Too Big ???

[Doogs]

Hey all,

 

Just interested in some opinions..................

 

CLICK

 

Even with this jet setup, who beleives it is still to big for a 4/5k ?

 

Cheers,

[Taz_Rx]

....a 4/5k with what done to it.......! :lolcry: I don't really think it too big when you consider some people put 2 large dcoe (40-45) webers on worked a 4/5k. Really just depends if its jetted and tuned correctly!

[Kid-Ae]

Would run fine with that carby setup, as long as you had it jetted and tuned properly. can't see any reason for it not to work.

 

Any other options in mind as an alternative? :lolcry:

[Falken_KE30]

32/36 should be great on a 4k with a lump stick and a set of extractors. as the others have said, a good tune does wonders!!!

[Doogs]

I am looking at building a warm 4/5k with a cam, extractors and head work.

 

A while back i was offered a 32/36 for free (offer is still on the table) but had noticed

a few people in various threads suggesting a 32/36 would be to big.

 

A few people thought they were overkill, so thought i would check when

I saw this.

 

Thanks,

[the Db king]

to put it simple, with correct tuning and some other bolt ons a 32\36 will be just fine.

 

ive got one on a 4k lump stick, head work, extractors, electronic dizzy, its great

[chrisandliz[RL]]

sorry to shot you guys down, but if you are going on the maths the carby it too big.

 

A 32/36 weber is a 180 CFM carby, even a hard tuned N\A 5k is under

 

http://www.4secondsflat.com/Carb_CFM_Calculator.html

 

For a daily driver you should be trying to get a 34/34 from a fiat 128 or some thing like that

 

Chris

[Taz_Rx]

They're 32/32's :lolcry: Thats what I was using in the turbo kit, and currently have another one on my NA car. Benefits of having a bro into Fiats! :y:

[Doogs]

Thanks chris and liz, thats what I was afraid of.

 

Will look out for something a little smaller like a 28/32 or the like.

 

Cheers,

[WinKE55]

I will be putting a 34 ADM carby on my Corolla. They are off the old Falcons. Engine will be worked etc and is going to be my daily.

 

If you WANT to do it, then go ahead. Carbys can be jetted down to suit.

[kangaroosa]

I had twin DHLA40's on my mild 5K with 36mm Chokes.

So that makes it a 36/36 36/36?

I had better power figures on the dyno with the 36mm Chokes in Twin DHLA40's over the 32/36 Weber and the Twin 1.5" SU's that i had run previously.

Not only did the dyno prove it, but i felt a noticeable difference in the driveability of the car.

can't argue with solid first hand evidence.

[Felix]

A 34ADM... :lolcry: That would be perfect on an old 3.3L holden 202. Not so good on a 1.3L 4k.

 

Go do some research on carb sizing. Seems most people don't have a clue.

 

Sure a big carb is good in the top end, but you will lose power, responsiveness and fuel economy in the low to midrange which is where you spend the majority of the time with a street engine.

 

I had twin DHLA40's on my mild 5K with 36mm Chokes.

So that makes it a 36/36 36/36?

 

No. With one barrel per cylinder, only one cylinder can draw on one barrel of the four at any given time.

With a single (twin barrel) carb feeding all cylinders, the cylinders take turns in drawing on both barrels.

 

A 32/36 (with 26/27mm venturis) carb actually flows more than a single barrel of a 40mm sidedraft with 36mm chokes. The advantage goes to the sidedraft though as the air has a much straighter path into the cylinder port. The airflow on the downdraft has to make a 90 degree turn below the carb.

Edited June 15, 2008 by Felix

[Redwarf]

DCOE me baby! :lolcry:

 

Agreed, drivability and fuel economy should be taken into consideration.

[Felix]

Read this:

 

 

 

28/36 DCD 1633 sq mm.

32/36 DGV 1822 sq mm.

 

 

28/28 Aisan 1231 sq mm.

 

 

 

 

 

PUMA TECH BULLETIN NO 2 - TWIN CHOKE CARB SYSTEMS

 

There are numerous carbs of the twin choke downdraft type which make excellent

road setups for those not wanting to go the single choke per cylinder route.

Mostly Weber such as the DGAV, DGAS, DFT, DCNF, DCD etc. together with Solex

and Holley types. There are so many variants that it is impossible to give

specific details on any particular type in a short bulletin such as this.

Handbooks are available on most carbs and Haynes do a very good Weber manual

with details of original equipment jetting specs, rebuild info and advice on

setting up.

 

These carbs are usually designed for specific vehicle applications and are

often not so readily tunable as the DCOE or IDA types in that chokes are often

of a fixed size, idle jets cannot be changed etc. The DCD and DCNF however do

allow all such changes and can be adapted to most engines with the correct

manifold. Some carbs have a smaller primary barrel for low speed running with

good fuel consumption - others have two identical barrels. Linkage systems are

of the following types:

 

1) - Differential Mechanical Linkage.

 

Here the primary butterfly opens first and at about 2/3 throttle position the

secondary butterfly comes in for full power operation. The main advantage is

that the primary can be jetted lean for good economy and drivability and

usually has a smaller butterfly and choke than the secondary barrel. For

general road use this is the best system to go for and applies to the DGAV,

DCD, DFT and most of the smaller standard fitment Webers.

 

2) - Simultaneous Mechanical Linkage

 

Here both barrels open together and are usually of the same size and contain

the same jetting. Low speed operation is not so good as with type 1 and economy

and low rpm pickup can suffer especially if the carb is at all oversized for

the application. The DGAS and DCNF are of this type.

