[Will]

Q-jets are great, no doubt about it. I love the Cliff prepped 800 Q-jet on my Formula.

But, my '73 'bird is a different animal. I need a carb that's a little more universal and easier to reconfigure for different engine combos. Holley stuff is dirt cheap and plentiful on Craigslist.

So for a carb that will cover a variety of applications from a warmed over 350 to a built 428, which Holley would be best? I'm guessing a 750, but other than that I don't know a lot about them. Vac secondaries or double pumper? other things to look for?

If you could provide list numbers so I can be sure of what I'm looking at while browsing CL, that would be appreciated.

[tom s]

For a street car a 3310 will be great.I have one on my 366 RA V.Tom

[Will]

Thanks Tom!

Looks like I have a lot to learn. Just spent 1/2 hour reading about booster design and why you would use one over another.

I know how to tune Q-jets but Holleys are another world for me. Wish the internet had all the information it does now back in '97 when I was trying to tune the Holley on my 6-cyl. Nova with pretty much no success.

[72blackbird]

A Holley 750 cfm vac.sec. will feed a 428 just fine, but clearly you'll need bigger jets to feed a 428 vs.a 350p. A DP is better suited to an engine with a bigger cam, less vacuum at idle- a vac. sec. carb will be running off the primaries most of the time, saving you fuel.

Geno

[tom s]

My 366 did not like the bigger primary's on a 850.Tom

[Tom Vaught]

About 95% of the time a good 780 cfm Holley Vacuum Secondary carb will give you excellent performance whether it be a Z-28 (302 cid engine) or a 428 cid Pontiac or Ford Engine. Today you can get the quick change Vacuum Secondary pods that allow spring tuning in less than 5 minutes.

The older 3310-0 and 3310-1 Holley 780 carbs had the down leg boosters and also had a rear metering block so jet changes were easy to do. The replacement 3310 rear block is still available from Holley and will allow you to Race Bowls with the slightly longer fuel line that the "Double Metering Block" carbs -Double Pumpers use.

You can get the carbs with an electric choke or a manual choke from the aftermarket stuff. Some of the aftermarket carbs come with the Straight Leg Boosters which are ok for a grocery getter type deal but the down-leg boosters are a better way to go.
Shaker455 has the Booster Tool, as do I for changing the Boosters if that was what someone wanted to do and they bought the 780 carb cheap.

Many times the extra .060" bigger throttle blades are not the poor drivability issue on a smaller engine but the overall fuel calibration installed in the 850 carbs.
Some of the 427 and 454 Chebby carbs (with vacuum Secondaries) RARE CARB would drive fine with those displacements but probably not very well on a 350 LT-1 engine.
The GM Engineers spent a lot of time with the Holley Engineers dialing in the performance Holley calibrations years ago, LOTS OF TIME!

So I will agree with Tom S on this one and say stick with either a 780 Vacuum Secondary carb or a 750 DP carb and lean the sucker down a bit on the primary calibration.

Tom V.

[Squidward]

I have a Quick Fuel HR 780 VS on my 40 over 350. I have been pleased. I think vac sec would give you most flexibility over a wide range of combos. I love the QF secondary adjustment - turn a screw til it bogs, and then back off until it goes away. It's much better than the old diaphragm/spring deal.

[tom s]

Tom,remember my 366 has 315 CFM ports and when built a single plane intake.That was the combo with the 366.I went to a dual plane intake and the 3310 really liked it.Have not gone back to try the 850 with the dual plane.Tom

[Tom Vaught]

If it really likes it with the 3310 then you might not see much difference with the 850 unless it was built with good boosters or annular boosters (830 cfm).

Tom V

[tom s]

Too big of pain to switch as it has lemans bowls.Its a factory Hemi NASCAR carb.Tom

[James408]

Quick Fuel slayer 750 with vacuum secondaries. Adjust the vacuum secondaries by the turn of a screw. no springs to change. has air bleeds that can be easily changed and has a secondary metering plate that you can change jets. sight glasses on bowls. The stock 3310 does not have these options. Best carb I've every used. I bought it from Summit Racing brand new a couple of years for $299. I think they've gone up a little but not much.

[Matt Meaney]

what do you do for idle/transition to part throttle? I would think there is a substantial difference in an idle circuit to properly feed a warmed over 350 to built 428. is the holley easy to change it's idle air/fuel up or down to accommodate different engine parameters? the enrichment circuit seems infinitely adjustable, with all its different pump sizes, cams, and nozzels. just have to find the right combination of them. then if you change the boosters to work well with a high vacuum warmed over 350 how are they going to respond to a lower vacuum built 428? is there a universal one that can cover both pretty good?

[Tom Vaught]

I have personally taken a 780 cfm carb that was on a Z-28 (that drove well) and installed it on a 428 Pontiac and the carb functioned just fine.

The idle feed restrictions do not really change much at idle as whether it be a 350 Chebby carb, that at idle is passing 16 cfm past the primary blades to get a nice idle or a 428 Pontiac that is passing 19 cfm past the primary blades to get a decent idle has more to do with the position on the blade vs the transfer slot lower opening.

