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MG MGB Technical - DUAL SU's

How much of a difference can be expected in the performance of a '77 MGB if the stock Stromberg carb is traded in for a pair of SU's?
randy olson

a bunch
chuck cougill

enough to make it worth it, but not a whole lot more :)

('75 B, sans Stromberg)
Aaron Whiteman

Randy,

Aside from poorer performance, one of the drawbacks of the Stromberg is that the float under the carb has a habit of leaking onto the hot catalytic converter and causing a fire.

A simple, trouble free alternative would be a Weber downdraft. They perform well, get good mileage and are virtually maintanance free.

I love SUs, but for the later cars, a Weber kit would be a great way to go. Call Bob at Brit-Tek (800 255-5883). He'll steer you toward the right kit and give you a good price.

Good luck!
Steve

Steve Lipofsky

I dunno. To go the weber route, you have to replace the stock intake and exhaust.

To go the SU route, you have to replace the stock intake and exhaust.

Advantages of the SU setup:
more uniform power over the entire rpm range
no "weber stutter" :)
if Cecil wanted weber carbs, he would have talked to the Italians in the first place!

Advantages of the weber:
no funny looks when dumb Americans look under the bonnet.
there is a chance that the VW owners will be able to help you troubleshoot.
(ok, a serious one) less likely to have clearance problems at the brake booster.
Aaron Whiteman

Seriously, I'm at the same crossroad. How does one choose between the down draft and the SU's? Where is the most useable power for an uprated motor? I plan on a 285 cam, Burgess Head, Peco Exhaust, etc...... , but what do I do for carbueration on a 75? Brit-tek seems to favor one, yet Burgess and others hardly mention the downdraft. Could someone who's been here before help us out. 1.75 or 1.5 or downdraft?

Luke
Luke Staley

I have an 18GB motor, .060 over HC (10:1) ported polished large valve aluminum head, Piper HR285 cam. As my car is a MKI (67 GT) I run a Weber DCOE sidedraft. I think that you would be dissapointed with the DGV carb. It is progressive, it runs on the front barrel until past 3/4 throttle. As your car is a later one, clearance is a problem. (brake servo) Personelly I would run SU's HS-4 or perhaps HS-6 depending on your driving style. The HR285 cam does not like to run at low RPM, and the famous DGV stumble would be even worse. With your cam power is made at higher RPM, The HS-4, HS-6 will be better suited.

HTH

Ron

PS look at Doug Jackson's web site mgamgb.com or is it mgbmga.com
Ron Smith

I upgraded my '79 to a Weber DGV when I bought it 5 years ago and must say it transformed the B into a reliable daily cruiser. About two years ago I installed a pair of HS-4's and what inpressed me was the spread of the power curve or in short, gain in low end grunt with the SU's. The Weber was pretty gutless at low rpms, ran great at high rpms, but not as great at high rpms as the SU's and the Weber never gave me a lick of trouble. The SU's on the other hand require more care in set up and without a doubt make driving the B more fun.

I'd recommend using Peter Burgess's book. On a '79, I do recommend upgrading the cam and porting the head. I'm using a Falcon Stainless big bore exhaust which is actually a smaller I.D. than the 2" Peco. I did install the Brit-Tek supplied Lucas dizzy four years ago with a pertronix Ignitor and haven't touched it since.
Andrew in Austin

I will chime in with Andrew. When I finished the restoration on my 72 B in 1992 I had the DGV with Piper 272 cam, headers, Mallory dizzy. The car went like it was turbocharged above 4,200 rpm but couldn't get a tire chirp on takeoff to save my life. I am now running a new motor with a BL3 grind cam, stock exhaust header and stainless big bore set from Moss along with HS4's from a 70 B. Now this thing drives like an MG with that nice kick off idle and plenty of low end torque. I don't mind doing the tune up on the carbs once a year and pretty much leave it alone. The Weber drove me nuts with the off idle stumble and I am glad to be rid of it.
Thomas Rynne

Almost all the "performance gains" from using the Weber DGV over the Stromberg are because of the switch to the early style exhaust manifold dictated. The Stromberg is actually not that bad a carb when set up on a decent manifold, ala Barry Kindig's setup on a custom Mike Brown intake manifold and Peco-like exhaust header.

A Weber DCOE (sidedraft) makes great power on a race engine, but you can forget trying to make it idle or run well on the street.

Twin SU's are definitely the best way to go for a street-driven car. Once set up properly, they do not require much, if any, fiddling. Power is available throughout the RPM range.
Paul Konkle

You'll end up spending more time trying to get rid of that anoying stumble on the Weber than you will on tuning your SU's, based on my personal experience. I went from a new downdraft Weber to a new set of SU's on my 74B, and it brought back all the pleasure of an MGB. Throw a set of Bob-cleaners on, and you'll be very, very happy! The archives have tons of comments of this subject.
SteveO

I'm being lazy by not looking it up, but there was a fellow here a few months ago who was installing a Weber 38/38(?) downdraft. This was a 2 barrel non-progressive set up I believe. Everyone was pretty excited about the prospects. I wonder how that worked out?
Mark
Mark Rotsky

Mark, I was one of the main proponents of the weber 38/38. I can't remember the guys name who did the swap (Gary?) but he lived in Nevada and contacted me via email after he had put the carb on. He said it screamed pretty good and he didn't even have the proper exhaust manifold or dizzy. He was running a stock late RB exhaust manifold that he had sawed off of the intake manifold (ugh) and the stock late RB dizzy. Now imagine if he got a proper header and an early dizzy with a little better curve. I still am a big 38/38 fan. Like I've said, if I hadn't gotten my DCOE 45 for such a deal I probably would be running the 38/38.
Its also pretty cheap, and a lot of cars run them so you can find better prices then some MG parts dealers have.
Bill 69 B-GT
Bill Mertz

Gentleman;
First let me say I am a big time SU fan. Haveing said this I have seen stromberg cars that were pretty amazing. I have a place I compare cars. About a quarter mile, gentle up hill going to steep. My wife's Gt is good for 67mph My 73 gt rather worn is good for 59. My sisters stock except for shallow dish pistons 73 B does 64! I had a strong stock stromberg do 60 a couple of weeks ago. These cars do very a lot and if your car happens to be a strong one SUs may not do all you expect. Do keep those choke screws tight thou as that petro is not good near the exhaust. By the way a 94 Neon does 77! Another interesting set up is a 1.75 su on a Marina manifold. Performs well and talk about gas mileage, Wow Bob
Bob Thompson

Getting back to Randy's original question, yes, there will be an improvement by changing to SUs but not as much as you might think. To really improve your car you will have to do some cylinder head work.

The Weber vs SU debate seems endless. I don't have the expertise to know what's best, but Peter Burgess, in his book, says
"The SU carb is easily capable of providing power outputs from the B series only marginally surpassed at very high rpm by competition-type sidedraught installations."---"It is interesting to note that a correctly set-up SU has more fuelling sites than computer controlled fuel injection systems, i.e. more ability to specifically alter fuelling to suit varying load and throttle positions - not bad for a prehistoric design!"

SUs look so much better and, it seems, work brilliantly.

Mike
Mike Howlett

I've had both the weber and su's. Go with the su's.
James Skinner

This thread was discussed between 02/10/2001 and 07/10/2001

MG MGB Technical index

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