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MG MGB GT V8 Factory Originals Technical - Chokes & Bob P

Bob, what have you got against chokes? What have they done to you ? I find that on my manual car( Holley 2300 350 cmf), I don't need the choke butterfly, which is removed, but I need the fast idle mechanism. So the choke control is virtually a hand throttle. On my automatic car(Holley 4160 465cmf),I definately need the choke (manual type fitted)for cold starts even in a temperate climate like Sydney.
Holley carbs don't normally need a secondary metering block unless used for racing/competition, which makes me wonder at the suitability of the 390cmf carb.
Curious,Barrie E
Barrie Egerton Sydney

The most important thing about chokes or doing without them,
if you read my mail is the "thing" the mechanism sits in, the
so-called "horn". This indubitably interferes with the ability
of a Holley to react to the conditions inside what is effectively
a plenum, the air filter. This interference is most noticable
when a low rider air filter,needed to allow bonnet clearance,
and only just clearing the vents and the Horn is used.
A holley is like a Weber a couple of prods of the accelerator and
the accelerator pumps prime the engine. I have never needed
the choke in New York, Florida or England in any of the three
V8S I have owned/built. The double pumpers secondary metering block
is effective in providing accurate mixture to be provided for
the second two barrels - not just for racing. I have done comparison
tests on a rolling road for a)a 390 vaccuum sec b) a 390 dp
and c) 600 dp. these were all on my factory GT before it got a 3.9.
The 390 dp was good, the 600 gave more power at the top end
the vaccuum gadget gave poor drivability at the onset of the secondaries
opening ie poor metering RIP.
Each to their own! My offer is still open.
BobP to Barrie

Thanks Bob, I guess I asked for it ! I'll still keep the choke on my automatic though. Cheers
Barrie E
Barrie Egerton Sydney


I am interested in you Holley 600 double pumper. I am building a 3.9 and I have been wondering which way to go. I want to go the Holley route initially and perhaps change to fuel injection one of these days.

I was thinking of using an Edelbrock Performer manifold and all advice that I have had so far is that a Holley 390 is as big as I should go. Obviously, you have had different experience. Please tell me a bit more about your experience with your 600.



My 3.9 has the following spec:
9.75:1 c.r.
David Eales big-valve flowed heads.
Crane hi-lift cam.
RV8 tubular manifolds into 2 1/2 inch exhaust
Lumenition ignition.
Choke assembly removed and carburettor Horn milled off.
K&N low rider filter.

The 600 double pumper just recently gave 140 bhp at the wheels
on the first pair of chokes and about 210 with all four chokes
opening. It only has about 3000 miles on the new engine so will give
quite a bit more after it has loosened up.
It idles perfectly and goes like hell.
Iv'e been using the 600 for something like 6 years now and even on a 3.5
it gave more power at the top end than a 390 without loss lower.
One of your fellow Cobbers claims to be using a "465".
There is no 465cfm Holley available. Hec probably means a 4650, 390 cfm
with vaccuum secondaries. I hope you havent bought an Edelbrock dual plane
manifold as that is for the Range Rover application.
I am goung to buy an Edelbrock (Weber built) 500cfm, (which is I believe,
a copy of the old Carter 4 barrel) and try it on the rolling road for
comparison with the Holley.
I hope this info helps.

Dave, this is your "cobber mate" (I haven't heard that expression in 30 years). My carby is a type 4160 465cmf. The reason I've used this one is that I couldn't get a 390cmf in Sydney or Melbourne at the time I was building the car.Now I'm glad i couldn't. The 465 doesn't need altering. It is a vac sec.
The Edelbrook performer manifold is 6" tall & is probably too high for an MG.
A formula you can use for finding the size for a carb. si :- CMF = CID x RPM x VE / 3456
VE is Volume Efficiency & is usually about 80%
actually it's 95% with an Edelbrook Perf.
Also you can increase the CMF by 10%--30% if you use a single plane inlet manifold.
Cobber Barrie E
Barrie EgertonSydney

Bob & Barry

Many thanks for your comments. What manifolds are you both using?

Offenhauser dual port. I think the part # is 30007.I'd have a look for you ,but the car is in Sydney & I'm just outside Detroit right now.
Cheers Barrie E
Barrie Egerton Sydney

Perhaps I should have used "drongo", istead of "cobber", mate!
The 465cfm is no longer listed in the Holley catalogue.
According to my Holley book it was a type 4130, not a 4165!
If you know the part number, let me know ,as Id like to check it out.
I repeat conventional wisdom says, DO NOT use the single plane as
it is a high torque gadget for Range Rovers and is not the
best one for BV8's. If you use Holleys cfm formula a 390 is
ample for any 3.5/3.9 V8. My results on the rolling road however
prove that a bigger carb can under some conditions give more power
without loss of flexibility.
BobP to

My three V8s use or have used Edelbrocks. In each case I had
a mounting welded in to take the fan thermostatic switch.
BobP to Those Down Under.

