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MG MGB GT V8 Factory Originals Technical - Air Filter Clearance

I am just finishing up the final stuff on my conversion, electrical, fans, plumbing etc. I have purchased a Mr. Gasket Low Rider air filter and upon fitting it is very, very close to the bonnet. I am restricted in that I can't drop the engine anymore due to having to clear the steering pinion and the block style headers. Some time ago there was a posting about squashing the air filter a bit. I am reluctant to do this without further information. I don't want to mess up a new part. Has any one any idea how I might go about this. I thought about a 1 air filter instead of the 2" one but I am unable to find one. It would drop the surface area of the air filter from 66 sq inch's to 55 sq inch's if in fact I could find one. Another option I have heard about is getting the intake or carb planned off a bit. But this is beyond my expertise. How much clearance do I really need between the air filter and the bonnet?
I have checked the archives with no luck.


You might try an offset base air filter bottom. The hole for the carb is not centered. This effectively moves the air filter back about 3 inches.
K&N as well as others make it for GM applications.
Hope this helps
bill jacobson

Bill, will this clear an electric choke on a Carter/Edelbrock? ... can't see how it could, that's why I ask.

Yes it does clear. The base dosn't drop as low as the lowrider type bases. Hood clearance is gained by moving the filter back where the hood hieght is greater. Offset or lowrider which one works best? Depends on the installation. I tried both (their inexspensive). The lowrider type would'nt clear my breather cap with the offenhauser valve covers so I went with the offset and trimed aprox. 1/4" (tapered cut) off the front mounting area to bring the front edge down slightly. I am using a 14"x2" element.

bill jacobson

Thanks all for you replies. I have decide to do the following which was sent to me by Kevin Brown. I have already purchased 2 air filters (my fault) so I am reluctant to spend more money. The following will help me out, perhaps some else can benefit as well.

"Essentially I flipped the base over and placed it on a smooth piece of metal (I used a spare MGB engine back plate) - the "doughnut" around the carb inlet hole (essentially the dropped portion of the air cleaner) will be resting on the metal (wood might work too, but you want to make sure that the metal of the air cleaner doughnut can slide on whatever you place it on as you press the carb inlet hole in to the air cleaner base)..
You then place a metal disc (I used a TR6 flywheel - the convex part was just the right size) on the air cleaner carb inlet hole (wood would probably work here also), and using a
hydraulic press (a bottle jack should work also as long as you jack it against something solid (like a car bumper - this doesn't take much force) press the air cleaner carb inlet hole in to the base of the air cleaner.
I probably gained 1/2-inch or so this way and there seems to be plenty of room inside the air cleaner for air to flow (certainly a lot more area than there is in the stock Buick 215 4bbl air cleaner intake horn!).
After I pressed it in a little, I then used the press to press down a little more on one half of the carb inlet hole so that the air cleaner tilts forward a little (though you tell can't from looking at it) to gain another quarter inch or so at the critical forward edge of the air
On the inside of the air cleaner from the top of the dropped portion of the air cleaner base to the inside of the top of the air cleaner is about 7/8", in the front where I dropped it a little more it is about 3/4". From the outside of the carb opening to the inside of the top is about 1 1/4".


Bruce, a couple of things for you to consider.
Doing what you have done will definitely affect the "signal to the carb and interfere with efficient air flow through the carb. The usual clearance problems on a V8 B are due to the centre bonnet (hood) stiffener web. This can be removed without harm.
On Holleys the best thing to do is to mill off the top "horn" of the carb so as to allow more flow into the carb. I presume you can do something similar with an Edelbrock.
I am surprised you have a choke. A couple of prods on the accelerator pedal and the pumps will give you a nice rich mixture to start. In addition the choke butterflies even when fully open, impede air flow.
How are you getting rid of the heat from around the carb so that nice cold air can replace it??
Good Luck with your car.
bob pulleyblank

I am praying my "ancient chinese secret" air filter will save the day, it is older Ford intake that has the carb inlet recesse into the air cleaner naturally. but the top of it is taller, so I may have to do some modifying like mentioned above. OR maybe I can get a K&N X-stream of the correct size to replace that lost airflow.

