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MG MGB Technical - Ideal engine spec



I'm going to undertake an engine rebuild with a professional mechanic friend on my 1977 B series engine from my roadster.

I'd like to hear people's views on the after market compnents that they'd use for rebuild. Ideally I'd like the end result to have a nice amount of midrange power for over taking, and something powerful enough to show MGF owners that there's still life in the older models as I fly past them

Many thanks,

Mark
Mark

Very quick and dirty, and not very expensive either. I'm sure a search of the archives will yield much of this info in greater detail. Here goes:

.060" overbore = 1868cc
Peter Burgess Fast Road head
For cam consult Mr. B. (maybe Piper 270 or ?)
K & N open filters (no cans around them)
Peco exhaust on stock exhaust manifold.
Aldon-modified dizzy.
Very important! Rolling road tuning afterwards for proper setup.

After that, the price per horsepower gain goes up exponentially.

Safety Faster!
Paul
Paul K

Lightened flywheel. Very inexpensive and I found it made a huge difference.
Fred H


Thanks for the replies, I'm currently working my way through the archives and have found myself on the Peter Burgess website already

Anyone else with more ideas to add?


Mark
Mark

Mark-
What paul describes is a pretty good combination, but it lacks one thing: a Maniflow intake manifold.
Steve S.



I can see the faces of MGF drivers now :) well when I'm not pulled over on the side of the road for something expensive thats gone wrong at least!
Mark

Mark: consider having your engine rebuilt by Burgess or Chris Betson at Octarine Services www.octarine-services.fsnet.co.uk He uses Burgess heads and will build to spec.
Terry

What will a Maniflow intake manifold do over and above the CI manifold.
Fred

Mark
If you would like serious performance from your car consider a V8. Not as thirsty as you might think as I can get 30mpg on a run from my 4.0L. With all that torque its just so creamy to drive with power from idle to 6500rpm. The down side is to do it properly its gonna cost in the region of 5k.
Just a thought.


Mark
Mark

This is for Fred H? Who lightened your flywheel and do you have any tips about how much should be removed?
Herb

The machine shop that worked on the engine. The engine side of the flywheel can be dished. Weight removed near the outside is much more effective than the same weight removed near the center.

Fred H

Herb: Up to 6 lbs can safely be removed from your flywheel bringing it's weight down to 16 lbs.
Terry

actually I'd get ahold of Tarcat Designs for one of their Cold Air Sneaker intake systems, they also offer a custom built combination intake housing & radiator cowl.

