Holley or Demon 650?
Thread Starter
Burning Brakes
Joined: Sep 2005
Posts: 1,078
Likes: 0
From: Santee CA
Holley or Demon 650?
We're in the process of rebuilding our engine, and are trying to buy some parts for our SB.
Well, one of the things that we're going to end up buying is an Edelbrock top end package, with the E-Tec heads, and the Performer Air Gap manifold. Well, the problem with this manifold is that it doesn't come in a spreadbore setup, so we can't use the old Q-Jet that's currently on the car.
Well, my dad's considering buying a Holley 650 cfm carb to drop onto the manifold, but I keep seeing the Demon Speed Demon carbs, with a 650 cfm mechanical secondary...Lots of people on the forum here seem to prefer the Demons, which is why I'm leaning towards one of those...
Ultimately, we're looking at about 425 hp after we get done with the rebuild, and will be going to a 383 stroker rebuild...
Anyone have any suggestions/ideas for which one we should go with? Pros/cons, ease of adjustment, etc?
Well, one of the things that we're going to end up buying is an Edelbrock top end package, with the E-Tec heads, and the Performer Air Gap manifold. Well, the problem with this manifold is that it doesn't come in a spreadbore setup, so we can't use the old Q-Jet that's currently on the car.
Well, my dad's considering buying a Holley 650 cfm carb to drop onto the manifold, but I keep seeing the Demon Speed Demon carbs, with a 650 cfm mechanical secondary...Lots of people on the forum here seem to prefer the Demons, which is why I'm leaning towards one of those...
Ultimately, we're looking at about 425 hp after we get done with the rebuild, and will be going to a 383 stroker rebuild...
Anyone have any suggestions/ideas for which one we should go with? Pros/cons, ease of adjustment, etc?
Racer
Joined: Apr 2006
Posts: 477
Likes: 43
From: Millbrae California
a air gap style manifold in my opinion have a carburetor that is richer than most other manifold require because there is little or no heat in the intake manifold to keep the air & fuel mixed together at lower engine speeds. the carb i would suggest is a mighty demon or the holley 4150 HP is close second but it costs more money. a speed demon does not have changable idle jets or air bleeds so if you need to tune the air/fuel mixture it is not as easy as a mighty demon.
you may gain a little power with a air gap manifold but at the cost of normal drivabilty but the choice is yours!
henry @ oles carb
you may gain a little power with a air gap manifold but at the cost of normal drivabilty but the choice is yours!
henry @ oles carb
Thread Starter
Burning Brakes
Joined: Sep 2005
Posts: 1,078
Likes: 0
From: Santee CA
Originally Posted by olescarb
a air gap style manifold in my opinion have a carburetor that is richer than most other manifold require because there is little or no heat in the intake manifold to keep the air & fuel mixed together at lower engine speeds. the carb i would suggest is a mighty demon or the holley 4150 HP is close second but it costs more money. a speed demon does not have changable idle jets or air bleeds so if you need to tune the air/fuel mixture it is not as easy as a mighty demon.
you may gain a little power with a air gap manifold but at the cost of normal drivabilty but the choice is yours!
henry @ oles carb
you may gain a little power with a air gap manifold but at the cost of normal drivabilty but the choice is yours!
henry @ oles carb
We're going to keep the Air Gap, though, due to the fact that it comes in the Edelbrock kit that Summit's got in their new catalog...
Pro
Joined: Sep 2002
Posts: 690
Likes: 1
From: near Memphis TN
You can always get one of those adaptor plates that adapt a spread- to squarebore. With the air gap you may have hood clearance issues however.
Read carefully some posts about the BG demon carbs, there have been quality control issues.
Finally - 425hp would be pushing it on a 650 carb, I doubt you will hit your mark. If you want that 425 HP you would probably need a 750.
Read carefully some posts about the BG demon carbs, there have been quality control issues.
Finally - 425hp would be pushing it on a 650 carb, I doubt you will hit your mark. If you want that 425 HP you would probably need a 750.
Thread Starter
Burning Brakes
Joined: Sep 2005
Posts: 1,078
Likes: 0
From: Santee CA
Originally Posted by SpyderD
You can always get one of those adaptor plates that adapt a spread- to squarebore. With the air gap you may have hood clearance issues however.
Read carefully some posts about the BG demon carbs, there have been quality control issues.
Finally - 425hp would be pushing it on a 650 carb, I doubt you will hit your mark. If you want that 425 HP you would probably need a 750.
Read carefully some posts about the BG demon carbs, there have been quality control issues.
Finally - 425hp would be pushing it on a 650 carb, I doubt you will hit your mark. If you want that 425 HP you would probably need a 750.
I'm kinda afraid I'm hitting the limit of a 650, too...I haven't heard anything bad about BG carbs until now, but I'm going to take a look...Holleys I know have been around for what seems like millenia now. Maybe I'll look at a double pumper Holley, or try to get some more info on the Edelbrock Thunder Series.
