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MG MGB Technical - Large B-Series Engines

I've just bought a 1977 rubber-bumper BGT. Its a nice little car but surprisingly 'gentle'. I suppose 84 bhp in a car weighing over a ton is unlikely to produce much excitement in modern day terms.

I'm considering upgrading my engine to one of the larger, 1950cc or 2000cc versions of the B-series engine. I'm looking for easy fast touring not competition use.

Does anyone have any experience, good or bad, of these conversions? Any comments welcome.

Peter Hills 77BGT
Peter Hills

There is plenty in the archives about what engine size is best. Personally, I would not go for one of these over bores. I understand that they can be troublesome. The cost of the pistons are quite a absurd too. With porous blocks letting water or oil escape either into each other or via the head gasket.

I have a 1860 engine, ‘stage 2 ‘ head, mild tune cam, non vacuum advance dizzy, balanced and lightened, last thing was an up rated oil pump with baffles in the pan.
I took the advice of a well know engine tuner and I am very happy with the results.
Don’t forget the more you change the cars original spec then the more you'll have to pay for insurance.
Ian Holliday

The best way to get more power I have heard is to port and polish the head and get a "Warmer" camshaft. Some better flowing filters help too.
Ross

www.paeco.com sells a stroker kit to bring your engine to 2.1 liters using 60 over pistons, so no overbore..Think the kit is around $1350.00.

greg
Greg Wilkerson

Peter,
Certainly you can get the engine opened out to 2.1 litres, but I'm told there can be problems. You have to remember that the B series engine was originally 1.2 litres. BMC, BL never made it bigger than 1.8.

As Ross says, the cylinder head is the place to start when looking for more power, but realistically, you are never going to have "fast" car in modern terms unless you stick a V8 under the bonnet. The design is 40 years old this year! Get hold of Peter Burgess' book on tuning the B series engine. He lays out in detail what is possible and even tells you whether the mods will make the car a usable street machine or a temperamental monster.

Mike
Mike Howlett

God help us all. I just recieved a Paeco catalog. Les B. would love this one, after we just got done discussing cost Vs rewards.

Let's see.....Stroker kit, titanium rods$570ea. and pins, alum flywheel, knife edged crank, and oh yeah, titanium half shafts $1,200 a piece(only $900ea. if you buy 10 or more).

It makes you wonder though, has anyone ever really tried ALL of that stuff at once?

Reminds me of the Montgomery Ward catalog that came around Christmas time when I was 8.


However; the stroker kit looks very interesting. Size without overboring too much, although I don't see how they can stroke .25" when I thought the big ends came too close to the cam. I Thought.035 was about the max?????
Fred Horstmeyer

Peter-
Unless you're willing to have headwork done, going for a big increase in displacement will only give you more low-TPM torque. The high-RPM power will peak at lower RPM as well. True, Big Bore kits do have the potential to give more power if the engine is properly developed, but only if you're lucky enough to have a block with unusually thick cylinders. If not, the cylinder walls will flex, resulting in a loss of compression, high oil consumption, frequent spark plug changes due to fouling, and cylinder wall warpage. Due to the higher pressures on the bearings, a higher-pressure oil pump is also a very good idea. If you choose to go this route, remember that there will be no room for an overbore, so the engine will be essentially disposable: when the pistons, rings, and bores wear out, you'll need to get another engine.
Steve S.

Steve, what do you know about changing the stroke, you seem to have the difinitive word on such issues?
Fred Horstmeyer

Fred-
Increasing the stroke of an existing engine shortens the connecting rod/stroke ratio. Although side-thrust loadings increase, this results in the piston accelerating faster down the bore, thus increasing the pressure differential between the outside and the cylinder. The increased difference in pressure thus occuring earlier in the stroke results in higher velocities in the fuel air charge. This higher velocity results in a larger charge filling the cylinder. However, to do this on an existing engine requires a shorter distance from the axis of the wristpin to the piston crown to avoid hitting the roof of the combustion chamber and a shorter distance from the axis of the wristpin to the bottom of the piston skirt to avoid hitting the crankshaft. The end result of this shortening of the piston is a decrease in its load-bearing surface. Couple this factor with the increased side-thrust loadings and the result is faster wear. Such an engine will obviously be harder on its oil and lower end bearings, although offsetting the bores will help avoid the worst of the lower end loads somewhat. I doubt that it would be possible to offset the bore of a B Series enough to make this approach worthwhile. Also, because the reciprocating masses of the assembly both accelerate and decelerate more rapidly, a different camshaft would have to be custom-developed, the maximum permissible RPM would have to be less, and balancing would become an important issue unless you're willing to tolerate some of the additional power being dissipated in the form of vibration. In addition, the shaft of the camshaft would have to be of minimal diameter to provide clearance for the connecting rods. Simply reducing the diameter of a standard camshaft wouldn't be a good idea at all. To accomplish this would require the use of an alloy that would have a high chromium (For rigidity), molybdenum (To avoid molecular shear), and vanadium (To control distortion) content, plus it would have to be heat treated to a hardness that might cause its small diameter to snap under the pressure of high-rpm stress. It would be expen$ive. To go from a displacement of 1.8L to a displacement of 2.1 would require an increase in stroke of 16%-17%, which would not result in a sufficient increase in power output to justify the hassles and the expense. A well-developed 1.8L would be far less expensive and would live far, far longer. The only rational justification for a stroker 2.1L B series engine would be in the eyes of those who want the ultimate in 4-banger power for use on a dragstrip. If you want maxipower for the street, fit a Rover V8 instead.
Steve S.

