The car is:
- 9.3:1 350
- 125HP nitrous shot.
- L31 Vortec heads
- Hyd roller: 222/234 @ .050, .499/.502 lift, 112lsa
- Edelbrock RPM intake
- 1 5/8" headers, single 3" exhaust
- 3.92 gears, 3500RPM stall
- Weighs about 3300lbs with me.

The car is driven a lot but I'm willing to give up some gas milage for more performance.

I've been eyeing up a 750 mechanical secondary Speed Demon. Do you think this is a good choice? From what I know about carbs you can get away with a "too big" carb when using vacuum secondaries but not when using mechanical. Would this be too big?

The 650cfm and 750cfm are the same price and I'm also thinking ahead. This motor isn't much but I'm slowly (very slowly) building a new, much more wilder, one for the car so I don't want to have to buy a new carb in another year.

Any opinions on this?

Thanks,
Chris

( (cid/2) x (max obtainable RPM/1728) )= Recommended carb CFM.

You might only need a 700 CFM.....

Chris,

I can't speak from experience (never owned a demon carb), but I've read somewhere that the demon carbs require a lot of adjustment. I read it either on this site or on the Team Chevelle site. I have a 650 mech secondaries Holley one my Z28 and it ran great out of the box. I was very impressed. I figured that I would have to do all kinds of tuning, but that wasn't the case. Simply bolted it on, hooked everything up, and it ran like a top. My 650 has no problem feeding my 302 up to as many RPMs that I want to turn, so I'd imagine that a 700 would do you just fine even on your engine in progress.

Good luck...

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X77, Stock matching number 302, 4:10 rear, black int, weld prostars, 2.5" Flowmaster 50 Series
http://community.webshots.com/user/lakemg

[This message has been edited by 1FASTZ (edited 01-17-2003).]

i think the 750 dp speed demon is an excellent choice, especially if you plan on going a bit more radical in the future, as you say. i'm running a 750 speed demon dp on my 406, and ran it on my mild 350 before it came out, and it ran/runs excellent on both motors. i don't find it hard or finicky to adjust at all. i made the first adjustments on it, and had to do very little else after that as far as fine tuning went. the most adjustment i had to do was when i went with the bigger higher flowing heads on my 406, and still it runs great even with the factory jetting. maybe just a tad rich. i have heard of needing to fiddle with the air bleeds,although. as far as i'm concerned, once these carbs are tuned, nothing beats them, imho.

I guess then it depends on what "wilder" combo you are building. You can make just about anything work if you have the patience to tune it . . . the more "oversize" the carb is on your current mill the more tweeking you'll have to do.

The right size for your current 350 is about 650 cfm, but I have no idea what the right size will be for your next build.

I have no experience with Demons but I'd consider myself pretty good with Holleys. From what I understand Demons aren't really harder to tune they are just a lot more sensitive and you have to realize that beforehand. I've also been told that Demons actually flow more than rated? This this true?

This makes me lean more towards the 650 rather than the 750.

If you run N2O they recommend 50 CFM more than a N/A motor. George

Many folks think either 650 or 750. I have a 700 DP and it works flawlessly. No extraordinary adjustment rituals were needed, either. Just a careful acc pump adjustment and float setting.

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Rick Dorion
69 RS Conv,355,Autogear M22,4.10's and I don't worry about stone chips ( yet ).