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MG MGB Technical - I'd Like a bit more power

I've had my 74B since 1983 And I've never had the head off. With about 125K miles I'd like to see if I can get a bit more power from it. I'm no great mechanic and usually don't work on the engine for fear of screwing it up! Carbs are HIF's. The exhaust is original up thru the front muffler but I had a local muffler shop Put on a GlasPac as the rear one. It sounds real good too! Would changing the whole exhaust system in back of the original manifold get me some power? If so, what do you recommend? Also the engine still has the original fan run by the belts. Would changing to an electric fan help it out a bit. Cooling is normally OK but in stop and go traffic the water temp does rize up some. In 1997 I had an OD box installed by a shop and I love it. The only real problem is on the hyway in overdrive the care will slow a bit on any grade, even a slight one. I don't need much power but a bit could help. Thanks for any input about this. Bob
Bob Ekstrand

Bob, the simplest and most reliable way to get more power is to re-condition the head. Properly done, it would increase compression and thereby power (probably reduce fuel consumption). It is a time-consuming and therefore expensive (one man/day) operation but if you don't feel confidant then look for an old-fashioned garage.

If you are writing about a long-term family pet and are thinking about half-life refits - you might consider having your head professionally cleaned up. On this side of the pond, Peter Burgess is the market leader but there will be competant US experts which will do the same job - just keep asking.

There a few extra BHP to be gained from the right exhaust. The most of it by replacing the manifold with a sculpted tubular variant but this allied to a cleaned up head will give you quite a lot more power.

HTH

Roger
Roger

A modified/improved flow cylinder head with an increase in compression ratio is by far the best value in cost per BHP gain.
It will allow you to accelerate up or at least hold a slight highway hill in OD.

Richard.
RH Davidson

Have you done any work on the distributor? The 74 has a distributor that was curved for emissions and it killed performance. It probably has worn out springs and the vacuum advance may leak. You may be surprised at the increase in performance by a distributor that has been rebuilt and curved for better performance. That would cost considerably less than reworking the head.

Jeff at Advanced Distributors re-curves distributors and he has an excellent reputation, never heard anything but praise for his work. Call or email Jeff for more information.
http://www.advanceddistributors.com/

I have no financial interest in Advanced Distributors, I'm recommending Jeff because he has helped many MG owners get their car running better.

Clifton
Clifton Gordon

Hello Bob,

I agree with everything said. But if you modify head on an old engine. The bottom, pistons, bearings, rings will suffer. In fact one of these parts will broke for shure. As beefing the upper part of engine will stress the lower parts of engine. And 125K miles is the time to overhaul a B engine anyway.

Another way of improving things is changing needles on carbs to deal with a new improved head. May be it is not a good idea. As I think it needs 3 Ph.D. in mechanic to do that properly.

Cheers,

Jean G.
Jean Guy Catford

125K is "long in the tooth" for a B engine. The 74 configuration engine with the SUs and standard exhaust was a good design, far better than following years with a single carb and different exhaust design. Most of your power loss is likely due to lower compression from engine wear. Clifton makes a good point about the distributor and Jeff rebuilt my distributor, I'll vouch for him. If you're not prepared to rebuild the engine, a little distributor work might help.
Rick Penland

This is one of those "how much do you want to spend" questions :)

I would start at a standard rebuild then look at improvements. Of course the difficulty then is the "might as wells"!

I suspect if you did a normal rebuild you'd notice a big improvement before you start looking at modified heads and exhausts and so on.

Simon


Simon Jansen

I suppose any 35 year old car with its original untouched engine is long in the tooth. I am good to it though in that I seldom rev it over 4500 and run it ussually far under that. Doing 5000 miles/year and changing oil twice each year seems good to me. The car starts right up faster than my QX4 so I'm a bit afraid to mess with it much. How long do these go before a rebuild is needed? A top end job would get more power but I think it would cause problems elsewhere like rings, crank or cam bearings or who knows what. As it is driving now it is not blowing smoke so except for being on the slow side it is just not telling me to have a rebuild done. I'm probably deaming but I wonder how far it can go before a rebuild? Thanks
Bob Ekstrand

Bob,

There is two diff. topics here. Raising compression and seeking performance lead to a overhaul.
But if your car still have a good comp. and engine works well, which is rare as most of B engine at that mileage are due for a rebuild, well enjoy it and dont ask to much on performance improvement.

