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MG MGB Technical - Mgb engine

Hi

I want to build An new engine for my 1968 B

I have An early engine 18gb and An 18v engine
Witch of Them would-be recomended?
I have a cylinderhead with THE biggen valves i want to use
I want want to build An engine witch has a goog iddle , and Some good torque . I dont want a lot of power in THE high revs
Should i bore THE engine to .30 or beter to .60 ?
Witch cam should i use ?
I want to use THE standard su carbs should i go for another Needle?
Standard air filters or K&N?
Is THE standard manifold ok or should i go for THE tubular ?

Serge
serge

First decide what you want to achieve, how much work you are prepared to do, and how much money you are prepared to spend.

Good idle, some good torque, not lots of power at high revs, standard carbs, doesn't sound much more than a standard engine.

The bigger the overbore the more performance you should gain. But standard overbores don't add much, and bigger ones can introduce issues elsewhere that need work.

The standard cam gives a good balance between tractability and performance. The more you go for performance the harder it is to drive smoothly at lower speeds.

If you start doing things like adding tubular exhaust manifold and K&Ns you will be upsetting the mixture balance through the rev range, which almost certainly will need a 'richer' needle.

You would probably be advised to read one or more of the power tuning books.
paulh4

Hi Paul
Thanks for the input

I have 2 engines a 18gb and a 18v
I have to bore them both so if i go for .30 or .60 the price will be same, just like the crankshaft, i have to do some work on it also.
THe camshaft and the followers i renew , here wil it be a different price on depending on witch i choose , now i have a standard one in my car . It has some torque till 3500 rpm and than it stops . I have a head ( 12h709) with bigger Valver on the shelf and want to use that one . ( This Will proberlay the biggest cost i was thinking to send iT to Peter burgess to do some work on iT).
What i dont want is a 1950 engine with high idle (1500rpm) a friend of mine has it and isnt fun to drive high idle and verry nervus.

Serge
serge

Serge. Simplistically speaking, increased capacity = increased torque. + .60 thou is about the max I would go, but if you have future issues you will have nowhere else to go in terms of further over-bore. The reason why your B runs out of breath is poor breathing, i.e., the inlet, head and exhaust can't move enough air fast enough. Gas flowing the head, improving inlet and exhaust flow with better filters and better exhaust manifold and system will get you higher up the rev range, a moderate cam will help make better use of the improved gas flow. Idle will only be drastically compromised by too radical a cam, not by improving gas flow, i.e., improving efficiency! As Paul mentioned, improving air flow into your engine will also require a commensurate improvement in the amount of fuel available; i.e., richer needles. Balancing the reciprocating bits, flywheel/crank and combustion chambers will make the engine smoother too.
Allan Reeling

"It has some torque till 3500 rpm and than it stops"

Something wrong there, it should rev into the red - albeit very noisily, it's too painful for me to want to hear. Torque peaks at about 3k (110 ft.lb), but then only drops to 90 ft.lb at 5500rpm.

You need to investigate that before modifications. Could be carbs, choked exhaust, valves, ignition/timing and so on.
paulh4

The engine what is now in does that, and iT wil go higher in revs and iT is to painfull for me to :) exhaust is a new stainles one ignition is a accu spark on 8°btdc carbs a set on a local garage ( timing also) who does only englisch car
If have 2 engines on the bench a 18gd and a 18v with a extra head 12h709 on the shelf ,i want to use one of those to build something better

Serge
serge

The engine what is now in does that, and iT wil go higher in revs and iT is to painfull for me to :)
If have 2 engines on the bench a 18gd and a 18v with a extra head 12h709 on the shelf ,i want to use one of those to build something better

Serge
serge

I think Serge you are mixing up Torque and Power. Torque will reach it's max fairly low down in the rev range then drop off. Power on the other hand tends to increase with engine speed then drop off towards the amber/red line. Torque gets you off the line, power gets you there faster........simplistic again! The dotted line is torque, the other BHP. This was my 1800 GT worked on as I suggested above.


Allan Reeling

Serge,
many questions with lots of possible answers and, as Paul says, you would be advised to get one of the tuning books. As Peter won't come on here and recommend his own works, I will :-)
Get a copy of this
http://www.ebay.co.uk/itm/How-to-Power-Tune-MGB-4-cylinder-Engines-by-Peter-Burgess-9781845846152-/351953935370?hash=item51f216dc0a:g:W4kAAOSw241YdIq2

And all your questions will be answered. I haven't got my copy to hand but from what I remember...The 18V conrods are a little lighter but the older ones are stronger! As Alan says, you will definitely need the head reworked and shipping it to Peter will be money well spent. As for the rebore, the difference between +30 & +60 will be 30cc which is about 1.4%, not worth the risk IMHO for a road car. I would stick at +30 which leaves room for more later. The standard manifold will be fine for the type of engine you looking for and as you've just fitted a SS exhaust I would stick with this set-up. Again, the standard carb's will be okay if in good condition but new needles will be required with a K&N and the other mods. The cam is where you will make or break the "refinement" of your engine. Your friends 1950 must have a wicked profile and I would takes Peters advice and go for something like a Piper 270. Correctly timed with a vernier sprocket should get you a very smooth engine with a good Torque profile from idle all the way up to 5.5K or higher.

Do let us know what you settle on and how the engine turns out in use.

Best of.......
MGmike
M McAndrew

Hi Mike

Thank you for the advice , i Will first Get the book
And Will go for the early 18gb and An .30 bore than probarly

Serge
serge

serge
1] the 12h2709 head will show more performance over a smaller inlet valve head - but in the higher revs

2] the 12H2709 requires exhaust valve cutouts in the block - only present on 18V block. but you can cut your own

3] 30 or 60 overbore? more cc, more torque. but enough to notice? i suggest a professional tune up will give more performance that you can use than a few extra cc.
However if you went for a 40, then you still have one bore left as 60 is maximum without installing sleeves. or if you have another block, then if you went 60 and needed a rebore, bore your second block to 60, make cutouts and reuse all the other bits like pistons....?
i went to 40. if i did it again i would go to 60. blocks are easy to buy.

4] for the mods you propose, stock manifold will perform well and a performance one will probably be a waste of money

5] 18v pushrods and cam follower are the ones to use. they are lighter than the old 18gb ones

6] most (including myself) fit K&N with AAA needle. For me there was a very good power gain. it was the first mod i did.

7] regarding cam, stock is good. you make wish to look at piper 255. a 270 may be too focussed on high rpm for you. both will give a good idle.
FYI i used 270.
if i did it again, i would use 255 instead for low to mid range torque. i have good power at 5k rpm+ but i do not drive there very often.

8] you mention Burgess head and it sounds like Econotune will serve you well. that is what i have too.

9] also crank. peter's book shows the better one to use. it is the later flat sided one from the 18V

G

Burgess book on EBAY now for £10. very good book.
http://www.ebay.co.uk/itm/How-to-Build-Modify-and-Power-Tune-Cylinder-Heads-by-Peter-Burgess-David-Goll-/152373064156?hash=item237a2471dc:g:X1MAAOSwXshWqbiv




Graham Moore

Hi Graham

Thanks , so the best block would then the 18V i supose
Lighter crank, Rods ect
The 18gb block when iT is bored at .60 , does it still need the eyebrow modification ?

Serge
serge

All blocks require ex valve cutouts unless you are going to 1950. This assumes std 1.34" ex valve. All 1800 heads need cutouts if skimmed to raise CR or if 18v heads to start with.
Peter
Peter Burgess Tuning

This thread was discussed between 13/01/2017 and 18/01/2017

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