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MG MGB Technical - Weber VS SU

Any body got some hard experience and opinion to offer on the daily driving performance between a set of Webers, either side or top, and the SU's. One Mr. Doug Jackson, in Novato California (I believe to be the "States" equivalent of Monsignor Peter Burgess), suggests that with comparable flow on the HS6, the SU's slightly outperform the weber. Further, there seems to be a heck of a lot of weber drivers out there that just cannot make the suckers work well, or keep them in tune, or get the right jet arrangement, or figure out the flat spot. After 31 years of fiddling with the SU's ( off and on folks, I do have a real life somewhere), I like em. My dilemma is I am about to upgrade to HS6, but have good advice that the snappy Weber is a better mousetrap.
Vic Myers

Never used a downdraft webber but poeple complain about no "punch" till the gas peddle is 3/4s down, I run a sidedraft and I would not recomend it if you do not have a modified engine. As for the SU's I dont knoww much about them sorry
Ross

Vic,
Having had both fitted to my car which was, apart from the air filters and cold air intake, totally stock in the engine dept. some observations follow:

The SU's set up properly and not fiddled with gave the same performance as the Weber for a road car

The Webers I had (2 x 40mm DCOE ie side draft) had to be cleaned every six months or so to remove any rubbish in the fuel which found it's way beyond the fuel filter. Never had that with the SU's.

I had my car set up on a rolling road dynomometer for both carbs and there was a slight power increase of about 5% with the Webers fitted but no air filters.
Fitting the filters (K&N foam elemnts) gave equal power to both Webers and SU's so I am guessing the Webers would be a better bet for competition but I am not totally sure since I was not competing at that time.

As for on the road day to day running I found no difference in either economy or performance between the two.

The best value of the whole exercise was in the money spend on the rolling road dyno testing.
That did yeild a power increase about 12% in the before and after modes and the other good value item was an electronic ignition which eliminated the drop off or tune and therefore power between tune ups.

The next best valus was to fit a cold air pipe from ahead of the radiator and up to the carbs with some sort of insulated barrier between the carbs and the exhaust to avoid hot air ingestion.
There is a thread on thsi in the V8 forum at the moment under "hot air / cold air induction"

As an aside there was no power increase from the foam filters over the pleated paper types either as the dyno operator tested all four combinations.

I should explain here I was a part owner in the rolling road dyneo business at the time so the aim of the day was to find out what actually worked and what did not so we could pass the information on to our customers.
Perhaps not surprisingly quite a few simply did not want to know believing thay had spend this vast amount of money on the latest "go faster" item the car just HAD to be faster.
These guys were a real pain but fortunately few and far between at the dyno since they would not come in and find out.A blessing in disguise really!

HTH Pete Sydney, Australia.


Peter Thomas

Vic-
The "snappy" characteristic of the Weber carburetors that you mention is the result of them having an accelerator pump. The "flat spot" in the powerband that most drivers experience with the Weber DGV 32/36 is the result of the abysmal intake manifold that its distributor, Pierce Manifolds, packages with the carburetor for mounting it to the stack fivr-port head, so no amount of fiddling elsewhere will cure the "flat spot". Since you're running a crossflow head, there is one theoretical advantage to a dual sidedraft Weber DCOE 45 setup: The multiplicity of jets will enable you to dial it in for your particular head & camshaft configuration. You'll need to set it up on a dynometer to accomplish this and run a centifugual-advance-only distributor, though. The problems with keeping the Weber DCOE 45 in tune can be greatly reduced by installing a soft mount kit (APT Part# SMW-45) to protect them from vibration. Overall, it's an expensive proposition when you total up all of the costs involved.
Steve S.

Peter/Steve- boocoo gracias for the input. P- Do I hear you saying, after all that day on the dyno, you wnet from say 70 BHP to about 79 BHP by using the best recipe? This is great stuff to us huffers. So exactly what did you end up running to get the 12% ???!? Good news for me is that with the x-flow, the exhaust header sits by itself on drivers side ( USA orientation) with absolutely nothing near it. I still hear you on under bonnet temp, and am wondering what type ducting you used, and how you connected it to the K & N's or whatever. So what's Tasmania like in March? We got 12 foot of snow on the ground right now.
Steve- thanx for the clear synop. Sounds like HS for me! Vic
Vic Myers

Vic, Do you have the Weber now?
Victor Gardino

This thread was discussed between 12/03/2002 and 15/03/2002

MG MGB Technical index

This thread is from the archive. The Live MG MGB Technical BBS is active now.