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Motochris 08-24-2012 12:53 PM

New Demon "Street Demon" 625cfm carb
Just thought I'de share my thoughts about this new carb since there seems to be little info on it out there so far. Demon Fuel Systems*-1900*-625 Street Demon - Ball Burnished Aluminum
I have a 59 Chevy Wagon w/ 350hp 350 SBC that had a Holley Street Avenger 670 on it. I went thru all the typical BS with trying to tune the stumble that carb is known to have. Ended up way rich on the primary jets, plus a good amount of tuning to the accel pump to get most of it away. It wasn't perfect by any means, but it was something you could deal with. Stomp on it and it was great.. the stumble was still there on light throttle regular driving however. The fuel milage sucked with the primary's as they were too.
I have had good luck with the Edelbrock carbs and drivability and was planning on going that direction, just never got around to it over that last year or two.
Soooo... I saw the ad for this new Street Demon 625 and it looked like it might fit the bill.. something more along the lines of the Edelbrock, but with smaller primarys so the fuel milage should be decent. You can look at the ads for the carb to see all the details.

Demon Fuel Systems*-1901*-625 Street Demon - Polymer with Ball Burnished Aluminum

Anyway, ordered one up with the composite fuel bowl (link above), as I live just outside Death Valley and we can see temps up to 120 occasionally. I had issues with heat soak on the Holley, so the plastic fuel bowl sounded like a good idea.

Here's the good with the carb so far.... The throttle response is nothing short of excellent. No matter what throttle setting, how light you roll into it, or how quickly you stomp on it, it does exactly what you would expect. After all the Holley issues and just living with some of them... the throttle response of the new carb is a breath of fresh air. Milage has increased as hoped (from 12mpg to 15mpg) thus far. Overall performance is very good... in fact, it may be better than the Holly was. The car seems to go thru the gears quicker... but that could be wishful thinking. I have ZERO complaints about how the carb performs in any instance.
I've had no issues with heat soak at all, and we've had a week or so in the 115 degree area. The Holley would be hard to start when hot, this carb, no issues.
Lots of easy adjustability. I like how easy it is to tune how quickly/slowly the air door for the secondaries can be tuned. I'm a fan of metering rods and did swap out the factory ones for a set with the initial section one step richer.

Here's the annoyances thus far... The ads show that the carb is all setup for different Chevy trans kickdowns from the factory... T350/400, or 200/700r4 areas for hookup. That was great and needed....BUT when I got the carb and went to install, that's when I discovered that if you have a Chevy throttle linkage, you need an optional part. First time I've had a carb that didn't have the big hole for a Chevy throttle. That alone sucked, as I had planned on having it usable that same day, and that wasn't going to happen. (seems stupid to set it up for Chevy trans but not throttle)
So I hooked everything else up... and then went to put the air cleaner on and dicovered it wouldn't fit. The elec. choke sits very high on the side of the carb and the regular reliefs in a low rise air filter base wouldn't work. I noticed then that Demon sells an air cleaner just for this carb and it's goofy choke position.I ended up ordering a 1/2" air cleaner spacer to fix the problem and still use my same filter.
The linkage location on the throttle with the optional Chevy throttle part was far enough away from the Holley location that I had to buy some additional threaded stock for my adjustable linkage to get it to fit correctly.
Let's see..what else.... Oh yea... the fast idle adjustment for the choke is accessed thru a hole in the back of the choke, facing the firewall. It's about impossible to adjust without a mirror.
The linkage to the choke plate is in the way of removing the metering rods on one side of the carb, so you have to remove a TINY E-clip to move the linkage. It's so small and right at the carb opening that it's scary to remove. I made sure to have a magnet right at the area it was..just in case.

I think that covers my initial impressions. Main thing I would like to see changed is for the carb to come with the Chevy throttle linkage hookup....or at least somehow make sure any ads show that it is needed.
Got any questions that I can answer.. fire away.

Jim Rockford 10-07-2012 12:59 PM

Thanks, been waiting for Normal folks to review this carb, I don't trust TV shows and magazine storys on products..

