Carl Heideman
Carl Heideman
8/13/20 8:04 a.m.

It’s an age-old question—and sometimes fuel for an argument: Which carburetors are better, SU or Weber? The answer is elusive. Everyone has an opinion, but no one seems to be able to offer definitive proof. 

We set out to find some concrete answers by measuring a couple of mule en…

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wspohn
wspohn SuperDork
8/13/20 1:19 p.m.

Good article. It is particularly true that on siamesed port engines the benefits of Webers re low and given that new Webers come set up for some other application and the tuning to your engine is a combination of experience and science that most owners lack, it really isn't that attractive a mod except to those who desire the look of the Webers for braggig rights.

 

Go to one intake port per cylinder and things shift a bit more toward the Webers and it becomes worth the exercise to fit and tune them for a street performance car or a race car (I have always used Webers only on my race cars powered by MG engines).

MG engine with after market 4 port crossflow head:

MG engine with factory DOHC head:

dougie
dougie Reader
8/13/20 11:10 p.m.

Would have been nice to see some test results on the SU 2" HD8's. Tuning on the dyno is the only way to accurately tune any performance motor.

https://youtu.be/8CmGFL54VlA

Sam12693
Sam12693
8/14/20 6:13 p.m.

I've worked with SU's and Webers.  Lucky enought to live close to Pierce Manifolds for my Datsun 240Z setup.  Webers let me tweak settings as I add modifications or change my driving style.  Jets x 6 are not cheap, so getting good advice from folks running similar modifications saves $$ and time.

wspohn
wspohn Dork
8/15/20 2:37 p.m.

Dougie - the BMC factory was in the habit of speccing too large SUs for racing. The Healey didn't need 2", nor did the race MGB, nor the street Rover 2000 TC. They even tried them on the factory MGA Twin Cam race cars.  Flow is too slow at part throttle and they don't run ell except on wide open throttle, and even then only when tuned exactly right.   I have tried them on my race cars (uop to 1950 cc MGB motors) and prefer the 1 3/4" . It gets you little to have a horsepower or two more at top rpm if you lost time getting there.

Sam - we are lucky to have local shops that specialize in Italian cars and keep full sets of jets that they will charge a fee for plus whatever it costs to replace stock once you know what you need. I am lucky that I never had to do anything but fine tuning on my V12 Lamborghini, but that would have been the way to go.

IIRC the Datsun wasn't homologated with Webers but with Solex PHH 44s, but that's pretty much the same thing except for jet availability. We had local racers that got them properly set up and they were one sweet set up once they got them optimized!

dougie
dougie Reader
8/17/20 9:03 p.m.
wspohn said:

Dougie - the BMC factory was in the habit of speccing too large SUs for racing. The Healey didn't need 2", nor did the race MGB, nor the street Rover 2000 TC. They even tried them on the factory MGA Twin Cam race cars.  Flow is too slow at part throttle and they don't run ell except on wide open throttle, and even then only when tuned exactly right.   I have tried them on my race cars (uop to 1950 cc MGB motors) and prefer the 1 3/4" . It gets you little to have a horsepower or two more at top rpm if you lost time getting there.

Sam - we are lucky to have local shops that specialize in Italian cars and keep full sets of jets that they will charge a fee for plus whatever it costs to replace stock once you know what you need. I am lucky that I never had to do anything but fine tuning on my V12 Lamborghini, but that would have been the way to go.

IIRC the Datsun wasn't homologated with Webers but with Solex PHH 44s, but that's pretty much the same thing except for jet availability. We had local racers that got them properly set up and they were one sweet set up once they got them optimized!

That hasn't been my experience, I'm very familiar with all the Healey Works and BMC prepared competition cars. With modern cam design, true technical head porting, and a few additional American tuner tricks the period factory teams couldn't do, didn't have knowledge of or have time to install and test, I've achieve performance far beyond any Healey they prepared for road racing. It was easier for them to switch to Webers, then to do additional testing & tuning with the 2" SU HD8's.

wspohn
wspohn Dork
8/18/20 12:43 p.m.

Well done if you have managed a triple 2" set up that has good transition through the rpm range. I don't think that could ever be done with the twin 2" on an MGB engine.

My favourite set up on the C series was a triple 1 3/4" intake that resolved all of the problems with the end cylinders that the stock twin carb set up caused (I think I've posted a pic before). The flow rate on those totals 630 cfm.

I beleive that Vizard said that a 2" SU can flow 330 cfm on the bench and I would think that a 3 liter pushrod C series would be hard pushed to need 990 cfm at red line

wspohn
wspohn Dork
11/2/20 12:18 p.m.

PS - for those times when really large capacity is called for SU had these racing carbs (DU6) that presumably had the capacity of two 1 3/4" SUs.......  420 cfm per carb?

 

 

 

Torqued
Torqued New Reader
6/1/21 11:52 a.m.

Very interesting article and comments too!  The power figures for the four different carbs are so close that I'd bet that a proper statistical analysis would find them indistinguishable. Then the choice comes down to the other factors -tuneability, drivability, convenience, ...

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