Holley Street Demon Carbs

[slant6billy]

So Anybody running one of these on a mild 318? It's only 625 cfm, but I'm thinking the bottom end torque is probably right where it needs to be. The othe size is 750 which might be too darn big for any mild small block.

The foot print looks a lot like a Thermoquad

https://www.holley.com/products/fuel_systems/carburetors/demon/street_demon/parts/1900

 

[Aspen500]

Unless it's a "built" small block, the 750 would be way to much carb. No experience with the carbs themselves. Had experience with "Brand E" in their chart and,,,,,,,,,,,,,,never again. Not impressed at all.

 

[89.Fifth]

They're just fine on 318s. They were designed and built as an updated and friendlier Thermoquad and even use the phenolic bowls. If you take them apart and compare them you'll start to see the similarities right away. I want one but I'm tempted to sink the money into EFI instead.

 

[got job]

That's what I run on the wagon. Two years plus, no problems and was great right out of the box. Mine is on a 340, mild build and is perfect. This is actually a three barrel and comes with a thin plate that has to be used and will space the carb above the divider in the intake to allow the secondary to operate correctly.

 

[SirRalliart]

I use the old adage, CID x 2 = CFM. Seems to work, my stroker LA is 426" x 2 = 850 CFM, and I run a Thunder AVS @ 800 CFM. I'm probably a little low on that one. Then again, on the Kit Car E58, I have the Street Demon @ 750 CFM, and I think it's over-carbed. Oh well, maybe someday I'll make the switch to the fuel injection.

 

[mirada80]

I put one on my 360 Mirada, tuned real well right out of the box, couple thousand miles no complaints

 

[MBDale]

Was going to run a 670 Street Avenger on my 9.5-1 compression, 2.02 J-head 360, but my engine builder claimed it be too small. Ended up running a 780 Quick Fuel Hot Rod series. Awesome carb, also jetted up the primaries one step and the plugs looked good on the dyno.

 

[MoparKidD-4]

I bought a brand new 750 Street Demon for the built 360 (now deceased and in pieces) in my '70 Duster, it ran great for me and was pretty straightforward to tune although I think it was a tad big; these carbs are made to mount on square-bore intakes so they can only make the secondaries so big, the 750 has bigger primaries for the extra airflow. The only thing I HATE is in order to change the jets you need to remove the carb from the intake entirely and make sure it's empty so you can take out the main screws from the bottom, kind of like a Holley but more stupid... You can swap the metering rods just like a Carter/Edelbrock though and there are quite a few sizes available from Holley/Demon (same thing now).

The 625 cfm version should run really nice on a mild 318, I would highly recommend tuning it though. OOTB jetting is pretty rich, depending on your elevation and the stock jet size it might be worth it to change jets before you install the carb to spare the hassle. And check for debris inside if it's brand new.

 

[Camtron]

Ever pull the trigger on this? I have the 625cfm demon and a Edelbrock intake sitting in my garage. Haven’t got around to installing them on my 89 Fifth Avenue. Did you have you change your throttle/kick down linkage at all?

 

[89.Fifth]

Here's a calculator that will give you actual numbers instead of using old rules of thumb.
Air Flow (CFM) | Widman International SRL

What you'll see is that even at 5000 RPM a 318 barely needs 370cfm of flow. Even the old 2bbl can just about support that.

On my car I have a 1406 Edelbrock which is 625 CFM and that's plenty but I wish it was a 500cfm. What really helps these engines isn't air flow but air speed. You want long skinny runners building lots of low end torque and swirl, especially on the later style heads.

Now if you're running a 3.55 gear and have a big lumpy cam that's a different story, but for most of us the smaller the carb the better.

I've never run the old style Demons but I hear they're good. Again I would get a 500 if I could. Personally my next carb attempt is a TQ because of those tiny tiny primaries. Ideally it would have 2 tiny primaries and two slightly larger ones so that I could get the best of both, air speed down low and extra flow (but not too much) up high.

Also my 1406 ran a bit lean from the factory so I jetted up until the plugs looked better and I got a little less ping.

 

[Camtron]

So, I pulled the trigger on a Demon 1901 carb at 625cfm. Complimented it with Lokar throttle and kickdown cables and billet mounting bracket, Edelbrock performer intake, summit racing long tube headers and a custom duel exhaust with Bassani X pipe...no regrets. Leaned down the idle mix a little but, the carb itself was solid out of the box otherwise. Leaves room to grow once I can afford cam, piston, head/valve work too.

 

[slant6billy]

Nice. Gator had one on his built 340 in the orange 78 roadrunner, but it was the bigger Street demon - 750. It was fine, but the 340 was a little more thirsty and a Holley now sits on it

 

[89.Fifth]

So, I pulled the trigger on a Demon 1901 carb at 625cfm. Complimented it with Lokar throttle and kickdown cables and billet mounting bracket, Edelbrock performer intake, summit racing long tube headers and a custom duel exhaust with Bassani X pipe...no regrets. Leaned down the idle mix a little but, the carb itself was solid out of the box otherwise. Leaves room to grow once I can afford cam, piston, head/valve work too.

How's the idle quality and throttle response?

 

[Camtron]

Idles solid at 550 on the timing light, strong vacuum a hair over 18in, was a little rich at idle out of the box, no big deal. Throttle is responsive throughout full RPM range, can really feel when the secondaries pull enough vacuum to open. Overall great improvement vs stock intake, 2 barrel and exhaust manifolds.