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| Weber (MG World article
1999.) |
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The
following is a recent contribution to MG World magazine, with regards to the
Weber 500
MG WORLD Contribution
Roger Williams. "Prospective Titles" |
WHICH MGB V8 CARB?
or HOLLEY v WEBER - A COMPARISION
or MGB V8 CARBUETTORS REVIEWED
or V8 CARB. CAPERS
or WEBER OR NOT TO V8
or CARBFUL CONSIDERATIONS
or FUELLING AROUND V8s
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Background and Plan
Funny how some things are meant to be. I had had my Holley 4150 (390 cfm List
8007) carburettor for years and it had given excellent service atop my Rover
powered MGB. Nevertheless I felt it time to try a Weber, the only practical
alternative that offers the essential facility of an accelerator pump and
corresponding performance. Simultaneously, while researching for a second book
(entitled “How to Improve your MGB, MGB V8 & MGC” to be published
late summer), I found it difficult to find any objective comparisons between
the Holley and the Weber.
They are the two most popular carburettors used by enthusiasts fitting Rover or
Buick V8 engines to their MGBs. My research led me to approach Chris Crane at
RPI Engineering. He focuses his whole business on the Rover V8 engine and has
an excellent reputation. I was also very influenced by RPI’s knowledge of
and commitment to a wide range of V8 performance parts, many from the USA. I
was particularly impressed to learn that Chris imported about 500 to 600
Edelbrock carburettors alone each year. It transpired that he was also keen to
objectively compare each carburettor's performance. Consequently we set up
these experiments and I would therefore like to thank Chris for his help,
personal interest, the workshop facilities and the excellent personnel support
that made the following tests practical.
We planned I would initially drove up to Norwich on my Holley carburettor,
carefully doing a fuel comparison check - which would preclude much by way of
spirited driving. Clive Athowe Tuning would carry out a “base-line”
Rolling-Road test whereupon RPI Engineering would fit an Edelbrock 1404 badged
version of the Weber carburettor. After RPI Engineering had fitted and tuned
the Edelbrock it would be back to Clive for a comparative rolling-road test
while the journey home would be used to carry out the comparative fuel
consumption test. At this point I should be armed with the raw statistics,
although we expected there would other important if subjective issues to report
upon, and this indeed proved the case. Consequently I planned to drive the car
(and Edelbrock) for a few hundred miles to enable me to assess its
characteristics against the Holley.
So that was the game plan. Let's find out how it worked out but first, by way
of additional information that may save confusion at a later date, could I also
explain that Weber make a range of 4-barrel carburettors and market them under
the names of Weber, Carter and Edelbrock. Apart from the label, it is generally
impossible to tell one brand from the other. For the Rover V8 engine range it
is important to select a Weber 500 cfm carburettor regardless of the brand name
& engine specification. In fact my engine specification is modest. I
rebuilt the engine some 35000 miles/9 years ago retaining the original 9.35:1
compression ratio pistons. I fitting new rings, a new standard SD1 camshaft,
cam followers etc, but basically sort an engine with plenty of smooth low down
torque similar to that fitted to the SD1 V8s. Consequently the inlet manifold
selected back in 1990 was a dual port Offenhauser. I fitted a Low Rider
14” x 2” air filter and these parts were to be retained during these
comparisons since the concept required we change the very minimum of ancillary
items. We wanted to isolate the effect of each carburettor on the engine's
performance.
Initial Purchase, Fitting &
Set-Up
Obviously the price I paid for my Holley 4150 is now quite irrelevant. I found
that there is in fact very little difference between the initial cost of the
Holley 4160 & the Weber/Edelbrock 1404 carburettors today. However the
Weber comes ready to go on the car whereas the Holley requires you purchase a
secondary metering plate, secondary jets & new primary jets for a further
£40/50 and to upgrade your purchase to the 4150 specification, which of
course makes it the more expensive choice. The Holley was the easier to bolt to
its manifold & connect controls to. As I recall I only had to make a small
bracket to hold the outer throttle cable. The Weber needed the same type of
bracket but also some minor modifications to its accelerator arm. Steve,
RPI’s Workshop Manager, had to bend the lower part of the arm by 45 to
clear the manifolds and cut a top “leg” off to allow the MGB’s
throttle cable to move freely. No big deal. The Holley proved to be the taller
of the two carburettors - by 0.25” or 6mm. Also no big deal I hear you
say. Well, it could be in the confined under-bonnet space of an MGB. The Weber
might just allow you to get the bonnet to close!
