My 355 has stock head castings, its a rebuilt 1974 350 out of a Nova Custom and has the crappy (more like cracky) 882 head castings. It has 2.02/1.60 valves, dual springs, studs, full roller 1.6 to one rockers, a CompCams 280H cam (230 at .050), 9.3 to 1 pistons, PM rods, and a Wieand Stealth intake.

I was going to go with the 650 CFM DP spread bore from Holley (4175) but the guy at the speed shop suggested the 700 CFM Classic. So I bought one.

My question is, will the 700 DP be too much carb for my 355? I expect to be shifting around 6K to 6250. So I did the math and I found out after I bought the carb that at 6500 RPM, a 355 will only require 568 CFM (at 85% volumetric efficiency).

I plan on running the carb as it comes right out of the box. What kind of tuning ussues will I run into? This is my first Holley, and the first time working with a double pumper. I was shown how to check the float levels after I mount the carb on the motor, and I will be checking the vacuum at idle and then changing the primary power valve if needed. I have read on this site about problems with wrong sized pump nozzles and wrong pump cams, since I will be running it out of the box will these items be a problem? The carb has a reddish-brown pump cam on it now.

This is strictly a play car, not for daily driving. I am looking for maximum performance from my engine, and fuel economy is not a concern. Any suggestions on the carb?

 

It's fine. 750 would probably be better.

Keep in mind, that equation only gives you the "steady-state" flow requirements of the engine, assuming that the engine appears as a continuous pump, like a vacuum cleaner or something. But that's not how an engine works in the real world. Instead, it draws in air in short pulses, one pulse as each cylinder needs to be filled; and the carb needs to support the peak flow during those pulses, which is much higher than the steady-state CFM value you calculated.

That formula will not tell you what size carb to use. It comes closer to telling you the absolute minimum size that could have any possibility of working at all. Don't imagine that you can solve it and buy that size carb and it will be perfect, because it will almost always be too small.

 

That carb should be fine. I'm running a 770 on my 355. I did have to down jet it a tad, though. Out of the box, it was too rich. Get the Holley jet kit. Will make it easy to "dial" in the right jet size.

 

cool. I was worrying for nutn.

Any word on which pump cam to try?

 

Primary side: Blue cam on #2 hole, start out with #31 shooters.

Secondary side is usually OK stock.

 

You have to keep in mind how a carb is rated for air flow when considering what size carb is right for your motor.

4bbl carbs are rated at 1.5" vacuum, where as your motor consumes X amount of air at WOT maximum rpm
while the manifold vacuum guage will read about .5" to 1"vacuum. (near atmospheric.) The actual amount of air consumed by an engine while running at peak performance can and is measured on a dyno with a air flow meter and a manifold vacuum guage.
The airflow fugure must be qualifed with a manifold vacuum guage reading to mean any thing. Then you can convert that figure to 1.5" vacuum an get the right size carb for your motor.
The right sized carb is the one that will allow maximum hp output at WOT high rpm without exessive restriction.
(manifold vacuum) {.5" to 1.5" is about right}
it also must be small enough to respond to throttle changes at low rpm.

here a general guideline to select the right carb based on the motor's expected airflow.
rpm x cid /3456 x ve (.85) = engine airflow consumption
But now you want to know what carb size will be pulling .5 to1" vacuum at WOT on this motor.
For a single plane manifold multiply the airflow by 1.20
to get the carb size. For a fully divided dual plane use 1.30 as a factor.
So a motor that is using 585cfm of air with a dual plane manifold needs a 585x1.30 =760cfm carb.

try it.

 

I came up with 680 CFM and the carb I have is a 700 CFM so it should to work acording to your calculation.

 

The carb has a 28 on the primary and 31 on the secondary and a pink primary pump cam in the #1 hole and a reddish-brown secondary pump cam in the #1 hole. I am going to try to get it running and break in the cam the way it is, then I will tune it.

 

I noticed that you are running the same cam I am, and pretty much the same engine setup. Same gears too. I have the 700R4 with a 2500 stall instead of the T-5.

Do you have any quarter mile times? I am just wondering what I can expect from mine when I get it broken in.