Welcome to our Site for MG, Triumph and Austin-Healey Car Information.
MG MGB GT V8 Factory Originals Technical - Lets Talk Weber Carbs
|I'm slowly gathering the parts for my 3.1 Chevy V6. In a trade I managed to end up with the 2 barrel upper for the 2.8 Edelbrock intake manifold, the PO bought a 4 barrel upper and went with a Holley 390. He was using the 2 barrel upper/Edelbrock lower with the stock Varajet.|
I must confess I'm not a big Holley fan (forgive me), and I seem to remember a recommendation in the archives (can't find it now) to use a Weber 38 DGES. Will this carb bolt up to the stock 2.8 intake or the Edelbrock 2 barrel upper? I've heard that the DGES is not good on gas mileage and this is an issue with me. And is there any real advantage to using the Edelbrock setup if the 38 DGES will bolt up to a stock manifold? And can you get the DGES with an auto tranny kickdown? And what about this new Weber DGEC 34?
I would love to find a Carter 400, but good luck on that. I think the Edelbrock 500 is too much for a stock 3.1 with auto tranny?
So I think I've narrowed my choices down to:
1. Holley 390
2. Holley 350 2 barrel on a modified intake.
3. Weber 38 DGES
4. Carter 400 AFB (long shot)
Which of these would give me the best combination of MPG and smooth performance? Any other carburetor ideas out there?
on my car, i use a Holley 390 as spares and jets can be picked nearly anywhere. That's the greatest advantage of the 4 bbl Holley.
Finding the right setup for the 390 on my B took a lot of time, changing jets, springs, cams rear metering block etc. With the Edelbrock/Weber it is more straight forward, although the calc. upon CFM at WOT
is more at the side of the 390 Holley.
With the 350 life would have been much easier and calculating the CFM for a 3.1, the 350 should be O.K.
When you decide which carb to use, also keep in mind the costs and availability of gaskets, jets and other spares for this instruments.
For cars with an automatic box, the smalles carb for this job would be the best one for drivability.
I have a rebuilt Carter AFB model D/C 4331S,originally on small block GM I think, I was going to use on my 302 V8 conversion, but went with an Edelbrock as I am not a Holley fan either. If you are interested I would sell this carb
gilpr at local net . com
|The Holley 390 is a reliable carb and sized right.|
I favour staying with injection. If you must go to carbs, what about this injection throttle body - a pair fo these would make a really nice looking engine (no idea if they would fit under the hood, mind you).
|> I seem to remember a recommendation in the archives (can't find it now) to use a |
> Weber 38 DGES.
Do you access to tuning parts for that carb?
> I would love to find a Carter 400, but good luck on that.
I have one here that could be used for a test.
> I think the Edelbrock 500 is too much for a stock 3.1 with auto tranny?
Maybe not. If it's stock, then it should have a decent vacuum signal.
> 1. Holley 390
Holley made at least 3 different 390 CFM carbs. List number 8007 is meant
for small displacement, street driven V8's and has an electric choke and is
the one most often used on Buick/Rover V8's. The 8007 is a 4160 Holley
which means it has a plate with fixed size orificesfor metering. These plates
are replaceable but cost much more than jets. If you plan on doing any tuning
(and you should), you may want to convert to the 4150 secondary metering block
which has removable jets. The 8007 also comes with a 6.5 power valve which
you may need to replace to match your engine's vacuum characteristics.
List number 6299 is meant for 4 and 6 cylinder applications. I checked my
listings and the jetting doesn't look much different but the 6299 doesn't
show a power valve. That may mean it has no power enrichment which is
surprising. I also checked the Holley site and it also lists no power
LIST # CFM STOCK JETTING POWER VALVE TYPE
6299-1 390 (F)50, (R)plate 134-34 N/A 4160
8007 390 (F)51, (R)plate 134-34 6.5 4160
80507 390 (F)65,(R)65 3.5,3.5 4150HP
If that's really the case, I'd bet the transition metering is quite different
in the 6299 than in the 8007. List number 80507 is meant for carb-restricted
racing applications, typically on larger displacement engines.
