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MG MGB Technical - The Great Experiment is Completed

OK, I'll preface this with the fact that I've never had any dyno numbers to substantiate any claim I might make with respect to my engine modifications, however I now believe I have the closest thing we'll ever see to an "apples to apples" comparison between a ZS in good condition and an excellent twin HIF-4 setup...well, sort of.

Anyhow, many of you will probably recall that I had been running a single ZS, with custom air cleaner setup (the best description would be that of a "ram tube" terminating in a large K&N filter at the front of the engine bay), custom intake manifold (similar to the single carb manifolds seen in David Vizard's "Tuning the A-Series Engine" book), excellent cylinder head work, well-fitted Peco header, 2" open exhaust (single glass-pack...yep, a bit loud, but it's my toy), earlier style/"Eurospec" points distributor, HC pistons, earlier OEM-spec cam, dual row timing chain, and some other details I can't recall at the moment. The single ZS carb was in excellent repair and employed a B1BT (Jaguar XJ6-spec) needle to provide the additional fuel needed for the vastly increased breathing capabilities. I went for some 25K miles with this setup and enjoyed it immensely.

So, not being able to leave well-enough alone and just having to know, once and for all, I decided to go with twin SUs (sticking with my friend and mentor for my hobby, Mike Brown). Based on everything I knew, having done the math, I assured Mike that I was in this for the fun of making the change and trying something new, realizing that I wouldn't see a major difference (or so I thought). Now, here's where the comparison is a bit unfair. Mike and Sean put together a set of HIF4s, modified to accept early HS4 needles (solid, non-biased, to prevent wear on the jet and provide more consistent metering), Sean had done a little flow work on the carbs, I went with the early HS4 throttle plates (no overrun valves, then again, my particular Zenith also had a plain throttle plate, with no valve), Sean had also done some flow work on the HIF4 intake manifold to ensure good flow and balance. These carbs are abolutely excellent! Now for the fun part...Mike fashioned a custom air box that used the original stub stacks (with a very smooth, generous radius), and had a single 3" deep K&N filter, with a very nice flowing radius at the opening of the box. The back of the box is nice and rounded (no sharp corners), yet clears the booster with approximately 1/4-1/2" to spare (NO fouling, regardless of how hard I press it, yet still provides unrestricted volume). I went with the T-handle choke in my '76 dash (which is the same dash used in all '72-76 cars) and it looks great. Mike painted everything up to look excellent and fashioned new aluminum lines for vacuum, crankcase breathing, and heater return, dressing the package up very nicely. He also provided me with a custom crankcase ventilation system (basically a PCV valve from a Ford Pinto...don't laugh...it looks like it belongs there...much nicer than the "mushroom shaped" PCV valve). This is the dryest my engine bay has ever been! The air box nicely covers the openings to both carbs and the single, large K&N filter at the front flows as if it wasn't even there. With the carbs flowing so well, they're a bit noisey, but considering my general sound level, it's only noticeable when your head is in the engine bay.

OK...drum roll please...

The ZS performed very well in this setup and theoretically (by the numbers) should've performed just as well as the twin HIF setup (after all, even a well flowing B-series engine can only drink so fast). The ZS had good low-rpm performance, EXCELLENT mid-range performance, and good high-rpm performance, just starting to flatten off a bit past 5K (not running out of breath, but flattening out just a bit).

My current, modified twin HIF4 setup has better part-open throttle response at low rpm, the SAME mid-range performance (albeit, feeling just a bit more "torquey") and requires me to watch my shift times because she now has MUCH more high-rpm pull. Once she clears 3500 rpm, she seems to just jump to a near red-line condition (no, not my new clutch slipping, as my head is nicely planted in the headrest and the speedometer is telling me I ordinarily would've already shifted). So, the big difference is in the APPARENT torque (remember, we're talking about the "seat of pants" feel here) AND, most-importantly in high-rpm feel.

So, what does this say. Well, the very simplified ZS installation I had was actually very easy to tune and very reliable, while offering better performance with the rest of my setup than most early-spec Bs. Bottom line, if you can find someone to fabricate the same modifications, it's an excellent option. There's nothing wrong with a well-conditioned ZS carb.

