Blow through with vacuum secondary Holley Carb.

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superchargeddrt

superchargeddrt

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Hey Guys,
Has anyone ever used a vacuum secondary carb with a blow through turbo. I have a buddy of mine considering turbocharging his 318 powered 1988 D150 pickup. Thanks for your help.
 
Seems to me on boost there wouldn't be any vacuum to open the secondaries.
 
TrailBeast said:
Seems to me on boost there wouldn't be any vacuum to open the secondaries.
Click to expand...

Except the 'vacuum' is just a pressure drop as the air accelerates through the venturi. So long as the whole carb is pressurized, it should be fine. It's the backside of the actuator that needs to see the same boost as the carb throats.

Doesn't mean it will work 'fine', but it should work.
 
Phreakish said:
Except the 'vacuum' is just a pressure drop as the air accelerates through the venturi. So long as the whole carb is pressurized, it should be fine. It's the backside of the actuator that needs to see the same boost as the carb throats.

Doesn't mean it will work 'fine', but it should work.
Click to expand...

Not disagreeing with you at all because I don't know for sure, but that just doesn't make sense to me.
Wait a dang minute, this is why those boost kits with the entire carb inside a pressurized box works, correct?
 
TrailBeast said:
Not disagreeing with you at all because I don't know for sure, but that just doesn't make sense to me.
Wait a dang minute, this is why those boost kits with the entire carb inside a pressurized box works, correct?
Click to expand...

I did the same thing! wait, no, yes, no... no.. yes... wait. Damn.

Yeah, that's why they make the pressure cookers. Keeps the float bowls and the vac actuator all seeing the same thing. It should work. But tuning it? No idea. Carbs aren't my thing :D
 
Phreakish said:
I did the same thing! wait, no, yes, no... no.. yes... wait. Damn.

Yeah, that's why they make the pressure cookers. Keeps the float bowls and the vac actuator all seeing the same thing. It should work. But tuning it? No idea. Carbs aren't my thing :D
Click to expand...

Got it, thanks, I think, wait, yea thanks, :D
 
It would be easier for your buddy, tuning and hardware wise, to swap the carb out for an AFB type.
 
TrailBeast said:
Wait a dang minute, this is why those boost kits with the entire carb inside a pressurized box works, correct?
Click to expand...
Yeah and that's why a boost referenced fuel pressure regulator is required for blow thru applications.
A regular fuel pressure regulator feeding 7 PSI of fuel would have 1 PSI of fuel pressure to the carb if you're running6PSI of boost.
 
MiradaMegaCab said:
Yeah and that's why a boost referenced fuel pressure regulator is required for blow thru applications.
A regular fuel pressure regulator feeding 7 PSI of fuel would have 1 PSI of fuel pressure to the carb if you're running6PSI of boost.
Click to expand...

Thank you, as I hadn't considered that.
 
TrailBeast said:
Thank you, as I hadn't considered that.
Click to expand...
I have a blow-thru setup running 15 pounds of boost on my 225 slant six.
When I was gathering parts for my project, I was told repeately, everywhere I searched, "Get a mechanically-operated secondary carb, not a vacuum-operated one." Everywhere. I never knew why, but when I asked people who were "in the business" and, should know, they ALL told me the same thing... So, I got a Holley 4150 "double-pumper," and it works great. My advice, though I am ignorant as to the reasons, I'd go with the "experts" who advised me, and say, forget a vacuum-secondary system if you're running a blow-thru carburetter.
 
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