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MG MGB Technical - SU intake manifold

For one of my winter projects on my 80LE, I've decided to remove the Weber DGV and manifold that came on the car and replace it with SUs. I have a set of SUs from a '71, AUD465Rs complete. That is, complete with spiders and such so will need complete rebuild. Emissions controls have all been removed so my question, is the original intake manifold suitable, or are you fellas using some sort of after market intake manifold when reverting to SUs. I'm running a pre-74 exhaust manifold by the way. I've looked in the archives, but haven't found anything on the manifold.
Rick Penland

The early manifold should suit your needs fine. Go over the carbs and recommision them to make sure they are in good working order before you get everything together and then have to dismantle them to fix a problem. Ray
RAY

Rick,

The SU intake and exhaust manifolds are of two types regarding the thickness of the "ears" where they are clamped down with the big "washers" onto the studs. If you look at an MGB parts book, you'll see that the SU exhaust manifolds had two numbers over the years. I don't think it makes any difference which you use, but check to make sure your available intake manifold and exhaust manifold match in this regard.

I have an abundance of intake manifolds here, and I'm sure both types are well represented in my "collection". Let me know if you need one.

FWIW,
Allen
Allen Bachelder

Rick-
The Maniflow intake manifold has high airflow potential coupled with good port velocity, enabling it to take advantage of the inertial effects of the fuel/air charge to better fill the cylinders at high engine speeds with the added benefit of maintaining excellent fuel suspension within the incoming fuel/air charge. In addition, because of the slower heat transference of steel as compared to aluminum alloy, it conducts less heat from the cylinder head into the incoming fuel/air charge, thus making for greater fuel/air charge density and hence more power potential. Polishing and chrome plating the exterior of this intake manifold will enable it to reflect away radiant heat emitting from the exhaust manifold, keeping it cooler. If you elect 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 that lacks provision for a vacuum takeoff, Advanced Performance Technology also offers the option of welding in a nipple on the crossover tube that will allow the use of a manifold-advance distributor. If you wish to run an anti-run-on valve and do not have the carbon canister (BMC Part# 13H 5994) of the 18GK and later engines, you will need to use the thinner Advanced Performance Technology's phenolic carburetor spacers (APT Part# MFA338) that come suitably modified to provide fittings for a vacuum line, as well as the later exhaust manifold (Casting# 3911) as both have a mounting flange thickness of 7/16". This phenolic spacer with a vacuum takeoff incorporated into its design is a Maniflow item intended to be used with the Maniflow intake manifold that, unlike the Original Equipment intake manifold, 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. Because both the angle of this intake manifold is higher (20°) than that of the Original Equipment intake manifold in order to enhance its air flow characteristics, and variances in production tolerances of the bodyshell of the car, in a few cases longer and larger diameter aircleaners will not allow the installation of an underhood insulation pad, hence the thinner design of the Advanced Performance Technology's spacers.
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 air flow by causing the mass of the fuel/air charge that has been vectored into the upper section of the intake manifold to swirl 180° towards its bottom. Not only does this vortex effect cause the incoming fuel/air charge to lose some of both its inertia and velocity, when the fuel/air charge reaches the turn into the throat of the port, its inertia then causes it to careen into the opposite wall of the throat of the port instead of flowing along its contours as it should, thus impeding its own flow past the intake valve into the cylinder. While smoothing the cast surface of the inside the manifold and blending the change of cross section, as well as making a .250" radius at both the leading and trailing edges of both ends of the balance tube can reduce this vortex effect, such compromise efforts can't take the place of the better design of the Maniflow intake manifold.
Steve S.

Steve,

Having struggled (with great fascination) through the first 50 pages of your treatise on the B-series engine, I am not only staggered by how much you know, but how much there is to know. I've rebuilt a few engines in my time, but I think it is only through good luck in my choice of machine shops that my naive attempts worked well. I'm just beginning to understand how they can be made to work so much better!

And now you mention the "Maniflow" intake manifold. ' Never heard of these before. Through some Googling, I found them. Oooooooooooh - there is soooooooo much to learn! Thanks for contributing your wealth of knowledge.

Allen
Allen Bachelder

Allen-
"Struggled"?! I thought that I'd made a careful effort at making the article as readable as possible.