The twin HIF4s beat out the ZS in terms of apparent torque and high-rpm performance. They're a little trickier to setup, but now that I've been through it, it's not that big a deal. However, the performance difference is NOT as pronounced as that experienced through the other modifications to my original setup (the lesson here is NOT to make a carb changeout the first thing on your performance mod list). The real performance gain came with the head work, change of induction and exhaust systems, and was complemented by the bottom end work. The HIFs let me squeeze that last bit of street performance potential in the high rpm range (and are more fun from a dead stop). It's lot's of fun when I'm running at about 4200 rpm and I drop my foot into it...suddenly she feels like the fastest thing on the interstate. However, if you're a conservative driver, the carb change would probably not have made that much difference. With that said, I feel that I have a bit more tuning lattitude with the HIF4s and can probably optimize them a bit more (I have both #005 and #006 needles to play with and probably haven't quite squeezed every last bit of performance out of this that a bit of more patient tuning would otherwise accomplish).

I know this probably created more questions than it answered, so I'd be happy to field any submitted. However, I felt that I owed the BBS this final chapter in my B's performance upgrade saga, just for the record. So, the next time one feels the need to malign that "piece of crap ZS", remember, the educated response is that it's the integral manifold and other restrictions...not the carb (unless you drive as I have lately...I suppose I should slow down but I'm just having too much fun).

Finally, I would like to take a moment to acknowledge Mike & Sean Brown's outstanding work and vision throughout this long journey...I would've never made the trip otherwise. Regardless of whether or not you agree with everything they post within this venue, you'll never find a more supportive or professional pair of craftsmen, who are willing to not only to work hard to optimize your setup but are also willing to dream right along with you, as members of the team. Thanks Mike/Sean!


Barry

Barry Kindig

Sounds good, Barry. I'd be interested in seeing pictures of the air box, if possible. Every time I take a drive when its a litle cool outside, I think about how I'd like a cold air box - you just feel a little more power there. And that noise from the carbs is a great sound!
Safety Fast, Wade
Wade Keene

Barry,

I was not aware of that.
WE'RE NOT WORTHY! :) (lame Wayne's World reference).

Allow me to be the first to approach the Zenith-Stromberg oracle with my pathetic little tuning question: My performance enhancements thus far entail removing the innards of my formerly clogged cat. and plugging all the orifices of my EGR device. Everything else is still stock, including smog pump, ignition, air cleaner, manifold. I also plugged the hose from the smog pump to the gulp valve to prevent air from getting into the manifold from there. Here's the question: Do I need a different needle because of the hollow cat., which I imagine causes lower back pressure? The car starts and runs fine (never backfires or hesitates, accelerates smoothly), but no matter how I adjust the ZS, I have the impression that it's still running a tad on the lean side. I believe the carb is in excellent condition, and it was professionally rebuilt only about 5,000 miles ago (June 2000).

Thanks!
DGV
Dan Vukmanich

Dan,

This is actually something about which I've posted relatively extensive information over the past couple of years (maybe only 20 months). If you made all the modifications I've made, your ZS with stock needle would be EXTREMELY lean, to the point of probably going flat at 3000 rpm or less. If you're running lean and you've done already adjusted for the entire range available as it's currently equipped, then it's one of a couple of things. One might be a clogged fuel evaporation line to the charcoal cannister (yep, this caused me to become increasingly lean and caused a surging idle condition). Another possibility could be an induction leak (although you'd likely experience a rougher idle, but not necessarily). You can check for leaks using spray carb cleaner at idle (be careful of the hot exhaust manifold). When you spray it on the intake manifold and various connected hoses at their respective manifold interfaces, you'll note an idle change (in your case, it would probably drop slightly). Is your crankcase vent line tightly attached to the carb? If not, then it'll let quite a bit of additional air in as well. If you're not venting to the carb (for whatever reason), then you'll want to ensure it's capped.

