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MG MGB Technical - Power, Power, Power

I was just reading a thread that suggested 120bhp at the rear wheels was possible from 1868cc. I thought that it might be interesting to compile a list of specifications and power outputs as a reference thread.

I'll start with my GT:

Bore: +0.030"
Compression: 10.5:1
Head: Burgess Big Valve Fast Road
Cam: Piper 285
Carbs: HS6s, custom needles, ram pipes and ITG filters
Exhaust: Peco 4 branch, two box (twin pipes)
Ignition: Aldon distributor with magnetronic and vacuum advance, NGK BP7EV plugs
Fuel: Shell V Power
Power: 102bhp at rear wheels
Measured at: Sigma Engineering, on a warm (for England) day

Anybody else want to join in?

Neil


Neil

these cars are a bit of fun , i have the same set up, a great improvement but you will get bored very quickly as a wispy boy racer will go straight by you in there corsa .i owned a rv8 and i dont think you would bother with the power upgrades to the b engine .i currently own a tvr chimaera 4 l 0to 60 in 4.5 second but i like driving both my cars .after driving the v8 tvr the tuned 110bhp b engine is little more than a joke .
daz

*peter burgess fast road head
*piper 285 cam
*4branch manifold ,ss exhaust
*K&N large twin air filtes
*aldon 101by2 dizzy , electronic ignition .
110 bhp at the wheels
its a bit of fun .
daz

Add a supercharger and the playing field changes quite a bit. RAY
RAY

i agree but , you need eather a standard cam or the cam for the job,allso eather a spacer for the head or a reworked head made for the super charger .i don't think sticking a supercharger on a standard engine is the answer you would get more power with my set up .
daz

Hi Neil

The biggest set back to compiling figures is the variation in bhps from dyno to dyno, what gear the car is run in etc etc. You need a wide variety of different specs from different dynos to try and see what-is-what.

Peter
peter burgess

I agree with Peter, it's hard to compare results from different dynos.

I would expect a little more power from Neil's engine, but again, it could be the dyno. How is your cam timed Neil?
Sean Brown

I'll third the dyno comment.
Our dyno at work, a dynapack hub style, consistently reads about 15% lower than our competitors dynos. The true values to look at are before after on the same dyno.

That being said I still like seeing what people are putting down with different setups.
I may have to throw my stock B up on the dyno one of these days to see what it pulls.

-Bill
Bill Mertz

stock engine 70bhp if your lucky !
daz

I used to have a car with a similar set-up to Daz (including the Peter Burgess head: Hi Peter! Your head was brilliant!).

I found the K&N filters to be a bit rubbish: fitted trumpets and socks, and immediately noticed a really big improvement in torque, and a few more revs at the top end.

Not sure how you had a 4-branch manifold, though: what was the extra one for? ;)
D Ainsworth

you know what i mean , there's three, im aware of that no need to be pedantic !
DAZ

I just wondered if you used the 4th one as a vase...
D Ainsworth

no to stick it up your a..e
daz

Hi!

182 hp at 5000rpm
197 ft/pound torque
@12psi boost (turbocharged)

feels so good.
luis rodriguez

Neil,

here are some of the mods made on my engine and it was tested at 122 RWHP:

18V Block bored to 1868 ccm, line bored and grid to 0,1 mm above the tops of the pistons
lightened and balanced crank from 1971-1973 18V
lightened and balanced conrods to 1/10 gramm
balanced flat top pistons to 1/10 gramm
CR (geometric) 11.75
lightened flywheel
Ralley-race big valve head with equalised 42ccm chambers
Piper 285/2 cam with light wight followers and tubular pushrods
modified rockershaft and rockers
Light alloy spring retainers
double valve springs no valve stem seals
ST distributer (Leyland Special Tuning)
Modified pulleys on water pump and alternator
close ratio gearbox.

Building the engine was very time consuming compared to a normal rebuilt of an 18V as everything was mesured after assembly, taken apart again and modified to give exact readings.

Ralph
Ralph

Neil,

forgot to mention the Carbs:

HIF 6 with red springs and BDR needles, ram pipes on modified HS 6 Manifold.
Carst exhaust manifold modified to match the ports, modified downpipe with Peco big bore exhaust

Ralph
Ralph

Ralph,

Are you sure you can get 11.75 CR with chambers that big? I used dished pistons (6cc dish, I measured them) and had to get the chamber volume down to 38mm to make 10.5:1 CR.

BTW, I watched the filter socks get sucked right onto the ends of the trumpets at full power, cutting back the filter area massively. The rolling road man (a Jag expert) spaced them off with some carpet tape which works a treat.

Neil
Neil

Hi,
I built two engine for my bgt 1972 one 1840 and one 1950 with the same specification, I don't know the power output but I prefer the 1840.
18V847 bloc with liner
JE forged piston with carillo rods
flat sided crankshaft, lightened, polished, balanced
steel flywheel with 7 ¼ clutch, concentric hydraulic release bearing
steel damper
piper285 camshaft, steel timing gear, iskanderian tappets, crane pushrod
cylinder head built by me, 43in, 36ex, 8mm stem
HS6 with maniflow inlet manifold, K&N filters
Maniflow LCB and exhaust system, one box
electric water pump, ally radiator, ect...
all ARP fastener
gearbox/OD, with sccr


mw michel

What year model engines are you different fellows running? There is quite a bit of difference in the earlier engines (late 60s to about '72) compared to the later engines from the mid 70s to 80. I have an 80 LE and plan to spend some winter time making power modifications. I also have a '70 engine in my shop.

Ralph from Germany noted an early 70s crankshaft in his and I wondered about the merits of taking my 80 engine and using the earlier crank. Or, would I be better off to just rebuild the '70 engine and drop it in the LE. The '70 engine was very strong compared to the '80 engine.

The LE engine is likely stock internally with a Weber DGV (came with the car) and the earlier exhaust manifold with a Peco exhaust that I added. Otherwise, I've only changed the distributor to a rebuilt/retuned one with the pertronix ignition.

From all that I've read, rebuilding the head and adding a mild street cam is where I'll begin. I'm looking for a "fast street" car, not one for the track. The '70 engine was about 90 bhp stock and fast enough in my experience. I'd just like to get this 80 LE to run as well without spending a fortune.
Rick Penland

Rick,

the early 70's crank does not have the large wedge style counterwights and is lighter as the later used version. It is also easier to lighten this crank further more.
The 80's engine is fine for power tuning. You should use the conrods of this engine too, as they were selected as a set of four for equal wight (1978-1980 only). A good step foreward are HC or flat top pistons.
If you go for a more sporty cam, the effective CR will be reduced due to longer overlap, so don't be afraight about to high a CR.
When rebuilding the engine it also is a good idea to change the single chain timing gear to the earlier double chain version. A set of offset keys is usefull to time the cam exactly. With a new cam, new followers must be used. the 18V followers are lighter (and there are even more lighter ones available from Moss UK). For tubular pushrods you should have a look upon the Crane Homepage.
A further point is the head. Porting depends upon the cam and the carbs you plan to use.
Be careful with porting, as big as possible is not allways helpfull as gas velocity might suffer or the power just comes in at 4000+ rpm. Modifying the valve seat angles is essetial (3 or 4 angle cuts).
If it is your project for the next winter, you should first plan everything perfect! A combination of only best items is no garantee for a fast engine!
Just read about some details here http://mgbmga.com and try to buy Peter Burgees book 'How to powertune the MGB'. On some sites there is also a copy of the old Special Tuning Manual placed for downloads. Just google for it.

Safety Fast!

Ralph
Ralph

This thread was discussed between 03/10/2008 and 13/10/2008

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