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Old 09-25-2003, 10:04 AM   #1 (permalink)
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Comparing Holley to Demon carb

I have 2 carbs on the bench. A Holley 750 and Speed Demon 750. Both are mech sec.. Here is the differences that I notice at first glance:

The Demon has 4 corner idle adjustment mixture screws. The Holley is only adjustable on the front.
The Holley mainbody and metering blocks are cast and rough and come with straight boosters. The Demon are billet with precise machining, smoother surfaces and use downleg boosters.
Demon has a billet baseplate with a secondary throttle plate adjustment screw just like the primaries. The Holley has a cast baselate with a secondary throttle plate adjustment that is hard to see and hard to get to (especially when on the engine).
The Demon throttle shafts use steel buttonhead screws for the plates and the levers are bolted with locknuts. Holley plates are attached with plain brass screws and the levers are attached by mushrooming the shaft ends.
The Demon metering block is a work of art. It has the same circuitry as the Holley, but that is where the similarities end. It has 3 stage emulsion and all circuits are precision machined. The Holley is rough cast and only uses 2 stage emulsion. All gaskets seen to interchange.
Holley fuel bowl has a screw in bass plug, Demon has a larger cc bowl and a screw in sight glass.
Rebuild and adjustments are the same. Holley comes with paper gaskets, Demon has all non stick teflon gaskets.

It's almost like comparing stock cast iron heads to AFR CNC heads.

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1966 Mustang, Custom glass hood, 331 stroker, 5.4 H-beams, Probe pistons, TrickFlow heads, ported Stealth 8020, XER solid roller, Holley 750 HP, Hedmans, 4spd, 9"/3.50, BFG DRs

"11.86 @ 116 N/A everyday driver"

[ This Message was edited by: bluestreek on 9/25/03 10:13pm ]
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Old 09-25-2003, 10:23 AM   #2 (permalink)
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Comparing Holley to Demon carb

If you want the 'good' stuff out of the Holley line, you'll be spending over $600 for their 'HP' line.

I used a 750 Speed Demon on my car and it worked just fine. It ran EXACTLY the same ET as the modified 650 double pumper than came off the engine. The 650 came from Fuel Curve Engineeering, and has stock primaries and full race secondaries... and was done back in the late 80's or very early 90's.

I was able to pick up (steal) a Holley 950HP from the guy I auctioned a bunch of parts for on ebay this summer. He wanted $450, but I didn't need the carb. He needed money fast, so he offered it for $300.... so it looks like we'll have another carb to test! The 950HP does not actually flow 950cfm. Flow-wise, it's just a 750 sized main body with downleg boosters bolted to a 850 sized baseplate with the airflow path all smoothed out. It also has screw-in air bleeds, and probably has a few tweaks inside. It will be fun to play with. It might be a little big for my 306, but we'll try it out and see what it does. At least the car is a 4-speed that gets launched WFO. Maybe the engine will have to grow into the carb... A stroker 351W sure would be nice between the fenders one of these days.

Good Luck!
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Old 09-25-2003, 10:25 AM   #3 (permalink)
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Comparing Holley to Demon carb

I compared my Road Demon 625 to my Holley 650 Double pumper. Other than the obvious of a vacuum secondary to mechanical, I like the Demon way better. Even with it giving me fits for tuning it (ie needing way bigger jets than I would have considered in the Holley), I'd rather work on it than the Holley.

The only thing I didn't like about the Demon was the "so-called" non stick gaskets. They ripped the first time I took off the float bowls. Only the metering block gaskets stayed perfect. I ended up using the holley blue gaskets that I've used before (re-useable) and haven't had a problem since.
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Old 09-25-2003, 10:54 AM   #4 (permalink)
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Comparing Holley to Demon carb

My 750 Speed Demon needed jetted up quite a bit as well. It needed jetted up several sizes from what came from the factory to get the best ET's.... jets that seemed larger than what would be required with the equivalent Holley. Hmmm... It runs fine though.
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Old 09-25-2003, 11:15 AM   #5 (permalink)
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Comparing Holley to Demon carb

OK, here is what I've noticed about the Speed Demons. The main air bleeds are larger than Holley for some reason. This coupled with the 3 stage emulsion tubes, would allow more air to be mixed with the fuel and maybe call for larger jets. I haven't had a chance to look at any Road Demons.
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Old 09-25-2003, 12:59 PM   #6 (permalink)
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Comparing Holley to Demon carb

I can not help but comment on "Bluestreeks" attempted accurate comparison between the two types of carburetors, Holley and Demon.

First off you need to compare both brands with similar models, IE HP750 and Demon's Speed Demon, not the #4777 650DP, #4779 750DP, or #3310 750VS with the 750 Speed Demon.

