Turbo carburettor

[Memmeddu]

Hi everyone , hope you're all doing well.
So that's more an educational thread for me , actually nothing I'm doing at this moment , just curiousity born after few YouTube videos.
One of those made my mind working.
So I've seen this video where someone took a fiat 126 with its 650cc engine and they put a Garrett GT15 turbo in it .
Keeping the original carburettor , putting a pop off valve ,an horrible exhaust manifold , and the most useless intercooler and components position I've ever seen .
So here we go to the coolest part ,it works and I can't understand why or better , I partially can.
With 1 bar boost pressure this thing should need double the fuel , isn't correct? Double the air double the fuel equals more power .
Now that's a naturally aspirated engine, so it has lots of compression, and they put a turbo
They didn't mention about valves ,pilot jet,main jet modifications.
But most importantly the thing that it's making my mind working is the ignition timing ,the original one should destroy the engine but it works.
Carburettor should automatically tune itself till you feed enough gasoline in the bowl (which has to be pressurised at boost pressure ).
Has someone made something similar? Or know something about , I've always thought that turbo has to work with electronic fuel injection and electronic ignition , with an ECU.
And this might be a cool project, since I can get two of this engines a turbo and intercooler from a smart fortwo , and after this it's all a matter of playing with electronics to get antilag and launch control

 

[Memmeddu]

That not the one I've seen but it looks better constructed

 

[Pete.]

Hi everyone , hope you're all doing well.
So that's more an educational thread for me , actually nothing I'm doing at this moment , just curiousity born after few YouTube videos.
One of those made my mind working.
So I've seen this video where someone took a fiat 126 with its 650cc engine and they put a Garrett GT15 turbo in it .
Keeping the original carburettor , putting a pop off valve ,an horrible exhaust manifold , and the most useless intercooler and components position I've ever seen .
So here we go to the coolest part ,it works and I can't understand why or better , I partially can.
With 1 bar boost pressure this thing should need double the fuel , isn't correct? Double the air double the fuel equals more power .
Now that's a naturally aspirated engine, so it has lots of compression, and they put a turbo
They didn't mention about valves ,pilot jet,main jet modifications.
But most importantly the thing that it's making my mind working is the ignition timing ,the original one should destroy the engine but it works.
Carburettor should automatically tune itself till you feed enough gasoline in the bowl (which has to be pressurised at boost pressure ).
Has someone made something similar? Or know something about , I've always thought that turbo has to work with electronic fuel injection and electronic ignition , with an ECU.
And this might be a cool project, since I can get two of this engines a turbo and intercooler from a smart fortwo , and after this it's all a matter of playing with electronics to get antilag and launch control

The secret to doing this is in pressurising the float bowl from a pitot tube set within the up pipe.

Normally the float bowl is at atmospheric pressure and the choke of the carb is at a lower pressure because air has to accellerate to get through it. The atmospheric pressure in the float bowl therefore pushes fuel up into the choke area via the jets and emulsion tube.

By compressing the air coming into the plenum you're upsetting the balance. Sure, the air in the choke is still at a lower pressure than the air in the plenum (because it's still being accellerated to get through) but because it's compressed by the turbo it's still higher than the pressure in the float bowl so fuel will get pushed down not up. So instead of leaivng the float bowls at atmospheric pressure you take an air feed from the pipe feeding air to the plenum and attach it to the float bowl vents. Now you are back to a condition where the choke is at a lower pressure than the float bowl, and fuel will flow upwards again.

 

[Memmeddu]

Thanks @Pete.
What about ignition timing?
Originally it's about 10° BTDC on those engines which doesn't looks bad from what I've read

 

[Pete.]

For 1 bar of boost don't mess with the timing. If you were cooling with nitrous then you'd need to retard the timing because the faster burn rate of increased oxygen ratio effectively advances the ignition. 1 bar of boost doesn't automatically mean double the power but it gets you up there especially with an intercooler. If there is one thing you can do to make it more reliable then fitting an intercooler would be it.