Yes, there's a lot to know. You'll note that I try to explain the "why" that lies behind the "what to do". Things always seem to go better when you know the reasons "why".
Steve S.

Great stuff, Steve and thanks. That's the sort of information I've been needing. I didn't want to squander money on an intake manifold if there was little or no benefit, nor did I want to install the SUs with little or no benefit. At least you likely noticed that the car is "desmogged". The OE intake manifold is an integral part of the emissions system and I recall many fellas back in the 70s ripping these systems off and turning their Bs into dogs by not understanding how the airflow through the SUs was affected. I've seen the Maniflow site and thanks again for the info. That will be my choice when I get into this project. I'd prefer beefing up the 1800 to dropping in a Rover V8.

I'm running a recurved, rebuilt dizzy with Pertronics module, so will need the manifold advance. Is there any need to install the anti-runon valve? The carbon cannister is still in the gases route, but the pump, rail, gulp valve and anti-backfire valve are gone.
Rick Penland

Steve S - excuse my ignorance, but could you direct me to where I could have a read of your B-series article (s). As soon as you said it was readable I realised that it was definitely missing from my shelf - is it published and available as hard copy, or do I have to download from somewhere. Would be grand to have another reference material, particularly one which explains 'why', but in a more approachable format.
thanks for help
mick
m rae

I believe the Maniflow manifold is supposed to add about 5 hp to a well built B series engine. The same effect can be accomplished by inserting a small crossover tube iside the factory manifold and filling the remainder of the manifold with epoxy. You still have an issue with heat tranfer through the aluminum, but a ceramic coated header will greatly reduce that issue.
jeff
Jeff Schlemmer

Steve,

Pardon my use of the term "struggle". Your piece is VERY readable, and with every paragraph, I find myself saying things like "I didn't know that!", or "so THAT"S why...!" "Struggle" was a poor term just to suggest that this stuff is not casual reading. It is only for enthusiasts who really want to understand all of the internal dynamics of this engine.

Perhaps the struggle comes in making the personal decision: "do I really want/need to know THIS much?" Do I have the interest and the mechanical perception to grasp it all? It would be a lot easier to simply call myself an "expert" and ignore the facts. But there are already more than enough of these self-proclaimed "experts" around.

But with all the performance products out there, and the huge amount of money one can spend only to obtain disappointing results, I'm beginning to understand that your piece (a book, really), along with Peter Burgess and a few others, is essential reading if one is going to pursue higher performance.

You have nothing less than my profound respect and gratitude! That is not an overstatement. At this stage, I am wondering if a home-builder such as myself can actually build an engine to the tolerances you suggest, because of the sequences of test-fitting, machining, more test-fitting, etc. If the test-fitting needs to take place in the machine shop, it just makes sense to let them do the final assembly- at least on the block. Then if one orders a Burgess head, I guess the DIYR's contributiion would be limited to installing the head, the Maniflow(!) intake manifold, and other things I have yet to read about.

You do have many suggestions for DIYRs who do not have access to some of the more sophisticated tools and measuring equipment, but is it possible to assemble the entire engine to your standards in a home shop? In assembling previous engines, I have naively presumed that the machine shop did everything right. And through dumb luck, it appears that, on the whole, they did - even though I had no idea what to ask for, and there was not opportunity for test-fitting. I had no way of determining if the end-result was indeed optimum, and I doubt that it could have been.

Thanks for an enormous effort and contribution to the hobby.

Allen
Allen Bachelder

If you take a look at the stock manifold, it has sharp edges, angles, etc.

With a stiff wire brush on a drill motor I was able to smooth out these transitions and turn angles into radiuses. Then smoothing out the finish with sand paper on a drill motor and finally hand finishing. You end up with what looks like a more efficient manifold. Tests have been done that show a slightly rough finish has less friction than a polished finish. Something about surface effect.

You probably don't get 5 hp, but there has to be some increase in power from cleaning up the flow. The problem is that what sometimes looks intuitively obvious may not be beneficial after all. A flow bench test will help by getting numbers to compare before and after. Even with a measured improved flow, you have the issue of what is dynamically happening in the manifold with the siamese ports and the resulting irregular pulses.

