Demon Carbs
Thread Starter
Melting Slicks
Joined: Sep 2004
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Demon Carbs
How do Demon carbs stack up against the competition? How do they do in terms of gas mileage? How well would one work on a street car?
I was looking at a Mighty Demon 825, no choke from what I can see.
I was looking at a Mighty Demon 825, no choke from what I can see.
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From: Forked River NJ
Gas mileage with a Mighty Demon 825 
You had better have a large cubic inch BB and a real healthy cam to run a Mighty Demon 825. I would not be worried about fuel mileage with this carb. Demon carbs are run by many here with pretty good results.
I just saw in your other post you have a 383 stroker. What cam are you running. The 825 is to big for a 383. The 750 would be a better choice. Do you need a Mighty Demon. They are recomended for cams with 244 @ .050 cams or larger.
You had better have a large cubic inch BB and a real healthy cam to run a Mighty Demon 825. I would not be worried about fuel mileage with this carb. Demon carbs are run by many here with pretty good results.I just saw in your other post you have a 383 stroker. What cam are you running. The 825 is to big for a 383. The 750 would be a better choice. Do you need a Mighty Demon. They are recomended for cams with 244 @ .050 cams or larger.
Last edited by Gordonm; Oct 14, 2005 at 06:34 AM.
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From: Arlington Va Current ride 04 vert, previous vettes: 69 vert, 77 resto mod
good gas mileage and performance engines cannot be realistically spoken about in the same sentence.....if you want perfomance and gas mileage go with a fuel injection system....my 750 speed demon with 700r4 trans and a 350 hp engine gets around 14mpg in town and much better then that on the highway.....smiles per mile is high though
Tech Contributor
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From: At my Bar drinking and wrenching in Lafayette Colorado
If gas mileage (or emissions) are a remote consideration, do not use a Demon or any of the Holley performance carbs. When tuned for best performance, these are not economy systems. But they do run good...
The Mighty Demon is set up and calibrated for engines running cams with durations around 260 degrees at .050". This is a big cam, and the carb will not be easily tunable if used with a milder cam. Although the 825 can be set up to run well on a 383, it's more carb than you need unless you're spinning some impressive rpms, and the fuel curve will not be right if you're using the carb on a mild-cammed engine. But it can be set up to run on your engine.
A nice performing carb for your setup would be the Speed Demon 750 mechanical secondary. This carb is set up for engines running cams in the 240 @ .050 range (more typical of a street engine), and it would be easily tunable for your application. The carb comes without a choke (which is not needed), but it has a choke tower to make it legal for use in certain NHRA classes requiring retention of the tower. The choke tower does not interfere with airflow, and has no adverse effect on performance.
Lars
The Mighty Demon is set up and calibrated for engines running cams with durations around 260 degrees at .050". This is a big cam, and the carb will not be easily tunable if used with a milder cam. Although the 825 can be set up to run well on a 383, it's more carb than you need unless you're spinning some impressive rpms, and the fuel curve will not be right if you're using the carb on a mild-cammed engine. But it can be set up to run on your engine.
A nice performing carb for your setup would be the Speed Demon 750 mechanical secondary. This carb is set up for engines running cams in the 240 @ .050 range (more typical of a street engine), and it would be easily tunable for your application. The carb comes without a choke (which is not needed), but it has a choke tower to make it legal for use in certain NHRA classes requiring retention of the tower. The choke tower does not interfere with airflow, and has no adverse effect on performance.
Lars
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From: Reno Nevada
2024 C3 of the Year Finalist- Modified
Originally Posted by torqvette
How do Demon carbs stack up against the competition? How do they do in terms of gas mileage? How well would one work on a street car?
I was looking at a Mighty Demon 825, no choke from what I can see.
I was looking at a Mighty Demon 825, no choke from what I can see.
But IMO with a small motor like your 383 I would use a 650 speed Demon with mech seconds. It's more important to have an instant on throttle responce than just few more HP at 7000 rpm
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From: Who says "Nothing is impossible" ? I've been doing nothing for years.
I have the 825 Race Demon, drag race version on mine and I was very suprised how well it runs right out of the box. I adjusted the idle mixture and it runs perfect. These carbs, apparently for some reason flow more than they are advertised so be aware of that 
Thread Starter
Melting Slicks
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I just talked with a guy at Demon. He suggested that I go with a 750 Mighty Demon but he also said that I'd be fine with a 750 Speed Demon with annular boosters and a mechanical secondary. I figured that I'd need bigger than a 750 from what my friends have told me. Also a 750 especially because I'll be going with nitrous in the future, any bigger wouldn't do aswell.
Hey GKULL, did I see your car in that Gumball Techademics video?
Hey GKULL, did I see your car in that Gumball Techademics video?
Last edited by enkeivette; Oct 14, 2005 at 04:19 PM.
Team Owner
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From: Reno Nevada
2024 C3 of the Year Finalist- Modified
I used a 750 speed Demon on my 383 for about 4 years. It ran okay right up to my 7500 red line. I tried a 825 race demon and it was to big. I always wanted to try something like a 650 just to see if it would be even more responcive.
I also had a 240@.050 cam on a single plane. If you have an automatic I would go smaller on a carb
I also had a 240@.050 cam on a single plane. If you have an automatic I would go smaller on a carb
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