 

3) - Vacuum Secondary Choke

 

This is a differential system with the primary opening first but instead of a

mechanical linkage to the secondary barrel there is a diaphragm operated

system. When the airspeed through the carb reaches a certain level the pressure

operates a diaphragm valve which opens the secondary butterfly. Mainly used on

the smaller carbs like the Weber TLD designed for economy rather than outright

performance. This type of carb often has a limited range of calibration

possibilities.

 

There are a number of pitfalls to beware of when trying to adapt these types of

carb to non standard applications. The main one which has caught many a good

engine tuner out is the presence of a "Full Power Valve" system in the carb.

 

The FPV consists of a diaphragm operated jet in the bottom of the float chamber

which opens under full throttle conditions and richens the fuel mixture. This

is primarily so that the carb can be jetted lean for good economy under normal

running and still provide a rich enough mixture for full power operation. You

can normally tell if a carb has this system because there will be a brass

fitment in the bottom of the float chamber with a small sprung loaded rod

protruding. Operating this rod will be a plunger sticking down from the carb

cover upper body with a spring wound round it.

 

The FPV is calibrated for the engine size of the original application and

problems can arise if this type of carb is fitted to a much smaller engine (say

more than 25% smaller in capacity). The symptoms will be that if the jetting is

correct for high rpm operation then the midrange will be very over rich.

Conversely if the mid range rpm band is jetted right then the mixture will go

very lean at high rpm. The only way round this is to seal off the FPV system by

soldering up the relevant parts or cutting off the operating plunger. The DGAS,

DGAV and DFT all have this type of system.

 

SELECTING THE RIGHT SIZED CARB

 

There is a good "Rule of Thumb" for dealing with single twin choke downdrafts

on 4 cylinder engines. First work out the total area of both butterfly valves

combined in sq mm (using the formula Area = 3.142 x Diameter / 4). For example

the DGAV has one 32mm butterfly and one 36mm butterfly giving a total area of

1822 sq mm.

 

For good all round high performance road operation go for 1000 sq mm per litre

of engine size. For more economy minded applications go 10% smaller and for all

out power go up to 1100 sq mm per litre. Any bigger than this and you may run

into problems of poor low speed operation with bad economy. Additionally very

little if any power will be gained from larger carbs than this in road use.

Above this level it's best to go the single choke per cylinder route.

 

For those carbs where the chokes are removable a good starting point is to fit

chokes in each barrel that are 80% of the diameter of the butterfly.

 

Often more can be gained from a little attention to detail when using these

types of carb than just slapping on the biggest one you can find. The manifold

is normally a bigger restriction to flow than the carb itself and rounding off

any sharp corners and just smoothing the path from the carb to the runners can

help airflow considerably.

 

JETTING

 

Heres the disappointing bit for all of you who think I can just pluck the right

jet sizes for any particular carb with any type of engine spec out of thin air.

I can't - neither can the people at Weber - so no posts or e-mails please. The

only way is to open that wallet, brush away the moths - yes I know it hurts -

and take the car to a good chassis dyno operator who knows that type of carb

and has the jets in stock. If you want to have a go yourself then the rules

stay basically the same as laid out in Tech 1. The main difference being that

you will usually have two different barrels with two completely different jet

sizes in them to cope with.

 

A good tip is to rig up a throttle stop so that the secondary barrel doesn't

open at all and get the primary running clean all through the range. Pay

particular attention to the idle and progression stages before changing main

jets and air correctors. Then take off the stop and just change the jets in the

secondary until full throttle high rpm operation is right. Trying to do both

barrels together is hard going even for an experienced tuner.

 

Set up the primary so it just runs clean - don't go over rich. That way you

will get good economy. The secondary barrel can do most of the fuelling for

full throttle operation.

 

POWER GAINS

 

Finally a quick word on the sort of power gains you are likely to expect from

carb swaps in most applications. These are general guidelines culled from years

of carb swapping on a variety of different vehicles and I'll bet the figures

are lower than you are hoping to hear. As a starting point I am going to assume

that the standard set up is a twin choke carb sized at about the 900 sq mm per

litre mark. Also I show comparisons for interests sake with fuel injection

systems.

 

A) - 1000 sq mm per litre twin choke +2%

B) - 1100 " " " " " " +3 to 4%

C) - Standard multi injector fuel systems +5 to 7%

D) - Single choke per cylinder (DCOE etc) +9%

E) - 4 butterfly throttle body system +15%

 

 

Dave Baker at Puma Race Engines (London - England) - specialist flow

development and engine work.

[chrisandliz[RL]]

A 34ADM... :lolcry: That would be perfect on an old 3.3L holden 202. Not so good on a 1.3L 4k.

 

Go do some research on carb sizing. Seems most people don't have a clue.

 

Sure a big carb is good in the top end, but you will lose power, responsiveness and fuel economy in the low to midrange which is where you spend the majority of the time with a street engine.

 

 

 

No. With one barrel per cylinder, only one cylinder can draw on one barrel of the four at any given time.

With a single (twin barrel) carb feeding all cylinders, the cylinders take turns in drawing on both barrels.

 

A 32/36 (with 26/27mm venturis) carb actually flows more than a single barrel of a 40mm sidedraft with 36mm chokes. The advantage goes to the sidedraft though as the air has a much straighter path into the cylinder port. The airflow on the downdraft has to make a 90 degree turn below the carb.

 

This is the carby i'm talking about (34 DGEC)

 

http://www.racetep.com/toysuzdgec.html

 

the problem is they are too many models!!!

 

Chris