FLA-C3

I finally got my short block and heads back from the shop. The previous owner was running a Victor Jr. intake with a Holley 800 DP, which is pretty much worn out. Since the motor is going in my '73 and will be used mainly for street driving, I'm going with dual plane intake...probably an rpm airgap. I'm not sure about which carb to go with.

The Holley tech says use a Street Avenger 670 or a 0-3310c 750cfm (both vac sec), BG recommends a 1402020 Speed Demon 750, and AED recommends their 750HO. Prices range from $270-500 plus. I want something that doesn't have to be continually tweaked and isn't gonna break the bank...I'm leaning toward the 3310s...

408 small block (400 +.040)
9.66 comp ratio
SRP forged flat top pistons
Lunati 60103 cam
993 75cc heads
Crane Roller Rockers
Edelbrock RPM Airgap 7501 Intake
MSD 8572 HEI tach drive & 6AL
Hooker Comp. Headers, 2 ½” exhaust into Magnaflow mufflers
Super T-10 trans.
3.70 rearend

billla

Your sizing and configuration is right on; 750 CFM and a vacuum secondary carb. The 3310 is a good choice - this was the factory LT-1 carb for comparison (albeit with a secondary metering block vs. plate and some other changes). You can't go wrong with any of your choices combined with a good tune...factor the cost of that tune into your build.

I'd suggest a more tuneable carb than the "classic" Holleys, however. The Speed Demon and Holley Street HP carbs are far better for getting a "perfect" tune on the street

canadian73

i've tried holley 650 dp and 3310 . i decided to keep the 3310 , cause it's a better cam all arond , at least for me . my engine is a 383 zz from gm with a air gap rpm manifold . dont get me wrong that 650 dp was real good ,but but the fuel economy's lot better with the 3310 ... be good phil

427Hotrod

With your tans and gearing I'd use a 4779 Holley Double pumper in a heartbeat. No way I'd use vacuum on that setup. You can use the Demons if you just like them..but the Holley DP is about one of the most versatile carbs out there and will run well on just about anything. A few tweaks is all it takes to run on a whole variety of combos. I've got one currently running on a buddy's car that I've had for 20+ years now. It's been on stock 302 fords, 427's, 350's, 454's, 440's, 383's etc etc and worked great on them all.

JIM

FLA-C3

Thanks for the replies. I haven't pulled the trigger on a new carb yet. I'm not really concerned with gas mileage, because this is for a weekend toy. Guess I'm now wrapped around the axel with the mechanical or vacuum secondary argument. Will a DP be that "much more responsive" than a vac sec carb for my setup? Or not so much in a street application? Thanks.

Edit...sorry Jim...I think we posted at the same time.
Yeah, a lot of people are giving me that same advice now. Actually, Holley says the 4778 (700DP) is the right mech carb for me....thanks.
Dewain

The Money Pit

Mine started out as a 3310, and worked well with the milder cams I had. But when I went to the Isky solid, I had tuning issues, and ended up reworking the carb quite a bit to get it right.


My website has more detailed info if you're interested.

billla

A DP carb is going to offer better performance in exactly one scenario: dead stop to WOT - i.e., drag racing. DPs are a race-only part, and the fuel economy trade-off isn't worth it. All IMHO, of course

Vacuum secondary carbs do take some tuning of the secondaries to get right; most of the "bog" nightmares are just incorrect secondary opening. But you'll want to invest in a good tune in any case.

427Hotrod

A double pumper doesn't use any fuel your right foot doesn't tell it to. Problem is it feels so good you use it a lot! The primary side of a double pumper is the same as a Vacuum carb. All the *universal* carbs are a little richer out of the box sometimes....but they have no idea what you are putting it on. Simple idle adjustments or maybe a jet tweek is about it.

The 700's seem to run a tad richer in my experience, same as the 800's. They do OK..but no reason to not use the 750. In fact with a dual plane intake..your motor is going to want a larger carb than the formulas say. Do some reading on Edelbrocks website about it...but don't use the Edelbrock carbs.

You've got 408 cubes to feed....don't strangle it.



JIM

Little Mouse

3310 is a late 60s carb out dated boosters has a metering plate in
back not very tunable. If you decide to go vacuum on your big engine with a dual plane go with the 770 avenger over the 4160 metering plate 3310, the avenger is a 4150 carb with back metering block easy to change jets. but to be honest if money is not the issue I would buy a 750 size dp with annular boosters. Totaly disagree with holley on a 670 with your size engine and
dual plane manifold.

billla

True - but a DP gives the engine fuel regardless of what the engine NEEDS...which IMHO is more important

A properly tuned vacuum secondary carb will always give better throttle response and fuel economy along with the same power levels...but will also always lag well behind a DP on WOT (flooring it) response.