My cold air will be force fed via intakes routed down to the front of the car.
Larry Embrey

I am lucky that my hood stiffener does not interfere with the carb.
I took a look at the top of the carb, thinking about having it milled off, but I can't see that working. With the Edelbrock there is the lip that the bottom of the air filter bottom sits on. I really don't like the idea of playing with this, it is way beyond my understanding.
The choke came with the carb and this my first MGB-V8 so I have no idea (until now) how it would start. I suppose I could always take out the butterfly if needed.
As far as the heat goes, I haven't done anything about removing the heat. I am going to buy a 3000CFM puller fan for cooling and hoped that this and normal air flow would take care of it.
I haven't remolded that air filter yet but will take some more measurements to make sure it will conform to the information I found which deals with tech info for the K&N filter. It is located at: - facts

A - effective filtering area
CID - cubic inch displacement
RPM - revolutions per minute at maximum power
A=(CID x RPM) / (20839)

Example a 215 CID Rover engine with a horsepower peak at 5500rpm
A=(215 x 5500) / (20839)
A= 56.74 sq in

If you are sizing a panel filter, multiply the width of the filter area (not the rubber seal) times its length. If you are sizing a round filter, use the following formula to determine the height of the filter.

A - effective filtering area
H - height
D - outside diameter of the filter
3.14 - pi
.75 - the rubber end caps
H=(A) / (D x 3.14) +.75

H = (56.74) / (14 x 3.14) +.75 = 1.290 inches thick required for an air filter.

So as long as I have this requirement after the remolding of the air filter I should be ok. As I said I will definitely check it.



Larry, I tried one of those very expensive K&N X stream filters, where the top of the thing is all radial filter elements. There was absolutely no difference on a dyno between that and a normal 2 inch lowrider with the chrome top, so dont waste your money. My 3.5 litre roadster has a three inch element on a lowrider and gives over 200 bhp at the wheels - maybe thats the answer - but it needed a bulge to clear it. I think it looks very nice as it was very well executed.
Bruce its all very well blowing air or pulling it in for that matter, but where is it going to get out. We have discussed this matter ad infinitum on the V8 BBS, basically you need to provide an exit. A lot of us have fitted RV8 style headers which exit via the inner wings, the holes you make allow better air flow.. My cars have bonnet vents as well, but even so, when at a standstill in traffic the engine warms up. People have suggested little 12v muffin fans mounted in the wings to extract air and also fitting a fan blade to the water pump. Bigger rads are available, some in aluminium (now Im back in the UK I can spell it properly again!)
Im off down the pub for a few pints of Ringwood so think on't eh.
bob pulleyblank

Hey, Bob's post just gave me an idea ... thanks Bob ... I think I agree that the choke flap itself is unnecessary. For a couple of reasons, though, I'm unwilling to give up fast idle. In other words, you'd leave the choke linkage assembly in place; you'd just have the tower milled off and of course you would lose the flap itself and I guess you would have to detach the last couple of pieces of linkage (I'm not looking at the car this second, so I don't have a perfect mental picture of what's there).

I think what I'll do, to be sure that this plan won't leave me with a car that refuses to start, is remove the flap temporarily and see if doing so gives rise to headaches. Bob's basic premise is sound; airflow would certainly be smoother without that choke tower when you are using those 2" drop-base air cleaners that almost all of us have on there. (Terminology, though -- all this has no effect on the carb's vacuum signal per se -- it just affects basic airflow.)

Gotta think this through first before having the carb modded ... they don't give these Carter 400s away these days.
Harry M. Peeters

Harry, according to the experts the very small gap between the chrome cover and the throats of the barrels does affect the signal to the carbs. I believe its not due to vaccuum but to the resonating columns of gas that are set up as the various inlet valves open and close! I have double pumper Holleys on both cars a 390 and a 600. By the way you need an uprated fuel pump with a pressure regulator for the Holleys. The standard SU pumps pressure was falling away to zero on the dyno at full throttle. I have Facit fuel pumps and I believe a Filter King pressure regulator.
bob pulleyblank

This thread was discussed between 17/02/2001 and 24/02/2001

MG MGB GT V8 Factory Originals Technical index

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