Stratos induction system on 246GT

There was a reason why Ferrari went with the DCNF- it worked
The only real mod i would make to the 246 is the ignition system / module other than that the car performs and sounds perfect. I have seen some V8 converted cars and they are awful.
Best
tony

 

I highly recommend the Winterburn CD ignition that is a direct replacement for the Dinoplex. It’s been super reliable and still uses the stock points. It even has the “Emergenza” switch that allows the use of the spare coil (just in case ). He’ll even build it into an empty Dinoplex. Rob and I replaced the stock starter (when it failed) with a high torque starter. That’s a huge improvement as it really spins the motor.

 

I have the Superformance unit fitted and although it works very well I feel there is something better. I did have the Black Stallion programmable ignition system which worked well but kept eating ignition coils so kind of lost faith in that piece of S H 1 tango.

I have looked at the Winterburn unit but getting one and import taxes are another thing!

Agree on the starter motor, thats a good mod as well.

 

I made the conversion to the Stratos induction system more than a year ago. I decided to keep it on the car because for me, it was a considerable and worthwhile performance upgrade.

The reason for my much more positive impression of this modification is, I believe, the fact that my installation included the larger 44IDF carburetors. In combination with the Stratos manifold, they are said to provide an extra 10-15 hp. I believe it, but my ambition is to measure and document this modification when the driving season starts again. In any case, the improvement is very noticeable, particularly at the top of the rpm range. I like it a lot!

 

If I was looking I would be considering the system that @Telaio developed with the Motec and Jenevy ITBs hidden in the carbs. 225bhp sounds pretty good.

 

If you contact Kevin at Mototechnique, he has lots of info, photos and data. It’s completely reversible as long as you keep the original parts. He mentioned to me it works beautifully in hot or cold weather, hot or cold motor at any altitude like a modern motor. I’ve never personally experienced it but hope to one day. I experienced his V8 conversion and it was thrilling!

 

Lars,
Standard engine?
If you dont mind sharing, what jets, emulsion tubes and venturis did you use?
Kind Regards
Tony

 

Tony,

Yes, standard engine. Or, perhaps I should say carefully optimized stock engine. Pistons with a bit higher compression, a lighter steel flywheel, stainless steel headers and muffler, otherwise completely stock. Stock camshafts, stock distributor and points with a Winterburn ignition built into original Dinoplex box, so wiring is completely stock as well.

Jetting is also nearly standard, as supplied with 44IDF carbs. I changed only the idle/low speed jet from 50 to 57:

Venturis 36 mm
Main jets 135
Air corrector jet 175
Emulsion tubes F11
Idle jets 57 (55 probably sufficient)

The change to larger idle jets was done to cure a slight tendency to ”pop” from the intakes at light throttle, just above idle, around 2000 rpm. Perhaps overdid it a bit, but it cured the popping. I plan to optimize the jetting on a dyno in the future, but the car runs very well now, so I am not in a hurry.

Best regards,
Lars

 

The main reason it seems Ferrari chose the DCNF was due to its compact height. The Stratos IDF’s are taller leaving very little room above for an air intake. My concept utilized an air box with a top with really short air rams. It created a venturi effect. I also mocked up a stock looking air box with the same concept. It worked really well and cleared the stock engine lid but I think if it was optimized it would want to be taller which I believe would create more power and torque. You can see this on the Stratos Comp motors with their large air box. For a road car it’s prudent to have an air box as it can prevent a carb fire and it equalizes and pressurizes the air creating more power. You also want to utilize the side air intake(s) for cold air. To achieve this I would have developed a second engine lid with a higher center bulge and to do it absolutely correct and undetectable you would start the bulge transition at the tail of the rear trunk (with an extra trunk lid) and raise the surface over the complete length. The ones I’ve seen thus far look ungainly and visually forced. I would do it all digitally and explore the options before modifying a car.

 

Thank you, It looks a great modification and from the spec's i would say you get a lot of high end power at the expense of low down torque. Not wishing to criticize in any way shape or form but do you think the DCNF with larger venturis (+jets) would achieve a similar performance.

I would definately get the car on a rolling road and map the engine as it does show up some real anomalies especially with the DCNF. I have mapped out the AF ratio (AFR) for given RPM and it does highlight some deficiencies in the standard jetting, especially with E10. Idle is silly rich but i can address that easily within the idle circuit.

I have considered changing the air corrector jets to smooth out the curves at certain RPM's but this will only change the AFR at low RPM or high RPM depending on which way you go. Changing the main jets will affect the AFR throughout the range but will (i think) shift the curve up or down depending on jet size.

What interests me is the emulsion tube design, each air port in the tube A,B or C can influence the AFR at specific RPM's, so any decrease or increase in these holes will raise or lower the AFR at a given RPM. From my perspective it could be worth altering these holes to smooth out the curve and bring it line.

This clearly shows how important it is to get the float level spot on as any difference increases or decreases the emulsion ratio in around the tube

Any thoughts?

Kind regards

Tony




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Tony,

I initially had the same concerns about sacrificing low end performance with the larger carbs. They turned out to be unfounded. The engine pulls strongly all the way from idle to redline, just like the stock version - only stronger overall. Keeping the stock cams retains the sweet linear torque curves that Ferrari engineers put so much effort into achieving. But the slightly larger carbs and freer breathing intakes allow the torque to be maintained up to a higher rpm, resulting in higher power.

And, yes, I believe the same results could be achieved with larger DCNF carbs. But then you would still have the sputtering on sharp, sweeping left turns. No reason to put up with that, as I see it, if you are changing carburetors anyway.

Your Air/Fuel ratio curves are very interesting. A good reference for what we can expect when we measure our own cars. They also show that trying to get a perfect A/F ratio under all conditions with a carburetor, is a hopeless proposition. The best thing we can hope for is to get the ratio correct at a few critical points like full power, steady state cruising, etc., and then try to minimize the errors at other points.

I can only wish you success with trying to alter the emulsion tubes, and hope you post the results here. Not something I would ever consider getting involved in, though. With so many different emulsion tubes available, I think I would settle on one, and call it close enough.

Your point about the importance of getting the float level right, is well taken. It affects almost everything in a carburetor.

Best regards,
Lars

 

Thats good to know, you are much braver than me changing the complete carb setup. Bold move and very commendable piece of engineering by both of you. (4camgt)

I tend to agree with you, emulsion tube tuning is best left alone unless you have full and un-interupted use of a rolling road, which i dont. If I did fiddle with them then I'd keep the F24's but alter the holes by increasing or decreasing the apertures for a given RPM range.

To be brutally honest the car is only ever driven on A roads and operates in the 3000 - 5000 rpm range so they are not to bad. Idle is stupidly rich but it runs sweet as a nut throughout its rev range, my only concern was the varying AF ratios. I guess for a stock carb and a 40 year old car, then it isnt too bad.

I only ever took it to 7000rpm once and that was when it was on a dyno. Just a bored frustrated owner who cannot use his car at the moment, roll on summer!

Best

Tony