CGGorman

Going to swap out my 3310 for a 4150-style Holley or Speed/Mighty Demon.

When I started buying parts over a year ago, I didn't know squat about carbs and picked the 3310 based on what I was reading about vacuum secondaries on the street. Well, I've since found out that this also generally reserved for automatic tranny cars...which I don't have. I'm also frustrated with added difficulty of tuning the secondaries. I've got the lightest springs in there that I can find and I still can't get them to open fast enough to bog. Swapping metering plates instead of jets also bugs me. I'm a control freak, so I should have seen this coming, but...live-n-learn.

Anyway, I want to stay with the square flange so I don't have to swap out the intake or use an adapter. I also know how to tune a Holley (not Lars-level, but not too shabby for a Gen-Xer), whereas a Carter or Rochester (or clones) would be a whole new game to learn.

That narrows it down (basically) to a 750cfm 4150 Holley or Speed Demon. The Mighty Demon looks nice, too (Especially the annular booster version), but not really recommended for my cam... I'm not too concerned about the choke. I only drive the car in the summer and I've got the choke plate removed from the current 3310 (still using the fast idle cam).

750 CFM is plenty for my mild 427. I've got zero (or close to) vacuum at WOT.

Now, a twist... I'm thinking about jumping to an 850 now in an effort to "beat the curve" when I build the new 427 sometime in the next two years. I've got everything gathered except the heads and cam. Planning an all-forged 427, solid lifters on a L88 grind, LS-6/LS-7 heads, Open plenum/dual-plane intake. Planning on a 7000 rpm redline and streetable idle/off-idle characteristics

Questions:
Any reason not to "upsize" now?
The L88 came with an 850, but is it necessary?
Demon or Holley? Why?
Speed or Mighty? Why? Is the L88 or ZL1 cam considered "radical" or "mild".

Gordonm

Hmmm. If you are going to go all forged lower why not put in a stroker crank and put some cubes in that BB. A 427 BB is considered small by nowadays standards. If you do that then the 850 Mighty Demon if you are going to use a cam with over 240 @ .050 duration. If your going to build it build it big.
I like the Demon carbs. They are just a little more updated than the old 4150 Holley. That being said I still run my little 350 SB with a 750 Holley. If I were doing it again I would go stroker with a Demon.

CGGorman

Building a stroker would require buying parts! I've already got the bottom end parts that I'm keeping from a stash of NOS parts. The rest get sold. Beyond that, it's just good Karma to have a 427 in your Vette, ya know?

I thought the Demons seemed to have some nice features at a great price point, but what's the quality and out-of-the-box calibration like?

I could rebuild an old 4150 I've got laying around, but would the newer features outweigh the savings?

yellow 72

FWIW my Speed Demon ran perfect out of the box with a quick run through check of all the initial settings. So far the best carb I've ever owned.
Summit is discontinuing the Barry Grant line and offering close out prices on some models

bobs77vet

i've got a speed demon but sounds like you have two winning choices....the Holley will have more stuff readily available for it such as heat shields etc....

MotorHead

Demon carbs are bigger than they advertise, my 825 Race Demon apparently flows 970CFM according to BArry Grant, don't know why they didn't call it a 970 Race Demon. Anyway I got the DR model set up for drag racing and slapped it on and adjusted the idle mixture and it works fine tooling around town or WOT, BG's are great carbs, so are Holleys

Brettmc

You'll get a lot of opinions on the BG vs. Holley....but they're just that...opinions. You'll hafta make up your mind on which based on several facts but the main ones are: how easy you will be able to find parts to mod the carb with and how easy it will be for YOU to tune it. I don't know how many parts are available for the BGs, but I know there are untold numbers of goodies for Holleys. Billet baseplates, cnc boosters, billet metering blocks, extended metering blocks for more bowl capacity, blah, blah. Anyway, I don't think you will go wrong with either one. .

Brett

SmokedTires

Having just installed a 750 Mighty Demon, I'm very impressed with the features of the Demon.

I happen to like the clear float bowl windows, and the bowls have fuel level lines cast into them for easy adjustments if you want to go either a bit higher or lower.

The 4 corner idle adjustment is also a nice feature, and it feels like they might have an o-ring or something in the idle adjustment screws because it's very smooth yet snug when turning them compared to a Holley I had that just felt loose.

I took the new Demon apart and cleaned it all out then reassembled it and preset it according to Lars Demon paper before installing onto my engine. It was nice and easy for me to adjust and the Demon instructions were also helpful. It's good to have as much setup info as I can get my hands on

CGGorman

Well, I wanted to get this thing back on the street this weekend, so after inventory-ing the carbs I've got lying around, I decided to ante up for a Mighty Demon. I didn't have any Holleys with mechanical secondaries... Opted for a 800 cfm Mighty Demon with annular boosters. Seems like a great compromise unit between the 750 that has great response on the current engine and an 850 that would support the high revs of the next engine. I figured the careful contours on the Demon will offer 850+ equivalent flow at WOT and Motorhead supports that reasoning. The closest I could find from Holley was an HP series and cost several hundred more. I'll miss the choke a little, but the ease of tuning, great feature-set, good looks, and performance will more than make up for it.

Anybody know if a BG choke kit will even fit on a Mighty? I'm not using the choke horn today, so if it would physically fit and operate a fast-idle cam, I'd be in-like-flynn.

SmokedTires

No choke housing on the Might Demons. When setup properly, you should be able to idle after about 30 seconds warm up. It won't be smooth, but it should stay running until it warms up

Also, visit BG's site to help you select the proper size carb