Speed Demon Advice
Thread Starter
Intermediate
Joined: Mar 2003
Posts: 37
Likes: 0
From: Youngstown OH
Speed Demon Advice
I spoke with BG today and they recommended a Speed Demon 650cfm for my 71 LT-1 (eventhough it came with a 780cfm Holley). I'd appreciate some input from those who have swapped a Speed Demon (or the like) from a Holley. Will the factory throttle cable set-up work on the Demon? Should I go to a mechanical secondary versus vacuum? (BG says you get better throttle response with a mechanical), is the fuel line set up compatable with the stock dual feed system? Any other issues I should be aware of regarding this swap. Thanks for your help.
Team Owner
Joined: Feb 2003
Posts: 30,183
Likes: 313
From: Lake Norman NC
Re: Speed Demon Advice (SC71LT1)
in my opinion..i had the same carb..and i HATED it! if you do decide to go with a demon...hope you like smelling gas and black smoke. i'd stick with a holley or edelbrok.
Team Owner
Joined: Feb 2003
Posts: 30,183
Likes: 313
From: Lake Norman NC
Re: Speed Demon Advice (SC71LT1)
you have to get a different throttle bracket. any of those chrome mr.gasket or spectre autozone specials will work. as for the carb...it was hard to start, choke tower side screw kept getting caught on the air cleaner base..the screw for the adjustments of the back butterflies broke off...i adjusted float, mixture screws, accelerator pump...always had a hesitation and kept my spark plugs black! some guys on the forum swear by them, however; my neighbor went through 3 demons and finally went back to a holley. i myself went back to a holley and am considering an edlebrock.
Burning Brakes
Joined: Mar 2001
Posts: 1,211
Likes: 5
From: Nashville TN
Re: Speed Demon Advice (SC71LT1)
Carb size sounds right. Demons flow a bit more than they are rated for.
I would go with a vacuum secondary, they are a little bit more forgiving in the tuning department. The fuel lines for the speed demon series are about $70, they are not the same as the holley lines.
You need to pay attention to the setup on the carb. It has a very sensative 4 corner idle circuit and needs the floats set correctly. I have run a number of carbs on my Corvette and have found the Demon to be the best by far.
I would go with a vacuum secondary, they are a little bit more forgiving in the tuning department. The fuel lines for the speed demon series are about $70, they are not the same as the holley lines.
You need to pay attention to the setup on the carb. It has a very sensative 4 corner idle circuit and needs the floats set correctly. I have run a number of carbs on my Corvette and have found the Demon to be the best by far.
Team Owner
Joined: Apr 1999
Posts: 21,953
Likes: 1,445
From: Reno Nevada
2024 C3 of the Year Finalist- Modified
Re: Speed Demon Advice (SC71LT1)
The 650 is a better choice for a 350ish ci. The discussion about vacuum seconds or mech seconds will go on forever. Throttle responce on either is up to your tuning ability. Nothing out of the box matches.
I like the BG fuel log to attach a Demon carb. the cable setup brackets can be bought from places like Summit or Jeg's
I like the BG fuel log to attach a Demon carb. the cable setup brackets can be bought from places like Summit or Jeg's
Team Owner
Joined: Jun 2001
Posts: 43,136
Likes: 155
From: Thomson Georgia
Re: Speed Demon Advice (REDSHARKONBOYDS)
in my opinion..i had the same carb..and i HATED it! if you do decide to go with a demon...hope you like smelling gas and black smoke. i'd stick with a holley or edelbrok.
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Le Mans Master
Joined: Apr 2001
Posts: 5,941
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From: Was New Orleans but swam to Baton Rouge LA
Cruise-In IX Veteran
Re: Speed Demon Advice (Alwyn678)
in my opinion..i had the same carb..and i HATED it! if you do decide to go with a demon...hope you like smelling gas and black smoke. i'd stick with a holley or edelbrok.
Dude I have never seen any black smoke or smelled gas..Looks like you had a bad carb or a bad set-up they are by far the best carb I have run on my 74 and it is built very close to LT1 specs.........GREAT CARB by the way the holley and edelbrock did not even hold a candle
Dude I have never seen any black smoke or smelled gas..Looks like you had a bad carb or a bad set-up they are by far the best carb I have run on my 74 and it is built very close to LT1 specs.........GREAT CARB by the way the holley and edelbrock did not even hold a candle
Instructor
Joined: Feb 2001
Posts: 217
Likes: 1
From: Suwanee GA
Re: Speed Demon Advice (Sigforty)
I have the predecessor to the Speed Demon and Race Demon, a BG Silverclaw 750 with mechanical secondaries. The carb has been blueprinted by BG within the last 6 months (They did it for free). It works great, but it is definitely set up to run rich. I reduced the size of the IFR (similar to adding a wire to the IFR on a Holley DP). After many hours of tuning and trial and error, it is working great. The carb you are looking at may not require all this adjustment.
This is the first mechanical secondary carb I have had on the street and I love it.
If I had it to do over, though, I might have bought an HP Series Holley. It took me a long time to get this carb to work right with my combo.
This is the first mechanical secondary carb I have had on the street and I love it.
If I had it to do over, though, I might have bought an HP Series Holley. It took me a long time to get this carb to work right with my combo.
Melting Slicks
Joined: Jun 2001
Posts: 3,281
Likes: 6
From: NC USA
Re: Speed Demon Advice (Alwyn678)
Dude I have never seen any black smoke or smelled gas..Looks like you had a bad carb or a bad set-up they are by far the best carb I have run on my 74 and it is built very close to LT1 specs.........GREAT CARB by the way the holley and edelbrock did not even hold a candle
BTW, if you prefer a more traditional look than the fuel log, get the chrome adjustable dual line with built-in filter and gauge from Summit with adapters which looks like the original oldschool chrome lines. :cool:
[Modified by Marks69BB, 11:37 PM 7/15/2003]
Drifting
Joined: Jul 2002
Posts: 1,254
Likes: 1
From: Edinburgh
Re: Speed Demon Advice (Marks69BB)
Dude I have never seen any black smoke or smelled gas..Looks like you had a bad carb or a bad set-up they are by far the best carb I have run on my 74 and it is built very close to LT1 specs.........GREAT CARB by the way the holley and edelbrock did not even hold a candle
Amen brother; I'm very pleased with my speed demon! The previous owner had a Holley, replaced it with a Demon, and swore by the Demon since it kicked butt right out of the box! Ask Lars here on the forum about them since he is a carb guru in my book]
Amen brother; I'm very pleased with my speed demon! The previous owner had a Holley, replaced it with a Demon, and swore by the Demon since it kicked butt right out of the box! Ask Lars here on the forum about them since he is a carb guru in my book]
Drifting
Joined: Jul 2002
Posts: 1,855
Likes: 0
From: Cocoa Beach FL
Re: Speed Demon Advice (SC71LT1)
I have a Speed Demon 650 on my ZZ4 (actually it's the one that supposedly built for the ZZ4 motor) and am pretty happy with it. It performs better than anything else I've had but I did encounter some "issues" with the choke. Turns out BG had a whole batch of them that had choke issues so they sent me a new choke. Everything seems to be fine now.
BG has a good racing reputation but there are definitely other choices that will perform well. For example, I've heard the Edelbrock Thunder series is a good one.
Good luck! :thumbs:
BG has a good racing reputation but there are definitely other choices that will perform well. For example, I've heard the Edelbrock Thunder series is a good one.
Good luck! :thumbs: