Which Demon carb to choose??
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Pro
Joined: Jun 2001
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From: Quebec
Which Demon carb to choose??
I have a daily driver with just under 400 hp. I want to change my Q-jet since it is 25 years old and leaking gas from the bottom. The Demon carb look really nice but I wonder which one to choose from.
First since I have a manual transmission, does a mechanical secondary would be best for performance or a vacuum would be better?
Second, I have to choose from Road Demon or Speed Demon. The Road Demon comes only vacuum sec..
Stephan
First since I have a manual transmission, does a mechanical secondary would be best for performance or a vacuum would be better?
Second, I have to choose from Road Demon or Speed Demon. The Road Demon comes only vacuum sec..
Stephan
Le Mans Master
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If you need a speed demon pm me. have about 120 miles on it, i have already done the "lar's paper tune" pm me or email supervette@gmail.com
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From: San Diego - Deep Within The State of CONFUSION!
Originally Posted by American Boy
I have a daily driver with just under 400 hp. I want to change my Q-jet since it is 25 years old and leaking gas from the bottom. The Demon carb look really nice but I wonder which one to choose from.
First since I have a manual transmission, does a mechanical secondary would be best for performance or a vacuum would be better?
Second, I have to choose from Road Demon or Speed Demon. The Road Demon comes only vacuum sec..
Stephan
First since I have a manual transmission, does a mechanical secondary would be best for performance or a vacuum would be better?
Second, I have to choose from Road Demon or Speed Demon. The Road Demon comes only vacuum sec..
Stephan
Le Mans Master
Joined: May 2003
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Originally Posted by SanDiegoPaul
Use the Edlebrock 1905 or 1910 Quadrajet. No muss, no fuss, OEM replacement and brand new. Many improvements over the original too. And none of the tune headaches taht the BG carbs have.
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From: San Diego - Deep Within The State of CONFUSION!
Originally Posted by munday
what tune headaches?
When running the Dyno Shop we actually hated them! Now even years later, I see friends with that model carb not being able to fine tune them, and the documentation that comes with the carb is of such poor quality they couldn't read it.
OTOH, the new Qjets are a much better design than the OEM ones. But they still have the same strengths that the most widely mass-produced 4BBL that G.M. ever made, had from way back then.
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From: Who says "Nothing is impossible" ? I've been doing nothing for years.
If you have 300RWHP and are drag racing the car then I would go with a mechanical secondary square bore carb in the 750CFM range for a Holley and for a BG I am not sure what CFM as they are supposed to flow more than advertised but if it were me I would get the "Classic" Holley double pumper 750CFM #4779 and an RPM Air Gap intake, I bet your RWHP goes up 25HP. You can get for a good price up here in Canada. It has everything you need, I have it on my 406ci and had it on my 355ci and both ran great 
Le Mans Master
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From: Silver City NM
St. Jude Donor '05-'07
1980 ,350 vortec, 307 rwhp @ 5300,
I'd say that's a tad more than "just under" 400HP.
Better keep the carb under 700CFM or you'll drown the engine.
Since it's a "daily driver" I would suggest vacuum secondaries. You COULD use mechanical secondaries, but you will be making frequent contributions to OPEC if you do
Dep
I'd say that's a tad more than "just under" 400HP.
Better keep the carb under 700CFM or you'll drown the engine.
Since it's a "daily driver" I would suggest vacuum secondaries. You COULD use mechanical secondaries, but you will be making frequent contributions to OPEC if you do
Dep
Last edited by DJ Dep; Jun 10, 2005 at 10:36 AM.
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From: CORVETTE 77 385 C.I. TEXAS
SEE Demon Selection Guide
http://www.barrygrant.com/demon/default.aspx?page=5
Holleys are working for me.
http://www.barrygrant.com/demon/default.aspx?page=5
Holleys are working for me.
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From: Arlington Va Current ride 04 vert, previous vettes: 69 vert, 77 resto mod
there are no tuning issues with the Speed Demon other then you have to tune it.....if you like being able to adjust everything on your carb then Speed Demon is the ticket...if you hate tuning Carbs then get something with less tuning capabilities....those of us that have the Speed Demons like them....it does require initial tuning and making friends with the carb....you do need to use a heat shield and the fuel rail is another $50
Drifting
Joined: Oct 2004
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From: Lafayette Louisiana
Originally Posted by bobs77vet
there are no tuning issues with the Speed Demon other then you have to tune it.....if you like being able to adjust everything on your carb then Speed Demon is the ticket...if you hate tuning Carbs then get something with less tuning capabilities....those of us that have the Speed Demons like them....it does require initial tuning and making friends with the carb....you do need to use a heat shield and the fuel rail is another $50
Pro
Joined: Nov 1999
Posts: 520
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From: Front Range
with a manual transmission you definitely want to go with mechanical secondaries. as for the tuneability of demon carbs... didn't you watch the instructional DVD that comes with the carb? they pretty much spell everything out for you.
good luck
the blonde weasel
good luck
the blonde weasel
Melting Slicks
Joined: Apr 2002
Posts: 2,337
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From: Norfolk VA
Originally Posted by SanDiegoPaul
Have you ever had one Dyno Tuned? Probably not. If the carb works outta the box the way you want it, great. It's when you want it to run as good as it SHOULD that you have problems.
