John Bonnett
|
| posted on 15/4/08 at 12:57 PM |
|
|
Another question for the Boffins
I'd really like some help here guys with respect to getting cold air to the engine.
I've cut an aperture in the bonnet side of the Phoenix, (I'll try to attach a picture). I intend to make a duct from the air box across
to the bonnet aperture so that it has to draw air in from the outside and hopefully will be independent of under bonnet temperature.
I've just had a bad thought. Will air running down the side of the car at speed cause a reduction in pressure in the duct and therefore starve
the engine of the very thing I am trying to improve.
Thank you for you help.
John.jpg)
|
|
|
|
|
Humbug
|
| posted on 15/4/08 at 01:02 PM |
|
|
Not sure of the scientific answer, but I would have though that some sort of scoop to "catch" the air and feed it into the hole would help
|
|
|
kendo
|
| posted on 15/4/08 at 01:02 PM |
|
|
I would have thought that it would tend to draw air out. So that may well improve things.
|
|
|
Mr Whippy
|
| posted on 15/4/08 at 01:05 PM |
|
|
Land rover series had the intake there, seemed quite happy. You’re not taking about serious vacuum here, not enough to hamper the engine. I'd
make sure though that hot air will not spill out the wheel arch over the vent, an inner arch should solve that.
Fame is when your old car is plastered all over the internet
|
|
|
caber
|
| posted on 15/4/08 at 01:12 PM |
|
|
LandRover Series 3 has air intake for heater there! Mine has a matching intake on the driver's side to feed my Turbo diesel however I
don't think aerodynamics is an issue at Land Rover speeds! Anyway as the LR has a flat front I would imagine there would be a ton of turbulence
around the intake if you ever got it going fast enough to matter! The location is very good for deep water as the bow wave causes a nice drop in level
along the wing and door
Caber
|
|
|
Mr Whippy
|
| posted on 15/4/08 at 01:34 PM |
|
|
oh yeah so it was, the intake was on the top of the wing...oops
my SIII did 90mph, a rounded brick what a beasty
Fame is when your old car is plastered all over the internet
|
|
|
02GF74
|
| posted on 15/4/08 at 01:35 PM |
|
|
Land Rovers had hole in side wing for the heater - this had fan to suck air in.
Back to origainal question - that hole lloks to far back to get air into the engine; as already entioned, unless you get a scoop to force air in a
certain direction, it will more likkeluy to act as a vent frawing airt out of the engine.
remind me what is it you are tring to do? - get cold air to the carb/EFI intake or get under bonnet temps down - not the same thing.
|
|
|
richardlee237
|
| posted on 15/4/08 at 01:38 PM |
|
|
A a rough guide you need to think in terms of aerodynamics.
All the air meeting the front of the car is pushed aside around the car and then meets up again at the back, the fact that it has travel around the
car forces the air to speed up. The pressure drops to provide this increase in kinetic energy. So generally speaking the sides and top and bottom of
the vehicle will be low pressure areas compared to the front. so air will flow in the front and out of the sides.
Where the car has air intakes at the side they are usually scooped to provide ram effect and the air is ejected from the engine bay into a low
pressure zone behind the car.
well you asked for the boffin approach
Quote Lord Kelvin
“Large increases in cost with questionable increases in performance can be tolerated only in race horses and women.”
Quote Richard Lee
"and cars"
|
|
|
alanr
|
| posted on 15/4/08 at 01:40 PM |
|
|
you need to locate the opening for the air right at the front to get maximum amount of cold air and at maximum pressure
|
|
|
John Bonnett
|
| posted on 15/4/08 at 01:41 PM |
|
|
I would have though that some sort of scoop to "catch" the air and feed it into the hole would help
I did think of this too but a forward facing scoop on the side could be a safety issue for pedestrians.
Thank you for your thoughts. I'll press ahead with it and hope for the best.
John
|
|
|
Humbug
|
| posted on 15/4/08 at 02:06 PM |
|
|
quote:
Originally posted by John Bonnett
I would have though that some sort of scoop to "catch" the air and feed it into the hole would help
I did think of this too but a forward facing scoop on the side could be a safety issue for pedestrians.
Thank you for your thoughts. I'll press ahead with it and hope for the best.
John
If you hit them when moving a scoop is probably the least of their worries! To avoid stationary catching of pedestrians you could make the scoop like
a hinged flap and fit a cable to open and close it from inside the car
|
|
|
designer
|
| posted on 15/4/08 at 02:13 PM |
|
|
Why not put a lip on the vent you have in the side and let it extract the warm air?
|
|
|
02GF74
|
| posted on 15/4/08 at 02:20 PM |
|
|
that bit between the bulge and the front of the bonnet - is that all cut out and have a fully enclosed cowl to the rear of the radiator - so all hot
air from radiatir is channellled out?
that would be the first place I wold look at - a bit like GT40.
