I have a mighty demon 650 I want to run on my truck. It was in a vortec box before and ran fine at 7psi. Can I run this carb with a hat instead of a box. Would I need to mod the carb? Can it be dun or should I just use the ugly box?

 

also this will be a 7-12psi set up. I dont see me running more than 12psi being its a street ride and the bottom end wouldnt hold 12 for but so long.

 

Ok so I have been looking and there is just not much info out there about any one using the older demons. No one on here has any experience with them?!?

 

do some additional research because my memory isn't the best.... but... If I remember correctly the demon line of carburetors has a slightly different method/dimensions for swedging the boosters into the main body than holley does. This leads to a smaller booster passage which of course is undesirable at higher fuel flow rates and can become a restriction. All my experience is with swap meet holleys and bonnets.

ALso, everyone that I can remember who has tried a bonnet and a box has ended up keeping the bonnet.

 

I'm using an older Demon, on E85 and blow-thru, there's a build thread on it here somewhere I believe, (or some info on it in the thread for my car), definitely some details about my BRPV setup.
My boosters aren't swaged, they are removable, I took them out and drilled them myself, then polished the passages a bit with some thin strips of emery cloth to remove any burrs.

 

I worked with 2 demons on blowthru setup. One was a 750cfm on 7 psi with just the floats changed out. This one worked flawless with vent tube extensions with factory jetting. This was with prochargers standard hat which is horrible.

The other was an 850. It was getting 20 psi pushed to it with a csu hat. Smaller HSB and lots of jetting and it was still lean. Put vent tube extensions on it and it pulled high 11s. Still had a bunch of jet and PVCR increased but it put down 980whp.

 

So basically what your saying is a 650 may not need any mods other than vent extensions floats and some jetting for a low boost set up?

 

http://www.hangar18fabrication.com/blowthru.html

 

hanger doesn't really talk about any thing demon specific. I keep seeing guys running the demons with out doing any real mods this is why I asked.

 

3~4 psi CRUSHED the brass floats in my Demon. IMHO, they won't work right without opening up the boosters, changing Primary and Secondary Jets, HSABs, IABs, and most likely PCVRs as well. Also, I am VERY pleased with the performance of my BRPV.




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what are u using for your boost referenced power valve???

 

Thats what Im saying.

 

Turbine pressure...drilled and tapped the passenger side turbine housing just above the flange for an 1/8 NPT fitting, running 3/16 steel brake line tubing, coiled up to dissipate some heat, teed to the P/V and to my back-pressure tell-tale gauge.

The one in the bowl is stock, the other two came out of my carb, now replaced by the nitrophyl floats...

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This is the pressure port on the carb body going to the P/V:

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I looked and looked, can't seem to find any pics of the turbine pressure line setup, but I can take a couple if anyone would like to see it.

 

Dont forget , if you use backpressure for the PVs , its got to be close to 2:1 .

1:1 will not open them all the way .

BUT .......I'm going to try this again with the new settings on the carb . I 'm going up in jetting and PVCRs to get enough fuel at the track . This is going to make it very fat on the street . So maybe a PV thats only 1/2 open will be just what I need on the street .

 

this looks nothing like my mighty demon.....

 

Post a pic of it? I've only worked on a few Demons, mostly Race Demons.

 

My carb was used in a box on a boosted car so it cant have the bras floats either. They would have already crushed. This is the only pics I have at the moment. Its raining its ass off and its out in the garage.

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My Demon is the older style that still used Holley bowls. The main thing with a BRPV is getting boost pressure into the P/V cavity, and keeping any vacuum out. I plugged the bottom passages with epoxy, (could drill and tap for a setscrew as well). Then drilled through the main body into the P/V cavity, and epoxied a piece of 3/16" tubing in there, (not shown in the pics). I used an old main body and metering block to test and adjust the opening pressure.

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If it ran fine with boost before 11.5-11.8 to one will I really need to do the boost power valve mod? He said the car ran flawless with the carb in the box. I would like to start with just removing it from the box and any hat related mods first. Then if I run it and I need to richen it up or what ever I can do those mods once its a running set up.