Bob, I'm sorry the Holley 465cmf carb isn't in your book, but I bought mine brand spanking new in Sept.1998. In Hardcastle's "How to tune Rover V8s" it states " a Holley 465cmf carb,. would be a good choice for a Rover V8 when fitted in a lightweight car like an MGB."
I was under the impression that the Offy dual port manifold was designed for some racing team ,Waltinshaw ?
Does the Edelbrook manifold ( I'm assuming it's the Rover Performer model) fit under the the MG without mods? I notice your cars have bonnet bulges (albeit neat ones).Was this the reason for them ?
Barrie E
Barrie Egerton Sydney

I have a friend who has an absolutley beautifully V8 converted 1979 mgb roadster. It's a concourse winner and he did the job himself.

Rover SD1 engine, Supra gearbox, Holley 465 (yes a 465) carb with a set down style filter on an Offenhauser manifold. I believe his choke is removed - reckons he's never needed it. He also believes the Holley 465 is too much for the 3.5 motor and would prefer a 390.

No bonnet bulges and no evidence of a V8 being there when the bonnet is closed - apart from the dual exhaust pipes and that sound!

John in Brisbane

Barry & Bob

Thanks Barry, I know the Offenhauser dual port, I was looking for something a with a little more grunt. That is why I was asking about the Edelbrock Performer. Dave Vale at the V8 Conversion Centre in the UK is currently using the Edelbrock and finding it very good.

I have just been checking my Holley book (Dave Emanuel; Super Tuning And Modifying Holley Carburetors, S-A Design) and it seems that your carb is a 4160 465cfm. According to my book, this is the only 465cfm that Holley made. It is part number 0-1848-1. It is interesting to note that compared to the 4160 390cfm the primary and secondary throttle bore diameters are 1-7/16 for the 390 and 1-1/2 for the 465. The primary and secondry venturi diameters are 1-1/16 for the 390 and 1-3/32 for the 465. Very close.

It seems that the 4160 465 could be the way to go on a well tuned 3.9. It seems to fall half way between the 390 and the 600.
David in Melbourne

Good info guys, thanks.Ill pull up the Holley website, which is and check again.
I only have a bulge on the roadsters bonnet which has a much deeper filter
to allow a better signal to the Holley.
The funny thing is when we tested thew GT, with the 3.9. 600
and the 2 1/2 inch filter, it made no difference whether the
top of the filter was on or off - and it barely clears the vents!
This has the low rider K&N filter assy, but the central bonnet
cross brace is cut away to clear. The nut on top still occasionaly puts
little marks on the inside of the bonnet though.
Bear in mind that the engine can be set lower as long as the sump clears
the cross-member and you dont screw up the alignment of the gearbox to prop shaft.
The dual plane is definitely high torque manifold, it has literally got
dual ports on the manifold per cyl head port. The small dia gives high gas velocity
good filling and thus torque. (At least I think thats the theory! I think you will
find it is mentioned in one of Hardcastles books. I started
messing with these cars in about '84 so I dont remember what
the manidolds are!! - and they are in England , not in Florida
where I am.

Just to throw another option into this discussion, what about the Holley 450CFM ,chokeless with mechanical secondary. It's listed in the JEGS catalog.


Here's a combination that has served me very well: Edelbrock 500 cfm w/manual choke (attached to the stock choke knob) sitting on an Edelbrock Performer manifold. Yes, it is too high for the MGB, but I "bubbled" the hood with a subtle bump which is open in the front (more like a scoop). It looks great and runs very well - grunt all the way through all 5 gears without any lag. I'm using a T5 going through a Ford 8" rear with 3.25:1 gears. The T5 has strong accelration in first gear and a tall overdrive (.7) so I get between 23 & 25 MPG with 1000 miles on the engine. I thought long and hard about the Offenshauser dual plane, but the question was 'do I want to cut the hood or not". I did and don't regret it. I think some of us fool ourselves trying to keep the car looking "original" when we know it needs to be lowered to handle, have wider tires for the same reason and usually has dual exhausts! Plus, the reason to install a V8 and t
o do all the work that conversion entails is to gain performance. Why hhandicap all that effort by using a low profile intake manifold? Well, most of this is off the original point ... the Edelbrock 500 manual choke carb and matching manifold is a wonderful combination. Mike
Mike in Western Colorado

Here follows the complete line up of HolleyAvenger carbs.
The 0-1848-1 is obsolete and replaced by the:
P/N 1-191 450 CFM Four Barrel, Model 4160.