In both cases you want that opening to be a tiny square opening when the engine has the correct amount of idle air passing into the engine. In some cases a carb man with leave the throttle blade exactly where it was on the 350 engine carb setting and drill one .060" hole in each primary throttle blade to get the extra 3 cfm needed for the engine to idle properly. And maybe the idle mixture screw has to be turned out an additional 1/8th of a turn.

So there is NOT "a substantial difference in an idle circuit to properly feed a warmed over 350 to built 428".

Tom V.

[Matt Meaney]

that's why the statement was prefaced with the word "think" instead of "know". thank you for the explanation.

[ta man]

Originally Posted by Tom Vaught

I have personally taken a 780 cfm carb that was on a Z-28 (that drove well) and installed it on a 428 Pontiac and the carb functioned just fine.

The idle feed restrictions do not really change much at idle as whether it be a 350 Chebby carb, that at idle is passing 16 cfm past the primary blades to get a nice idle or a 428 Pontiac that is passing 19 cfm past the primary blades to get a decent idle has more to do with the position on the blade vs the transfer slot lower opening.

In both cases you want that opening to be a tiny square opening when the engine has the correct amount of idle air passing into the engine. In some cases a carb man with leave the throttle blade exactly where it was on the 350 engine carb setting and drill one .060" hole in each primary throttle blade to get the extra 3 cfm needed for the engine to idle properly. And maybe the idle mixture screw has to be turned out an additional 1/8th of a turn.

So there is NOT "a substantial difference in an idle circuit to properly feed a warmed over 350 to built 428".

Tom V.

I've started squaring that slot quite a few years ago...and use the rear blades to set idle speed..seems to work....On my 950hp I had to do opposite of many..and replaced the drilled out blades with non drilled blades to bring the idle down so I could run a square transfer slot.

[Sprocket]

Myself and some others have had great success with the Holley 4150 HP street series. Look for 0-82750, that is the 750 cfm model with vacuum advance, and is the same model that I use. Easy to service, easy to adjust, and just plain works. I got tired of playing the Q-jet game and haven't looked back.

https://www.holley.com/products/fuel.../parts/0-82750

[Will]

One of the reasons I want to go Holley is because there's always a bunch of them on Craigslist. How do I identify this 0-82750 model if someone's selling a used one? Is that number stamped on it somewhere?

Also, that carb doesn't appear to have a choke... I plan to drive the car in all weather, or at least in the winter/spring/fall when its dry.

Can't other 750 vac-sec models be modified with things like the adjustable secondaries, various boosters, etc.

Which leads me to another question - Why do you need a special tool to change the boosters? What is it about their design that requires something special? Is there no way around that?

[Tom Vaught]

Originally Posted by Will

One of the reasons I want to go Holley is because there's always a bunch of them on Craigslist.

A) How do I identify this 0-82750 model if someone's selling a used one? Is that number stamped on it somewhere?

B) Also, that carb doesn't appear to have a choke... I plan to drive the car in all weather, or at least in the winter/spring/fall when its dry.

C) Can't other 750 vac-sec models be modified with things like the adjustable secondaries, various boosters, etc.

D) Which leads me to another question - Why do you need a special tool to change the boosters? What is it about their design that requires something special? Is there no way around that?

A bunch of good questions Will and I will try to answer them in order.

Answers:

A) Holley carbs like the 0-82750 typically have the model number 3310-2, 4779-3, 4781-2 stamped on the metering blocks top edge (on the right). So you should have both a metering block number and a carb "List #" the carb List # being 0-82750.

B) Unless someone cut the choke horn off the main body or it is a HP series "race" type (no choke designed into the main body) you can add the choke parts again. If no choke, then I have just given the carb a couple of pump shots and then sat there and put a little heat into the engine before I drove away, not a bad idea to do that even with a choke on the carb.

C) Changing secondary parts to secondary metering blocks is easy, adding race bowls is easy, changing boosters is not easy, without the tool.

D) Holley carb have always had the boosters 'swedged' into the main body on the Higher performance carbs. A few 600 cfm carbs had cast in boosters.
The way the swedging process works is that you have a drilled hole going thru the main body into the venturi area. The booster has a long straight nose that gets inserted into the drilled hole. The nose sticks out on the metering block side of the casting.

The special tool holds the booster tightly in the correct position and the swedge forms a rounded lip from the straight nose that permanently locks the booster into the main body casting (if done correctly). It also makes a very smooth funnel shape for the fuel to flow smoothly into the booster from the metering block. Once it is swedged in place it is there unless you physically remove the swedging and knock the booster out of the main body.

Barry Grant made some carbs with "Screw On" nut boosters, Sometimes they stayed screwed together and sometimes the booster or nut fell into the engine intake manifold and wedged a valve open. That is why you need the special tool and knowledge on how to install the boosters properly.

Hope that helps.

Tom V.

[Will]

Tom, thanks much! - just to clarify; you're saying both the model # AND the list # will be stamped on the carb?

Ah, that makes sense about the boosters being swedged in place. I didn't think about that.

The one sprocket linked to doesn't have a choke tower on it. I've often run cars without chokes but we get some really nice but cold winter days around here where its good to have one.

[Tom Vaught]

On the metering blocks. If it has a airhorn the list number # and a date code will be stamped there.

Tom V.

ps Sometimes you can get by with using a exhaust manifold heat stove (like bart has for sale) and a tube to the air cleaner and get by without the choke on a cool day.