Differences in parts between QV FI and QV DD engines?

DaniT who is restoring both variants compared the internals, and there are differences.

For example, the camshafts for the Downdrafts are part numbers:
1220848
1220847
1220845
1220846

They are illustrated in the 1st & 2nd images.

The camshafts for the Fuelies are part numbers:
1221851
1221852
1221871
1221872

They are illustrated in the 3rd & 4th images.

And more besides, for example, the pistons are different.
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Basically cams, pistons (different compression ratio) headers (vs manifolds on the FI engine) and the induction plenum. They may have messed with ignition timing for emissions reasons, I forget - but if so that's just an adjustment.

The induction is a bigger deal than most people realize. If you look at the path the air takes from the intake trumpets of the six Weber 44DCNF carbs into the combustion chambers, it is a short and relatively straight column that is only 12-14 inches tall. This is why the throttle response of the DD is so sharp, and the immediate juice of the accelerator pumps in the carbs give you such a kick in the ass. I learned how important induction is in a big way after I had an upper-end overhaul from George Evans. I remember his words - "the bottom end only has to stay on one piece...you make all your power with how well the engine breathes". It was a stark and noticeable difference after my top end was refreshed.

Go look at a FI engine, and trace the path the air has to take into the combustion chamber and you see it is much longer and has to turn 180 degrees, and use some of its energy to move the flexible tubing (which is why you will sometimes see the flex tubing replaced with hard metal elbows)

 

Have you noticed the location of the fuel nozzels in the fi engines,?they spray fuel 2 inches avay from the combustion chamber,far more direct than the old carb/pump/butterfly the fi system was actually engineered by Bosch,if that rings a belle, think Slr,911,probably a few hrs of engineering involved

 

From what I understand, the whole column of air you have to move is what determines the response and power delivery. I'm no engineer, but it seems to bear out in my own experiences driving FI cars after living with my DD. Didn't we have a big monkey-poo fight over this on another thread somewhere?

Don't forget, you need 15 air molecules for every fuel molecule you want to burn.

 

+1 avoid the poo flinging.....

Correct me if I'm wrong, pictures of DD's along with enjoying them in person, I seem to recall them having an air box enclosure over the carbs, which then have the same type of flexible hose that runs towards either side of the engine bay where it connects to the air filter boxes. I get where your coming from though.

I feel carbs will always be crisper on the throttle response. The DD has an abondance of air accumulated right on top of the carbs. It's sucked in immediately.
The FI has the restrictions of the fuel distributor and the throttle body. The restrictions are so minor , imo, they would only be noticed if your into sitting there at an idle and stomping your feet on the loud pedal. Put the car in motion and the FI will move you up the road as fast as you want it too. No flat spots, or burps, just pulls as hard as hell.

This is a great thread.
Does anyone have parts for both variants that could be photographed side by side showing what the changes are vs looking at part numbers?

 

It also helps the process if the fuel is ignited earlier in the air movement process,carbs are sexy,no doubt,but these german engineers put a lot of work inn to this system.
Mercedes uesed this (amongst several others) on their s class late 70s inn to the late80 s ,the 280 s had 2 carbs,great car for its time,at the same time a 280 se, E for einspritznung,injection, (i think the fuel distriburtors on the Countach might be a pair of these units,the mercedes had one beeing a in line 6,) the power increase from the s to the se was i think 15% or so, anyway,there is real engineering involved in this system by the possibly best company in the world in their field,( fuel pumps on the Dd i belive is Bosch as in fi)stick headers on the fi, remove the cats,as the saying goes,if i was a betting man,

 

I think it has also to do with where the throttle plate is. On the carbs, those throttle plates are right there in the carb throats whereas the FI system there are two bigger butterflies where the flexible hoses meet the air plenum. The DD setup has the Venturi of air pulling from that air on top of the carbs in the air box, so from where it begins to becomes high flow it is a small and straight path into the combustion chamber.

Not an engineer, may be proven wrong, but I did stay at a Holiday Inn Express last night!

 

Sure.

The DD uses higher-compression pistons and more aggressive camshafts.

Comparing the DD pistons with the FI pistons its clear that they are shaped differently and the DD units are more aggressively domed, DaniT has been in the fortunate position to make the direct comparison as he is restoring both variants.

As regards the pistons:
- Those used in the DD are part number 001420801 with a 9.5 : 1 compression ratio
- Those used in the FI are part number 001420828 with a 9.3 : 1 compression ratio.

Below in the 1st image is an example of the DD's domed higher-compression piston.

The 2nd image is an example of the FI's flat-top lower-compression piston.

Both images by Daniel T.

BTW I think he noted that comparing the DD camshafts with the FI camshafts, the the DD units are more aggressively lobed.
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FWIW, this is a good description of how our Downdraft GLA12997 drives.

 

Thankyou Joe, I appreciate the pics.
This is interesting. Do you know the reasons for the engineering behind this? Why the lower compression which looks like they achieved this by machining additional material out of the top of the DD piston?
Lower compression/ slightly lighter piston, maybe would assist with quicker revving?

 

I could ask Luigi Marmiroli, the Chief Engineer at Lamborghini at the time who oversaw the production of both variants of engine being discussed here, he could give a definitive answer as to the reason, so we don't have to speculate.

Meanwhile, I don't think the lower-compression ratio creates revving that is quicker, and the latter probably would be the basis for the variance.

