I just got a 4 barrel holley carb. It's a 390 cfm carb, the numbers on it are : LIST 6390-1. I think I read the holley pdf right.

So if this is a 390-425 CFM carb, will this be enough fuel and air for a stock 13b 6-port???? I know that RACING BEAT's carbs are 600 CFM and are jetted for the 13b.

What are your opinions????

 

There's no one simple answer to whether it's "enough". It'll work, and it'll flow better than a stock Nikki/Hitachi carb at least. A bigger carb will get you more power, but if you go too big you'll sacrifice drivability.

I'd prefer something in the 500-600 CFM range for a stock or mildly ported 13B, but hey, if you've got it, might as well use it.

 

If any one knows, what CFM is the Nikki carb??? Also, the 48 IDA webers??? I just want to get a ball park figure of what I'm dealing with. I also think that this carb is a better choice because it will utilize the 6-port's in the higher range. I just hope I don't lean out too much...

If you have a carb setup please post with as much detail as possible, I.E:

Size of the carb
Jetting (if any mods)
type of intake
Distributor advance
type of engine 13b/12a/ 4-port/port mods/ turbo

Please any info helps...

 

The stock Nikki is usually quoted as 313 CFM, though I know there's some variance between years. JayCee flowed a 48 IDA with 44mm venturis at 622 CFM. Those are some pretty big venturis, and smaller ones will of course reduce the flow number. Figure high 500s to low 600s depending on which venturis you use.

Fuel is determined by jetting, not carb size. You're not likely to run into fuel delivery issues with that Holley. Certainly not on an NA engine.

I've used a bunch of different carb setups on rotaries over the years: Edelbrock, Holley, Weber, Hitachi, Nikki, NA, supercharged, turbocharged...

Right now my FB has a 45 DCOE with 40mm venturis on a Racing Beat wraparound manifold. The motor is a large streetport 4-port 13B with an S5 turbo in a blow-through configuration. The carb is on the small side at ~440 CFM, but it was the best choice of what I had at the time. Doesn't matter since I'll be redoing the whole setup soon with an REW block, EFI, and a much bigger turbo.

My REPU has a Nikki on a 6-port 13B with smoothed stock ports, using a hack-job modified 6-port 12A intake manifold. It's just temporary until I can pick up another MegaSquirt (notice a trend here? ).

 

Has anyone used this carb at all on their 12a or 13b??? I've heard of some using it on their turbo blow through set up's but none that have done N/A. How can a smaller CFM Run better on TURBO and not N/A??? My guess is richer fuel mix when used as turbo but ???

Well I just got my carb to idle (just needed a new power valve 6.5) and now it idles. Now on to adjusting the vacuume secondaries. Hope fully this carb solves my red hot headers at 4000 RPM....

 

Jeff20B used a Holley 390 on his Cosmo for a while. Drove pretty well and had good midrange. A lot better than the stock Hitachi, anyhow.

In my experience, turbo sizing is much more important than carb sizing for a blow-through setup. You can compensate for a restrictive carb by just turning up the boost. A fast-spooling turbo will also reduce the bog from a carb that would normally be too large. I can't imagine people using your exact model of carb for blow-through, though, since it's a vacuum secondary carb and vacuum secondaries don't work when you force compressed air through them.