Havn't had time to read all of this, but i did browse through..

I read somewhere having a gap at the back of the bonnet is a bad idea, it causes the engine temperature to increase as the air comes straight in and out the back, rather than being pushed out the LH guard where the radiator is..makes sense to me...probably would help intake temperature much as hot air still has to pass the carby intake on it's way out..

I have a pipe that runs up from the front grill, to where the carby is..i'll tell you now it does SFA

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Starlet Conversion:
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firstly thsu discussion has continued at my work, we build air management systems plenems as big as houses and deal with airflows hot and cold from furnaces to A/C cooling ,negative and positive preasurization and velocity. bla bla bla
from my point of view the airbox of Justminis (hope i got that right) is a very good example for a number of reasons, which i will get to after a bit of a ramble..
...cold air is more dense, as anything is heated it expands. the molecules vibrate more and spread further apart.. so in any specified area there will be less molecules of air if the temperature is increased, and more as the temperature decreases..on the induction stroke of the cycle a certain volume is drawn into the chamber. thus if the air is cooler there will be more molecules in that chamber ie more oxygen..
so the airbox is getting more oxygen into the chamber
there would be a certain amount of preasurization in the system as the car moves forward.on the assumption the air entry point is facing forward or in a direction toward the natural airflow.
but the airbox doesnt appear to be sealed to the carb and inlet manifold, so the majority of the increased preasure can escape arount the inlet, probably maintaining a very slight but reasonably constant positive preasure around the carb..( a more stable slight positive preasure is good) also the escaping cooler air helps keep the area and box a bit cooler. that air would join thre natural flow out past the exhaust
the fact the air enters the box at an opposite angle to the carb intake means there is a quick directional change just outside the carb.. this wether intentional or not adds a non restrictive filtration point.. air can change direction very easily, and in effect is very lazy (it will take the easiesst route) ..heavier dirt particles dont change direction as fast and will hit and stick to the flat surface opposite the turn..(you can see this in action on any fans in your house..do you get a buildup of dust on the fan blades?? that dust didnt move out of the way as easily as the air did)
so the box is getting denser cooler air(more oxygen) it probably is maintaining a reasonably stable slight preasurization (except when stationary), and is probably doing a little extra filtration while its at it (a sticky sunstance on the back wall of the box would trap crud) the germans are trial using directionchange to filter the air on their tanks, not filters..
the intake pipe is big enough to ampley handle the air supply neededwithout increasing the velocity of the air.. anything over 2m per second (i think from memmory) will cause water pulling.. ie it would suck droplets of water of any condensationtrap, and there would be the risk of icing...
anyone read any of visards small block chev books?? from memmory he was an advocate of cold air intakes when he wrote them, i think he quotes quite high gains too, more than i expected...

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No longer Ms Westwoods mini outside her original kings road shop

danidad..that's one big block of text..

I'm going to try and attempt to read it in the morning when my eye's dont hurt

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Starlet Conversion:
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yep its a biggy but only gets as much credit as posting one smiley face LOL

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No longer Ms Westwoods mini outside her original kings road shop

spam....why not almost everyone else is LOL

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No longer Ms Westwoods mini outside her original kings road shop

Good dialogue Danidad, the air box is not sealed to the carb/manifold. Was never intended to be, so any "excess" can escape.
Also, rest assured, I will not be fording any flooded creeks or streams in my sprint mini! Have run it in the rain, and no problem with water etc on the carb or filter.

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Steve

Danidad.... impressive reasoning.... now the whole arguement is becoming very clear........ i never really understood the physics of it all but that goes a long way to clearing up my misconceptions.............

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I got nuthin......................

I still don't get why the carbies can't handle pressure, well I have an idea why SUs can't but I don't know if webers/dellortoes can handle pressure.

Sorry, what I wrote before was wrong (well at least in part) Throttle positiion determines air flow(past the butterflys) and through that fuel supply, throttle position does not directly determine fuel supply. I wasn't very clear on how carbies did thier thing, so I was just theorizing...

It is pretty clear to me anyway that cold air is advantageous in combustion, but so also is pressurized air for pretty much the same reasons(more air) but not if the carby can't adjust to the increased airflow it is getting by supplying more mixture. Can webers / dellortoes adjust and why can't the SUs

justminis is there a reason you have not setup for rammed air as well is it because the carby has problems with pressurized air . When it was setup on the dyno I pressume the cold air intake was out so that they could get at your jets and stuff on your weber / dellorto so there was no advantage from the cold air intake you put it back on and the increased air supply was felt therefore you needed the richer jet.

