also, demon carbs are wet flowed so the flow more than they are rated, I can tell you I have a 408 stroker with big heads and a cust hyd roller, I went and bought a custom pro-systems 950hp, my 650 vs speed demon un touched starts easier, idles cleaner and better, has way better throttle response and low end the power is about the same except the PS hits harder and a hair more top end but overall I like the demon better and mine is a reman I bought off ebay for under 300.00 my prosystems cost over 700.00........its for sale by the way......30 miles on it!
Thoughts on Demon carb?
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jasonn
Founding Member
I am a machinest so I know what I see. And I seen Many demons apart, and heard from other people as well. Sliver? Are you kidding? As soon as I took them apart, I would just tip over the metering blocks and bowls and I would have a PILE of chips on the bench! A couple of people I know called the tech line and each one was told they say they have never heard of this?! Yea right. Although I think if it wasn't for this issue, demons are good carbs.I have had many apart myself and to say there is a "pile" of chips is a gross exageration. We have openly admitted and addressed this issue on numerous websites so not sure who they spoke with here that would have said that. As stated earlier this issue WAS addressed and has been corrected as of about a year ago. Since that time the amount of warranty claims we are seeing with claims of debris has just about stopped.
You kinda comparing apples to oranges here. A smaller carb will have all the benefits you described. Easier starting, and snappier throttle and so on. Bolting on a 950 that didn't work quite as well as you thought it should wasn't really the fault of PS. I'm sure they built that carb for a nasty motor with poor vacuum and exhaust dilution problems at idle and compensated for it in the IFR's If your motor was not up to par for the 1000 hp motor it was intended. Not to take away from your motor at all.
But a 650 built for a 302 with a crazy cam with tons of overlap will be different than a 408 with a tiny cam, even if they make the same HP.
I think this is why some guys bolt on a carb and it works great, then next guys hates it because he's got a wicked cam, and the IFR's aren't big enough.
Tech here can probably agree and elaborate. I haven't used one. But I think that's why you see different carbs from Demon that are the same size, but they are noted from different cams.
I gave them every spec of my motor, the cam is not big but not small either 232 243 576 574 @050 it has almost 114 lca and pulls about 14hg at idle, neither carbs have a choke. The PS carb turned my plugs black, you would think the richer carb would be better at cold start, when cold and I hold the idle at 1500-2000 I have to feather the throttle with the PS carb or it will die, the demon will hold steady, like I said if I dial in the PS carb I'm sure it will run better than the demon BUT you would think it would be pretty close, when talked to Patrick at PS after going over my specs he said this will be an easy one and it shipped one day later.
I've ran that 650 on my 351w (a bit rich) my friends 289 214 478 cam and 351w heads and it ran absolutely perfect, and on my 408 close to perfect I could probably jet up a bit but it hasn't been touched. I hate tuning carbs, I may try a bigger demon but I'm leaning towards efi, I ran it before and loved it........frankly I hate carbs except I love my demon........
I've ran that 650 on my 351w (a bit rich) my friends 289 214 478 cam and 351w heads and it ran absolutely perfect, and on my 408 close to perfect I could probably jet up a bit but it hasn't been touched. I hate tuning carbs, I may try a bigger demon but I'm leaning towards efi, I ran it before and loved it........frankly I hate carbs except I love my demon........
jasonn
Founding Member
To answer a few of the questions, we do wet flow each of our carburetors and at this time I believe we are still the only ones that do that. Not sure why you would want to use a dry flow number since the carburetor is never moving air without fuel unless it's on a flow bench. With that said we also calibrate the carburetors as mentioned for different cam duration ranges based of what we know an engine will have for vacuum and signal in that range.For example... a Speed Demon is intended for duration up to .240 and a Mighty Demon is rated for .240 - .260. Also because of our patented air entry design our carburetors will flow more than the advertised number. Our 650's typically flow a little over 750 and our 750's flow a little over 900 cfm.
I don't think there is any dispute to that, but the key word there is saw, as in past-tense. BG has acknowledged the problems and taken steps to correct them. Has anyone seen what you saw on a unit manufactured after the corrections were implemented?