When running the Dyno Shop we actually hated them! Now even years later, I see friends with that model carb not being able to fine tune them, and the documentation that comes with the carb is of such poor quality they couldn't read it.
OTOH, the new Qjets are a much better design than the OEM ones. But they still have the same strengths that the most widely mass-produced 4BBL that G.M. ever made, had from way back then.
When running the Dyno Shop we actually hated them! Now even years later, I see friends with that model carb not being able to fine tune them, and the documentation that comes with the carb is of such poor quality they couldn't read it.
OTOH, the new Qjets are a much better design than the OEM ones. But they still have the same strengths that the most widely mass-produced 4BBL that G.M. ever made, had from way back then.
That is what people usually say when they are unable to tune a carb. I personally watched Lars tune several Demon carbs. The owners also stated the vehicle performed much better than before.
Melting Slicks
Joined: Dec 1999
Posts: 2,116
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From: Mid West
Cruise-In III Veteran
I'm running a BG 650 mechanical secondary on my ZZ4 (w/ GM's HotCam) .....just back from the chassis dyno yesterday .... 328HP and 355 ft-lbs at the rear wheels. Love the carb.
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Originally Posted by SanDiegoPaul
Have you ever had one Dyno Tuned? Probably not. If the carb works outta the box the way you want it, great. It's when you want it to run as good as it SHOULD that you have problems.
When running the Dyno Shop we actually hated them! Now even years later, I see friends with that model carb not being able to fine tune them, and the documentation that comes with the carb is of such poor quality they couldn't read it.
OTOH, the new Qjets are a much better design than the OEM ones. But they still have the same strengths that the most widely mass-produced 4BBL that G.M. ever made, had from way back then.
When running the Dyno Shop we actually hated them! Now even years later, I see friends with that model carb not being able to fine tune them, and the documentation that comes with the carb is of such poor quality they couldn't read it.
OTOH, the new Qjets are a much better design than the OEM ones. But they still have the same strengths that the most widely mass-produced 4BBL that G.M. ever made, had from way back then.
Over the last couple weeks I have seen much discussion about the quality/performance/tunability of DEMON carbs V. Holley Carbs. Today I changed from a Speed Demon Vac Sec, to a Mighty Demon 650 (DP). The carb was ok right out of the box, I was able to set the floats and idle fairly easily.
Before I purchased this carb I spent some time on the phone with Eric at Barry Grant and was able to voice the concerns of those on this site. We went over my engine combination and dyno charts from my past dyno tuning and decided on the Mighty Demon 650.
Results: 18.6 Rear Wheel HP Increase and 12.4 ft lbs increased torque.
I also now have a more crisp throttle and the engine ramps up quicker. So those that say Demons are hard to tune... maybe you just picked the wrong one..? All I changed was a 2-size increase in both primary and seconday jets and up 1 size in pump cam. Off to the dragstrip tomorrow so I'll Post the results.
Steve
Before I purchased this carb I spent some time on the phone with Eric at Barry Grant and was able to voice the concerns of those on this site. We went over my engine combination and dyno charts from my past dyno tuning and decided on the Mighty Demon 650.
Results: 18.6 Rear Wheel HP Increase and 12.4 ft lbs increased torque.
I also now have a more crisp throttle and the engine ramps up quicker. So those that say Demons are hard to tune... maybe you just picked the wrong one..? All I changed was a 2-size increase in both primary and seconday jets and up 1 size in pump cam. Off to the dragstrip tomorrow so I'll Post the results.
Steve
not everyone has problems tuning....guess it maybe it's just dumb luck
Thread Starter
Pro
Joined: Jun 2001
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From: Quebec
Thanks for the replies...
I want maximum performance over MPG so I'll go with a 650 mechanical secondaries. I'll have to wait I little bit but when I'm ready, I'll check with you Munday for your carb.
Stephan
I want maximum performance over MPG so I'll go with a 650 mechanical secondaries. I'll have to wait I little bit but when I'm ready, I'll check with you Munday for your carb.
Stephan
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From: FL
Two things:
1) Holleys and Demons are square-bore. Q-Jets are spread-bore. You should think about replacing your intake manifold if doing the carb swap.
2) If the only problem with the Q-Jet is leaking well plugs, that is an easy fix. This is common problem. Pull the carb, drain the gas, dry the area completely. Then, cover the plugs with some JB Weld. Let dry and reassemble.
Why spend a couple of hundred dollars to fix a $5 problem?
1) Holleys and Demons are square-bore. Q-Jets are spread-bore. You should think about replacing your intake manifold if doing the carb swap.
2) If the only problem with the Q-Jet is leaking well plugs, that is an easy fix. This is common problem. Pull the carb, drain the gas, dry the area completely. Then, cover the plugs with some JB Weld. Let dry and reassemble.
Why spend a couple of hundred dollars to fix a $5 problem?