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Rebuilding '77 MGB 18V engine looking for rebuild/performance tips.

Last post 12-31-2008, 4:35 PM by randallvoss. 6 replies.
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  •  10-23-2008, 5:33 PM 16775

    Rebuilding '77 MGB 18V engine looking for rebuild/performance tips.

    My 1977 B has 59K on the clock but had been sitting for quite awhile prior to me getting it in april. It had been garage kept and undercoated so bodywise it's a very good survivor with very very little rust.  I replaced some fuses, Fuel pump, Sparkplugs, Cap, Rotor and Wires,  Speedo Cable/Angle Drive,  Put in an Aftermarket Cooling fan on a relay,  had the Carb Rebuilt,  The previous owner didnt take care of it much, it just sat in storage.

      IT has average compression of 150lbs in cyls 1,2,3 and 140, on #4,  after doing some checking we put a little oil in the 4th cyl and checked compression again and got back up to 180lbs.   It burns & leaks oil. so odds are it will need a ring job and seals replaced. The rockers are making a little noise, so odds are they either need adjusted or i have a failing lifter/cam lobe. All the pollution control gear has been removed. It also will idle very rough around the 850-900 rpm mark, but levels off at 1000rpm, I'm considering a bigger cam and possibly the new alloy head.  does any one have any suggestions as to what combination will make the best bang for the buck performance wise.

     The car has a Freshly rebuilt Mikuni 44PHH  carb (similar to a DCOE, Rebuilt by Todd @ Wolf Creek Racing) with the aftermarket intake, Header and Pirhana electronic ignition.   

  •  10-24-2008, 11:00 AM 16786 in reply to 16775

    Re: Rebuilding '77 MGB 18V engine looking for rebuild/performance tips.

    Oil burning might also be due to worn valve guides and perished/misssing valve guide oil seals - There's not necessarily one single cause...

    The noisy valve train often (usually) arises because the rockers AND the rocker shaft are worn. When I rebuilt my engine, the rocker shaft had grooves of 20 thou where the rockers pivoted. This resulted in valve clearences that just could not be set accurately and lots of noise. You can do a crude check by twisting the rockers and checking for play - there shoudn't be any. If there is, replace the shaft and fit new bushes to the rocker arms. Also, the rocker ends that contact the valve stem should be checked for wear (this imperfection can be ground out & repolished).

    The best advice I can give is to do as complete a check as you can, as it will pay off in the long run. If one part of the engine is worn, chances are this is true all the way through. If something is missed out, it will come back to haunt you later. How do I know this?: See my thread on "engine trouble lurking"...

     I've no experience with the Mikuni carburetors, so can't comment except to suggest checking for vacuum leaks etc. - but perhaps another member has an insight.

     Cheers, and good luck with the project,


    I want my MGB
  •  10-24-2008, 1:10 PM 16787 in reply to 16775

    Re: Rebuilding '77 MGB 18V engine looking for rebuild/performance tips.


    Let's think about the condition of the powerplant first. Your compression numbers aren't all that bad, yet you indicate the engine burns oil. Have you changed the oil? A compression test is really only a good way to see if there are any gross problems in the cylinders. (holes in the pistons, burnt valves,etc.) In order to know where your losses really are, you need a cylinder leakage test.

    If the previous owner was lax in his maintenance you probably do indeed have deteriorated lifters and the cam lobes may also be suffering. The rough running you describe may be nothing more than tuning issues. I suspect, though, that you are determined to modify this engine for better performance.

    There's an old saying in the performance game. "Speed costs money. How fast did you want to go?" I wish performance was something we could simply order up in the form of one or two parts and bolt on. If wishes were horses we'd all have five or six hundred of them under our bonnets. I don't wish to discourage you. There are items which can give reasonable gains for fair money. But, you need to set reasonable goals and expectations for what is essentially a nearly sixty year old design.

    Your question concerning the best bang for the buck is a classic. The easy answer is a freshly built total overhaul in stock form. I have the impression that easy answer is dissapointing to you. It would be to me as well, but the fact is that dollar for dollar that's where the greatest gains in an old engine are to be had for the least expenditure. But there is indeed more.