CJ
CJD Dark

Fred-
The Maniflow intake manifold (British Automotive Part# SUB4-2) the improvements become even more impressive an impressive item. Why not stay with the OE intake manifold? Due to the sudden change of cross section that occurs in the area of the balance tube intersection, the airflow within them is markedly disrupted into a vortex effect. The resulting turbulence causes the fuel/air mixture to condense somewhat and also impedes airflow by causing the fuel air charge which has been vectored into the upper section of the intake manifold to swirl 180 degrees towards its bottom. When the fuel/air charge reaches the turn into the throat of the port, it then careens into the opposite wall of the throat of the port instead of flowing along the contour of the top of the port as it preferably should, thus impeding its own flow past the head of intake valve into the cylinder. While smoothing the inside the manifold and blending the change of cross section can reduce this vortex effect, it can't take the place of the better design of the Maniflow intake manifold which eliminates this vortex effect. If you choose to use this intake manifold with SU HIF4 carburetors you will need to use either the early version of the UK/European Market SU HIF4 carburetors with the vacuum takeoff fitting on the carburetor body for provision for a ported advance mechanism, or, if you use the North American Market SU HIF4 which lacks provision for a vacuum takeoff, you will need to use the thinner Advanced Performance Technology's phenolic carburetor spacers (APT Part# MFA338) which come suitably modified to provide fittings for the vacuum lines to a manifold advance distributor, as well as the later exhaust manifold (Casting# 3911) as both have a mounting flange thickness of 7/16". This penolic spacer with the vacuum takeoff incorporated into its design is a Maniflow item intended to be used with the Maniflow intake manifold which has no provision for vacuum takeoff on its crossover balance tube. A companion unported phenolic spacer of the same thickness is also available from Advanced Performance Technology, although a second spacer with a vacuum takeoff may be substituted to allow the use of a vacuum-assisted servo for a power brake system. Advanced Performance Technology also offers the option of welding in a nipple on the crossover tube which would allow the use of an anti-run-on valve. Because both the angle of this intake manifold is higher (20 degrees) than that of the Original Equipment intake manifold in order to enhance its flow characteristics, and variances in production tolerances of the bodyshell of the car, in a few cases larger diameter aircleaners will not allow the installation of an underhood insulation pad, hence the thinner design of the Advanced Performance Technology's phenolic spacers. The Original Equipment dual carburetors are insulated from the heat of the head by a pair of thick phenolic spacers. Unfortunately, these are only partially effective at their task of keeping heat out of the induction system. Because the Original Equipment intake manifold is made of aluminum, heat from the head is rapidly transferred through its runners into the incoming fuel/air charge, reducing its density and decreasing performance. However, this rapid transfer of the heat does effectively prevent it from reaching the carburetors which are protected from the heat of the exhaust manifold by their heat shield. To eliminate this hindrance to performance, Jet-Hot coating of the intake manifold is highly recommended.
Steve S.

I better find a picture of the intake I'm talking about, it'll be much easier to see how it'll work for an mgb twin carb set-up. It's a central air intake design, with an upward angle and uses tornado style fins over the carbs to increase the speed and air-fuel mixture better then the original air plenums did, it keeps the air pressure equalized so that each carb gets the correct amount of air rather then the older barrel air-intake designs I've seen which is absolutely horrible at keeping proper intake pressures. Anyway I'll get a pic of it soon for you all to see.
CJD Dark

Steve S, many thanks I think I understand what you are saying, essentially the design improvements offered by Maniflow etc. offer very real improvements over the OE design.

Presumably, similar improvements can be obtained from the exhaust side by dumping the old CI manifold, and substituting one of those tubular big bore jobs, true?
Fred

