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MG MGB Technical - flowed heads

Need to upgrade my head to include hardened valve seats as I'm using the GT everyday. Have bought Peter Burgess book about power tuning etc and would like to try a flowed head. Does any one out there think that it is a worthwhile change?

Gary
G Roberts

Gary-
One crucial bit of advice about Do-It-Yourself heads: Be Careful! Once you remove metal, you can't put it back. To take a Dremel tool and smooth the existing contours is one thing, but to alter the contours is something else. Peter Burgess gives some crude drawings and simple instructions in his book "How to Power Tune MGB 4-Cylinder Engines" and says that you can do it yourself, but a Master often forgets how hard it is for a rank beginner. He gives a much fuller and more detailed description of what is actually involved in his later book "How To Build, Modify, &Power Tune Cylinder Heads" which should be read prior to deciding to set out on such a venture. Remember, the B Series head is special. Siamesed ports are an antiquity in this modern era of separate ports, and there are very few people who truly understand the subtleties of them. This is no Ford or Chevrolet V8 head we're talking about here! Serious work on these heads entails specialized knowledge. Just removing the valve guide bosses is very tricky due to the fact that the difference between removing just enough metal and breaking into the cooling passages is very, very small. If you don't have genuine blueprints of the ports in the particular head casting that you're working on (there were four that were used on US Market engines), complete with dimensions, radiuses, etc., and the appropriate precision measuring tools, then you're taking a big gamble with all of the odds stacked against you. You'll need a Flowbench, too. This is a machine equipped with sensing probes that sucks room temperature air in through the intake ports and blows combustion temperature air out through the exhaust ports. It's a must-have for getting the flow rates of the ports individually matched. Many well-intentioned local Good 'Ol Boy Hot Rod Motor Builders (the ones that the local pimply Hot Rodders call "experts") have reduced MGB heads to scrap metal. Once this happens you'll spend at least as much money buying another head and getting the parts for it as you would have spent shipping the head to a qualified professional, having him do the work, and then shipping it back again, complete with insurance. The one thing that you can't cheapo your way through on an engine is the headwork. Without access to a flowbench, blueprints, measuring instruments, and the specialized skills, the likelihood of an amateur doing it correctly on a first attempt is so small that it makes me shudder. How do I know? About twenty years ago I worked for Rockwell International making valves for use in nuclear power plants. The valves had to be flowed on a bench to be government-certified for use in a nuclear installation. This meant custom work, all done by hand with a die-grinder-type Dremel tool. It took about three years of prior experience and a practiced eye to be able to do it right every time, and this was working with a flow bench, repeatedly making small corrections on every individual port! Recontour ports in my garage? Hey, my name isn't Peter Burgess! Ship the head to Peter or purchase one from him outright, you'll be glad you did. After all, you wouldn't try to bore your cylinders in the garage with a file, would you?
Steve S.

It's a worthwhile improvement for not only power but often fuel efficiency as well, providing there is ample consideration taken by the modifier. All our customers are more than happy with the work we do and I think that (providing you deal with a reputable firm), you ought to have as good an experience.

I will say, that it is the single most important step to better performance which is not equaled by any other mod I'm familiar with.

Sean
Sean Brown

I was in much the same situation as you, since my MG was my only car for a while and I wanted to be able to run on unleaded. I got a Peter Burgess flowed head and (when I finally got round to putting the engine back together) was pretty happy with the results.

It's hard to know how much increase in power it gave because I'd hardly driven the car before I replaced the head but I did notice a drop in fuel consumption.
Carl Kambites