Motochris 10-09-2012 03:42 PM

Still diggin' it.
I did have the clip to the accel. pump linkage fall off and it was a PIA to put it back on... The clips are super small. Thank god for magnets. :)

ap72 10-09-2012 03:46 PM


Originally Posted by Motochris (Post 1597640)
Still diggin' it.
I did have the clip to the accel. pump linkage fall off and it was a PIA to put it back on... The clips are super small. Thank god for magnets. :)

Did you try the carb with the stock rods in it? With the heat of your area if anything I would expect you to go one step leaner than stock.

Motochris 10-09-2012 03:50 PM


Originally Posted by ap72 (Post 1597644)
Did you try the carb with the stock rods in it? With the heat of your area if anything I would expect you to go one step leaner than stock.

Yea, and I'll most likely go back to them.
I noticed a small temp increase after the carb swap so I thought it may be a lean condition. Turns out the temp sensor is jacked up and when changing the carb I hit it and it started reading goofy.

xxllmm4 10-09-2012 07:03 PM

Thanks for the review, sounds like a great carb for the price. Anyone know if they plan on making some bigger versions?

V305 10-10-2012 12:04 AM


Originally Posted by xxllmm4 (Post 1597723)
Thanks for the review, sounds like a great carb for the price. Anyone know if they plan on making some bigger versions?

Maybe they are waiting for customer response, I was hypnotized by this carb, maybe next time I need a carb this will be the one, I was already thinking in fixing a Qjet for my car, but the thing about this carb is that you don't need to swap the intake if you have a square bore intake

abyars 02-26-2014 09:50 AM

Is it still working great for you?

Does anyone have anymore reviews of this carb?

yellow88monte 04-10-2015 02:54 PM

my experience with the new 625 Street Demon
For everyone who has questions about the performance of the new 625 street demon I hope this report helps others make a better informed decision about their carb purchases.
I put the new 625 street demon with polymer fuel bowl on my '88 Monte Carlo a year ago and like it. Here are my specs:
355 sbc, vortec heads, 9.4 comp.ratio, comp cams xe 262 flat tappet cam, performer rpm air gap intake, 200r4 trans, 3.73 gears, Hooker 1 5/8 super comp headers with x-pipe/ 2 1/2" exhaust, dual flowmasters.
The 625 street demon was pretty close out of the box and I had no issures with setting the idle etc. On the chassis dyno I got 292 rwhp and 312 ft. lbs. torque. A/F with stock metering rods was steady at 13:1 all the way from 3500 to 6000 rpm. Initially, there was a bad bogging situation when I floored the gas pedal from 50 mph but was easy to remedy with tightening the screw/nut assembly for the secondary air valve door so it wouldn't open so quickly. The throttle response is incredibly good at any rpm.
My only question is...did I leave performance on the table by trading mid and upper range performance for great throttle response due to the smallish 1 3/8 triple stack primary venturis? I wonder if I would be happier with a 625 road demon jr, Quick Fuel 650 SS or 650 Speed Demon (all with vacuum secondaries).
Any input from experienced carb guys would be appreciated. Have fun everyone.

BuzzLOL 04-10-2015 03:05 PM


Originally Posted by yellow88monte (Post 3069922)
I put the new 625 street demon with polymer fuel bowl on my '88 Monte Carlo. On the chassis dyno I got 292 rwhp and 312 ft. lbs. torque. did I leave performance on the table by trading mid and upper range performance for great throttle response I wonder if I would be happier with a 650

. From the power you're getting, looks like the engine might like a little bigger carb... the time to ask was when it was on the dyno... check to see if about 1/2" of vacuum at WOT full RPMs... or the vacuum was significantly higher because the carb. was an airflow restriction...

eric32 04-11-2015 08:54 AM

From my experience with edelbrock carbs which is very close to that street demon by going over to a holley has always given me better results overall and still being in the same cfm range give or take about 25 cfm.

The street demon like an edelbrock or a quadrajet has smaller primary bores and will always give better signal in city driving compared to a square bore holley.