If there's no leak, and you don't have a clogged evaporation line AND you've adjusted to the maximum enrichment point, then a richer needle is in order. I don't know which one you have, but there's about 3 different needles available in the Moss catalog. However, unless you have access to a dyno, it's a guessing game. I believe the richest needle available in the standard catalogs is the 45F in the Victoria British catalog. It may be too much for your application. The B1BT I used would definately be too rich (remember, I had extensive modifications). You'd need to go to another source for this one, but I doubt it would be correct for your circumstances anyhow (if you look at everything I had changed, the ZS was sitting atop a completely different setup).

With all of that said, the integral intake/exhaust manifold used on the '75 and later U.S. spec Bs is awful and the primary cause of the performance limitations experienced on these models. There are a number of others (unmodified cylinder head, possibly the late spec cam if yours has not been replaced with something with better performance, just to name a few). BUT the manifold, coupled with that ridiculous air cleaner ARE the primary reason for the late model's restricted performance, so even if you do get your mixture right, you'll suffer limitations.

Of course in CA, one needs to be willing to remove just about everything attached to the left side of the cylinder head and swap the "original" equipment back on to pass emissions AND have a performance setup when they're not being tested...not something everyone wants to do.

BTW, were you the one who noted that CARB had offered $500.00 for his B? My question is...did they do this without any request on your part? Was your car catagorized as a "gross polluter" (which is a ridiculous term invented by the CARB nazis and nothing to feel badly about)? Or did they just assume that you'd take $500.00 for your older car? I'm just curious. Someday, all responsible and successful citizens will have left CA...it's inevitable. I grew up and lived there for more than 40 years...it's never gotten better...food for thought.

Hope this helps.

Barry
Barry Kindig

Barry,

Indeed, CARB in year 2000 did offer to buy my MGB for $500, in the event it failed smog check. This year they generously upped the ante to $1000, which I am now disqualified from receiving because I passed the smog check in March. The offers are printed on a flyer that they include in the envelope with the renewal notice. Perhaps the car had been branded "Gross Polluter" once before I owned it? I don't know. I'm not supposed to have to pass a smog check any more, the 30 year rule, as I'm sure you've heard. That's what their web site says, anyway. I'm not ready to take the smog pump off just yet...

I have done the checks for leaks with carb cleaner as you have described; the idle stays smooth and steady regardless of where I spray. If remove a vacuum line, for instance the one connected to the brake booster, then the idle becomes very rough. Also, if I disconnect the line going to the vacuum advance, idle becomes erratic, as expected. Now get this: if I remove the line from the charcoal cannister, there is no change, still smooth. If I then completely plug that little tube it connects to, just behind the air cleaner, there is no change in idle, still smooth, and when I put my finger over the opening and rev the engine, I do not feel any suction at all. Does this indicate a problem?

Thanks again,
DGV
Dan Vukmanich

Barry-
I've long held that converting a Rubber Bumper model to dual SUs and filters with decent flow potential requires much work, such as fitting the earlier non-servo-boosted master cylinder and its pedal box, complete with its pedals. A cold-air box that would permit the mounting of dual SUs onto a Rubber Bumper model without these changes has long been a quest for many of the posters on this BBS, including myself. Could you post a few pictures of your system where we can all see it? If this is a really practical system, the Brown Brothers may have a nice profitable little sideline in fabricating it for all those Rubber Bumper owners who want to go for serious increases in power output without all those mechanical hassles.
Steve S.

Dan,

No, plugging that tube for a few moments and not noticing any change doesn't mean anything. However, if it remained plugged (causing the float bowl not to vent) then you'd notice a surging idle and very lean operation (if it were completely plugged for a prolonged period, it probably wouldn't even idle). Sounds like you MAY have enhanced your breathing to the point where when you removed the cat innards, you may have exceeded the capability of the very lean emissions needle to accommodate your flow. Just imagine how much worse it would be if you were to actually move on to a well-breathing system with accompanying cylinder head work! Are you sure you've used the ZS carb adjusting tool and gone as rich as you can (don't try to twist it any farther than it'll go, I'm just curious)? If you have the very lean 45H or 45M (intended for high-altitude applications as I recall) , I can see where you would have little lattitude for tuning. If you have the 45G and you've somehow exceeded your ability to enrich the mixture, I would still look for something else (I can't think of anything else for the moment, but I'll ponder it a bit further...then again, I'm sure I actually saw everything weird that the ZS carb can introduce). Why do you think you're lean?