Next cowling to the front of radieter from nosecode hole - a small part of that is directed to the engine intake.
|
|
|
Jenko
|
| posted on 15/4/08 at 03:15 PM |
|
|
I would have thought it depends on which way the pipe is pointing inside the engine bay......So, if the pipe is pointing towards the back of the car
there will be a suction effect, if it points forwards, then the air may get sucked / blown in.....
|
|
|
JeffHs
|
| posted on 15/4/08 at 03:23 PM |
|
|
If you fit a well-designed NACA duct there, you'll get a gale of wind down it. See Staniforth's book. Merlin sell them in several sizes.
|
|
|
John Bonnett
|
| posted on 15/4/08 at 03:39 PM |
|
|
If you fit a well-designed NACA duct there, you'll get a gale of wind down it. See Staniforth's book. Merlin sell them in several
sizes.
I'm sorry, I should have said right at the start that the main worry is when stationary for example in a traffic jam. After ten minutes
stationary, the engine begins to cough and misfire and sound generally miserable. With the bonnet open, it will run for ever quite happily. I'm
fairly certain that the ducting and side vent will solve the idling problem but my concern is that it will introduce a new problem of air starvation
at speed caused by the negative pressure down the side of the car trying to draw air out.
I'm fairly happy that the measures I have taken like the forward facing scoop and the horizontal grille will remove the heat whilst moving.
The amount of heat this engine produces is incredible. The 13.5:1 compression may have something to do with it!!
I'm sorry for the confusion which was totally down to my poor communication.
Thank you all for your help.
John
|
|
|
RK
|
| posted on 15/4/08 at 04:23 PM |
|
|
I don't think being able to draw warm air from the engine compartment of a Phoenix is a proven scientific phenomenon, at least by people wearing
white coats.
|
|
|
John Bonnett
|
| posted on 15/4/08 at 05:18 PM |
|
|
quote: I don't think being able to draw warm air from the engine compartment of a Phoenix is a proven scientific phenomenon, at least by
people wearing white coats.
People who drive a Phoenix are most likely to be carried away by people in white coats 
|
|
|
chriscook
|
| posted on 15/4/08 at 06:58 PM |
|
|
Can you not use the scoop on top of the bonnet to feed the airfilter and your hole in the side to let air out from under the bonnet?
|
|
|
John Bonnett
|
| posted on 15/4/08 at 07:23 PM |
|
|
quote: Can you not use the scoop on top of the bonnet to feed the airfilter and your hole in the side to let air out from under the bonnet?
Hi Chris,
I've tried this but when stationary, heat from the exhaust manifold builds up under the bonnet and cannot get away. This is then sucked into the
engine. Your suggestion could work if I could isolate the inlet manifold and t/bodies perhaps by some sort of partitition touching the bonnet so that
no hot air came across. I have thought about this but came to the conclusion that the duct idea from the airbox would be the easiest to make.
I'm just a bit concerned about the possible negative pressure problem.
atb
John
|
|
|
MikeRJ
|
| posted on 15/4/08 at 08:08 PM |
|
|
quote:
Originally posted by John Bonnett
I'm sorry, I should have said right at the start that the main worry is when stationary for example in a traffic jam. After ten minutes
stationary, the engine begins to cough and misfire and sound generally miserable. With the bonnet open, it will run for ever quite happily. I'm
fairly certain that the ducting and side vent will solve the idling problem but my concern is that it will introduce a new problem of air starvation
at speed caused by the negative pressure down the side of the car trying to draw air out.
But this is exactly what a NACA duct is for. It is specificaly designed to push air into the duct in this scenario, rather than air being pulled out
which is what would happen with a simple "hole" style duct .
http://www.stockcarproducts.com/naca.htm
|
|
|
02GF74
|
| posted on 16/4/08 at 09:37 AM |
|
|
quote:
Originally posted by John Bonnett
The amount of heat this engine produces is incredible. The 13.5:1 compression may have something to do with it!!
Are you sure? I suppose I could work out the air temp when compressing air this amount but can't be asked - but would have thought the
temperature of the burning fuel is far more significant.
Land Rover diesel engine run notorioulsy cool and they have CR of over 20. (?)
|
|
|
MikeRJ
|
| posted on 16/4/08 at 10:04 AM |
|
|
quote:
Originally posted by 02GF74
Are you sure? I suppose I could work out the air temp when compressing air this amount but can't be asked - but would have thought the
temperature of the burning fuel is far more significant.
Land Rover diesel engine run notorioulsy cool and they have CR of over 20. (?)
The higher the thermal efficiency the cooler the engine will run, as more of the energy is going into producing cylinder pressure rather than heating
things up. As thermal efficiency is directly related to CR, the higher the better (within the engine and fuels limits of course).
|
|
|
