Thoughts on Demon carb?

mrmustangman357 · Dec 13, 2007

I am looking into buying a new carb for my 351W. it is 9.8:1 compression with twisted wedge heads and a .530 lift cam at 220 duration. It has an rpm air gap manifold and headers. I had a 750 edelbrock on it but wasn't satisfied with the tuning at cruise. So now I'm finally going back to holleys. I notice Barry Grant has their carb line with specific recommendations for cam duration and such. They recommended me a 650 speed demon with vacuum secondaries. Their carbs are a bit underrated and often flow more than what they rate them for, so I would like to use a 650 for good tuning. I am using a manual trans with 3.73 rear gears. I can't wait to do power tour next year, so it will see some highway miles as well. some people say the demons only run best at WOT, but seeing this carb is recommended specifically for my cam duration and combo, will I have any problems with that? Tell me what you think.

85ragtop · Dec 13, 2007

My buddy has a race demon 650 on his 347. He makes over 650 to the ground before the spray, he has never had a problem driving it around town. It runs good off the line and up top.

HookandLadder · Dec 13, 2007

Most tunable out of the box. It works great at WOT and the 90% of the time when you are just cruising around. The 650 sounds like the one for your set up. Include the electric choke if you drive it year round.

coolblue65 · Dec 13, 2007

I put a 650 Mighty Demon (mechanical secondaries no choke) on my 347 when I built it, I have yet to have it professionally tuned, and I ran a 13.2@109 my first time at the track and get 21 MPG on the highway in 5th gear.

I started with a Edel 750 on my 289 and on the 347 but I wasn't getting the throttle response out of it that I wanted. Overall I am much happier with the Demon. Plus it looks good!!

BullittStangV8 · Dec 13, 2007

Call Prosystem Carbs. Tell them your set up, and what you want, and they will at the least give you a suggestion for a carb that will best suit you. You can make a request online on their website, and they email you a response with what carb they feel will best fit you. They did not even push their products on me, but just gave me an honest response to what size carb I need. You could do that do get a better estimate for your demon set up if thats what your set on?

Shakin66 · Dec 14, 2007

I have just bought a Demon blow through but after attempting to thread in a hose bard that ended up being cross threaded from the factory I have had to send it back for a new baseplate. When I did install it and hooked it all up the secondary float lever was completely off and it flooded. Great carbs for the money but dont bolt it down and think the job is though. It ran great for the first two trips around the block and I cant wait to get it back next week.
View attachment 342405

97speedster · Dec 14, 2007

I have one I will sell for $275. Only been ran for a month and not driven that much in that month. Let me know.

htwheelz67 · Dec 14, 2007

I have a 650 speed demon I ran on my 351 w and on my 408 stroker. I bought a prosystems 950hp a couple weeks ago for 700.00.....I thought it would be real close out of the box and it isn't, it bogs at WOT, super rich and lopes more,runs crappy cold.. frankly theres not much difference between the two and the demon runs better in many ways and its a vac sec too boot. I wish I would have saved 300-350 and bought a speed or mighty demon 750-850.

You are correct, demons flow 60-100 cfm more than rated as they are wet flowed, I removed an edel 750 and replaced it with the 650 demon and it was like night and day.

Vinyl66 · Dec 14, 2007

I've been very happy with my 650 vacuum Demon on my 347. It worked great on my old 306 as well as my current 347. All I have done to it is jetted up a few sizes and put in a lighter secondary spring. I also have a Mighty Demon 750 on the shelf at home to try out next racing season. Can't wait...

theautomatics · Dec 15, 2007

I have a speed demon 575. Horrible. I couldn't tune it, my mechanic couldn't tune it. I'm going with holley next. I have a 289 though. I suppose BG's are great on certain applications. however, for some reason it wasn't the right application for me. Holley will work just fine.

351carlo · Dec 15, 2007

I've had a 625 Road Demon, worked great.

750 Speed demon, worked great.

750 Mighty Demon, worked amazing.

Now I'm in the market for a King Demon. I've just gotta have one of each. They're tricky to tune at first, but they make great power and they look very nice. For my street car I like the look of the carburetor and to be honest that's the only reason I go with the Demon over the Holley equivalents.

mrmustangman357 · Dec 15, 2007

what was your setup, and what demon carb did you use?

and 10secgoal knows alot about this carb stuff, where's he at??!!!!

65fastbackresto · Dec 15, 2007

I have an Edelbog 650

I think its too big and not very tunable. It either floods or runs lean, I cant find the just right setting.

Only good thing I can say about it is when you flog it, it comes alive.

D.Hearne · Dec 15, 2007

85ragtop said:
My buddy has a race demon 650 on his 347. He makes over 650 to the ground before the spray,.

650 to the ground BEFORE the spray? What's he a magician ? Sounds like a Nascar motor there bubba.

danny clemens · Dec 15, 2007

D.Hearne said:
650 to the ground BEFORE the spray? What's he a magician ? Sounds like a Nascar motor there bubba.

Must have Chevy LS heads on it.

iskwezm · Dec 15, 2007

mrmustangman357 said:
and 10secgoal knows alot about this carb stuff, where's he at??!!!!

h's probably relaxing,taking a nap somewhere, i know he doesnt do much but lay around

10secgoal is my carb guy and will be doing my carb tuning in a few weeks

64point5 · Dec 15, 2007

I have a mighty demon 750 on my 10.8:1 393W. It works great. With out of the box Victor Jr Heads, Out of the box Victor Jr. Intake, and a small street solid roller (~600 lift ~240dur) it made over 430rwhp and over 430rwtq on straight 93 octane pump gas with 32 degrees total timing. The driveability is superb.

No complaints at all.

Vinyl66 · Dec 16, 2007

85ragtop said:
My buddy has a race demon 650 on his 347. He makes over 650 to the ground before the spray, he has never had a problem driving it around town. It runs good off the line and up top.

I would also like to know more about this 347 with a 650 carb that is street driven that makes over 650 to the ground without N2O.

iskwezm · Dec 16, 2007

my boss just got one of these, a little overkill,but cool

bnickel · Dec 16, 2007

iskwezm said:
my boss just got one of these, a little overkill,but cool

what the hell is it? i like those big ass annular boosters, i bet they make HUGE power. annular boosters are the way to go, especially on a street motor. but i doubt this thing is going on a street motor, then again mybe that's why it's so overkill.

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