Fred-
The standard pre-1975 factory exhaust manifolds, of which there were two models, are surprisingly good performers. The exhaust manifold used with the SU HS4 carburetors’ intake manifold have a mounting flange thickness of 9/16" and can be readily identified by an external casting number of 12H709, while the exhaust manifold used with the SU HIF4 carburetors’ intake manifold has a mounting flange thickness of 7/16" and can be readily identified by an external casting number of 12H3911. I highly recommend electropolishing to improve the flow capacity of a cast iron exhaust manifold. Electropolishing is an electrochemical process used to smooth metal, usually prior to plating. It is commonly performed on a precision casting (such as a window winder handle) or on prepolished sheet metal after it has been formed to shape (such as a bumper) prior to plating it. The item to be electropolished is thoroughly cleaned, then emersed in a chemical bath. A current is then run through and the highest points on the surface of the metal are removed. In a sense, it's the reverse of plating in that metal is removed instead of deposited. The advantage of electropolishing a cast iron exhaust manifold is that because the item is completely emersed, the process can get inside the manifold, reaching into every crevice so that it will polish the interior of an exhaust manifold quite nicely where human hands and mechanical tools can't reach, the smoother surface making for reduced turbulence in the exhaust gas flow just like the smooth walls of an exhaust manifold constructed of tubular steel. Be sure to instruct the firm doing the electropolishing to protect the gasket surfaces with plater's tape as an overly smooth mating surface may give sealing problems when used with some gaskets. I sincerely believe that a 1 3/4" tubular steel exhaust manifold won't flow any better than an electropolished OE cast iron exhaust manifold if they have the same basic design. It can also be beneficial to electropolish combustion chambers and exhaust ports (reduced carbon buildup, for example). Because of the lesser heat conductivity of the cast iron and the decreased surface area, the electropolished exhaust manifold will radiate less heat into the engine compartment. Its greater mass will also have the side benefit of reducing noise to a level less than that attainable with a tubular steel header.
Another technique for attaining a smooth interior surface in the exhaust manifold is called Forced Extrusion Honing. In this technique a dense mixture of abrasive clay is forced through the interior of the manifold, polishing the surfaces to an even greater degree than can be achieved on a casting through electropolishing. I've seen a head in which both the intake and exhaust ports have been subjected to this process and it is very impressive.
Reducing temperatures inside the engine compartment is beneficial for power output. For every 3 degrees Centigrade (5.4 degrees Fahrenheit) that the air injested by the engine is lowered, power output is raised by 1%. Although wrapping the exhaust manifold in insulating tape (sometimes called lagging) may seem to be a good idea in principle, it is a very bad idea in practice. Why? The heat can't escape from a wrapped cast iron exhaust manifold and both the head and the exhaust manifold will consequently run hotter. The heat will just build up and up, far beyond what the factory engineers designed it to handle, with the result that the exhaust manifold will warp. In addition, the heat is also transfered to the head, heating the walls of the intake ports and thus reducing the density of the incoming fuel/air charge. Peter Burgess mentions this problem in his book "How to Power Tune MGB 4-Cylinder Engines." Even worse, the coolant passages in the head were not designed to remove so much heat, thus preignition of the fuel/air charge can become a problem and valve seat life can be shortened. In extereme cases, the head can actually warp beetween #2 and #3 cylinders. In the case of tubular steel headers, the metal will become so hot that it will spall and form flakes that will eventually disintegrate to form a hole in the area where the heat accumulation is greatest, usually at the junction of the pipes. The tape also becomes a moisture trap, accelerating the rusting process that can plague exhaust manifolds.
Instead of wrapping the exhaust manifold, get it Jet-Hot coated. Jet-Hot coating is a ceramic coating that can be applied to coat both the interior of the exhaust manifold as well as the exterior. The heat will have nowhere to go except out through the exhaust system, thus it will greatly reduce underhood temperatures. The biggest advantage of this is that the air being inhaled into the engine being denser, more fuel can be mixed with it to result in a more powerful fuel/air charge. Another benefit is that the setting of heat-sensitive SU HIF4 carburetors can remain more consistent. One word of warning to those considering Jet-Hot coating or any other type of ceramic coating: Be sure that the entire surface of the manifold, both the interior as well as the exterior of the manifold and that of the flanges is coated so that the heat of the exhaust gases will pass on through the system instead of being absorbed and trapped in the metal of the manifold, otherwise the manifold will create the same problems as in the case of wrapping the manifold with insulating wrap. Jet-Hot has a website at http://www.jet-hot.com/ . Should you decide to use a tubular exhaust manifold that is not Jet-Hot coated, be sure to use a rubber gasket on the rear tappet chest cover as cork gaskets tend to fail under prolonged exposure to the extreme heat radiated by such headers. Use of the more warpage-resistant rear tappet chest cover from the 18V-883-AE-L, 18V-884-AE-L, 18V-890-AE-L and 18V-891-AE-L engines will assist in this as well.
When using a gasket with a metalized face to install the exhaust manifold, it is wise to install the metalized side of the exhaust manifold gasket facing toward the exhaust manifold so that the mating surface of the exhaust manifold can expand and contract along the metalized face of the gasket. However, it is best to use the gasket available from Advanced Performance Technology (APT Part# CMG-02) as it has excellent compressibility and oversize holes for modified ports. Its graphite-impregnated material allows for superior ease of expansion and contraction of the exhaust manifold and also makes for very easy removal.
Steve S.

How important is the distributor, Aldon is mentioned earlier.
Jack

This thread was discussed between 27/10/2003 and 07/11/2003

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