DP vs vacuum secondary has nothing to do with the size of the engine or the carb CFM needed to feed it - so either way it's not going to get "strangled".

73, Dark Blue 454

Agree with 427Hotrod. I wouldn't even consider a VS carb with a T-10 and 3.70's. It would take a ton of tuning to make the VS carb respond on demand like a DP does out of the box.

You say you have a 800-DP that's worn out. There's not a part on that carb that can't be replaced. I'd rebuild what you have, or if you have to have a new one, go with the Holley 4779 (750 cfm) or 4780 (800).

Quite simply, there's nothing more simple than tuning a DP,..jets, pump cam(s) etc, are swapped out in minutes.

Good luck!

billla

The factory thought it was good enough for the LT-1

I'm interested in the thinking here regarding tuning - DPs typically require less tuning because a big shot covers up a ton of bog. Why do you think a "ton of tuning" is required to make a VS carb work?

I realize this is the age-old VS vs. DP debate and it's not going to be resolved here - just interested in more detail on the perspective

Finally, agree that a carb is almost never "worn out" unless Bubba's been drilling on things Just about any carb can be salvaged with a good overhaul. If it's really been abused, sending it to Holly for their overhaul service sometimes is the best bet.

b71vette

I'd recommend the AED 750HO. They are built by hand and tested on a live engine before they are shipped. They get the base parts from Holley and do the machining and hand build themselves, not like a production carb like holley or speed demon..

billla

http://www.aedperformance.com/HO.htm

Not sure exactly what the value add is...

fetorino

the metering of the DPs is richer than the VS models pretty much across the board. I'm not just talking about jet sizes I mean the air bleed sizes and the emulsion tube passages. DPs are made for racing and are superior for that purpos when properly tuned. A VS will get you virtually the same hp better idle quality and better throttle response with less tuning. Your combo sounds strong but it is far from radical and would respond well to an out of the box 3310. The 3310 was originally factory chevy carb for the 396 I believe and later the LT1. The later universal ones do have slightly richer metering than the original 780 version but for a motor such as yours with some mods that will work out fine. If you find the secondary jetting needs some tweaking you can buy a secondary metering block from Holley and make it a 4150 style carb that is really no big deal. Now unless you have a good Air/fuel meter or some type of tuning device other than seat of the pants and reading plugs you are likely to do more harm tuning than just bolting on a carb. I would bet that a 3310 and the basic tuning of dialing in the idle mixture screws, possibly adjusting the primary jetting and properly sizing the power valve using a vacum guage will give you good results probably beter than trying to tune a 750dp.

Definaltely dissassemle the carb and ensure it is clean before bolting it on both Holley and Barry Grant have had lots of complaints the past couple of years over quality control.

FLA-C3

Thanks for all of the feedback...it's been very informative. I talked to a different Holley tech today at great length. He said that I'm basically on the borderline of going either way with my setup...vac or mech. He actually went back and forth on the phone...LOL But said that he would still recommend a vacuum secondary carb...3310s or more preferably the a Street Avenger 770 in my setup. Bottom line, both the vac or mech carb will work great...quess it just depends on your personal preference....

Little Mouse

The price tag for the 4150 style avenger carb is close to the same as the 3310 already has the back metering block removable jets, its not cheap to buy the kit to change the 4160 syle 3310 to 4150 carb, if you go vacuum secondary just buy the 770 avenger.

FLA-C3

Yeah, I agree....found it for $340...thanks.

73, Dark Blue 454

No offense to the LT-1, a bad-*** 350, but we're we're talking 408 CID with a T-10 (not a close ratio M-21), and 3.70's.

LT-1 350 received a VS but a ZL-1 427 and a LS-6 454 got a DP.

I have a 406 Camaro with a M-20 and 3.73's, it has a 750 DP with the Pro Form main body (I highly recommend it if you can live without a choke) and the car is driven all over the state of TX. The DP runs like stink. Tune it and forget it,..and you will love the response.

Also, I don't think the Air-Gap will fit under the hood of your 73.

FWIW.

Little Mouse

don't have a dog in this vacuum secondaries vs double pumper fight
I have run a bunch of 3310s a few of the older double pumper
carbs on street cars. Between the 3310/avenger there is no good reason to buy the older 3310. If you had a car with slugish 3.08/3.36 rear gearing 3 speed auto you would want the vacuum secondaries carb. But with your 4 speed 3.70 gearing the DP would be a better performance carb on the street or strip thats the up side to the DP, the downside I'm talking about the cheaper less adjustable older carbs still available like a 4977 the jetting is richer thats not a big deal if needed can be changed very easly,the real problem is the richer idle circut they are set up richer to deal with the low vacuum pull at idle of a radical cam, you put this carb on a car with a high vacuum pull at idle with a milder street cam the bigger restriction hole for fuel lets a lot more fuel be pulled in at idle, you can end up with a pretty rich idle.