$1,000.00 now...these guys are something else. "We're from CARB, we're here to help..." yea, right. I must tell you my friend, I don't miss CA one bit.

Steve,

Man, I wish I had a digital camera handy (I can't believe I'm in a technology business and DON'T have such a toy, but I still like to take regular pictures [you know with the film]...guess I had best get with the times).

The air box is a thing of beauty. Any "right angles" are located at the front of the box, where it doesn't matter as the air filter is attached to a VERY NICE wide and smooth entrance...Mike and Sean really out did themselves on this one. The rear of the air box is rounded, with a nice removable cover. They even accounted for the carb mounted angle, allowing the box to appear level in appearance. Of course, the rounded rear of the box allows the air to enter and rush to the back of the box without any undue turbulance...really nice thinking. NO servo fouling. I have both the high-performance and servo-assisted brakes...pretty nice really, as it makes for a very relaxing, yet thrill-packed ride (I've kept on top of my brakes and suspension and ensured they were in excellent repair to handle the additional power...what I really notice now is my ability to power through the "non-jug-handled" [only some of you will get this] left turns here in Jersey from a dead stop and take a command of the traffic situation...very nice).

Now for the pictures. I almost feel as if I've said more than I should, as I'm not sure there's an interest in "mass-producing" (now there's a relative term) these units. I feel that you're correct on the search for a well-flowing solution that's compatible with the servo (you and I both know that the conical filters are a mere "kludge" and not a optimal solution). When I get the chance, I'll capture some pics, however, it may take some time. It's really quite impressive...it actually looks like a factory installation...no better! I mean, not only did they build a really nice looking box, but they worked the entire installation so it would look absolutely "show quality"...now I just need to get my car into a show out here (everythings either painted or polished). Sometimes, I wish my B were either BRG or "resale" red...glacier white just doesn't turn many heads and there's only a few of us who can really appreciate something special under the bonnet when we see it...at least my B is shiny ;-)

Take Care,

Barry
Barry Kindig

Barry,

When you get your film developed, have them put it on a CD or disc along with the prints. Then you can Email 'em (like, to me!) or post them on a web site somewhere. Glad you're keeping busy with your car! As much fun as you're having on the other coast, we still miss you. Not enough wrench turners in the Club!
Paul Konkle

That cold air box sounds like one that TWM makes.
http://www.twminduction.com/Home/Home-FR.html
Wade Keene

Barry- You are starting a landslide here dude. I need to see this boxwork. Can I send down my cheap digi-cam and you can fill up a 4mb disk? Vic
Vic Myers

Barry,

My engine has the classic "hesitation" when cruising at steady 2500 RPMs. It's not too pronounced, just noticeable. At 55 MPH or higher, it seems to run smoothly. I've advanced the timing a bit, but that doesn't cure it. Valve clearances are set to where I can just hear the tappets tapping. Everything else seems fine, runs fairly cool, and decent power. When I'm rolling along with engine turning 1,500 RPM, she'll pull away smoothly when I floor it. I've used the adjustment tool and turned it clockwise as far as it will go. I still think there must be an air leak somewhere, maybe underneath where I can't reach with the carb spray, or maybe I haven't sprayed enough. Otherwise, I'm wondering if a different needle might be necessary. Seems like a relatively easy thing to do, mainly just removing 4 screws from top of carb? Hopefully inexpensive, too. I'm just trying to squeeze as many miles as possible out of my tired old engine, performance is low on my list of concerns, since my 'B is on daily commute duty in typical city driving, 7 miles one way.

Cheers,
DGV
Dan Vukmanich

Wow.

Anyhow, Wade, I looked at the TWM site and the idea is pretty much similar. The major difference is that mine is smoothly tapered torward the back, so as to create clearance for the servo/master cylinder.

Paul...THANKS! I'm now remembering the advertisements for that product...and yes, I miss all the SD folks. The SDMGC gang and some of my other friends are the only thing I miss about CA, but it wouldn't have been very practical to bring everyone out here this way.

Vic...thanks for the offer. I think Paul's idea will likely work but I understand your interest and will work something up (heck, when this idea was presented to me I could hardly contain myself).