The Holley 4160 I had initially purchased proved an absolute nightmare to
set-up initially. In fact I still remember I could hardly get the car to run
and the bore wash was so great that I had to change the engine oil twice before
the engine had run for more than 15 minutes. I ended up trailering the car to
Oselli in Oxford and, as described in my first book “How to give your MGB
V8 Power”, they really had to make a number of changes to the Holley on
top of upgrading it to a Model 4150. While expensive at the time, their work
has stood the test of time. I have had 9 years of immense pleasure and reliable
service from the resulting carburettor that is justification in itself, but
furthermore Clive Atthowe told me after his first Rolling-Road run that it was
the most effective and powerful Holley carburettor he had ever seen. The Weber
however started first twist, ran smoothly straight away and would have allowed
the car to be driven straight away. True the carburettor was set-up with 1441
Metering rods (“needles” to many readers) and 1421 jets - a
combination that in RPI’s experience suited my specification 3500cc
engine. Certainly the settings were then refined using Crypton equipment to
correct the omissions - but if you had fitted the Weber at home the car would
been perfectly drivable to your local garage for this diagnostic work to be
carried out with the minimum of fuss & cost. To give you an idea as to how
small the adjustments on the Crypton were, we started with the Holley’s
timing at 2.9 BTDC and advanced that by 3 (5.9 BTDC). The initial CO figure was
9.9%, which of course is high but this was a “straight from the box”
figure. Five minutes later we were showing 3.3%. Hydrocarbons were not too bad
“from the box” at 600 ppm but Steve quickly had the un-burnt fuel
down to 300 ppm. Carbon Dioxide was 11.8% & Oxygen at 0.9%. I did not time
Steve, but I doubt it took him 15 minutes to carry out these adjustments. In
fact my maintenance deficiencies took longer to correct (Steve’s sharp
eyes noticed a split water hose!).
RPI’s experience was such that the jets and metering rods they selected
were perfect for the Weber on my car. However, they demonstrated the ease with
which they could be changed (10 minutes) if you got something wrong or wanted
to use your Weber on a different capacity (say upgrading from a 3500cc to
4600cc) engine. The Edelbrock range of carburettors come with a very helpful 36
page Owners Manual. It covers the operational theory of the carburettors over 9
pages and explains the metering, transient control and effect of external
fixtures. Section 2 of the booklet covers the turning of the carburettor,
revising it and includes calibration charts, rod/jet reference charts, exploded
diagrams and trouble-shooting/solution pages. I don’t recall any
supporting information when I bought my Holley 9 years ago although I have
since been able to buy a very helpful book ("Holley 4150 & 4160
Carburettor Handbook") from John Woolfe Racing.
Starting/Running/Drivability/Tractability
Full marks to both carburettors for their cold starting & indeed to the
Holley for its hot starting capabilities. The Weber has proved slightly
reluctant to fire-up unobtrusively when hot. I resort to putting the pedal to
the floor to get her going - - - which is effective but she starts with a major
boy-racer style roar! The Weber idle is, however the superior. The engine ticks
over at 550 rpm smoothly & quietly. This is more of an advantage than it
may sound since the lower idle significantly increased the time it took to
trigger my electric fans in traffic. The Holley idled at 950 rpm in spite of
numerous unsuccessfully attempts to slow it down.
Tolerance to slow speed pick-up from say 1000 rpm (I am so lazy at times!) is
marginally better with the Holley - which was effortless & fuss free. I
feel the Weber is saying to me "you should not really do this, but I will
do my best"! At first the Holley also seemed better at mid range rpm where
its "pick-up" had been faultless. The Weber initially had a split
second hesitation before the power came in. The characteristic was particularly
marked after a spell on trailing-throttle, say when easing-off on a motorway or
running up to a roundabout. I felt the hesitation and subsequent power-punch
uncomfortable and asked RPI if they could smooth the take up of power from a
closed throttle. In fact Steve managed to improve the performance of the Weber
still further and reduced the hesitation somewhat but, we agreed, the problem
was due to a stretched timing chain and worn timing gears in my engine. The
extra aggressiveness and punch of the Weber had highlighted a problem that I
had been vaguely aware of for some time. So I will have to live with the
occasional hesitation until I can replace the timing gears with, probably, the
upgraded duplex chain and hardened gear set that RPI sell in preference to the
standard Rover single chain and plastic gear. Consequently I am delighted with
the additional responsiveness and enjoyment the Weber gives and consequently
asked Chris Crane if we could "do a deal" enabling me to retain it!
