I can't believe this. I took my 67 Camaro 350 Double hump 2.02 462's/ with radical cam (.550 lift), to a very well known speed shop, and asked them to install and tune on the dyno a Demon Carb... that is all they use: Demons. Like an idiot, I thought they would be the experts, not me. Just found out after getting the car home, they installed a speed demon 850cfm!!! That can't be right. The Demon site recommends a 650. I'm calling them in the morning when they open, but I'm sitting here wondering if it is ME that is off base or wrong. They are the experts. I also realize they dyno'd/tuned it with the air filter not installed. I don't think that is a good idea either. As to how it runs... idles great, monster above 4000 rpm, stumbles all the time off idle up to 2000 rpm.

They probably only had an 850 in stock :rolleyes:

How did you determine they installed an 850 anyways?

Demon carbs are not easy to identify imho... but you take off the cleaner on the Speed Demon, and on the back side within the "ring" supporting the air cleaner, was the number 8... that is all, btw, just one number. LOL.

Just got off the phone with the shop... I took a deep breath before calling them, and told myself to both calm down, and initially treat the shop as the experts they are known to be in this area. Old age does teach you a few lessons.

The shop owner said they will use the 850 on built engines... I DO have a very aggressive cam, purported by the the previous owner as .550 lift. Don't have the specs off it, because the gentleman I bought the poor car from was a COMPLETE CAR MORON. LOL. But it idles and roars in the hi rpms like this one time he was correct in telling me what type of cam is in there... it pulls only six inches of vacuum also, at idle. Additionally, the heads are 462's with 2.02 valves, ported. Intake manifold has GM 10185024 on it, and is no longer produced by GM... I BELIEVE it is a hi-performance part, aluminum, and it IS a dual plane...

The shop owner said to bring it by, and they most likely would look at the "squirter", to determine if more fuel was needed off idle... he seemed reasonable about it, and for now, I will treat this as a learning experience, but in my gut, I still think the 850 is too big, and unneccesary... see this link:

http://www.chevyhiperformance.com/techarticles/148_0403_choose/

Basically, I will have them reprint the fuel/air curve they have when they dyno'd the engine, and work with them, but I MAY have an 850 Demon for sale on e-bay soon smile.gif

[ 06-16-2004, 07:08 AM: Message edited by: jethro ]

The 850 tuned down may be alright. When they Dyno'd the motor they started at? 2000-3000rpm? You won't see an off idle stumble then. I agree with you about the 850 being too big< only if a street/strip car> Track only car would be fine IMO. Not knowing all the spec.s its hard to tell,but I feel a 750 would be max, and give much better throttle responce.

.550 lift is not a radical cam ......just an FYI. Its in the small to medium range. Did they run dyno numbers and provide them to you? The 850 like someone above said may be detuned and run the most hp. But it would be at a sacrifice of low end torque. Which would explain the stumbling.

An 850 is way to big for your combo, as mild as your 350 sounds go with
a 650, or a 750 if you plan on upgrading later. If you have an 850 its easy
to tell - just look down the butterflys at the ventui (carb body) walls, if they
are the same diameter as the throttle blades then its a 850. A 750 or smaller
will be much smaller around the booster and will taper out to the bigger
throttle blades.
FYI .550" lift cam could be 220dur. or 260dur. so lift doesnt have anything to
do with how "big" a cam is, it could be a daily driver cam or a full strip cam,
and the duration will tell you which.

How do you detune a carb? An 850 is still an 850 no matter what you do to it. Either those guys had an 850 laying around and wanted to get rid of it or go to another shop they have no clue what they are doing. Most street 454s really don't need an 850 let alone your 350.

I agree... I can NOT see how this carb fits a 350, I'm still waiting on the Demon Tech rep to get back to me. Plus, this shop wants to now modify the 850 to get over the low end torque/stumble problem. Hmmmmm... I'm a little lost here, I admit, but my gut feeling is that this carb is hindering me more than helping. In regards to the cam comment, you may be right, but with the lopey idle, lack of vacuum, and the top end response, I think this cam profile would be out of the "mild" range. Don't you hate it when you get in this position, trying to guess critically important things about a vehicle because the previous owner was incompetent?

My friend sucessfully runs an 850 mighty demon on a 350,it has throttle response, and dosent stumble a bit but he did alot of tuning, and ended up having to drill holes in the butterflies. He also runs a very radical setup, 268@.050 duration and the motor to match. I agree though you have no business running that carb, id take it back and DEMAND the correct carb!!!!

Sucks when people dont know whats in their motor because someone else
built it... makes it more difficult down the road.
The only way to de-tune (make it smaller / flow less) the carb would be to
stick annular boosters in it, otherwise its still gonna be too big and give up
plenty low end throttle response. Get the right carb! No matter how much tuning
you do it will always bog off idle, especially if you put tires on it and take it to
the track.