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MG MGB Technical - Engine performance improvments and Emmissions

I am located in a state (NC) which when implemented will require a visual only inpsection of my 79 MGB for emmissions equipment. Would it be worthwhile to have any Peter Burgess type head work done if I can only go with a single carb. I am hoping to desmog between the annual inspections, however, felt the hassle of changing out carbs and manifolds might be too much to have to do on an annual basis. Any thoughts or experience out there on what is the best way to approach this. I know I probably should have bought a pre single carb MG however I got what I got and am trying to make the best of it.
Frank

Frank-
If you're going to stick with the OE intake/exhaust manifold there's no point in having headwork done. That one piece intake/exhaust manifold just doesn't breath. Actually, switching the system over to something more performance-oriented on an annual basis isn't all that difficult if you approach the task in an organized manner. Once you've done it, you'll know the drill, so you can do it in an easy day's work.
Steve S.

Frank. As I understand it, you are allowed to run a single carb and must have a cat. Barry Kindig had a custom intake manifold made to function with his Z-S (but an SU HS-6 or HIF-44 should also be acceptable) by Mike Brown. Barry claims significantly increased performance from the custom intake which is far less restrictive than the original design. Similarly, either an early exhaust manifold or a set of headers, with a custom aftermarket cat should meet the general requirements. The original intake/exhaust may also be modified so that only the exhaust portion is functional allowing the use of a single Weber, as I have done on one of my cars. Yes, I would go ahead and have the head work done by either Peter or Mike, have Mike fabricate another custom intake manifold and set up an exhaust with a cat. You will get better performance than you will with the stock system. Les
Les Bengtson

Frank, here are some photos of the manifold on Barry Kindig's 'B.

http://www.ph.utexas.edu/~yue/MGBcarbs/MGBcarbs.html
Andrew in Austin

Hey, I guess I tuned in at the right time. Steve S. is correct concerning the manifold and Les is correct with respect to the solution I applied. It should also be noted that I went with a much richer metering needle for the ZS (#B1BT), to complement the custom intake manifold, head work, and custom air cleaner assembly. Mike Brown certainly knows how to build this setup. I also run a Peco header and custom exhaust Mike built for me. Very nice power. I'd put her up against any slightly tuned early B. She also has HC pistons, an earlier OEM style cam, and the earlier dual chain cam sprockets (I'm probably forgetting something, but you get the idea).

Unfortunately, she's been in the garage a bit as of late due to weather and salt (I've been too busy during this latest "heat wave" to get her out, with job-related travel and all). Hmm. I'm going to have to get some post-build pictures posted sometime...my engine compartment was awful dirty when I first installed this system atop the old block, as shown on Andrew's site.

Now with that said, I'm about to register my B as "historic" in this state (I drive her a lot less now, but enjoy it more...hey, there's an interesting analogy here, but I'll pass) so I can pretty much make whatever changes I wish and never go back. One of the first things I'm going to try (without any concern for emissions at that point) is to go with twin SUs, modified for better than stock flow...I just had to know. However, I stand by my findings with the modified single ZS setup...the real performance hit was never the carb (assuming proper operation), but rather the incredible restriction imposed by the air cleaner, intake/exhaust manifold, and cat converter.

With the setup depicted at Andrew's site, you'll be able to add an air pump, injection rails, and perhaps even an in-line cat converter (as described on Doug Jackson's site) and probably just leave it alone between inspections. What you'd be missing is the gulp valve and EGR valve. These could be accommodated, but we'd be talking about some interesting plumbing on your custom intake manifold and header (in the case of the EGR valve). I guess the point I'm making is that you should go over the visual "checklist" for a late MGB for the NC inspection manual and see what is actually needed. The setup I'm currently running, however, can be a great way to go. My problem is that it just isn't sufficiently "maintenance intensive" to keep it fun...hence my planned swap to the twin carb setup.

Have fun,

Barry
Barry Kindig

Frank,
I've done two late model MGBs up with performance mods, mine and one of my brothers. This was in California at the time and of course if it will pass emissions there it will pass anywhere in the US. My plan was to get as much power as possible while still passing both the visual and emissions testing. Both engines were built up similarly with the aid of Peter's guidelines from his book. The heads both got 1.625 intake valves and were re-worked to midway between the D.I.Y. and rally spec. Both engines have the Piper BP270 cam. My engine was rebored 0.060 oversize with stock dish pistons and head shaved .020, while his used flat-top pistons but standard bore and no head shave. So the compression ratios were probably similar at around 9.25-1.

My brother intended from the start to set his up as dual SU carbed but he had to get it smogged so he first used the stock ZS carb and manifold. All his emissions equipment were operational and he had a new cat installed. After tuning with a Gunsen gas tester for CO he was able to get it to pass the emissions test with nearly undetectable CO levels. The technician was quite surprised thinking it would fail just because it was an MGB, he was never even aware of the internal mods. The best part of all this was that the car had substantially improved performance over stock. My brother thought it was quite "peppy" at that point. It might have been overkill for the nominal improvement in power but there's no way to tell exactly what could have been left undone for the gains obtained.

Then he afterward proceeded to remove the ZS setup. He bolted on a stock early model exhaust manifold and a pair of 1.5" SU carbs. The SUs were modified as per Peter Bugess's recomendations with thinned butterfly shafts and some cleanup work. K&N conical air filters were fitted. This resulted in a transformation of the car. Now it was seriously sporty with enough power to smoke the tires and pull strong all the way up to redline. He was stunned. Peter's formulas are no BS. We never dynoed it. My brother was too thrilled with the results to care as he doesn't race but just uses it for pleasure driving.

Now for the story about mine. Starting with the mods discussed already, I set mine up with the ZS carb and manifold too. My exhaust system was shot so I replaced it with the Falcon "Big Bore" exhaust. This comes with a pipe that replaces the cat section. Instead of the standard cat I installed a generic aftermarket cat that was much higher flowing with 2" piping. This was placed under the car where normally the front silencer goes. The ZS carb was reworked taking tips from Peter's book. I thinned the butterfly shaft and removed the poppet valve from the butterfly to increase the flow rate. The manifold also got reworked. The intake and exhaust sections were smoothed up inside and the ports matched to the head. The inside corners were also radiused smoothly to improve air flow. After all this the result was a quite noticeable improvement in the performance. I know that it sounds like a ton of work but the good part is that it still passed the emissions test. After the smog test I removed the stock air filter box and installed a K&N filter and a home-made 1/2" radius flow plate between the carb and filter. The fan belt to the air pump was also removed. I would say that it was performing about like a stock twin carbed setup in new condition would be expected to.

Because of the great results my brother had when taking the next step moving up to the twin carbs, I plan on doing that to mine too very soon. But I'm going to have to then live with swapping it out every year.



Gerald O'Docharty

Realizing the shortcomings of the ZS intake design and the heat coming from a combined exhaust, I know it would be limited. But, has anyone ever tried to see how much flow you could get out of one of these ported or more easily extrude honed? I already purchased the 1.5 SU's but for the CA group any help could be used. On convuluted intakes like the 5.0 Ford, they can pick up 20% flow and even out the port to port difference with extrude honing. You would at least reduce the awful "S" in the fuel flow then. I would still be tempted to try and separate the exhaust to run an earlier manifold, because these are just plain pathetic. When your trying to get improved performance from an engine you must reduce the bottle necks. There is no reason to have a head flow 150 cfm if the intake can only flow 90cfm.

As an alternative they market a SU that is a bolt on replacement for the ZS, if that is appealing to you.
Luke S

This thread was discussed between 31/01/2002 and 02/02/2002

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