Does anyone have experience with demons carburators???

I am considering a Speed Demon 650 cfm.. for my GM ZZ3 engine.

I want a carburator that I can easily tune, that will hold a tune, that give me the fredon to adjust the air/fuel mixture (as opose to changin jets), and I want some fuel efficiency and lean emissions.. I am looking for something reliable.

I only have experience with electronic Q-jets, Can i use a holley technical manual to guide my seld with a DEMON carburator?

Any other carburator suggestion???

 

Your still going to have to Change jets...


But they seem to be great Carbs.

When I build a Motor wich My lust for Qjets cannot supply, I will use a Demon ( oFI haha )



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60 Ranchero - Project ( Money Hole )
85 Sport Coupe LG4 - Daily Driver 14.82 @ 91.1
Reader's ride -> My Ride

Just another Hot Rod kid, or thats what they all tell me.
Livin' the Stereotype

 

MY demon was calibrated perfectly right out of the box. I won't ever have another holley.
Later
John

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82 Firebird,408,Dart Iron Eagle 215's,Cam 229/239, .498/.520,TH350 Tranny, 750 Speed Demon carb, Hooker Headers(I.E. POS) Manual steering, Bfg DR's.
Check out my birds new home.
Best et 8.21 @84mph in the 1/8th

 

I use a Speed Demon 850 DP on my race car. It's just a fancy Holley. Every tuning aid you know of with a Holley will work with BG carbs. They just have different castings and shapes than a Holley. A BG carb is better than the run of the mill Holley but the Holley HP carbs are even better.

Having to change jets is a fact of life but on a street driven car, once you find the jet size that works best, you just leave it. How often do you see people changing jets on a q-jet? It's no different than a Holley just different in how to change them.

I've found that BG carbs are jetted a little rich out of the box. The only way to tell is to read the plugs and adjust the jets so you're not lean.

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87 IROC bracket car, 91 454SS daily driver, 95 Homebuilt Harley

 

Just my 2¢, but take a look at the Road Demon. If you are gonna drive this car on the street most of the time, then that's the carb you want. It has elec. choke and a diff idle mixture set up than the Speed Demon. It's fine for up to 400hp and 11:1 comp ratio. I think it's got the same casting as the Speed Demon, just smaller venturies for more velocity, which gives better throttle response and torque. That's really what the ZZ3 is set up for anyway, right? Torque and drivability? Plus the Road Demon is $100 cheaper. Why spend the extra money if you don't have to?

BTW, I just looked at the www.barrygrant.com website and the venturies and butterflies on the Speed and Road Demons are the same. Maybe the Road Demon comes with the air bleed sleeves already in place. Maybe that reduces the flow below 650cfm so they just call it a 625 instead. I duno for sure.

AJ

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92 RS w/t-tops 305 TBI Auto.
170K miles and don't burn a drop o'oil
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i think the road d is vacuum secondary only. SD is Mech but is also available in VS.

Stephen, why do you prefer the Holley Race series?

I heard they are more trouble than they are worth to tune. Don't they have a three stage metering system that prevents any interchange between regular holley? I thought they also have the same issues as porosity as other holley cast parts. As opposed to billet parts in bg carbs.


[This message has been edited by jcb999 (edited June 26, 2001).]

 

You are right, but if you want elec. choke, then you can only get the Speed Demon w/ vac secondaries. Well that's listed in Jeg's for $399.99. The Road Demon is listed at $299.99. Is 25 cfm worth $100?

Plus for the street, mech secondaries are horrible. They're good for drag racing, but unless you got the engine & launch rpms, (i.e. the torque converter, or clutch release) set up for it, mech. secondaries will cause a huge bog when you stomp on the gas. It'd be OK if you want to use a 50cc accelerator pump. Vacuum secondaries only open when the engine's rpm range needs it. Just much more streetable.

 

I would not say that mech secondaries should not be used for the street. They do require some more turning and proper sizing. For a ZZ3, Vac might be better. But vacuum secondaries can bog just as bad (if not worse) than a mech if the secondary spring opens too fast. Look at quadrajets.

I have a Race demon 1000 cfm (which did come with a 50cc reo pump) and it does not bog at anything more than 2000 rpm when floored. But, I do have 4.10 gears. Most holley equipped cars do not need anytype of choke let alone electic. But it is nice to have.

 

jcb999,

Thanks for repeating what I just told him. I guess that's why I said "They're good for drag racing". Who wants to fart around that much for a street car? BTW, if the stall on your converter (or your launch rpm) was set up to match the power range of the engine, you wouldn't get any bog at all.

And vacuum secondaries don't open at a specific rpm range due to the spring. The engine (cam) still dictates that. All changing the spring does is cause them to open quicker and a little more at the same rpm range. If you go to a softer spring, for ex., then the back butterfies will open at the same rpms as the stiffer spring, they just open a little more and at a faster rate.
Mech. secondaries open the back 2 butterflies whether or not the engine wants the added air yet. That is what (usually) causes the bog. That's why they suggest (and usually include) using a 50cc pump. That way you still get fuel along with all that air.

I had a 72 Nova, Muncie 21, 4 bolt 350 block, Holley hi-rise intake, 462 heads ported & polished, Hedman 1 5/8" headers, 3.73 gears on 25" tires. It had the Crane Fireball solid cam, adv. 302 dur, .510 lift. 11.5:1 compression. I had a 650 Holley #1850 w/ vac. secondaries on it and thought maybe it needed more. I fell into the "bottom of the page" syndrome. So I bought an Edelbrock 750 w/mech. secondaries, #1407 I think. I'd heard that Edelbrocks are better for the street. I used Edelbrock's tech-line for suggestions on jet sizes/metering rods with my combo. Ever since then (I drove this car mostly on the street) anytime I tried to get it going under 3K rpms, it fell on it's face for 1-2 seconds. If I took off at 2500rpms, it was fine because the tires spun like hell. I tried everything to change it. It did pull harder from 3500-7000 rpms, but I lost the "drivability". I was barely able to catch up to Mustangs on the street after that.

