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MG MGB Technical - Supercharging an MGB GT

Just looked at an old thread on supercharging with the Moss kit. I am about to embark on this venture but thought of rebuilding as engine specific for this task. I have read both relevant books by Peter Burgess. I will attend to all parts of the engine but now, what about the cam, leave it standard? and the head, Peter has one specifically for supercharging, what would be the difference/ then again shall I use low compression pistons. I guess peter with his head has probably worked it but perhaps has bearly skimmed it just to straighten ie compression will be low? What are the general thoughts? Mike
J.M. Doust

You'll want to keep your compression around 8 to 1 to get the most out of your supercharger. A Peter Burgess head would be a great investment. I spent 13 hours modifying mine and I know it is no where near the precision work that Peter turns out. There supercharger specific cams available in AU. I went with a Kent 280 and have experienced excellent performance. If your budget allows, you should go with forged, rather than cast pistons, for added strength and longer life. ARP fasteners are a great investment and will hold your engine together indefinitely. Finally, Fel-Pro gaskets will give you a well sealed engine and many years of reliable performance driving. RAY '67 supercharged Tourer
rjm RAY

Thanks Ray, I have an engine 18GH-WE-H26514, this I will build up for the project. But so far,( and I have not seen it yet!) I make out it is probably a 1969 engine which may have been fitted to a 70 roadster? most likely have a steel crank with weaker caps? ie not the slab sided crank? the rods will be horizontally split, but of the heavy variety etc pity it is not an 18V, but I did not have a choice. The car will be used on the road,( not race track!) with occasional demonstrations of power, so I suppose it will be stressed little. Forged pistons you say? Thanks Mike
J.M. Doust

G/day Mike I have been using the Moss SC for close to seven years and its been great. Its a 68 still with the angle rods and the OE MOOG pistons but uses no oil and goes as well as ever. Its been one of those magic engines that just keeps going. The rods you have are as good as any and can be prepped close to the 18V rods which are very hard to get anyway. JE make a special forged 8:1 CR piston for the SC Bee that I would use for sure if building a new engine. I use a dedicated SC cam made in Melbourne and could not be happier although others have also had excellent results with the Piper 270* and one from APT in the US. There was very little info around when the Moss SC came out mistakes were made in a few cases but there are no problems now and plenty of help. The only problems I have had in 40000 miles with the SC are a blown head gasket in the first couple of hundred miles. A Payen gasket and ARP studs fixed that and I would do that even if not a rebuild. Replaced the drive belt at 30000 miles and replaced a leaking gasket between the SC and manifold. (That has now been modified on the new ones) The SC itself is the big power maker with a huge lift in torque but the other things also add up. Even with a stock engine in good nick it will put a smile on your face. Get in touch any time if you want to. I am in northern Victoria
Denis
Denis4

Your choice of ignition systems will be a very important decision. After fighting with a modified stock Lucas unit for 2 years, I purchased a GM HEI based distributor with a coil output of 50,000 volts. It's made by Davis Unified Ignition systems. I used a MSD Boost Timing Retard Master to control the distributor's timing advance under boost. It has worked out better than I could have have hoped for. My engine is a '65 GB, with the angled rods, and beyond what Dennis has experienced with head gasket problems ans stock head studs, The engine runs perfectly. The ARP head studs make a world of difference and blown head gaskets are now a thing of the past especially when using the Payen aka Fel-Pro head gasket. After almost 8 years the only problems that I ran into were a blown intake manifold to blower gasket, which I fixed using some neopreme gasket material. Also, my supercharger kit was one of the first produced, #12, and the intake manifold to head ports were misaligned by 6mm. The use of a grinder brought this back into spec. Good luck with your project. I'm sure you'll be quite pleased with the end result and amazed by the way it changes your car for the better. RAY
rjm RAY

Hi Ray and Denis, Many thanks for your input I am learning more. Denis indeed I will probably take you up on a contact some time. I am adding things up as I go along and thinking, ooh, this is going to get pricey! I might just, for the hell of it, put the supercharger on the existing engine that is already in the car, and slowly build the other! I got an 'e' mail from Peter Burgess, He said; JE Forged pistons would be good and possibly a mild piper cam. Now, ignition side, I currently run a 123 ignition which I am well pleased with. Is it possible to use an MSD and this so as to get a fatter spark? thanks Mike
J.M. Doust

Installing the supercharger on your current engine is a very good idea. It will give you important firsthand knowledge about how each part of the engine works with the other components. Not being familiar with the 123 ignition system, I can't say whether the MSD unit will work in conjunction with it. RAY
rjm RAY

Mike the 123 will do the job nicely with a good sports coil. With the SC you would pick a curve that comes in quick for a total advance of about 30* at about 2500 - 3000rpm. I use 15* initial 15* mechanical for 30* total, all in by 2500rpm and it works for me. To start off 26* total works well, avoiding detonation and slowly work up a bit as you learn the tricks. I started off with a dead stock engine and have had fun gradually working it up without spending an arm and leg.
Denis
Denis4

Denis, Thanks for your input. I am inclined to agree, my 123 at present is using a Bosch sports coil, and really I have no complaints. Indeed when I got the set up, I decided to once again tune the carbs, But I obtained rebuild kits first, then went about syncronisation etc I obtained richer needles as per Peter Burgesses' suggestion as I had sports air filters and my 'home grown' cold air system ( more about this later!) and do you know it certainly feels much stronger, there are no flatspots or hesitation ( 4 oz springs lighter oil, and an enlarged dashpot vent hole. ) I want to take this further and start to modify my needles ( By using an Air/fuel meter etc. ) Anyway to get back onto the subject, the 123 takes ignition out of my list of worries or concerns. It was just that in supercharging, one will be trying to initiate a flame front in a very ( hopefully ) dense charge where a fat spark would be advantageous.
J.M. Doust

I/m using a Bosch Scorcher points distributor with a Lucas sports coil and it works well. I run 9lb of boost and it will turn over 6000rpm without a miss, so your 123 will certainly do the job with the Bosch sports coil, which is also a good choice. A Moss SC will never be cheaper than now with the AU$ as high as it is. By t6he way there is a "Supercharger" category near the bottom of the list if you wish to use it, but it does not matter to me.
All the best. Denis
Denis4

This thread was discussed between 29/11/2010 and 06/12/2010

MG MGB Technical index

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