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MG MGB Technical - Air Filters SU Conversion

Anyone know if moving the engine mounting spacers will increase clearance for air filters on a twin SU HIF4 conversion on a LHD '80 roadster.

Mine has two spacers each side, and the question posed by the mechanic was if we removed one or both spacers from the RHS to the LHS, effectively shifting the engine to the RHS,would it give us the room to get the K&N pancakes onto the rear carb, and would there be any adverse consequences.

I seem to recall we need around a 1/2" -3/4" extra gap to get it onto the rear carb.

mark smith

Wouldn't that screw up the alignment of the driveshaft? It is my understanding that the output shaft of the transmission must be parallel to the pinion shaft of the differential, or vibration will occur. Shifting only the engine mounts, without a corresponding shift of the transmission mounts, would result in the two shafts being at a slight angle. The shafts need not be concentric, but they must be parallel.

In any case, K & N makes a cone-shaped filter that many MGB owners in the US use to provide clearance between the filter and the brake booster, when doing dual carb retro-fits. I don't know the part number, though. Perhaps someone else can provide that.
Paul Noble

Yes, Paul is right. You need the conical K&N filters and they will clear the brake booster. I have the box right here - Moss part #222-985. The K&N number is 56-9320.

I hope to get my 79 B put back together in the next 2 months and finally get these installed!!!

John
John Reynolds

If what Paul says is true, why have spacers in the first place, and why have UJ's on the propshaft, which must provide for some leeway.

Do all MG's have two spacers each side of the engine mounts, for example is this perhaps unique to the North American version, with a different spacing arrangement for the English version.
Jo

Each B's mounts are a little different from factory. Some had spacers, some didn't. Some had spacers to only one side or more on one than the other. It seems it had to do with the alignment at the factory.

With these engines going in and out after so many years, I don't think it'll make much of a difference.

The inclusion or removal of one or two spacers at the motor mount won't really give you much more clearance for the pancake filters.

The only alternative is to install the conical K & N filters as stated above.

Good luck
Luigi

Really confused now.

Paul says no spacer shifting, yet Luigi thinks 'I don't think it'll make much of a difference.'

Cannot imagine those precision engineers at Abingdon aligning anything other than approximately, so if that is the case, surely a spacer shift, coupled with a shaving of those phenolic carb spacers, should do the trick.

Comments? T sure would like to know just in case I have to try it.
Jo

Hey guys,
When you install the K&N's, are you rejetting?
PhotoEd

Paul may be right but in real life experience (ownership of four or 5 Bs, I forget)and countless engine removals over the decades (OK, four or five) I haven't had any issues when I forgot which side had the shim or how many.

About changing needles. Sometimes you may need to change up to a richer needle when you change to K & Ns because of the greater airflow. If you can't retain the bottoms from the original filters, try to also procure some low stacks for the correct airflow into the carbs. These stacks are about $25, fit inside the airfilter housing and help the carbs suck the air in the correct flow characteristic. They supposedly also get you .5 hp, give or take .5
Luigi

Mark-
There is an alternative solution. The problem with the conical airfilters is their shallowness which creates induction pulseproblems, their small internal volume which will not allow the fitting of a set of stub
stacks, and their small surface area. The K&N airfilters all use the same filtering medium, so the smaller the surface area of the filter, the less the airflow potential will be. Conversely, the bigger the surface area, the greater the airflow potential. This is why the 6" X 3 1/4" deep filters are preferred by those who go for serious power increases with a B Series engine. Induction pulse problems aside, the airflow capacity of the little conical or pancake filters is more appropriate to a mildly power-enhanced 1275cc A Series engine, such as is fitted to the MG midget or the Austin Healey Sprite. In addition to this problem, the remote floatbowls of the SU HS4 carburetor will interfere with the master cylinder, thus such a conversion requires the use of a set of SU HIF4 carburetors. Retrofitting the earlier non-boosted master cylinder is the common solution, but this is not a bolt on affair as its mounting flange is turned 90 degrees so the mounting holes of the pedal box won't line up, and the appropriate earlier pedal box assembly is radically different, even having a different mounting hole pattern at its base that requires drilling a new pattern in the body of the car. This is just one of the reasons that it's unusual to see a Rubber Bumper model with an uprated B Series engine: It's much more work. When somebody wants to go for really dramatic power increases, he swiftly comes to think that he'll need to retrofit the earlier brake master cylinder and pedal box assembly so that he can mount airfilters that have a decent airflow capacity onto the carburetors like the Chrome Bumper model owners do. "After all," he reasons, "it's not that difficult, really, it just requires some persistence and time, plus another master cylinder and the earlier pedal box assembly. If my boosting servo and master cylinder are in good shape, then I can always sell them as a unit to help cover the cost of the earlier master cylinder and pedal box assembly because the servo is getting harder and harder to find." And, to the conventional, orthodox thinker, this reasoning holds true. However, read on- Fabrication of a plenum chamber to go on the carburetors and running a large diameter breather duct hose to a remote aircleaner housing would enable the retention of the existing boosted brake system. From the aircleaner housing the intake hose can be run to the air passages neatly provided beneath the bumper in the vented front valance of the 1972 through 1974 1/2 models of the chrome bumper cars. You'll need to do some scavenging in the junkyards to find the right box (more work) and then figure out a mounting system for it (still more work), but the larger, more commodious engine compartment of the later Rubber Bumper models should make it a relatively easy task. To equal the airflow capacity of a pair of 6" diameter 3 1/4" deep round airfilters you'll need an airfilter housing box with a filter that has an area of about 122 square inches (11" X 11").
Steve S.