Ian,

Can you give me informations on the power of this 1860 'stage 2' engine ?
(when I write 'power' I speak of the actual one i.e. : a 3 L. BMW is something like 200 CV (HP) )

And how many Liters /100 Km (octane 95 or 98) in normal road use ?

Thank's for the response.

Arthur


arthur

Arthur
The power from my 1860 is about 86 BHP at rear wheels. But the torque seems to be its best point. I have loads of it. However, I have no graph from the rolling road to say exactly what it is.
I don’t have the exact miles per gallon figures. I suppose it does an average of 28 mpg on a run going down to 25 around town. I would say the car does anything significantly more or less, than an un-tuned car does. I still run the car without an unleaded conversion. I use Lead Replacement Fuel with additives.
I have not done anything that will overload the engine like the 2 litre conversions seem to do.
Does this answer your question? Or do you want more info? I am happy to help.
Ian Holliday

Arthur / Ian, this is the power curve from one of my 1860cc unleaded engines with a Piper BP270 cam and fast road head;

RPM BHP at rear wheels
2000 28.6
2500 40.3
3000 50.6
3500 61.3
4000 68.2
4500 74.3
5000 80.2
5400 83.6
Chris Betson

Thank you Ian & Chris for the responses

First of all excuse my english : I am not fluent in this language.

One month ago, I bought a 64 MGB and I will receiv it (full new) end of jun.
Concerning the engine, the seller advise me to take the 1860 'stage 2' (unlead) whith a special cam and outlet bore of 2"; He also spoke about special needles for the SUHS4 carbs (with SU air-filters). I take the 5 mecanic gear box.
The rear transmit is the banjo one. and the wheel are 15" with 72 arms.
I hope it is a good choice... and I am honestly waiting for any critics and suggestions.
He advices me to take the classical ignition (I have to say I would prefer a full electronic one because I don't want to have any problems).

My topic is do go to the Pyrénées with this car (about 2'000 miles go and return), is it realist ?

About the tools (gunson for ex.) I look on internet in UK and I don't understand the big difference of prices for the same article (colortune for ex.) have you any idea for a good provider of all those tune parts?

Arthur
arthur

Arthur, your english is fine.

You have made a good choice - you should enjoy the car.

I would recommend the Aldon Ignitor electronic ignition - it is good value for money and works well.

The main benefit of it is that it smoothes the idling of the engine and does not go off tune like points and so does not need constant attention.

If this is a new engine then run it in for 1000 miles and then take it to a rolling road tuner to have it properly set up.

Your trip to the Pyrénées is easily done in the car - have fun.
Chris Betson

Arthur,

The MGOC club in England supplies a lot of the Gunsons tools at reasonable prices, but i am not sure what it will cost to ship to Belguim.

It may be worth looking in you local motorists store, as i managed to find both the colour tune & the carbalancer for under £16.

Good luck

Scott
Scott Ralph

Arthur

Don’t worry about your English, it is fine we can understand it.
From your description of the engine, it sounds like a good choice. Have you changed the air filters too? If not I would suggest K&N or pipercross.
I have done a long tour of Northern Spain with my car carrying a lot of camping equipment too. I am hopefully moving to The Netherlands very soon, taking the M.G. with me. In the summer I too will be heading back to the Pyrenees and onto Galicia in Spain. Using the M.G. of course.
If you want to obtain any Gunson equipment I would suggest you contact Halfords. I understand that they have branches in Holland. If you can't find them here is the U.K. web site. https://www.halfords.com/default.asp
Click on the online store button then the workshop & tools button then Diagnostic Equipment you should find what you’re looking for.
Ian Holliday

So, thank's to all very much.