Economy
No question, Weber also wins this comparison easily. Its fuel consumption seems
to be 15% to 20% better than the Holley based on just the basic statistics I
gathered. However there are some extenuating circumstances which probably
reduce the differential to about 10%. The Holley had done some 35000 miles and
may have been in need of some maintenance. I had recently fitted Peter Burgess
“Econotune” cylinder heads & noticed that there seemed to be more
carbon in the heads and pistons that I removed than I would have expected. On
reflection this may have been due to a long-standing float-level/cut-off valve
problem. This possibility was endorsed by a problem that in fact came to a head
just at the wrong moment. Don’t they always, I hear you say. Well, not
always, but certainly I wasn’t amused when the Holley’s secondary
jets started to flood fuel into the cylinders quite uncontrollably on the
Norwich ring-road shortly after the first Rolling-Road test run! Maybe the high
level of fuel flow during the test run had lodged a spec of dirt under the
float cut-off seat or maybe it had been weeping for some time. I do suspect the
latter. A second extenuating circumstance definitely effected the Holley’s
fuel consumption test run. The test runs were similar in that they were both a
mixture of motorway, fast “A” roads, slow “A” roads &
slow urban driving. Obviously one has no control over traffic conditions but
the Holley’s 203 mile run was marred by two traffic jams that necessitated
stop/start crawling for maybe a total of 10 miles. The Weber run necessitated
only about 1 mile of start/stop driving. So possibly the difference isn’t
quite so great as the following statistics suggest:-
|
Holley 390 |
Weber 500 |
| Distance Covered |
325 kilometres (203 miles) |
328 kilometres (205 miles) |
| Elapsed Time |
3h 15min |
3h 10mins |
| Fuel Used (95 RON,Unleaded) |
35.9 litres (7.9 Imperial gals) |
29.9 litres (6.6 Imperial gals) |
| Fuel Consumption |
9.06 kpl (25.7 mpg) |
10.98 kpl 31.0 mpg |
| Average Speed |
100Kph (62.5 mpg) |
104 Kph (64.7 mpg) |
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Performance
From the cold statistics provided by the accompanying charts, the performance
of the two carburettors would appear remarkably similar. The Weber carburettor
did show a very small advantage from 4500 rpm as the Graphs 1 and 2 show -
perhaps 4 bhp on power & maybe 6lb ft on torque. However bearing in mind
how infrequently one uses 4500 plus rpm anyway and that the torque and power
curves both drop away quite predictably once one gets above 5000 rpm, then the
difference is of no practical consequence. Certainly one cannot choose between
the carburettors on the basis of the graphed performance below 4500 rpm.
Consequently an interesting and originally unplanned experiment was introduced
by RPI, who suggested we evaluate one of their imported Mallory twin points
distributors on the rolling road. The benefit of the Mallory’s different
characteristics, particularly its earlier advance curve, are clearly shown in
Graphs 3 and 4. There were a few inconsequential bhp to be had in the mid-range
as shown in Graph 3, but the improvements in torque that resulted from the
change of distributor can be clearly seen in Graph 4. The maximum benefit is in
fact 8 lbs ft but its real benefit comes from its position in the rpm range. It
is placed along the frequently used low-down to mid-range rpm and even has a
peak benefit as low as 2150 rpm. The resulting 5% or so improvement will
translate into easier driving, less frequent gear-changes and better
acceleration. All very desirable and I also made a mental note to change my
standard SD1 electronic Lucas Opus dizzy as soon as practical!
What the cold statistics do not tell you is that the
Weber does provide much more by way of acceleration and throttle response right
up the rev range. Although totally subjective, I have absolutely no doubt that
the car is quicker off the mark with the Weber, although the graphs would give
little hint of this
| Overall
Assessment You will note I have weighted the marks in favour of the
ongoing benefits that Economy and Performance provide. Consequently I assess
the carburettors as follows: |
| Assessments/Marks (Maximum) |
Holley 390 |
Weber 500 |
| Initial Set-up (15) |
3 |
14 |
| Starting/Drivability (15) |
11 |
14 |
| Economy (30) |
25 |
30 |
| Performance (30) |
24 |
30 |
| Totals (90) |
63 (70%) |
88 (98%) |
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We can Summarize by
saying that the Weber seems to my mind to be far easier to fit than the Holley
and to offer better fuel economy and performance, so I am please to report that
a deal was indeed struck and I am sticking with the Weber!
RPI Engineering
RPI Engineering was established some 15 years & have focused their business
on Rover V8 engines all that time. Chris Crane is the proprietor but has been
ably assisted for the life of the business by Steve Chambers, Workshop Manager.
Today they have nine supporting members of office, workshop & stores staff.
