[Chris-Austria]

Hi,

What's the difference between the Road and the Speed Demon carb?
I'm planning to use one of these with 850cfm, mechanical sec., e-choke and not sure if annular or downleg boosters.

Are there any disadvantages over a Holley DP? Don't know if they offer the same quality.
Also not sure, if I really want annular boosters.. some say they perform better overall, otherwise they are not very common I guess.

Car is a 66 GTO, 462cui, E heads, HR cam, Performer RPM manifold, HEI, 4-speed, 3.55 rear.
(intended for street and strip use)

Chris

[Tom Vaught]

There is a guy on the PY Board with a early (66 I believe) GTO like yours (MIKE DAVIS) that had very good luck with a Demon Carb. Course he played with it a lot to get it to run like it did. So it is possible to have it perform properly. He has a recent post in the Race Section. PM Him.

Most like myself and Skip Fix have had Demon Carbs what had metal particles in the carbs that were never cleaned out. Poor Final Quality Control (but Barry Grant is gone) so can't hurt him with the truth.

The Holley Carbs usually had much better Quality Control and better calibrations.

For years the BG stuff had calibrations that had circuit drillings with-in .001" of the Valid Holley Calibrations. But Holley waited until a lot of the BG carbs were built and then went to court.
In the end killed both companys.

BG bankrupt once, Holley I think two or three times after going south and basically spun off from Holley-OEM/Borg Warner.

As far as the Annular Boosters go the drive might be slightly better with the Annular stuff if you had a large camshaft with minimal signal to the metering blocks from the boosters.

But Pontiacs are not SB Chebbiesm and the engines usually have enough signal even with good performance cams to make down leg boosters work just fine.

Hope that helps.

Tom V.

[Skip Fix]

My Demon actually had no metal(my Holley 850DP did) and my Demon has performed flawlessly. I think it was before they started having quality issues. It does go a little rich on cruise as rpm increases probably a main bleed on my 78's 455 the Holley is more flat on AFR . Demon is going on my 500" IA motor as it made 695 hp on it. Has down leg boosters. Even being an 850 it take richer jetting than the Holley 850.

[Chris-Austria]

Thanks, thats information I couldn't find on the webpage.
I guess the 850 Demon is enough carb for my application.
Still wondering why jets are 6 sizes smaller even with more cfm than before?

Do you think I should remove the bowls and check the metering blocks etc. like many guys did some years ago before Holley took over? Maybe even use some larger jets from the beginning?

[surfsama]

Just to add a little more information to the discussion.

Not all 950s are the same.

A "classic" 950HP uses the 750 body while the "street HP" 950 uses a larger 850 body.

- 950HP CFM Classic 0-80496-1
1.375" venturi x 1.750" butterfly

- 950 CFM Street HP 0-82951
1.563" venturi x 1.750" butterfly

[shaker455]

Originally Posted by Chris-Austria

Do you think I should remove the bowls and check the metering blocks etc. like many guys did some years ago before Holley took over? Maybe even use some larger jets from the beginning?

No,
Holley has owed Demon for years now as they did Quick Fuel so quality will be p to Holley standard ,
Invest in a wideband to help narrow your jetting to your needs

[Chris-Austria]

I changed the configuration and now use the port on the back of the RPM manifold for the power brakes and connected PCV on the back of the carb.

Drove the GTO today with my AFR meter. Idle now is very good, at about 13.5 to 14:1 and 800rpm.

Cruising with low rpm's create about 13.5:1 but higher rpm's will make it run a little too rich.. up to about 12.5:1.
At the moment when I suddenly increase rpm's it will get lean for a moment (up to 15:1) no matter if it's at low rpm or higher rpm's to WOT. WOT will show 12:1 after the short lean condition.

I need to do some adjustment but it ran pretty nice even with this AFR and the short lean conditions.
I'll change the power valve from 6.5 to 7.5 or 8.5 and maybe use smaller jets. If the power valve won't solve the lean condition I may change the pump nozzles to a bigger size.

[Tom Vaught]

Thanks for the correction, Skip.
Thought I read that on one of the other Forums on the web. Got the Demon and the Holley mixed up apparently.

[Skip Fix]

Holley just has some stuck to the blue metering block gasket and not in the bowls like some Demons did later on. I figure I just got lucky with that Demon. Holley is on the 78 car now and runs flawlessly also . Had to go a step leaner on jetting from factory and moved the 50cc pump up front.

Bought a cheap Demon 850 refurb from Summit had Jeff(Shaker 455) machine for removable venturis and interchangeable boosters. Tried it with the largest venturis and downlegs on the IA and no difference in HP than the standard 850 so the standard will stay on the motor when it goes in the Camaro soon.

[Chris-Austria]

Thanks for the replies.

Are the new Demons better? (quality control?)
I think the 850cfm electric choke, mechanical sec., annular Speed Demon is a pretty new model?

At the moment I use a 750cfm Holley UDP... I think because of the dual plane manifold it could benefit from a larger carb.. there is also the 850cfm Holley UDP.