In regard of this thread, it seems that for me the 1860 'stage 2' is a good choice; probably, I have to speak with my seller concerning a 'bigger' oil pump as Ian mention it and I have to find the Adlon Ignitor of Chris.
This week, I'll compare the Gunson's tools of the Halfords.com 's site with the others.

From the thread of Peter, I appreciate the analyse of Ian and Mike, the word of Ross, Fred ans Scott, the internet reference site of Greg and of course the Octarine's site of Chris (whith is beautifull but a little bit slow ??) and finally the very nice teach authority of Steve (E=mc² and ... 1860 is the best).

Anyway, for my first contact with this MGB's forum, and in english (...) I appreciate the results and probably when I'll buy the tools for the "perfect-little-mécanicien-in-his-garage", I'll call you for help once again ...

If begin of august Ian and/or the others are in the Pyrénées, I can offer the first bottle (but this is another thread).

Arthur

arthur

Many people in this thread argue against bigger MGB-engines. While I agree with the 2100 cc conversion with the longer stroke (this seems to be very unreliable) I disagree with many of the other points against a big engine. I do speak from experience: I am running a 2 litre MGB-engine in my 1964 MGB since 1985.
This is an 18V-block bored to 83,5 mm using Lotus Hepolite pistons, with a leadfree Stage2-head with big valves and some other mods (dissy, camshaft, exhaust, HS6 carbs). The engine is revving like a turbine up to 6000 rpm and it is bullet proof. I have no leaks between cyls #2 + 3, no overheating, little oil consumption and the engine is as docile as you can think of. (not much power below 2500 rpm, I admit it – just rev it higher!)
On the rolling road I got 106 hp at the rear wheels @ 5400 rpm, it´s a genuine 120mph-car.
Do it right and you will have a superb engine and enough power to upset some bigger machines. AND you will have a reliable engine.
BTW: this engine was built by Browns & Gammons and may be one of the earliest 2-litre conversions around: it was built in 1984 and has done more than 100.000 miles since then . The engine was fitted with new bearings in 1993 and had a rebuild last year with new pistons. Now the block is leeved and still does give no problems.
joernm

Some time ago the O series 2000 engine was discussed at length. Has any one dropped the O series engine in their B? If so, how’s the performance over the 1800 B series? And if no one has done it, Why not? Just curious.

Bob Ritter
Ribert Ritter

Ribert-
It's been done, but primarily over in the UK as the engine was never sent here in any numbers (if at all). The O Series was essentially a B Series engine with a SOHC. Power was about 105 HP on the carbureted version, 117 HP on the fuel injected models, and 152 HP on the turbocharged models.

Joern-
A Big Bore engine with "not much power below 2,500 RPM"?! Which camshaft are you using?
Steve S.

Steve,
that´s the part of the engine I have to correct. At the moment I am using an Oselli B271 cam which has an unsatisfactory torque-chararcteristic. Before I used the original leymalnd 714 halfrace-cam and that was much better (Couldn´t get one while rebuilding the engine in 1993 so I took the Oselli).

"Not much power" means that I can still drive the car below that mark but it just isn´t as fun as using higher revs.
The rolling road figures were:
80 hp @ 4000 rpm
104 hp @ 5000 rpm
106 hp @ 5500 rpm

with the 714 the figures were much better:
90 hp @ 4000 rpm
101 @ 4500 rpm
110 @ 5000 rpm
112 @ 5500 rpm
106 @ 6000 rpm
Joern

I´ve just reread this thread and have some more remarks.
with 83,5 mm bore the capacity is actually short of 1950 cc, thats as big as you can get if you want a reliable engine.

@ Ian: The Hepoplite pistons are not that expensive. A set of +0.40 Lotus Hepolite AE-pistons with 83,5 mm and rings sets you back around £ 250.00 (if I remember it correctly) which is not prohibiting! Looking at the cost of a complete rebuild the bigger pistons will cost you maybe £ 100.00 more, which is much less than 10% of the total cost.

@ Steve: Even with 83.5 mm bore the engine is not at the end of its life when worn: you can get sleeves for the bigger bore, they are not cheap at about £ 100.00 for the set of four, but then you can rebore to 83,5 again. The machine shop will have to offset the bores slightly to avoid cracking the block, but it works and is still reliable. I bought the liners from MG Motorsports.
joern

This thread was discussed between 18/04/2002 and 22/04/2002

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