Blow thru Fuel questions

[Rodavo]

I am turboing my G200 with a blow thru carbie setup and I have a few questions. Do I need a rising rate regulator with this setup, and if I do, is it possible to get one from the wreckers or do I need to buy a Malpassi one? If I run a max of 7psi, what sorta fuel pump will I need? Do I need to buy a new one or can I get one of these from the wreckers also? Will a fuel pump from an injected car work with a carbie setup or will they flow fuel too hi psi for the stock fuel lines?

[zzz]

for the fuel pump buy an efi camira one as they are the same as a vlturbo but a bit cheaper
hope this help's
zzz

[Ben Wight]

Yes you need a Rising Rate Fuel Pressure Regulator (RRFPR). As you boost the air bonnet on top of the carb, the fuel bowl will pressurise. If the boost you run is greater than your fuel pressure, then it will force the fuel back into the tank. A RRFRP will increase your fuel pressure if boost is present. The theory is that this way, your fuel pressure is always higher than your boost, so your carby will work properly.

Next thing to consider is that when idling and running off boost, most carbs will only put up with about 7psi of fuel pressure, before the bowl will flood. But, you need a pump that delivers a few psi over the boost you want to run. ie, if you want to run 7psi, you need a pump that will deliver sufficient flow at at leat 10psi, 12 would be better. There are heaps of pumps that can do this, I think a Carter is available that outputs 12psi.

Holley blue pumps come with a regulator, that can be boost referenced, thus making them a RRFPR, they will apparantly ouput over 20psi of fuel pressure, and have a decent flow.

Obviously any efi pump will deliver enough pressure, but they must be regulated to a low enough pressure to suit the carbs max limit whilst idling.

You can buy a malpassi off the shelf to handle an efi pump with a carb, or you could modify a factory efi regulator to do the same thing. All factory efi regulators reference engine vacuum, but they will also reference boost on a turbo engine, with a rise of approximately 1:1.

The spring tension inside the regulator determines at what fuel pressure it will deliver before openning the return line to the tank. If you slacken the spring, the pressure is reduced. I can modify a standard efi regulator by cutting open the can, and then putting a sleeve over the entire can the houses the spring. You then 'set' the two ends of the can apart so that the tension on the spring will give you the desired base fuel pressure. I used a copper tube that was slightly larger than the regulator housing, and then sealed it with silicone so it was air tight.

If going to a really high fuel pressure, then it is advisable to replace all your rubber fuel lines with efi type hose.

If you are confused about how the regulators work, get an efi one from the wreckers and chop it up to investigate, you'll build your own custom one in no time.

Ben Wight

[Rodavo]

Thankyou for your help Ben. A few more questions though. I only want to run a max of 10 psi fuel pressure as this project will only be a low boost setup, probably no more than 7psi boost pressure. It looks like a Holley Blue pump would keep things simple, eliminating the need for a rising rate regulator as the pump has one 'built in'. Do you know for sure that this pump will work for my setup? It seems to be the neatest way of doing it. Do you know roughly how much these pumps are? Thanks for your help.

[Ben Wight]

If you want to run 10psi fuel pressure, then it will probably flood the carby, you will need to increase fuel pressure when boost comes on. Either with a rising rate regulator, or with an electrical circiut, such as a boost switch and soleniod.

A holley blue pump comes with a regulator that can be boost referenced (by simply fitting a hose barb), and it will do what you need. The regulator is a seperate unit. I know of a guy using this setup on an engine running over 20psi.

Around $200 I think.