I would LOVE to keep the Q-Jet, but clearances with a spread-to-square riser & the Air Gap won't allow it. As it is, I'm going to have to run a drop base air cleaner...Either that, or change to a riser hood, which I'm not wild about doing. I'm trying to keep the car with a stock appearance so that it doesn't attract too much of the wrong gaze (i.e. the 5-0)...Sounds like maybe I've got a lot more research on my hands, trying to weed out what works from the marketing
. Thanks guys!
Racer
Joined: Apr 2006
Posts: 477
Likes: 43
From: Millbrae California
the edelbrock thunder (and performer) carbs are very good for a mild engine but they are not the best choice for a air-gap manifold and we never use a edelbrock larger than a 650cfm because of a lean of idle problem that is very common on the 750 and 800 cfm units. a hot cammed engine or a engine with a air gap manifold will respond well to a carburetor with 4 corner idle (4150HP or mighty demon)
if you choose a mighty demon i would use a 650 cfm unit (demon under rates the cfm flow while other brands overstate the cfm flow) if you go a holley 4150HP a 750 cfm should be ok. i have had as same amount of quality control problems with edelbrock, holley and barry grant, so to me it is personal preference on which carb to use.
henry @ oles carb
if you choose a mighty demon i would use a 650 cfm unit (demon under rates the cfm flow while other brands overstate the cfm flow) if you go a holley 4150HP a 750 cfm should be ok. i have had as same amount of quality control problems with edelbrock, holley and barry grant, so to me it is personal preference on which carb to use.
henry @ oles carb
Corvette Stories
The Best of Corvette for Corvette Enthusiasts
Top 10 Most Expensive Corvettes Ever Sold on Bring A Trailer
Brett Foote
10 Things Every Corvette Owner Needs (2026 Edition)
Michael S. Palmer
8 Most "Only Corvette Owners Understand" Quirks and Problems
Pouria Savadkouei
10 Reasons the C6 Z06 is Still A Performance Benchmark After 20 Years
Joe Kucinski
How Much Horsepower Every Corvette Engine "LOST" in 1972
Joe Kucinski
Top 10 DOs and DON'Ts for Protecting Your Convertible Top!
Michael S. Palmer
Top 10 Most Explosive Corvettes Ever Made: Power-to-Weight Ratio Ranked!
Joe Kucinski
150 hp to 1,250 hp: Every Corvette Generation Compared by the Specs That Matter
Joe Kucinski
8 Coolest Corvette Pace Cars (and Replicas) of All Time
Verdad Gallardo
Safety Car
Joined: Mar 2002
Posts: 3,780
Likes: 442
From: Southwest MI
Originally Posted by Daryl Lawman
I still like the Holley.....I have the Holley and its been great.cfm? 750 min... depend on RPM range and primary use.
me? i tried a Demon, went back to a Holley....... i'm sure you can make either work with enough tuning.
Instructor
Joined: Aug 2004
Posts: 204
Likes: 16
From: Holly Springs NC
i have had alot of problems with my speed demon. Mainly float settings, and flooding. It shot fuel out of the top right out of the box. After taking it apart 3 times (twice b/c spare parts were left inside the carb 
) and having a carb. specialist take it apart and finally get the floats to stay set. It runs great now, but I was cussing barry grant for a while. I may still eventually switch to a double pumper, but for now the demon does fine.
) and having a carb. specialist take it apart and finally get the floats to stay set. It runs great now, but I was cussing barry grant for a while. I may still eventually switch to a double pumper, but for now the demon does fine.
Pro
Joined: Jun 2005
Posts: 660
Likes: 4
From: Fredericksburg VA
Quick Fuel with annular discharge it will atomize the fuel better in those longer runners. Idle quality is better and low-end torque is substantially higher. I have tried most carbs out there and this is by far the best route! Bar none! It is also fully tunable. That is my .02
Thread Starter
Burning Brakes
Joined: Sep 2005
Posts: 1,078
Likes: 0
From: Santee CA
Originally Posted by Little Mouse
Use a 750 cfm carb for that size engine and HP the 770 street
avenger holley or a vacuum secondary demon, if you are going
to race it a double pumper 750.
avenger holley or a vacuum secondary demon, if you are going
to race it a double pumper 750.
*IF* I race it, it'll be on the 1/8th mi. drags here once in a blue moon...But I probably won't. My dad keeps pushing for mechanical secondary, but I've been reading some stuff by Vizard that basically says we don't need a mechanical unless it's going to be full street/strip.
Cost wise, it looks like it'd be cheaper to go with the Holley, but previous posters have stated that the Demon carbs are underrated for the CFMs, whereas Holleys are overrated for CFM. So, maybe the Demons might be better? Or should I look at the Edelbrock Thunder Series, with that AVS?
Le Mans Master
Joined: Apr 2006
Posts: 5,403
Likes: 95
Originally Posted by Sprzout
*IF* I race it, it'll be on the 1/8th mi. drags here once in a blue moon...But I probably won't. My dad keeps pushing for mechanical secondary, but I've been reading some stuff by Vizard that basically says we don't need a mechanical unless it's going to be full street/strip.
