nastee383

I'm getting ready to order a boatload of parts since my engine came. I need your opinions on the carb. Here are the vehicle specifics: 3500lbs, 3:73 gears, 700R4, 3000 stall, 383 w/242/248 @.050 hydraulic roller cam, Performer RPM AirGap. Will be 75% street, 25% strip.

The choices are 1) 750cfm vacuum secondary Speed Demon
2) 750cfm mechanical secondary Speed Demon 3) 750cfm mechanical secondary Mighty Demon.

Any and all opinions are appreciated.

stingr69

I vote 750 VS. Gotta be a good choice here.

-Mark.

SpyderD

I vote mechanical secondary. 25% strip almost requires it.

an81shark

i vote contacting barry grant, they can help you select the perfect carb.

gdh

I would like to see some results run using the Mighty Demon but given that the majority of your time will be spent on the street I would opt for the SD mech.

mrherren

I would vote the VS. with 75% on the street depending on how much you drive it, the mech. will just kill your mpg. When you go to the stip you can either put a lighter spring for the secondary or you could even put a bolt on the throttle which will make it mech secondary. Plus will a 3000 stall (which high if you are talking track) mech with 750 Cfm will probably drown your engine and make it stall off the line with WOT.

mrherren

Actually the more i think about it, your CAM is not too wild and depending on what you have for heads and valves i would probably be looking for something with about 650 cfm instead of 750.

1979toy

I have a 750 double pump Speed Demon on my '79. That would be the carb that I would recommend unless you are daily driving your car. It WILL use a lot of gas running around town but the better hit when you get on it will make up for every other problem!
My set up is 406, Edelbrock RPM aluminum heads, 300/310 cam, 3000 RPM torque converter, T350, and 3.55 gears.

Ryan77

I'd go with the Speed Demon 750 mechanical. I spoke with Lars when I was looking for a carb for my 383 (also from AR) and he said in dyno testing the mechanical Speed Demon beat the vacuum secondaries by up to 20hp on some motors

Brettmc

Where are the Holley choices??? If I gotta choose a BG then it's #3 on your list.

Brett

GrandSportC3

Speed Demon 750 with mech. secondaries.. Vacuum secondaries don't have a big disadvantage at the track...and mech. secondaries are very streetable.. Well - the fuel economy isn't as good as with vacuum secondaries.. but the mech. secondaries will give you a much better response and more power...
I personally go with Holley HP series mech. secondaries carbs... I used the 80528 on my old engine and the 80514 on my new engine...

nastee383

I considered the Holley HP series but I kinda like that "idleze" that BG has incorporated to tame the idle on those BIG cams.

nastee383

I'm willing to give up a few ponies in exchange for better driveability. I'm leaning towards vacuum secondaries but eventually I think I'll have a single plane/Mighty Demon setup to swap on for the 'BIG EVENTS" and use the dual plane/vacuum sec setup the other 90% of the time.