What clued me into thinking you compared a 650 Holley or 750 Vacuum Secondary to the Holley 750DP is because those two Holley's don't come with down-leg boosters, only straight-legs. If this was even close of a comparison it would have been a Holley 750DP or a HP 750DP which does incorporate a down-leg boosters. On occasion the 750DPs due come with 2-corner idle but this characteristic is always found on the 650DP and 750 Vacuum along with straight-leg boosters.

Something I bet you didn't catch either is that the Demon does have a superior down-leg booster over the HP version because of it's double cut design, veiwed from underneath the carburetor. This provides a better fuel sheer or fuel atomization as most understand it, then the Holley HP version. Another awesome feature of the Demon is their changeable booster design, which allows booster changes all day long as per calibration, not performed at a novice level with Holleys.

With respect to Demon's external air-bleeds being larger, they are not. A 0.026" orifice, for example, is uniform among both brands if calibrated as such, it's just Demon's is recessed and Holley's isn't. The non HP versions of Holley do include press in air bleeds and are difficult to adjust without steady drilling, but can be easily converted with a 10/32 threaded tap. I'll give that one to Demon for out-fitting all of their carbs with this feature.

But the irony of it all is a too much information could be deadly because now you have adjustability that only a dyno enviroment should see from experienced hands. Sure you can tweak those air-bleeds at the track, and Demon frequently incourages their customers to do so, but how could one read the A/F spikes or dips within a certain RPM band, that's very important to know. But Demon must feel comfortable in taking that sort of liability, I know I am not.

Now the Demon does have externally adjustable secondary opening and Holley doesn't out of the box, but you can retrofit it with the modification for under $10.00 which allows track-side adjustment. But the good thing about it is once it's adjusted, Holley or Demon you shouldn't have to mess with it again.

As far as gaskets go, well that all depends on the material used. Demon's come with one type of gasket material which always tears when over-torqued, the same as Holley does on their blue gaskets. Now the HP version doesn't come with paper, only the 4779 and 4777 (just two examples). There is only one gasket I have used, and I still use to this day, and that's the green viton coated version from our supplier, hands down the best gasket in town. I would bet money that BIGS uses this component as well as we do. Those Holley Blue and BG Red (hmmm a little color theme going there? )normally always...I mean always rip when over-torqued. The Viton greens do not, and we run alcohol throught them. Funny thing is they work for both Holley and Demon as well.

Now what I was trying to point out on my comparisons is that you need to compare like items, such as a Z-71 Chevy to a 4X4 Ford, not a Dodge Viper to a Ford Focus. That's just not accurate, it's misleading.

Now this is my opinion.....I think Demon out of the box are great carburetors in comparison to the HP Holleys. They require alot more tuning because of the blanket calibrated fuel curve they're delivered with out of the box, but when in the right hands they can really perform once manipulated. I have seen more box HP Holley's run clean out of the box "on the track" then Demons.

With respect to custom built carburetors, I could make either one better than the other, or even both run the same. Now it's also my experience that the Demon flows a cleaner more consistent fuel curve then the Holley only because of the billet metering design.

All in all....they aren't much different, and their isn't much contrast in price between the Speed Demon 750 and Holley HP.

I hope this sheds some light to the topic. I could care less which brand someone likes, I sell them both and I can tweak both to perfection.
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Old 09-25-2003, 03:28 PM   #7 (permalink)
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Comparing Holley to Demon carb

Good call!! After further investigation, I found out that the 750 is a 3310 that was professionaly converted to a DP. That's the reason for the straight leg boosters. The Speed Demons are a lot cheaper than the Holley HP series. That's why I didn't compare the HP. I own a 750 and 950 HP also and they are nice carbs compared to the standard Holley. I still say the overall fit and finish is a lot better on the Demons.

Thanks for posting your expertise TPC!
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Old 09-25-2003, 03:54 PM   #8 (permalink)
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Comparing Holley to Demon carb

Actually, the Speed Demon is around the $400 price range, and is in competition more with the standard double pumpers.

The Mighty Demon and Race Demon are the ones that would be compared to the HP series Holleys.

Personally, I'd choose a Speed Demon over a standard double pumper. (many double pumpers are still sold with generic straight leg boosters and a bunch of plastic parts) I'd probably choose a HP Holley over a Speed Demon. I don't have a lot of experience with the Mighty and Race Demons, so I can't really give a valid comment on those.

Holley's 'generic' #1850 and #3310 vacuum secondary 600 and 750 carbs would be better compared to Demon's cheapest linup. Actually, I'd use about any other carb before one of those from Holley's generic line. Edelbrock makes an excellent street carb.

Good Luck!
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http://www.mustangworks.com/cgi-bin/moi-display.cgi?220
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