I bought a Speed Demon last year for my 230/236 @ .050 cam and now stepped up to a 242/248 @ .050. It is supposedly only rated for cams with 240 @ .050...how much is this hurting me and how difficult is this going to be to tune? I am fairly new to carbs.

Is that the 670 CFM version? If so, yeah, it's a bit too small for a big cammed 383. BUT, it's nothing to jump off a bridge over. And certainly nothing you want to spend multiple hundreds of dollars on to upgrade to a carb that flows 100-150 CFM more. The power difference won't be that dramatic.

I say run what you got. Doesn't matter what carb you start with, it's going to require some tuning if you want it to run it's best.

No its a 750 DP but Demon advertises the Speed at 240 degrees @ .050 for some reason. I'm assuming it has to do with the metering blocks but am unsure.

It may turn into a total PITA to tune it correctly.

it'll be fine to tune, probably just going to need to adjust the idle/high speed air bleeds and do some general jet changes, perhaps just paying to have the car wideband dyno tuned and let them make the adjustments would be best if you are unsure of how to proceed. Perhaps go buy a book on tuning holleys or go to a local library and take it out for a while.

that should be more than enough carb i ran 750 holley when i dynoed my 436 chevy made 595hp/645ftlbs tq. just be patient and get it tuned properly.

xpndbl3...I sure hope it works out. While I don't want a choke horn on my carb (the Mighty Demon comes without one) I don't want to have to buy a new carb at the moment.

irocz436...I am confident the CFM rating is more than adequate (even too big depending on who you talk to) I am worried why Demon advertises this as only good to 240 duration.


I guess some serious trial and error will be in store for me!

that carb is MORE than sufficient, go grab a "good" holley tuning book and you'll be fine.

Thanks for the advise.


Can anyone explain to me the reason a carb would be listed for a specific duration? (Briefly of course, I still need to do some reading)

it's PV rating, the idle/high speed air bleeds, the idle restrictors, etc etc. no different than a marketing gimmick.

Thanks for the info!!