Then, all of a sudden, "Edelbrock sucks". That's what I thought. Then a local machine shop owner/engine builder said that I over carbed the motor for street driving. It's pretty common from what he told me.

fulo,

Just learn from other's mistakes (like mine), not your own. It'll save you time and money. And plan, plan, plan. A good plan is better than any time spent guessing.

One more thing jcb999. 1000 CFM?!! What is your engine set up for? Do you have a site that I can see this car at? What are your mods? It must be a sub-10 second car. I LIKE FAST CARS!!! Show it off man. That's what fast cars are for, right?

 

Nobody seems to want mechanical secondaires for the street but all Q-jets are mechanical secondaries. They use progressive linkage so the secondaries don't open until you really push down on the gas pedel.

Some Holley's are like that and at least the road and speed demons are progressive linkage. Not sure about the race series. If you don't have a heavy foot then you'll only use the primaries most of the time.

Edelbrock carbs are just a new version of the old Carter AFB. Although not a bad carb, many people don't like them because of how they are tuned.

 

I really don't understand where this is going but. There were several over simplifications I was attempting to address in the previous posts. Universal statments about mechanical secondaries and the street not being compatiable was the main thing.

In the context I was referring, there was no diffence between drag and the street. And that is why I thought the mechanical secondary statment needed clarification.

Once you get a carb setup with a combination, it does not matter where you drive it it the there will not be any penalty by using mechanical secondaries other than fuel mileage.

AJ, I really don't think you qualified your statment very well in the previous post. That is why i felt it important to indicate that for a ZZ4, Vac might be the best way to go. Especially with an auto. But i feel this is likely the exception than the rule.

You had a bad experience with an edelbrock carb. Don't black list all mechanical secondaries configurations because of that.

I think they will provide much more performance when properly setup (600cfm double pumpers do not need 50cc pumps).
Look at your average dyno test of going from a 780holley to a 600 or 650dp. Usually about 15 hp and 15 ft/lbs of torque.

I know a 283 that ran a 600dp out of the box with nothing but screaming performance. Much the same parts you listed above.

And as far as my motor not bogging below 2000 if it had been properly setup, I don't think that is likely. Considering the cam is not desgined to start making hp until about 3000. It is not a concern that it be able to go to full throttle at 2000. I don't try to race it at 2000 rpm.

Its basically a 500 hp 400. Track1 heads and custom roller. No no pics. As of right now its not together.


[This message has been edited by jcb999 (edited June 27, 2001).]

 

I sorry. I wasn't directing the bad statements toward mech. secondaries. I was directing them at over cabing an engine. Mine bogged because it was over carbed below 3000rpms. And your right about not racing below 2000rpms, but sometimes on the street, you want that. Like when your in the wrong gear, and want to change lanes, etc. Sometimes it isn't possible to downshift right away.

I'll bet above 4000 rpms.

I never said that a 600 could use 50cc pumps. I was refering to anything like 750cfm and above, and again, with the right combo. Why do you think most dynos are set up to test at 2000-2500 rpms and above.
BTW, Quadrajets are both mech. secondaries, with vacuum release. I think that's the progression you were refering to, right?


I guess I am just trying to keep this guy from trying to do to much by using the "bigger is better" thinking that all of us experienced at one time. Sorry for the misleading.

 

it's all good. Good advice is always welcome. And the age old problem of overcarbing and or over caming will always be with us.

I think it is much less likely to occur with the information that is now available to hotrodders (i never really liked that term) and parts available from the aftermarket (because so many performance options are available now). I think a lot of the problems of the past were associated with someone who wanted really good performance and did not want to use an RV cam. So they were forced to select something that was had many draw backs on the street (a cam out of the racing column).

The 283 i talked about was from my highschool days (lets not say how long ago that was). The guy had a crane solid cam and he ended up hurting the motor from both broke pushrods and later spun bearings. If it had been less of a 7200 rpm screamer, it would have lived longer.

As far as the q-jet goes, I consider it more of a vacuum secondary carb than anything. Because it had the adjustable air valve, no matter when you floor it, the top air doors will not open until it has suffient airflow. But, if that valve is too loose, it will just fall on it's face when you nail it. So, in that instance, a vacuum secondary can be just as hard to live with (when just a 5 second adjustment can fix it).

I think the carbs that have the spread bore design are much more likely to have a big old flat spot than traditional square bore holley double pumpers. Because there is such a large secondary volume.

Another question that I like to include when I am asking what mods someone has is if they ever plan on doing anything else to it. This is often the toughest question for them to answer but it might avoid buying something that will be less than ideal in the future. It also gets them thinking about how fast they really want to eventually go. Which is very rarely considered but very important. The only time I think it really does not need to be considered is if the combination is a daily driver. Then the answer is clear.
(man that got long).

And your right, most of the dp test made better hp at 4000 and up. But, thats when there supposed to. Most engines have torque peaks very close to 4000 when optimized.
I think a zz3 is probably 3750 and it has very mild cam timing.

They really did not give up in the lower ranges as much as they gained in the higher.


The thing that is really nice about all demons is the 4corner idle screws. You can get them to idle like glass and have very good throttle response.

I did not really have a problem with finding my car in the wrong gear. With 4.10s, and 400cubes, by the time you think you needed to downshift, its buzzing past 5000.

be cool



[This message has been edited by jcb999 (edited June 28, 2001).]