    Next would be to take that freshly rebuilt engine and add a supercharger kit to it. WHOA! that's about four grand when you take into account the heat shield and the larger exhaust to handle the flow and the boost gauge, etc. And then there's the installation time and the tuning to take advantage of the money spent. It's a pile of bucks, but in terms of bucks spent versus power gained, it's the best bargain out there. So... do we need to reframe the question?

    Maybe, maybe not. If you can afford the complete overhaul down to the last detail (We generally wind up charging about six thousand for this, but do EVERYTHING you can imagine and warranty the unit for two years of unlimited use). Perhaps you can accomplish the work yourself. That will save you a bunch. But there are still the parts and the machining and balancing to consider, and you do not want to skimp when you plan this phase. Well, if you can make this outlay of cash and then pop for the blower, that's definitely what I'd do.

    If, on the other hand, the real question is, "What can I do that will brighten up the performance of this car without a great deal of extra dollars above the engine work, I'd say, "Make it breathe". You've already got a start with that Mikuni. Next is some mild port work on the head, followed by a header port matched for good flow, and a larger diameter exhaust system. A better cam will also help in the breath department.

    The subject of camshaft details is too long and too full of controversy to even start to discuss here, but there are a number of mild upgrades from Kent, APT, Moss (Crane, I believe) and others. I would not advise going too far here until I knew exactly what I wanted in the way of performance and what I was willing to sacrifice in the way of tractability. (Low speed drivability) It goes on...

    How about higher ratio roller rockers? How about increasing the compression? As you get into it, you'll find that each little increase over what you've already done to get to a certain point costs exponentially more and subjects the engine to just that much more stress. So, you need to ask yourself how much more you want and how much more you are willing to spend.

    The aluminum head is nice. In fact, we rarely rebuild a street MGA or B without adding this part. This is actually more for reliability and cooling than for performance. You will find many who say that the porting is not optimal in these heads for top performance. We've had very good experience using them along with a mild performance camshaft such as the Kent stage one or two. We usually shave the head a bit and deck the block to raise compression. Be aware that we operate at five thousand feet of altitude here!

    Here is the engine I am currently putting together to install in my MGA: 18V series MGB block and crankshaft, .060 oversize 8.75:1 pistons, APT VP10 camshaft w/matched lifters and springs, Isky pushrods. vernier adjustable cam sprocket set, 1.6:1 roller tip rockers, non crossflow aluminum cylinder head. oversize "gas flowed" valves, reworked distributor with electronic ignition, high volume oil pump. Weber DCOE 45 carburetter, Maniflow header which will be ceramic coated, and an improved crankshaft damper. Those are the major improvements in the parts area.

    Next, the block will be decked and aligned in all dimensions, the crankshaft will be ground and polished to a fair-thee-well, the rods will be rebuilt and aligned and balanced end for end so they match. The pistons will be match balanced. The head will be milled to achieve as close to 10 to 1 ratio as possible, the block will be relieved to allow for the oversized valves and to "unpocket" flow around them. The combustion chambers will be equalized for volume. The ports will be mildly reworked in the head and matched to the manifolds, the flywheel will be lightened (This will improve response, but not increase horsepower), every reciprocating or rotating part will be balanced to a high degree.

    There's more, but I can't remember it all right now! What will all this give me? I'm hoping for about 127 horsepower. Big deal, eh? Well, I wanted to build a lively unsupercharged engine as an exercize to show customers what is possible in an engine that can be tolerated on the street. I bet you can begin to see how much more easily a supercharger could be applied to a stock engine, and I haven't even begun to describe the hours of careful assembly to assure that everything clears and that I'm not building a two minute grenade.

    Obviously, I'm not writing this post just to respond to your question. Lots of folks speculate as to what they should do for some more power. The fact is, there is little that is meaningful that you can do without considering the entire system, end to end. Sure, a header and better induction is a relatively inexpensive way to make an improvement, and I think that's a fine way to go, but a real leap requires consideration of the entire package.

    If power is more important to you than "MGness", consider adapting any of a large number of high performance twin cam four valve per cylinder Japanese engines and gearboxes. The modern engineering and reliability are incomparable. Or... think about that supercharger...Please let me hear from you about your goals and desires. There are lots of options and opinions. Above all, enjoy that car.

