Performance rear silencer on a B14 engine

[kesk]

Hi,

I would like to get an optically and sound enhancement (I don't expect a power gain) with a cool rear silencer from Remus or Sebring (I would fit an universal one). But I'm worrying about the back-pressure. Would it be OK if I keep all the other exhaust parts and just replace the rear silencer?

I'm also thinking to purchase the K&N RC-9000 air filter (http://www.knfilters.com/search/product ... od=RC-9000). It looks very cool. But I don't want to mess up the air / fuel mixture.

My 340 GL has a B14.4E engine and a Weber 32 Dir 104-100 carb.

What do you think?

Please excuse my lack of knowledge. I'm a newbie.

I hope you could understand what I mean. Sorry but my English is awful, I'm trying to get better.

[Jason B]

Dont worry about being a noob, we are gentle here!!

Feel free to stick a backbox on (and induction kit) if you are not expecting power gains and just want some sound as nothing bad can happen (except if you do fit an induction kit then the carb could ice if its very cold - but thats just annoying not bad for the car).

A little background knowledge about exhausts to sort out some silly rumours that exist about them. In an average car the engine will not care about anything past the manifold/downpipe as long as it does not seriously restrict flow and isn't so comcally oversized that gas will stall/turn around in the pipe. A common misconception is the need for backpressure, which is rubbish! the whole point is to get gas out of the car as effectively as possible! it is best to have an exhaust from downpipe/manifold back which can flow as much as the manifold will give it. Only on extremely high spec racing cars is an entire exhaust perfectly tuned to an engine as they use carefully chosen pipe lengths and diameters to give desired modes within the pipes which promote a "scavenging" effect to help pull gas out of the cylinders. On a standard car it is just the manifold that is tuned to help a bit in this department. - in summary a good exhaust is one that is big enough to flow what the manifold gives it and as straight as possible to keep velocity profile nice

you may find that by fitting a backbox to a volvo that you do get a little more (probably unnoticeable) power, as 300's have pretty poor exhaust design.

[classicswede]

Jason, (sorry to pick on you again)

I do have to point out that on a n/a engine back pressure as such is not a myth. If you romove the front pipe off the down pipe on a mini it will hardly drive! There are modern cars now that use variable exhausts to improve low down power and keep good top end. The optimum exhaust for an exgine will vary with RPM (gas flow). Exhaust flow is a fairly complex thing and is normaly a case of settling on a balnce between low down and top end (does not apply to turbo engines so much)

Just changing the back box will not creat a problem. Stick to one with about a 2" (50mm) bore size and you will be fine

Asuming the air is fairly warm where you are carb freezing should not be a problem so the K&N should be ok.

[mac]

Afternoon all,

Must confess Jason I heard my high horse trotting up when you started to talk about the need for back pressure being rubbish - then you went and spoilt it all by clarifying what you said (back pressure is rather important - just not in a B14 exhaust system) Actually as Dai says it's quite important on some cars and in this age of "efficiency and low emissions" back pulse cylinder scavenging is part of the overall design. On an old 340 - narh! - matters not a jot!. You're quite correct though - bolting a dustbin sized pipe on the back is a wonderfull way of loosing power (as you say - promotes stalling of the gas flow).

Will just take slight issue over carb icing though - Dai is correct that it is less likely at higher temperatures - but far more important is the moisture content of the air! Dai and Jason will know this but icing can occur at up to 9 or 10deg. (in some circumstances higher) and is caused by the drop in air temp. caused as it expands beyond the venturii in the carb (low pessure zone created also draws fuel from the jets and "makes the carb work") The same principle is used in fridges/air con etc.. The air can easily fall below -1deg. causing water from the air to build up,as ice, in the ventui throat -
restricting it, causing greater suction, more cross venturi expansion and more freezing. The engine runs badly and often stops due to in part reduced air flow BUT mainly due to grossly overrich mixture caused by the greater low pressure pulling more fuel from the carb jets (far too much for the reduced flow).

