Bongo Fury

rustyp wrote:

Fuel/air ratio isn't at all critical on diesel until you get too rich.


Fuel/air ratio on a diesel is what determines your speed.

No fuel = stopped
more fuel = more revs = faster.

The air inlet is wide open all the time as there is no butterfly valve as on a petrol and all you do to go faster is add more fuel and add it at the right time. Add too much at the wrong time or without enough oxygen (not enough air) and all you get is black smoke.

More air (or cooler, denser air and thus more oxygen) allows you to burn more fuel to produce more power

Much better put than I did, I meant not critical compared to a petrol engine.

Getting more air into the engine means better and more complete combustion/better efficiency/potentially more power. More air and fuel = more power.

I don't think there would be much to show on a dyno simply changing the gasket, comparable to removing the EGR or adding a K&N filter, perhaps a little noticable difference, but when combined should make a difference.

scanner wrote:

rustyp wrote:Fuel/air ratio isn't at all critical on diesel until you get too rich.

Fuel/air ratio on a diesel is what determines your speed.

No fuel = stopped
more fuel = more revs = faster.

The air inlet is wide open all the time as there is no butterfly valve as on a petrol and all you do to go faster is add more fuel and add it at the right time. Add too much at the wrong time or without enough oxygen (not enough air) and all you get is black smoke.

More air (or cooler, denser air and thus more oxygen) allows you to burn more fuel to produce more power

..and I imagine the volume of air going through the engine increases with rpm, and the volume of fuel is increased to maintain efficient combustion. I understand that too rich is pointless, but is too weak dangerous, or just a missed opportunity for density of energy release?

mikeonb4c wrote: ..and I imagine the volume of air going through the engine increases with rpm, and the volume of fuel is increased to maintain efficient combustion. I understand that too rich is pointless, but is too weak dangerous, or just a missed opportunity for density of energy release?

It is quite difficult to get ones head around diesels as it is the opposite in some respects of petrol engines ie. when diesel engines run lean (less fuel to air ratio) the combustion is cooler, diesels can't run at less than 50:1 (50 parts air to 1 part diesel at tickover) when the fuel is increased more heat is added to the combustion but as diesel is very slow burning and has rather large molecules rich mixtures 22:1 or 20:1 or more smoke is created as there are still unburnt diesel particles which carry on burning long after the main combustion has taken place causing issues with heat than can melt turbos/warp manifolds etc.

http://www.amazon.co.uk/High-Performanc ... 303&sr=1-1 is a good book to read to get a good grounding although it is mostly about modern direct injection yank behemoths!

As my Bongo is my everyday driver I am more interested in better fuel efficiency/increasing torque rather than outright power. I am aiming for more cooler/denser air entering the engine increasing the volumetric efficiency and obtaining a better more complete combustion.

Northern Bongolow mention earlier about removing the crankcase breather from the air intake and venting the breather to the atmosphere to stop hot oily vapours going into the engine. I am a bit undecided on this as the vapours are basically oily burnt exhaust gases which unless vented well away from the cabin could potentially be breathed in having had a warped exhaust manifold and running veg oil it could be smelt from the drivers seat with the windows shut! I have been looking into an oil catch tank/seperator for the breather which then goes into the intake. Not ideal but I do spend a lot of time in traffic grrrr! Also some engines does need the gasses sucked out of them. There is a way of connecting the breather to the exhaust and using a venturi setup to suck the gasses out into the exhaust!

I hope we haven't sent some of the other members off to sleep!

mikeonb4c wrote:

scanner wrote:

rustyp wrote:Fuel/air ratio isn't at all critical on diesel until you get too rich.

Fuel/air ratio on a diesel is what determines your speed.

No fuel = stopped
more fuel = more revs = faster.

The air inlet is wide open all the time as there is no butterfly valve as on a petrol and all you do to go faster is add more fuel and add it at the right time. Add too much at the wrong time or without enough oxygen (not enough air) and all you get is black smoke.