Yes I was getting cold air and rammed air confused thanks for distinguishing them

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Roads need more corners
A Deluxe(CG13DE), 2 Clubbies(998 and 1275) and 2 Morris 1100Ss

[quote="fuzzy-hair-man"]I still don't get why the carbies can't handle pressure, well I have an idea why SUs can't but I don't know if webers/dellortoes can handle pressure.
quote]

Ok I will hae a go at this. NO carby will handle an air supply condition that goes from negative to positive unless it is allowed for. On forced induction systems it is jetted to do just that but it is not a great way to do it and in general is not done unless there is no other alternative. The whole carby has to be pressurised so that the all the carby sees the same overall pressure. If this does not happen the fuel supply goes up the spout. The venturi has the air pushed through it by virtue of having a lower air pressure on the manifold side and static air pressure , which is greater, at the intake to the venturi. By virtue of this, when the throttle butterfly is opened the air travels down the venturi over the jet(s) and creates a low pressure point at the jet face and uses this to draw petrol through the jet. Fuel is only pumped into the float bowl it is not pumped from the float bowl but is drawn into the venturi by air speed. Everyone looks at carbies but very few of us understand the principles. This act of drawing air through across the jet is called the AIR SIGNAL at the jet. The air signal decides how much fuel is required. In all NA situations this air signal is supplied by atmospheric pressure and all carbies are designed using atmo pressure as the supply. As an aside this is the problem with installing a carby with a venturi that is to large for the application. If this is done the air signal at low speeds will be insufficient to draw fuel through the jet and consequently the motor gets that familiar flat spot until the air speed rises enough to enable the required fuelling through the jet.
As for jetting for forced induction with blowers it can be broken down into turbos and superchargers. You will rarely see any attempt to turbo through a carby as the pressure rise is not linear and as such the carby cannot be readily jetted to allow for this. A supercharger is relatively linear in its operation and a lot of blow throughs were built, why I don't know, as I can see no true advantage except new manifolds did not have to be fabricated.
The carburettor sees a constant static air pressure and this has been relied on by the designer for all calibration. Once we add a change of static pressure like proposed with a cold air duct it removes all known calibration for that carby. The SU is a CONSTANT DEPRESSION CARBURETTOR and as such relies on the difference between manifold vacuum and static air pressure to work, so it cannot be used in a blow through like other carbies. It is this difference that may be confusing some people. No one in their right mind would build a blow through system today. It is simply to limiting in the performance stakes and the job of tuning it is a pain with having to work on a seal carby.
Another thing about forced induction is that there is no manifold vacuum to run boosters. Just a small point that escapes a lot of people. I don't know how the guys do it today but it was done by putting a vacuum pump on the back of the alternator.
All cars will benefit from colder and more humid air, it adds oxygen as Jeff said. Water injection was used years ago to facilitate this but the delivery system was a bit hit and miss and everyone found that topping up the system was a pain. It is used today with turbos mainly to reduce the detonation point by reducing combustion chamber temps. Metho is a good additive to run in conjunction with water in this situation.
I will add a bit here on the SU. I said it is a constant depression carby. What that means is that the pressure over the top of the piston is at ALL TIMES less than at the bottom WHEN THE BUTTERFLY IS OPEN. This is what causes it to lift. We control the speed of the lift and the subsequent fuel supply by oil and springs. We control the fuel supply at any point in lift by needle profile. The control of the piston lift speed could have been controlled by directly affecting the vacuum but the designers chose to do it a different way.
The above was written off the top of my head without planning. It jumps around a bit but I ain't re-writing it. Hope it sheds some light on the subject.

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Chris

Everything I like is either
illegal, immoral or fattening.

"You will rarely see any attempt to turbo through a carby as the pressure rise is not linear and as such the carby cannot be readily jetted to allow for this"

? sureley not.... every MG Metro Turbo, and just about every Turbo mini Uses a HIF-6 - a BLOW-Through Turbo setup .... so does the Maserati Bi-Turbo, the Corvair Spider, the porsche 911 Turbos (early ones...) etc etc etc

well accepted practice .........

all you need to do is make a restriction at the mouth of the carb, and direct un-restricted boost into the float bowl, ensuring that the fuel is always has a pressure a percentage HIGHER than that of the air going through the venturi .....

J

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reads well to me thanks

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No longer Ms Westwoods mini outside her original kings road shop

ok i skimed over this subject had a quick look and well i have tried this and i know of one other person who has tried this and on both cars we found higher fuel consumption no extra horsie's or anything else just more fuel consumption i have no logical explination nor am i going to atempt to give one ..... one was a 998 (mine) 1100 was mates parents car both with inch and a half su's standard everythiong else so do ya experiment's use ya uni degrees and dribble on it should work in theorie
but it dont just one of them black arts .... the mini
makka

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Anonymous moderation means the agro that is built up towards the mods isn't aimed at an individual (fewer "Makk" attacks). Less stress for mods means less moderator "retirements".

And all of them were in the end proven to be unsatisfactory. If this were not the case then the practise would have been more widespread. Masers are not the most reliable car ever made, corvairs in the same boat and the first turbo porsches were real animals. I perhaps should have qualified my statement by excluding factory made cars. The average person has little chance of making them work in anything like a satisfactory manner. I bet all the carbies they used were designed with positive pressure as the goal. The after production converter cannot do this. I will repeat what I said.....the boost is not linear, therefore for the average person very hard to jet for as standard fixed jet carburettors cannot be readily tuned to allow for this. Blow through injection is an entirely different animal.

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Chris

Everything I like is either
illegal, immoral or fattening.

Bit too much for you to take in makka??????.... Too many big words perhaps?

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I got nuthin......................

Ah, just put a bonnet scoop on
That's give you cold air intake...

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Too many cars, and too little time.