Cost wise, it looks like it'd be cheaper to go with the Holley, but previous posters have stated that the Demon carbs are underrated for the CFMs, whereas Holleys are overrated for CFM. So, maybe the Demons might be better? Or should I look at the Edelbrock Thunder Series, with that AVS?
Cost wise, it looks like it'd be cheaper to go with the Holley, but previous posters have stated that the Demon carbs are underrated for the CFMs, whereas Holleys are overrated for CFM. So, maybe the Demons might be better? Or should I look at the Edelbrock Thunder Series, with that AVS?
Holley/Demon they both look like a copy of one another to me LOL.
Never had an edelbrock or Demon.
Safety Car
Joined: Mar 2002
Posts: 3,780
Likes: 442
From: Southwest MI
Originally Posted by Sprzout
*IF* I race it, it'll be on the 1/8th mi. drags here once in a blue moon...But I probably won't.......... basically says we don't need a mechanical unless it's going to be full street/strip......Cost wise, it looks like it'd be cheaper to go with the Holley......
in that case just pick up a Holley 780 Vac Sec..... very inexpensive, easy to tune to you setup (Sec spring and jets)
Last edited by 66427-450; Aug 21, 2006 at 09:56 AM.
Instructor
Joined: Dec 2004
Posts: 124
Likes: 0
From: Gainesville GA
On a combination like this you’ll be on the borderline between a 650 and 750. A 750 with Annular boosters will give you better top end performance, however a 650 will have a little better air velocity which should give you a little crisper throttle response, and acceleration. It really boils down to what you want out of the car, more throttle response low speed driving go smaller, more top end go bigger.
As far as vacuum secondary vs. mechanical secondary; usually you’ll find a vacuum secondary carburetor on cars with automatic transmissions with less than a 2800-RPM stall speed. You’ll find mechanical secondary carburetors on vehicles with manual transmission or automatics with 2800 RPM or higher Stall Speeds. The mechanical secondary will give better throttle control in these applications.
Technical Support,
Barry Grant, Inc.
As far as vacuum secondary vs. mechanical secondary; usually you’ll find a vacuum secondary carburetor on cars with automatic transmissions with less than a 2800-RPM stall speed. You’ll find mechanical secondary carburetors on vehicles with manual transmission or automatics with 2800 RPM or higher Stall Speeds. The mechanical secondary will give better throttle control in these applications.
Technical Support,
Barry Grant, Inc.
Racer
Joined: Mar 2000
Posts: 352
Likes: 0
From: Frisco, TX
I have run both the BG Speed Demon 850 and a Holley 850 and Holley HP1000 on my Big Blocks. The HP1000 worked the best for me. The tune was very close out of the box for my application, and I like the fact that I could change air bleeds.
The Demons are certainly more aesthetically pleasing than the Holleys, but there have been issues. I did not experience this with my Demon, but some people have reported leftover machining shavings in their brand new Demons. If you go the Demon route, it wouldn't hurt to pull apart and make sure that there are no nasty suprises waiting to enter you motor.
Having said all of that, I know of many people that love Demons and hate Holleys and also love Holleys and curse Demons wishing hateful things on Barry Grant. I think it all comes down double checking everything before you bolt it on and knowing how to properly tune a carb.
The Demons are certainly more aesthetically pleasing than the Holleys, but there have been issues. I did not experience this with my Demon, but some people have reported leftover machining shavings in their brand new Demons. If you go the Demon route, it wouldn't hurt to pull apart and make sure that there are no nasty suprises waiting to enter you motor.
Having said all of that, I know of many people that love Demons and hate Holleys and also love Holleys and curse Demons wishing hateful things on Barry Grant. I think it all comes down double checking everything before you bolt it on and knowing how to properly tune a carb.
Thread Starter
Burning Brakes
Joined: Sep 2005
Posts: 1,078
Likes: 0
From: Santee CA
Originally Posted by Doug S
On a combination like this you’ll be on the borderline between a 650 and 750. A 750 with Annular boosters will give you better top end performance, however a 650 will have a little better air velocity which should give you a little crisper throttle response, and acceleration. It really boils down to what you want out of the car, more throttle response low speed driving go smaller, more top end go bigger.
As far as vacuum secondary vs. mechanical secondary; usually you’ll find a vacuum secondary carburetor on cars with automatic transmissions with less than a 2800-RPM stall speed. You’ll find mechanical secondary carburetors on vehicles with manual transmission or automatics with 2800 RPM or higher Stall Speeds. The mechanical secondary will give better throttle control in these applications.
Technical Support,
Barry Grant, Inc.
As far as vacuum secondary vs. mechanical secondary; usually you’ll find a vacuum secondary carburetor on cars with automatic transmissions with less than a 2800-RPM stall speed. You’ll find mechanical secondary carburetors on vehicles with manual transmission or automatics with 2800 RPM or higher Stall Speeds. The mechanical secondary will give better throttle control in these applications.
Technical Support,
Barry Grant, Inc.