> 2. Holley 350 2 barrel on a modified intake.
> With the 350 life would have been much easier and calculating the CFM for
> a 3.1, the 350 should be O.K.
Remember that 350 CFM for a 2 barrel carb does not equal 350 CFM for a 4 barrel
carb. Two barrel carbs are usually rated at a different pressure differential
(3.0 In Hg). The reason for this is primarily historical. When 4 barrel carbs
first came into popular use, the vacuum pumps used to rate 2 barrel carbs were
unable to pull the same pressure differential across a 4 barrel carb, so the
4 barrels were rated at a lower pressure drop. Flow ratings from one standard
can be related to flow ratings from another standard. For 2 and 4 barrel carbs:
Flow @ 1.5 In Hg = (CFM Rating @ 3.0 In Hg)/SQRT(3.0/1.5)
Which is approximately:
Flow @ 1.5 In Hg = (CFM Rating @ 3.0 In Hg)/1.414
That Holley 350 CFM 2 barrel carb would flow around 247 CFM if rated like a
4 barrel. An Edelbrock 500 CFM carb flows a bit less than that on the primary
side so the two would have roughly the same part throttle driveability.
> Which of these would give me the best combination of MPG and smooth performance?
My money would be on the Carter 400 or the Weber (assuming it is of similar
design as an IDA or IDF where all circuits are tuneable).
> Any other carburetor ideas out there?
What about the stock carb (Varajet?). That wouldn't require any tuning.
Or perhaps a TBI set-up?
> I have a rebuilt Carter AFB model D/C 4331S
I believe that was used on a 1967 Buick 340 cubic inch V8. It's not
the same as 9400 or 9410 Carter 400 that Terry is looking for.
|About that TWM induction, the throttle body injection idea, does anyone have a Mangoletsi water-heated manifold to mount four doundraught Webers or Dellortos? See David Hardcastle's "Tuning Rover V8 Engines" at page 64. Looks like those TWM throttle bodies could be adapted with the right intake like the Mangoletsi. JB|
|If you feel that the Holley will not please you, then consider the Edelbrock 500 cfm it can be tune to fit you engine. I use a 525 Demon.|
Also, if you feel like doing some work, fine a FI manifold either MPFI or SQFI bottom section, build some long tubes and a plate to accpet the 3v Webber carbs and install one on each side. this has been done and it takes a litle (lots) of work to fabricate and tune. Power will come from 3500 and up. Looks good and is somewhat ok in the street. Alot simpler is the 390 CFM with a electric chocke. Just make sure the jets are correct for the manifold and exhuast.
|I saw some pics of a setup a guy on another forum did and I like it. He took a stock 2.8 V6 2 barrel intake, and made an adapter to mount a Holley 350 cfm 2 barrel sideways. I thought it looked terrific and it is a low cost option to the Varajet. And he claims it all fits under the hood. I'm not a Holley fan, but.....|
|You can also make the same changes and instal a 4v.|
|Just from looking at how narrow the manifold is, it appears to me that a 4 barrel, while it would work, is very wide if placed close to the engine. The highrise by Edelbrock compensates for that. I'm certainly not the expert, but on a modified stock intake, a 2 barrel looks to be a better choice. Am I wrong on this Bill?|
|It's a matter of choice. In the early days of the V6 60 degree in the Chevy Citation. the stock 2v manifolds were modifed to accept the Holley 4v and they won several tiltles in SCCA. Yenko, yes the same guy that did the big block Camaros. Modified the manifolds to accept the 4v.|
This modification would take some cutting of the top and weld the 4v adapter, then grind all of the weld inside and do some porting.
The bottom linkage of the carb has to be cut, otherwise it would hit the manifold and valve cover.
If you decide to go this route, then use a TBI manifold, this manifold has a bit longer runners.
|Thanks Bill, YGM|
This thread was discussed between 07/05/2007 and 11/05/2007
This thread is from the archives. Join the live MG MGB GT V8 Factory Originals Technical BBS now