Technical Information (MGB 7)
03/08/01 18V ENGINE UPGRADE MGB 1975 ONWARDS
Our first and foremost objective was to improve engine performance without circumventing by way of removing or disabling smog emission related components, and to use original parts where practical. If you follow the outlined modifications, you will be pleasantly surprised by your engine's performance. These recommendations should be carried out along with normal engine rebuild procedures.
Before reboring your engine block, check to see if OEM cylinder sleeves have been installed. Apparently the factory, to remedy block casting imperfections, did this. Reboring depends entirely on the thickness of these sleeves. If you have an engine block that has thin cylinder sleeves fitted, it would be necessary to machine and resleeve the engine block with thicker wall sleeves or proceed to find another 18V engine block assembly. Let your local machine shop make this decision. Recommended bore size 3.180" (+020") for a capacity of 1822cc.
Use part No 420-435 piston set (+020) or, any of the other oversizes. These pistons were fitted to earlier MGB engines with 8.7:1 GCR (geometric compression ratio), piston dish size 6.2cc. For precise GCR control, we can supply custom-made pistons P/N MGB1822cc. These are manufactured by J.E. Pistons with a thicker than normal piston crown ready for piston dish cc machining.
Have your camshaft reground to pre-1975 specifications, OEM P/N 88G303. We highly recommend Demitri Elgin Racing Cams
P/N 6625075-15 reground camshaft. This reground camshaft will be nitrided (heat treating process) and parkerized (aids in initial lubrication, avoids scuffing). The camshaft should be installed and the intake valve peak lift set to between 104 and 106 deg. ATDC. A selection of offset camshaft keys are available to accomplish this. We usually find that a 8 degree key is required to arrive at this setting. Supplied on an exchange basis only.
Fit modified lifters that have been Rockwell hardness tested. Lifters should also be drilled for oil drainage, which will offer improved camshaft lobe lubrication. Installing lifters that do not meet Rockwell 50RC standards spells "DISASTER".
Removing approximately 1 to 3lbs from the back and front face (other than the clutch disc surface) can safely lighten the flywheel.
Before having your machine shop regrind your crankshaft assembly, have them modify the rod bearing journals by drilling an additional oil feed hole, (18V crankshafts have only one oil feed hole). Balance your crankshaft along with crank pulley, flywheel, clutch cover, pistons and rods. We do not supply exchange reground crankshafts.
If you modify your crankshaft, we recommend having your new oil pump modified to increase output volume. This relatively simple job should cost no more that $25. Install uprated pressure relief valve spring P/N 1H756/A, however, if have not had the crankshaft modified, then it will not be necessary to fit this spring or have the oil pump modified.
Your original cyl/head (CCV combustion chamber volume 39cc) may be used but with the fitment of the +.020 pistons, or any other oversize, we may have a higher GCR (approx. 9.2:1) which could cause detonation problems, however, this will depend upon several factors which we have outlined in previous technical information. You may use the earlier style cyl/head (68 thru 71) which has a CCV of 42.5-43.5cc and would necessitate the use of the earlier style rear rocker shaft pedestal. Use of this cyl/head will bring you into the region of 8.8:1 GCR and will require, if you are retaining your original Zenith/Stromberg automatic choke assembly, the heater valve to be drilled and tapped to accommodate a 1/4" NPT x 3/8" tube fitting and a hose directed to the carburetor choke heat mass cover.
Zenith/Stromberg Automatic Choke Unit
Because of the problems associated with this unit, namely gasoline leaks, carburetor fires, excessive fuel ingestion into the engine, and the resulting in catalytic converter "glow" syndrome and subsequent meltdown, we recommend the fitment of a manual choke assembly. Don't throw away your old unit. Your particular State will, in all probability, require that it be refitted as part of their smog inspection program.
1976 (Fed) and 1975/76 (Cal) had no provisions for vacuum advance. You will find that some distributors had a vacuum unit fitted, unfortunately, the distributor base plate was pinned to prevent movement. 1977 and onwards had distributors with vacuum units that were activated by inlet manifold vacuum by way of a 4th gear switch. Set ignition timing to between 10 and 15 deg. BTDC @ 1500 RPM. On 1975-76 models, you will benefit by using the 1977 and later distributors and hooking up the vacuum advance. However, with no provisions for a 4th gear activating switch, it would be necessary to reduce your ignition timing, and set to between
5 and 10 deg. BTDC @ 1500 RPM (vacuum removed).
Catalytic Converter and Exhaust System
We strongly recommend the relocation and fitment of an inline free flow style system. This will prevent premature engine sideplate cover gasket failures (see MGB3 for one-piece side plate cover information). This will also prevent oil carbonation in the lifter/tappet chest area, which causes lack of lubrication to the camshaft lobes in the immediate area. See "Zenith/Stromberg Automatic Choke Unit" paragraph for additional problems.
NOTE: With the catalytic converter relocation (under the car) caution should be taken, when the vehicle has been driven, as to where the vehicle is parked. Any combustible materials, such as leaves, could be become a fire hazard.
These modifications will require you to use the highest premium unleaded fuel commercially available in your area; 91 or 92 RON.
PARTS RECOMMENDED AND SUPPLIED BY BRITISH AUTOMOTIVE
QTY PART DESCRIPTION
1 MGB1822cc JE Forged Piston Set +.20"
1 9526/020 Hastings Piston Ring Set
1 NPN Piston Dish cc Machining
1 420-435 8.7:1 +.020" Piston
1 420-440 8.7:1 +.030" Piston
1 420-445 8.7:1 +.040" Piston
1 420-450 8.7:1 +.060" Piston
1 6625075-15 Reground Camshaft(Heat treated)
1 WKN505/8 Offset Camshaft Key 8 deg.
1 2A13/HP Modified Lifter Set
1 4E9300 Exhaust Front Pipe
1 4002 " " " Flange
3 CHS2515 Exhaust Manifold Stud
3 SSL51624 " " " Locknut
1 93002 Inline Catalytic Converter
1 NBM2 Manual Choke Unit
PARTS RECOMMENDED BUT NOT SUPPLIED BY BRITISH AUTOMOTIVE
QTY PART DESCRIPTION
1 F18 Glasspack Center Muffler
1 F16 " Rear "
1 NPN Connector Pipe(93002 to F18)
1 NPN " " (F18 to F16)
The above exhaust components should be available from your local muffler shop.
For price quotations please submit your part numbers by FAX or
E-MAIL (email@example.com). Prices will be quoted by return FAX only. Please be sure to include a return FAX number.
All other engine parts can be found in your current Moss Motors MGB Parts Catalog. Please be reminded we discount 10% off all list prices. Please submit your additional parts request in the manner prescribe above.
NOTE: In closing, we consider the outlined modifications to be cost effective and convenient. For further information, please feel free to call Doug Jackson at 415 883 7200