carbie turbos
 

Hi guys,
I was just wondering if any of you know websites or can explain how turbos work on carbs. I know there are two set ups, suck through and blow through and how this relates to to the position of the turbo in the system but I don't understand how the carb is able to increase the amount of fuel as the pressure from the turbo increases. Is anyone able to help?

As far as I can tell, the carb would work just like it does in an n/a application. Airflow through the venturies creates a pressure differential which draws fuel out of the float bowl.

The only difference is in the blow-through version which requires a boost referenced fuel pressure regulator for the carb to function properly due to it being pressurized. Fuel pressure would be whatever the required pressure for the carb is plus boost pressure.

Yeah, what he said. SO if you have a carb that runs on 4 PSI, and you wanna run 8 PSI of boost, youre gonna need 12 PSI of fuel pressure :). Otherwise, as I understand it, the fuel pressure will be over come by the boost pressure and basically be blown back into the tank :).

~T.J.

oh, o.k thanks that clears it up a little. Does the fuel pressure increase by itself as boost increases or do you run a high fuel pressure all the time? Is this done from running a higher pressure from the fuel pump? Sorry for the newbie questions!

The pump supplies a "constant" pressure. The regulator regulates it down to the base pressure. Then, theres a vacuum line from the manifold or somewhere thats under boost pressure that goes to the "boost referenced" regulator. When the regulator gets boost pressure it will chage the amount of pressure in the system. Does that help ya?

~T.J.

Yeah, that's great. Thanks RotorMotorDriver. I assume that suck through would be cheaper due to being less complex (I also heard it is not as good, with worse throttle response). Would it be expensive to do this kind of set up?

Id personally reccomend a blow through. I think its easier. You still have and need all the same basic components either way. Blowthroughs just seem to be more popular. Im sure theres reason for that :).

~T.J.

Draw-through is probably cheaper to set up but there's some draw backs. Firstly, you can't use an intercooler due to the possibility of fuel condensing inside the core.

Also, due to it's placement, airflow is ultimately restricted to the size of the carb. You need something large (typically a 55mm side draft Weber) to make good power. As a result off boost driveability is sure to suffer. In blow-through carb size isn't much of a problem as air is forced through the carb under pressure.

I have a 40IDF on my blow through and it works well.

That is until I tried to replace it and now it sucks.