Dan. It's nearly 7:00 AM EDT, so I'm going to have to run off to my office pretty soon, however, I should have more time to read your posting in detail...talk to you soon.

Have fun,

Barry
Barry Kindig

Dan,

From what you've described, your B seems to be operating reasonably well, given the setup you have. BTW, you're engine probably isn't too "tired" as you did pass the CA emissions test...it may not be as bad as you think. I'm sitting here trying to consider everywhere it might be leaking. You indicated that you were still running the air pump. I seem to remember that when I removed this unit, the air rails, and the gulp valve and properly sealed everything up, my mixture was generally richer. Now this doesn't mean that you should necessarily do this (and BTW, it may be because I had a leak somewhere in my system at the time, as this system is intended to inject air into the exhaust valves and inject air into your intake on overrun [hey, how's your gulp valve?], which should't have that much bearing on your enrichment). However, it's another area to consider. Is the carb on nice and tight? Are the manifold nuts secure? What's the condition of your vacuum hoses (air escaping through tiny cracks might be difficult to detect...new hoses are cheap and readily available at most auto parts stores). Is the crankcase vent tube on airtight? Here's one...how about the state of the Anti-Run On valve? Is it stuck in the "kill" state (does it have power when you're running...it shouldn't but rather only when you shut down, until your oil pressure drops). If this were stuck in the kill position (with power applied...I can't remember if this means opened or closed off the top of my head...but the effect is that it leans out the mix to prevent running-on), it would definately cause lean running. (This is not necessarily a typical condition, I'm just trying to consider everything.)

How about the vacuum line that runs from the EGR valve (if you still have it) to the intake manifold? New rubber hoses would probably help if applied everywhere.

New needles aren't terribly expensive (they're between $20-$25 as I recall), the trick is finding one that will provide you with a tunable range. They're relatively easy to install (four screws for the dashpot, pull out the works, remove the grub screw, and [using the ZS adjustment tool] adjust until the needle travels to it's leanest position and loosens. There's a slot on the biased needle base to align with the grub screw, but assembly is essentially the reverse of disassembly. You'll want to dump out the oil when you first remove it so it doesn't come out when you turn the assembly upside down or at whatever angle is most comfortable for you to work (when you least expect it, of course...if my actions in the garage were videotaped, it would make for amusing "reality TV").

Now, which needle? Yep, that's the question. I believe an original CA emissions controlled vehicle used a 45H, so your next choice would be a 45G (assuming my memory is correct, and it DOES fail me from time to time). Was your needle replaced with your carb rebuild? Does your carb rebuilder know what he installed? This MAY help.

FIRST, you really need to ensure you've eliminated all possible air leaks throughout your induction system. Manifold tight, carb tight (how are your carb gaskets?), all new rubber hoses, all hoses on tight, a clear line to the charcoal cannister, brake booster line renewed and on tight everything as AIR TIGHT as possible.

Hope this helps.

Barry
Barry Kindig

Barry,

>how's your gulp valve?
It's pretty new, and so are the associated hoses. I have "temporarily" plugged the hose going to it from the air pump. I guess the next step is to completely block off the connection betweent the gulp valve and the manifold, but that would eliminate the vacuum connection to the distributor advance, since that line comes from the gulp valve.

>Is the carb on nice and tight?
Yes

>Are the manifold nuts secure?
Yes, and the gasket was renewed in late '99 (only about a year ago in MG years:-))

>What's the condition of your vacuum hoses
Most are new, except for the one to the brake booster

>Is the crankcase vent tube on airtight?
I'm not sure where that is. If it's the one coming out of the valve cover, then it's on tight.

>how about the state of the Anti-Run On valve?
I never even thought about it. I'll disconnect the power, and see if there's any difference. If not, then I guess I should block it off to test?

>How about the vacuum line that runs from the EGR valve?
I have plugged it up with high-temp sealer, and the EGR is also plugged, so it is basically an ornament at this time.

>how are your carb gaskets?
New in June 2000, only about 5K mi. ago

You've given me the basis of a good, simple strategy to follow. Just need to systematically knock down each of the open questions and eliminate all possible sources of air leaks, and double-check that there is no blockage from the charcoal cannister.