From my limited knowledge on the subject [I am many things but an engineer is not one of them, although I do try & learn!], a lower compression engine will allow for more timing adjustment to tune, say, a fuel-injected engine.

As Go Mifune said, you make horsepower by how much air you move through the motor, and a high compression engine is more efficient than a lower compression one, in general.

That said, the differences we are talking here are so small, my feeling is the main difference is the actual induction setup difference between a Carb engine and a Fuelie, that's what creates the horsepower & performance difference.

 

The FI engine is all about emissions. The lower compression ratio reduces peak cylinder pressures. Lower peak cylinder pressures reduce NOX emissions. The cams have less overlap to prevent the exhaust from over scavenging the cylinder at the end of the exhaust stroke to reduce hydrocarbon emissions. Milder cams in general make it easier to minimize carbon monoxide and hydrocarbon emissions. Fuel injection is more precise than carbs which also improves emissions.

If you take an FI engine and put DD cams and DD pistons in it, more than likely you will make very close to the same power as a DD. The FI engine will have a slightly stronger bottom end due to the longer intake runners, and possibly a little less top end for the same reason. If you actually built this engine the biggest risk is the cams may have to much overlap and cause the plate in the fuel distributor to oscillate up and down making the mixture unstable at low RPM. This is most likely a small risk.

The air hoses on the inlet typically do not cause any flow losses. However I have not measured this one so I can not be 100% sure. The thing most people forget is only one cylinder at a time is flowing air so it does need to be a lot bigger than the port.

The lower compression pistons effect torque the most. While the shorter duration cams reduces the total air flow into the cylinder, this has the most effect on horsepower.

Cheers Jim

 

Which is exactly why they were utilized for Tipo USA cars to conform to EPA mandates.

 

Agreed

 

Beeing the comp ratio diff is minimal, and the added bonus of a presice induction system,cam specs unknown, cam lobe diff in lift less duration different overlap?perhaps more agressive beeing fed by a presise supply of fuel,sqirted /sprayed in to the cyl as opposed to a carburator,wich sprays only during the initial stomp on the trottle,(acclelerator pump) also the fact that the cars zero to 60 time where only 0,2-3 sec off in an average, 911Porsche997 s to non s 0,4 sec diff @30 hp difference aprox tips the scale very close to the Countach, with this in mind, my exhast/header sugg similar to Joes system,and cat removal would make for a really quick responsive vell behaved countach,perhaps consistently quicker than a dd.

 

In 2001 I was given the task of bringing a BMW M5 into compliance with EPA regulations. The differences between US and European cars were staggering. I am sure this holds true with so many other performance cars.
The most difficult test in what was then a five step procedure was the cold start emissions test. My feelings are it would be nearly impossible to get a Carb car to pass, hence the advent of FI. I prefer Carb cars myself.

 

David,

Your experience mirrors mine.

We can bring Ing. Luigi Marmiroli himself back into the discussion to affirm the differences, but the fact remains that the Fuelie Countach exists for a reason and one reason alone: to conform to USA EPA mandates as stated above. The fact also remains that the net resultant difference between the QV Fuelie and the Carb engines is the basic fact that the former are less potent and result in less performance than the latter. The extent to which depends on who you are talking to and what alternative facts they are spinning.

 

Fantastic information, and great reading!

Thankyou to everyone, - (so I'm not 'quoting' practically the entire first page)

 

Agreed,the way they where shipped out,but given the same opportunity reg exhaust and non catalytic converter,wich now 30 years later is an option in most states, fair is fair, beeing the smog thing was to conform to a specific countrys regulation.as the bumpers,bolt the dd exhaust on the fuelie from header to tail/tip, then compare.

 

The biggest difference is emission equipment. Period DD cars tested had no emissions equipment, optimally tuned by the factory. Remove it on the Fuelie, and you are good to go.

 

No the biggest difference is the DD is a one of one configuration and the swan song of the carb era. Period the end. I dont care what HP it produced. It happens to be FIA homologated to boot.

Emission for USA market cars no matter the marque, are NEVER sought after more than the original euro configurations. This is not new and in the future will accelerate as cars become automated and standardized in powertrains.

The thread is about the differences not about how to make them closer to each other in power or whatever...

 

The difference is carbs versus fi, imho the greatest ,coolest car ever.not whatever thefuture cars become automated ,standarized. We are talking about an old hand/home made italian supercar wich started the whole thing. Why not stick together and promote the car as a whole? Its ,or used to be 1900 cars or so, 600 qv aprox, they are all great, promote and praise them as such ,

 

We have been down this road on other threads.

Just because some people are interested in a particular variant and extol its virtues, does not mean they are disparaging other variants.

As rmolke85 says, this thread is about the DIFFERENCES between the 2 variants, that's interesting to some people.

I often say "all Countachs are great", and I mean that respectfully, but its not my job to be equally interested in and promote all variants.

I think most people feel the same.

 

Job, has nothing to do with it,at least not for me, its the enthusiastic spirit as a whole,especially from the ambassadors of the hobby, personally i think there is a wibe here,wich i dont agree on, i am shure newcombers and existing Countach owners reading the bickering between some of us, will do their own homework and draw their own intelligent conclusion. personally,i like them all,and a few years from now,if there still is any interest at all in cars, a Countach will simpley be just that, a Countach.all good