This story opens with a breakdown of the Demon line of carbs. It covers not only the cfm ratings of the streetable Demons but also explains the adjustability of the top-of-the-line Race Demon RS. The Race Demon carbs, with their removable main venturies, can, unlike any other carbs on the market, have the venturi size optimized to the application.

After showing the advanced tuning capability of the Demon carbs, Damon goes on to test to see if this actually translates into real performance.

The test engine used was a 454 big block Chevy crate motor originally rated at 425 hp. This low compression street power plant was treated to a good aftermarket two-plane manifold and a Comp Cams Extreme Energy 274H-10 cam. Replacing the stock 795 cfm Q-Jet with our 750 Speed Demon resulted in a 25 hp increase along with 11 lbs-ft more torque.

As good as this is, it was not all that Damon observed. His measurements of the air/fuel ratio during the tests showed very consistent air-to-fuel ratios along with good brake specific fuel consumption figures. This article confirmed why Demon carburetors deliver such good fuel consumption figures and sharp throttle response.
Engine Masters 2000
(For reprint information: Phone 714-939-2400)


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Cornucopia of Carburetion
Muscle Mustangs & Fast Fords - December 2000
by Richard Holdener
This was nothing short of a hot feature - but we have almost come to expect that of Richard Holdener.

In this story, Richard baselines a 392-inch Ford crate motor equipped with some of Air Flow Research’s hot 185 Ford heads and the 750 Holley carb recommended by Ford Racing.

From here he investigates the power delivered by 650, 750 and 850 Speed Demon carbs. The first on the dyno after baselining was the Speed Demon 650. Even though it replaced a carb rated at 100 cfm more, the 650 on this big inch motor still outpaced the competition.

When the Speed Demon 750 was installed the output of this 392-inch Ford increased further. The 750 was up by over 19 hp and 14 lbs-ft of torque! Next to ride the dyno was Speed Demon 850. The 850 made one hp less at peak, produced the same peak torque but allowed the motor to hang on better after peak power rpm.

The last carb tested was a King Demon RS. The replaceable venturi sleeves allowed Richard to test at both 795 and 1095 cfm. As we suspected, the King Demon proved marginally too large and output dropped slightly by just over 1%.
Muscle Mustangs & Fast Fords -- December 2000
(For reprint information: Phone 714-939-2400)


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Pulse Width Vs Power Valve
Muscle Mustangs & Fast Fords - December 2000
by Richard Holdener.
The volume of tests Richard Holdener does lead us to believe he lives in a dyno cell!

In a big two-part feature titled, “Pulse Width vs Power Valve” looked at the performance capabilities of fuel injection versus carburetion...our state of art carburetion, that is.

As Richard pointed out, a similar test a few years previously, done with some of our competitors carbs, showed superior results only at peak rpm where the carburetor’s greater airflow made the day.

But that was a few years ago, and not with Demon carbs. In this series of tests, Richard compares injection and carburetion on a 302 Mustang engine. The injection manifold was the excellent TFS ‘R’ intake, along with a big throttle body and mass airflow sensor. The carburetor was with our Speed Demon 650 cfm on an Edlebrock Victor Jr. manifold.

This was almost a ‘no contest’ deal. As you can see from the graph, the carbureted setup out-performed the EFI setup over the entire rpm range tested. Now think about this…Detroit replaced carbs with hi-tech injection and has spent hundreds of millions on its development.

We claim the Demons are state of art and with results like this; the claim is hardly an empty promise.
Muscle Mustangs & Fast Fords - December 2000
(For reprint information: Phone 714-939-2400)







[Modified by Alwyn678, 3:02 PM 1/9/2003]

 

I wouldn't doubt it. I've also heard that the flow (cfm) ratings aren't consistent between the different carb producers. And that Speed Demon are consistently higher than Holley and Edelbrock. So, for example and I can't remember the specifics, if you have a Holley 750 and a Speed Demon 750 the Holley is really closer to 700cfm whereas the SD is closer to 800cfm. So this may not necessarily prove that the SD is better but that you need a bigger Holley.
But that's just my opinion....I could be wrong. :lol:

 

Who did the test? That is all that needs to be said. Also nothing in the lower rpm ranges where a street engine operates.

