Topic: Advise on A112 70HP+40DCOE

[bibito]

Hello, everyone,
recently decided to go with the weber 40dcoe on the standart A112
abarth 70HP engine.
Please, advise need adjsutsments and possible pros and cons of that set up.
Thank you.
Lubo

[Pantdino]

Hello, everyone,
recently decided to go with the weber 40dcoe on the standart A112
abarth 70HP engine.
Please, advise need adjsutsments and possible pros and cons of that set up.
Thank you.
Lubo

I don't recall seeing a 40DCOE on a 4 cylinder engine with the standard Autobianchi A112 / Fiat 850 style single inlet head. Those are usually seen on "4 canal" heads, either Abarth, Aztek, or other aftermarket type, and use 2 of them.

Does someone make an intake manifold for that?

I saw one on an Abarth 695 motor and 2 liter Alfas run a pair of them, so it should work.  But you'll probably have to put the car on a chassis dyno and have someone who knows Webers well do the venturi, jets, and airs to make it run right.

Jim Oddie

[Carlos]

Hello pantdino!

Have a look on this side!
newbielink:http://www.abarth-motorsport.nl/ [nonactive]
There you can find inlets for one 40DCOE!

Greatings
Carlos

[guy moerenhout]

a intake manifold of this type was made for the A112 like one piece valvevover/intake on the 58 hp.The difference with a single one is only 2 our 3hp but easy regulation.On the old mini you have the same set.You can better play with the venturis.But fuel becomes hotter and for this the changes it back.Hot fuel =loosing power and vaporlook but is a nice looking set and drives very good.

[Paul vander Heyden]

I have tried using a single side draft Weber on several customer engines, and I have NEVER made more (usually less) HP than with a two barrel downdraft carburetor.  The preferred down draft is a 36DCD7, although I have also done successful installations of 38DCNF, 40 DCNF and Solex CCI 40-42.

I have intake manfolds to suit any of these carburetor combinations.

Paul Scuderia Topolino
www.scuderiatopolino.com

[bibito]

Thank you, Paul, Guy,
the reason beening that it looks better and should perform about the same, + a have a few of those/40dcoe/  I have to use.
Any ideas on the ventury and jet sizing, cams..
Paul perhaps you have a cam to suit.... ? and I still plan on getting those ARP's...from you
so might just combine them, so if you have any ideas pleas,share.
Thank you,
Lubo 

[zippyfiat]

Hi Lubo,

I have had a few people tell me that they tried the sidedraft Weber DCOE only to find that the engine ran poorly after ("like crap" according to one).  They all said they immediately switched to downdraft carbs and the engines ran much better.  The DCOE sure looks good but you should be prepared to be disappointed with the results.  The design of the stock Fiat cylinder head just does not work well with a sidedraft carb. 

You can still find a DCD carb with a bit of patience, but finding a "correct" older version (eg., DCD7) can be harder.  You could always try a DCNF as Paul suggests.

Gil

[Pantdino]

Hi Lubo,

I have had a few people tell me that they tried the sidedraft Weber DCOE only to find that the engine ran poorly after ("like crap" according to one).  They all said they immediately switched to downdraft carbs and the engines ran much better.  The DCOE sure looks good but you should be prepared to be disappointed with the results.  The design of the stock Fiat cylinder head just does not work well with a sidedraft carb. 

You can still find a DCD carb with a bit of patience, but finding a "correct" older version (eg., DCD7) can be harder.  You could always try a DCNF as Paul suggests.

Gil

Anyone know why a side draft does not work well?
I have read that the fuel has to make a sharp turn, which is a problem.

Also, having a long distance between the throttle butterfly and the intake valves will tend to tune the engine for lower- rev operation, which is not where these engines make power.

Jim

[zippyfiat]

Jim, I think that is a question that Paul would be a good one to answer.  I believe the reason is that because of the extra 90 turn and longer runner the fuel does not stay in suspension properly.  I think that by the time the fuel/air gets into the combustion chamber there is actually gas in liquid form that washes onto the surfaces of the chamber.  I might be somewhat off on this, but it's something like that.

To compound the problem, with the design of the Fiat head, cylinders 1 & 4 always run leaner than 2 & 3 because of the extra distance the fuel/air mix has to travel.  It is my understanding that a sidedraft carb. only makes this situation worse.  PBS used to make their "stager" cams to delay the fuel charge getting to cylinders 2 & 3.

The only successful application of sidedraft carbs is with two sidedraft carbs.  These setups (PBS, Abarth OTR for example) have intake runners that are quite short and are of equal length to each cylinder.  There have been some heads where people have welded up the stock opening and added 4 new ones for dual carbs along with a custom intake manifold.  I've seen 2 or 3 of those on ebay in Germany in the past few years.

Maybe some expert out there will correct what I've said or add to it.....

Gil

[bibito]

Thank you, Gil,Jim,
for shearing your thoughts.... but still,
is there anyone, in the forum, that has been or still is using that set up?
I already got the manifold , so I guess I'll have to give it a try, any practical tips will be welcomed thou.