Thanks again for all your advice.

DGV




Dan Vukmanich

Dan, I don't think your distrubutor vacuum advance should be hooked up to the gulp valve. It should have direct manifold vacuum.

Wayne
Wayne Pearson

Wayne,

You're right, there is a vacuum line from the manifold that has a "T" junction, one line from there goes to the gulp valve and the other goes to the distro. Plugging up the gulp should have no effect on the vacuum advance.

Thanks,
DGV
Dan Vukmanich

Congratulations, Barry! It has been a long tale, but the results were definitely worth the commitment. And thanks too for sharing your knowledge the folks here. You always present it in depth and that is very much appreciated by those who wish to copy your good work. I too will be interested in seeing what your photos will show - a well thought out and laid out installation to be sure. :-)
Bob Muenchausen

Dan,

Actually I was referring to the crankcase vent tube that runs from the forward side cover to the port on the Zenith carb. If this were loose where it meets the carb, it could allow quite a bit of additional air in.

Hope this helps.

Bob,

Thanks. Yep, it's been interesting. Now I'll just have to drive and focus on things like cleaning up various interior pieces ;-)

Barry
Barry Kindig

Barry
Can you be a little more specific than "custom intake manifold (similar to the single carb manifolds seen in David Vizard's "Tuning the A-Series Engine" book"

Do you feel one of the Pierce manifolds that often come with the weber carburatters can compare to the one you have? Why did you go with a custom? and what might a comparable manifold on the market be? ie what does the one you have look like. There are many in the 'A-series book'.

Is there comparable flow data available for the B series engine manifolds as there is for the A-series manifolds?

thanks
werner
Werner Haussmann

Werner,

This was a custom manifold for a ZS carb on an MGB. Not something that most would consider. The manifold design could also be compared to one from an Austin Marina, however, it [the custom unit] probably had better flow characteristics (very smooth and rounded). Since I don't think Pierce makes such a manifold (or anyone else for that matter, at least not for the B-series), it needed to be a custom job. On the other hand, you could probably get by with an Austin Marina intake manifold, if you could put together a decently breathing air cleaner (which in my case, was also a custom-fabricated unit, geared toward better breathing as I described). I compare the intake manifold with some of the preferred single carb manifolds in Vizard's book, as he pictures the closest thing I could think of to what I had. As far as comparable data for the B-series engine (for a single carb application)...I rather doubt it. Bottom line, if you're talking about a Weber DGV, it wouldn't stand a chance of flowing as well as my custom setup did (you can only expect air to make a 90 degree turn through a straw so smoothly). On the other hand, a DCOE 45 setup would certainly have a great deal more potential (as compared with the single ZS setup I described)...it's simple math at that point.

FWIW,

Barry
Barry Kindig

Thanks Barry

I have a Marina manifold that fits the 'B'. It is the log type, and it has an exhaust hot spot. Is that the same as you mention as the 'Marina' manifold. Vizard describes log types as some of the worst. Maybe mine is not a 'Marina' manifold.

And yes I do want to pursue the single carb manifold.

On page 132 Vizard shows many types of Manifolds for the 'A-series' Which of these are closest to what you have?

Sorry to keep after you like this, but you really started an interesting thread here.

regards
werner

Werner

Werner,

I have personally never seen a Marina manifold, I've only heard that they would work (fit on a B-series and accommodate a ZS carb if one wanted to dump the integral manifold). The manifold I was running with the ZS (that's now sitting in a box) is shaped more or less like a "U" with a ZS flange on the end (angled as per the original carb mounting angle). My custom ZS manifold looks just like the one on page 139 of Vizard's book, as made by "Janspeed", only it accommodates a 1 3/4" carb, of course. The figure states "Shown here we have just about the best power producing, single 1 1/2 inch intake manifold for the smaller Series A engine". Now again, mine was of course larger. Same principle, applied to the ZS.

Anyhow, I hope this clears things up.

Barry
Barry Kindig

So, Barry....think your guy would make up a couple more of those air boxes?
Tony Barnhill

Thanks Barry

That does it for me.

Werner
Werner

This thread was discussed between 01/05/2002 and 03/05/2002

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