 

There's a reason why Holleys and Demons are the most used carbs in Racing... For performance applications - I wouldn't even consider any other carb than a Holley (or Demon).. Well - Demons are the same basic design as the Holley - using higher quality pieces..

:cheers:

Olivier


[Modified by GrandSportC3, 3:19 PM 1/9/2003]

 

Exercising the Demon
Engine Masters 2000
by Damon Lee.
I am just passing along info

 

My question is what rod/jet combination is in the "stock 795 cfm QJet". I bet a little playing with the carb would put it on a par with the Demon. :) MJ

 

One thing I notice is the meager increase of about 10 HP in the usable power
range. That's 10 HP out of 400+ !! 2.5% power gain ? At what cost ?

I guess at some point, you take what ever you can get - 5 here 10 there.

I'm not sure if you were trying to illustrate the superiority of the Demon
carbs - but you've convinced me that the old Quadrajets are in good
company. I'd even go as far as to say that a good tuner could get the
10 HP back from the QJ - and maybe more.

I'm saving my money. My L48 only stands to gain about 0.78 HP with this mod. :rolleyes: :lol:

Those of you with kickin' motors may appreciate the gain more than me ... :steering: :seeya

 

On the street - it doesn't make too much difference.. but at the track 10HP can make the difference between winning an losing...

 

Olivier,

Exactly. That was my point. You need to go to the extremes for this to make
any difference - and even then you will need to fine tune it for maximum
return. Sometimes bolt-on gains aren't exactly 'bolt-on'.
:smash: :crazy: :smash:

 

im with you dave. i like demons, but i thought you would gain more than that. ill stick to my q-jet i get excellent throttle response, and good reliable power up to 6000. i guess you could say, im happy with it. :cheers:

 

I'd put a Lars-tuned QJet up against a Demon any day of the week!

Right, Lars? :cheers:

 

The Q-Jet is a awsome street carb.... There's a reason that you won't find a Q-jet in any serious performance application... I'm 100% sure that for example a well tuned 4779 Holley (750 mech. secondaries) will outperform a well tuned Q-jet for peak HP and torque...

:cheers:

Olivier

 

I also wonder why would people spend on high $ performance carbs if they could just get a used q-jet, rebuild it for a total of less than $100 and run the Q-jet...

:cheers:

Olivier

 

Actually Lars is a big Demon fan :yesnod: :D

 

Holley, demon are designed to be easily and quickly tailored at the track and have many variables. Q-jets actually have a greater number of variables but are not so easy to work on, especially at the track. A simple jet change to compensate for say the temerature or altitude can make a huge difference in performance. This is very easy on a Holley but not on a Q-jet. Also Holley and demon parts are everywhere but you cannot find the parts for Q-jets. Q-jets can be set-up to actually out-perform holley. Regardless of which carb you choose. it must be set-up for each patricular engine/car combination.

:)

 

I just checked on the price of a brand new Rochester Quadrajet at Friendly Chev and it listed at $778. I don't think the Speed Demon is all that bad of a deal at $440. I would rather have the 10 HP for 338 dollars less.

AC

 

There are alot of 9,10 and 11 seconds Super stockers and Stockers using Q-jets and other so called non performance carbs, they can be made to run with a little work and can be gotten cheap because a lot of people don't want them.
Ken :cheers:

 

Search the archives...there is a swap from the "correct" big Holley to a comparable sized Demon by Lars.

They gained 25 RWHP if I remember right. I just missed being there for the testing...

 

http://forums.corvetteforum.com/zerothread?id=170591

See link for the story I mentioned above.


Got the post in the right thread this time! :hurray:

 

you can go to edelbrock and get a quad for a little over $400. you can probably buy that Speed Demon carb from Friendly Chevrolet for about $800 also. regarding the test, if you fine tune that quad like they did that SD carb, the results would be darn close. a quadrajet will give you good performance and reliability day in and day out. you won't have to keep jacking with it, especially where the temps vary widely from season to season, like the midwest, just don't let gas sit in it when its not in use or keep Stabil in your fuel,true with any carb.