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blow through carb
https://slantsix.org/forum/viewtopic.php?t=51176
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Author:  Junior [ Thu Feb 21, 2013 1:53 am ]
Post subject:  blow through carb

i keep reading that a vacume secondary carb is a no no. but i i were to block off the vacume port running the secondaries and put a screw in the linkage to make the secondaries open with the primaries would that work? if not why not?

Author:  DusterIdiot [ Thu Feb 21, 2013 7:26 am ]
Post subject:  Need...

You need to read the section of Dave Emmanuel's Holley book on Modifying for Turbocharging. It explains the mods for draw through and blow through apps. There are companies that should have the linkage you need to make that mod, homemade linkages can bind up and not give good results...Also it might just be cheaper to get a 600 cfm mech linkage carb off craigslist to boost through than the hassles of converting a vacc. secondary carb...

-D.Idiot

Author:  Junior [ Thu Feb 21, 2013 2:21 pm ]
Post subject: 

i was planning on getting the dp but was curious about he vac secondary carb because i have a dozen of them laying around

Author:  terrylittlejohn [ Fri Feb 22, 2013 4:00 pm ]
Post subject: 

with a blow throw you have no were to get a vac signal, everything is on the pressure side. with the vac secondaries you have no pump shot to over come the idle circuit to main system flow starting point even with a pressurized intake charge(bog).

Author:  DusterIdiot [ Fri Feb 22, 2013 4:33 pm ]
Post subject:  But...

Quote:
with a blow throw you have no were to get a vac signal, everything is on the pressure side. with the vac secondaries you have no pump shot to over come the idle circuit to main system flow starting point even with a pressurized intake charge(bog).
He already knows this, but is inquiring if there is a way to make a vacc. secondary carb a mechanical secondary carb. I know that a secondary idle system can be done with the correct metering block and some drilling. Ther are some mods to do what he wants, but Holley had disavowed the procedure sine the linkage can bind and cause problems or throttle shaft problems. I do agree, that if he needs a 'fat' pump shot, a single pump with the 50cc conversion and the biggest shooter may not cover it, and the double pumper is the ticket here to cover both sets of bores.

-D.idiot

Author:  Turbo Toad [ Fri Feb 22, 2013 6:42 pm ]
Post subject: 

Don't be cheap when it comes to your fuel delivery the fastest way to break something is from lean spikes. There all kinds of info on the net on modifying a DP. I can understand you already have a carb or two but my opinion is I'd sell them and pick up a 500 cfm two barrel. You have half as much to deal with.
I have a blow thru setup and there not hard to dial in for lower boost levels under 12 psi but when you start turning up, the boost that's were your going to have issues.
Just one man's opinion that's dealing with the tuning process now
Aaron

Author:  Junior [ Fri Feb 22, 2013 9:00 pm ]
Post subject: 

I ordered the book today. Gonna give it a read and go from there.I'm gonna go with the double pumper,i was just curious to see if it want gonna be a hassle to make the carbs I have work. also I'm only planning on running 8-12lbs of boost or whatever it can handle reliably using the boost referenced mechanical pump.

On a side note, I have successfully run my vacuum secondary carb with a screw in the linkage to make the secondaries open with the primaries. (not boosted) I put a larger squirter in it and adjusted the secondary float so that almost as soon as the plates open it's letting out fuel. Throttle response was awesome and there was no hesitation what so ever when everything was properly set. I wound up going back to the normal setup because it needed to be adjusted before each day of racing to work properly.it just got to be a hassle. I would not recommend that setup for street driven car for that reason. But if you like fiddling with your stuff it can be done with good results.

Author:  terrylittlejohn [ Sat Feb 23, 2013 4:58 am ]
Post subject: 

will if you got it to work with no boost then that same carb will work with boost!! i had trouble with double pump 750cfm untill i got a looser converter.

Author:  Junior [ Thu Feb 28, 2013 6:13 pm ]
Post subject: 

so the book came in today and from my readings at theturboforums.com im gonna run the 600 dp. making a blow through carb has always in some part put me off of turboing a slant. if i would have known that it was really that easy to setup a carb for it i would have been boosted a long time ago.

http://www.hangar18fabrication.com/blowthru.html
that is a good writeup on how to do it if anyone else was concidering it. if you dont plan on running more than 10psi dont bother drilling. also another mod to make would be vent tube extensions.

Author:  RyGuyTooDry [ Fri May 17, 2013 9:50 am ]
Post subject: 

A 4 barrel is too much carb for 10 - 12 psi. I only plan on running a 350 cfm 2 barrel on my turbo build, plus it'll be better off boost than the 4 barrel as well.

Author:  1974duster kev [ Fri May 17, 2013 10:17 am ]
Post subject: 

I run a 650 blowthrough barry grant demon daily driver and don't have any issues once I got the tune close.

Kev

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