Gary-
Peter offers multiple levels of headwork suitable for an easily streetable engine: Standard Leadfree, Econotune, Fast Road, and Fast Road Big Valve. The simplest is his Standard Leadfree specification which features bronze valve guides to aid heat removal, stainless steel exhaust valves, EN52 inlet valves, leadfree compatible exhaust seat inserts and 'top hat' style inlet valve stem oil seals. The seats are cut using three angles. The Econotune specification adds bulleted inlet guides, and the combustion chambers, valves and valve throats are modified to enhance flow and smooth combustion. The valve and port sizes are not increased, thus the resulting high port and seat velocities produce a broad spread of very useable power from idle to a maximum of around 4800 rpm. This results in a power increase at 3000 rpm of approximately 30% and maximum power is increased by approximately 18% at 4800 rpm. The third level is the Fast Road specification in which the head is fully reworked before the lead free seats and bulleted bronze guides are fitted. The inlet and exhaust ports are modified to enhance air flow without increasing the port sizes to any great extent. This keeps the port velocities high and aids the production of low rpm torque. Power is increased from idle to a maximum at 5200 rpm with a standard camshaft. There is a gain of approximately 25% at 3000 rpm and a maximum increase of approximately 30% at 5200 rpm (with a standard camshaft and K&N filters). Beyond that point the power will fall off much more gradually than with a stock head, so you can say good-bye to that frustrating "after-that-the-engine-seemed-to-run-into-a-wall" experience. If you add a Peco Exhaust system it will extend the peak further (to about 5,500RPM) and give yet more power and the power will decline less precipitously after that. The head also takes beautifully to a Piper BP270 camshaft, the combination sacrificing a little power down very low in the powerband where you rarely go anyway (below 2,000RPM) and singing merrily all the way to 6,000RPM. As you can see, the Fast Road Head should be considered to be the jumping-off point when it comes to a quest for really serious power. It's the foundation that everything else is built on. To do it last is putting the horse behind the cart. This specification of head performs well with a standard camshaft and shows even more impressive gains not only with the Piper BP270 camshaft, but also with the Piper BP285 camshaft. While the head works extremely well with the standard twin SU's, it will show worthwhile gains with twin 1 3/4" SU's. The Piper BP285 camshaft is recommended to compliment this increase in carburetion. The Fast Road Big Valve head features larger inlet valves and is ideally suited to a Fast Road camshaft such as the Piper BP285. The increased breathing capacity of the head will show good returns with twin 1 3/4" SUs or a Weber 45 DCOE. With a Big Bore engine conversion the head is well suited to restore the peak horsepower rpm to its original position. BHP increase is approximately 25% at 3000rpm and 35% at 5300 rpm when used with a standard camshaft and K&N filters. Peter offers a fifth option which, although not falling into the "easily streetable" category, is mentioned here for the sake of completeness. The Fast Road Plus head is fully modified and is fitted with one piece 214N Austenitic stainless steel tuftrided 1.72" inlet valves. The combustion chambers are dressed back to increase flow and the inlet ports are very slightly increased in size to allow the engine to rev out more. The head has been developed for very fast road use with 'hairy' camshafts and increased carburetion. Although not really suitable for standard/mild camshaft use, BHP increase is approximately 25% at 3000 rpm and approximately 38% at 5300 rpm when used with a standard camshaft and K&N filters. It is highly appropriate for use on Big Bore engines.
Steve S.

Should the block be oversize bored to +40 or +60, to complement the BP270 Cam, or left standard.

Also if fitting a Peco Exhaust system, do we have to throw out the original manifold, and fit a steel one.
Sam

Can anyone express in percentage terms how much of a boost a re-bore to +40 does, also +60.

Steve S quotes percentages for other things above.
Phil

.040 overbore increases the displacement by 2.55%, to approx. 1844cc. .060 gives a 3.83% increase to 1867cc. I don't know how much power increase that results in. By itself, probably not much.
Paul Noble

Boring out not only increases swept volume - it increases compression ratio also.

Alone, a bore out to +40 probably adds around 3-5 bhp, +60 around 5-8 bhp.

But don't be fooled into thinking you can just add the 8 bhp gained by using a better cam (like the BP270) to the 5-8 bhp gained by going to +60. In practice +60 and a BP270 with richer carb needles will give about 10 bhp.

Peter's book give a number of "recipes" for power which demonstrate the variables and their combined impact on power output.
Chris Betson

Chris-
Quite so. Increased displacement increases low end torque more than high rpm horsepower, plus the power peak tends to move downward due to flow capacity being reached at a lower rpm. Installing a hotter cam tends to move the peak back in the direction from whence it originally came. If optimum gains are desired, having the heads reworked by an expert almost always accomplished more than a change in the camshaft and leaving the head stock. Add the right camshaft to a properly flowed haed and the results can be startling!
Steve S.

I installed an alloy head in my 67 gt. I used the stock valves, a mild modified grind cam and 1.5 ratio roller rockers, stock intake with original 85,000 mile carbs. Tube headers, modified ignition and .040 over shallow dish pistons. I had Crowther racing open up the combustion chambers to unshroud the valves and also had them radius some of the sharp edges and transitions in the ports. The Pierce stock style alloy head has the large early style combustion chamber, the crossflow head has a small hi compression combustion chamber. The added combustion chamber volume from unshrouding the valves reduced my compression ratio and I could advance the spark far enough to lose power, but never far enough to ping even on 87 octane gas. I had about 130 lbs compression. However the power was great! Under 10 seconds to 60. All good things come to an end. The cam began to go flat after 3k miles and I now have a set of flat top pistons ready to install to get the compression back up and a new cam to try out.
From my point of view, the great power output I got with low compression tells me that increasing the flow with head modifications is effective.
Barry
Barry Parkinson

I opened-up my head ala Peter's book. It was a great experience and laots of fun. If you have your head off, just try to stick your finger through the exh port to the exh valve. You can hardly get your little finger in there. The roughness of the inside ports is unbelievable. Also, You can match the ports to the intake maniflod where there is also a great amount of misalignment. The valve guide boss is huge and there are many casting marks, parting lines etc. that can be smothed.

I've heard lots of warnings about diy from the experts. You're not going to create maximum power like Sean or Peter, but no one can tell me that you can't improve the rough, misaligned, munged-up and convoulted passages in the heads. There's plenty of info in the MG special tuning book and in Peter's book and other sources, to do the job. Just research it well first and don't go for the full-race mod dimensions. My engine runs great, and could probably use some other mods to get the most out of the porting that I did.

Use the sandpaper drums, they are much easier to use and much more forgiving than stones. Don't try to take much out of the chambers(pretty thin). Read ALL the archives you can find!
Fred Horstmeyer

This thread was discussed between 18/05/2003 and 23/05/2003

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