I have two carburetors in my possession: 1) Speed Demon 750 Mech. 2) Holley 750 Vac Sec.
This is a weekend warrior that is used for cruising during the summer, however I would like to have maximum performance for the street and maybe a few runs at the drag strips with the joy of breaking into the mid 11 sec. This engine dyno with two different carbs and the 4779 won hands down. How would you compare the Speed Demon 750 Mech. VS Holley 3310VS

Holley 4779- jets:70/80 timing: 34
Torque Horsepower
502@ 4300 464@ 5800

Holley 4779- jets:70/80 timing: 32
Torque Horsepower
495@ 4300 455@ 5600

Holley 3310VS jets: 72/75 timing: 36
Torque Horsepower
484@ 4600 467@ 5900

Holley 3310VS jets: 72/75 timing: 34
Torque Horsepower
479@ 4700 459 @ 5600

Holley 3310VS jets: 72/75 timing: 37
Torque Horsepower
481@ 4600 457@ 5700

Here ar the specs of my engine:
My SBC 409

Engine Block: 400 SBC ID# 330817/14y139664/ T0508CSU
(4.125 bore X 3.750 stroke) after .040 bore (4.165 bore x 3.75 stroke =409)

Deck Plate Bored, Mains Align Honed, Block Deck .002, Deck Plug Holes & Tap w/3/16 Holes, Starter Bolt Drilled, Front Three Gallery Plugs Tap for ¼ Pipe Plugs.

Crank: Scat 4340 Crank 3.750 6.00, Internally Balance, Part# 4-400-3750-6000

Bearing: Clevite– MS1038H Mains and CB663H Rods

Piston: Wiseco Pistons, .040 over, 5.4cc; 430 grams, Part# PT020H4

Rods: Eagle ESP 4340 H-Rods 6.0, Part# CRS6000B3D

Block: Zero Deck: 0.002

Compression Ratio: Static-10:44 Dynamic-8:27

Cam: Grind: Solid Lunati/ (Recommended by Harold Brookshire) 280/284F10 .525/.530 Lift, 247/251@.050, 159/162 at .200, .500/ 504 valve lift, 2500-7000 RPM, Installed Straight up, .026" Valve Lash Hot, .026 Adjustment Range: .018" to .030" Hot.

Valve Springs: Lunati Part#73124 130 Seat 330 Open.

Heads: AFR 195 Part# 1035 w/23º valve angle, 74cc, drilled steam holes.

Head Gasket: Fel-Pro-1014 / .039 in. compressed thickness, 4.200 in. bore, 9.0 cc compressed volume

Intake: Edelbrock RPM #7101

Carb: Speed Demon 750 Mechnical

Rear End Gear: 3:73

Transmission: Pro-Built Street/Strip 700R4

Stall Converter: A.C.T. 3000 Stall

Exhaust:
Hooker Super Comp headers 1 5/8 Headers part # 2460-1 ceramic coated;

Hooker Super Competition high flow cat-back exhaust system, Intermediate pipe: 3 in.
* Tail pipe diameter: 2 1/2 in.
* Dual tail pipes out the rear under the bumper

Looking at this combination do you think will be the "right" carburetor for my application or what would you recommend.

Thanks: David

what is the weight of your car and what do you want to do with it? For a heavier car with an auto trans, you'd be better off with the 3310.

I would also say that peak numbers really don't mean anything, take a look at your HP and torque curves and use those data to make your decision.

K

Here is a look at the dyno sheet. For whatever reason they did not display the air/fuel ratio on the sheets.
SBC 400 Dyno

David,

You're combination looks real good. The cam is a little larger than we would normally use with a Speed Demon series carburetor, but you should be able to make it work. With a Stall speed as loose as you're using a Mechanical secondary carburetor should work extremely well. If you have hood clearance you may want to use a 4-hole carburetor spacer between the carb and intake manifold. It will increase the air velocity which will help with the drivability.

Tech@BG
A few Question:

1. What carb would you have recommended for this combination?

2. Will I have a hard time tuning this carb w/ such a large solid cam?

3. What major changes should I be looking into to make this carb work?

Dahlonega, GA: WOW was there in 1995 for mountain phase Ranger School......

Thanks: David

David,

We would have recommended a 750 on your combination. It would be a little easier to in, and give a few more top end horsepower. That being said, if you run enough initial timing (probably about 18 degrees with your combination), and a 4-hole spacer you should be OK.

We're about 7 miles out of town North of the Ranger camp.

Happy Holidays to all.

Tech@ BG
Which model of 750 are you talking about, "Mighty Demon"? My current initial timing is about 20* with the Holley 3310VS, I will get the 4 hole spacer to go with the Speed Demon, so I should be ok right!

Also I have read and look at the video and their is some conflicting information that I hope you can clear up. My engine idles at about 900-950:

The video and the owners manual state to have about .020 open on equal both the primary and secondary butterflies.

The addendum states that their should be .020 on the primary and the secondary transfer slot should not be visible when viewed from the bottom.

1.Which of these methods is correct/updated information for the Speed Demon?


2. What type of 4 whole spacer does the Demon respond well to
Phenolic, aluminum, or wood?

David,

Sorry about that. Yes a 750 Mighty Demon. On engines that idle at or above 1000 RPM you'll open both the primary and secondary butterflies the same amount. On your engine that idles at 900 RPM you'll open the primary butterflies to about .020" of the transfer slot, and set the secondary butterflies to the bottom of the slot. As far as the spacer goes we'd recommend using either an aluminum, or phenolic, not wood.

dtl504,

Is your converter loose or tight? In other words, does it act like a normal converter until you put your foot in it, of does it take a few rpms more than normal to get the car to move? Does it take keeping the foot on the brake at a stop light?

I would say its a little loose, but I do have the capability to be lock up the convertor in 3rd with the 700 R4.

Do you have a model 3310-1? That is the 780 CFM one with downleg boosters. I have a similar 400SBC. It did not like the 3310-1. The bottom end and mids sucked. The 3310-2 and up seemed were a lot better. They have straight boosters and are 750 CFMS.

I have used a lot of different carbs on my engine. So far the best running carb is the current one. It is a model 84013-1. It is the "New" Holley. It has annular boosters. Supposedly it is 750 CFMs, but judging by the venturi size I think it is closer to 800. It has metered the best all around.

I haven't tried the Demon carbs yet.

lluciano77
The Holley carb that I have is a Holley 0-3310S Vac Sec. Model 4160, 750 CFM, Square Bore, Manual Choke, 4-Barrel, Vacuum, Dual Inlet, Silver

I did not try jetting the carb or changing the power valve knowing the carb needed a 4.5PV. She was also burning a little rich and smoking at idle, but would clear up once warm and I drove the engine about a mile or two.
The main reason I want to change the carb is my engine made more torque and horsepower with a double pumper than the vac. sec. on a dyno.
That might not compare to actual street/strip power, but I want to give the Demon a shot and tune it on a chassis dyno later in the new year.

DTL504,

If you are putting this engine in a medium weight to heavy vehicle, then I would use the vacuum secondary carb, especially having an automatic with a slightly loose converter. It will keep you from bogging out.