K&N Filters

[PeteH]

Not easy to remember which vehicle, But one or two had a "flap" Valve in the system which opened and closed according to air temperature in an effort to regulate on cold or hot days?.

Pete

[NonMember]

9 hours ago, Peter Truman said:

the small size of the two flexible inlet pipes from the front of the car to the air filter box always seemed Mickey Mouse to me such that in reality there wasn't any ram effect cold air

Sadly that's because you've completely misunderstood the physics.

First, they're not "ram air" pipes. You need careful shaping for that. You also need them to be small, at least by the far end. If the pipes are big then the air in them flows really slowly. Any sort of ram effect needs fast air flow to work, for exactly the same reason you don't "slowly position" your hammer against the nail.

Cold air pipes also need to be small, so as to get high air speeds. This time it's simply a case that slow moving air has plenty of chance to get heated up, and then it's no longer cold.

So as with so many things in life, don't be fooled into thinking that bigger is better.

[Colin Lindsay]

My Daihatsu Charade (1982) had a manual flap on the manifold which you moved from 'summer' to 'winter' to aid the warm up process. Never tried it on a daily basis, tho.

[Peter Truman]

8 minutes ago, NonMember said:

Sadly that's because you've completely misunderstood the physics

I understand & accept your explanation, but why are the modern PI air inlet/air flow pipework  so large in dia by comparison? most of my moderns by design have the inlet at the front to get cold air

[68vitesse]

My Vitesse air box has drilled holes in the bottom, rain water drain?, over the exhaust, so is the engine drawing air from the front or bottom of the airbox?.

Its how Triumph designed it.

Regards.

Paul.

 

[cliff.b]

While on this subject, as the diameter of the filter box inlet pipes appears to be less than that of my HS4 carbs, why would this not "strangle" them. 

I'm sure there's a good explanation but it's bugging me that I don't know what it is lol

[Ian Foster]

Triumph had various versions of the air box on the 4 and 6 cyl cars, both with and without feed tubes from the front. Some have holes/slots in the bottom and or sides and top, suggesting they were trying to address issues if getting equal airflow to the front and rear carb. There are some Triumph original designs that do similar. The box shown in Piglet's OP has slots in the top, which would appear to drawing hot air from the top of the engine bay???. I previously found this image of an airbox (probably modified) on a 4 cyl car which looks to have been designed specifically to get air to the rear carb, although there is no ducting to the front of the car. 

On the GT6 the box is of uniform thickness and the WSM and original brochures show inlet tubes on the front of the box, but no pipes, which seem to appear later (perhaps on the Mk3). The saloons have a particular problem due to the proximity of the suspension turret and as a consequence have very thin airboxes. Late versions (2500S IIRC) have a unique airbox enlarged and fed centrally from the bottom. On my GT6 Mk2, I have CD175 carbs (as fitted when I bought the car in 1977) so I have limited space between the face of the carb and the wheel arch and currently use K&N filters until such time as I can come up with an airbox designs which ticks enough of the boxes.

Ian

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[Pete Lewis]

back in the old days they design "Hot Spots"  where the exhaust gas was circulated to the heat the inlet manifold to warm up the cool atomised fuel/air  to get better mixtures 

later these disappeared and air filters when emissions  took over they added a vacuum operated flap controlled by a Thermac valve 

this operated the flap to modulate and keep a steady 70F air intake temperature so mixtures stayed consistent with stable air temperatures 

by taking a mix of air from cool or off the exhaust 

now these days  you have a air sensor and a ECU controlling injection  

triumph never seemed to use the Hot spot idea but many others did like Vx Viva H's many Rootes  and some Bmc

on some triumph 4 cly there is a physical connection between inlet and exhausts manifolds  to transfer heat  but not on the 6 cly.

Pete 

[NonMember]

2 hours ago, Peter Truman said:

I understand & accept your explanation, but why are the modern PI air inlet/air flow pipework  so large in dia by comparison?

An entirely fair question! Partly it's because modern engines put out a lot more power. In essence, the size of tube you need is governed almost entirely by the rate of air flow you're targetting, and that is closely proportional to the power you're getting. So a 140BHP modern 1400cc engine needs twice the pipe area that a Spitfire 1500 does. But also, a lot of modern engines are designed with intake systems way too big for them. The throttle body that BMW insisted on fitting to the 1800 engine when I was at Rover was sized for a 3-litre. It didn't improve anything using that - just meant a common part across the range.

[NonMember]

1 hour ago, cliff.b said:

as the diameter of the filter box inlet pipes appears to be less than that of my HS4 carbs,

Is it? I'm pretty sure the air box inlets on my 1500 Spitfire (completely standard engine, albeit in the wrong car) are the same size as the carbs.

[cliff.b]

24 minutes ago, NonMember said:

Is it? I'm pretty sure the air box inlets on my 1500 Spitfire (completely standard engine, albeit in the wrong car) are the same size as the carbs.

The internal diameter of each metal inlet stub on my airbox is 1.25". Obviously the plastic pipe is slightly bigger as it needs to fit over it.

So in total, I think that gives a combined inlet area of about 2.45 sq inches whereas 2 X 1.5" would be about 3.5 sq inches area.

But do both carbs ever demand maximum flow at the same time🤔

[Pete Lewis]

with the taps open from anywhere up from idle to Full both should demand the same /similar air flow/volume  etc 

there are considerations that the front (if its the tubed filter box )  will get predominance over the rear

but hopefully the box has the capacity to even this out 

Pete

[Peter Truman]

11 hours ago, NonMember said:

An entirely fair question! Partly it's because modern engines put out a lot more power

Thanks for the explanation and enlightenment much appreciated

[ahebron]

My personal interpretation of performance filters (size for size) is the only way to get more air through is to have bigger 'holes' which allows bigger 'dirt' particles.
On a slightly different subject this is interesting about oil filters.