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MG MGB Technical - D.U.I. 123 411

As promised, for those that care, I have finally fitted the very expensive GB123 to the 77 MGB. PreRamble: the car was purchased 5 years ago with 38k original, a blown engine with OD, never parked outside, nor in an accident of any kind. Price at the time $1700 cash. I had Doug Jackson rebuild the front end, and Lawrie Alexander finish up the motor build, that featured 60 over, P285, 50 Rockwell hard followers, D.Jackson rollers ( and composite leaf springs with tube shocks with 1 1/2 lowering and chrome bumper conversion)9.75:1 ACR, squish equal over 4 at 15 thou, Burgess "Fast Road Big Valve" head, lightened fly, and everything balanced persnickety. Rebushed/rebuilt 1 1/2 SU tuned with Innovate AF, and #6 needles, originally a pertronix and BriTek "Eurospec" dizzy, stock balast coil, at 25k voltsI think.
Well, this car has been fun in the past but now is transformed into a thorough pleasure to drive. I have bussiness between sea level San Francisco and Lake Tahoe Area at 6800 feet, 225 miles between.I have run through 3 tanks of gas as of this writing, using a lead additive at each fill of the highest octane available in Northern Calif., advertised at 91 octane.
I fitted the 123 GB MGB, set to advance curve GB#1 of the 16 choices: prettymuch all in at 3000 RPM for 31*, and set the initial timing at 18* and used the vacuum advance supplied with the GB unit. I figured what the hey and also screwed in a 40k volt Pertronix Flamethrower ballasted coil I had rolling around the boot for 2 years or so, purchased 4 new Champion N9YC plugs and set the gap to 42 thou. I set the timing mark per instrux to TDC, and pulled the old dizzy, replacing with GB 123 aiming the rotor at 2 OClock and using the vac nipple to initial set pointing straight up at 12 noon. Turned the key and she fired right up first crank, and was idling high. I checked timing to find my seat of pants was 22*, so I rotated back to 19*, tightened down, and reset the idle to 700 ( smooth as a baby's behind with a P285 mind you).When I jumped in, first notice was the tach needle being dead steady, like the engine wasn't running and the needle was stuck at 700. They must've put a damper in, because up, down and cruise, the needle was rock solid, noticeble as heck over the way it was, and that was just the beginning...........
The car, running noticeably smoother, accelerated like a scalded cat. On the freeway, in OD at 3900 or so, the lightest pedal blip transmitted instant power. I could pull from 2500 in OD back up to 80 mph in seconds. In fact, I made the climb up the hill, 7272 feet of elevation, in 5th gear OD and never shifted once! Drive up I got 24.9 mpg, drive down 34.7. Previously I had averaged about 22-26 depending on which way the wind was blowing.
Oddly, I heard pinging at low RPM under load, 1st and some of 2nd at sea level, so I have some experimentation to do with the remaining curve choices. I'll keep you all informed, and would appreciate other's story on this new device. Cheers aplenty, Vic
vem myers

Vic ---

It sound like you have an A1 car,
. . . and a very understanding wife.

Dan Robinson

Thanks for the report. It is good to hear the results of the 123 conversion rather than the steady round of "It's too expensive"
Since my Pertronix died after 400 miles use I have been running on points with the warranty replacement Pert set aside until I decide whether to go the 123 route instead. I would rather pay for a good system up front than do roadside repairs at 0-dark-30, and from the sound of it the performance increase makes the unit worthwhile by itself.

Please keep us posted.

Rich McKIe

Rich- My pleasure, believe it. I've contributed real time experience to this board for 5 years now and have always felt that that is the purpose. "Too expensive" is too short a schrift for this precious, I say.
Yep, it is expensive, but then all things worthwhile are.

FWIW, I carry a spare water pump, coil, full set of rad hoses, plug wires, new plugs, points, and condenser AND the old stock dizzy just in case. I'd never want to meet you, black night, at Zero Dark Thirty ol son. Extrapting ( sic or sick as you like) then, at 10 miles better per gallon, and hi-test at $3.25 per gallon in my area, I should trade off the purchase price many miles class?
vem myers

Vem, I went with the DUI system when I installed the Moss supercharger 4 years ago. After trying the "new" updated distributor from Moss, that they reccomended, I realized that a stock unit wouldn't work up to the supercharger's needs. At the time the 123 was just appearing on the market and the curves listed were based on stock settings. I'm glad to see that you are having success with it as the DUI unit, which runs flawlessly, is one huge ugly S.O.B. Ray

So Ray,

What is your opinion on the DUI with the Moss Supercharger?

What is your opinion on the Moss distributor with Supercharger?

I do agree the DUI is HUGE and ugly and I like showing off my supercharged engine.

Regards, Ray
Ray 1977mgb

Just curious, what about the stock dizzy won't "work up to the supercharger's needs"? I just had my 25D recurved by Jeff Schlemmer for a SC installation.
Steve Simmons


What was the curve numbers Jeff used on your recurved dizzy, and how does it feel with the supercharger?