EDIT:
I've just got a plain old Holley 750-vac on mine, wishing I chose the 650 demon myself. For a 357W with a 226 234 506 506 110-degree cam and RPM heads/intake...would that be an improvement?
I never understood this about demon. A carb is called a 650, because it is supposed to flow 650cfm @ in of vacuum. If it flows more, than it's a bigger carb. A 650 on a 351 that pulls 4in of vac @ 6500 is flowing more than 650, but would not be called anything else. I guess what I'm saying is when people go to pick a carb based on what if flows, why give more on something that can be so critical. Kinda like buying a cam and it not spec'ing out as made.
I hope you are joking?
Physics does tend to play a part in HP numbers, but 750 hp at the crank, for a N/A 347, I don't think so Tim
A carburetor in actuality will only flow on any given engine what that engine requires .It is a little more complicated than a camshaft where a lobe can be mechanically measured. Yes the cfm can be measured at 1.5hg but as noted above once on an engine will have different characteristics. When we list a carburetor as say a 650, it is because that carburetor has a 1.282 venturi and a 1 11/16 butterfly. These measurements are commonly know to be "650" in modular carburetors. We also wet flow our carburetors as opposed to everyone else who uses dry flow numbers but think about it.... at the point the carburetor is being used, when is it only moving airflow and not fuel other than on a flow bench? The 650 listed above will flow approx 753 and the "750" which is 1.402 venturi and 1 11/16 butterfly will flow a little over 900. My best comparison is that if you have xxx brand and series of heads they are xxx, if you port those heads they are still referred to as xxx much like our air entry design is similar to back in the day when we ported the other carburetors.
I think I am probably going to drive your convertible around for a few days while I think on it.....j/k, on the 357w the 650 would work just fine. Another option is an annular 750 depending on what the weight of the car is and the rpm range. The annular boosters take some air flow away from the 750 making it act similar to the 650 but on a heavier car can have better throttle response and imporved signal.
brianj5600
Active Member
I have a few of trivial questions.
1. Why are 2 barrells rated at different vacuum?
2. How much vacuum does a circletrack V8 pull at max rpm that is limited to a 390 4 barrell?
3. What does it flow at that vacuum?
1. Why are 2 barrells rated at different vacuum?
2. How much vacuum does a circletrack V8 pull at max rpm that is limited to a 390 4 barrell?
3. What does it flow at that vacuum?
hey tech@BG you could drive my vert around for a few days if I can have a free demon.......http://htwheelz.smugmug.com
Nice looking car! I'm afraid if I drove it for a few days it would have a new home.
2 bbls are rated at twice the vacuum level due to the fact that at WOT, you have two fewer throttle bores moving air. A Holley 500 cfm 2 bbl carb is exactly one half of their 750 DP carb. Those two bores will let your motor see a stronger vacuum signal at WOT than the 4 bores of the 750.
I run vacuum sec's on my 89 Ranger's 5.0 with a Toploader 4 speed and have no driveability issues. The carb is a Holley 570 Street Avenger. I've also run this motor with a list 3310 Holley and an list 1850 and all have performed flawlessly after tuning them. With fuel prices where they are the vacuum sec's will get better mileage than a mec sec carb. I tune the sec's to come on a couple seconds after the pedal is nailed. Typically the lightest to next to lighest spring allows this.
Good to see someone else who understands this. There are far to many that take that "carb sizing formula" as gospel on what carb flows what cfm on any given engine.
Yep. An engine is just an air pump. The carb regulates how much air and gas goes in it. Bigger ports and valves, cams, and such will allow the engine to have the capability to make it pump more air.
LOL...alll engines suck!
Agreed, but the same carb will still flow different volumes at different vacuum levels, and at a given vacuum it will flow the same regardless of displacement/cam and valve sizes.
I always wondered if they factored in barometric pressure too. Because one cubic foot of air in Denver is not the same as one cubic foot of air in Houston. Or on a hot/cold day it is different too. I always guessed that density was not part of it, but to have a uniform standard they'd still have to consider it.
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