Bottom line flow is flow and the engine will take what it wants as far as power overall. I have just liked the better overall performance of a holley style carb compared to others. If it runs good and your happy with it just run it and enjoy it. I stopped trying to do this and that with mine a few years ago and now just enjoy it and take it for a ride and not worry about every last detail. Its matched good and runs good and performs good and I enjoy my rides for what they are.

My mild 350 is similar to your build but with just a little more cam and head size but I run a plain old holley 600 vacuum secondary and for a short time ran a quick fuel 680 vacuum secondary and get 19mpg on my setups and they run and have a very snappy throttle response. As far as power at the top end of things going to a bigger say 650cfm carb really won't make much of a difference. If you go with a classic 750 cfm vacuum secondary holley style carb then it might make more on the top end but your talking less then 10 horsepower at the most.

That's why I use a 650 ish range on both of my 350 builds. Don't buy a new carb if you really don't have too and if your happy with how it runs but do what makes you happy and what will satisfy you the most for your build. That's the nice thing to hotrodding as you always have options :)

JohnTN 04-11-2015 09:33 PM

I just put a 625 cfm Street Demon on my mild Olds 350 with 2004R transmission, 3:42 rear gear to replace a 10 year old remanufactured QJet. The QJet gave good service an averaged 18 mpg over 25,000 miles until last fall when it started flooding at startup and leaking at the air horn gasket.

The SD has better throttle response and snappier when blipping the throttle. Also, starts reliably. But I have had two issues which may be sorted out.

1. The secondary opening seemed to have a "catch" in it initially. Felt like the secondary throttle blades were sticking and it took noticieable extra foot pressure on the throttle pedal to get through this resistance (more than just the extra spring resistance on the secondary throttle shaft). This significantly affected driveability of the car. Now after about 400 miles on the carb this catch seems to have gone away, maybe whatever was hanging up has "wore in".

2. I have a leak at the filler tube to my gas tank so I can't fill the tank above 3/4 full. So my estimate of fuel mileage is just that - an estimate. On the first 160 trip on secondary highways and interstate I estimated I got 14-15 mpg versus 18 or so I would have gotten on the QJet. After that drive, I changed the primary metering rods from stock to one step leaner. On a 155 mile drive last weekend, all on state highways, I estimate I got 19 mpg. Hard to believe one step leaner in metering rods would make this big a difference. My method of estimating is based on the gas gauge moving from 1/8 of scale to 3/4 scale when I added 10 gallons of gas before the trip. After 155 miles the gauge had only dropped back to 1/4 of scale. So, I used less than 10 gallons and estimated the mileage assuming I burned 8 gallons.

If the secondary sticking problem has gone away and I can get fuel mileage similar to the QJet then I will be very happy with the change. Like I said, I think the car is more responsive now. And the secondaries opening do have a nice sound similar to the howl of the QJet.

Would like to hear any feed back from others who have tried the Street Demon.


yellow88monte 04-12-2015 12:41 AM

Thanks everyone for your advice and point of views.
Thanks to everyone for the feedback to my first post on here. You guys rock.

yellow88monte 04-12-2015 08:17 AM

To JohnTN
I just wanted to add that on the dyno my Monte with the 625 street demon registered 12.5-1 AFR at cruising speed. Ideally, I'd like to see that number at 13.5-1 AFR. I have since played with a leaner setting with my primary fuel rods and richened up the rear holley style jets in the secondaries to achieve closer to a 12-1 AFR at WOT. I'll post again when I get it back on the dyno to check my power numbers after removing the choke butterfly on the primaries.
I checked the gas mileage on my last trip and registered about 16 mpg. But you must remember that I have 3.73 gears, 200r4 trans., edelbrock performer rpm air gap, headers, dual exhaust, etc. so there is quite the volume of air moving around that the motor must be happy with too.
Like most older cars, there probably are other improvements where money would be better spent than my carb. Such as replacing my bench seat with bucket seats to improve the general "feel" of driving. As I drive my family car, I'm spoiled at how nice the form fitting seats are and I would feel safer if I didn't feel like I had to lean into the corners etc... lol
Thanks again everyone for the advice.

JohnTN 04-12-2015 10:27 AM


Do you have any fuel mileage data before installing the Street Demon?


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