A modified cam with high overlap can exagerate the siamese port issues at certain speeds.
You end up jetting the carb for the leanest cylinder.
Is it art? or science?
Barry
Barry Parkinson

Mick-
Post your Email address and I'll send a copy of it to you. Yes, the anti-run-on valve is definitely worth having.

Allen-
The precision machining has to be done by a really good shop. You can't build any better than the machinework permits. As for assembly at home in your garage, it's really just a matter of being patient and checking your work rather than just slapping the engine together. The art comes in the application of the science. That's why there's so much information in the article. Once you know the "whys" decisions become much easier and less money gets wasted.
Steve S.

Steve S., I would greatly appreciate a copy of your manual, THANKS!
mayuhm@cs.com
Rick

Steve,
I would like a copy as well or a link if it's posted somewhere else. I'm on a dial-up connection and my mail box only has 10MB of storage space. THANKS
Steve Buchina

Steve; I would also appreciate a copy of the article. Thanks for your help and continued support.
pwkeenan@twcny.rr.com
Patrick Keenan

Steve - I too would like a copy of your article also if thats OK with you. vesterback@shaw.ca - I've read alot of your comments in this forum - thanks for sharing your wealth of knowledge.

Erick
Erick Vesterback

Steve

Me too.

Have you considered talking to Les B or Bob M about posting the entire article on either of their web sites?

Thanks

Larry
Larry Hallanger

I also would like a copy of your article. Thanks, Kelly k3engstrom@wavecable.com
Kelly Engstrom

Larry-
Yes, someday the finished article will be posted for posterity. In the meantime, it's still "under development" (and has been for more than six years), but the latest version is always available through me to anybody who desires a copy. I'll consider it to be finished when I've suceeded in getting all of the part numbers from manufacturers (and in some cases the machining dimensions and tolerances), and when I complete the sections on the carburetion options, how to tear down and rebuild the transmission, etc. I expect that it'll go well over 200 Kb of pure text. Who knows, I may even start adding blueprints, photo illustrations, etc? If I do that, it might grow so large that it would require its own website.
Steve S.

Pardon me, I said "I expect that it'll go well over 200 Kb of pure text" when I should have said that I expect that it'll go well over 200 typewritten pages of pure text. The darn thing is already approaching 900 Kb!
Steve S.

For Steve S:

my email is marionmilne10@hotmail.com

thanks for this, much appreciated.

Mick
m rae


Steve

I also would like a copy of the artical. cheers Mike
m jones

Steve-
I would also like a copy of the article. Thanks!
drewbhelge@sbcglobal.net
Drew Helgeson

Steve, you've collected quite a following of eager enthusiasts. Count me in. Your comments above to my original question were very thorough and enlightening for this old "shade tree" mechanic. I'd like to read more.
Rick Penland

Steve,
Could you forward me a copy as well?
Thanks,
Scott
S. M. Chafian

The Maniflow manifold is quite expensive. Does anybody have a lead on one which is under $265 American?
Robert

Steve S - i am still working my way through the document you sent myself (and others!) on this thread - at present its my bedtime reading. Just wanted to let you (and anyone who still hasnt got a copy) that i think its an excellent bit of work, not nearly so dry as most workshop manuals etc, has a great mix between the 'this is how you do it' and the 'this is why you do it' and the 'this is how and why you are doing any of this in the first place' history . A very detailed, considered bit of work, so useful to relative beginners like myself. Nice one.
A big thanks
Mick
m rae

Steve S

I would appreciate a copy of your tretise as well. I promise to never use the word "struggling" in reference to your work.

Many thanks, Joe Lucas
Joe Lucas

Steve

May I have a copy as well please

Thanks

Dave
David Lambert

Just realized I hadn't included e-mail address!
S. M. Chafian

Hi Steve! I would also like to become a fan! May I please have a copy of your article? philip[dot]s[dot]jones[at]comcast[dot]net. Thanks very much in advance.

Phil
Phil Jones

Steve, Could you please send me a copy of your manual. I would be most appreciative. Thank you.
James Johanski

Steve, I would appreciate a copy of your manual as well.
This winter I planned to pull off the single ZS carb and install 2 HIF4s so your info will be valuable.
If my address dosn't come up it is
wadds@shaw.ca
Thanks
Morris
M. E. WADDS

This thread was discussed between 27/10/2006 and 25/11/2006

MG MGB Technical index

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