It's this overfuelling that is my "slight issue" - under "normal" circumstances you just get a car that runs badly (switch off, wait for ice to melt, and all is tickety boo again) But (at least) in the UK some '90' and all '91' models were fitted with two way catalytic converters and they are every bit as sensitive to excess hydrocarbons (excess temps due to both "physical" as well as chemical combustion causing structural failure of the ceramic matric - metallic matrix was well in the future). Persistent carb icing will kill cats!

Mac.

[Jason B]

don't worry, I didn't dismiss pressure balance within exhausts completely - I just simplified by saying that in a normal car the engine usually only "sees" the manifold (and possibly downpipe depending on design), after that an exhaust won't make too much difference as long as it is not so large that flow stalls occur (as I mentioned in the post), or that it is much too small.

I still maintain the idea that it is primarily the manifold that controls pulse tuned scavenging effect within standard (not formula 1 etc) exhaust systems. This is because on an extremely basic model the point of convergence of all cylinders can be viewed as a semi-rigid boundary hence a reflected wave will pass from this boundary back to the cylinder port. (and ideally create a rarefaction at the precise moment of exhaust valve open) In reality this problem is hugely multifaceted, as amongst lots of other principles, directionality effects exist that promote different reflections dependant on which cylinder the pulse originated and the number of converging flows at a junction. People seldom understand that the importance of backpressure is largely to alter the speed of sound within the gas flow at a given operating temperature, not just as a simple requirement for pressure within an exhaust!

For a basic exhaust alteration I would be more concerned with creating smooth pipework to reduce pressure losses between transitions i.e. avoid sudden expansions as huge pressure loss occurs, and avoid sudden contractions as a vena contracta will squeeze the velocity profile making the flow very inefficient.

All that I have mentioned is largely simplification of a much bigger picture but you get the idea.

[xtrmjks]

Simons (jetex) boxes are good value and good performance..and made in Sweden!!

[Ronnie]

Once drove a Volvo 240 GLT coast to coast across Scotland with nothing connected beyond the down pipe - lots of backfire, lots of noise, not much power

[kesk]

Hi and thank you all,

I'm driving the last 4-5 years without the automatic winter/summer regulation. I don't have the air-pipe from the manifold to the air-filter housing, and my carb did never ice. And the RC-9000 is placed directly on the carb, so the air should be heated a tad with the radiator.

Some time ago I have lost my whole exhaust (from behind the downpipe) on the road (in the middle of nowhere), I have driven this way about 100 km, and haven't noticed any difference in engine power or temperature (but the sound was great ). But that was only 100km.

I will do some experimenting about this all, and I will keep an eye on the engine temperature and fuel consumption.

I don't risk too much, I have a big collection of spare parts, also a spare B14.4E engine.

I have also a carb from a yugo (zastava) converted for the B14 engine, the guy who sold it to me said that the car with this carb consumes fuel just like a cigarette lighter. I haven't tried it.

@xtrmjks

Thank you for the tip! I like this one (but it has a bore size of 63 mm), ebay link

[jtbo]

Icing can cause also some smaller problems, bigger fuel consumption, lack of power for example and it can be pretty hard to find out it is icing that does that.

But probably you will have no trouble.

With K&N + little better flowing exhaust it can be that car runs tad leaner mixture, which may result unwanted kangaroo effect when returning to throttle after engine braking for example.

Remember that renix adjust ignition advance by vacuum and amount of vacuum at certain driving situation can be then different resulting bit different advance. With carbs, such small changes seem to cause sometimes quite lot of gray hairs I have found out.

But certainly nothing too great trouble and if there is something bad things, you can always revert back to originals

[littlered]

sowhere could someone purchase a new sportier back box please?

[volvodspec]

ebay, universal sport exhaust.

this one cost me €75 and is a full stainless steel quality exhaust. had to make myself a piece to make the 60mm entry of the sportsilencer to fit on top of the std 340 exhaust, and this was the result of an easy afternoonz work:




this car is a '89er. it has a b14.4e but comes with a catalyist, this will make the exhaust sound fully open! it was cool but it also got me to be big friends with the police..

that's why i had to weld an extra 340 mid-silincer just behind the catalyst:


no noticable powergain, but it sounds just right at the moment. non-stock but not too loud:)