Engine makes about 15"HG at idle, cam is 224/230 @ .05.
@Tom
Thats not a large cam for a 462, so you think there might be no real benefit if I use the annular boosters? The Demon is the same price, annular or downleg... Holley only comes with downleg.

You can find many negative opinions on the Demon, but they all talk about carbs from lets say 1995 to 2010. I wonder if there is a quality difference between a 2017 Holley and Demon.

[Chris-Austria]

Thats good to know.
I have already used a wideband for my Holley carb, it was almost perfect out of the box. I wanted it to run a little richer on the primary side so I used 74 jets instead of 72 (about 13.2:1 AFR). At WOT it's in the 12-12.5:1 range and idle is 13.5:1.

Does the Demon also use these small filters in the bowls like Holley?
I have a 40 microns filter after the fuel pump and I'm not sure if I need these small filter or if it would be better not to use them.

[Tom Vaught]

Because Holley has owned the Demon and BG other Carb brand name carbs for several years now, if you buy a 2017 Demon you are getting a Holley Carb. Same deal if you buy a Quick Fuel Carb, again owned by Holley Carb.

The Quality is going to be the same.

As far as the Boosters go the Annular Boosters buy you nothing with a Ram Air 3 224/230 duration type camshaft. Carb signal is great with that camshaft.

Tom V.

[Chris-Austria]

Can I be sure that a new carb like this is build within the last years, so it won't have quality issues?
https://www.holley.com/products/fuel...rts/SPD-850-AN

If there is no disadvantage over a downleg I guess I'd rather use the annular, so I don't have to worry about carbs if I ever change to a larger cam.

I have a jet assortment from Holley, far as I know a Demon uses the same parts?
I probably will have to change jets (68/74 are used in the carb from the link) and in my 750cfm Holley DP I have 74/80 (tested with an AFR meter, they work great.. 13.2:1 at part throttle and 12:1 at WOT).

Because they use rather small jets in such a big carb with annular boosters, I have to think that they require less jet size. Is that true? I thought more cfm carbs might need bigger jet sizes, but I'm not a carb expert...

[Chris-Austria]

Do you think 40 microns is okay as well or should I change to 10?
Whats the micron rating of the stock Holley filters?

I don't have the wideband at the moment.. do you think there is a chance that the new 850cfm is on the lean side on an engine like mine (out of the box)? If so I may not install the new carb until I get the wideband.

[Tom Vaught]

I would not pay too much attention to a dyno article. Work with the A/F meter and let the carb tell you what it wants. No engine is EVER the same as a second engine.

You will lose about 20 cfm from your carb using annular boosters. Bigger part blocks more airflow but higher fuel signal.

Tom V.

[steve25]

You do not need the Annular boosters with that Cam, its overlap and your amount of cid .

[shaker455]

Originally Posted by Chris-Austria

Hi,

What's the difference between the Road and the Speed Demon carb?
I'm planning to use one of these with 850cfm, mechanical sec., e-choke and not sure if annular or downleg boosters.

Are there any disadvantages over a Holley DP? Don't know if they offer the same quality.
Also not sure, if I really want annular boosters.. some say they perform better overall, otherwise they are not very common I guess.

Car is a 66 GTO, 462cui, E heads, HR cam, Performer RPM manifold, HEI, 4-speed, 3.55 rear.
(intended for street and strip use)

Chris

Chris,
If your buying a new Demon you should be fine as Holley cleaned up Demon's quality mess.
And yes most parts are common, jets, PV's, gaskets
I like downleg boosters as they are small and do no take up cfm
Annulars are very hard to beat but for most part you should be fine with the annular
Jeff

[Skip Fix]

FWIW buddy with a 500" 383 Mopar dialed in it better AFR with annulars.

[Chris-Austria]

Holley 750cfm downleg with choke:

Primary Main Jet 74
Primary Power Valve 6.5
Primary Pump Nozzle Size 28
Secondary Main Jet 80
Secondary Pump Nozzle Size 31

Speed Demon 850cfm annular with choke:

High Speed Air Bleed 36
Idle Air Bleed Size 70
Primary Main Jet 68
Primary Power Valve 6.5
Primary Pump Nozzle Size 31
Secondary Main Jet 74
Secondary Pump Nozzle Size 31


I don't have more information. The Holley with these specs runs on the rich side on my engine.
The second one is the new carb, there is a larger Primary Pump Nozzle, but jetting is 6 numbers lower on the primary and the secondary side. But it's an annular booster carb instead of the downleg. Both don't have a secondary power valve,

[Chris-Austria]

That's very interesting, thanks. So i just have to ask when the carb was build, when I place an order.

I may not need the annular boosters, but if they don't hurt (except 20cfms) I tend to use them.

In gerneral, do you think a 850cfm carb (or lets say 830cfm) is a good size for my engine with the dual plane intake? On the strip I shift at about 5800rpm, redline for me is 6000 (it won't make more power at this point).