Lubo

[guy moerenhout]

I use it on a 850 spider and works very well.Use very small chokes 25 our 28 .The adventage from this set is that you can find all parts easy for a 40 Dcoe.Start with 125 /190.Think on a NSU 1000 TT our TTS,this have also very long and high intakes.Also the first prototype  A112 (with TCR head)had long intake manifold and over the engine.

[bibito]

Hi, Guy,
I have the manifold with holes for 38mm, I guess 38DCOE,
should I be looking for a 38DCOE or just use 40 and change the chokes and jets accordingly.
Could you please, post some pictures of your car with that set up.
Thank you,
Lubo

[guy moerenhout]

you can open the holes to 40.The 38 dcoe was use on fiat 2300 S.Car is sold .A populair set for the A112 first serie was a intake manifold and valvecover in one piece for the DCOE.

[grant gauld]

I also made a 40 DCOE to work very well on a 850 sports motor (903cc).The car won its class in a few hillclimbs and a 4 day classic rally.You just have to find someone who is genuinely skilled at jetting when you run the motor on the rolling road.I made a large kidney shaped inlet port in the head,about 75% larger (to suit the manifold).
 I think I have tried 5 different carbys and I do prefer a 36/36 DCD,but if its what you want,go for it.
 A pretty common cam grind like a 30/70/70/30 worked well with the DCOE.If you can reduce your cars weight this will also make a very big difference.
Grant

[trevor]

Re Guy's comment (reply #11) re A112 with TCR head; see photo; one wonders how vibration effect on dcoe's was controlled, if possible ?
Trevor

[bibito]

Here is a picture of the manifold I intend to use,
and the head set up.
I guess not much room left for kidney shape?

Grant, finally I'm getting some positive comments ...thank you,
would you please, attach a few pictures of your car with that set up...
Where can I get the cam you are talking about?
Thanks
Lubo

[grant gauld]

That 30/70 cam works well on the 903cc motors.For 1050cc try 35/75 or the original A112 cam.This is assuming that its just a fun weekend car.For competition a much more applicable cam choose will be needed.Your inlet port size is OK again for fun but not competition.
 Grant
 

[bibito]

I'm going to stick to fun weekend car,
so hopefully it will all work out well.
Will I be able to tell the difference between the A112 original abarth cam, which I have,
and the 35/75 that you suggest, using the DCOE?
Lubo

[Paul vander Heyden]

Hello all,

There are two principle issues with using a single side draft carburetor (weber/dlellorto/solex/etc).

1.  Fuel/air mixtures do NOT like to make 90 deg. turns.  Almost invariably the fuel comes in and hits the far wall at the 90 deg turn and separates.  Remembering that fuel must be in a well mixed and agitated state in order to properly ignite and burn, this fuel/air separation is not ideal.

2.  Because of the problems associated the necessarily long intake runners with a side draft carburetor, tuning the 4 different circuits in the carburetor becomes much more difficult.  Don't make things too large, as you will actually lower the intake charge velocity.  This will worsen the problem discussed in Point #1.  The longer runners will also mean that the engine will not produce maximum HP over 7500.

If you must, use 25mm venturis, but be prepared for the fact that the engine probably will not be happy above 7500 RPM.  It may rev to more than this, but it will not be making any HP.

Main fuel 125   
Main air 170
Emulsion Tube F11
Idle  50 F8
Accelerator Pump 40
Venturi from 25 to 30 depending on conditions and application.

Here is a good starting point for jets.

There are as many opinions on camshafts as there are camshaft grinds.  However, there is no arguing that the goal is to get as much combustible mixture into the cylinder, as this is what makes HP.  I prefer camshafts that are shorter duration and have larger lift at the valve.  This combination does mean that the valve train must be optimised and the geometry double checked.  As there is a limited time to accomplish all the tasks in 300 degrees for example, if we want to achieve 12mm+ of valve lift the the acceleration of the opening ramp of the lobe is going to be quite radical.  Likewise, if we delay the closing as far as possible, then the closing ramp will also be very quick.  So this means that using the lightest components and better valve springs are indicated.  So the valve opens faster and stays open the maximum amount.  This is primarily determined by the diameter of the foot of the lifter and the maximum surface pressure that the cam lobe/lifter interface will withstand.  The payoff is in having a "greater area under the curve" and thereby getting maximum volumetric efficiency. 

If you can combine this with a well designed exhaust system that does a proper job of scavenging at peak torque RPM, then the volumetric effiency of the engine can be as high as 110%.  Again, if the engine is seeing 1.1 Bar of inlet pressure (instead of 1.0 Bar) more combustible material will make it into the cylinder to be burned.  A note of caution here - If you engine is 110% efficient at peak torque, and your computed compression is 10:1, then the REAL compression at peak torque RPM is 11:1.  This can have devastating effects if you are using a grade of fuel that is marginal.  It goes without saying that most pistons damaged by detonation occur at peak torque RPM (5500-6000).

I hope this provides some of the technical background as to why the single side draft set up may not meet everyones expectations.

Good luck
Paul