars are running around with bits that could be bodged to make the car run as opposed to the exact specifications. Really makes a mockery of using a franchise dealer!!!
Nuff said. Cheers Nigel

But seriously -- the reduced exhaust diameter will **** up performance. The back-pressure it will certainly be reducing boost pressure and could also overheat the catalyst.

Go get 'em!

[foggyjames]

My dad also has a 97 940 LPT, and the exhast system is (i would guess 2.5") throughout. its one of those wierd things like loudspeakers - they never quite see to be the diameter they claim to be.

Also the exhast manifold is quite thick - do they measure the inside or the outside?

anyway, his is certainly a big(ish)-bore system, and its the factory on, so if you want me to measure it, i can!

cheers

james

[sheerwater]

It would be appreciated if you could measure it , externally of course. I think that starting at 7cm or so and ending at 5cm is kind of crazy especially when you consider the back pressure this creates at the end of the system. A blip in the middle in hydraulic systems where a tube is slightly constricted speeds up the fluid at that point and then it settles back down. A restriction at the end causes back pressure throughout the system. Cheers Nigel. PS I read an article in the Volvo Mag recently about the importance of freeflow but also some back pressure is essential to make some engines run.

[foggyjames]

I probably cant measure it till the weekend, as dad is out, and by the time he is home, its dark! But I will do...!

2 stroke engines lose power without back pressure - im no expert, but i believe that the pressure helps make up for the lack of the other two strokes :) We had a great time ripping it out of a mate who removed the silencer on his scooter, thinking it would sound really good...except he couldnt get it above 23mph then :)

cheers

james

[foggyjames]

just thought of something...i remember noticing that standard B230 740s have much smaller tail pipes...maybe there was a mix-up?

james

[sheerwater]

Its a long story in a catalogue of, well F*** ups and failures. Currently awaiting promised phonecall from dealer which was ''I'll sort things out and get back to you maybe tonight or tomorrow'' Well that was 2 weeks ago. I have the LEMON. Interesting about the turbo being affected. Just had the master clutch cyl fail. This was a failing on earlier turbos until they fitted heat guards but of course if excessive heat is being created in the turbo area by the blockage then a heat shield will only have a partial effect. Ive had more problems on this 940 in 60k miles than I had in my old 740 which is now 15yrs old with 168K on the road and it had a really hard life being thrashed fully loaded for most of its life. (and it still purrs like a good un) Cheers Nigel

PS my email is sheerwater@ntlworld.com for direct contact