Demon flow question...Big JOE...Troy....carb guy's

gasman5.0 · Post by **gasman5.0** » Tue Jun 30, 2009 1:28 pm

I addressed this too Big Joe knowing he uses the demon carbs on several of his motors and likes them, or anyone have any flow data on these carbs.... race demon 825DR and Mighty Demon 850GC.
Joe I've read a few post where you have flowed several different cards on your flow bench. I was woundering if you have had these carbs on your bench and could confirm the flow #'s I was given. I talked with the Guy's at Berry Grant about the cfm on the 825-DR race demon and the mighty demon 850GC carbs. They said the 825DR flows 975 cfm and the 850GC flows 1000cfm any truth to these #'s.

Thanks Darrin

bigjoe1 · Post by **bigjoe1** » Tue Jun 30, 2009 4:30 pm

Those numbers are very close to what I remember. I do not have that info at hand, but I do remember that the 1025 race demon flowed right at 1020, I thinke the 850 Demon was 996 or 997- These numbers were at 20.4 inches on the super flow 600 bench, and iI flowed one barrel at a time and added the four togeter
On average , the Demon size number is about 75 CFM MORE than the Holleu of the same rated flow ( 750 Demon=825 Holley )

JOE SHERMAN RACING ENGINES

TOP38 · Post by **TOP38** » Tue Jun 30, 2009 5:08 pm

Not that this really means anything but since you asked, dry flow is a good 7% more than wet flow for gas as fuel takes up space and reduces dry flow CFM numbers! To date I haven't seen too many dry flowing carbs on running motors!!! It's a big numbers game so don't get overly concerned if it advertizes 850 CFM and you need 890, the metering of the carb to your combo is way more important to performance than a few CFM!

Rick1999 · Post by **Rick1999** » Tue Jun 30, 2009 5:21 pm

bigjoe1 wrote:Those numbers are very close to what I remember. I do not have that info at hand, but I do remember that the 1025 race demon flowed right at 1020, I thinke the 850 Demon was 996 or 997- These numbers were at 20.4 inches on the super flow 600 bench, and iI flowed one barrel at a time and added the four togeter
On average , the Demon size number is about 75 CFM MORE than the Holleu of the same rated flow ( 750 Demon=825 Holley )

JOE SHERMAN RACING ENGINES

Joe, what have you seen when flowing the different brands that are the same size dimensionally, ie, 1 3/8 venturi by 1 11/16 throttle bore.

I wish Holley had never started the practice of rating carbs by cfm, it can be very misleading.

bigjoe1 · Post by **bigjoe1** » Tue Jun 30, 2009 5:41 pm

The 750 examlpe I just put up is what you are asking about-- The Demon 750 flowa 75 MORE CFM than the holley 750 of the same size

JOE SHERMAN RACING

Troy Patterson · Post by **Troy Patterson** » Tue Jun 30, 2009 6:14 pm

Never flowed them. My focus has almost always been on the venturi diameter relative to velocity rather than CFM. To me, velocity is more important. But, when I estimate I simply take known flow values of generally the HP Holley for a given venturi diameter and make an approximation based upon the type of booster used.

Sorry I can't help you more.

Troy Patterson TMPCarbs.net TMP Carbs

Rick1999 · Post by **Rick1999** » Tue Jun 30, 2009 7:19 pm

Troy Patterson wrote:Never flowed them. My focus has almost always been on the venturi diameter relative to velocity rather than CFM. To me, velocity is more important. But, when I estimate I simply take known flow values of generally the HP Holley for a given venturi diameter and make an approximation based upon the type of booster used.

Sorry I can't help you more.

Troy Patterson TMPCarbs.net TMP Carbs

I was just curious as to what Joe found in his flow tests, I haven't had the opportunity to flow a Demon but I have compared them to identically sized Holley's on the dyno and quite honestly, once the fuel metering deficincies are worked out power is usually the same with in 3-5 HP.

In most cases I too am more concerned about venturi diameter and booster signal than I am how much air my very expensive vacuum cleaner motor can suck through a hole

However, in some Circle Track classes that have rules that mandate an extremely small carb (390) you gain about 1hp per 1.3 cfm, when you are in that situation you have no choice but to go after the airflow first and then find a workable calibration secondly.

trmnatr · Post by **trmnatr** » Tue Jun 30, 2009 8:07 pm

bigjoe1 wrote:Those numbers are very close to what I remember. I do not have that info at hand, but I do remember that the 1025 race demon flowed right at 1020, I thinke the 850 Demon was 996 or 997- These numbers were at 20.4 inches on the super flow 600 bench, and iI flowed one barrel at a time and added the four togeter
On average , the Demon size number is about 75 CFM MORE than the Holleu of the same rated flow ( 750 Demon=825 Holley )

JOE SHERMAN RACING ENGINES

If i remember correctly doesnt the 1.401" venturii / 1 11/16" butterfly flow like 942 or 952

The 1.401" venturii / 1 11/16" butterfly works good on small engines

MadBill · Post by **MadBill** » Tue Jun 30, 2009 8:47 pm

Speaking of big venturiis, anybody yet tried one of the new 'spread bore' high-flow (1200-1240 CFM) 4150-style main bodies from Braswell or Dr. J? Seems like the ~200 CFM added flow should be good for a solid 20 HP on any 800 plus HP single carb app...