Carb. overhaul with non-leaking shaft+KN filter, new distributor and electronic ignition like Pertronic will be fine. Not too expensive also,


Jean
Jean Guy Catford

Can you buy/borrow a compression meter and test the compression. Be interesting to see what you get.

Simon


Simon Jansen

Bob,

As has been said, run a compression test on it. Then see that it has good oil pressure when warmed up.

If that checks out okay, then you have a tuning issue and don't need a rebuild.

You need to know if you have a high or low compression engine so that you know your target value. I think low compression engine cranks at about 135 psi and the high cranks at about 155 psi. This is from memory, and someone may need to correct me.

If the compression is low, do a wet compression test (after sloshing a tablespoon full of oil in the cylinders) to see how much that brings it up. If the wet is not much more than the dry, you need a valve job. If the compression jumps up a lot when wet, your rings are loosing compression. One caveat is that low compression can be caused by very badly adjusted valves or the valve timing being off because of a stretched or jumped timing chain.

If you need a valve job, be sure to get a good three-angle valve job with narrow seats, consider unleaded inserts in the valve seats, and consider head modification.

If you want to look at options for increasing power, you should get the book "How To Power Tune MGB 4-Cylinder Engines" by Peter Burgess, ISBN 1-874105-61-8. That will give you some possibilities from mild upgrade to race engines. It should help you decide what to do, or if you want to do it.

Charley
C R Huff

if the engine checks out ok
Than the easyest way to get more power is to bolt on parts and not tear down your engine.

start with the induction side
make sure the carbs are in perfect working order (jets needle etc)
than fit rampipes with (itg) filter socks
other than flowing (carbs/head)or going biger induction is done

then the exhaust
fit a good tubilair manifold and a good freeflow exhaust.
done with the exhaust other than flowing (head)

now the shady bit
fit a higher ratio roler rockers (harland sharp makes them)
fit a high strength rocker shaft as well
it can be done without removing the head.

then have the engine setup on a roling road!!!!
full monty
curving and timing the distributor searching the right nedles and setting up the carbs

now the most important bit
REV IT OVER 4500RPM
if the engine is hot it is no problem!

remeber it is no low reving v8 it is a old brithis engine and they take revs quit wel (5500 would be my limit)
Onno Könemann

If you keep the revs WELL below 4500 (ie shifting at 2500 almost all the time) then you may have somewhat dirty piston rings, possibly contributing to lower combustion. How is oil consumption?
I am a firm believer that these engines like revving. In fact when paired with a non-overdrive gearbox, you would be cruising at well above 3000 (probably even approaching your 4500 limit) to keep up with traffic on the highways these days. I agree with Onno, let it rev! One of my favorite sounds is my engine pulling up to the redline.
Erick Vesterback

Bob
Onno-Erick-----I like your style-Keep em revving that's the way. Willy
WilliamRevit

Bob I have DRIVEN & built british cars for 39 years, I have 3 M.G.B.s with over 300,000 miles EACH! & my first V-8 B I built in 1983 when she had 103,000 miles & I just turned 500,000 miles on her. The B motor is a good motor, IF you change the oil, never run her hot,run it out of oil, keep the head torked & the valves adj. On the 4 cyl. of my own I will change the lifters every 40,000 miles, there is a wear problem hear! The O/E lifters are better than what you can buy today (thank you E.P.A.) If you were to build a head & put on the old motor it WILL USE OIL! You need good rings & with 125k on your motor you don't have good rings, you have a good used motor that will run more miles AS IS! If you put the higher raito rocker on I think you will have problems. Valve springs work harden. What this is you have a valve (lets say) opens .350 tho. & you put a set of rockers on that makes the valve open to .425, I have seen were the spring breaks!, thin you will have a real problem. The best thing you can do with what you have is get up with Jeff & put his dizzy in, if & whin you pull the motor lighten the flywheel, this will let the motor turn up r.p.m. faster. When you rebuild your motor there are a lot of things you can do & I build a motor for a lot of miles and thin the power. If you run higher comp. you get more power & if you get to high of comp, you will have to run a higher grade of gas. I have a motor that we rebuilt & she has now 150lbs of comp. & I can run her on 87oct. What I did was pollish the combustion chamber, good comp., good power & 87 oct. I can not get this motor to spark knock & I am going to pull the head & cut .040 more off the head to raise the comp. to get more power & I hope I can still run 87 oct.Another thing you can do at rebuild is go to the early 2 row timming ch., the late (18V) single row ch. is shot at 100,000 miles. If you port the head you will get more power but is does cost & with what I see you are a mild driver & I think you will not drive what you will have. I put 200,000 miles on a motor that we built in 82 & we ballanced it, lighten the rods, factory 1/2 race cam, port head, lightem the flywheel & raised the comp. to 9.5-1 & I ran her!!!! 4,000 r.p.m. + every shift, was a lot of fun to drivr! Had time, pulled the motor & we put std. rings & rods back in her! The bore was like it was when it was new (bought a new block assem. from B/L in 75-76 for $100.00)The motor now has another 100,K on her. Bob, have fun & drive her, I put 5,000 miles on mine in 4 to 8 weeks!
Glenn Towery