More air (or cooler, denser air and thus more oxygen) allows you to burn more fuel to produce more power

..and I imagine the volume of air going through the engine increases with rpm, and the volume of fuel is increased to maintain efficient combustion. I understand that too rich is pointless, but is too weak dangerous, or just a missed opportunity for density of energy release?

The volume of air (per induction stroke) would be constant if there were no turbocharging as each piston would suck in the exact volume of it's cylinder on each stroke - a diesel inlet is completely open at all times as there is no butterfly valve.

Turbocharging simply increases the amount of air (and thus oxygen) that can be drawn in on each stroke by increasing the "pressure" of the atmosphere.

Anything that helps the engine draw in as much air (and oxygen) as easily as possible, enables more fuel to be usefully burned and thus release more power.

Just pumping in more fuel without enough oxygen to allow it to be burnt = black smoke.

Diesels are "lean burn" engines by their very nature and there is no such thing as "too weak" only "stopped".

someone i know has the oil catch tank set up on a 2 year old replacement headed bongo, there is never any oil caught, possibly as the valve stem seals are good, but the bottom end is 15 years old.
the test was done on mine to atmosphere to aid the input of cooler air. if its drawing just a small amount of crank case hot air that must be bad.
i accept what you say about some engines needing to be sucked out by the suction on the inlet manifold pipe, the lack of this may raise temps in the rocker cover and bottom ends. no difference in temps or coolant pressure have been noticed to date, but it is early days.

Northern Bongolow wrote: the suction on the inlet manifold pipe,

There is no induction suction on a diesel, in fact on a turbo diesel there may even be positive pressure instead.

i understand what you mean, but the air is drawn from the air filter/ housing towards the turbo, its this pipe that the crankcase breather goes into so it is drawn out of the engine and into the air inlet system on the negative side of the turbo. once it enters the turbo it becomes positive.






i hope.

I replaced the valve seals on mine about 2 years ago but my bottom end was a bit of an unknown quantity replacement. Mine breathes quite heavily losing the odd drop of oil

Northern Bongolow wrote:
just opened up the crankcase/top end breather to atmosphere, the improvement in performance is very noticeable,

Can you explain a bit more please?
Just disconnect one end and angle down?
How does it feel improved?

Thanks.

As well as venting the crankcase breather he also removed the egr which probably accounts for the largest improvement in performance.

The crankcase breather vents hot spent (as in burnt) oily gasses from the crankcase into the air intake, I joined another section of pipe (waste pipe from my old washing machine) to dangle down, I can't say I noticed an improvement with this modification although I did with removing the egr.

Often it is a case of a lot of small changes in the right direction all add up.

Regarding the thermal gaskets, here is a link http://honda-tech.com/showthread.php?t=2628596 showing back to back dyno runs on a Honda Civic, initially there is only a 1 BHP gain but after three successive dyno runs the heat builds up in the inlet manifold without a heatshield gasket and it is down 8bhp whereas no change in the engine when the gasket is fitted.

The Bongo suffers from high under "bonnet" temperatures so the improvements may be quite noticable. Please note the gaskets I intend to have made are not made by the company listed in the link, I have used the link as an illustration.

skater wrote:

Northern Bongolow wrote:
just opened up the crankcase/top end breather to atmosphere, the improvement in performance is very noticeable,

Can you explain a bit more please?
Just disconnect one end and angle down?
How does it feel improved?

Thanks.

as rustyp says above.
remove the crankcase pipe from the air inlet pipe at the rear of the head, blank off the socket that it fits to as it will suck air into the turbo supply pipe, bypassing the air filter.
then extend the crankcase pipe down past the head towards the ground and clip to the sump.
its hard to say what/why its improved things as i did the egr at the same time. mines a manual g/box and when i rev it hard to work it, it dont half fly now.

This is a heatshield gasket I got for my old CRX.