Rick1999 · Post by **Rick1999** » Tue Jun 30, 2009 9:23 pm

trmnatr wrote:
bigjoe1 wrote:Those numbers are very close to what I remember. I do not have that info at hand, but I do remember that the 1025 race demon flowed right at 1020, I thinke the 850 Demon was 996 or 997- These numbers were at 20.4 inches on the super flow 600 bench, and iI flowed one barrel at a time and added the four togeter
On average , the Demon size number is about 75 CFM MORE than the Holleu of the same rated flow ( 750 Demon=825 Holley )

JOE SHERMAN RACING ENGINES
If i remember correctly doesnt the 1.401" venturii / 1 11/16" butterfly flow like 942 or 952

The 1.401" venturii / 1 11/16" butterfly works good on small engines

Is the Demon 750 a 1.401" venturi? A holley 750HP has a 1.375" venturi and will flow 890-900 cfm on my bench, opening the venturi to 1.400" will put it in the 960 range, thin shafts will get it right at 1000.

With as much emphasis that some people put on cfm numbers I feel people should understand that just because company A says there 750 outflows company B's 750 it doesn't really mean they are the same physical size. If I made a 1.500" carb and called it a 750 it would be the baddest flowing 750 on the planet but in reality it is just a bigger venturi.

gasman5.0 · Post by **gasman5.0** » Wed Jul 01, 2009 12:34 am

The 825 race demon I have has 1.425 Venturi and 1-3/4 butterfly's. My reason for asking a few guy's recommended a 850 mighty demon and a few recommended a 825 race demon. The 850 has 1.562 venturi and some felt the smaller 1.425 venturi of the 825 would have a better signal "crisper" for a street/ strip car.
I'm asking myself how H.P. if any am I leave on the table with a 825 instead of 850 in respect to the demon carbs. Motor is going in a 91 mustang that is lightened up a little glass hood,tubular arms , coil-over struts & k- member, manual transmission
Here's a little motor info:
AFR-205cc heads #1450
11.3:1 compression
4.030 x 4.00 408w
super victor
solid roller cam info:

Any suggestion on carb size for this motor.

Thanks Darrin

289nate · Post by **289nate** » Wed Jul 01, 2009 3:01 am

Rick1999 wrote:With as much emphasis that some people put on cfm numbers I feel people should understand that just because company A says there 750 outflows company B's 750 it doesn't really mean they are the same physical size. If I made a 1.500" carb and called it a 750 it would be the baddest flowing 750 on the planet but in reality it is just a bigger venturi.

Yup. It seems Demon was pretty smart.

Never flowed them. My focus has almost always been on the venturi diameter relative to velocity rather than CFM. To me, velocity is more important. But, when I estimate I simply take known flow values of generally the HP Holley for a given venturi diameter and make an approximation based upon the type of booster used.

Troy beat this into my head while hanging around in his shop after he built me a carb several years ago. Venturi diameter is the accurate way to talk carb size. The carb will flow whatever it's on top of wants it to.

Rick1999 · Post by **Rick1999** » Wed Jul 01, 2009 9:37 am

289nate wrote:
Rick1999 wrote:With as much emphasis that some people put on cfm numbers I feel people should understand that just because company A says there 750 outflows company B's 750 it doesn't really mean they are the same physical size. If I made a 1.500" carb and called it a 750 it would be the baddest flowing 750 on the planet but in reality it is just a bigger venturi.
Yup. It seems Demon was pretty smart.

Never flowed them. My focus has almost always been on the venturi diameter relative to velocity rather than CFM. To me, velocity is more important. But, when I estimate I simply take known flow values of generally the HP Holley for a given venturi diameter and make an approximation based upon the type of booster used.
Troy beat this into my head while hanging around in his shop after he built me a carb several years ago. Venturi diameter is the accurate way to talk carb size. The carb will flow whatever it's on top of wants it to.

Someone gets it

Demon just rates the flow of their carburetors more accurately. Holley's 950's and 1000 cfm HP carbs are reasonably close, but everything smaller than that actually flows quite a bit more than advertised

Doug Schriefer · Post by **Doug Schriefer** » Wed Jul 01, 2009 11:19 am

MadBill wrote:Speaking of big venturiis, anybody yet tried one of the new 'spread bore' high-flow (1200-1240 CFM) 4150-style main bodies from Braswell or Dr. J? Seems like the ~200 CFM added flow should be good for a solid 20 HP on any 800 plus HP single carb app...

We run them all the time on Big HP engines

(but I probably don’t count in this conversation)

I did want to clarify though we DO NOT advertise any time of CFM numbers on ANY of our carburetors as they’re all bogus.

Let’s take a quick second to look at “Flow-Bench” racing or numbers. If you put a carburetor (wet or dry) on a flow bench and test it a set pressure drop, and then install a larger carburetor and reset the bench to the same pressure drop of course it’s going to flow more air.
Now let’s look at reality your engine is an air pump which means unless you’re going to change the combination it is going to draw the same amount of air through the carburetor regardless of what size carburetor you’re using within a very small range (unless you’re restricted due to carburetor sizing). This is why you’ll usually see the HP very close with different size carburetors on the same engine when testing. You have to choose what size, and design of carburetor is going to work best for your combination. Based on what you’re trying to do with the engine, and chassis combination.

1: We don’t race dynos.
2: We don’t race flow benches.
3: We don’t flow rate our carbs.
‘CAUSE THE FIRST LIAR DON’T STAND A CHANCE!!!

gasman5.0 · Post by **gasman5.0** » Wed Jul 01, 2009 12:00 pm

Considering this is a 80% street 20% strip car is why I went with the smaller 1.425" venturi in the 825 instead of the 850 which has 1.562" venturi. Does the 825 look to be the right size carb for the motor? I was afraid the larger venturi carb may be too big for my 408 inch street motor, and not be as responsive so I errored on the smaller side was that a mistake?

I was hoping to make around 575-600 hp with this motor. Do I need to step-up to the 850 demon carb?

Thanks Darrin