I had my dizzy recurved and it is still on my car. Won't change that baby unless I know for sure there is a better curve out there.


PS: IMHO all stock dizzy's will have to be recurved to work with the Supercharer. I went down the entire list and there is no curve that will work except the old/new 40897/41427, but that curve ends at 2200 rpm. You still want it to go a bit further to at least 2600-3000 rpm. Recurve is necessary.
Ray 1977mgb

Any chance you might try this out on your SC'ed MGB and report back. I see you do have the GB version and not the MG version of the 123. Proportedly this is the one with the curves better suited for the SC'ed MG.

Ray, I am extremely pleased with the performance of the D.U.I. system. The company that builds them curved it to their specs for a blown B. I've made a few adjustments to it but nothing radical. Their attention to detail gives a linear dwell to over 6000 RPM. It is a quality unit and shows in it's ability to give a smooth idle as well as great acceleration. That said, I did install a MSD boost retard controller so I can have exact control of the timing when under boost and climbing some of the very steep hills in Northern California using our wonderful gas. P.S. I had purchased the 143-110 distributor from Moss but was disapointed with its limitations and build quality. After 3 months there was noticable shaft wobble allowing the dwell to scatter over 6 degrees across the rev range. After fitting a Pertronox, It ran somewhat better but did not give the performance that I was expecting. Perhaps I could have had Jeff recurve it for me, but the poor quality of the unit dissuaded me from that route. Ray N.CA


Is your DUI curved to blown spec's the GB123 that Vem has?

I also had the 143-110 from Moss. Wrong springs and and very poor quality. I sent this one to Jeff to see what he could do and it wasn't much.

Vem, When are you going to try it with the supercharger. Would be nice to hear more comment like Ray's.

Ray 1977mgb

Ray, I done't know the curve numbers and the engine isn't complete yet. I'll let you know once it's in and working though.
Steve Simmons

I've really screwed the pooch here. There is a DUI distributor and there is a 123 distributor. I have the GB 123 from Seven Shops in Auburn California for $380 as I recall not $408. The curve #1 on the GB unit is starting to ping and I plan to change up to sometning milder soon. Yes, I will try it on the SC. The curve choices are plentiful and I can find one for both the stage 2.5 and the SC car. I'll keep you posted.
Rich- Your Pertronix died? First time I have heard of a consumer reporting sudden death of a Pertronix. I had one that wouldnot work outta the box, but once installed the 6 I've used are all up and runnig. A couple with 10's of thousandfs of miles. Please tell us your story in another thread.

vem myers

My post above pretty much described my Pertronix experience but here are the details in brief:
Car running well, shut off car, car would not start. Had fuel, had power to coil, no spark. Pulled Pert, installed points, car ran.
According to my dealer it is unusual for a Pert to have a sudden death, DOA is more common, but he did give me a replacement.
Today I installed the replacement Pert and the car is running well...spare points are in the boot!

Rich McKIe

Ray, DUI curved my distributor to a theroretical curve that they computed based on CR, head work, cam, exhaust system and carb. All advance is in by 3000 RPM. Ray '67B


When I first tried to get a distributor to work with the supercharger I contacted 123 to get a distributor and they told me that none of the curves they have would work with the supercharger. Hopefully we will see how Vem's GB123 works out....

You have a DUI distributor and not the 123. If I may ask is there a web-site for the DUI or where did you get yours from?

Ray 1977mgb

Ray, DUI stands for Davis Unified Ignition. They sre located in Memphis, Tennenesee. Their web site is I purchased mine, on the web, through them. Ray '67B

Vem, The issue you're having is too much initial advance. You should play with the curves and find one that allows you to start closer to 12-14 BTDC and still run up to 31-34 degrees total at 3000 or so.
Jeff Schlemmer

Jeff- Yes, you are dead on. The GB #7 is looking promising. To further the record data, I came up the hill 7272 feet of elevation over a 225 mile ride with 26.7 mpg. Stopped in Reno to pickup mail, and came out to pool of gas. Unbeknownst and for how long, the tank pickup hose has been steadily leaking, drip drip drip. My this should make a difference eh? New 5/16th hose and new records to be made and reported.
Ray-No, I left a contingency with the Auburn supplier: get me a vac advance off the new line, and I'll buy it. A month later I had the 123 GB in hand with the vac connection for $380, and NOT, I say not, the DUI distributor:
I apologize again for the misspeak.

Ray, in Samoa, rumor is out that you have some stunning data to share on the G-tech and that gorgeous Golden Glow SuperCharged MGB.....Vic
vem myers

Thanks for the report Vic, glad it seems to be going so well!

Keep us posted please.

Alexander M


Thanks for the info on the DUI. It would be nice to see what curve they gave you?


I posted the results on the Supercharger Forum earlier today and also placed the rsults on my website if anyone wanted to see the results. Seems nobody wants to respond. Maybe they think I am BS, but I am not. Just trying to get an answer to "WHY" ?????????????

Ray 1977mgb

Ray, 20 degrees @ 3,000 RPMs. Ray '67B

This thread was discussed between 22/03/2007 and 30/03/2007

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