I am presently using an Edelbrock 800 cfm carb on my 383. It performs very well as the car runs high 11's at the strip. But I've been told that I would get even better performance or HP from a Demon carb (maybe 825 cfm).......I have not seen in any magazine a head to head comparison between carb brands...Edelbrock vs. Holley vs. Demon of compareable sizes. ALL comparisons were of various sizes within the same brands. Other than spending money buying them all, how would you begin to determine which works best for your engine? Any experiences across brands that showed a difference or performance boost?......(mechanical secondaries better performance?)

 

Personally, I think carbs is carbs. They all do the same thing: mix air and fuel. They are all rated to the same standard: measured airflow at 1.5 inHg" pressure drop. There are differences in the way the idle, transition, and main fuel circuits are set up and this is where most of the differences are, but at WOT, as long as the air/fuel ratio is correct for your motor for generating best torque at any given RPM they all do pretty much the same thing.

I used to prefer Holleys because they are simple in construction, but as I've become familiar with Q-jets and Carters, I believe for driveability and ease of tuning on the vehicle, these carbs are superior as dissassembly does not require you to remove the carb or dump fuel all over the place to access the metering orifices or rods.

If you're confident that your carb is tuned for your best power then get a manifold vacuum reading while at WOT near the power peak of your motor. If you're seeing more than 1" Hg of vacuum, your carb is too small or there is some other restriction to airflow in your system. This is where you'll see addtional power: more CFM capacity--Not necessarily in the brand of carburetor your're using.

 

look at the options.....when i picked my Speed Demon i looked at the options available for what i wanted to do....i wanted maximum flexibility for tuning and swapping componets, i wanted 4 post a/f mixture screws, i wanted to be able to adjust the butterflies, iwanted to be able to adjust the floats externaly and see the float level externally....i wanted maximum tuning ability....this got me to the speed demon.....admittedly the Holley sells more accesories that could make life easier such as less expensive fuel lines and a heat shield...

 

I have an Edelbrock EPS 800 for reference.

Hot Rod did a swap from an Edelbrock (750 I think) to a Demon (don't remember which one) and they picked up a few ponies (20hp).

Now, I think the Demon was larger and that may have been where the extra power came from.

 

I'm wit cha brothu!

 

I have done a lot of comparisons of cfm on my Performance Trends program and I do not think that such a small cfm change will benefit you much. One thing is, is that a vacuum secondary carb? If it is, a mechanical will give you better secondary control. Otherwise a cfm is a cfm. The question is how much flow are you getting and is your secondary 100% at full throttle? Now, if your going up 100 cfm, that's a different ball game. If you want to post or IM me with all your engine specs, I'll run some numbers for you.

 

I'll definitely get a manifold vacuum reading at WOT to determine if I can gain power with more CFM.....at the dyno, max power was produced at 5600 RPM with air-fuel ratio of 12.6 to 1 at full throttle. While Edelbrocks are not truly mechanical or vacuum secondaries, I'm curious if mechanicals (like Demon or Holleys) would give better mid-range acceleration.