Carb bell mouth 2200TC

Tom W

Active Member
#1
Some idle daydreaming. I wonder, has anyone experimented with fitting carb bellmouths on their 2200TC? On the 2000TC carbs, it looks like there’s a nice radiused inlet from the air box to the carburettor. On the 2200TC, the air box bolts directly to the carb flange, and presents a sharp edge, with no radius into the inlet. This effectively reduces the cross section of the inlet, as any air coming from the side of the inlet has to make an abrupt turn. Maybe it’s this way on the 2200, as by the time it came out, the V8 was the performance option, and keeping things simple made it cheaper when developing the 2200?

There’s not much space between the air filter and the back of the air box, but it might be possible to get something short in there. Has anyone tried this, and did it make any difference? If I can find something cheap and universal, I might give it a go to see if it makes any difference.
 

clive P62

Active Member
#2
Fitted them on minis and are a recommendation for better torque and are used on the stage 1 tuning, no reason they shouldn't work on our cars.
 

Demetris

Well-Known Member
#4
I have done just that, at the time that i installed A/C in my TC. Before that i have converted to HIF6's, but the standard 2200 filter box does not leave any space for the A/C compressor. Since i wanted to avoid bare filters for various reasons, my only option was to adapt the HD8s filter system with the HIF6s. I had to make 2 conical spacers though in order to step down smoothly from the 2" to 1 3/4". I can't really tell if there was an improvement in performance, but in my eyes it looks certainly better.

DSC00072.JPG
 

Chalky

Active Member
#6
Surely the main restriction is the amount of air coming into the air box and that paper air filter. Take it off put on k&n filters plenty of airflow then change needles to get more petrol in.
 

Tom W

Active Member
#8
I doubt the standard air filter is the restrictive part in the whole system. The same filter I used on the Jag XJ6, so is capable of flowing enough air for a far more powerful engine.

The standard air box is actually quite well designed. It draws air from the front of the car, where it’s nice and cool. It’s also very good at cutting down induction noise. It just looks to me, that the interface to the carburettor isn’t particularly well optimised.

With your K&N filters, bellmouths would be even more important. All the airflow has to approach the carburettors from the sides, and make the sharp turn into the carburettor mouth. It’s on this corner that the air gets caught up, and this region of stationary air reduces the effective size of the carb inlet.
 

Chalky

Active Member
#10
The air box entrance is under the bonnet no cool air under there. The air box is a big tin box which takes up room therefore increasing under bonnet temperatures. I can assure you an air box with flutes will not match k&n filters for air flow.
 

Tom W

Active Member
#12
What performance difference have you got with the K&Ns over the standard airbox? Have you had the car on a dyno?

The stock air box inlet is alongside the radiator end tank, just behind the inner headlamp bowl. Not quite in the airflow, but not drawing hot air from within the engine bay. With K&N filters directly on the carbs, you’re drawing air from directly above the exhaust manifold. Whilst you might get more air, there might be a net loss if the air is hotter. Rover’s airbox incorporates a thermostatic valve so the engine draws air from either behind the grill or from next to the exhaust manifold. There must be an optimum intake temperature they were trying to maintain.

I don’t know what the airflow is like through the under bonnet area on the P6. The design dates from before this was widely understood, or applied to road car design.

Typically a K&N filter will flow more air than the same sized paper element. However, it’s still important to have the right shape transition into the carb mouth. The link I posted earlier shows the effects of the various commonly available trumpet shapes, verses an open carb. Surprisingly, some can actually make things worse, despite what the product marketing would have you believe.

With any of these mods to improve airflow, there will only ever be an effect at wide open throttle. At any other throttle opening, the butterfly will be the most restrictive element, not the air filter. Even then, that assumes the air filter is the most restrictive element in the whole system. The effects of drawing in air that’s too warm will be present at all throttle openings though.
 

Chalky

Active Member
#13
I’ve driven my car with air box and with k&n. There is no doubt that there is more air flow with k&n. The biggest difference is in torque which gives much better pull up hills. With regards to air flow through the carbs you seem to have forgotten the piston with the needle on that significantly blocks air flow except when full throttle.
 

sdibbers

Well-Known Member
#14
I switched to a factory 2200TC air box from pancake filters after I fitted hifs to my car. That was a huge improvement there to start with. I do need to fit ducting to pick up cool air ahead of the engine bay, that shouldn’t be too bad to make up.

On the ram pipe I’ve looked at making something similar for the air box. The big issue is the distance between the carb mouth and the back of the filter element. It only leaves about 3/8” (10mm) for the roll edge. I think I’ll make up the part up in plastic and use VHB tape to attach to the housing. Not as much height as I’d like but without changes to the air box I don’t think we’d find more space. If you change the size of the air box I can see it affecting performance because of a change in intake resonance causing weird issues with fueling.
 

sdibbers

Well-Known Member
#15
With regards to air flow through the carbs you seem to have forgotten the piston with the needle on that significantly blocks air flow except when full throttle.
The issue is more turbulence before the jet. The sharp edge on the mouth creates a lot of turbulence before the jet which can affect fueling. In fact I’ve worked on a friends ‘68 Cooper S carbs and added velocity stacks. We ended up having to lean out the needles as fueling improved so much it was running too rich. PS: We had a wide band 02 sensor on the down pipe so we could actually see the difference with real numbers.
 

Tom W

Active Member
#16
I’ve not forgotten about the piston. That’s not the major restriction in the SU design. The piston moves to suit engine demand and airflow, giving the appropriate venturi size at all times. Which is just enough restriction to create enough vacuum across the jet to draw the fuel out.

Anyway, I’m not planning on removing the stock airbox. If I want to drive around listening to induction roar, I’ll use my Jag. If I can find some suitable bellmouths though, I will see if it makes any difference. I suspect not, apart from wide open throttle, but it’s fun to tinker.
 

Chalky

Active Member
#17
There’s no induction roar just a hiss that you can’t hear when you’re driving because of the wind noise ccreated by the recessed windscreen design.
 
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