The business still revolves (!) around the Rover V8 but has expanded into
several new but related technologies. It is still based some 5 miles north west
of Norwich and still, says Chris Crane, tries to do properly first time what
others don't do quite so conscientiously. Chris told me he has plans for an
additional three-bay building facing straight on to Holt Road in Horsfold &
indeed started clearing the ground when I was on site. The expansion is a
consequence of the breadth & popularity of the businesses work on Rover
engines. There appears to be no limit on the type of vehicle RPI will handle
-so long as a Rover V8 is in evidence. There were several Range Rovers (both
carburettor and EFI models) in for LPG/Petrol dual-fuel conversions, an RV8 in
for a 4.6 litre engine conversion and re-chipped ECU and a one-off
“Mud-Plugger” (which is in fact one of the leading Hill Rally
vehicles) four wheel drive was delivered for an engine upgrade. Not, of course,
to mention a certain MGB V8 in for carburation changes! Chris felt this mixture
was quite typical, sometimes augmented with several V8 top end overhauls or
Stage I, II and Stage III cylinder head up-grades. Chris explained that most
automotive products are a compromise & frequently RPI are able to improve
the original company's product performance as a result. The RV8 in the workshop
was a case in point for Steve fitted an RPI re-chipped ECU while we were at the
Rolling-Road to release some 20 bhp “at the wheels”. Chris believed
the Rover ECU will have been originally mapped to cope with Tokyo’s
traffic, Johannesburg’s 6000ft altitude, Australia’s heat and the
UK’s cooler, damper climatic conditions. Since RPI’s client was
unlikely to require all these extremes, the RPI chip could optimize the car's
performance and generate the extra power. Chris also emphasized that RPI were
committed to LPG gas conversions and saw much of their future growth coming
from this market. He told me he believed Low Pressure Gas fuel conversions
would become more and more common place as Europe became "Greener",
that there was even a possibility that such conversions could be compulsory one
day as the emissions were so very clean and that Weber carburettors could
accommodate LPG fuel!
Roger Williams
A retired Engineering Manufacturing Consultant & Company Doctor. Roger has
built, restored & enjoyed motor cars as a hobby all his life. His first
"interesting" car was aluminium clad space-framed Ford 10 Williams
Special he built during his apprenticeship in the late 1950's. He has restored
numerous MGB's but feels a need for speed - - - hence his especial interest in
V8 engined MGBs. His wife maintains a balance within the household via her
beautifully restored Triumph TR6 which she uses whenever possible.
Differences and Workings
In very simple terms, Holley carburettors are assembled from three
sub-assembles that are split vertically; a main body and two (pannier style)
float bowls bolted fore and aft. This construction means there are assembly
joints below the level of the fuel and although there are gaskets incorporated
into the design, I must report I found it essential to tighten the eight-float
bowl/chamber retaining bolts every few thousand miles if I was to avoid a smell
of fuel in the car. The Weber is built from two main sub-assembles split
horizontally above the fuel level thus dramatically reducing the possibility of
a fuel leak. Both carburettors use twin float bowls or chambers, although the
Holley only utilizes the secondary bowl after you have fitted the secondary
metering plate & a longer cross fuel-transfer tube (thus upgrading from a
model 4160 to model 4150). The Holley controls the volume of fuel fed to the
engine via the primary chokes (or venturi) by jets which have different
carefully controlled hole sizes. These metering orifices control the fuel
flowing into the discharge nozzles which are clearly visible at the top of each
primary choke. The secondary chokes or venturi are held shut by a spring when
the engine is on light load. However an increase in vacuum within the primary
chokes (brought about by high engine loads) displaces the secondary's diaphragm
against its spring and thus opens the secondary throttle plates appropriately.
The Weber, also in the simplest of terms, uses vacuum controlled needles
(similar to SU carburettors) to control the primary system. Obviously these
needles (called Metering Rods really) can be changed to suit each engine's
particular characteristics just as the Holley's jet sizes can be altered at
will. The Weber's needles move up and down in response to manifold vacuum, just
like the SU. When the engine load is high (wide throttle opening) manifold
vacuum is low and the needle's control spring is able to lift the needle out of
its seat and extra fuel flows. On low engine load the vacuum is high and closes
the fuel control needle against its spring. The Weber's secondary system only
delivers fuel when the throttle position AND the airflow through the
carburettor warrant extra fuel. Both carburettors have supplementary controls
such as accelerator pumps and chokes. The Holley choke is automatic and
operated electrically whereas the Weber enrichment is in my mind simpler,
manually operated and thus more desirable. You can buy a manual choke kit for
the Holley at modest but nevertheless extra cost
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Disclaimer
Prices do not include local EU.Tax.(VAT).
Prices & stock are subject to change without notice. Information and advice, as always, is free.
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