I checked on the Edelbrock part number and forgot to bring it to work.
Tomorrow gents.

Fuel Management Systems
and Accessories


The Avenger carburetor line consists of Holley
models 4150 and 4160 "Street Performance"
carburetors in various CFM sizes.

Street Legal
Application Guide
Models 4160 (Square Flange) and
4175 (Spread Bore)


P/N 0-1850S 600 CFM Four Barrel, Model 4160 (shiny)

P/N 0-2818-1 600 CFM Four Barrel, Model 4150

P/N 0-3310S 750 CFM Two Barrel, Model 4160 (shiny)

P/N 0-4412S 500 CFM Two Barrel, Model 2300 (shiny)

P/N 0-4742 600 CFM Four Barrel, Model 4150

P/N 0-4776S 600 CFM Four Barrel, Model 4150 (shiny)
"Best of Class"

P/N 0-4777S 650 CFM Four Barrel, Model 4150 (shiny)
"Best of Class"

P/N 0-4778S 750 CFM Four Barrel, Model 4150 (shiny)
"Best of Class"

P/N 0-4779S 750 CFM Four Barrel, Model 4150 (shiny)
"Best of Class"

P/N 0-4780S 800 CFM Four Barrel, Model 4150 (shiny)
"Best of Class"

P/N 0-4781S 850 CFM Four Barrel, Model 4150 (shiny)
"Best of Class"

P/N 0-6709 750 CFM Four Barrel, Model 4150

P/N 0-7448 350 CFM Two Barrel, Model 2300

P/N 0-8007 390 CFM Two Barrel, Model 4160

P/N 0-80145 600 CFM Four Barrel, Model 4150

P/N 0-80431 (Primary) P/N 0-80432 (Secondary)
1100 CFM (2x4), Model 4150 550 CFM Four Barrel

P/N 0-80457S 600 CFM Four Barrel, Model 4160 (shiny)

P/N 0-80508S 750 CFM Two Barrel, Model 4160 (shiny)

P/N 0-80531 850 CFM Four Barrel, Model 4150
(Replaces 0-80436)

P/N 0-80555S 650 CFM Four Barrel, Model 4175

P/N 0-80572S 700 CFM Four Barrel, Model 4150 (shiny)

P/N 0-80573S 750 CFM Four Barrel, Model 4150 (shiny)

P/N 0-80574S 800 CFM Four Barrel, Model 4150 (shiny)

P/N 0-80575 600 CFM Four Barrel, Model 4150

P/N 0-80576 750 CFM Four Barrel, Model 4150 HP

P/N 0-80577 950 CFM Four Barrel, Model 4150 HP

P/N 0-80578 1150 CFM Four Barrel, Model 4500 DOMINATOR HP

P/N 0-80776 600 CFM Four Barrel, Model 4150

P/N 0-80777 650 CFM Four Barrel, Model 4175

P/N 0-80778 700 CFM Four Barrel, Model 4150

P/N 0-80779 750 CFM Four Barrel, Model 4150

P/N 0-80780 800 CFM Four Barrel, Model 4150

P/N 0-80781 850 CFM Four Barrel, Model 4150

P/N 0-9188 780 CFM Four Barrel, Model 4150
"The Original 3310"

P/N 1-191 450 CFM Four Barrel, Model 4160

Now Im going to call Holley and ask for their reccomendation,
but Im pretty sure it will be a 600cfm vaccuum secondary.
Let you all know later!

While we are on the subject of carbs, can any idenify the flow rate of this set up I have acquired.

Edelbrock Performer 3.51 manifold with Webber 4 barrel
The carb body is stamped 4404 1786 and the attached tag reads WEBER 15533 351.6.

Does the 351 refer to the flow rate and how does this setup compair to the Holly 390.

Nick Smallwood

I looked up the part numbers in an Edelbrock catalogue and
they are not listed. However I happen to know, that what you
almost certainly have is an Edelbrock 1404 500cfm carb set up.
Weber actually makes these and Aldon Automotive amongst others
sells them for some astronomical price. The carb costs $205
in the USA and the manifold is I think $137.
I hope this helps you. What ever you do, fit a K&N Low Rider Filter assy.
and get the thing set up on a rolling road.

Thanks Bob, appreciate your advice. Its a nice setup, nearly new to. Paid 150 for it.

All i've got to do now is decide to fit the webber or the fuel injection.

You got a good deal! Fit the carb. If you need any parts or jets let me know.
Bob to Nick

Thanks Bob, had already come to that conclusion over the weekend.

Many Thanks

Nick Smallwood

This thread was discussed between 15/08/1999 and 06/09/1999

MG MGB GT V8 Factory Originals Technical index

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