Steve, I don't like the conical filters, they lack the symmetry of the pancakes, however I'm appalled to note your comments that retro fitting the older version of the servo-less MC appears to be the best way forward, if power is to be maintained.

Has anyone fabricated the plenum chamber discussed, or know of any plans, drawings or pictures, which could be used to enable such a thing to be made.

When Steve S talks about 'scavenging in the junkyards to find the right box', does anyone know exactly what old banger I should be scavenging for in a UK yard.
mark smith

regarding engine spacers, they were/are all custom fitted to allow for steering column to engine part (exhaust manifold here, distributor(?) there) clearance as best I know. There are no spacers or shims for the trans mounts so I really don't think they have anything to do with aligning the pinion and main shafts.

As far as going to tandem non-boosted MCs, I prefer the feel of my 'B brakes to power brakes and don't feel the need at all for power brakes in such a small car. Personal preference I guess, but if it makes things roomier under the hood, I don't see any big negatives. Luckily my car's a '70 so I don't have such problems:)
Wade Keene

My HS4s fit fine with the conical K & Ns. I did do, as Steve S mentions, drill new mounting holes in the pedal box assembly in order to fit the later power booster and pedals onto my '69. No clearance problems, tho it is tight, just as tight as the later models. I do know that the larger air filter assembly is preferred, but I made my choice and wanted the power assist. I was also able to purchase low profile velocity stacks for the conical filters and they seem to work fine. The stacks rise 1/2" above the flat backing plate of the conical filters with a nice smooth curvature. Can't seem to remember where I purchased the stacks from, although I know it wasn't from the usual suspects (Vicky Brit, Moss, etc.).
Luigi

Re: "Has anyone fabricated the plenum chamber..."

Yes, I've seen one advertised. It was semicircular in cross section, with the flat side running along the face of the carburetor. I think the arced side was about 3-4" in radius. I don't recall what it used for an air filter. Nor do I recall if it would fit behind a brake booster. But being made of sheet metal, customization would be as easy as swinging a hammer.

I apologize that I can't find the link for it. It seemed like it came from one of our more well known sources in the kin of APT or K&N. If you're interested, maybe another member will know who was selling it.

When I did the research I passed on it because the price outweighed my interest. (I was looking for a cool intake air solution.)

If I were to search the archives, I'd look for a post around two years old that contained the words "Volvo" and "Kindig".

Hope this is of some help.
Matt Kulka

I think, Matt, you're thinking of one made by TWM Induction. It is "universal" in that the plate which mounts onto the carbs needs to be drilled for mounting and venturi holes. It looks like it could easily accommodate velocity stacks within the box, and has a 3" dia. opening at one end to which one could connect an air cleaner or a tube which could in turn be connected to an air cleaner. I think it would fit into a manual-brake 'B very nicely but I don't know about one with a brake booster. It seemed expensive to me too.
Marvin Deupree

A photo of the Kindig modification can seen here. His mod was made to use the ZS carb. Other photos show some twin SU conversion. Clifton
http://www.ph.utexas.edu/~yue/MGBcarbs/MGBcarbs.html
Clifton Gordon

Great link Clifton.
Jo

Marvin,

The TWM box was the one I was thinking of. I was wrong, it's fiberglass, not steel. So denting it to fit around a brake booster is out. And, as has been mentioned, the $199 price (on sale, no less) makes this a bit out of reach for the casual interest I have in the item.

If I were in a pinch, as is Mark Smith, I think I'd visit the local home improvement warehouse and see what kind of ducting I could find to emulate the TWM box. Perhaps some heating duct or raingutter downspout could be fashioned into a serviceable airbox.

Matt Kulka

I'm really surprised so little effort has gone into getting a good filter alternative sorted out for this, as it appears from Steve S's comments that the K & N route is an expensive waste of time.

I sure like the pictures in Clifton's link, which I can imagine fitting to twin SU's as a Y type fabrication.

http://www.ph.utexas.edu/~yue/MGBcarbs/MGBcarbs.html

Haven't checked out if anyone would make such a thing, but it must be reasonably simple, and therefore inexpensive to fabricate.

Anymore ideas like Clifton's out there, I wonder.

Once again, anyone know if there is an old banger I should be scavenging for in a UK scrapyard, which might have something similar.

mark smith

I know that Volvo's had twin SU's and then twin Strombergs up to about 1978 (677, 120 and 140 models). Someone said they had an air box. Of course, the carbs were on the other side of the motor in a Volvo. But it might give you a head start on fabricating something.
Matt Kulka

Thanks Matt, I'll chase that lead up.

Nevertheless, I'm still hoping someone can confirm that a simple move over of the engine, coupled with a shaving of those phenolic spacers, will solve my tight squeeze.

I don't like the conical filters, and reading Steve S's comments inclines me away from them anyway.

As I already have the pancakes fitted at least to the forward carb, my preferred solution would be to figure out how to squeeze the other pancake onto the rear carb.

Apart from eyeeing up the hammer, someone please tell me I can move and shave.
mark smith

Take out one or more spacers, try it for fit, if OK you are home and dry, if not chop those phenolics in half, and hope for the best.

Failing that, get those conicals ordered.
Sam

This thread was discussed between 09/03/2004 and 23/03/2004

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