MG-Cars.net

Welcome to our resource for MG Car Information.

Recommendations

Parts

MG parts spares and accessories are available for MG T Series (TA, MG TB, MG TC, MG TD, MG TF), Magnette, MGA, Twin cam, MGB, MGBGT, MGC, MGC GT, MG Midget, Sprite and other MG models from British car spares company LBCarCo.

MG MGB Technical - Exhaust Manifolds

I am currently gathering parts to convert my 77 B to dual SU's. I noticed in the Moss catalog that different part #'s are listed for use on HS and HIF equipped cars. What is the difference and are they interchangeble. I have both HS and HIF carb sets but only HS exhaust manifolds. I am planning on using the HIF carbs after reading on here that the float chambers may come in contact with the brake booster.
Scott Shirk

Scott, The mounting flange for the HS exhaust manifold is 9/16" thick, the HIF exhaust flange is 7/16". The respective inlet manifolds are the same thickness. If you mix them you will need to fabricate some shims so the manifold mounting washers and nut will tighten both manifolds evenly, otherwise you will have a serius leak from the thinner manifold. Some thick washers cut in half make good spacers/shims.
I have not converted a rubber bumper car, I cannot answer your question about the brake booster contacting the float chamber but I thought the big problem was the filter. Clifton
Clifton Gordon

I agree with Clifton, the brake booster can interfere with the rear air cleaner. Using the K&N tapered ones, Stellings and Hellings or the Longflow type eliminates the problem. I recall reading the interferance statement as well. I checked my setup. The rear float bowl on the HS4 is no where near the brake booster.

Mike
'79B
Mike Janacek

Scott. Both the HS and HIF carbs seem to bolt up to the same manifold with no problem. When I bought my 68GT it had HIF carbs on it. Ran well but would not pass emissions testing. Bought new HS carbs and fitted them to the existing heat shield and intake manifold and it has been running fine for years. So, from a practical point, I consider the two to be interchangable. Les
Les Bengtson

Scott-
The HS4 compatible exhaust manifolds have a mounting flange thickness of 7/16" and can be readily identified by an external casting number of 12H 709, while the HIF4 compatible exhaust manifold has a mounting flange thickness of 9/16" and can be readily identified by an external casting number of 12H 3911. If you want to mount North American Market HIF4 carburetors you'll need to use the HIF4 Compatible intake manifold because it has a vacuum takeoff for the advance mechanism of the distributor.
Steve S.

I rechecked my information on the exhaust manifold flange thickness, and the 12H 3911 manifold I'm looking at now is 7/16" as I stated in my first response. I just got it back from AirBorn Coatings so it's off the car and easy to measure. I also measured my spare inlet manifold with spare HIF carbs and it has 7/16" mounting flanges, it also has a takeoff for vacuum advance. On my two HS inlet manifolds you can remove a plug and install a vacuum takeoff so that's not a big problem. BTW the mounting flange thickness on my HS inlet manifolds is 9/16". FWIW, Clifton
Clifton Gordon

Clifton-
Looks like I got the thicknesses reversed. That's what happens when you go by memory intead of a ruler. Thanks for the correction.
Steve S.

Steve, Not a problem, when I first posted I went by memory, after your posting I checked the dimensions to verify if my memory is still on track. Regards, Clifton
Clifton Gordon

This thread was discussed between 06/11/2002 and 07/11/2002

MG MGB Technical index

This thread is from the archive. The Live MG MGB Technical BBS is active now.