Straight Throu exhaust

Hi,

My exhaust has finally broken up on my series 2 SWB and I'm thinking of getting a straight throu stainless one made up at a local exhaust place.

It's fitted with a 2.8TD daihatsu engine and I was just wondering if I would have any problems with not enough back pressure using a straight throu pipe. Also I'm not sure what bore diameter to ask for as the current original landy pipe seems too small for the engine fitted.

Anyone got any advice?..

Cheers

Tim

i am presumming your gonna have to use the same bore as your manifold. ???
the result will end up a touch of bhp gain, maybe 3-4bhp and a loss in torque. choose you back box carefully and youll get it right.

wots all this bollacks about back pressure. a injun needs to breath as easily as possible so the less restrictions yer got the better.


them big folk orf dragsters that produce about 5 brazillion HP don't got no eggsauce therefore no back pressure and they seem to work quite well.


here's a cut n paste from another site ....

"Back pressure in the exhaust sense of the term, is usually termed as being a "bad thing" for performance; however, in the interest of reducing exhaust sound to levels allowable by public noise ordinances, back pressure can be regulated using systems from simple butterfly valves to fully computer controlled units sensing pressure in the exhaust pipe itself."

Comes down to each engine. I know people who have had big problems on turbo engines because exhaust wasn't giving enough back pressure. but then there are plenty of engines which run OK. Best way is find someone, somewhere that has already tried it on your engine.

It might sound pretty awful too without any silencers :\

it might be more because the engine isn't getting fuelled properly. if the injun is getting too much air then the backpressure will limited the amount of air coming in and push the fuel/ratio back to what it should be. without the backpressure the injun will run lean.

am sure if yer do a search on the net fer exhaust backpressure yule find more about it. what it boils down to is ..if yer injun is tuned fer backpressure then the lack of backpressure will cause problems in which case tune the folker without backpressure

here yer go save yer bother of searchin fer it

i was always under the impression that diesl endens are less tollerant for back pressure than petrol due to higher exhust tempreture of petrol and that could lead to burned ex valves same as running to lean

eh?

Thanks for all your advice guy's,

I think I understand now. So I'll get a straight throu exhaust then re-tune the engine to get the mixture right.

Cheers...

n/a........back pressure good thing,
Turbo, back pressure bad thing.

Raz you might be correct to a degree but many turbo engines will get boost creep without sufficient backpressure. As I say, I have no idea about the engine above and may not have this problem at all.

how can back pressure be good? yer want to get the burnt stuff out and new stuff in as quickly as possible, if yer got back pressure then yer int gonna achieve that.

I agree you don't want too much back pressure as that will restrict it, but the correct amount of back pressure (to the state of tune/ignition timing/etc) is what you want.

A big bore, short pipe, less mufflers etc, when past a certain point (for the tune/timing/etc) of the engine, doesn't necessarily mean a better flow of gases.


p.s when I am talking about back pressure...it is more to do with flow velocity rather than a "pressure" at a particular point...but I am guessing you are too?

yer want to get as much air in as possible so you can burn as much fuel as possible so therefore you don't want anything that will restrict that. once you have maximum air flow you can then tune yer injun to suit (course with all this new fangle lectronic injection thats all taken care of fer yer )but it dint alter the fact the more air you get in the more fuel you can burn and the more power you can produce.

all this talk of back pressure being good is bollocks, why do you think engine tuners stick big valves in and smooth out the manifolds etc?

its so you can get more air in. it defeats the object if you then restrict the exhaust side by applying backpressure to the outlet side of yer injun

heres a short snippet i found


The goal of performance exhaust headers is mainly to decrease flow resistance (also know as back pressure), and to increase the volumetric efficiency of an engine, resulting in a gain in power output. The processes occurring can be explained by the gas laws, specifically the ideal gas law and the combined gas law.

It is a common myth among drag racers and motor-enthusiasts that not enough back pressure in the exhaust will cause a loss of torque. This myth stems from the phenomena associated with exhaust scavenging. A diminished scavenging effect can result from lower velocity exhaust flow when using headers with large primary tubes. Most enthusiasts incorrectly conclude that their restrictive OEM exhaust provided more torque because of the back pressure it creates. The correct reason for the loss in torque is explained below.

and if yer still have doubts look here

these are feed throught yer exhaust boxes fer street use and opened up for racing. now why would that be except to get more power from the same injun set up

Your your snippet actually concludes what I am trying to say....read on if you so wish ....

yer want to get as much air in as possible so you can burn as much fuel as possible so therefore you don't want anything that will restrict that

Click to expand...

Of course because at the end of the day it's a combustion engine burning air and fuel. But it is only up to a point of what the engine, management, etc etc can take.

Can't quite describe what I am trying to put across. Back pressure itself is not needed...infact you wan't low back pressure. However... what many people mean by back pressure is how free-flowing the exhaust is...and this is the tract that I am going down. A bigger bore/shorter/straighter/un-muffled exhaust doesn't necessarily mean that the gases will get out of it quicker. Of course it could improve performance, up to a certain point, but if you go too big bore etc for your state of tune it will impede performance....

Why? Well....

Ignore backpressure for a minute...as we know that isn't what we are really talking about....The ideal exhaust system will have a high gas flow but maintaining the ability for a vacuum to develop behind the closed exhaust valve (or the "scavenging" effect, as you pasted above). If your system is too big bore/free flowing/short/etc for the timing/tune/etc for your engine, the flow will be be slower and the scavenging not as good. Does that make sense?

I understand where you are going about the drag cars running no exhaust, just headers, and that link for the cut off device etc...but these are designed for cars with a huge amount of gas flow....so they don't need suffer with the normally associated problems. And infact, people running these drag cars dont just get the biggest headers they can get (which would back up the bigger bore the better arguement)...it all gets matched to the engine.

As for the application on the TD engine above...being a turbo the effect of having a bigger bore/free flowing/etc exhaust wont be as great when compared to a NA engine because turbo engines have a lot more gas flow than a NA engine and as suggested adjusting the fuel mixture could probably sort it, if that is needed at all (and maybe not at all if he is not going to a big bore). If it is only a tiny turbo on the engine then you may need to do more to make it run right, because you will have less gas flow.

It's fitted with a 2.8TD daihatsu engine and I was just wondering if I would have any problems with not enough back pressure using a straight throu pipe. Also I'm not sure what bore diameter to ask for as the current original landy pipe seems too small for the engine fitted.

Click to expand...

Would be useful for you to know what the 2.8TD is fitted with as standard - perhaps go and measure one subtly in a supermarket car park!

slob said:

yer want to get as much air in as possible so you can burn as much fuel as possible so therefore you don't want anything that will restrict that. once you have maximum air flow you can then tune yer injun to suit (course with all this new fangle lectronic injection thats all taken care of fer yer )but it dint alter the fact the more air you get in the more fuel you can burn and the more power you can produce.

all this talk of back pressure being good is bollocks, why do you think engine tuners stick big valves in and smooth out the manifolds etc?

its so you can get more air in. it defeats the object if you then restrict the exhaust side by applying backpressure to the outlet side of yer injun

Click to expand...

thank you slob. i did mention the manifold is where yer wanna start but no one seems to wanna listen.

ah think we've agreed back pressure is bollocks and yer need to 'tune' yer eggsauce as much as you need to tune the rest of the airflow.

ah mean if backpressure wur good then supercharging would not be good as that raises yer intake and cylinder pressure and would negate any back pressure yer had in yer eggsauce.

yer need free flowing exhaust and as yer man says if yer can get a vacccccummmmmmm behind the valves so much the better