    From Lola to Land Rover, If it's British and has wheels, it's likely I've bloodied me knuckles thereupon
  •  10-25-2008, 4:05 PM 16792 in reply to 16787

    Re: Rebuilding '77 MGB 18V engine looking for rebuild/performance tips.

    One thing I'd hate to lose in the driving characteristic of my 'B (virtually standard 18GB engine with +.040 overbore) is the pulling power it has at low revs, and the sound Smile. That is a feature that makes the car such a pleasure to drive, especially if one is just puttering about. If there's one thing I'd change in our family car (2003 X-Type Jag) it would be to make it more like the MG in the touque department.

    Bill, thanks for the description engine you are building/planning for your MGA project. 127 HP is a significant increase from the 95 or so I understand was available from the best "standard" B series configurations!



    I want my MGB
  •  10-25-2008, 11:13 PM 16793 in reply to 16775

    Re: Rebuilding '77 MGB 18V engine looking for rebuild/performance tips.

    I am not very talkative on this site but I think I have input on your project.

    I would run the car to get to know it first. The addons on the motor tell me the motor may have been rebuilt at some time. If you want a out the backdoor what you can do number I am into my '77 for $25,000 without knowing if it even runs yet. IF mine is as good as it should be****** I am scaird to turn the key. I drove the wheels off this car for 8 years before it was hit with a blown motor and then a desert hail storm. When you know the car it will tell you how to take care of it. Get what you have right first then upgrade is my out look. Hows the paint? The compression PSI is spot on for a parked runner. Change the oil , Flex the motor, Get good gas through, Change the oil ... then see what you have. I just feal you have a realy good starter ride, take it slow.

     Start the day with a smile and a song,


  •  10-27-2008, 1:49 AM 16810 in reply to 16775

    Re: Rebuilding '77 MGB 18V engine looking for rebuild/performance tips.

    I've been running a Mikuni 44PHH in my '73 B for years. At least I should say I ran it for years before I stored the car for about 10 years. I recently completed a complete tear down and restoration of the car which included pulling apart the engine. I had always experienced the same rough idle you describe and I found that I had not been getting a good seal between the manifold and the head. There was evidence that the whole assembly had been rocking. To remedy this I carefully matched the thickness of the intake manifold flange to the exhaust manifold thickness to insure equal clamping force. I also added a diagonal brace from the carb air filter flange to one of the mechanical fuel pump blanking plate bolts on the left side of the block. I assume this plate is also on the later blocks. If not, you may be able to tie into the oil pan flange some how. There is a similar brace shown in the shop manuals tunning section used with the Weber side draft carb. Bottom line is the carb is now mounted rock solid and idle is very smooth. As much as I enjoyed fiddling around with the old SU's, there is a lot to be said for carbs with accelerator pumps in them instead of vacuum floats and tapered mixture needles. The carb came with a variety of different jets and through trial and error I found a combination that seems to work very well. The only short comming is the carb tends to get heat soaked a bit in heavey traffic and on hot days will tend to stumble starting out from stop lights. Before the restoration I had a heat shield I had made from some old scrap aluminum plate but it was too junky looking for the new engine bay. I plan on making up something cleaner befor next summer.
  •  12-31-2008, 4:35 PM 17507 in reply to 16787

    Re: Rebuilding '77 MGB 18V engine looking for rebuild/performance tips.

    I can echo your comments on demonstrating you can do quite a bit while keeping the "MGness".  I built the motor in my B along similar lines - 60 over, 10.5:1 compression, head and cam from Dave Headley, balanced everthing, lightened flywheel, 2" exhaust, etc.,  Differences are iron head, stock rockers and race prepared HIF4's.  Car has not been on a dyno but Dave estimated power at 130hp.  Car is now really quick, pulls strong well past 6 grand and sounds great to boot.  A real joy to drive and very tractable around town.  Also passed emissions without air pump!

    Total cost with me doing all the build was around $3500 with a good chunk of that on the head and cam/lifters.  I know you can go much further as Dave's race engines approach 190hp.  But keeping cost reasonable, and British can still make a world of difference if you approach the whole system. 

    Randy Voss
    80 MGB Roadster 130hp - "Herschel"
    04 Audi A4 Avant Quattro 3.0L "Black Pearl"