Bob, I had a 70 B that ran over 250K, but the overhaul interval was a little less than 100K. The head needed work about every 50K. However, that was in "leaded" gas days and likely less frequent with unleaded gas and components. A compression gauge is less than 20 bucks and worth a check. There is one component that compression won't tell you about and that's the rear main bearing which is likely somewhat worn at 125K. If worn, you'll notice your oil pressure lowering when dropping back to idle after a good drive. If you're still holding 50 lbs or so at idle, your engine is doing amazingly well for its age. If it's dropping into the 30 lb range, they're wearing down and the crank journals will need machining when rebuilt. Rebuilding is not that expensive, nor do you need an MG specialist. With proper tools, a good manual and patience, you can pull the engine, assemble and disassemble and use a good local machine shop for the other work. You can consider modifications, but your engine is a strong design as is.
Rick Penland

Thank You all for your comments. This has been very helpful. A couple things. In 1997 I had the tranny replaced with a same series O/ D unit which I love. It works well. At the same time the timing chain was renewed and I had the radiator recored. Sometimes I think the recore was the best thing I did! The engine getting hot has never been a problem for me. By the way, as far as RPM goes I tend to shift at about 3500 which seems fine. Thanks again for allthe help! Bob
Bob Ekstrand

As rick says
rebuilding is not that expensive

i am just doing my a-series (the older/litle brother of the B)
And in the Netherlands (where machining is verry expensive)i payed €850.- to get the head and block machined
That is full monty overbore hone line bore cam guides seats, everything
Then the only thin you need is a good set of pistons a cam and some gaskets and you are up and running!

the total will cost me less than €2000.- okay you have to build it yourselfs but that is half the fun

And you can get a mild road cam some small head mods and nice rockers on ther an have some nice power

btw B series don't realy rev
A-series are the screamers (at 6500 you shift)
Onno Könemann

Pound/Dollar power value, wich also improves reliability. Improve the breathing....match up the ports to the manifolds; tubular,staighthrough exhaust; K&N's with richer needles; rebuild carbs and tune. Electronic ignition, and spot on dizzy and timing. All normal stuff and no great expense. Oh and ditching the engine driven fan for an electric is good for 4-5 BHP!
Allan

Bob, here's some food for thought. I drove a 70 MGB daily from 1971 until 1987. The best investment I ever made was a 1971 engine for $100 that I chanced upon. It gave me the opportunity to carefully and completely rebuild the engine out of the car while still driving it daily. When an engine would begin to get "long in the tooth", I prepped the other and could do a complete engine swap overnight or easily on a weekend. I noticed you're in California. From what I see on E-Bay, MGBs are quite common out there (in Missouri, I can find rare Morel mushrooms more often than I can find MGBs). There should be plenty of engines available from V8 conversions, wrecks, etc. Search for the same "series" of engine that you have. All you need is the short block and a cylinder head. Thus, you can take your time prepping the replacement engine exactly as you wish and at your leisure.
Rick Penland

This thread was discussed between 21/04/2009 and 08/05/2009

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